@article {1660,
	title = {Ambient Ammonia Electrosynthesis from Nitrogen and Water by Incorporating Palladium in Bimetallic Gold{\textendash}Silver Nanocages},
	journal = {Journal of The Electrochemical Society},
	year = {2020},
	author = {Nazemi, M. and Soule, L. and Liu, M. and El-Sayed, M. A.}
}
@article {1661,
	title = {Electrosynthesis of Ammonia Using Porous Bimetallic Pd{\textendash}Ag Nanocatalysts in Liquid- and Gas-Phase Systems},
	journal = {ACS Catalysis},
	year = {2020},
	chapter = {10197},
	keywords = {display},
	author = {Nazemi, M. and Ou, P. and Alabbady, A. and Soule, L. and Liu, A. and Song, J. and Sulchek, T.A. and Liu, M. and El-Sayed, M. A.}
}
@article {1653,
	title = {Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine},
	journal = {Biochimica et Biophysica Acta (BBA)-General Subjects},
	year = {2020},
	author = {Falahati, M. and Attar, F. and Sharifi, M. and Saboury, A.A. and Salihi, A. and Aziz, F.M. and Kostova, I. and Burda, C. and Priecel, P. and Lopez-Sanchez, J.A. and Laurent, S. and Hooshmand, N. and El-Sayed, M.A.}
}
@article {1649,
	title = {Operando Investigation into Dynamic Evolution of Cathode{\textendash}Electrolyte Interfaces in a Li-Ion Battery},
	journal = {Nano letters},
	year = {2019},
	author = {Chen, D. and Mahmoud, M.A. and Wang, J.H. and Waller, G.H. and Zhao, B. and Qu, C. and El-Sayed, M.A. and Liu, M.}
}
@article {1625,
	title = {Design of Hybrid Electrochromic Materials with Large Electrical Modulation of Plasmonic Resonances},
	journal = {ACS Applied Materials \& Interfaces},
	year = {2016},
	author = {Ledin, P. A. and et al.}
}
@article {1593,
	title = { Electrically Controlled Plasmonic Behavior of Gold Nanocube@ Polyaniline Nanostructures: Transparent Plasmonic Aggregates},
	journal = {Chem. Mater.},
	year = {2016},
	author = {Jeon, J.-W. and Ledin, P. A. and Geldmeier, J. A. and Ponder, J. F. and Mahmoud, M A and El-Sayed, M. and Reynolds, J. R. and Tsukruk, V. V.}
}
@article {1592,
	title = { Photoexcited Surface Frustrated Lewis Pairs for Heterogeneous Photocatalytic Co2 Reduction},
	journal = { Am. Chem. Soc. },
	year = {2016},
	author = {Ghuman, K. K. and Hoch, L. B. and Szymanski, P. and Loh, J. Y. and Kherani, N. P. and El-Sayed, M. A. and Ozin, G. A. and Singh, C. V.}
}
@article {1587,
	title = {Probing Structural Evolution and Charge Storage Mechanism of Nio2hx Electrode Materials Using in Operando Resonance Raman Spectroscopy},
	journal = { Advanced Science},
	year = {2016},
	author = {Chen, D. and Xiong, X. and Zhao, B. and Mahmoud, M A and El-Sayed, M. A. and Liu, M.}
}
@article {1575,
	title = {Light-responsive plasmonic arrays consisting of silver nanocubes and a photoisomerizable matrix.},
	journal = {ACS Appl Mater Interfaces},
	volume = {7},
	year = {2015},
	month = {2015 Mar 4},
	pages = {4902-12},
	abstract = {We report on the synthesis of novel branched organic-inorganic azo-polyhedral oligomeric silsesquioxane (POSS) conjugates (Azo-POSS) and their use as a stable active medium to induce reversible plasmonic modulations of embedded metal nanostructures. A dense monolayer of silver nanocubes was deposited on a quartz substrate using the Langmuir-Blodgett technique and subsequently coated with an ultrathin Azo-POSS layer. The reversible light-induced photoisomerization between the trans and cis states of the azobenzene-terminated branched POSS material results in significant changes in the refractive index (up to 0.17) at a wavelength of 380 nm. We observed that the pronounced and reversible change in the surrounding refractive index results in a corresponding hypsochromic plasmonic shift of 6 nm in the plasmonic band of the embedded silver nanocubes. The reversible tuning of the plasmonic modes of noble-metal nanostructures using a variable-refractive-index medium opens up the possibility of fabricating photoactive, hybrid, ultrathin coatings with robust, real-time, photoinitiated responses for prospective applications in photoactive materials that can be reversibly tuned by light illumination.},
	issn = {1944-8252},
	doi = {10.1021/am508993z},
	author = {Ledin, Petr A and Russell, Michael and Geldmeier, Jeffrey A and Tkachenko, Ihor M and Mahmoud, Mahmoud A. and Shevchenko, Valery and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.}
}
@article {1576,
	title = {Silver nanocube aggregation gradient materials in search for total internal reflection with high phase sensitivity},
	journal = {Nanoscale},
	volume = {7},
	year = {2015},
	pages = {5230-5239},
	abstract = {We fabricated monolayer coatings of a silver nanocube aggregation to create a step-wise optical strip by applying different surface pressures during slow Langmuir-Blodgett deposition. The varying amount of randomly distributed nanocube aggregates with different surface coverages in gradient manner due to changes in surface pressure allows for continuous control of the polarization sensitive absorption of the incoming light over a broad optical spectrum. Optical characterization under total internal reflection conditions combined with electromagnetic simulations reveal that the broadband light absorption depends on the relative orientation of the nanoparticles to the polarization of the incoming light. By using computer simulations, we found that the electric field vector of the s-polarized light interacts with the different types of silver nanocube aggregations to excite different plasmonic resonances. The s-polarization shows dramatic changes of the plasmonic resonances at different angles of incidence (shift of 64 nm per 10[degree] angle of incidence). With a low surface nanocube coverage (from 5\% to 20\%), we observed a polarization-selective high absorption of 80\% (with an average 75\%) of the incoming light over a broad optical range in the visible region from 400 nm to 700 nm. This large-area gradient material with location-dependent optical properties can be of particular interest for broadband light absorption, phase-sensitive sensors, and imaging.},
	doi = {10.1039/C4NR06430E},
	url = {http://dx.doi.org/10.1039/C4NR06430E},
	author = {Konig, Tobias A. F. and Ledin, Petr A and Russell, Michael and Geldmeier, Jeffrey A and Mahmoud, Mahmoud. A. and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.}
}
@article {1363,
	title = {Electrically Tunable Plasmonic Behavior of Nanocube-Polymer Nanomaterials Induced by a Redox Active Electrochromic Polymer},
	journal = {ACS nano},
	year = {2014},
	isbn = {1936-0851},
	author = {K{\"o}nig, Tobias AF and Ledin, Petr A and Kerszulis, Justin and Mahmoud, Mahmoud A. and El-Sayed, Mostafa A. and Reynolds, John R and Tsukruk, Vladimir V.}
}
@article {1362,
	title = {High-temperature surface enhanced Raman spectroscopy for in situ study of solid oxide fuel cell materials},
	journal = {Energy \& Environmental Science},
	volume = {7},
	number = {1},
	year = {2014},
	pages = {306-310},
	author = {Li, Xiaxi and Lee, Jung-Pil and Blinn, Kevin S and Chen, Dongchang and Yoo, Seungmin and Kang, Bin and Bottomley, Lawrence A and El-Sayed, Mostafa A. and Park, Soojin and Liu, Meilin}
}
@article {1389,
	title = {High-Frequency Mechanical Stirring Initiates Anisotropic Growth of Seeds Requisite for Synthesis of Asymmetric Metallic Nanoparticles like Silver Nanorods},
	journal = {Nano Letters},
	volume = {13},
	number = {10},
	year = {2013},
	note = {Mahmoud, Mahmoud A. El-Sayed, Mostafa A. Gao, Jianping Landman, Uzi},
	month = {Oct},
	pages = {4739-4745},
	isbn = {1530-6984},
	doi = {10.1021/nl402305n},
	author = {Mahmoud, M A and El-Sayed, M. A. and Gao, J. P. and Landman, U.}
}
@article {1393,
	title = {Well-organized raspberry-like Ag@ Cu bimetal nanoparticles for highly reliable and reproducible surface-enhanced Raman scattering},
	journal = {Nanoscale},
	volume = {5},
	number = {23},
	year = {2013},
	pages = {11620-11624},
	author = {Lee, Jung-Pil and Chen, Dongchang and Li, Xiaxi and Yoo, Seungmin and Bottomley, Lawrence A and El-Sayed, Mostafa A. and Park, Soojin and Liu, Meilin}
}
@article {1331,
	title = {Aggregation and Interaction of Cationic Nanoparticles on Bacterial Surfaces},
	journal = {Journal of the American Chemical Society},
	volume = {134},
	number = {16},
	year = {2012},
	note = {Times Cited: 1Hayden, Steven C. Zhao, Gengxiang Saha, Krishnendu Phillips, Ronnie L. Li, Xiaoning Miranda, Oscar R. Rotello, Vincent M. El-Sayed, Mostafa A. Schmidt-Krey, Ingeborg Bunz, Uwe H. F.},
	month = {Apr},
	pages = {6920-6923},
	abstract = {Cationic monolayer-protected gold nanoparticles (AuNPs) with sizes of 6 or 2 nm interact with the cell membranes of Escherichia coli (Gram-) and Bacillus subtilis (Gram+), resulting in the formation of strikingly distinct AuNP surface aggregation patterns or lysis depending upon the size of the AuNPs. The aggregation phenomena were investigated by transmission electron microscopy and UV-vis spectroscopy. Upon proteolytic treatment of the bacteria, the distinct aggregation patterns disappeared.},
	isbn = {0002-7863},
	doi = {10.1021/ja301167y},
	author = {Hayden, S. C. and Zhao, G. X. and Saha, K. and Phillips, R. L. and Li, X. N. and Miranda, O. R. and Rotello, V. M. and El-Sayed, M. A. and Schmidt-Krey, I. and Bunz, U. H. F.}
}
@article {1333,
	title = {Application of surface enhanced Raman spectroscopy to the study of SOFC electrode surfaces},
	journal = {Physical Chemistry Chemical Physics},
	volume = {14},
	number = {17},
	year = {2012},
	note = {Times Cited: 3Li, Xiaxi Blinn, Kevin Fang, Yingcui Liu, Mingfei Mahmoud, Mahmoud A. Cheng, Shuang Bottomley, Lawrence A. El-Sayed, Mostafa Liu, Meilin},
	pages = {5919-5923},
	abstract = {SERS provided by sputtered silver was employed to detect trace amounts of chemical species on SOFC electrodes. Considerable enhancement of Raman signal and lowered detection threshold were shown for coked nickel surfaces, CeO2 coatings, and cathode materials (LSM and LSCF), suggesting a viable approach to probing electrode degradation and surface catalytic mechanism.},
	isbn = {1463-9076},
	doi = {10.1039/c2cp40091j},
	author = {Li, X. X. and Blinn, K. and Fang, Y. C. and Liu, M. F. and Mahmoud, M A and Cheng, S. and Bottomley, L. A. and El-Sayed, M. and Liu, M. L.}
}
@article {1417,
	title = {Nano and Molecular Science and Technology Special Issue Honoring Paul Barbara},
	journal = {Accounts of Chemical Research},
	volume = {45},
	number = {11},
	year = {2012},
	month = {2012/11/20},
	pages = {1842-1843},
	publisher = {American Chemical Society},
	isbn = {0001-4842},
	doi = {10.1021/ar300271q},
	author = {El-Sayed, Mostafa and Masuhara, Hiroshi and Pileni, Marie-Paule and Landes, Christy}
}
@article {1334,
	title = {The unusual fluorescence intensity enhancement of poly(p-phenyleneethynylene) polymer separated from the silver nanocube surface by H-bonded LbL shells},
	journal = {Journal of Materials Chemistry},
	volume = {22},
	number = {33},
	year = {2012},
	note = {Times Cited: 0Lisunova, Milana Mahmoud, Mahmoud Holland, Neal Combs, Zachary A. El-Sayed, Mostafa A. Tsukruk, Vladimir V.},
	pages = {16745-16753},
	abstract = {The fluorescence intensity of poly(p-phenyleneethynylene) (PPE) polymer separated from the surface of plasmonic silver nanocubes (47 nm AgNCs) is measured by varying the number of layers of polyvinyl pyrrolidone (PVPON) and polymethyl acrylic acid (PMAA), n. The shell thickness is sensitive to the solvent due to the formation of a solvent-sensitive hydrogen bonding network. The fluorescent behavior of the PPE on the core-shell PPE-(PVPON-PMAA) n-AgNCs structures fabricated here was evaluated as a function of n as well as the nature of the surrounding solvent. Surprisingly, the fluorescence intensity of the outer PPE shell is found to increase dramatically (by more than an order of magnitude) as its separation from the nanoparticle surface increases and then decreases at a distance that depends upon the swelling behavior of the polymer shells. The distance for the highest fluorescence enhancement was found to be 20.0 nm and 24.0 nm, in water and ethanol respectively. The observed change in the fluorescence intensity of the PPE polymer with increasing its separation from the plasmonic surface is proposed to result from the interplay between a short range quenching mechanism and a relatively long-range plasmonic fluorescence enhancing mechanism. DDA calculations gave support to the significant contribution of the latter mechanism.},
	isbn = {0959-9428},
	doi = {10.1039/c2jm32450d},
	author = {Lisunova, M. and Mahmoud, M. and Holland, N. and Combs, Z. A. and El-Sayed, M. A. and Tsukruk, V. V.}
}
@article {1132,
	title = {Time-resolved investigation of the acoustic vibration of a single gold nanoprism pair},
	journal = {Journal of Physical Chemistry C},
	volume = {112},
	number = {30},
	year = {2008},
	note = {Burgin, J. Langot, P. Del Fatti, N. Vallee, F. Huang, W. El-Sayed, M. A.},
	month = {Jul},
	pages = {11231-11235},
	abstract = {The acoustic vibration of single gold nanoprism pairs on a glass substrate has been investigated in the time-domain combining a spatial modulation spectroscopy microscope with a high-sensitivity femtosecond pump-probe setup. Three modes were observed and ascribed to two in-plane and one out-of-plane vibration of the nanoprisms forming the pair, in agreement with a theoretical analysis. The periods of the two former modes with similar nature show weak (about 10\%) and well correlated pair to pair fluctuations that can be unambiguously ascribed to variation of the prism geometry. In contrast, strong fluctuations, by almost a factor of 6, of the mode damping are evidenced with no correlation with their period. This indicates large variations of the prism-substrate coupling, providing a unique way for its local investigation.},
	isbn = {1932-7447},
	doi = {10.1021/jp802365s},
	author = {Burgin, J. and Langot, P. and Del Fatti, N. and Vallee, F. and Huang, Wenyu and El-Sayed, Mostafa A}
}
@article {1150,
	title = {Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: Applications in biological imaging and biomedicine},
	journal = {Journal of Physical Chemistry B},
	volume = {110},
	number = {14},
	year = {2006},
	note = {Jain, PK Lee, KS El-Sayed, IH El-Sayed, MA},
	month = {Apr},
	pages = {7238-7248},
	abstract = {The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed (similar to 40 nm) show an absorption cross-section 5 orders higher than conventional absorbing dyes, while the magnitude of light scattering by 80-nm gold nanospheres is 5 orders higher than the light emission from strongly fluorescing dyes. The variation in the plasmon wavelength maximum of nanospheres, i.e., from similar to 520 to 550 nm, is however too limited to be useful for in vivo applications. Gold nanoshells are found to have optical cross-sections comparable to and even higher than the nanospheres. Additionally, their optical resonances lie favorably in the near-infrared region. The resonance wavelength can be rapidly increased by either increasing the total nanoshell size or increasing the ratio of the core-to-shell radius. The total extinction of nanoshells shows a linear dependence on their total size, however, it is independent of the core/shell radius ratio. The relative scattering contribution to the extinction can be rapidly increased by increasing the nanoshell size or decreasing the ratio of the core/shell radius. Gold nanorods show optical cross-sections comparable to nanospheres and nanoshells, however, at much smaller effective size. Their optical resonance can be linearly tuned across the near-infrared region by changing either the effective size or the aspect ratio of the nanorods. The total extinction as well as the relative scattering contribution increases rapidly with the effective size, however, they are independent of the aspect ratio. To compare the effectiveness of nanoparticles of different sizes for real biomedical applications, size-normalized optical cross-sections or per micron coefficients are calculated. Gold nanorods show per micron absorption and scattering coefficients that are an order of magnitude higher than those for nanoshells and nanospheres. While nanorods with a higher aspect ratio along, with a smaller effective radius are the best photoabsorbing nanoparticles, the highest scattering contrast for imaging applications is obtained from nanorods of high aspect ratio with a larger effective radius.},
	isbn = {1520-6106},
	doi = {10.1021/jp057170o},
	author = {Jain, Prashant K and Lee, K. S. and El Sayed, I.H. and El-Sayed, Mostafa A}
}
@article {1147,
	title = {Gold and silver nanoparticles in sensing and imaging: Sensitivity of plasmon response to size, shape, and metal composition},
	journal = {Journal of Physical Chemistry B},
	volume = {110},
	number = {39},
	year = {2006},
	note = {Lee, Kyeong-Seok El-Sayed, Mostafa A.},
	month = {Oct},
	pages = {19220-19225},
	abstract = {Plasmonic metal nanoparticles have great potential for chemical and biological sensor applications, due to their sensitive spectral response to the local environment of the nanoparticle surface and ease of monitoring the light signal due to their strong scattering or absorption. In this work, we investigated the dependence of the sensitivity of the surface plasmon resonance (frequency and bandwidth) response to changes in their surrounding environment and the relative contribution of optical scattering to the total extinction, on the size and shape of nanorods and the type of metal, that is, Au vs Ag. Theoretical consideration on the surface plasmon resonance condition revealed that the spectral sensitivity, defined as the relative shift in resonance wavelength with respect to the refractive index change of surrounding materials, has two controlling factors: first the bulk plasma wavelength, a property dependent on the metal type, and second on the aspect ratio of the nanorods which is a geometrical parameter. It is found that the sensitivity is linearly proportional to both these factors. To quantitatively examine the dependence of the spectral sensitivity on the nanorod metal composition and the aspect ratio, the discrete dipole approximation method was used for the calculation of optical spectra of Ag-Au alloy metal nanorods as a function of Ag concentration. It is observed that the sensitivity does not depend on the type of the metal but depends largely on the aspect ratio of nanorods. The direct dependence of the sensitivity on the aspect ratio becomes more prominent as the size of nanorods becomes larger. However, the use of larger nanoparticles may induce an excessive broadening of the resonance spectrum due to an increase in the contribution of multipolar excitations. This restricts the sensing resolution. The insensitivity of the plasmon response to the metal composition is attributable to the fact that the bulk plasma frequency of the metal, which determines the spectral dispersion of the real dielectric function of metals and the surface plasmon resonance condition, has a similar value for the noble metals. On the other hand, nanorods with higher Ag concentration show a great enhancement in magnitude and sharpness of the plasmon resonance band, which gives better sensing resolution despite similar plasmon response. Furthermore, Ag nanorods have an additional advantage as better scatterers compared with Au nanorods of the same size.},
	isbn = {1520-6106},
	doi = {10.1021/jp062536y},
	author = {Lee, K. S. and El-Sayed, Mostafa A}
}
@article {1168,
	title = {Dependence of the enhanced optical scattering efficiency relative to that of absorption for gold metal nanorods on aspect ratio, size, end-cap shape, and medium refractive index},
	journal = {Journal of Physical Chemistry B},
	volume = {109},
	number = {43},
	year = {2005},
	note = {Lee, KS El-Sayed, MA},
	month = {Nov},
	pages = {20331-20338},
	abstract = {The Current intense interest in the properties of plasmonic nanostructures for their applications in chemical and biochemical sensors, medical diagnostics and therapeutics, and biological imaging is fundamentally based on their enhanced optical absorption and scattering properties. In this study, the optical extinction, absorption, and scattering efficiencies were calculated as a function of shape definition, aspect ratio, surrounding medium, and material selection. The discrete dipole approximation method was used, which is known to be a very useful and versatile cornputational too] for particles with any arbitrary shape. Relative contribution of scattering to the total extinction for the longitudinal mode was found to be significantly dependent on the aspect ratio of the nanorod in a somewhat complex manner, different from a typical linear relationship for the resonance wavelength. A slight elongation of An nanosphere gives rise to a drastic increase in the relative scattering efficiency, which eventually reaches a maximum and begins to decrease with further increase in the aspect ratio. This is ascribed to the increasing absorptive contribution from the larger imaginary dielectric function of the metal particle in the longer wavelength region where the red-shifted excitation of the longitudinal resonance mode Occurs. For transverse mode exhibiting the blue-shift in the resonance peak, on the contrary, the absorption efficiency is relatively enhanced compared to the scattering efficiency with increasing aspect ratio. This is thought to result from the dominant effect of the interband transition present in this wavelength re-ion. Besides the dependence of plasmonic characteristics on the aspect ratio of nanorod, the DDA results for a small change of the end-cap shape and the index of the surrounding medium lead us to conclude that there exist two competing key factors: a weighting factor assigned to the shape parameter and the dielectric function of the metal particle, which control the relative enhancement in the scattering and absorption as well as the linearity of resonance wavelength with regard to the aspect ratio.},
	isbn = {1520-6106},
	doi = {10.1021/jp054385p},
	author = {Lee, K. S. and El-Sayed, Mostafa A}
}
@article {823,
	title = {Simulation of the Optical Absorption Spectra of Gold Nanorods as a Function of Their Aspect Ratio and the Effect of the Medium Dielectric Constant},
	journal = {The Journal of Physical Chemistry B},
	volume = {109},
	year = {2005},
	note = {doi: 10.1021/jp058091f},
	month = {2005},
	pages = {10531 - 10532},
	publisher = {American Chemical Society},
	isbn = {1520-6106},
	doi = {10.1021/jp058091f},
	url = {http://dx.doi.org/10.1021/jp058091f},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {840,
	title = {Picosecond Self-Induced Thermal Lensing from Colloidal Silver Nanodisks},
	journal = {The Journal of Physical Chemistry B},
	volume = {108},
	year = {2004},
	note = {doi: 10.1021/jp049943z},
	month = {2004},
	pages = {5230 - 5234},
	publisher = {American Chemical Society},
	abstract = {The optical and nonradiative relaxation dynamics of 5 nm thick silver nanodisks with a 25 nm diameter have been investigated in an organic solvent by continuous wave (cw) and femtosecond pump?probe time-resolved spectroscopies. Several surface plasmon absorption bands are observed due to the disk shape of these particles. In the time-resolved experiments, the time dependence of the bleach resulting from femtosecond pulsed excitation is studied. On the 1?3 ps time scale, a decay resulting from electron?phonon relaxation is observed. On a longer time scale (>20 ps), a rise rather than a further decay of the bleach intensity is observed. This is shown to result from the formation of a thermal lens due to the induced thermal gradients produced from heating the organic solvent by the phonon?phonon relaxation processes of the photoexcited nanodisks.The optical and nonradiative relaxation dynamics of 5 nm thick silver nanodisks with a 25 nm diameter have been investigated in an organic solvent by continuous wave (cw) and femtosecond pump?probe time-resolved spectroscopies. Several surface plasmon absorption bands are observed due to the disk shape of these particles. In the time-resolved experiments, the time dependence of the bleach resulting from femtosecond pulsed excitation is studied. On the 1?3 ps time scale, a decay resulting from electron?phonon relaxation is observed. On a longer time scale (>20 ps), a rise rather than a further decay of the bleach intensity is observed. This is shown to result from the formation of a thermal lens due to the induced thermal gradients produced from heating the organic solvent by the phonon?phonon relaxation processes of the photoexcited nanodisks.},
	isbn = {1520-6106},
	doi = {10.1021/jp049943z},
	url = {http://dx.doi.org/10.1021/jp049943z},
	author = {Maillard, Mathieu and Pileni, Marie-Paule and Link, Stephan and El-Sayed, Mostafa A}
}
@article {1178,
	title = {Picosecond self-induced thermal lensing from colloidal silver nanodisks},
	journal = {Journal of Physical Chemistry B},
	volume = {108},
	number = {17},
	year = {2004},
	note = {Maillard, M Pileni, MP Link, S El-Sayed, MA},
	month = {Apr},
	pages = {5230-5234},
	abstract = {The optical and nonradiative relaxation dynamics of 5 unit thick silver nanodisks with a 25 nm diameter have been investigated in an organic solvent by continuous wave (cw) and femtosecond pump-probe time-resolved spectroscopies. Several surface plasmon absorption bands are observed due to the disk shape of these particles. In the time-resolved experiments, the time dependence of the bleach resulting from femtosecond pulsed excitation is studied. On the 1-3 ps time scale, a decay resulting from electron-phonon relaxation is observed. On a longer time scale (>20 ps), a rise father than a further decay of the bleach intensity is observed. This is shown to result from the formation of a thermal lens due to the induced thermal gradients produced from heating the organic solvent by the phonon-phonon relaxation processes of the photoexcited nanodisks.},
	isbn = {1520-6106},
	doi = {10.1021/jp049943z},
	author = {Maillard, Mathieu and Pileni, Marie-Paule and Link, Stephan and El-Sayed, Mostafa A}
}
@article {838,
	title = {Propylene hydrogenation over cubic Pt nanoparticles deposited on alumina},
	journal = {BULLETIN-KOREAN CHEMICAL SOCIETY},
	volume = {25},
	year = {2004},
	pages = {843-846},
	publisher = {Korean Chemical Society},
	abstract = {Pt nanoparticles loaded on alumina through an impregnation at room temperature was prepared using K2PtCl4 and acrylic acid as capping material. Transmission electron microscopy showed that the deposited Pt particles indicate ca. 80\% cubic shapes with a narrow distribution of 8-10 nm in size. Propylene hydrogenation over the catalyst has been carried out to evaluate their catalytic performance by the values of activation energy. It is determined from the initial rate, reaction order, and rate constant and is found to be 9.7 {\textpm} 0.5 kcal/mol. This value has been discussed by comparing to those of encapsulated- and truncated octahedral Pt nanoparticles deposited on alumina, respectively, to study influence of the particle size and shape, and capping material used
on the activation energy.},
	isbn = {0253-2964},
	url = {http://www.journal.kcsnet.or.kr/main/j_search/j_abstract_view.htm?code=B040616\&qpage=j_search\&spage=b_bkcs\&dpage=ar},
	author = {Yoo, J. W. and Lee, S.M. and Kim, H.T. and El-Sayed, Mostafa A}
}
@article {839,
	title = {Shape control of platinum nanoparticles by using different capping organic materials},
	journal = {BULLETIN-KOREAN CHEMICAL SOCIETY},
	volume = {25},
	year = {2004},
	pages = {395},
	abstract = {No Abstract},
	keywords = {Cube, Nanoparticle, Platinum, Transmission electron microscopy, Truncated octahedra},
	url = {http://newjournal.kcsnet.or.kr/main/j_search/j_abstract_view.htm?code=B040315\&qpage=j_search\&spage=b_bkcs\&dpage=ar},
	author = {Yoo, J. W. and Lee, S.M. and Kim, H.T. and El-Sayed, Mostafa A}
}
@article {1187,
	title = {Medium effect on the electron cooling dynamics in gold nanorods and truncated tetrahedra},
	journal = {Advanced Materials},
	volume = {15},
	number = {5},
	year = {2003},
	note = {Link, S Hathcock, DJ Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {393-+},
	abstract = {A study on the electron relaxation dynamics and thermal cooling of colloidal gold nanoparticles (see Figure) in air and water finds that the local energy exchange with the surrounding medium occurs on the picosecond time scale, comparable with the electron-phonon relaxation, while a slow heat dissipation by water ensures that the particles remain heated for hundreds of picoseconds.},
	isbn = {0935-9648},
	doi = {10.1002/adma.200390088},
	author = {Link, Stephan and Hathcock, D. J. and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {848,
	title = {Optical Properties and Ultrafast Dynamics of Metalic Naocrystals},
	journal = {Annual Review of Physical Chemistry },
	volume = {54},
	year = {2003},
	note = {doi: 10.1146/annurev.physchem.54.011002.103759},
	month = {2003},
	pages = {331 - 366},
	publisher = {Annual Reviews},
	abstract = {? Abstract? Noble metal particles have long fascinated scientists because of their intense color, which led to their application in stained glass windows as early as the Middle Ages. The recent resurrection of colloidal and cluster chemistry has brought about the strive for new materials that allow a bottoms-up approach of building improved and new devices with nanoparticles or artificial atoms. In this review, we discuss some of the properties of individual and some assembled metallic nanoparticles with a focus on their interaction with cw and pulsed laser light of different energies. The potential application of the plasmon resonance as sensors is discussed.? Abstract? Noble metal particles have long fascinated scientists because of their intense color, which led to their application in stained glass windows as early as the Middle Ages. The recent resurrection of colloidal and cluster chemistry has brought about the strive for new materials that allow a bottoms-up approach of building improved and new devices with nanoparticles or artificial atoms. In this review, we discuss some of the properties of individual and some assembled metallic nanoparticles with a focus on their interaction with cw and pulsed laser light of different energies. The potential application of the plasmon resonance as sensors is discussed.},
	isbn = {0066-426X},
	url = {http://dx.doi.org/10.1146/annurev.physchem.54.011002.103759},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1189,
	title = {Why is the thermalization of excited electrons in semiconductor nanoparticles so rapid? Studies on CdSe nanoparticles},
	journal = {Chemical Physics Letters},
	volume = {373},
	number = {3-4},
	year = {2003},
	note = {Darugar, Q Landes, C Link, S Schill, A El-Sayed, MA},
	month = {May},
	pages = {284-291},
	abstract = {Quantum confinement of electronic motion in semiconductor nanoparticles leads to quantization of its band continua of the bulk. The relaxation between the resulting quantized levels by electron phonon coupling was expected, but not found, to be slow due to the small phonon frequencies (phonon bottleneck). Studying the electronic relaxation from the band gap and a higher excited state in CdSe dots and rods under different perturbations suggest the importance of coupling the excited electron to the surface. The surface species act as an efficient heat bath or as electron trapping sites in the linear or nonlinear (Auger) relaxation processes. (C) 2003 Elsevier Science B.V. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(03)00213-6},
	author = {Darugar, Q. and Landes, Christy F. and Link, Stephan and Schill, A. W. and El-Sayed, Mostafa A}
}
@article {1191,
	title = {Comparison of the dynamics of the primary events of bacteriorhodopsin in its trimeric and monomeric states},
	journal = {Biophysical Journal},
	volume = {83},
	number = {3},
	year = {2002},
	note = {Wang, JP Link, S Heyes, CD El-Sayed, MA},
	month = {Sep},
	pages = {1557-1566},
	abstract = {In this paper, femtosecond pump-probe spectroscopy in the visible region of the spectrum has been used to examine the ultrafast dynamics of the retinal excited state in both the native trimeric state and the monomeric state of bacteriorhodopsin (bR). It is found that the excited state lifetime (probed at 490 nm) increases only slightly upon the monomerization of bR. No significant kinetic difference is observed in the recovery process of the bR ground state probed at 570 nm nor in the fluorescent state observed at 850 nm. However, an increase in the relative amplitude of the slow component of bR excited state decay is observed in the monomer, which is due to the increase in the concentration of the 13-cis retinal isomer in the ground state of the light-adapted bR monomer. Our data indicate that when the protein packing around the retinal is changed upon bR monomerization, there is only a subtle change in the retinal potential surface, which is dependent on the charge distribution and the dipoles within the retinal-binding cavity. In addition, our results show that 40\% of the excited state bR molecules return to the ground state on three different time scales: one-half-picosecond component during the relaxation of the excited state and the formation of the J intermediate, a 3-ps component as the J changes to the K intermediate where retinal photoisomerization occurs, and a subnanosecond component during the photocycle.},
	isbn = {0006-3495},
	author = {Wang, Jianping and Link, Stephan and Heyes, C D and El-Sayed, Mostafa A}
}
@article {849,
	title = {Determination of the localization times of electrons and holes in the HgS well in a CdS/HgS/CdS quantum dot{\textendash}quantum well nanoparticle},
	journal = {Physical Review BPhys. Rev. B},
	volume = {66},
	year = {2002},
	month = {2002/11/11/},
	pages = {205312 - },
	publisher = {American Physical Society},
	abstract = {The femtosecond time-resolved electron-hole dynamics of the CdS/HgS/CdS quantum dot{\textendash}quantum well system (QDQW) was investigated as a function of excitation energy. In the transient absorption spectra four bleach bands and a stimulated emission signal in the visible spectral range between 450 and 780 nm were resolved. By using an IR probe pulse at 4.7 μm a transient induced absorption due to intraband transitions was found. The decay and rise times of these signals were measured when the CdS core or the HgS well of the nanoparticles was excited by the pump pulse. After excitation within the HgS well the transient signals rise within the resolution of our pump pulse, while after core excitation slower rise times were measured. From the 1.5 ps rise time of the stimulated emission originating from the HgS well and the intraband hole IR absorption (150 fs) after excitation into the CdS core, the electron localization time (transfer time from the core to the well) is found to be 1.5 ps while that of the hole is \~{}150 fs. This large difference in the observed dynamics of the electron and hole in crossing the CdS/HgS interface is discussed.},
	doi = {10.1103/PhysRevB.66.205312 },
	url = {http://link.aps.org/doi/10.1103/PhysRevB.66.205312},
	author = {Braun, Markus and Link, Stephan and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1202,
	title = {The effect of surface adsorption on the hyper-Rayleigh scattering of large and small CdSe nanoparticles},
	journal = {Chemical Physics Letters},
	volume = {363},
	number = {5-6},
	year = {2002},
	note = {Landes, C Braun, M El-Sayed, MA},
	month = {Sep},
	pages = {465-470},
	abstract = {Hyper-Rayleigh scattering is used to compare the effect of the addition of n-butylamine to large (3.2 nm) and small (1.6 nm) Use nanoparticles (NPs). It is found that although the adsorption of n-butylamine on large NPs enhances their nonlinear optical response, it has the opposite effect when adsorbed on the small nanoparticles for which the amine adsorption was found previously to induce structural changes. This observation is consistent with an increase in the symmetry of the nanocrystal structure such as would be observed in a phase change from a 4-coordinate wurtzite crystal structure to that of a 6-coordinate zinc-blend form. (C) 2002 Published by Elsevier Science B.V.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(02)01169-7},
	author = {Landes, Christy F. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1196,
	title = {Hot electron relaxation dynamics of gold nanoparticles embedded in MgSO4 powder compared to solution: The effect of the surrounding medium},
	journal = {Journal of Physical Chemistry B},
	volume = {106},
	number = {5},
	year = {2002},
	note = {Link, S Furube, A Mohamed, MB Asahi, T Masuhara, H El-Sayed, MA},
	month = {Feb},
	pages = {945-955},
	abstract = {To test the influence of the surrounding medium on the relaxation dynamics of the plasmon band bleach recovery of gold nanoparticles after excitation with femtosecond laser pulses, we embedded 14.5 and 12.1 nm colloidal gold nanoparticles (synthesized electrochemically) in MgSO4 powder and investigated these samples by femtosecond diffuse reflectance spectroscopy. By measuring the relaxation dynamics over a wide range of excitation energies, we found that the fast decay component is slower by about a factor of 2 for the particles in the MgSO4 powder compared to those in solution while no significant change in the slow decay component is observed. In agreement with this observation, we found that adding solvent to the particles embedded in the powder caused a decrease in the relaxation time from about 10 ps to 5 ps for the fast decay component. This leads to the conclusion that the electron-phonon relaxation in these gold nanoparticles depends on the chemical nature and/or physical phase (solid vs solution) of the surrounding medium. A discussion of this in terms of the type of phonon involved, and the nature of the electron-phonon and phonon-phonon relaxation processes is discussed. To our knowledge, this also presents the first time that a transient bleach could be observed by diffuse reflectance spectroscopy.},
	isbn = {1520-6106},
	doi = {10.1021/jp013311k},
	author = {Link, Stephan and Furube, A. and Mohamed, MB and Asahi, T. and Masuhara, H. and El-Sayed, Mostafa A}
}
@article {852,
	title = {The pump power dependence of the femtosecond relaxation of CdSe nanoparticles observed in the spectral range from visible to infrared},
	journal = {The Journal of chemical physics},
	volume = {116},
	year = {2002},
	pages = {3828},
	abstract = {The pump power dependence of the relaxation dynamics of CdSe nanoparticles (NPs) was studied with femtosecond pump probe spectroscopy at observation wavelengths of the first exciton transition at 560 nm, the near infrared (NIR) absorption at 2 μm, and the transient mid-infrared (IR) absorption at 4.5 μm. Excitation with less than one photon per particle leads to bleaching of the excitonic transitions, and the bleach intensity is initially linear to the pump power. At higher pump power the bleach intensity levels off, when complete saturation of the excitonic transition is reached. At the same time, increasing pump power causes an acceleration of the bleach decay, which is due to additional Auger processes when multiple excitons are formed in the NPs. In addition, the pump power effect was investigated for the NIR and IR regions, at 2 and 4.5 μm wavelength, respectively. Whereas the IR transients are very similar to the ones observed for the bleach, the NIR transients behave completely different. No pump power dependence was found for the transients at 2 μm when pumped in a power range from 0.5 to 5 μJ per pulse. The results show that the fs transients in the visible (bleach) and IR (absorption) regions are due to electron relaxation in the conduction band and the NIR transients are due to the relaxation of the hole. Furthermore, it suggests that in the investigated CdSe NPs, Auger processes act much more efficiently on the electrons than for the holes. },
	doi = {10.1063/1.1446851},
	url = {http://link.aip.org/link/doi/10.1063/1.1446851},
	author = {Burda, Clemens and Link, Stephan and Mohamed, MB and El-Sayed, Mostafa A}
}
@article {1198,
	title = {Room temperature optical gain in CdSe nanorod solutions},
	journal = {Journal of Applied Physics},
	volume = {92},
	number = {11},
	year = {2002},
	note = {Link, S El-Sayed, MA},
	month = {Dec},
	pages = {6799-6803},
	abstract = {We have performed femtosecond transient absorption measurements on CdSe nanorods in hexane solution as a function of pump wavelength and pump intensity. We found that although it is not possible to achieve optical gain when pumping at energies (400 nm) high above the band-gap energy, this problem can be circumvented by pumping the CdSe nanorods directly at the lowest 1S transition. We attribute the difference to alternative relaxation pathways and possibly trapping, resulting in a competing induced absorption below the band-gap energy when excitation is carried out at high energies. Our results suggest that it is possible to achieve stimulated emission from CdSe nanoparticles in solution at ambient temperature if the excitation wavelength is chosen properly. (C) 2002 American Institute of Physics.},
	isbn = {0021-8979},
	doi = {10.1063/1.1512689},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1200,
	title = {Size effects of PVP-Pd nanoparticles on the catalytic Suzuki reactions in aqueous solution},
	journal = {Langmuir},
	volume = {18},
	number = {12},
	year = {2002},
	note = {Li, Y Boone, E El-Sayed, MA},
	month = {Jun},
	pages = {4921-4925},
	abstract = {A series of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized Pd nanoparticles with varying particle size are prepared by using the stepwise growth reaction. The effect of Pd particle size on the Suzuki reaction between phenylboronic acid and iodobenzene is investigated by the use of four Pd catalysts with mean particle sizes of 3.0, 3.9, 5.2, and 6.6 nm, respectively. The catalytic activity of the Pd nanoparticles expressed in terms of the initial turnover frequency (moles of the biphenyl product per mole of total surface Pd atoms per min) is found to be in the order of Pd (3.9 nm) > Pd (3.0 nm) approximate to Pd (5.2 nm) > Pd (6.6 nm), indicating that surface Pd atoms do not all have the same reactivity in this reaction. The general trend of increased catalytic activity with the decrease in the particle size suggests that the low-coordination number vertex and edge atoms on the particle surface are active sites for the Suzuki reaction. The lower catalytic activity for the smallest Pd nanoparticles might be due to stronger adsorption of the reaction intermediates on the particle surface, in which the strongly adsorbed species act as a poison to the reaction thereby decreasing the rate of the reaction.},
	isbn = {0743-7463},
	doi = {10.1021/la011469q},
	author = {Li, Y. and Boone, E. and El-Sayed, Mostafa A}
}
@article {1201,
	title = {Thermodynamic and kinetic characterization of the interaction between N-butylamine and similar to 1 nm CdSe nanoparticles},
	journal = {Journal of Physical Chemistry A},
	volume = {106},
	number = {33},
	year = {2002},
	note = {Landes, C El-Sayed, MA},
	month = {Aug},
	pages = {7621-7627},
	abstract = {When butylamine (0.1-0.25 M) is added to a colloidal solution of CdSe nanoparticles (NPs) that are 1-2 nm in diameter, the band gap absorption changes from a broad, relatively weak band centered at 445 nm to a narrow, relatively strong absorption centered at 414 nm. The effect of concentration on the observed spectrum shows an isobestic point, suggesting an equilibrium between two species. Thermodynamic and kinetic studies of this process were carried out. The transition was found to be exothermic, with a size-dependent heat of reaction,that suggests that there is a direct proportionality between the NP size and the exothermicity of the interaction. The decay kinetics of the original peak were studied and compared to the rise kinetics of the 414 nm peak. The decay of the original NPs was biexponential, with a lifetime that depends on the NP size, concentration of reactants,. and the temperature. The rise in the 414 nm peak was found to be multiexponential, reflecting 2 transformations from the ensemble having different NP sizes. A mechanism is proposed for this interaction that depends on the binding of butylamine to the NP surface, followed by a release in energy. The nature of the new species absorbing at 414 nm is discussed.},
	isbn = {1089-5639},
	doi = {10.1021/jp0201130},
	author = {Landes, Christy F. and El-Sayed, Mostafa A}
}
@article {854,
	title = {Transfer times of electrons and holes across the interface in CdS/HgS/CdS quantum dot quantum well nanoparticles},
	journal = {Chemical physics letters},
	volume = {361},
	year = {2002},
	pages = {446-452},
	publisher = {Elsevier},
	abstract = {The electron and hole trapping times in the HgS well of a 6 nm CdS/HgS/CdS quantum dot quantum well nanoparticle were determined from the rise time of the ultrafast transient absorption in the visible and IR regions as well as the trap fluorescence when the CdS core is excited. From the 1.5 ps observed rise time of the well fluorescence (which is determined by the trapping time of the slowest carrier) and the intraband hole IR absorption (150 fs), the electron localization time is found to be 1.5 ps while that of the hole is \~{}150 fs. This large difference in the observed dynamics of the electron and hole in crossing the CdS/HgS interface is discussed.},
	isbn = {0009-2614},
	doi = {10.1016/S0009-2614(02)01001-1 },
	url = {http://dx.doi.org/10.1016/S0009-2614(02)01001-1 },
	author = {Braun, Markus and Link, Stephan and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1197,
	title = {Transition from nanoparticle to molecular behavior: a femtosecond transient absorption study of a size-selected 28 atom gold cluster},
	journal = {Chemical Physics Letters},
	volume = {356},
	number = {3-4},
	year = {2002},
	note = {Link, S El-Sayed, MA Schaaff, TG Whetten, RL},
	month = {Apr},
	pages = {240-246},
	abstract = {The ultrafast electron dynamics of chemically prepared gold nanoclusters with a 28 atom gold core surrounded by 16 glutathione molecules were investigated. After excitation with femtosecond laser pulses these clusters show an induced transient absorption in the visible from 2.58 to 1.65 eV (480-750 nm) with a maximum around 2.07 eV (600 nm). The excited state relaxation shows a biexponential decay with a subpicosecond and a longer nanosecond decay time independent of the laser pump power. These results are different from those observed previously for larger gold nanoparticles, which suggests that the Au-28-glutathione system shows molecular properties. (C) 2002 Elsevier Science B.V. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(02)00306-8},
	author = {Link, Stephan and El-Sayed, Mostafa A and Schaaff, T. G. and Whetten, R. L.}
}
@article {1199,
	title = {Visible to infrared luminescence from a 28-atom gold cluster},
	journal = {Journal of Physical Chemistry B},
	volume = {106},
	number = {13},
	year = {2002},
	note = {Link, S Beeby, A FitzGerald, S El-Sayed, MA Schaaff, TG Whetten, RL},
	month = {Apr},
	pages = {3410-3415},
	abstract = {The luminescence properties of chemically prepared gold nanoclusters, each composed of a 28-atom core and a glutathione (GSH) adsorbate layer consisting of 16 molecules, were investigated. These clusters show a distinct absorption onset at 1.3 eV corresponding to the opening of an electronic gap within the conduction band (HOMO-LUMO gap). Here we report on the radiative properties of these molecular-like Bald clusters. By using a combination of different detectors with sensitivities in the visible to the infrared (2.0-0.8 eV), a broad luminescence extending over this entire spectral range was observed. Our results further suggest that the luminescence can be separated into two bands with maxima around 1.5 and 1.15 eV indicating that radiative recombination between the ground state and two distinctively different excited states takes place. The: origin of the observed luminescence bands is discussed using a solid state as well as a molecular model for the electronic structure and relaxation of the clusters. The total quantum yield of the luminescence: as measured at ambient temperature was approximated to be about (3.5 +/- 1.0) x 10(-3).},
	isbn = {1520-6106},
	doi = {10.1021/jp014259v},
	author = {Link, Stephan and Beeby, A. and FitzGerald, S. and El-Sayed, Mostafa A and Schaaff, T. G. and Whetten, R. L.}
}
@article {1204,
	title = {Direct observation of charge-transfer dynamics in a conjugated conducting polymer poly (3-octylthiophene)-fullerene composite by time-resolved infrared spectroscopy},
	journal = {Physical Review B},
	volume = {64},
	number = {23},
	year = {2001},
	note = {Wang, JP Li, Y Hong, XY El-Sayed, MA},
	month = {Dec},
	abstract = {Transient infrared-active vibrational (IRAV) modes observed in the pi -conjugated conducting polymers upon photoexcitation are usually used to characterize the dynamics of the photoinduced charge separation and recombination processes. In this paper, the dynamic behavior of photogenerated charge carrier in the poly(3-octylthiophene) (P3OT) conducting polymer doped with fullerene (C(60)) has been studied by using step-scan time-resolved Fourier-transform infrared spectroscopy at room temperature in the 2500-900-cm(-1) (0.31-0.11-eV) frequency region. Upon photoexcitation with a 10-ns laser pulses, it is observed that IRAV modes appear in the similar vibrational frequency regions for pure P3OT and C(60)-doped P3OT; however, the observed IRAV modes is enhanced by 800\% in intensity in the presence of small amount of C(60) (e.g., 10\%). Our results also show that the charge separation occurs instantaneously within the laser pulse width (10 ns), whereas the charge recombination processes occur in the microseconds to a few milliseconds time domain. In addition, the observed enhancement in the IRAV modes upon C(60) doping indicates an enhanced photogeneration efficiency of the charge separation.},
	isbn = {1098-0121},
	doi = {10.1103/PhysRevB.64.235413},
	author = {Wang, Jianping and Li, Y. and Hong, X. Y. and El-Sayed, Mostafa A}
}
@article {1214,
	title = {The effect of stabilizers on the catalytic activity and stability of Pd colloidal nanoparticles in the Suzuki reactions in aqueous solution},
	journal = {Journal of Physical Chemistry B},
	volume = {105},
	number = {37},
	year = {2001},
	note = {Li, Y El-Sayed, MA},
	month = {Sep},
	pages = {8938-8943},
	abstract = {Transition metal nanoparticles used in catalysis in solution are stabilized by capping the surfaces that are supposed to be used for catalysis. Determining, how these two properties, that is, the catalytic activity and stability of nanoparticles, change as different capping materials are used is the aim of this work. Pd nanoparticles prepared by the reduction of metal salts in the presence of three different stabilizers-hydroxyl-terminated poly(amido-amine) (PAMAM) dendrimers (Gn-OH, where Gn represents the nth generation), block copolymer polystyrene-b-poly(sodium acrylate) and poly (N-vinyl-2-pyrrolidone) (PVP)-are used as catalysts in the Suzuki reactions in an aqueous medium to investigate the effects of these stabilizers on the metallic nanoparticle catalytic activity and stability. The stability of the Pd nanoparticles is measured by the tendency of the nanoparticles to give Pd black powder after the catalytic reaction. The Suzuki reaction is a good "acid test" for examining the stability of these nanoparticles, as it takes place when refluxed at about 100 degreesC for 24 h. The stability is found to depend on the type of the stabilizer, the reactant, and the base used in the reaction system. Pd nanoparticles stabilized by block copolymer, G3 dendrimer, and PVP are found to be efficient catalysts for the Suzuki reactions between phenylboronic acid (or 2-thiopheneboronic acid) and iodobenzene. G4 dendrimer is found to be an effective stabilizer; however, strong encapsulation of Pd particles in the dendrimer results in a loss of catalytic activity. The Suzuki reactions between arylboronic acids and bromoarenes catalyzed by Pd nanoparticles result in byproducts due to the homo-coupling of bromoarenes. A summary of the catalytic activity and stability of the Pd nanoparticles in these different systems is tabulated. As one would expect. these two properties are anticorrelated that is the most stable is the least catalytic active.},
	isbn = {1089-5647},
	doi = {10.1021/jp010904m},
	author = {Li, Y. and El-Sayed, Mostafa A}
}
@article {1212,
	title = {Formation of quantum-dot quantum-well heteronanostructures with large lattice mismatch: ZnS/CdS/ZnS},
	journal = {Journal of Chemical Physics},
	volume = {114},
	number = {4},
	year = {2001},
	note = {Little, RB El-Sayed, MA Bryant, GW Burke, S},
	month = {Jan},
	pages = {1813-1822},
	abstract = {Two-dimensional heterostructures have been exploited extensively in the synthesis of optoelectronic devices. Structures with small lattice mismatch can be synthesized readily. Large lattice mismatch in II-VI film heterostructures makes synthesis of devices with these materials more difficult. However, these large mismatch heterostructures usually have useful optical properties. One such heterostructure is the ZnS/CdS system with a large exciton binding energy and a large band gap useful for blue-green emitting devices. In this work, small II-VI nanoparticles are studied. We show that II-VI heterostructures can be made in quantum dots, despite the large bulk lattice mismatch. Two well-known techniques are combined to synthesize first very small ZnS and CdS seed nanoparticles and then do nanoepitaxy on them to produce ZnS/CdS core/shell quantum-dot quantum-well heteronanostructures. These structures are characterized by UV visible absorbance. Measured spectra are compared with electronic level structures calculated for the fabricated heteronanostructures with a tight-binding model. The consistency of the observed spectra with the predicted transitions indicates that the desired core/shell and core/shell/clad structures were grown. The metastability of the ZnS/CdS/ZnS heteronanostructures is attributed to low-temperature construction and small crystal size (<3 nm). The small particle size should produce large surface forces and ZnS core contraction. Also, the small particle size should accommodate strain, as a result of the ZnS/CdS interfacial curvature, which is not possible for planar systems. Furthermore, this new structure is kinetically stabilized against alloying by the large size difference between the Cd2+ ion and Zn2+ ions. We suggest that all of these factors contribute to the formation of quantum-dot quantum-well ZnS/CdS/ZnS heteronanostructures. (C) 2001 American Institute of Physics.},
	isbn = {0021-9606},
	doi = {10.1063/1.1333758},
	author = {Little, Reginald and El-Sayed, Mostafa A and Bryant, G. W. and Burke, S.}
}
@article {1210,
	title = {Hot electron and phonon dynamics of gold nanoparticles embedded in a gel matrix},
	journal = {Chemical Physics Letters},
	volume = {343},
	number = {1-2},
	year = {2001},
	note = {Mohamed, MB Ahmadi, TS Link, S Braun, M El-Sayed, MA},
	month = {Jul},
	pages = {55-63},
	abstract = {Using pump-probe technique, the dynamics of the hot carriers in metallic nanodots induced by femtosecond laser pulses are investigated in gold nanoparticles embedded in hydrogel and in organic gel and compared to that in aqueous solution. We found that changing the surrounding matrix from aqueous solution to hydrogel and then to organic gel leads to a large increase in the relaxation time of both the electron-phonon (e-ph) and the phonon-phonon (ph-ph) coupling. Furthermore, the ph-ph relaxation time becomes sensitive to the type of the organic solvent trapped in the gel network. This indicates that the relaxation dynamics depend on the thermal conductivity, chemical structure and the molecular dynamics of the surrounding medium. (C) 2001 Elsevier Science BN. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(01)00653-4},
	author = {Mohamed, MB and Ahmadi, Temer S. and Link, Stephan and Braun, Markus and El-Sayed, Mostafa A}
}
@article {855,
	title = {On the Nanoparticle to Molecular Size Transition:  Fluorescence Quenching Studies},
	journal = {The Journal of Physical Chemistry B},
	volume = {105},
	year = {2001},
	note = {doi: 10.1021/jp0118726},
	month = {2001},
	pages = {10554 - 10558},
	publisher = {American Chemical Society},
	abstract = {Semiconductor nanoparticles, NPs, exhibit fluorescence properties that are closely related to the nature of their surface. CdSe NPs that range in size from 2 to 15 nm in diameter fluoresce with both near-band-edge emission and deep-trap emission, depending on the quality of the surface. When butylamine is added to colloidal solutions of NPs in this size range, the amine is thought to bind to the NP surface and eliminate radiant recombination pathways that lead to luminescence. Since the amine binds to the NP surface, the decrease in fluorescence intensity does not follow standard molecular models of collisional fluorescence quenching. NPs that are smaller than ?2 nm are composed entirely of a discontinuous arrangement of atoms that are all in constant chemical contact with capping material, solvent, and contaminants. When butylamine is added to solutions of these smaller NPs, the fluorescence quenching follows more standard collisional quenching models. Thus, by monitoring the interaction between NPs and a hole acceptor such as butylamine, one can observe the transition from NP, with atoms both in the core and on the surface, to molecular cluster, with no core atoms to dominate the electron density, but with only surface atoms that can participate in molecular processes such as electron transfer.Semiconductor nanoparticles, NPs, exhibit fluorescence properties that are closely related to the nature of their surface. CdSe NPs that range in size from 2 to 15 nm in diameter fluoresce with both near-band-edge emission and deep-trap emission, depending on the quality of the surface. When butylamine is added to colloidal solutions of NPs in this size range, the amine is thought to bind to the NP surface and eliminate radiant recombination pathways that lead to luminescence. Since the amine binds to the NP surface, the decrease in fluorescence intensity does not follow standard molecular models of collisional fluorescence quenching. NPs that are smaller than ?2 nm are composed entirely of a discontinuous arrangement of atoms that are all in constant chemical contact with capping material, solvent, and contaminants. When butylamine is added to solutions of these smaller NPs, the fluorescence quenching follows more standard collisional quenching models. Thus, by monitoring the interaction between NPs and a hole acceptor such as butylamine, one can observe the transition from NP, with atoms both in the core and on the surface, to molecular cluster, with no core atoms to dominate the electron density, but with only surface atoms that can participate in molecular processes such as electron transfer.},
	isbn = {1520-6106},
	url = {http://dx.doi.org/10.1021/jp0118726},
	author = {Landes, Christy F. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1216,
	title = {Observation of large changes in the band gap absorption energy of small CdSe nanoparticles induced by the adsorption of a strong hole acceptor},
	journal = {Nano Letters},
	volume = {1},
	number = {11},
	year = {2001},
	note = {Landes, C Braun, M Burda, C El-Sayed, MA},
	month = {Nov},
	pages = {667-670},
	abstract = {When butylamine In relatively high concentrations (0.1-0.25 M) is added to a colloidal solution of CdSe nanoparticles (NPs) that are approximately 1.6 nm in diameter, the band gap absorption changes from a broad, relatively weak absorption centered at 445 nm to a narrow, relatively strong absorption centered at 414 nm. The effect of concentration on the observed spectrum shows an isobestic point, suggesting an equilibrium between two species. The possible mechanisms for such a transformation are discussed.},
	isbn = {1530-6984},
	doi = {10.1021/nl015619t},
	author = {Landes, Christy F. and Braun, Markus and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1215,
	title = {Photoluminescence of CdSe nanoparticles in the presence of a hole acceptor: n-butylamine},
	journal = {Journal of Physical Chemistry B},
	volume = {105},
	number = {15},
	year = {2001},
	note = {Landes, C Burda, C Braun, M El-Sayed, MA},
	month = {Apr},
	pages = {2981-2986},
	abstract = {Addition of butylamine to a solution of colloidal CdSe nanoparticles (NPs) caused a decrease in fluorescence intensity, with no effect on the picosecond bleach recovery of the exciton formation or on the luminescence dynamics. The relative fluorescence quantum yield was found to decrease with increasing butylamine concentration and to level off at high concentrations, but the fluorescence lifetimes were not influenced. The nonlinear concentration dependence of the fluorescence quantum yield did not follow the Stern-Volmer equation. This is in agreement with the observation that the CdSe luminescence lifetime was not affected by the addition of butylamine. A mechanism is proposed in which the emission observed in CdSe is assumed to result from the combination of surface-trapped electrons and holes. n-Butylamine occupies hole sites, thus blocking the recombination process, which results in decreasing the density of luminescent centers. These results will be discussed in terms of the nature of the binding sites of the amine on the nanoparticle surface.},
	isbn = {1089-5647},
	doi = {10.1021/jp0041050},
	author = {Landes, Christy F. and Burda, Clemens and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1211,
	title = {The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {98},
	number = {15},
	year = {2001},
	note = {Logunov, SL Volkov, VV Braun, M El-Sayed, MA},
	month = {Jul},
	pages = {8475-8479},
	abstract = {We present the results of two-pump and probe femtosecond experiments designed to follow the relaxation dynamics of the lowest excited state (S-1) populated by different modes. In the first mode, a direct (S-0 --> S-1) radiative excitation of the ground state is used. In the second mode, an indirect excitation is used where the S-1 state is populated by the use of two femtosecond laser pulses with different colors and delay times between them. The first pulse excites the S-0 --> S-1 transition whereas the second pulse excites the S-1 --> S-n transition. The nonradiative relaxation from the S-n state populates the lowest excited state. Our results suggest that the S1 state relaxes faster when populated nonradiatively from the S-n state than when pumped directly by the S-0 --> S-1 excitation. Additionally, the S-n --> S-1 nonradiative relaxation time is found to change by varying the delay time between the two pump pulses. The observed dependence of the lowest excited state population as well as its dependence on the delay between the two pump pulses are found to fit a kinetic model in which the S-n state populates a different surface (called Si) than the one being directly excited (S-1). The possible involvement of the A(g) type states, the J intermediate, and the conical intersection leading to the S-0 or to the isomerization product (K intermediate) are discussed in the framework of the proposed model.},
	isbn = {0027-8424},
	doi = {10.1073/pnas.141220198},
	author = {Logunov, Stephan L. and Volkov, V. V. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1213,
	title = {Spectroscopic determination of the melting energy of a gold nanorod},
	journal = {Journal of Chemical Physics},
	volume = {114},
	number = {5},
	year = {2001},
	note = {Link, S El-Sayed, MA},
	month = {Feb},
	pages = {2362-2368},
	abstract = {Gold nanorods in colloidal solution can be melted into spherical nanoparticles by excitation with intense femtosecond laser pulses of the proper energy. The threshold of the laser pulse energy for the complete melting of the nanorods with a mean aspect ratio of 4.1 in solution is determined by observing the change in the absorption intensity of the longitudinal absorption band (measure of the rod concentration) at 800 nm with increasing number of laser pulses of known energy. The number of laser pulses needed to reduce the band intensity (rod concentration) by 1/e of its initial value is determined as the laser energy per pulse increases. For pulses of lower energy than threshold, it is found that the number of pulses required to melt the gold nanorods present in solution increases significantly with decreasing laser pulse energy. Above threshold, this number is constant since the additional absorbed laser energy will only further heat the particles to temperatures above their melting point. The gold concentration in the colloidal solution is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), from which the gold nanorod concentration is determined from the known shape and size distribution obtained from transmission electron microscopy (TEM) results. A simple analysis using the determined threshold energy and the nanorod concentration showed that it takes an average of similar to 60 femtojoule (fJ) to melt a single gold nanorod. Experiments using 820 nm as well as 410 nm femtosecond laser pulses yield similar values, indicating that the laser induced shape transformation of the nanorods is independent of the irradiation wavelength and that this process is therefore photothermal in origin. (C) 2001 American Institute of Physics.},
	isbn = {0021-9606},
	doi = {10.1063/1.1336140},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1205,
	title = {Temperature-jump investigations of the kinetics of hydrogel nanoparticle volume phase transitions},
	journal = {Journal of the American Chemical Society},
	volume = {123},
	number = {45},
	year = {2001},
	note = {Wang, JP Gan, DJ Lyon, LA El-Sayed, MA},
	month = {Nov},
	pages = {11284-11289},
	abstract = {The dynamics of the deswelling and swelling processes in thermoresponsive poly-N-isopropylacrylamide (pNIPAm) hydrogel nanoparticles have been studied by using time-resolved transmittance measurements, in combination with a nanosecond laser-induced temperature-jump (T-jump) technique. A decrease in the solution transmittance associated with deswelling of the particles has been observed as the solution temperature traverses the volume phase transition temperature of the particles. Upon inducing the T-jump, the deswelling transition only occurs in a small percentage (< 10\%) of the particle volume, which was found to be a thin periphery layer of the particles. The particle deswelling occurs on the microsecond time scale, and as shown previously, the collapse time can be tuned via adding small amounts of hydrophobic component to the particle shell. In contrast, the reswelling of the particles was thermodynamically controlled by bath equilibration, and only small differences in particle reswelling kinetics were found due to sluggish heat dissipation (millisecond time scale) from the sample cell.},
	isbn = {0002-7863},
	doi = {10.1021/ja016610w},
	author = {Wang, Jianping and Gan, D. J. and Lyon, L. A. and El-Sayed, Mostafa A}
}
@article {1230,
	title = {Activation energy of the reaction between hexacyanoferrate(III) and thiosulfate ions catalyzed by platinum nanoparticles},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {47},
	year = {2000},
	note = {Li, Y Petroski, J El-Sayed, MA},
	month = {Nov},
	pages = {10956-10959},
	abstract = {A temperature-dependent study was carried out for the platinum-nanoparticle-catalyzed electron-transfer reaction between hexacyanoferrate(III) and thiosulfate ions in the temperature range of 20-70 degreesC. The Pt nanoparticles are dominantly truncated octahedral in shape and have an average particle size of 7.0 +/- 0.8 nm. The catalyzed reaction is compared with the uncatalyzed reaction in the same temperature range. The activation energy of the reaction is found to be 38.3 +/- 2.0 kJ/mol for the uncatalyzed reaction and 17.6 +/- 0.9 kJ/mol for the catalyzed reaction in the lower temperature range (20-50 degreesC). In the higher temperature range (50-70 degreesC), the rate remains nearly constant. This behavior is attributed to the cancellation of two effects: the temperature dependence of the catalytic reaction and the decrease in the catalyst surface area due to the increase of nanoparticle aggregation.},
	isbn = {1089-5647},
	doi = {10.1021/jp002569s},
	author = {Li, Y. and Petroski, J. M. and El-Sayed, Mostafa A}
}
@article {1233,
	title = {Femtosecond dynamics of a simple merocyanine dye: Does deprotonation compete with isomerization?},
	journal = {Journal of the American Chemical Society},
	volume = {122},
	number = {28},
	year = {2000},
	note = {Burda, C Abdel-Kader, MH Link, S El-Sayed, MA},
	month = {Jul},
	pages = {6720-6726},
	abstract = {The primary photochemistry of the trans isomer of a simple merocyanine dye of the stilbazolium betaine type 1-methyl-4-(4{\textquoteright}-hydroxytyryl)pyridinium betaine (M-trans) and its conjugate acid MHtrans+ in aqueous solution is studied by femtosecond time-resolved pump probe spectroscopy. The measured rate of the primary photodynamics is determined to be k = 1.1 x 10(12) s(-1) for M-trans at pH 10 and 0.8 x 10(12) s(-1) for MHtrans+ at pH 6. This was assigned to either conformational changes or a simple vibrational relaxation before the actual isomerization takes place. Wavelength excitation studies give support for the former assignment. These results an discussed in terms of the recent results found for the primary processes of retinal in bacteriorhodopsin. Time-resolved transient measurements show that no excited-state deprotonation of MHtrans+ occurs in aqueous solutions at pH 6 or pH 0, suggesting that the deprotonation occurs on a longer time scale than the picosecond time domain. This is in agreement with present theories of intermolecular proton-transfer reactions, which require solvent reorganization as well as the time of deprotonation estimated from the pK(a) value of this molecule in the excited state. The results of our MO calculations on the electronic structure of these two compounds could account for the fact that, while MHtrans+ photoisomerizes, its deprotonated form does not.},
	isbn = {0002-7863},
	doi = {10.1021/ja993940w},
	author = {Burda, Clemens and Abdel-Kader, M. H. and Link, Stephan and El-Sayed, Mostafa A}
}
@article {1229,
	title = {Femtosecond transient-absorption dynamics of colloidal gold nanorods: Shape independence of the electron-phonon relaxation time},
	journal = {Physical Review B},
	volume = {61},
	number = {9},
	year = {2000},
	note = {Link, S Burda, C Mohamed, MB Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {6086-6090},
	abstract = {We studied the femtosecond dynamics of colloidal gold nanorods encapsulated in micelles after excitation with 400 nm pulses of 100 fs duration. It is found that the laser heating of the electron gas of gold nanorods with an average aspect ratio of 3.8 leads to the bleaching of both the transverse and longitudinal mode of the surface plasmon oscillation at 520 and 750 nm. The bleach recovers with the same time constant for both the transverse and longitudinal oscillation, for gold nanodots prepared by photothermal reshaping of the rods as well as for nanodots synthesized chemically by citrate reduction (and known to have twin boundaries and surface defects). Since the bleach recovery on the 3 ps time scale is assigned to electron-phonon relaxation processes, these results suggest that phonon dependent relaxation processes in gold nanoparticles are independent of the shape, size, type of the surfaces, or the mode of the surface plasmon, oscillation excited. The fact that the mean free path of the electron in metallic gold is in the nanometer length scale (similar to 50 nm) raised the question of the importance of surface scattering to the electron-phonon relaxation process in gold nanoparticles. Our previous studies showed little dependence of the relaxation rate of the size of gold nanodots (from 9 to 48 nm). In the present study, the electron-phonon relaxation is measured in gold nanorods, which have different facets from those of gold nanodots.},
	isbn = {1098-0121},
	doi = {10.1103/PhysRevB.61.6086},
	author = {Link, Stephan and Burda, Clemens and Mohamed, MB and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1226,
	title = {How does a gold nanorod melt?},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {33},
	year = {2000},
	note = {Link, S Wang, ZL El-Sayed, MA},
	month = {Aug},
	pages = {7867-7870},
	abstract = {Structural transformation of gold nanorods are investigated by high-resolution transmission electron microscopy after they have been exposed to low-energy femtosecond and nanosecond laser pulses in colloidal solution. The pulse energies were below the gold nanorod melting threshold, but allowed early stage shape transformation processes, It is found that while the as-prepared nanorods are defect-free, laser-irradiation induces point and line defects. The defects are dominated by (multiple) twins and stacking faults (planar defects), which are the precursor that drives the nanorods to convert their {110} facets into the more stable {100} and {111} facets and hence minimize their surface energy. These observations suggest that short-laser pulsed photothermal melting begins with the creation of defects inside the nanorods followed by surface reconstruction and diffusion, in contrast with the thermal melting of the rods or the bulk material, where the melting starts at the surface.},
	isbn = {1089-5647},
	doi = {10.1021/jp0011701},
	author = {Link, Stephan and Wang, Z.L. and El-Sayed, Mostafa A}
}
@article {1228,
	title = {Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {26},
	year = {2000},
	note = {Link, S Burda, C Nikoobakht, B El-Sayed, MA},
	month = {Jul},
	pages = {6152-6163},
	abstract = {Gold nanorods have been found to change their shape after excitation with intense pulsed laser irradiation. The final irradiation products strongly depend on the energy of the laser pulse as well as on its width. We performed a series of measurements in which the excitation power was varied over the range of the output power of an amplified femtosecond laser system producing pulses of 100 fs duration and a nanosecond optical parametric oscillator (OPO) laser system having a pulse width of 7 ns. The shape transformations of the gold nanorods are followed by two techniques: (1) visible absorption spectroscopy by monitoring the changes in the plasmon absorption bands characteristic for gold nanoparticles; (2) transmission electron microscopy (TEM) in order to analyze the final shape and size distribution. While at high laser fluences (similar to 1 J cm(-2)) the gold nanoparticles fragment, a melting of the nanorods into spherical nanoparticles (nanodots) is observed when the laser energy is lowered. Upon decreasing the energy of the excitation pulse, only partial melting of the nanorods takes place. Shorter but wider nanorods are observed in the final distribution as well as a higher abundance of particles having odd shapes (bent, twisted, phi-shaped, etc.). The threshold for complete melting of the nanorods with femtosecond laser pulses is about 0.01 J cm(-2). Comparing the results obtained using the two different types of excitation sources (femtosecond vs nanosecond laser), it is found that the energy threshold for a complete melting of the nanorods into nanodots is about 2 orders of magnitude higher when using nanosecond laser pulses than with femtosecond laser pulses. This is explained in terms of the successful competitive cooling process of the nanorods when the nanosecond laser pulses are used. For nanosecond pulse excitation, the absorption of the nanorods decreases during the laser pulse because of the bleaching of the longitudinal plasmon band. In addition, the cooling of the lattice occurring on the 100 ps time scale can effectively compete with the rate of absorption in the case of the nanosecond pulse excitation but not for the femtosecond pulse excitation. When the excitation source is a femtosecond laser pulse, the involved precesses (absorption of the photons by the electrons (100 fs), heat transfer between the hot electrons and the lattice (<10 ps), melting (30 ps), and heat loss to the surrounding solvent (>100 ps) are clearly separated in time.},
	isbn = {1089-5647},
	doi = {10.1021/jp000679t},
	author = {Link, Stephan and Burda, Clemens and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1224,
	title = {The {\textquoteright}lightning{\textquoteright} gold nanorods: fluorescence enhancement of over a million compared to the gold metal},
	journal = {Chemical Physics Letters},
	volume = {317},
	number = {6},
	year = {2000},
	note = {Mohamed, MB Volkov, V Link, S El-Sayed, MA},
	month = {Feb},
	pages = {517-523},
	abstract = {Gold nanorods capped with micelles and having an aspect ratio of 2.0-5.4 are found to fluoresce with a quantum yield which is over a million times that of the metal. For rods of the same width, the yield is found to increase quadratically while the wavelength maximum increases linearly with the length. We assign this emission to the electron and hole interband recombination. The increase in the emission yield results from the enhancement effect of the incoming and outgoing electric fields via coupling to the surface plasmon resonance in the rods. This is similar to the previously proposed fluorescence and the Raman enhancement on noble metal rough surfaces. (C) 2000 Published by Elsevier Science B.V. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(99)01414-1},
	author = {Mohamed, MB and Volkov, V. V. and Link, Stephan and El-Sayed, Mostafa A}
}
@article {857,
	title = {Origin of emission from porous silicon: Temperature-dependence correlation with proton conductivity},
	journal = {Physical Review B},
	volume = {62},
	year = {2000},
	pages = {16595},
	publisher = {APS},
	abstract = {The excitation, emission, and Fourier transform infrared (FTIR) spectra of freshly prepared and aged porous silicon (PS) are examined. The effects of aging and temperature changing on the emission and excitation spectra of fresh and aged PS samples is also studied. Aging in air is found to result in a redshift in the emission spectrum, but a blueshift in the excitation spectrum. Increasing the temperatures leads to a general decrease in the emission intensities of both samples: however, the green emission of fresh sample shows an unusually large and sudden increase in its intensity at the same temperature at which the proton conductivity in the silicon wafer increases. The temperature dependence of the O-H vibration intensity of silicon wafers shows a sudden decrease at that temperature. These results are consistent with a model in which the excitation leads to the formation of exciton in the confined nanostructure, and the formation of electron and hole that are trapped by surface traps, whose nature is dependent on the chemical composition of the surface (and thus its age). These conclusions are confirmed by the results of the FTIR spectra of the two samples, the temperature dependence of the emission, and its correlation with the proton conductivity in the fresh PS.},
	doi = {10.1103/PhysRevB.62.16595},
	url = {http://link.aps.org/doi/10.1103/PhysRevB.62.16595},
	author = {Zou, Bingsuo and Wang, Jianping and Liu, C. and Zhang, J.Z. and El-Sayed, Mostafa A}
}
@article {1227,
	title = {Shape and size dependence of radiative, non-radiative and photothermal properties of gold nanocrystals},
	journal = {International Reviews in Physical Chemistry},
	volume = {19},
	number = {3},
	year = {2000},
	note = {Link, S El-Sayed, MA},
	month = {Jul-Sep},
	pages = {409-453},
	abstract = {Driven by the search for new materials with interesting and unique properties and also by the fundamental question of how atomic and molecular physical behaviour develops with increasing size, the field of nanoparticle research has grown immensely in the last two decades. Partially for these reasons, colloidal solutions of metallic (especially silver and gold) nanoparticles have long fascinated scientists because of their very intense colours. The intense red colour of colloidal gold nanoparticles is due to their surface plasmon absorption. This article describes the physical origin of the surface plasmon absorption in gold nanoparticles with emphasis on the Mie and also the MaxweIl-Garnett theory and reviews the effects of particle size and shape on the resonance condition. A better understanding of the relationship between the optical absorption spectrum (in particular, the plasmon resonance) and such particle properties as its dimensions or surrounding environment can prove fruitful for the use of the plasmon absorption as an analytical tool. The plasmon resonance has also had a great impact on the Raman spectrum of surface-adsorbed molecules and a large enhancement of the fluorescence quantum yield of gold nanorods is observed. Furthermore, following the changes in the plasmon absorption induced by excitation (heating) with ultrashort laser pulses allows one to monitor the electron dynamics (electron-electron and electron-phonon interactions) in real time, which is important in understanding such fundamental questions regarding the thermal and electrical conductivity of these nanoparticles. Very intense heating with laser pulses leads to structural changes of the nanoparticles (nuclear rearrangements in the form of melting and fragmentation).},
	isbn = {0144-235X},
	doi = {10.1080/01442350050034180},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1231,
	title = {Suzuki cross-coupling reactions catalyzed by palladium nanoparticles in aqueous solution},
	journal = {Organic Letters},
	volume = {2},
	number = {15},
	year = {2000},
	note = {Li, Y Hong, XM Collard, DM El-Sayed, MA},
	month = {Jul},
	pages = {2385-2388},
	abstract = {[GRAPHICS] Palladium nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) are efficient catalysts for the Suzuki reactions in aqueous medium. The time dependence of the fluorescence intensity of the biphenyl product in the reaction between iodobenzene and phenylboronic acid is used to determine the initial rate of the catalytic reaction. The initial rate depends linearly on the concentration of Pd catalyst, suggesting that the catalytic reaction occurs on the surface of the Pd nanoparticles.},
	isbn = {1523-7060},
	doi = {10.1021/ol0061687},
	author = {Li, Y. and Hong, X. M. and Collard, D. M. and El-Sayed, Mostafa A}
}
@article {1240,
	title = {Alloy formation of gold-silver nanoparticles and the dependence of the plasmon absorption on their composition},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {18},
	year = {1999},
	note = {Link, S Wang, ZL El-Sayed, MA},
	month = {May},
	pages = {3529-3533},
	abstract = {Gold-silver alloy nanoparticles with varying mole fractions are prepared in aqueous solution by the co-reduction of chlorauric acid HAuCl4 and silver nitrate AgNO3 with sodium citrate. As the optical absorption spectra of their solutions show only one plasmon absorption it is concluded that mixing of gold and silver leads to a homogeneous formation of alloy nanoparticles. The maximum of the plasmon band blue-shifts linearly with increasing silver content. This fact cannot be explained by a simple linear combination of the dielectric constants of gold and silver within the Mie theory. On the other hand, the extinction coefficient is found to decrease exponentially rather than linearly with increasing gold mole fraction x(Au). Furthermore, the size distribution of the alloy nanoparticles is examined using transmission electron microscopy (TEM). High-resolution TEM (HRTEM) also confirms the formation of homogeneous gold-silver alloy nanocrystals.},
	isbn = {1089-5647},
	doi = {10.1021/jp990387w},
	author = {Link, Stephan and Wang, Z.L. and El-Sayed, Mostafa A}
}
@article {1235,
	title = {Crystallographic facets and shapes of gold nanorods of different aspect ratios},
	journal = {Surface Science},
	volume = {440},
	number = {1-2},
	year = {1999},
	note = {Wang, ZL Mohamed, MB Link, S El-Sayed, MA},
	month = {Oct},
	pages = {L809-L814},
	abstract = {Crystal structures of gold nanorods synthesized electrochemically using micelles as a capping material have been studied by high-resolution transmission electron microscopy. Short gold nanorods with aspect ratios of 3-7 are enclosed mainly by (100) and (110) facets and their axial growth direction is [001], whereas long gold nanorods of aspect ratios 20-35 are dominated by (111) and (110) facets and their growth axial direction is (112). The short rods are the dominant constituents, whereas the long rods are observed occasionally. Spherical-like Au particles with equivalent mass to the short rods are dominated by (111) and (100) facets with shapes of truncated octahedra, icosahedra and decahedra. The unique (110) facets of Au nanorods are expected to have interesting surface properties. (C) 1999 Elsevier Science B.V. All rights reserved.},
	isbn = {0039-6028},
	doi = {10.1016/s0039-6028(99)00865-1},
	author = {Wang, Z.L. and Mohamed, MB and Link, Stephan and El-Sayed, Mostafa A}
}
@article {1234,
	title = {Effect of different capping environments on the optical properties of CdS nanoparticles in reverse micelles},
	journal = {International Journal of Quantum Chemistry},
	volume = {72},
	number = {4},
	year = {1999},
	note = {Zou, BS Little, RB Wang, JP El-Sayed, MA},
	month = {Apr},
	pages = {439-450},
	abstract = {CdS(E = 2.5 eV) nanoparticles were synthesized in reversed micelles and capped with materials of different band gaps and charge compensation ability: Cd(OH)(2) (4.0 eV), ZnS (3.2 eV), and CdO (2.3 eV). The preparations allowed the examination and comparison of the efficiencies of confinement of the electron and hole by the various capping materials. The absorption and emission spectra of the capped CdS nanoparticles suggest the following: (1) Efficient capping and strong quantum confinement are observed for CdS particles of small size (< 3.8 nm), showing well-resolved photoexcitation spectra; (2) the confinement efficiency improves with capping thickness; (3) although ZnS has smaller band gap than Cd(OH)(2), it was more efficient in surface-charge compensation and it is the best capping agent of the three materials; and (4) the similar band gaps of CdO and CdS resulted spectroscopically in strong mixing between the excited states of these materials. (C) 1999 John Wiley \& Sons, Inc.},
	isbn = {0020-7608},
	doi = {10.1002/(sici)1097-461x(1999)72:4<439::aid-qua27>3.0.co;2-q},
	author = {Zou, Bingsuo and Little, Reginald and Wang, Jianping and El-Sayed, Mostafa A}
}
@article {1244,
	title = {Electron dynamics in gold and gold-silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron-phonon relaxation},
	journal = {Journal of Chemical Physics},
	volume = {111},
	number = {3},
	year = {1999},
	note = {Link, S Burda, C Wang, ZL El-Sayed, MA},
	month = {Jul},
	pages = {1255-1264},
	abstract = {Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electron-electron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band (i.e., when the excitation wavelength is 630 or 800 nm). However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electron-phonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas (low excitation powers). No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy (HRTEM) reveals that these gold nanoparticles possess defect structures. The effect of this on the electron-phonon relaxation processes is discussed. 18 nm gold-silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system. (C) 1999 American Institute of Physics. [S0021-9606(99)71427-3].},
	isbn = {0021-9606},
	doi = {10.1063/1.479310},
	author = {Link, Stephan and Burda, Clemens and Wang, Z.L. and El-Sayed, Mostafa A}
}
@article {1291,
	title = {Electron Shuttling Across the Interface of CdSe Nanoparticles Monitored by Femtosecond Laser Spectroscopy},
	journal = {The Journal of Physical Chemistry B},
	volume = {103},
	year = {1999},
	note = {doi: 10.1021/jp9843050},
	month = {1999},
	pages = {1783 - 1788},
	publisher = {American Chemical Society},
	abstract = {The formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with adsorbed electron acceptors (1,4-benzoquinone and 1,2-naphthoquinone) and the rise and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were investigated by femtosecond laser spectroscopy. The ultrashort (200?400 fs) rise times of the bleach at the band-gap energy of the CdSe NP as well as of the acceptor radical anion are found to increase with increasing the excitation energy. This suggests that the electron transfer from the CdSe NP to the quinone electron acceptor occurs after thermalization of the excited hot electrons. The decay times of the transient absorption for the electron acceptor radical anions are found to be comparable to that of the CdSe NP bleach recovery time (3 ps). This suggests that the surface quinones shuttle the electron from the conduction band to the valence band of the excited NP. We contrast this behavior with the excited-state dynamics of the recently investigated CdS?MV2+ system in which the electron acceptor does not shuttle the accepted electron back to the hole in CdS.The formation and decay of the optical hole (bleach) for 4 nm CdSe nanoparticles (NPs) with adsorbed electron acceptors (1,4-benzoquinone and 1,2-naphthoquinone) and the rise and decay of the reduced electron acceptors formed after interfacial electron transfer from the CdSe NPs were investigated by femtosecond laser spectroscopy. The ultrashort (200?400 fs) rise times of the bleach at the band-gap energy of the CdSe NP as well as of the acceptor radical anion are found to increase with increasing the excitation energy. This suggests that the electron transfer from the CdSe NP to the quinone electron acceptor occurs after thermalization of the excited hot electrons. The decay times of the transient absorption for the electron acceptor radical anions are found to be comparable to that of the CdSe NP bleach recovery time (3 ps). This suggests that the surface quinones shuttle the electron from the conduction band to the valence band of the excited NP. We contrast this behavior with the excited-state dynamics of the recently investigated CdS?MV2+ system in which the electron acceptor does not shuttle the accepted electron back to the hole in CdS.},
	isbn = {1520-6106},
	doi = {doi: 10.1021/jp9843050},
	url = {http://dx.doi.org/10.1021/jp9843050},
	author = {Burda, Clemens and Green, T.C. and Link, Stephan and El-Sayed, Mostafa A}
}
@article {1245,
	title = {How long does it take to melt a gold nanorod? A femtosecond pump-probe absorption spectroscopic study},
	journal = {Chemical Physics Letters},
	volume = {315},
	number = {1-2},
	year = {1999},
	note = {Link, S Burda, C Nikoobakht, B El-Sayed, MA},
	month = {Dec},
	pages = {12-18},
	abstract = {Using pump-probe femtosecond transient absorption spectroscopy, we determined the rate of the bleach of absorption around 700-800 nm due to the longitudinal surface plasmon band of gold nanorods. Using TEM of the spotted, completely irradiated solutions suggest that the dominant products of the photothermal conformation of the rods are spheres of comparable volume. This lead to the conclusion that the melting of the rods is at least 30-35 ps, independent of the power used (5-20 mu J) or the nanorod aspect ratio (1.9-3.7). (C) 1999 Elsevier Science B.V. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(99)01214-2},
	author = {Link, Stephan and Burda, Clemens and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1246,
	title = {Laser photothermal melting and fragmentation of gold nanorods: Energy and laser pulse-width dependence},
	journal = {Journal of Physical Chemistry A},
	volume = {103},
	number = {9},
	year = {1999},
	note = {Link, S Burda, C Mohamed, MB Nikoobakht, B El-Sayed, MA},
	month = {Mar},
	pages = {1165-1170},
	abstract = {We studied the shape transformation (by use of TEM and optical absorption spectroscopy) of gold nanorods in micellar solution by exposure to laser pulses of different pulse width (100 fs and 7 ns) and different energies (mu J to mJ) at 800 nm, where the longitudinal surface plasmon oscillation of the nanorods absorb. At moderate energies, the femtosecond irradiation melts the nanorods to near spherical particles of comparable volumes while the nanosecond pulses fragment them to smaller near-spherical particles. At high energies, fragmentation is also observed for the femtosecond irradiation. A mechanism involving the rate of energy deposition as compared to the rate of electron-phonon and phonon-phonon relaxation processes is proposed to determine the final fate of the laser-exposed nanorods, i.e., melting or fragmentation.},
	isbn = {1089-5639},
	doi = {10.1021/jp983141k},
	author = {Link, Stephan and Burda, Clemens and Mohamed, MB and Nikoobakht, Babak and El-Sayed, Mostafa A}
}
@article {1248,
	title = {New transient absorption observed in the spectrum of colloidal CdSe nanoparticles pumped with high-power femtosecond pulses},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {49},
	year = {1999},
	note = {Burda, C Link, S Green, TC El-Sayed, MA},
	month = {Dec},
	pages = {10775-10780},
	abstract = {The power dependence of the transient absorption spectrum of CdSe nanoparticle colloids with size distribution of 4.0 +/- 0.4 nm diameter is studied with femtosecond pump-probe techniques. At the lowest pump laser power, the absorption bleaching (negative spectrum) characteristic of the exciton spectrum is observed with maxima at 560 and 480 nm, As the pump laser power increases, two new transient absorptions at 510 and 590 nm with unresolved fast rise (<100 fs) and long decay times (much greater than 150 ps) are observed. The energy of each of the positive absorption is red shifted from that of the bleach bands by similar to 120 meV. The origin of this shift is discussed in terms of the effect of the internal electric field of the many electron-hole pairs formed within the quantum dot at the high pump intensity, absorption from a metastable excited state or the formation of biexcitons.},
	isbn = {1089-5647},
	doi = {10.1021/jp991503y},
	author = {Burda, Clemens and Link, Stephan and Green, T.C. and El-Sayed, Mostafa A}
}
@article {834,
	title = {Simulation of the Optical Absorption Spectra of Gold Nanorods as a Function of Their Aspect Ratio and the Effect of the Medium Dielectric Constant},
	journal = {The Journal of Physical Chemistry B },
	volume = {103},
	year = {1999},
	note = {doi: 10.1021/jp990183f},
	month = {1999},
	pages = {3073 - 3077},
	publisher = {American Chemical Society},
	abstract = {Gold nanorods with different aspect ratios are prepared in micelles by the electrochemical method and their absorption spectra are modeled by theory. Experimentally, a linear relationship is found between the absorption maximum of the longitudinal plasmon resonance and the mean aspect ratio as determined from TEM. It is shown here that such a linear dependence is also predicted theoretically. However, calculations also show that the absorption maximum of the longitudinal plasmon resonance depends on the medium dielectric constant in a linear fashion for a fixed aspect ratio. Attempts to fit the calculations to the experimental values indicate that the medium dielectric constant has to vary with the aspect ratio in a nonlinear way. Chemically, this suggests that the structure of the micelle capping the gold nanorods is size dependent. Furthermore, comparison with the results obtained for rods of different aspect ratios made by systematic thermal decomposition of the long rods further suggests that the medium dielectric constant is also temperature dependent. This is attributed to thermal annealing of the structure of the micelles around the nanorods.Gold nanorods with different aspect ratios are prepared in micelles by the electrochemical method and their absorption spectra are modeled by theory. Experimentally, a linear relationship is found between the absorption maximum of the longitudinal plasmon resonance and the mean aspect ratio as determined from TEM. It is shown here that such a linear dependence is also predicted theoretically. However, calculations also show that the absorption maximum of the longitudinal plasmon resonance depends on the medium dielectric constant in a linear fashion for a fixed aspect ratio. Attempts to fit the calculations to the experimental values indicate that the medium dielectric constant has to vary with the aspect ratio in a nonlinear way. Chemically, this suggests that the structure of the micelle capping the gold nanorods is size dependent. Furthermore, comparison with the results obtained for rods of different aspect ratios made by systematic thermal decomposition of the long rods further suggests that the medium dielectric constant is also temperature dependent. This is attributed to thermal annealing of the structure of the micelles around the nanorods.},
	isbn = {1520-6106},
	url = {http://dx.doi.org/10.1021/jp990183f},
	author = {Link, Stephan and Mohamed, MB and El-Sayed, Mostafa A}
}
@article {1241,
	title = {Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {16},
	year = {1999},
	note = {Link, S Mohamed, MB El-Sayed, MA},
	month = {Apr},
	pages = {3073-3077},
	abstract = {Gold nanorods with different aspect ratios are prepared in micelles by the electrochemical method and their absorption spectra are modeled by theory. Experimentally, a linear relationship is found between the absorption maximum of the longitudinal plasmon resonance and the mean aspect ratio as determined from TEM. It is shown here that such a linear dependence is also predicted theoretically. However, calculations also show that the absorption maximum of the longitudinal plasmon resonance depends on the medium dielectric constant in a linear fashion for a fixed aspect ratio. Attempts to fit the calculations to the experimental values indicate that the medium dielectric constant has to vary with the aspect ratio in a nonlinear way. Chemically, this suggests that the structure of the micelle capping the gold nanorods is size dependent. Furthermore, comparison with the results obtained for rods of different aspect ratios made by systematic thermal decomposition of the long rods further suggests that the medium dielectric constant is also temperature dependent. This is attributed to thermal annealing of the structure of the micelles around the nanorods.},
	isbn = {1089-5647},
	doi = {10.1021/jp990183f},
	author = {Link, Stephan and Mohamed, MB and El-Sayed, Mostafa A}
}
@article {1243,
	title = {Size and temperature dependence of the plasmon absorption of colloidal gold nanoparticles},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {21},
	year = {1999},
	note = {Link, S El-Sayed, MA},
	month = {May},
	pages = {4212-4217},
	abstract = {The size and temperature dependence of the plasmon absorption is studied for 9, 15, 22, 48, and 99 nm gold nanoparticles in aqueous solution. The plasmon bandwidth is found to follow the predicted behavior as it increases with decreasing size in the intrinsic size region (mean diameter smaller than 25 nm), and also increases with increasing size in the extrinsic size region (mean diameter larger than 25 nm). Because of this pronounced size effect a homogeneous size distribution and therefore a homogeneous broadening of the plasmon band is concluded for all the prepared gold nanoparticle samples. By applying a simple two-level model the dephasing time of the coherent plasmon oscillation is calculated and found to be less than 5 fs. Furthermore, the temperature dependence of the plasmon absorption is examined. A small temperature effect is observed. This is consistent with the fact that the dominant electronic dephasing mechanism involves electron-electron interactions rather than electron-phonon coupling.},
	isbn = {1089-5647},
	doi = {10.1021/jp984796o},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1242,
	title = {Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {40},
	year = {1999},
	note = {Link, S El-Sayed, MA},
	month = {Oct},
	pages = {8410-8426},
	abstract = {The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron-electron and electron-phonon scattering) in these metal nanoparticles. It: is found that the electron-phonon relaxation processes in nanoparticles, which are smaller than the electron mean free path, are independent of their size or shape. Intense laser heating of the electrons in these particles is also found to cause a shape transformation (photoisomerization of the rods into spheres or fragmentation), which depends on the laser pulse energy and pulse width.},
	isbn = {1089-5647},
	doi = {10.1021/jp9917648},
	author = {Link, Stephan and El-Sayed, Mostafa A}
}
@article {1250,
	title = {Application of liquid waveguide to Raman spectroscopy in aqueous solution},
	journal = {Applied Spectroscopy},
	volume = {52},
	number = {10},
	year = {1998},
	note = {Song, L Liu, SY Zhelyaskov, V El-Sayed, MA},
	month = {Oct},
	pages = {1364-1367},
	isbn = {0003-7028},
	author = {Song, Li and Liu, S. Y. and Zhelyaskov, V. and El-Sayed, Mostafa A}
}
@article {1257,
	title = {Charge separation effects on the rate of nonradiative relaxation processes in quantum dots quantum well heteronanostructures},
	journal = {Journal of Physical Chemistry A},
	volume = {102},
	number = {33},
	year = {1998},
	note = {Little, RB Burda, C Link, S Logunov, S El-Sayed, MA},
	month = {Aug},
	pages = {6581-6584},
	abstract = {Using time-resolved optical hole (oh)-burning techniques with femtosecond lasers, the time dependence of the spectral diffusion of the oh is examined for both the CdS quantum dot (QD) and the CdS/HgS/CdS quantum dot quantum well (QDQW) nanoparticles. It is found that the nonradiative relaxation of the optical hole is at least 3 orders of magnitude slower in the QDQW than in the QD system. Analysis of the second derivative of the broad transient bleach spectrum of the QDQW system in the 1.6-2.5 eV energy region at 50 fs delay time is found to have a minimum at 2.1 eV, corresponding to a minimum in the radiative probability. Around this energy, the rise and decay times of the transient bleach in the spectrum an found to change greatly. These results suggest that spectral diffusion in the QDQW is a result of relaxation from high- to low-energy exciton states, involving an intervening dark state at an energy of similar to 2.0 eV. The energies of the maxima and minimum of the second-derivative curve are found to be in good agreement with recent theoretical calculations by Jaskolski and Bryant(1) of the energies of the radiative and dark charge-separated state, respectively. In the latter, the hole is in the CdS clad and the electron is in the HgS well. The slow nonradiative relaxation processes involving this state are expected to be slow owing to the large change in the charge carrier effective masses as they cross from the CdS clad to the HgS well.},
	isbn = {1089-5639},
	doi = {10.1021/jp9822687},
	author = {Little, Reginald and Burda, Clemens and Link, Stephan and Logunov, Stephan L. and El-Sayed, Mostafa A}
}
@article {1292,
	title = {Femtosecond Interfacial Electron Transfer Dynamics of CdSe Semiconductor Nanoparticles },
	journal = {MRS Proceedings},
	volume = {43},
	year = {1998},
	pages = {419-424},
	abstract = {The effect of the adsorption of an electron donor (thiophenol, TP) on the surface of CdSe nanoparticles (NPs) on the emission and electron-hole dynamics is studied. It is found that while the emission is completely quenched, the effect on the transient bleach recovery of the band gap absorption is only slight. This is explained by a mechanism in which the hole in the valence band of the NP is rapidly neutralized by electron transfer from the TP. However, the excited electron in the conduction band is not transferred to the TP cation, i. e. the electron does not shuttle via the organic moiety as it does when naphthoquinone is adsorbed [1]. The excited electron is rather trapped by surface states. Thus the rate of bleach recovery in the CdSe NP system is determined by the rate of electron trapping and not by hole trapping. Comparable conclusions resulted previously [2] for the CdS NP when the CdS-MV2+ system is studied. A comparative discussion of the electron-hole dynamics in these systems (CdSe-NQ, CdS-MV2+ and CdSe-TP) is given.},
	doi = {10.1557/PROC-536-419 },
	author = {Burda, Clemens and Green, T.C. and Link, Stephan and El-Sayed, Mostafa A}
}
@article {1256,
	title = {Interfacial carriers dynamics of CdS nanoparticles},
	journal = {Journal of Physical Chemistry A},
	volume = {102},
	number = {28},
	year = {1998},
	note = {Logunov, S Green, T Marguet, S El-Sayed, MA},
	month = {Jul},
	pages = {5652-5658},
	abstract = {The relaxation dynamics of charge carriers in 4 nm CdS colloidal quantum dots are studied by means of picosecond time-resolved fluorescence and femtosecond transient absorption experiments. We also studied the effects of the adsorption of viologen derivatives as electron accepters on the surface of these particles. From these experimental measurements, we reached a model of the electron-hole dynamics in these nanoparticles consistent with previous proposals. In particular, we have confirmed that the electron trapping in these particles is slower than the hole trapping (30 ps versus a few picoseconds). After excitation, rapid formation of an optical hole (bleach) within the lowest energy exciton (band gap) absorption region appears. The maximum of the bleaching band is red-shifted by 20 meV in 2.5 ps, and the bleach intensity recovers in 30 ps. Upon the adsorption of electron accepters, the rate of the red shift of the optical hole is not affected while the bleach recovery time is reduced to a few picoseconds. This leads to the following conclusions: (1) the shift in the bleach band results from hole trapping dynamics, and (2) the bleach recovery is rate limited by the electron trapping process in the CdS nanoparticles (30 ps) or by the hole trapping process (a few picoseconds) in the presence of the electron accepters. The latter conclusion supports a previous proposal by Klimov et al., that the rate of the recovery in CdS nanoparticles is determined by the electron surface trapping process. The electron transfer to the viologen accepters is found to be very efficient and takes place in 200-300 fs, which efficiently competes with surface trapping and electron-hole recombination processes and thus quenches both the band gap and the deep trap emissions.},
	isbn = {1089-5639},
	doi = {10.1021/jp980387g},
	author = {Logunov, Stephan L. and Green, T.C. and Marguet, S. and El-Sayed, Mostafa A}
}
@article {1254,
	title = {Low-temperature retinal photoisomerization dynamics in bacteriorhodopsin},
	journal = {Journal of Physical Chemistry B},
	volume = {102},
	number = {13},
	year = {1998},
	note = {Logunov, SL Masciangioli, TM Kamalov, VF El-Sayed, MA},
	month = {Mar},
	pages = {2303-2306},
	abstract = {Retinal photoisomerization dynamics are studied at both room temperature and 20 K in wild-type bacteriorhodopsin using femtosecond pulses. We were able to resolve the decay at 20 K into two components with the dominant component having a similar lifetime to that observed at room temperature. This strongly suggests that the retinal lifetime at physiological temperature is barrierless. The minor, low-temperature long-lived component is discussed in terms of previous results obtained for fluorescence and transient absorption with lower time resolution, and the origin of this component is discussed in terms of low-temperature glass heterogeneity.},
	isbn = {1089-5647},
	doi = {10.1021/jp972921a},
	author = {Logunov, Stephan L. and Masciangioli, Tina M. and Kamalov, Valey F. and El-Sayed, Mostafa A}
}
@article {1255,
	title = {Quantitative determination of the protein catalytic efficiency for the retinal excited-state decay in bacteriorhodopsin},
	journal = {Journal of Physical Chemistry B},
	volume = {102},
	number = {41},
	year = {1998},
	note = {Logunov, SL Masciangioli, TM El-Sayed, MA},
	month = {Oct},
	pages = {8109-8112},
	abstract = {It was previously found that by removing the negative charge of Asp85 in bacteriorhodopsin (bR), either by protonating it (as in deionized bR) or by mutation to Asn, the decay time of the retinal excited state increases from 0.5 ps to either 1.5 or 10 ps. The two decay components result from the presence of all-trans and 13-cis,15-syn (13-cis) retinal isomers in the modified retinal protein. To quantitatively determine the protein catalysis for the primary process in native bR, we need to determine which decay component results from the excited state of the all-trans isomer (present in the native bR). It is known that the all-trans isomer absorbs at longer wavelength than the 13-cis isomer in blue bR. In this communication, we report the results of pump-probe experiments using 100 fs laser pulses. Probing is carried out at 490 nm, where the excited state in both isomers absorbs. It is found that the ratio of the amplitudes of the two decay components in blue bR changes with variation of the excitation wavelength. The shorter-lived component is found to increase in amplitude as the excitation wavelength increases, i.e., as we excite more of the all-trans isomer. This leads to the conclusion that the short-lived component (1.5 ps) is for the decay of the all-trans excited state while the long-lived component (10 ps) is for the 13-cis retinal excited-state decay. Thus, the presence of the negative charge of Asp85 in native bR catalyzes the rate of the excited-state decay of the all-trans retinal by 300\% and that of the 13-cis isomer by >2000\%.},
	isbn = {1089-5647},
	doi = {10.1021/jp9813600},
	author = {Logunov, Stephan L. and Masciangioli, Tina M. and El-Sayed, Mostafa A}
}
@article {1253,
	title = {Thermal reshaping of gold nanorods in micelles},
	journal = {Journal of Physical Chemistry B},
	volume = {102},
	number = {47},
	year = {1998},
	note = {Mohamed, MB Ismail, KZ Link, S El-Sayed, MA},
	month = {Nov},
	pages = {9370-9374},
	abstract = {Gold nanorods are prepared in aqueous solution by an electrochemical method and are shape controlled by using capping micelles as described by Yu et al. (J. Phys. Chem. B 1997, 101 (34), 6661). Transmission electron microscopic (TEM) images are determined for these gold nanorods, taken from solutions heated to various temperatures in the range of 25-160 degrees C. Size and shape analysis of their TEM images showed that the mean aspect ratio of the nanorods in solution decreases with increasing temperature, mostly as a result of reduction in their length. Heating the dried nanorods themselves on a TEM slide to much higher temperatures does not produce any shape changes. This suggests that the observed relative instability of the longer nanorods in the micellar solutions is attributed to the relative instability of the micelles capping the longer gold nanorods. Following the change with time of the longitudinal surface plasmon absorption band of the gold nanorods at five different temperatures, the activation energy for the thermal decomposition of the micelles is found to be 21.0 +/- 1.0 K cal mol(-1). The most stable rod-shaped micelle is found to have an aspect ratio of 2.0. The craft decomposition (dissolution) temperature of these micelles is found to be similar to 155 degrees C. This study offers a new method in which the thermal stability of micelles of various shapes is used to change the size distribution of metal nanorods in solution. On the other hand, TEM or the absorption maximum of the longitudinal plasmon resonance of gold nanorods can be used as a sensitive monitor in studying the physical properties of the host micelles themselves.},
	isbn = {1089-5647},
	doi = {10.1021/jp9831482},
	author = {Mohamed, MB and Ismail, K. Z. and Link, Stephan and El-Sayed, Mostafa A}
}
@article {868,
	title = {Electron Dynamics of Passivated Gold Nanocrystals Probed by Subpicosecond Transient Absorption Spectroscopy},
	journal = {The Journal of Physical Chemistry B},
	volume = {101},
	year = {1997},
	note = {doi: 10.1021/jp962923f},
	month = {1997},
	pages = {3713 - 3719},
	publisher = {American Chemical Society},
	abstract = {The electronic dynamics of gold nanocrystals, passivated by a monolayer of alkylthiol(ate) groups, were studied by transient spectroscopy after excitation with subpicosecond laser pulses. Three solution-phase gold samples with average particle size of 1.9, 2.6, and 3.2 nm with size distribution less than 10\% were used. The photoexcitation in the intraband (surface plasmon region) leads to the heating of the conduction electron gas and its subsequent thermalization through electron?electron and electron?phonon interaction. The results are analyzed in terms of the contribution of the equilibrated ?hot? electrons to the surface plasmon resonance of gold. A different spectral response was observed for different sizes of gold nanoparticles. The results were compared to the dynamics of the large (30 nm diameter) gold nanocrystals colloidal solution. The size-dependent spectral changes are attributed to the reduction of the density of states for small nanoparticles. The observed variation in the kinetics of the cooling process in gold nanoparticles with changing the laser intensity is attributed to the temperature dependence of the heat capacity of the electron gas.The electronic dynamics of gold nanocrystals, passivated by a monolayer of alkylthiol(ate) groups, were studied by transient spectroscopy after excitation with subpicosecond laser pulses. Three solution-phase gold samples with average particle size of 1.9, 2.6, and 3.2 nm with size distribution less than 10\% were used. The photoexcitation in the intraband (surface plasmon region) leads to the heating of the conduction electron gas and its subsequent thermalization through electron?electron and electron?phonon interaction. The results are analyzed in terms of the contribution of the equilibrated ?hot? electrons to the surface plasmon resonance of gold. A different spectral response was observed for different sizes of gold nanoparticles. The results were compared to the dynamics of the large (30 nm diameter) gold nanocrystals colloidal solution. The size-dependent spectral changes are attributed to the reduction of the density of states for small nanoparticles. The observed variation in the kinetics of the cooling process in gold nanoparticles with changing the laser intensity is attributed to the temperature dependence of the heat capacity of the electron gas.},
	isbn = {1520-6106},
	url = {http://dx.doi.org/10.1021/jp962923f},
	author = {Logunov, Stephan L. and Ahmadi, Temer S. and El-Sayed, Mostafa A and Khoury, J. T. and Whetten, R. L.}
}
@article {1289,
	title = {On the molecular origin of the protein catalysis of the primary process in bacteriorhodopsin photosynthesis: Retinal photoisomerization},
	journal = {Pure and Applied Chemistry},
	volume = {69},
	number = {4},
	year = {1997},
	note = {Times Cited: 816th IUPAC Symposium on PhotochemistryJul 21-26, 1996Helsinki, finlandIupac},
	month = {Apr},
	pages = {749-754},
	abstract = {Using subpicosecond transient optical absorption spectroscopic techniques, the photoisomerization rates and quantum yields were determined for. bacteriorhodopsin, its relevant mutants, its dionized form and at different pH and Cl- concentrations. It is found that the rate is catalyzed and made highly specific around the C-13-C-14 bond by the presence of negative charges within the retinal cavity (e.g., Asp85 and Asp 212). Any perturbation that genetically removes, acid neutralizes, or changes the geometry of these negative charges is found to decrease the tate of photoisomerization, but does not greatly change its quantum yield. These results sue discussed in terms of the changes in the electronic structure of the retinal as well as in the anisotropic charge distribution within the cavity that result from the photoexcitation process. The different potential energy surfaces proposed to explain the dynamics of the photoisomerization process are examined in terms of our observed results.},
	isbn = {0033-4545},
	doi = {10.1351/pac199769040749},
	author = {El-Sayed, Mostafa A and Logunov, Stephan L.}
}
@article {1260,
	title = {Redetermination of the Quantum Yield of Photoisomerization and Energy Content in the K-Intermediate of Bacteriorhodopsin Photocycle and Its Mutants by the Photoacoustic Technique},
	journal = {The Journal of Physical Chemistry B},
	volume = {101},
	year = {1997},
	note = {doi: 10.1021/jp970955c},
	month = {1997},
	pages = {6629 - 6633},
	publisher = {American Chemical Society},
	abstract = {Data obtained previously in our lab for the quantum yield retinal photoisomerization and the energy content of the K-intermediate formed in the bacteriorhodopsin and its mutants (bR) photocycle are reexamined using time-resolved transient spectroscopy and laser-induced photoacoustic spectroscopy. In the present experiment both nanosecond and subpicosecond laser pulses are used for excitation, with different reference compounds. From these new results it can be concluded that using CoCl2 as a reference compound in the photoacoustic experiment with subpicosecond laser pulses gives a large amount of prompt heat release resulting from multiphoton absorption processes. This results in an overestimated energy content of the K-intermediate of bR and its mutants. Using different reference compounds, the corrected values are 40 {\textpm} 10 kJ/mol, which is in agreement with previously reported values. The apparent quantum yield and energy content values (for each of the isomeric compositions) of the mutants D212N, D85N, R82Q, A53G, W182F, V49A, deionized blue bR, and acid purple bR are also recalculated using bR as a reference compound and are similar to those of bR. (Φ is in the range 0.55?0.65, and EK is in the range 40?50 kJ/mol.) The relative insensitivity of the apparent average quantum yield value is discussed.Data obtained previously in our lab for the quantum yield retinal photoisomerization and the energy content of the K-intermediate formed in the bacteriorhodopsin and its mutants (bR) photocycle are reexamined using time-resolved transient spectroscopy and laser-induced photoacoustic spectroscopy. In the present experiment both nanosecond and subpicosecond laser pulses are used for excitation, with different reference compounds. From these new results it can be concluded that using CoCl2 as a reference compound in the photoacoustic experiment with subpicosecond laser pulses gives a large amount of prompt heat release resulting from multiphoton absorption processes. This results in an overestimated energy content of the K-intermediate of bR and its mutants. Using different reference compounds, the corrected values are 40 {\textpm} 10 kJ/mol, which is in agreement with previously reported values. The apparent quantum yield and energy content values (for each of the isomeric compositions) of the mutants D212N, D85N, R82Q, A53G, W182F, V49A, deionized blue bR, and acid purple bR are also recalculated using bR as a reference compound and are similar to those of bR. (Φ is in the range 0.55?0.65, and EK is in the range 40?50 kJ/mol.) The relative insensitivity of the apparent average quantum yield value is discussed.},
	isbn = {1520-6106},
	url = {http://dx.doi.org/10.1021/jp970955c},
	author = {Logunov, Stephan L. and El-Sayed, Mostafa A}
}
@article {863,
	title = {Catalysis of the retinal subpicosecond photoisomerization process in acid purple bacteriorhodopsin and some bacteriorhodopsin mutants by chloride ions.},
	journal = {Biophysical journal},
	volume = {71},
	year = {1996},
	month = {1996 Sep},
	pages = {1545-53},
	abstract = {The dynamics and the spectra of the excited state of the retinal in bacteriorhodopsin (bR) and its K-intermediate at pH 0 was compared with that of bR and halorhodopsin at pH 6.5. The quantum yield of photoisomerization in acid purple bR was estimated to be at least 0.5. The change of pH from 6.5 to 2 causes a shift of the absorption maximum from 568 to 600 nm (acid blue bR) and decreases the rate of photoisomerization. A further decrease in pH from 2 to 0 shifts the absorption maximum back to 575 nm when HCl is used (acid purple bR). We found that the rate of photoisomerization increases when the pH decreases from 2 to 0. The effect of chloride anions on the dynamics of the retinal photoisomerization of acid bR (pH 2 and 0) and some mutants (D85N, D212N, and R82Q) was also studied. The addition of 1 M HCl (to make acid purple bR, pH 0) or 1 M NaCl to acid blue bR (pH 2) was found to catalyze the rate of the retinal photoisomerization process. Similarly, the addition of 1 M NaCl to the solution of some bR mutants that have a reduced rate of retinal photoisomerization (D85N, D212N, and R82Q) was found to catalyze the rate of their retinal photoisomerization process up to the value observed in wild-type bR. These results are explained by proposing that the bound Cl- compensates for the loss of the negative charges of the COO- groups of Asp85 and/or Asp212 either by neutralization at low pH or by residue replacement in D85N and D212N mutants.},
	keywords = {Acoustics, Anions, Bacteriorhodopsins, Biophysical Phenomena, Biophysics, Catalysis, Chlorides, Halobacterium salinarum, Hydrogen-Ion Concentration, Kinetics, Photochemistry, Point Mutation, Retinaldehyde, Spectrophotometry},
	issn = {0006-3495},
	doi = {10.1016/S0006-3495(96)79357-8},
	author = {Logunov, Stephan L. and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
@article {1267,
	title = {Effect of Changing the Position and Orientation of Asp85 Relative to the Protonated Schiff Base within the Retinal Cavity on the Rate of Photoisomerization in Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp960734r},
	month = {1996},
	pages = {10479 - 10481},
	publisher = {American Chemical Society},
	abstract = {Replacement of either Val49 with Ala or Ala53 with Val by site-specific mutagenesis is known to change the position and orientation of the protonated Schiff base relative to Asp85 within the retinal cavity of bacteriorhodopsin (bR) (Brown, L. S.; Gat, Y.; Sheves, M.; Yamazaki, Y.; Maeda, A.; Needleman, R.; Lanyi, J. K. Biochemistry 1994, 33, 12001). The effect of mutation on the rate of the subpicosecond photoisomerization of retinal in bR is examined by using a pump?probe technique. A decrease in the rate of photoisomerization of retinal in V49A and A53V is observed. This is discussed in terms of the previously proposed mechanism of the protein catalysis to the retinal photoisomerization process in bR.Replacement of either Val49 with Ala or Ala53 with Val by site-specific mutagenesis is known to change the position and orientation of the protonated Schiff base relative to Asp85 within the retinal cavity of bacteriorhodopsin (bR) (Brown, L. S.; Gat, Y.; Sheves, M.; Yamazaki, Y.; Maeda, A.; Needleman, R.; Lanyi, J. K. Biochemistry 1994, 33, 12001). The effect of mutation on the rate of the subpicosecond photoisomerization of retinal in bR is examined by using a pump?probe technique. A decrease in the rate of photoisomerization of retinal in V49A and A53V is observed. This is discussed in terms of the previously proposed mechanism of the protein catalysis to the retinal photoisomerization process in bR.},
	isbn = {0022-3654},
	doi = {doi: 10.1021/jp960734r},
	url = {http://dx.doi.org/10.1021/jp960734r},
	author = {Song, Li and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
@article {869,
	title = {Excited-State Dynamics of a Protonated Retinal Schiff Base in Solution},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp962046d},
	month = {1996},
	pages = {18586 - 18591},
	publisher = {American Chemical Society},
	abstract = {The dynamics of all-trans and 13-cis retinal protonated Schiff base (RPSB) were studied in different solvents by means of picosecond transient spectroscopy. The decay time of the excited state absorption was found to be wavelength dependent due to the contribution of the faster decay of stimulated emission. The stimulated emission has a lifetime of a 2.5-4 ps while the excited state absorption decay is biexponential with lifetimes of 2.5-4 and 10-12 ps. The fluorescence quantum yield is strongly temperature dependent, but viscosity has a small effect on both excited-state lifetime and fluorescence quantum yield. This leads to the conclusion that there is a 600 cm-1 barrier in the excited-state which results from intramolecular electronic factors and not from the solvent viscosity. The comparison of these results with those for the retinal in rhodopsin and bacteriorhodopsin is discussed in terms of the protein catalysis for the retinal photoisomerization.},
	isbn = {0022-3654},
	url = {http://dx.doi.org/10.1021/jp962046d},
	author = {Logunov, Stephan L. and Song, Li and El-Sayed, Mostafa A}
}
@article {872,
	title = {Photoisomerization Quantum Yield and Apparent Energy Content of the K Intermediate in the Photocycles of Bacteriorhodopsin, Its Mutants D85N, R82Q, and D212N, and Deionized Blue Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp9515242},
	month = {1996},
	pages = {2391 - 2398},
	publisher = {American Chemical Society},
	abstract = {The quantum yield of photoisomerization and the energy content of the K intermediate in the photocycle of bacteriorhodopsin and its mutants D85N, R82Q, and D212N and deionized blue bR were measured. Transient optical absorption and photoacoustic spectroscopy with excitation using 400 fs laser pulse were combined to obtain results. The spectroscopic characteristics of the excited state, the J and K intermediates in the photocycle of the mutants, and deionized blue bR were determined. The presence of both 13-cis and all-trans isomers in the ground state of light-adapted D85N, R82Q, and D212N and deionized blue bR makes extraction of the quantum yield for each isomer difficult. Thus, only average values of the quantum yield for these samples were determined. The replacement of charged groups in the vicinity of the retinal Schiff base was found to decrease the rate of the photoisomerization by up to 30 times, but with no signficant change in either the apparent quantum yield of the photoisomerization or the energy stored in the K intermediate. The results are discussed in terms of the different models for the excited and ground state potential surfaces of the retinal configuration in bacteriorhodopsin.The quantum yield of photoisomerization and the energy content of the K intermediate in the photocycle of bacteriorhodopsin and its mutants D85N, R82Q, and D212N and deionized blue bR were measured. Transient optical absorption and photoacoustic spectroscopy with excitation using 400 fs laser pulse were combined to obtain results. The spectroscopic characteristics of the excited state, the J and K intermediates in the photocycle of the mutants, and deionized blue bR were determined. The presence of both 13-cis and all-trans isomers in the ground state of light-adapted D85N, R82Q, and D212N and deionized blue bR makes extraction of the quantum yield for each isomer difficult. Thus, only average values of the quantum yield for these samples were determined. The replacement of charged groups in the vicinity of the retinal Schiff base was found to decrease the rate of the photoisomerization by up to 30 times, but with no signficant change in either the apparent quantum yield of the photoisomerization or the energy stored in the K intermediate. The results are discussed in terms of the different models for the excited and ground state potential surfaces of the retinal configuration in bacteriorhodopsin.},
	isbn = {0022-3654},
	url = {http://dx.doi.org/10.1021/jp9515242},
	author = {Logunov, Stephan L. and El-Sayed, Mostafa A and Song, Li and Lanyi, Janos K.}
}
@article {867,
	title = {Picosecond Dynamics of Colloidal Gold Nanoparticles},
	journal = {The Journal of Physical Chemistry},
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp960484e},
	month = {1996},
	pages = {8053 - 8056},
	publisher = {American Chemical Society},
	abstract = {Colloidal gold nanoparticles with an average radius of 15 nm have a surface plasmon absorption band at 530 nm. Excitation by laser pulses of 450 fs duration, and wavelength of 600 or 380 nm ?bleached? the plasmon band and produced a transient absorption at the wings of the ?bleach? spectrum. The transient absorption was found to have a similar temporal behavior at different wavelengths. Analysis of their temporal behavior showed two time constants:? 2.5 ps, and a slower component of >50 ps. Laser excitation close to the plasmon band at 600 nm leads to the formation of ?hot? non-Fermi electronic distribution within the colloidal particles. Transient absorption from these ?hot? electrons led to different absorptions from that of the plasmon absorption of ?cold? electrons. The ?hot? electrons relax via electron?phonon coupling in 2.5 ps, and the phonon?phonon relaxation of the lattice occurs in >50 ps. At 380 nm excitation, the amplitude of the blue wing becomes smaller, and the slow component becomes longer, which could be due to possible excitation of the d-band electrons. These results are discussed in terms of Mie theory and a two-temperature model (TTM), and their consequences on the optical absorption spectrum.Colloidal gold nanoparticles with an average radius of 15 nm have a surface plasmon absorption band at 530 nm. Excitation by laser pulses of 450 fs duration, and wavelength of 600 or 380 nm ?bleached? the plasmon band and produced a transient absorption at the wings of the ?bleach? spectrum. The transient absorption was found to have a similar temporal behavior at different wavelengths. Analysis of their temporal behavior showed two time constants:? 2.5 ps, and a slower component of >50 ps. Laser excitation close to the plasmon band at 600 nm leads to the formation of ?hot? non-Fermi electronic distribution within the colloidal particles. Transient absorption from these ?hot? electrons led to different absorptions from that of the plasmon absorption of ?cold? electrons. The ?hot? electrons relax via electron?phonon coupling in 2.5 ps, and the phonon?phonon relaxation of the lattice occurs in >50 ps. At 380 nm excitation, the amplitude of the blue wing becomes smaller, and the slow component becomes longer, which could be due to possible excitation of the d-band electrons. These results are discussed in terms of Mie theory and a two-temperature model (TTM), and their consequences on the optical absorption spectrum.},
	isbn = {0022-3654},
	url = {http://dx.doi.org/10.1021/jp960484e},
	author = {Ahmadi, Temer S. and Logunov, Stephan L. and El-Sayed, Mostafa A}
}
@article {873,
	title = {Picosecond Electronic Relaxation in CdS/HgS/CdS Quantum Dot Quantum Well Semiconductor Nanoparticles},
	journal = {The Journal of Physical Chemistry },
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp953708m},
	month = {1996},
	pages = {6381 - 6384},
	publisher = {American Chemical Society},
	abstract = {Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.},
	isbn = {0022-3654},
	url = {http://dx.doi.org/10.1021/jp953708m},
	author = {Kamalov, Valey F. and Little, Reginald and Logunov, Stephan L. and El-Sayed, Mostafa A}
}
@article {861,
	title = {Replacement effects of neutral amino acid residues of different molecular volumes in the retinal binding cavity of bacteriorhodopsin on the dynamics of its primary process.},
	journal = {Biophysical journal},
	volume = {70},
	year = {1996},
	month = {1996 Jun},
	pages = {2875-81},
	abstract = {We have determined the rate and quantum yield of retinal photoisomerization, the spectra of the primary transients, and the energy stored in the K intermediate in the photocycle of some bacteriorhodopsin mutants (V49A, A53G, and W182F) in which residue replacements are found to change the Schiff base deprotonation kinetics (and thus the protein-retinal interaction). Because of their change in the local volume resulting from these individual replacements, these substitutions perturb the proton donor-acceptor relative orientation change and thus the Schiff base deprotonation kinetics. These replacements are thus expected to change the charge distribution around the retinal, which controls its photoisomerization dynamics. Subpicosecond transient spectroscopy as well as photoacoustic technique are used to determine the retinal photoisomerization rate, quantum yield, and the energy stored in the K-intermediate for these mutants. The results are compared with those obtained for wild-type bacteriorhodopsin and other mutants in which charged residues in the cavity are replaced by neutral ones. In some of the mutants the rate of photoisomerization is changed, but in none is the quantum yield or the energy stored in the K intermediate altered from that in the wild type. These results are discussed in terms of the shapes of the potential energy surfaces of the excited and ground states of retinal in the perpendicular configuration within the protein and the stabilization of the positive charge in the ground and the excited state of the electronic system of retinal.},
	keywords = {Bacteriorhodopsins, Binding Sites, Biophysical Phenomena, Biophysics, Halobacterium salinarum, Kinetics, Mutagenesis, Site-Directed, Photochemistry, Quantum Theory, Retinaldehyde, Schiff Bases},
	issn = {0006-3495},
	doi = {10.1016/S0006-3495(96)79857-0},
	author = {Logunov, Stephan L. and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
@article {1287,
	title = {Fourier Transform Infrared Spectroscopic Studies of the Effect of Ca2+ Binding on the States of Aspartic Acid Side Chains in Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {99},
	year = {1995},
	note = {doi: 10.1021/j100019a066},
	month = {1995},
	pages = {7776 - 7781},
	publisher = {American Chemical Society},
	abstract = {View http://dx.doi.org/10.1021/j100019a066 for article{\textquoteright}s front page in lieu of an abstract},
	isbn = {0022-3654},
	doi = {doi: 10.1021/j100019a066},
	url = {http://dx.doi.org/10.1021/j100019a066},
	author = {Masuda, Satoshi and Nara, Masayuki and Tasumi, Mitsuo and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
@article {1268,
	title = {Retinal Isomer Composition in Some Bacteriorhodopsin Mutants under Light and Dark Adaptation Conditions},
	journal = {The Journal of Physical Chemistry},
	volume = {99},
	year = {1995},
	note = {doi: 10.1021/j100024a056},
	month = {1995},
	pages = {10052 - 10055},
	publisher = {American Chemical Society},
	abstract = {View http://dx.doi.org/10.1021/j100024a056 for the article{\textquoteright}s first page in lieu of an abstract},
	isbn = {0022-3654},
	doi = {doi: 10.1021/j100024a056},
	url = {http://dx.doi.org/10.1021/j100024a056},
	author = {Song, Li and Yang, Difei and El-Sayed, Mostafa A and Lanyi, Janos K.}
}
@article {1277,
	title = {pH Dependence of the Rate and Quantum Yield of the Retinal Photoisomerization in Bacteriorhodopsin},
	journal = {The Journal of Physical Chemistry},
	volume = {98},
	year = {1994},
	note = {doi: 10.1021/j100093a003},
	month = {1994},
	pages = {10674 - 10677},
	publisher = {American Chemical Society},
	abstract = {View http://dx.doi.org/10.1021/j100093a003 for article{\textquoteright}s front page in lieu of an abstract},
	isbn = {0022-3654},
	doi = {doi: 10.1021/j100093a003},
	url = {http://dx.doi.org/10.1021/j100093a003},
	author = {Logunov, Stephan L. and Song, Li and El-Sayed, Mostafa A}
}
@article {859,
	title = {The pH dependence of the subpicosecond retinal photoisomerization process in bacteriorhodopsin: evidence for parallel photocycles.},
	journal = {Biophysical journal},
	volume = {67},
	year = {1994},
	month = {1994 Nov},
	pages = {2008-12},
	abstract = {The pH dependence of the subpicosecond decay of the retinal photoexcited state in bacteriorhodopsin (bR) is determined in the pH range 6.8-11.3. A rapid change in the decay rate of the retinal photoexcited state is observed in the pH range 9-10, the same pH range in which a rapid change in the M412 formation kinetics was observed. This observation supports the previously proposed heterogeneity model in which parallel photocycles contribute to the observed pH dependence of the M412 formation kinetics in bR.},
	keywords = {Bacteriorhodopsins, Biophysical Phenomena, Biophysics, Hydrogen-Ion Concentration, Isomerism, Kinetics, Molecular Structure, Photochemistry, Retinaldehyde},
	issn = {0006-3495},
	doi = {10.1016/S0006-3495(94)80684-8},
	author = {Song, Li and Logunov, Stephan L. and Yang, Difei and El-Sayed, Mostafa A}
}
