@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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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 {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}
}
