%0 Journal Article %J Journal of Physical Chemistry C %D 2011 %T Plasmonic Enhancement of Nonradiative Charge Carrier Relaxation and Proposed Effects from Enhanced Radiative Electronic Processes in Semiconductor-Gold Core-Shell Nanorod Arrays %A Dreaden, Erik %A Neretina, Svetlana %A Qian, Wei %A El-Sayed, Mostafa A %A Hughes, Robert A %A Preston, John S %A Mascher, Peter %X Plasmonic field enhancement of nonradiative exciton relaxation rates in vertically aligned arrays of high aspect ratio CdTe-Au core-shell nanorods was investigated by transient absorption spectroscopy, computational electromagnetics, and kinetic modeling. Increasing shell thickness in the high aspect ratio nanorods was found to result in dramatic differences in polarization-dependent nonradiative exciton relaxation rates, which we attribute to differing mechanisms of plasmonic field enhancement associated with predominant ground- or excited-state absorption processes. These results are compared with previous investigations of low aspect ratio CdTe-Au core-shell nanorods, and overall conclusions regarding plasmonic enhancement of nonradiative relaxation rates in this system are presented. We propose that when the resonantly coupled dipolar plasmon field of the shell is polarized parallel to the ground-state absorption transition moment of the core, Auger recombination dominates carrier relaxation and slower second-order decay kinetics are observed. When contributions of the resonantly coupled plasmon field are nondipolar or orthogonal to the ground-state absorption transition moment of the core, excited-state absorption processes are believed to dominate and increasingly rapid first-order relaxation kinetics are observed. We find that these processes can vary greatly, depending on shell thickness and the orientation of the array, but are insensitive to aspect ratio. These investigations have significant implications in the design of photovoltaic and optoelectronic devices incorporating anisotropic plasmonic elements. %B Journal of Physical Chemistry C %V 115 %P 5578-5583 %8 Apr %@ 1932-7447 %G eng %M WOS:000288885900050 %R 10.1021/jp112129k %0 Journal Article %J Nano Letters %D 2008 %T Plasmon Field Effects on the Nonradiative Relaxation of Hot Electrons in an Electronically Quantized System: CdTe−Au Core−Shell Nanowires %A Neretina, Svetlana %A Qian, Wei %A Dreaden, Erik %A El-Sayed, Mostafa A %A Hughes, Robert A %A Preston, John S %A Mascher, Peter %X The intense electromagnetic fields of plasmonic nanoparticles, resulting from the excitation of their localized surface plasmon oscillations, are known to enhance radiative processes. Their effect on the nonradiative electronic processes, however, is not as well-documented. Here, we report on the enhancement of the nonradiative electronic relaxation rates in CdTe nanowires upon the addition of a thin gold nanoshell, especially at excitation energies overlapping with those of the surface plasmon oscillations. Some possible mechanisms by which localized surface plasmon fields can enhance nonradiative relaxation processes of any quantized electronic excitations are proposed.The intense electromagnetic fields of plasmonic nanoparticles, resulting from the excitation of their localized surface plasmon oscillations, are known to enhance radiative processes. Their effect on the nonradiative electronic processes, however, is not as well-documented. Here, we report on the enhancement of the nonradiative electronic relaxation rates in CdTe nanowires upon the addition of a thin gold nanoshell, especially at excitation energies overlapping with those of the surface plasmon oscillations. Some possible mechanisms by which localized surface plasmon fields can enhance nonradiative relaxation processes of any quantized electronic excitations are proposed. %B Nano Letters %I American Chemical Society %V 8 %P 2410 - 2418 %8 2008 %@ 1530-6984 %G eng %U http://dx.doi.org/10.1021/nl801303g %N 8 %! Nano Lett. %R 10.1021/nl801303g %0 Journal Article %J Lasers in Surgery and Medicine %D 2007 %T The potential use of the enhanced nonlinear properties of gold nanospheres in photothermal cancer therapy %A Huang, Xiaohua %A Qian, Wei %A El Sayed, I.H. %A El-Sayed, Mostafa A %X Background and Objective: Laser photothermal therapy (PTT) is practiced at the moment using short laser pulses. The use of plasmonic nanoparticles as contrast agents can decrease the laser energy by using the optical property of the nanoparticles and improve the tumor selectivity by the molecular probes on the particle surface. In this study, we aim at selective and efficient PTT by exploiting the nonlinear optical properties of aggregated spherical gold nanoparticles conjugated to anti-epidermal growth factor receptor (anti-EGFR) antibodies using short NIR laser pulses. Study Design/Materials and Methods: Spherical gold nanoparticles are synthesized and conjugated to anti-EGFR antibodies to specifically target HSC oral cancer cells. The nanoparticles are characterized by micro-absorption spectra and dark field light scattering imaging. Photothermal destructions of control and nanoparticle treated cancer cells are carried out with a ferntosecond Ti:Sapphire laser at 800 nm with a pulse duration of 100 femtoseconds and repetition rate of 1 kHz. Results: The laser power threshold for the photothermal destruction of cells after the nanoparticle treatment is found to be 20 times lower than that required to destroy the cells in the normal PTT, that is, without nanoparticles. The number of destroyed cells is quadratically dependent on the laser power. The number of dead cells shows a nonlinear dependence on the concentration of gold nanoparticles that are specifically targeted to cancer cells. Conclusions: The energy threshold and selectivity of PTT can greatly benefit from the use of the plasmonic enhanced nonlinear optical processes of spherical gold nanoparticles conjugated to anti-EGFR antibodies. The quadratic dependence of the photothermal efficiency on the pulsed NIR laser power indicates a second harmonic generation or a two photon absorption process. The observed nonlinear dependence on the gold nanoparticle concentration suggests that aggregated nanospheres are responsible for the observed enhanced photothermal destruction of the cells. %B Lasers in Surgery and Medicine %V 39 %P 747-753 %8 Oct %@ 0196-8092 %G eng %M WOS:000250818200007 %R 10.1002/lsm.20577 %0 Journal Article %J Journal of Applied Physics %D 2005 %T Photothermal reshaping of prismatic Au nanoparticles in periodic monolayer arrays by femtosecond laser pulses %A Huang, Wenyu %A Qian, Wei %A El-Sayed, Mostafa A %X Prismatic gold nanoparticles in the periodic monolayer arrays prepared with nanosphere lithography technique can be reshaped with femtosecond laser pulses at different powers and wavelengths. As the power density of 400 nm femtosecond laser increases, the prismatic particle tips begin to round and the overall particle shape changes from a prism to a sphere with a tripodal intermediate. The formation of the tip-rounded nanoprisms is probably due to the dewetting properties of gold on quartz surface and the low melting temperature at the tips. The formation of the tripodal nanoparticles is attributed to the inhomogeneous heating and lattice rearrangement of the as-deposited nanoparticles to a metastable state, which is more stable than the prismatic shape but less stable than the spherical shape. With 800 nm femtosecond laser irradiation, only tip-rounded nanoprisms are observed and no spherical nanoparticles are formed at the laser powers used. This is most likely due to the blueshift of the plasmon absorption band for the transformed particles, so that they cannot absorb the required energy to overcome the barrier to make the spherical shape. With 700 nm femtosecond laser irradiation, the tip-rounded and the tripodal nanoparticles are formed and few spherical particles are observed at the higher laser power density. From the results of this work, it is shown that by changing the wavelength and power density of the femtosecond laser, one can control the final shape of the particles formed from the original prismatic nanoparticles. %B Journal of Applied Physics %V 98 %8 Dec %@ 0021-8979 %G eng %M WOS:000234119600067 %] 114301 %R 10.1063/1.2132515