The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

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 t...

Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods

A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon-electron interactions (microscopic in both space and time), and pure phonon scattering The model is generalized from the dual-phase-lag concept accounting for the laging behavior in the high-rate response While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon-electron interaction)

A Unified Field Approach for Heat Conduction From Macro- to Micro-Scales

Optical Studies of Dynamics in Noble Metal Nanostructures

Electron and lattice dynamics following optical excitation of metals

We have observed ultrafast heat transport in thin gold films under femtosecond laser irradiation. Time-of-flight (from-pump back-probe) measurements indicate that the heat transit time scales linearly with the sample thickness, and that heat transport is very rapid, occurring at a velocity close to the Fermi velocity of electrons in Au.

Femtosecond electronic heat-transport dynamics in thin gold films.

Vacuum-emission and carrier-separation techniques, together with novel metal-oxide-semiconductor structures, have been used to observe the threshold field for the onset of electron heating in silicon dioxide. The magnitude of this electric field is \ensuremath{\cong} 1.5-2.0 MV/cm, independent of oxide thickness and composition. This value is consistent with all of the current theoretical calculations. A minimum average electronic energy of \ensuremath{\cong} 1.0 eV is shown to be necessary to observe emission of the electrons into vacuum.

Direct observation of the threshold for electron heating in silicon dioxide.

Surface plasmon mediated light emission from rough metal films can be driven in a number of different ways. They all show characteristic features independent of the driving mechanism. The unifying feature is that each mechanism injects hot electrons into the metal. We describe surface plasmon mediated emission from tunnel junctions in terms of a hot-electron picture. We show how this emission can be used as a spectroscopic probe of hot electron dynamics in tunnel junctions. We then describe how we used this tool to probe hot electron processes in electron injector structures, leading to important new insights into electron heating in SiO2.

S. D. Brorson

Papers

Femtosecond electronic heat-transport dynamics in thin gold films.

Direct observation of the threshold for electron heating in silicon dioxide.

Surface Plasmon Emission as a Probe of Hot-Electron Dynamics