Nonlinear optical studies of electronic properties on metal and semiconductor surfaces

Second Harmonic Generation (SHG) and Transient Grating Scattering (TGS) techniques are used to study electronic response to light and relaxation on metal and semiconductor surfaces. In the first part of this thesis, the SHG signals as functions of azimuthal angle and light wavelength was measured on a clean Ag(111) surface to reveal the importance of dielectric function in SHG process. Model analysis shows that the SHG feature at 2$\hbar\omega$ = 3.9 eV is caused by the enhancement of the SH radiation efficiency by the Ag interband transitions. The importance of the radiation efficiency effect is further demonstrated with multilayer pyridine adsorption experiments on Ag(111) surface. The molecular adlayers on Ag(111) surface was found to strongly modulate the radiation efficiencies of the fundamental and the SH lights through optical interference. This phenomenon allows us to use SHG for measuring the growth rate of molecular thin films on surfaces. And last, we have also examined how the nonlinear susceptibility components due to electric dipoles and those due to nonlocal surface response would be influenced by adsorbates. It was found that nonlocal surface response cannot be totally suppressed by conventional surface SHG quenching methods, such as surface oxidation or ion sputtering. This observation indicates that one cannot simply use the decrease in SHG for determining adsorbate coverage. In the second part of the thesis, TGS experiments were done on Si samples both in reflection and transmission geometries where near-surface and bulk diffusivities of band edge carriers were measured, respectively. Comparison of surface and bulk diffusivities shows no significant surface effects affecting carrier diffusion near the Si surface with naturally grown oxide layer. The studies of carrier density dependence of carrier diffusivity shows that in high carrier density region, the carrier-carrier scattering effect together with the band gap narrowing effect significantly decreases diffusivity up to a factor of 4 compared with the intrinsic diffusivity at low carrier density. This study shows that there is an optimal carrier density region with low diffusivity that is most suitable for inducing photochemistry with efficiency