| Hexagonally close packed monolayer films of organically passivated silver quantum dots undergo a reversible metal-insulator (MI) transition which depends on the two dimensional pressure in the film. At this transition, a very large increase (a factor of ∼500) in the resonant optical second harmonic generation (SHG) signal from the film is observed. The enhancement may be due either to changes in the linear optical properties of the film, or a change in the 2nd order susceptibility. In this dissertation, the linear dielectric function of the film is calculated quantitatively through the MI transition. The dielectric function was calculated from measurements of the reflectance and transmittance. A Kramers-Kronig analysis, with no approximations, was used to unambiguously determine the optical constants and thus the dielectric functions of the films. Not only do the changes in the dielectric function reflect the development of metallic character in the film, but it is also shown that these changes cannot account for the nonlinear optical results.; The second part of the dissertation describes the extension of the nonlinear optical studies of these films. A scanning SHG microscope with ∼1mm resolution was designed and built, and applied to the silver films. It was found that the particle films are actually modified by the intense electromagnetic fields generated by the microscope at the focal point of the fundamental laser and the effects are size dependent. Films of large particles (>6 nm diameter) are ionized and produce an enhanced SHG signal, while smaller particles (<4 nm diameter) are heated and move, resulting in a diminished signal. These effects can be understood in terms of established theories of the electronic dynamics of metal nanoparticles. |
