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UBC Theses and Dissertations

Linear transmission and reflection spectroscopic studies of colloidal PbS(x) nanocrystal films : paving the way for nonlinear optics in such films Ning, Hailong

Abstract

This thesis investigates the feasibility of conducting nonlinear degenerate four-wave-mixing experiments on colloidal PbS or PbSe semiconductor nanocrystal films. It concludes that such experiment cannot be effectively carried out in the conventional forward geometry due to large scattering from the emulsive nanocrystal films, while it may be possible in the backward geometry. These conclusions were reached by studying the linear transmission and reflection spectra from a variety of PbS and PbSe NC films on both silicon and glass substrates. These studies suggest that the electronic structure of the PbS and PbSe NCs in close-packed films are well-maintained while the scattering inside these NC films is Rayleigh-like and quite strong. Theoretical fitting of these spectra reveals the refractive indicies and absorption rates of these films, which match those recently reported in the literature. It also suggests the presence of a distinct interfacial layer with a low concentration of nanocrystals between silicon and the dense NC emulsion, which was also confirmed by optical microscopy. This layer, on the order of 100 nm thick, has important consequences for optical studies of these films.

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