Spectroscopic ellipsometry (SE) is used to study the dependence of the band-gap energy for Cu2ZnSnSe4 (CZTSe) on temperature ranging from 50 to 350 K. A CZTSe thin film prepared by the pseudo-bulk approach allows direct observation of the fundamental band-gap E0(A,B) in the SE data without need for multi-layer modeling. We obtain accurate energy values for E0(A,B) and its spin-orbit splitting component E0(C) from standard lineshape analysis of the secondenergy-derivative spectra. The E0(A,B) and E0(C) energies for CZTSe decrease with increasing temperature, as for many semiconductors, but their temperature dependencies are relatively weak. Our experimental observation can be explained in terms of relatively small change in bond-length and strong p-d states coupling at the valence band maximum.
In situ imaging ellipsometry is employed to monitor the morphology of collapsed films of fatty acid Langmuir monolayers on pure water and on CaCl2 solution. The ellipsometry images reveal the existence of multilayer domains in the collapsed region, and analysis of the images yields the thicknesses of these domains. The multilayer films formed on water are mainly trilayers, while those on CaCl2 solution are mainly bilayers. The structure of the collapsed films also changes sensitively depending on the history of compression of the molecular layer.
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