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We present the optical function spectra of Cu2SnSe3 determined from 0.30 to 6.45 eV by spectroscopic ellipsometry (SE) at room temperature. We analyze the SE data using the Tauc-Lorentz model and obtain the direct-bandgap energy of 0.49 ± 0.02 eV, which is much smaller than the previously known value of 0.84 eV for the monoclinic-phase Cu2SnSe3. We also perform density-functional theory calculations to obtain the complex dielectric function data, and the results show good agreement with the experimental spectrum. Finally, we discuss the electronic origin of the main optical structures. [ABSTRACT FROM AUTHOR]

We report the x-ray absorption spectra for two hard carbon films grown by filament-assisted chemical vapor deposition in gas mixtures of 1% and 0.18% methane in hydrogen. Although the Raman spectra of these two films suggest significant differences in structure, the x-ray absorption near-edge structure and extended x-ray absorption fine structure (EXAFS) are very similar. Analyzing the EXAFS from these films with a diamond crystal as a reference gives carboncarbon bond lengths of 1.53±0.03 Å. This result is consistent with diamond and incompatible with graphite. We conclude that the carbon films have the same local structure as diamond. [ABSTRACT FROM AUTHOR]

We present the optical function spectra of Cu2SnSe3 determined from 0.30 to 6.45 eV by spectroscopic ellipsometry (SE) at room temperature. We analyze the SE data using the Tauc-Lorentz model and obtain the direct-bandgap energy of 0.49 ± 0.02 eV, which is much smaller than the previously known value of 0.84 eV for the monoclinic-phase Cu2SnSe3. We also perform density-functional theory calculations to obtain the complex dielectric function data, and the results show good agreement with the experimental spectrum. Finally, we discuss the electronic origin of the main optical structures. [ABSTRACT FROM AUTHOR]