eV For Parallel Research Articles

Electronic and optical properties of stanane and armchair stanane nanoribbons

In this study, we performed a density functional theory based investigation of the structural, electronic, and optical properties of a stanane, fully hydrogenated stanene SnH, and armchair stanane nanoribbons ASnHNRs. Our full geometry optimization calculations show stanane has 0.84 A buckled height and the buckled structure is preserved in ASnHNRs. The optimized lattice parameter of stanane, Sn–Sn, and Sn–H bond length are 4.58 A, 2.75A, and 1.73 A, respectively. Electronic structure calculations show that stanane is a moderate-band-gap semiconductor with a direct band gap of 1.2 eV and ASnHNRs are wide-band-gap semiconductors. The band gap of ASnHNRs decreases as the ribbons width increases. We investigated the optical properties for two directions of polarization. For perpendicular-polarized light, the imaginary part of dielectric function $$\varepsilon _2(\omega )$$ of stanane peaks between 5 and 10 eV; while for the parallel-polarized light, the peaks are seen in a wide range of energy. According to the results, stanane is a good absorptive matter, especially for visible regions of the electromagnetic spectrum. The presence of anisotropy with respect to the type of light polarization is observed in ASnHNRs also. In these structures, the main peak of $$\varepsilon _2(\omega )$$ is located at 3.4 eV for parallel- and in 6–8 eV for perpendicular-polarized light.

Optical anisotropy of [formula omitted] superlattices: Resonant Raman scattering in in-plane geometry

Using a micro-Raman setup, we performed a systematic resonant Raman scattering study on short-period (Si) n (Ge) n superlattices ( n = 4–12) in in-plane geometry from polished sample edges. Due to the confinement of optical phonon modes electronic states in Si and Ge layers can be probed separately. The Raman efficiencies measured between 1.7 eV and 2.6 eV for parallel and crossed polarization are compared with calculations of the dielectric function decomposed into contributions of Si and Ge atoms. A pronounced polarization dependence of the Raman cross section is found in qualitatively good agreement with theory. For polarization of the light parallel to the layers strong transitions around 2.2 eV localized in the Ge layers are observed. These transitions are considerably weakened for polarization of the light perpendicular to the layers.

Determination of the anisotropy of the optical constants of electrochemically formed platinum oxide films by reflection spectroscopy and Kramers-Kronig analysis

Reflection spectroscopy in connection with Kramers-Kronig analysis was used to evaluate the complex optical constants of a thin anisotropic film of assumed uniaxial symmetry. The change in reflectivity of a platinum electrode, due to the formation of an oxide layer, was measured between 0.9 eV and 5.2 eV for parallel and perpendicular polarization. The corresponding phase-shifts were calculated from these data. The complex optical constants normal n̂ n and tangential n̂ t to the surface are now obtainable. The spectral dependence of the complex optical constants shows the expected anisotropic behaviour. The results are explained by means of a simple band model.