Layer-dependent optical and dielectric properties of centimeter-scale PdSe2 films grown by chemical vapor deposition

Palladium diselenide (PdSe2), a new type of two-dimensional noble metal dihalides (NMDCs), has received widespread attention for its excellent electrical and optoelectronic properties. Herein, high-quality continuous centimeter-scale PdSe2 films with layers in the range of 3L–15L were grown using Chemical Vapor Deposition (CVD) method. The absorption spectra and DFT calculations revealed that the bandgap of the PdSe2 films decreased with the increasing number of layers, which is due to the enhancement of orbital hybridization. Spectroscopic ellipsometry (SE) analysis shows that PdSe2 has significant layer-dependent optical and dielectric properties. This is mainly due to the unique strong exciton effect of the thin PdSe2 film in the UV band. In particular, the effect of temperature on the optical properties of PdSe2 films was also observed, and the thermo-optical coefficients of PdSe2 films with the different number of layers were calculated. This study provides fundamental guidance for the fabrication and optimization of PdSe2-based optoelectronic devices.

Temperature dependence of the dielectric function and critical points of α-SnS from 27 to 350 K

We report the temperature dependence of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of biaxial α-SnS in the spectral energy region from 0.74 to 6.42 eV and temperatures from 27 to 350 K using spectroscopic ellipsometry. Bulk SnS was grown by temperature gradient method. Dielectric response functions were obtained using multilayer calculations to remove artifacts due to surface roughness. We observe sharpening and blue-shifting of CPs with decreasing temperature. A strong exciton effect is detected only in the armchair direction at low temperature. New CPs are observed at low temperature that cannot be detected at room temperature. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that contains the Bose–Einstein statistical factor and the temperature coefficient for describing the electron–phonon interaction.

Carbon-vacancy modified graphitic carbon nitride: enhanced CO2 photocatalytic reduction performance and mechanism probing

Enhanced charge carrier generation, attenuated exciton-effect as well as upgraded CO2 adsorption/activation lead to a promoted CO2-to-CO photocatalytic conversion ability for C-vacancy modified GCN.

POLARIZABILITY AND SECOND HYPERPOLARIZABILITY OF SEMICONDUCTING SINGLE-WALL CARBON NANOTUBES

Considering the exciton effect, the polarizability and second polarizability spectra of semiconducting single-wall carbon nanotubes (S-SWCNTs) have been calculated by PPP (Pariser, Parr, and Pople) approximation and the single-excitation configuration interaction (single-CI) method and sum-over-state method. We have studied the nonlinear optical (NLO) properties of the S-SWCNTs with different lengths and diameters. The highest and first peak positions, bandgap, and the spectra shape of the polarizability and second hyperpolarizability change as N (the number of atoms) increases. Also, the peak values of γzzzz are very bigger than that for γxxxx. Our results indicate that the nonlinear optical properties of fullerenes are similar to S-SWCNTs.