Electronic structure of a NbC0.9(100) surface: Angle-resolved photoemission study

Carbon dioxide hydrogenation over the carbon-terminated niobium carbide (111) surface: a density functional theory study

Carbon dioxide (CO₂) hydrogenation is an energetic process which could be made more efficient through the use of effective catalysts, for example transition metal carbides. Here, we have employed calculations based on the density functional theory (DFT) to evaluate the reaction processes of CO₂ hydrogenation to methane (CH₄), carbon monoxide (CO), methanol (CH₃OH), formaldehyde (CH₂O), and formic acid (HCOOH) over the carbon-terminated niobium carbide (111) surface. First, we have studied the adsorption geometries and energies of 25 different surface-adsorbed species, followed by calculations of all of the elementary steps in the CO₂ hydrogenation process. The theoretical findings indicate that the NbC (111) surface has higher catalytic activity towards CO₂ methanation, releasing 4.902 eV in energy. CO represents the second-most preferred product, followed by CH₃OH, CH₂O, and HCOOH, all of which have exothermic reaction energies of 4.107, 2.435, 1.090, and 0.163 eV, respectively. Except for the mechanism that goes through HCOOH to produce CH₂O, all favourable hydrogenation reactions lead to desired compounds through the creation of the dihydroxycarbene (HOCOH) intermediate. Along these routes, CH₃* hydrogenation to CH₄* has the highest endothermic reaction energy of 3.105 eV, while CO production from HCO dehydrogenation causes the highest exothermic reaction energy of -3.049 eV. The surface-adsorbed CO₂ hydrogenation intermediates have minimal effect on the electronic structure and interact only weakly with the surface. Our results are consistent with experimental observations.

Characteristic Electronic Structure of SnO Film Showing High Hole Mobility

Actual knowledge of the intrinsic electronic characteristics of p-type oxide semiconductors should help guide the design of innovative electronic devices. The electronic characteristics of oxide semiconductors in thin-film form potentially differ from those in the bulk form owing to lattice strain. In this Letter, we report on the empirical band structure of stannous oxide (SnO) film, which has been shown to have a higher hole mobility than the theoretically expected values for SnO in the bulk form. In vacuo angle-resolved photoemission spectroscopy measurements reveal that the uppermost valence band is anisotropic between the out-of-plane and in-plane directions, and more dispersive than the theoretical predictions. Our findings unveil the underlying mechanism of the semiconductor properties of SnO films and suggest a suitable device structure based on the electronic characteristics.