First-principles study of the electronic structure of cubicGaS: Metallic versus insulating polymorphs

Abstract

The electronic structure of different polymorphs of gallium sulphide ͑GaS͒ with cubic structure is investigated by means of first-principles band structure calculations in connection with experimental reports on a metastable semiconducting cubic form of this material. The expected metallic character of simple cubic phases containing one GaS group per unit cell ͑rocksalt or zinc-blende͒ is confirmed by the calculations. A cubanebased zinc-blende structure is found to exhibit a band gap which is compatible with experimental results but the unit cell parameter is much larger than the reported ones. We have also studied cubic phases containing hydrogen. It is found that two insulating polymorphs can be stable: ͑i͒ a simple cubic structure based on ͓HGaS͔ 4 cubane units and ͑ii͒ an insulating zinc-blende structure in which hydrogen atoms occupy the empty sites of the cubic unit cell. The last structure seems to be the more likely structural alternative for the phase so far described as a semiconducting cubic phase of GaS. The presence of hydrogen could explain the reported instability of cubic GaS under thermal annealing.

Interaction of Graphene-on-Al(111) Composite with d-Glucopyranose and Its Application in Biodetection

“…By using the graphene-on-Al(111) composite as a substrate for STM, we simulated constant-current STM images for the d -glucopyranose adsorbed on the substrate using the Tersoff–Hamann approximation. , The tunneling current was proportional to the local density of states integrated in the bias window close to the Fermi level. , In the calculation, considering that the Fermi level was −3.6 eV, we used a bias window of −3.9 to −3.4 eV, which corresponds to a bias voltage of 0.5 eV. The reference plane was located parallel to and above the graphene-on-Al(111) composite, with a distance of 10.07 Å to the top layer of Al(111).…”