Two-Dimensional Semiconducting Boron Monolayers

The two-dimensional boron monolayers were reported to be metallic both in previous theoretical predictions and experimental observations, however, we have firstly found a family of boron monolayers with the novel semiconducting property as confirmed by the first-principles calculations with the quasi-particle G0W0 approach. We demonstrate that the vanished metallicity characterized by the pz-derived bands cross the Fermi level is attributed to the motif of a triple-hexagonal-vacancy, with which various semiconducting boron monolayers are designed to realize the band-gap engineering for the potential applications in electronic devices. The semiconducting boron monolayers in our predictions are expected to be synthesized on the proper substrates, due to the similar stabilities to the ones observed experimentally.Comment: 12 pages, 4 figure

Surface Oxidation and S Atom Vacancy in Tuning the Photoelectric Properties of Monolayer SnP₂S₆

Two-dimensional (2D) layered SnP2S6 has been synthesized in experiments, which has attracted much attention for application in optoelectronic devices. However, the influence of common adsorbates (i.e., H2O and O2) and vacancy defects may play a key role in optoelectronic devices. Herein, we systematically investigate the optoelectronic properties of the SnP2S6 monolayer in the presence of H2O, O2, and vacancies by first principles. The results show that the O2 and H2O molecules behave qualitatively differently on the SnP2S6 surface. The presence of S atom vacancies significantly enhanced the adsorption of H2O and O2 molecules. Furthermore, H2O reduces the dissociation potential of O2 on the surface of pristine SnP2S6, while S vacancies significantly facilitate the dissociation of O2, indicating that SnP2S6 will readily be oxidized under ambient conditions in the presence of S vacancies. Importantly, it is confirmed that the H2O adsorption slightly influenced the electronic properties of monolayer SnP2S6. In sharp contrast, O2 adsorption and vacancies enable significant changes in the properties of monolayer SnP2S6. Furthermore, an indirect-to-direct band gap transition was observed when the S atom vacancy concentration of monolayer SnP2S6 was 6.25%