2 research outputs found
Adsorption Induced Indirect-to-Direct Band Gap Transition in Monolayer Blue Phosphorus
In
this work, we systematically studied adsorption induced indirect-to-direct
band gap transition in monolayer blue phosphorus from first-principles
calculations by combining one-shot GW approximation and the Bethe-Salpeter
equation. Our results revealed that surface adsorption (i.e., O<sub>2</sub>, −OH, −COOH, and −CN) strongly modifies
the conduction and valence band edges, resulting in an indirect-to-direct
band gap transition. More importantly, the direct band gap can be
dramatically tuned by either the in-plane strain or the coverage ratio
of adsorbates, which enables monolayer blue phosphorus to efficiently
adsorb visible light. The mechanism of strain effect and surface adsorption
on band gap tuning was deeply discussed. Moreover, our results clearly
showed that the adsorbates have an important influence on the exciton
binding energies (EBE), while the coverage of adsorbates play a crucial
role in the linear scaling behavior between EBE and quasi-particle
band gap. Our findings suggest that monolayer blue phosphorus has
potential applications in electro-optical devices
Oxidation-Induced Topological Phase Transition in Monolayer 1T′-WTe<sub>2</sub>
Monolayer
(ML) tungsten ditelluride (WTe<sub>2</sub>) is a well-known
quantum spin Hall (QSH) insulator with topologically protected gapless
edge states, thus promising dissipationless electronic devices. However,
experimental findings exhibit the fast oxidation of ML WTe<sub>2</sub> in ambient conditions. To reveal the changes of topological properties
of WTe<sub>2</sub> arising from oxidation, we systematically study
the surface oxidation reaction of ML 1T′-WTe<sub>2</sub> using
first-principles calculations. The calculated results indicate that
the fast oxidation of WTe<sub>2</sub> originates from the existence
of H<sub>2</sub>O in air, which significantly promotes the oxidation
of ML 1T′-WTe<sub>2</sub>. More importantly, this low-coverage
oxidized WTe<sub>2</sub> loses its topological features and is changed
into a trivial insulator. Furthermore, we propose a fully oxidized
ML WTe<sub>2</sub> that can still possess the QSH insulator states.
The topological phase transition induced by oxidation provides exotic
insight into understanding the topological features of layered transition-metal
dichalcogenide materials