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The recent synthesis of "borophane" polymorphs through hydrogenation has promoted the development of boron-based two-dimensional (2D) materials. In this work, the electronic structures and transport properties of hydrogenated borophene are investigated using first-principles calculations. The results show that the metallic character is preserved after hydrogenation, whereas electronic structures are greatly modulated by the position and number of introduced hydrogen atoms. More importantly, the presence of three-center-two-electron (3c-2e) bonds results in the formation of distorted Dirac points below the Fermi level in rect-1Hbridge and rect-2H borophane structures. The transport properties and the current–voltage (I–V) curve characters in those borophane structures can be efficiently modulated by the type of hydrogenations. Different hydrogenation patterns dominate diverse electronic transport behaviors. Such hydrogen atom-participant transport states endow borophane structures with potential applications in boron-based 2D electronics devices. [ABSTRACT FROM AUTHOR]

The breaking of the out-of-plane symmetry makes a two-dimensional (2D) Janus monolayer a new platform to explore the coupling between ferroelectricity and ferromagnetism. Using density functional theory in combination with Monte Carlo simulations, we report a novel phase-switchable 2D multiferroic material VInSe 3 with large intrinsic out-of-plane spontaneous electric polarization and a high Curie temperature ( T c ). The structural transition energy barrier between the two phases is determined to be 0.4 eV, indicating the switchability of the electric polarizations and the potential ferroelectricity. Carrier doping can boost the Curie temperature above room temperature, attributing to the enhanced magnetic exchange interaction. A transition from the ferromagnetic (FM) state to the antiferromagnetic (AFM) state can be induced by carrier doping in octahedra-VInSe 3 , while FM coupling is well-preserved in tetrahedron-VInSe 3 , which can be regulated to be either an XY or Ising magnet at an appropriate carrier concentration. These findings not only enrich the family of high -T c low-dimensional monolayers but also offer a new direction for the design and multifunctional application of multiferroic materials.

Group IV monochalcogenides exhibit spontaneous polarization and ferroelectricity, which are important in photovoltaic materials. Since strain engineering plays an important role in ferroelectricity, in the present work, the effect of equibiaxial strain on the band structure and shift currents in monolayer two-dimensional (2D) GeS and SnS has systematically been investigated using the first-principles calculations. The conduction bands of those materials are more responsive to strain than the valence bands. Increased equibiaxial compressive strain leads to a drastic reduction in the band gap and finally the occurrence of phase transition from semiconductor to metal at strains of -15 and -14% for GeS and SnS, respectively. On the other hand, tensile equibiaxial strain increases the band gap slightly. Similarly, increased equibiaxial compressive strain leads to a steady almost four times increase in the shift currents at a strain of -12% with direction change occurring at -8% strain. However, at phase transition from semiconductor to metal, the shift currents of the two materials completely vanish. Equibiaxial tensile strain also leads to increased shift currents. For SnS, shift currents do not change direction, just as the case of GeS at low strain; however, at a strain of +8% and beyond, direction reversal of shift currents beyond the band gap in GeS occur., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)