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.

The transport and photoelectric properties of four two-dimensional (2D) silicene/MX 2 (M = Mo, W; X = S, Se) heterostructures have been investigated by employing density functional theory, nonequilibrium Green’s function, and Keldysh nonequilibrium Green’s function methods. The stabilities of silicene (SiE) are obviously improved after being placed on the MX 2 (M = Mo, W; X = S, Se) substrates. In particular, the conductivities of SiE/MX 2 are enhanced compared with free-standing SiE and MX 2 . Moreover, the conductivities are increased with the group number of X, i.e., in the order of SiE < SiE/MS 2 < SiE/MSe 2 . An evident current oscillation phenomenon is observed in the SiE/WX 2 heterostructures. When a linear light illumination is applied, SiE/MSe 2 shows a stronger photoresponse than SiE/MS 2 . The maximum photoresponse with a value of 9.0 a 0 2 /photon was obtained for SiE/WSe 2 . More importantly, SiE/MS 2 (M = Mo, W) heterostructures are good candidates for application in designing solar cells owing to the well spatial separation of the charge carriers. This work provides some clues for further exploring 2D SiE/MX 2 heterostructures involving tailored photoelectric properties.

Opposite responses of the transport and photogalvanic properties of the two-probe devices based on covalent functionalized black phosphorus.

Single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. Here, we focus on a family of organometallic complexes with a conjugated curved buckybowl as the ligand. Using first-principles calculations, a multi-mode reversible spin switching based on the CpFe·corannulene complex is predicted by the temperature control of the CpFe+ coordination position in corannulene. The different spin conductance states for three coordinated modes are ascribed to the different electronic spin states of the organometallic complex due to crystal field effects. The predicted relative stabilities of isomers and the energy barriers of isomerization reactions can ensure that the conversion among the three isomers can occur quickly and, at a specific temperature, a dominant isomer has a higher proportion than the other two isomers. This provides a new framework for understanding transport in organometallic complexes with localized d states. This presents an exciting opportunity for exploiting junctions involving molecular spin switching.