Structural and electronic properties of epitaxial thin-layer SinGen superlattices

Electronic and magnetic properties of the Janus MoSSe/WSSe superlattice nanoribbon: a first-principles study

The electronic structure properties of Janus MoSSe/WSSe superlattice nanoribbons (SLNRs) are investigated by first-principles calculations. The band structure, density of states and partial charge density are calculated. The results show that the ribbon width, combination ratio and period length have a great effect on the properties of SLNRs. Adjusting the distribution of outer S and Se atoms can restrict the spontaneous bending of the Janus nanoribbons while the properties are well preserved. The zigzag MoSSe/WSSe SLNRs (Z-SLNRs) show semiconductor and half-metal behavior depending on the ribbon width, which is quite different from the metallic properties of pristine MoSSe or WSSe nanoribbons. By modulating the ratio and period length of the two construction units, the bandgap and magnetic properties of Z-SLNRs can be tuned. The armchair MoSSe/WSSe SLNRs (A-SLNRs) are semiconductors, and the bandgap is similar to that of the corresponding armchair MoSSe or WSSe nanoribbons. As the width increases, the bandgaps of A-SLNRs show a variant behavior. It is found that A-SLNRs are all semiconductors regardless of the composition ratio, and the bandgaps also vary with the composition ratio of the constituent materials.

Prediction that uniaxial tension along <111> produces a direct band gap in germanium

We predict a new way to achieve a direct band gap in germanium, and hence optical emission in this technologically important group-IV element: tensile strain along the <111> direction in Ge nanowires. Although a symmetry-breaking band splitting lowers the conduction band at the corner of the Brillouin zone (at the L point), a direct gap of 0.34 eV in the center of the Brillouin zone (at Gamma) can still be achieved at 4.2% longitudinal strain, through an unexpectedly strong nonlinear drop in the conduction band edge at Gamma for strain along this axis. These strains are well within the experimentally demonstrated mechanical limits of single-crystal Ge (or Ge(x)Si(1-x)) nanowires, thereby opening a new material system for fundamental optical studies and applications.