The electronic and lattice dynamical properties of compressed solid SiH4 have been calculated in the pressure range up to 300 GPa with density functional theory. We find two energetically preferred insulating phases with P2(1)/c and Fdd2 symmetries at low pressures. We demonstrate that the Cmca structure having a layered network is the most likely candidate of the metallic phase of SiH4 over a wide pressure range above 60 GPa. The superconducting transition temperature in this layered metallic phase is found to be in the range of 20-75 K.

A gate is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and Seebeck coefficient to obtain the optimum thermoelectric figure of merit in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate affects the electronic structures, further determining the thermoelectric properties.

Density functional calculations have been performed to analyze the electronic and mechanical properties of a number of 2D boroxine-linked covalent organic frameworks (COFs), which are experimentally fabricated from di-borate aromatic molecules. Furthermore, the band structures are surprising and show flat-band characteristics which are mainly attributed to the delocalized π-conjugated electrons around the phenyl rings and can be better understood within aromaticity theories. Next, the effects of branch sizes and hydrostatic strains on their band structures are systematically considered within generalized gradient approximations. It is found that their band gaps will start to saturate when the branch size reaches 9. For boroxine-linked COFs with only one benzene ring in the branch, the band gap is robust under compressive strain while it decreases with the tensile strain increasing. When the branch size is equal or greater than 2, their band gaps will monotonously increase with the strain increasing in the range of [-1.0, 2.0] Å. All boroxine-linked COFs are semiconductors with controllable band gaps, depending on the branch length and the applied strain. In comparison with other 2D materials, such as graphene, hexagonal boron nitride, and even γ-graphyne, all boroxine-linked COFs are much softer and even more stable. That is, they can maintain the planar features under a larger compressive strain, which means that they are good candidates in flexible electronics.

The effect of sintering temperature on thermoelectric properties of CdO ceramics was investigated by solid-state reaction method within the temperature range of 700-1000 ℃. With the increase of sintering temperature, both the grain size and the carrier concentration of these samples increased, while the Seebeck coefficient decreased. The highest dimensionless figure of merit ZT, 0.34, was obtained at 1023 K for the sample sintered at 800 ℃, suggesting the potential application of CdO ceramics in thermoelectric (TE) devices.