First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated ${\mathrm{SiO}}_2$ (0001) surface and a fully hydroxylated ${\mathrm{SiO}}_2$ (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated ${\mathrm{SiO}}_2$ surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and ${\mathrm{SiO}}_2$ (0001) surfaces. We also find that the graphene adsorbed on ${\mathrm{SiO}}_2$ is a semiconductor irrespective of the adsorption arrangement due to the variation of on-site energy induced by the ${\mathrm{SiO}}_2$ substrate.

Hydrogen boride nanosheets (HB sheets) are facilely synthesized via ion-exchange treatment on magnesium diboride (MgB₂) in an acetonitrile solution. Optical absorption and fluorescence spectra of HB sheets indicate that their bandgap energy is 2.8 eV. According to first-principles calculations, optical absorption seen at 2.8 eV is assigned to the electron transition between the σ-bonding states of B and H orbitals. In addition, density functional theory (DFT) calculations suggest the other allowed transition from the σ-bonding state of B and H orbitals to the antibonding state with the gap of 3.8 eV. Significant gaseous H₂ release is found to occur only under photoirradiation, which causes the electron transition from the σ-bonding state to the antibonding state even under mild ambient conditions. The amount of H₂ released from the irradiated HB sheets is estimated to be 8 wt%, indicating that the sheets have a high H₂-storage capacity compared with previously reported metal H₂-storage materials.

The carrier-density-dependent conductance and thermoelectric properties of large-area $\mathrm{Mo}{\mathrm{S}}_2$ and $\mathrm{WS}{\mathrm{e}}_2$ monolayers are simultaneously investigated using the electrolyte gating method. The sign of the thermoelectric power changes across the transistor off-state in the ambipolar $\mathrm{WS}{\mathrm{e}}_2$ transistor as the majority carrier density switches from electron to hole. The thermopower and thermoelectric power factor of monolayer samples are one order of magnitude larger than that of bulk materials, and their carrier-density dependences exhibit a quantitative agreement with the semiclassical Mott relation based on the two-dimensional energy band structure, concluding the thermoelectric properties are enhanced by the low-dimensional effect.