The existence of the edge states of single-layered H-terminated graphitic ribbons predicted by Nakada et al. [Phys. Rev. B 54, 17 954 (1996)] has been confirmed by first-principles calculations within the framework of the local-density approximation and the pseudopotentials. The edge states in cases of stacked ribbons have also been examined, and it has been found that the existence of the edge states is dependent on the stacking manner. This phenomenon can be understood from the electronic structures of $\mathrm{AA}$- and $\mathrm{AB}$-stacked bulk graphite.

Atomic-sized fluorescent defects in diamond are widely recognized as a promising solid state platform for quantum cryptography and quantum information processing. For these applications, single photon sources with a high intensity and reproducible fabrication methods are required. In this study, we report a novel color center in diamond, composed of a germanium (Ge) and a vacancy (V) and named the GeV center, which has a sharp and strong photoluminescence band with a zero-phonon line at 602 nm at room temperature. We demonstrate this new color center works as a single photon source. Both ion implantation and chemical vapor deposition techniques enabled fabrication of GeV centers in diamond. A first-principles calculation revealed the atomic crystal structure and energy levels of the GeV center.

We report the successful synthesis of ${\mathrm{B}}_{\mathit{x}}$ ${\mathrm{C}}_{\mathit{y}}$ ${\mathrm{N}}_{\mathit{z}}$ nanotubes. Arc-discharge methods were used to produce stable nanotubule structures identified by high-resolution transmission-electron microscopy. Local electron-energy-loss spectroscopy of K-edge absorptions for B, C, and N atoms was used to determine the atomic compositions of individual tubules. Tubes of stoichiometry ${\mathrm{BC}}_2$N and ${\mathrm{BC}}_3$ have been observed, in agreement with theoretical predictions.

We propose a family of nanotubules originating from a hexagonal ${\mathrm{BC}}_2$N sheet. Because of the anisotropic structure of the ${\mathrm{BC}}_2$N sheet, there are a variety of ways to obtain chiral structures by rolling the ${\mathrm{BC}}_2$N sheets into tubules. We performed first-principles and tight-binding band-structure calculations and predict that the chiral ${\mathrm{BC}}_2$N tubules will behave as semiconductors that can be doped with either acceptors or donors. Since the ${\mathrm{BC}}_2$N sheets have anisotropic conductivity in the in-plane directions, helical currents are expected for the chiral tubules. The tubules will resemble nanoscale coils.