We show in a combined study of four-point conductance measurement and tunneling microscopy that surface state conductance induced by one monolayer of Pb on Si(557) can be quasi one dimensional with conductivity values close to typical three-dimensional metals. At a critical temperature of $T_{\mathrm{c}}=78\mathrm{K}$, associated with an order-disorder phase transition and a tenfold superperiodicity along the Pb chains, the system switches from low to high conductance anisotropy, with a semiconductor-insulator transition in the direction perpendicular to the chain structure, while along the chains conductance with a $(1/T+\mathrm{const})$ temperature dependence was found.

${\text{DySi}}_2$ monolayers were prepared by thermal evaporation of Dy at room temperature followed by annealing to $500°\text{C}$ on Si(111), which yields a perfect $\left(1\times 1\right)$ low-energy electron diffraction pattern. These monolayers of ${\text{DySi}}_2$ were investigated by electron energy loss spectroscopy with both high energy and momentum resolution. A low-energy acoustic-like dispersion was found with very small anisotropy in reciprocal space, consistent with the characteristic losses due to a two-dimensional plasmon in the hexagonal monolayer structure of ${\text{DySi}}_2$, and effective hole densities of $N_{2d}=4.1\times {10}^{13}{\text{cm}}^{-2}$ with an effective mass of $m^{\ast }=0.37m_e$. Deviations of the expected dispersion due to single-particle excitations in the Si substrate were found above $q_{\parallel }=0.08{\text{Å}}^{-1}$. On (111) facets with terrace widths of 12 lattice constants, these properties change little along the terraces, but no plasmon wave propagation across step edges is possible, leading to strong suppression of characteristic loss signals in the direction normal to the steps.

In order to find criteria for discrimination between surface color centers at terraces and steps, and bulk color centers, the characteristic losses of these centers have been investigated by electron energy loss spectroscopy on an epitaxial MgO film grown on a Ag (1,1,19) surface. This film contains a significantly higher step density compared with a film grown on Ag(100). The generation of four distinct losses at 2.0, 2.4, 2.8, and 3.4 eV and a broad loss centered at 5.5 eV have been observed that are induced by electron bombardment of the MgO surface. The latter loss is attributed to bulk color centers ${(F}_b$ centers). By comparing the measured loss energies with experiments performed on MgO/Ag(100) and with theoretical literature data, the observed losses at 2.0 and 2.8 eV can be consistently assigned to transitions of color centers located on step sites, whereas those at 2.4 and 3.4 eV are attributed to terrace sites. The kinetics of color center formation during electron bombardment, as well as the annihilation of F centers by simple exposure to ${\mathrm{O}}_2$ gas at room temperature, was determined and compared for differently coordinated color centers. While all surface color centers follow the same kinetics, we show that the $F_b$ centers can only decay as long as the existence of surface color centers provides active sites for dissociating oxygen molecules. This corroborates the assignment of $F_b$ centers.

We present in this work the electronic structure and transition energies (both thermodynamic and optical) of Cl vacancies in NaCl by hybrid density functionals. The underestimated transition energies by the semilocal functional inherited from the band-gap problem are recovered by the PBE0 hybrid functional through the nonlocal exact exchange, whose amount is adjusted to reproduce the experimental band gap. The hybrid functional also gives a better account of the lattice relaxation for the defect systems arising from the reduced self-interaction. On the other hand, the quantitative agreement with experimental vertical transition energy cannot be achieved with hybrid functionals due to the inaccurate descriptions of the ionization energies of the localized defect and the positions of the band edges.

One-dimensional wires are known to be inherently unstable at finite temperature. Here, we show that long-range order of atomic Au double chains adsorbed on a Si(553) surface is not only stabilized by interaction with the substrate, but spontaneous self-healing of structural defects is actually enforced by the adsorption of atomic species such as Au or H. This is true even for random adsorbate distribution. Combining atomistic models within density functional theory with low energy electron diffraction and high-resolution electron energy loss spectroscopy, we demonstrate that this apparently counterintuitive behavior is mainly caused by adsorption-induced band filling of modified surface bands, i.e., by the strong electronic correlation throughout the whole terrace. Although adsorption preferably occurs at the step edge, it enhances the dimerization and the stiffness of the Au dimers. Thus, the intertwinement of quasi-1D properties with delocalized 2D effects enforces the atomic wire order.