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We theoretically demonstrate that screw dislocation (SD), a 1D topological defect widely present in semiconductors, exhibits ubiquitously a new form of spin-orbit coupling (SOC) effect. Differing from the widely known conventional 2D Rashba-Dresselhaus (RD) SOC effect that typically exists at surfaces or interfaces, the deep-level nature of SD-SOC states in semiconductors readily makes it an ideal SOC. Remarkably, the spin texture of 1D SD-SOC, pertaining to the inherent symmetry of SD, exhibits a significantly higher degree of spin coherency than the 2D RD-SOC. Moreover, the 1D SD-SOC can be tuned by ionicity in compound semiconductors to ideally suppress spin relaxation, as demonstrated by comparative first-principles calculations of SDs in Si/Ge, GaAs, and SiC. Our findings therefore open a new door to manipulating spin transport in semiconductors by taking advantage of an otherwise detrimental topological defect.

The defect formation in epitaxial NaCl films (up to 5.6 nm thick) during low-energy (50--1500 eV) electron bombardment has been studied by a combination of low-energy electron diffraction and energy loss spectroscopy. At temperatures below 200 K two types of color center are generated at the surface, showing distinct electronic transition energies and different kinetics of formation. A rate equation analysis provides evidence for a random distribution of stable, immobile $F$ and $M$ centers on the surface. Their saturation density increases with the film thickness, indicating an indirect generation mechanism involving the whole film, presumably via self-trapping of excitons. The angular distribution of the inelastic electron scattering of excitons reveals their surface polariton character, providing the energy transport from film bulk to surface and within the surface. At room temperature the aggregation of Na clusters is observed. Patterns of high and low surface $F$- and $M$-center densities are potentially invaluable as templates for nanostructure devices on ionic crystal surfaces like NaCl(001), because of the chemical reactivity of surface color centers.

It is demonstrated, using reflectance difference spectroscopy, scanning tunneling microscopy, and low-energy electron diffraction, combined with deliberate straining of the surface, that the presence of atomic steps dramatically changes the optical anisotropy of the Si(001) surface. The step-induced reflectance difference signal originates predominately from rebonded steps and is comparable in magnitude to that of the terrace signal.

Collective surface electronic excitations on Ag(111) and Ag(110) have been studied by energy-loss-spectroscopy LEED. The data allow separation of the contribution to the loss intensity due to monopole and to multipole surface plasmons, thus demonstrating the existence of the latter mode also on noble-metal surfaces. Multipole plasmons are therefore a general property of the optical response of metal surfaces whenever the charge-density profile at the interface is not too abrupt. {copyright} {ital 1996 The American Physical Society.}

The evolution of the plasmon spectrum of the Si(111) (7×7)-Cs surface has been studied by energy loss spectroscopy individually resolved in energy and momentum during the transition from substrate to Cs overlayer metallization. The multipole plasmon is identified by an extremely narrow angular distribution of the inelastic electron scattering, unaccounted for by standard dipole scattering theory. A crossover between multipole and monopole surface plasmon is observed at finite surface wave vectors q∥, depending on Cs coverage, and reveals a high sensitivity of the short-wavelength multipole components on surface morphology. © 2006 The American Physical Society.

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 Tc=78K, 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+const) temperature dependence was found. © 2005 The American Physical Society.

A low-energy electron microscopy study of two-dimensional Si(001) island shapes near thermal equilibrium on $10\ifmmode\times\else\texttimes\fi{}15 \ensuremath{\mu}{\mathrm{m}}^{2}$ large single-domain terraces reveals a continuous increase of island aspect ratio and a shape transition from elliptical to ``American-football''-like with increasing island size. The size-dependent island shapes are driven by elastic relaxation caused by the intrinsic surface stress anisotropy present on Si(001). Analysis of the measured elliptical island shapes based on an elastic-model calculation allows a quantitative determination of step energies and of the surface stress anisotropy as a function of temperature.