Electron conduction through quasi-one-dimensional indium atomic wires on silicon

Electron conduction through quasi-one-dimensional (1D) indium atomic wires on silicon (the Si(111)-4x1-In reconstruction) is clarified with the help of local structural analysis using scanning tunneling microscopy. The reconstruction has a conductance per square as high as 100 uS, with global conduction despite numerous surface steps. A complete growth of indium wires up to both the surface steps and the lithographically printed electrodes is essential for the macroscopic transport. The system exhibits a metal-insulator transition at 130 K, consistent with a recent ultraviolet photoemission study [H. W. Yeom, S. Takeda, E. Rotenberg, I. Matsuda, K. Horikoshi, J. Schaefer, C. M. Lee, S. D. Kevan, T. Ohta, T. Nagao, and S. Hasegawa, Phys. Rev. Lett. 82, 4898 (1999)]Comment: 4 pages, 3 figure

Phase transition of the Si(111)-4x1-In surface reconstruction investigated by electron transport measurements

We measure the electron conductivity of the surface states and the subsurface space charge layer originating from the Si(111)-4x1-In reconstruction as a function of temperature. The conductivity of the surface states drops sharply around 130 K with decreasing temperature, revealing a metal-insulator phase transition of the surface reconstruction. In contrast, the influence of the phase transition on the conductivity of the space charge layer is limited to temperatures above 60 K. This means that the surface Fermi level remains strongly pinned despite the phase transition, indicating the presence of free carriers in the surface states down to rather low temperatures.Comment: 10 pages, 3 figures, submitted to Surface Scienc

Strong Electron Confinement By Stacking-fault Induced Fractional Steps on Ag(111) Surfaces

The electron reflection amplitude $R$ at stacking-fault (SF) induced fractional steps is determined for Ag(111) surface states using a low temperature scanning tunneling microscope. Unexpectedly, $R$ remains as high as $0.6 \sim 0.8$ as energy increases from 0 to 0.5 eV, which is in clear contrast to its rapidly decreasing behavior for monatomic (MA) steps [L. B{\"u}rgi et al., Phys. Rev. Lett. \textbf{81}, 5370 (1998)]. Tight-binding calculations based on {\em ab-initio} derived band structures confirm the experimental finding. Furthermore, the phase shifts at descending SF steps are found to be systematically larger than counterparts for ascending steps by $\approx 0.4 \pi$. These results indicate that the subsurface SF plane significantly contributes to the reflection of surface states

One-dimensional surface states on a striped Ag thin film with stacking fault arrays

One-dimensional (1D) stripe structures with a periodicity of 1.3 nm are formed by introduction of stacking fault arrays into a Ag thin film. The surface states of such striped Ag thin films are studied using a low temperature scanning tunneling microscope. Standing waves running in the longitudinal direction and characteristic spectral peaks are observed by differential conductance (dI/dV) measurements, revealing the presence of 1D states on the surface stripes. Their formation can be attributed to quantum confinement of Ag(111) surface states into a stripe by stacking faults. To quantify the degree of confinement, the effective potential barrier at the stacking fault for Ag(111) surface states is estimated from independent measurements. A single quantum well model with the effective potential barrier can reproduce the main features of dI/dV spectra on stripes, while a Kronig-Penney model fails to do so. Thus the present system should be viewed as decoupled 1D states on individual stripes rather than as anisotropic 2D Bloch states extending over a stripe array.Comment: 10 pages, 6 figure

Molecular Dynamics Simulations of Dynamic Force Microscopy: Applications to the Si(111)-7x7 Surface

Molecular dynamics simulations have been performed to understand true atomic resolution, which has been observed on the Si(111)-7$\times$7 surface by dynamic force microscopy in ultra high vacuum(UHV). Stable atomic-scale contrast is reproduced in simulations at constant mean height above a critical tip-sample separation when monitoring the interaction force between tip and sample. Missing or additional adatoms can be recognized in such scans, although they are less well resolved than native adatoms. The resonance frequency shift, as well as arbitrary scans, e.g. at constant force can be computed from a series of force-distance characteristics. By means of dynamic simulations we show how energy losses induced by interaction with an oscillating tip can be monitored and that they occur even in the non-contact range.Comment: 5 pages, 5 figures, accepted publication in Applied Surface Scienc