Scanning tunneling spectroscopy

About: Scanning tunneling spectroscopy is a research topic. Over the lifetime, 7886 publications have been published within this topic receiving 213828 citations.

Conductivity sensitivity of inelastic scanning tunneling microscopy

Abstract: We present some considerations for the inelastic increase in conductivity in scanning tunneling microscopy (STM) by using the dipole approximation for the vibrating molecules. We show that the relative increase in the case of vacuum tunneling can be considerably larger than that obtained in tunneling through oxide layers, even for a single adsorbed molecule. With the present state of STM, such current changes are readily detectable. We further propose an alternative experimental approach unique for STM.

Superconducting tunneling without the tunneling Hamiltonian

Abstract: The theory of superconducting tunneling is extended to treat superconducting junctions with arbitrarily thin, but structureless tunnel barriers. An exact expression for the tunneling current is obtained, using standard, many-body, nonequilibrium Green's function techniques, assuming Fermi distributions in each electrode. The tunneling current result agrees with the recent theory of Blonder, Tinkham, and Klapwijk, but extends their results to treat strong coupling superconductors, proximity effect tunneling, and the effects of tunneling angle. Results for the Josephson critical current in S' INS (superconductor S', insulator I, metal N, superconductor S) junctions, where NS is a proximity effect double layer, are presented for barrier thicknesses ranging from zero to barrier thicknesses for which the tunneling Hamiltonian approach is correct, and for varying N metal thicknesses. Results forI-V curves are presented for normal metal (M)-INS junctions for a similar range of barrier thicknesses and N metal thicknesses. It is shown that the tunneling currentI is the sum of a supercurrentISUP carried solely by Cooper pairs through S, and a quasiparticle currentIQP carried solely by quasiparticles. The influence of leakage on phonon structure observed on tunneling into strong coupling superconductors is described. The nonoscillating portion of the Josephson current is plotted as a function of voltage for the S' INS junction in the tunneling Hamiltonian limit.

Density-gradient analysis of MOS tunneling

Abstract: The density-gradient description of quantum transport is applied to the analysis of tunneling phenomena in ultrathin (<25 /spl Aring/) oxide MOS capacitors. Both electron and hole tunneling are included in the one-dimensional (1-D) analysis and two new refinements to density-gradient theory are introduced, one relating to the treatment of Shockley-Read-Hall recombination and the other a modification of the tunneling boundary conditions to account for the semiconductor bandgap. Detailed comparisons are made with experimental current-voltage (I-V) data for samples with both n/sup +/ and p/sup +/ polysilicon gates and all of the features of the data are found to be understandable within the density-gradient framework. Besides providing new understanding of these experiments, these results show that the density-gradient approach can be of great value for engineering-oriented device analysis in quantum regimes.

Quantum States and atomic structure of silicon surfaces.

Abstract: The electronic and geometric structures of surfaces are closely related to each other. Conventional surface science techniques can study one or the other, but not both at the same time. Recent developments in scanning tunneling microscopy have made it possible to study simultaneously the electronic and geometric structure of Si(111) and Si(001) surfaces. Surface states can be atomically resolved in space and energy; thus the electronic structure of single atoms on surfaces can be studied in detail. The various surface states observed on silicon surfaces are found to derive from different atomic-scale features in the surface geometric structure. Scanning tunneling microscopy has now bridged the gap between electronic and geometric structure, providing a unique opportunity to obtain a better understanding of many surface processes at the atomic level.

Systematic modulation of quantum (electron) tunneling behavior by atomic layer deposition on nanoparticulate SnO2 and TiO2 photoanodes.

Abstract: Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3–. Films thicker than 2 A engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling th...