Unpinning of the Fermi level on GaAs (100) surfaces by photochemical reactions resulting from simultaneous exposure of specimens to flowing water and light was recently reported. We discuss here a series of experiments carried out to provide further information on the changes in surface electronic structure responsible for unpinning of the Fermi level under these conditions. The present work supports the conclusion that the surface states which pin the Fermi level are associated with elemental arsenic and arsenic sesquioxide (As2O3). Effects of each of these two species on pinning are distinguished experimentally. We find that, in addition to photochemical reactions, exposure to flowing water alone can result in Fermi level unpinning under certain conditions. The oxygen content of the wash water and the specimen preparation are shown to be important variables.

Nanofabrication of high aspect ratio (50:1) sub-10nm silicon nanowires using inductively coupled plasma etching J. Vac. Sci. Technol. B 30, 06FF02 (2012); 10.1116/1.4755835Fabrication of ferromagnetic single-electron tunneling devices by utilizing metallic nanowire as hard mask stencil Fabrication of nanometer size photoresist wire patterns with a silver nanocrystal shadowmask

The effect of probe geometry on the classical Hall response to a weak perpendicular inhomogeneous magnetic field is studied numerically. An electric potential equation based on a classical model of the two-dimensional Hall effect is solved numerically for a generalized flux distribution to find the Hall response function. We find that the magnitude and shape of this response function is strongly affected by probe geometry. Asymmetric cross-shaped Hall probes, with one narrow voltage lead, have a strongly peaked response more localized than in symmetric probe arrangements. This suggests novel lithographic patterns that may improve the spatial resolution of Hall magnetometry and scanning Hall probe microscopy.

We report imaging of molybdenum disulfide by scanning tunneling microscopy (STM) in air. MoS2, a layer lattice material, is an interesting compound scientifically and is technologically important as a solid lubricant and as a catalyst. Images with atomic spatial resolution were formed only at negative (−0.8 to −1.9 V) sample bias, i.e., by electrons tunneling from the sample into the tip. Our observations are consistent with an electronic model in which the valence electrons are located in bonding or nonbonding orbitals largely confined within the S-Mo-S ‘‘sandwich’’ layers which make up the MoS2 lattice. There are no sigma or pi sulfur bonding orbitals in the basal plane from which electrons can tunnel. The STM image is produced by electrons originating from the filled molybdenum dz2 orbitals. These orbitals do not participate significantly in the formation of chemical bonds. They do project sufficiently far spatially above the basal plane in the presence of an applied electric field to permit formation of a STM image.

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