Adiabatic Edge Channel Transport in a Nanowire Quantum Point Contact Register.

We report on a prototype device geometry where a number of quantum point contacts are connected in series in a single quasi-ballistic InAs nanowire. At finite magnetic field the backscattering length is increased up to the micron-scale and the quantum point contacts are connected adiabatically. Hence, several input gates can control the outcome of a ballistic logic operation. The absence of backscattering is explained in terms of selective population of spatially separated edge channels. Evidence is provided by regular Aharonov-Bohm-type conductance oscillations in transverse magnetic fields, in agreement with magnetoconductance calculations. The observation of the Shubnikov-de Haas effect at large magnetic fields corroborates the existence of spatially separated edge channels and provides a new means for nanowire characterization.

Ballistic Transport and Exchange Interaction in InAs Nanowire Quantum Point Contacts.

One-dimensional ballistic transport is demonstrated for a high-mobility InAs nanowire device. Unlike conventional quantum point contacts (QPCs) created in a two-dimensional electron gas, the nanowire QPCs represent one-dimensional constrictions formed inside a quasi-one-dimensional conductor. For each QPC, the local subband occupation can be controlled individually between zero and up to six degenerate modes. At large out-of-plane magnetic fields Landau quantization and Zeeman splitting emerge and comprehensive voltage bias spectroscopy is performed. Confinement-induced quenching of the orbital motion gives rise to significantly modified subband-dependent Landé g factors. A pronounced g factor enhancement related to Coulomb exchange interaction is reported. Many-body effects of that kind also manifest in the observation of the 0.7·2e(2)/h conductance anomaly, commonly found in planar devices.

A precise optical determination of nanoscale diameters of semiconductor nanowires.

Electrical and optical properties of semiconducting nanowires (NWs) strongly depend on their diameters. Therefore, a precise knowledge of their diameters is essential for any kind of device integration. Here, we present an optical method based on dark field optical microscopy to easily determine the diameters of individual NWs with an accuracy of a few nanometers and thus a relative error of less than 10%. The underlying physical principle of this method is that strong Mie resonances dominate the optical scattering spectra of most semiconducting NWs and can thus be exploited. The feasibility of this method is demonstrated using GaAs NWs but it should be applicable to most types of semiconducting NWs as well. Dark field optical microscopy shows that even slight tapering of the NWs, i.e. diameter variations of a few nanometers, can be detected by a visible color change. Abrupt diameter changes of a few nanometers, as they occur for example when growth conditions vary, can be determined as well. In addition a profound analysis of the elastic scattering properties of individual GaAs NWs is presented theoretically using Mie calculations as well as experimentally by dark field microscopy. This method has the advantage that no vacuum technique is needed, a fast and reliable analysis is possible based on cheap standard hardware.

Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures.

We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.

Material and doping transitions in single GaAs-based nanowires probed by Kelvin probe force microscopy.

We demonstrate the potential of Kelvin probe force microscopy for simultaneously probing the topography and the work function of individual nanowires. Our technique allows us to visualize both the material and the doping contrast in single GaAs-based nanowires without the need to electrically contact the nanowires. In a GaAs/GaP heterostructure nanowire, a core-shell structure is found. This is attributed to a thermally activated radial overgrowth of GaAs, while in the GaP region the vertical nanowire growth dominates. In partially p-doped GaAs nanowires the doping transitions can be localized and the width of the depletion layer is estimated.

Minor surgery of the foot.

Ingrown toenails, hallux valgus and Morton's neuroma are common problems in family practice. All are amenable to surgical treatment. Ingrown toenails, in particular, are easily treated in the office. The indications for conservative treatment, surgical management, and some surgical techniques are discussed.

Common foot problems in the arthritic patient.

The various arthridities, particularly rheumatoid arthritis and osteoarthritis, are a significant cause of pain in the foot. Symptoms may be due mainly to arthritis, but also may be complicated and even initiated by abnormal biomechanics of the foot. This article discusses the various arthritidities-osteoarthritis, rheumatoid arthritis, gout, psoriatic and non-specific arthritis-and how they affect the foot. By initiating appropriate conservative or surgical treatment in the arthritic disease's early stages, family physicians can prevent serious deformities from developing in the foot.