We report on electrical transport in the dark and under ultraviolet (UV) illumination through GaN nanowhiskers grown by molecular beam epitaxy (MBE), which is sensitively dependent on the column diameter. This new effect is quantitatively described by a size dependent surface recombination mechanism. The essential ingredient for the interpretation of this effect is a diameter dependent recombination barrier, which arises from the interplay between column diameter and space charge layer extension at the column surface.

Based on nanofocusing refractive x-ray lenses a hard x-ray scanning microscope is currently being developed and is being implemented at beamline ID13 of the European Synchrotron Radiation Facility (Grenoble, France). It can be operated in transmission, fluorescence, and diffraction mode. Tomographic scanning allows one to determine the inner structure of a specimen. In this device, a monochromatic (E=21keV) hard x-ray nanobeam with a lateral extension of 47×55nm2 was generated. Further reduction of the beam size to below 20 nm is targeted.

Optimized sputtered YBa2Cu3O7 (YBCO) thin films on CeO2-buffered sapphire substrates are patterned into square lattices of submicrometer holes (antidots) with diameters of 250–450 nm and lattice parameters of d=500–1000 nm without deterioration of superconducting properties. In the mixed state, matching effects between the Abrikosov vortex lattice and the artificial antidot lattice are observed. These effects are in the form of peaks or cusps in the critical current density recorded as a function of magnetic induction at integers n and specific rationals k/l of the matching field Bm=(Φ0/d2). The experimental results are discussed in the context of existing theories. The existence of multiquanta vortices confined by the holes in YBCO films are considered.

No abstract

Using low-pressJre chemical vapour deposition, shgle-layer S:Ge and single-quanlum-well (sow) Si/SiGe dots were deposited by selective epitaxy in Si02 windows using a SiC12H~/GeH2/H~-based chemistry. The un:formih/ of selective deposition was investigated over a range of pads from 300 p m down to 0.14 um. No change of growth rate and Ge fraction in SiGe was Observed for patterns down to 2 pm. Only for 0.18 p m wide dots was a slight increase in Si height measured as compared wsh the unpattemed area. However, the SiGe layer in the sow dois was 3-4 times thicker, which could be dye to islands or to an enhanced growrh of S:Ge in the small openings. Arrays with hundreds of millions of 0.15 Mm single-quantum-well Si/SiGe oots vely uniform in height could oe deDosited.

The authors report on current-induced magnetization switching ͑CIMS͒ in single-crystalline nanopillars. Fe͑14 nm͒ /Cr͑0.9 nm͒ /Fe͑10 nm͒ /Ag͑6 nm͒ /Fe͑2 nm͒ multilayers are deposited by molecular-beam epitaxy. The central Fe layer is coupled to the thick one by interlayer exchange coupling over Cr, while the topmost Fe layer is decoupled. Nanopillars with 150 nm diameter are prepared by optical and e-beam lithographies. The opposite spin scattering asymmetries of the Fe/ Cr and Fe/ Ag interfaces enabled the authors to observe normal and inverse CIMS for the two subsystems, which are combined in a single device. At high magnetic fields, steplike resistance changes are measured at positive currents and are attributed to current-driven magnetic excitations.

No abstract

Superconducting Nb–In0.53Ga0.47As/In0.77Ga0.23As/InP–Nb contacts with an electrode separation of 450 nm were fabricated. Due to the high mobility of the two-dimensional electron gas, the current transport can be described within the clean limit regime. At 0.3 K a critical current of 3.8 μA was obtained for 6 μm wide contacts leading to a characteristic voltage of 190 μV. The decrease of the critical current with increasing temperature can be explained by a theory developed by A. Chrestin, T. Matsuyama, and U. Merkt [Phys. Rev. B 49, 498 (1994)], which takes δ-shaped barriers at the superconductor/semiconductor interfaces into account.