Daniel Schwen

Manganese-doped ZnO nanobelts for spintronics

Zinc oxide (ZnO) nanobelts synthesized by thermal evaporation have been ion implanted with 30 keV Mn+ ions. Both transmission electron microscopy and photoluminescence investigations show highly defective material directly after the implantation process. Upon annealing to 800 °C, the implanted Mn remains in the ZnO nanobelts and the matrix recovers both in structure and luminescence. The produced high-quality ZnO:Mn nanobelts are potentially useful for spintronics.

Alignment of Semiconductor Nanowires Using Ion Beams

Gallium arsenide nanowires are grown on 100 GaAs substrates, adopting the epitaxial relation and thus growing with an angle around 35 degrees off the substrate surface. These straight nanowires are irradiated with different kinds of energetic ions. Depending on the ion species and energy, downwards or upwards bending of the nanowires is observed to increase with ion fluence. In the case of upwards bending, the nanowires can be aligned towards the ion beam direction at high fluences. Defect formation (vacancies and interstitials) within the implantation cascade is identified as the key mechanism for bending. Monte Carlo simulations of the implantation are presented to substantiate the results.

Catalyst–nanostructure interaction and growth of ZnS nanobelts

Details of the vapour-liquid-solid Au droplet catalysed growth of ZnS nanobelts are elucidated in this work. The inclination of the Au droplet after solidification shows that it is indeed in the liquid state during nanobelt growth. Numerous stacking faults are observed when (0001) wurtzite is the side surface of the nanobelt. Compressive stress at the droplet-nanobelt-atmosphere triple interface is the cause of the stacking faults. Sawteeth-like structures are observed on the Zn-terminated polar (0001) side surface only. These surfaces are chemically active, while S-terminated [Formula: see text] surfaces and non-polar surfaces are not. On these active surfaces, autocatalysed vapour-solid growth leads to the formation of the observed sawteeth.

Conductivity of ion tracks in diamond-like carbon films

AbstractHigh-energy heavy ions (e.g. 1 GeV uranium ions ) passing through a diamond-like carbon (DLC ) film create conductingtracks along their path. The conductivity of these channels is due to a conversion of diamond sp bonds to graphite sp bonds 32 caused by the large energy deposited along the ion track. The tracks have a diameter of approximately 10 nm and representconducting filaments embedded in the insulating diamond-like matrix. They might be used as electron field emitters in vacuumelectronic devices. 2003 Elsevier Science B.V. All rights reserved. Keywords: Diamond-like carbon, Ion tracks, Field emission, Nanostructures 1. IntroductionFig. 1 shows the concept of a field emission cathodebased on ion tracks in diamond-like carbon films. Theelectron–emitting layer consists of an amorphous dia-mond-like carbon (DLC ) film containing cylindrical iontracks as conductive filaments. These tracks are createdwhen energeticheavy ions pass through the DLC layerw1,2x. The large energy deposition along the ion pathleads to graphitization of the material within a cylindri-cal zone of a few nanometers in diameter. These con-ducting channels facilitate the electron transport fromthe back contact to the surface. Due to their large aspectration, field emission of electrons is expected and hasto be investigated.In this paper, we report the characterization of theseion tracks by means of scanning force microscopy(SFM ). Some preliminary measurements on the fieldemission behavior were performed.2. Experimental detailsThe DLC films were produced by ion deposition onheavily doped Si substrates. Two different methods, the

Optical activation of implanted impurities in ZnS nanowires

Nanostructures of zinc sulfide (ZnS), a II-VI compound semiconductor with a direct band gap of 3.66eV in the cubic phase and 3.74eV in the wurtzite phase, show interesting optical properties, making it a promising candidate for optoelectronic devices. Single-crystalline nanobelts and nanowires were synthesized in a computer-controlled process according to the vapor-liquid-solid-mechanism. We investigated the morphology, structure, and composition by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The optical properties were studied by low-temperature photoluminescence (PL) and cathodoluminescence. The synthesized ZnS nanowires were implanted with nitrogen and boron as potential donor and acceptor, respectively. The implanted nanowires were investigated directly after ion implantation and showed a high quantity of defects resulting in nonluminescent material. Annealing procedures recovered the crystal structure and the luminescence, and we found emerging and varying P...