Below-band-gap electroluminescence related to doping spikes in boron-implanted silicon pn diodes

The origin of two luminescence bands with maxima around 1.05 eV and 0.95 eV is studied in silicon pn diodes prepared by boron implantation. The two peaks are related to the formation of p-type doping spikes on a nanometer scale. These doping spikes are generated by long-time thermal activation of preformed boron clusters. The peak with a larger binding energy stems from spatially indirect excitons bound to doping spikes in a strained environment, while the peak with a lower binding energy is related to doping spikes without strain. The doping spikes are able to capture spatially indirect bound excitons with a low recombination rate, thus effectively suppressing the fast nonradiative recombination at defects. This effect leads to an efficient room temperature electroluminescence in silicon light-emitting diodes prepared by boron implantation

Fabrication of horizontal silicon nanowire arrays on insulator by ion irradiation

We report a simple and potentially mass productive technique to fabricate horizontal single crystalline Si nanowire arrays on insulating substrate based on a self-organized pattern formation mechanism during Xe+ ion beam irradiation of Si-on-insulator material. A periodic ripple surface pattern is created by ion irradiation at 67o incidence angle to the surface normal. The transfer of this pattern to the oxide interface results in an array of electrically disconnected parallel ordered Si nanowires on the insulating oxide. Doping of the nanowires was demonstrated by boron ion implantation and annealing. The morphology and resistivity of the narrow nanowires with large aspect ratio were analysed by cross sectional transmission electron microscopy and scanning spreading resistance microscopy, respectively. Physical reasons of the observed low carrier activation are discussed

Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape

Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au(+9 )ions at a fluence of 5 × 10(13 )ions/cm(2). The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au(+9 )ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (H(c)) and remanence ratio (M(r)/M(s)) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction

Persistent Current Reduction in Metal-Semiconductor FETs With a ZnCoO Channel in an External Magnetic Field

Abstract — Transparent metal-semiconductor field-effect transistors (MESFETs) with a ZnCoO channel have been fabricated by pulsed laser deposition on c-plane sapphire substrates at a temperature of 550 °C. The paramagnetic properties have been confirmed by magnetotransport measurements on undepleted ZnCoO films without Schottky gate contacts. The Au/AgxO Schottky gate contacts were processed by optical lithography and metallization. Below 50 K, the MESFET characteristics are persistently changed from a low resistance state (LRS) to high resistance state by an external magnetic field. The MESFET can be switched back into the LRS only by heating it up to room temperature. Index Terms — Bound magnetic polaron, magnetic channel, metal-semiconductor field-effect transistor (MESFET), s-d exchange. I

Testing antimicrobial surfaces for spaceflight applications and clinical use

Inhalt: Built and enclosed environments provide ideal conditions for studying microbial adaptations to defined indoor environments. Humans contribute a majority of the microbial population of enclosed environments and microorganisms are impossible to eliminate from indoor inhabited environments. This applies for spaceflight missions during which the crew lives in indoor conditions with often harsh outside conditions as well as for clinical settings, with patients being especially vulnerable to their environment. Among the omnipresent microorganisms are also opportunistic pathogens, which may cause infections in astronauts and patients alike. In the latter group intensive care patients are especially prone to opportunistic infections. With the ever-increasing antimicrobial resistance of microorganisms posing one of the top ten global public health threats, the need for alternative approaches to tackle this problem is essential. Hence, consideration and evaluation of microbial dispersal, growth, and adaptation during long term missions to prevent contaminations throughout the respective enclosed environment and its potential health impacts is crucial. To evaluate antimicrobial properties and application potential of antimicrobial surfaces for spaceflight purposes and use in clinical settings, surface- microorganism interactions have to be tested in multiple ways: First of all, the surfaces need to be tested under standardized conditions with model organisms in the laboratory to define antimicrobial properties as well as learning more about the mode of action. This is being done using contact killing experiments as well as further going analyses such as proteomics and transcriptomics. Additionally, the surfaces are tested in direct application by frequent touching. This is in the objective of several studies: In the project “Touching Surfaces” novel antimicrobial surfaces are tested application-based under real space conditions on the International Space Station as well as in schools and in clinical settings. Additionally, surfaces are tested in spaceflight analogue habitats such as the Concordia station in Antarctica in the project ConTACTS. For application- based analysis, the microbial community on the surfaces is analyzed using culture-dependent and culture-independent strategies such as next generation sequencing