102 research outputs found
Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation
The manipulation of the antiferromagnetic interlayer coupling in the
epitaxial Fe/Cr/Fe(001) trilayer system by moderate 5 keV He ion beam
irradiation has been investigated experimentally. It is shown that even for
irradiation with very low fluences (10^14 ions/cm^2) a drastic change in
strength of the coupling appears. For thin Cr-spacers (below 0.6 - 0.7 nm) the
coupling strength decreases with fluence, becoming ferromagnetic for fluences
above (2x10^14 ions/cm^2). The effect is connected with the creation of
magnetic bridges in the layered system due to atomic exchange events caused by
the bombardment. For thicker Cr spacers (0.8 - 1.2 nm) an enhancement of the
antiferromagnetic coupling strength is found. A possible explanation of the
enhancement effect is given.Comment: Submitted to PR
Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin-Film Transistor and Sensor Behavior of ZnO Films and Rods
Zinc oxide thin films are fabricated by controlled oxidation of sputtered zinc metal films on a hotplate in air at temperatures between 250 and 450â°C. The nanocrystalline films possess high relative densities and show preferential growth in (100) orientation. Integration in thinâfilm transistors reveals moderate charge carrier mobilities as high as 0.2â
cmâVs. The semiconducting properties depend on the calcination temperature, whereby the best performance is achieved at 450â°C. The defect structure of the thin ZnO film can be tracked by Dopplerâbroadening positron annihilation spectroscopy as well as positron lifetime studies. Comparably long positron lifetimes suggest interaction of zinc vacancies (V) with one or more oxygen vacancies (V) in larger structural entities. Such VâV defect clusters act as shallow acceptors, and thus, reduce the overall electron conductivity of the film. The concentration of these defect clusters decreases at higher calcination temperatures as indicated by changes in the S and W parameters. Such zinc oxide films obtained by conversion of metallic zinc can also be used as seed layers for solution deposition of zinc oxide nanowires employing a mild microwaveâassisted process. The functionality of the obtained nanowire arrays is tested in a UV sensor device. The best results with respect to sensor sensitivity are achieved with thinner seed layers for device construction
Low temperature and radiation stability of flexible IGZO TFTs and their suitability for space applications
In this paper, Low Earth Orbit radiation and temperature conditions are mimicked to investigate the suitability of flexible Indium-Gallium-Zinc-Oxide transistors for lightweight space-wearables. Such wearable devices could be incorporated into spacesuits as unobtrusive sensors such as radiation detectors or physiological monitors. Due to the harsh environment to which these space-wearables would be exposed, they have to be able to withstand high radiation doses and low temperatures. For this reason, the impacts of high energetic electron irradiation with fluences up to 1012 e-/cm2 and low operating temperatures down to 78 K, are investigated. This simulates 278 h in a Low Earth Orbit. The threshold voltage and mobility of transistors that were exposed to e- irradiation are found to shift by +0.09 ± 0.05V and -0.6 ± 0.5cm2 V-1 s-1. Subsequent low temperature exposure resulted in additional shifts of +0.38 V and -5.95 cm2 V-1 s-1 for the same parameters. These values are larger than the ones obtained from non-irradiated reference samples. If this is considered during the systemsâ design, these devices can be used to unobtrusively integrate sensor systems into space-suits
Flexible IGZO TFTs and their suitability for space applications
In this paper, low earth orbit radiation (LEO), temperature, and magnetic field conditions are mimicked to investigate the suitability of flexible InGaZnO transistors for lightweight space wearables. More specifically, the impacts of high energetic electron irradiation with fluences up to 10 12 e - /cm 2 , low operating temperatures down to 78 K and magnetic fields up to 11 mT are investigated. This simulates 278 h in LEO. The threshold voltage and mobility of transistors that were exposed to e - irradiation are found to shift by +(0.09 ± 0.05) V and -(0.6 ± 0.5) cm 2 V -1 s -1 . Subsequent low temperature exposure resulted in additional shifts of +0.38 V and -5.95 cm 2 V -1 s -1 for the same parameters. These values are larger than the ones obtained from non-irradiated reference samples. Conversely, the performance of the devices was observed not to be significantly affected by the magnetic fields. Finally, a Cascode amplifier presenting a voltage gain of 10.3 dB and a cutoff frequency of 1.2 kHz is demonstrated after the sample had been irradiated, cooled down, and exposed to the magnetic fields. If these notions are considered during the systems design, these devices can be used to unobtrusively integrate sensor systems into space suits
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