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- ItemResistive switching in polycrystalline YMnO3 thin films(New York, NY : American Inst. of Physics, 2014) Bogusz, A.; Müller, A.D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O.G.; Schmidt, H.We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.
- ItemPreparation and characterisation of carbon-free Cu(111) films on sapphire for graphene synthesis(Bristol : IOP Publ., 2018) Lehnert, J.; Spemann, D.; Surjuse, S.; Mensing, M.; Grüner, C.; With, P.; Schumacher, P.; Finzel, A.; Hirsch, D.; Rauschenbach, B.This work presents an investigation of carbon formed on polycrystalline Cu(111) thin films prepared by ion beam sputtering at room temperature on c-plane Al2O3 after thermal treatment in a temperature range between 300 and 1020°C. The crystallinity of the Cu films was studied by XRD and RBS/channeling and the surface was characterised by Raman spectroscopy, XPS and AFM for each annealing temperature. RBS measurements revealed the diffusion of the Cu into the Al2O3 substrate at high temperatures of > 700°C. Furthermore, a cleaning procedure using UV ozone treatment is presented to remove the carbon from the surface which yields essentially carbon-free Cu films that open the possibility to synthesize graphene of well-controlled thickness (layer number).
- ItemGaN-based radial heterostructure nanowires grown by MBE and ALD(Bristol : Institute of Physics Publishing, 2013) Lari, L.; Ross, I.M.; Walther, T.; Black, K.; Cheze, C.; Geelhaar, L.; Riechert, H.; Chalker, P.R.A combination of molecular beam epitaxy (MBE) and atomic layer deposition (ALD) was adopted to fabricate GaN-based core/shell NW structures. ALD was used to deposit a HfO2 shell of onto the MBE grown GaN NWs. Electron transparent samples were prepared by focussed ion beam methods and characterized using state-of-the-art analytical transmission and scanning transmission electron microscopy. The polycrystalline coating was found to be uniform along the whole length of the NWs. Photoluminescence and Raman spectroscopy analysis confirms that the HfO2 ALD coating does not add any structural defect when deposited on the NWs.
- ItemIron-assisted ion beam patterning of Si(001) in the crystalline regime(Bristol : IOP, 2012) Macko, S.; Grenzer, J.; Frost, F.; Engler, M.; Hirsch, D.; Fritzsche, M.; Mücklich, A.; Michely, T.We present ion beam erosion experiments on Si(001) with simultaneous sputter co-deposition of steel at 660 K. At this temperature, the sample remains within the crystalline regime during ion exposure and pattern formation takes place by phase separation of Si and iron-silicide. After an ion fluence of F ≈ 5.9×10 21 ions m -2, investigations by atomic force microscopy and scanning electron microscopy identify sponge, segmented wall and pillar patterns with high aspect ratios and heights of up to 200 nm. Grazing incidence x-ray diffraction and transmission electron microscopy reveal the structures to be composed of polycrystalline iron-silicide. The observed pattern formation is compared to that in the range of 140-440K under otherwise identical conditions, where a thin amorphous layer forms due to ion bombardment.