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- ItemConversion of carbon dioxide into storable solar fuels using solar energy(London [u.a.] : Institute of Physics, 2019) Ennaceri, Houda; Abel, BerndNowadays, there are two main energy and environmental concerns, the first is the risk of running out of fossil fuels in the next few decades, and the second is the alarming increase in the carbon dioxide concentrations in the atmosphere, causing global warming and rise of see levels. Therefore, solar-driven technologies represent a substantial solution to fossil fuels dependence, global warming and climate change. Unlike most scientific research, which aim to use solar energy to generate electricity, solar energy can also be harnessed by recycling the carbon dioxide in the atmosphere through high-tech artificial photosynthesis with the objective of producing storable and liquid solar fuels from CO2 and water. There are two types of solar fuels, the first being hydrogen, which can be produced by mean of water splitting processes. The combustion of hydrogen generates water, which is a completely clean option for the environment. The second type of solar fuels consists of carbon-based fuels, such as methane (CH4), carbon monoxide (CO), or alcohols such as methanol (CH3OH) and ethanol (C2H5OH). The production to liquid solar fuels liquid fuels is of great interest, since they can be used in the current industrial infrastructures such as the automobiles' sector, without substantial changes in the vehicles' internal combustion engines. Therefore, guaranteeing a smooth transition from fossil fuel energy to renewable energy without radical economic consequences. Also, and most importantly, when these solar fuels are burned, they will only release the exact amount of CO2 which was initially used, which represents an optimal process for sustainable transport.
- ItemStrong out-of-plane magnetic anisotropy in ion irradiated anatase TiO2 thin films(New York, NY : American Inst. of Physics, 2016) Stiller, M.; Barzola-Quiquia, J.; Esquinazi, P.; Spemann, D.; Meijer, J.; Lorenz, M.; Grundmann, M.The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.
- ItemTopography evolution of germanium thin films synthesized by pulsed laser deposition(New York, NY : American Inst. of Physics, 2017) Schumacher, P.; Mayr, S.G.; Rauschenbach, B.Germanium thin films were deposited by Pulsed Laser Deposition (PLD) onto single crystal Ge (100) and Si (100) substrates with a native oxide film on the surface. The topography of the surface was investigated by Atomic Force Microscopy (AFM) to evaluate the scaling behavior of the surface roughness of amorphous and polycrystalline Ge films grown on substrates with different roughnesses. Roughness evolution was interpreted within the framework of stochastic rate equations for thin film growth. Here the Kardar-Parisi-Zhang equation was used to describe the smoothening process. Additionally, a roughening regime was observed in which 3-dimensional growth occurred. Diffusion of the deposited Ge adatoms controlled the growth of the amorphous Ge thin films. The growth of polycrystalline thin Ge films was dominated by diffusion processes only in the initial stage of the growth.
- ItemCharacteristics of diamond turned NiP smoothed with ion beam planarization technique(London : [Springer], 2017) Li, Yaguo; Takino, Hideo; Frost, FrankBackground: Diamond turning is widely used in machining metals and semiconductors but the turning marks are incurred on machined components due to the mechanics of the technology. The marks are generally harmful to the systems comprising of the machined components. Therefore, the capability of ion beam planarization (IBP) to reduce turning marks of diamond turned metal surfaces was investigated using NiP as an example. Methods: The turning marks and thereby roughness was reduced by IBP with respect to different spatial wavelengths and amplitudes of turning marks. Different thickness of coating resist was also examined in order to find out the potential effects of resist thickness on the reduction of turning marks and roughness. Additionally, the effect of multiple planarization steps was also analyzed. Results: The spatial wavelength and depth of turning marks have only minor impact on the degree of surface roughness reduction. Thicker coating tends to achieve smoother surface after coating turned NiP while ion beam etching can keep surface roughness almost unchanged in our experiments. The surface roughness of diamond turned NiP drops exponentially with processing steps under experimented conditions. Using up to five IBP steps, the surface roughness can be reduced up to one order of magnitude (from Rq ~ 6.5 nm to Rq ~ 0.7 nm). Conclusions: IBP technique performs very well in reducing turning marks on diamond turned NiP surfaces. The surface roughness can be further improved by optimizing the properties of planarizing resist layer and coating processes to enhance the IBP technique as a final surface finishing technology.
- ItemLaser-induced surface modification of biopolymers - Micro/nanostructuring and functionalization(Bristol : IOP Publ., 2018) Stankova, N.E.; Atanasov, P.A.; Nedyalkov, N.N.; Tatchev, Dr.; Kolev, K.N.; Valova, E.I.; Armyanov, St.A.; Grochowska, K.; Śliwiński, G.; Fukata, N.; Hirsch, D.; Rauschenbach, B.The medical-grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine for preparation of high-tech devices because of its remarkable properties. In this paper, we present experimental results on surface modification of PDMS elastomer by using ultraviolet, visible, and near-infrared ns-laser system and investigation of the chemical composition and the morphological structure inside the treated area in dependence on the processing parameters - wavelength, laser fluence and number of pulses. Remarkable chemical transformations and changes of the morphological structure were observed, resulting in the formation of a highly catalytically active surface, which was successfully functionalized via electroless Ni and Pt deposition by a sensitizing-activation free process. The results obtained are very promising in view of applying the methods of laser-induced micro- and nano-structuring and activation of biopolymers' surface and further electroless metal plating to the preparation of, e.g., multielectrode arrays (MEAs) devices in neural and muscular surface interfacing implantable systems.
- ItemInvestigation of room temperature multispin-assisted bulk diamond 13C hyperpolarization at low magnetic fields(Bristol : IOP Publ., 2018) Wunderlich, Ralf; Kohlrautz, Jonas; Abel, Bernd; Haase, Jürgen; Meijer, JanIn this work we investigated the time behavior of the polarization of bulk 13C nuclei in diamond above the thermal equilibrium. This nonthermal nuclear hyperpolarization is achieved by cross relaxation between two nitrogen related paramagnetic defect species in diamond in combination with optical pumping. The decay of the hyperpolarization at four different magnetic fields is measured. Furthermore, we use the comparison with conventional nuclear resonance measurements to identify the involved distances of the nuclear spin with respect to the defects and therefore the coupling strengths. Also, a careful look at the linewidth of the signal give valuable information to piece together the puzzle of the hyperpolarization mechanism.
- 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).
- ItemEvidence for Efficient Pathway to Produce Slow Electrons by Ground-state Dication in Clusters(Bristol : IOP Publ., 2017) You, Daehyun; Fukuzawa, Hironobu; Sakakibara, Yuta; Takanashi, Tsukasa; Ito, Yuta; Maliyar, Gianluigi G.; Motomura, Koji; Nagaya, Kiyonobu; Nishiyama, Toshiyuki; Asa, Kazuki; Sato, Yuhiro; Saito, Norio; Oura, Masaki; Schöffler, Markus; Kastirke, Gregor; Hergenhahn, Uwe; Stumpf, Vasili; Gohkberg, Kirill; Kuleff, Alexander I.; Cederbaum, Lorenz S.; Ueda, KiyoshiWe present an experimental evidence for a so-far unobserved, but potentially very important step relaxation cascades following inner-shell ionization of a composite system: Multiply charged ionic states created after Auger decay may be neutralized by electron transfer from a neighboring species, producing at the same time a low-energy free electron. This electron transfer-mediated decay (ETMD) called process is effective even after Auger decay into the dicationic ground state. Here, we report the ETMD of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.
- ItemReactive ion beam figuring of optical aluminium surfaces(Bristol : IOP Publ., 2017) Bauer, Jens; Frost, Frank; Arnold, ThomasUltra-smooth and arbitrarily shaped reflective optics are necessary for further progress in EUV/XUV lithography, x-ray and synchrotron technology. As one of the most important technological mirror optic materials, aluminium behaves in a rather difficult way in ultra-precision machining with such standard techniques as diamond-turning and subsequent ion beam figuring (IBF). In particular, in the latter, a strong surface roughening is obtained. Hence, up to now it has not been possible to attain the surface qualities required for UV or just visible spectral range applications. To overcome the limitations mainly caused by the aluminium alloy structural and compositional conditions, a reactive ion beam machining process using oxygen process gas is evaluated. To clarify the principle differences in the effect of oxygen gas contrary to oxygen ions on aluminium surface machining, we firstly focus on chemical-assisted ion beam etching (CAIBE) and reactive ion beam etching (RIBE) experiments in a phenomenological manner. Then, the optimum process route will be explored within a more quantitative analysis applying the concept of power spectral density (PSD) for a sophisticated treatment of the surface topography. Eventually, the surface composition is examined by means of dynamic secondary ion mass spectrometry (SIMS) suggesting a characteristic model scheme for the chemical modification of the aluminium surface during oxygen ion beam machining. Monte Carlo simulations were applied to achieve a more detailed process conception.
- ItemSERS analysis of Ag nanostructures produced by ion-beam deposition(Bristol : IOP Publ., 2018) Atanasov, P.A.; Nedyalkov, N.N.; Nikov, Ru.G.; Grüner, Ch.; Rauschenbach, B.; Fukata, N.This study deals with the development of a novel technique for formation of advanced Ag nanostructures (NSs) to be applied to high-resolution analyses based on surface enhanced Raman scattering (SERS). It has direct bearing on human health and food quality, e.g., monitoring small amount or traces of pollutants or undesirable additives. Three types of nanostructured Ag samples were produced using ion-beam deposition at glancing angle (GLAD) on quartz. All fabricated structures were covered with BI-58 pesticide (dimethoate) or Rhodamine 6G (R6G) for testing their potential for use as substrates for (SERS).