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- ItemAtomically controlled CVD processing of group IV semiconductors for ultra-large-scale integrations(Bristol : IOP Publishing, 2012) Murota, Junichi; Sakuraba, Masao; Tillack, BerndOne of the main requirements for ultra-large-scale integrations (ULSIs) is atomic-order control of process technology. Our concept of atomically controlled processing is based on atomic-order surface reaction control by CVD. By ultraclean low-pressure CVD using SiH4 and GeH4 gases, high-quality low-temperature epitaxial growth of Si1−xGex (100) (x=0–1) with atomically flat surfaces and interfaces on Si(100) is achieved. Self-limiting formation of 1–3 atomic layers of group IV or related atoms in the thermal adsorption and reaction of hydride gases on Si1-xGex (100) are generalized based on the Langmuir-type model. By the Si epitaxial growth on top of the material already-formed on Si(100), N, B and C atoms are confined within about a 1 nm thick layer. In Si cap layer growth on the P atomic layer formed on Si1−xGex (100), segregation of P atoms is suppressed by using Si2H6 instead of SiH4 at a low temperature of 450 °C. Heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si1−xGex/Si heterointerface. It is confirmed that higher carrier concentration and higher carrier mobility are achieved by atomic-layer doping. These results open the way to atomically controlled technology for ULSIs.
- ItemAntibacterial Ti-Cu alloy with enhanced mechanical properties as implant applications(Bristol : IOP Publishing, 2020) Yi, ChangBo; Ke, ZunYun; Zhang, Lei; Tan, Jun; Jiang, YeHua; He, ZhengYuanThe service life as hard tissue implantation for clinical application needs compatible mechanical properties, e.g. strength, modulus, etc, and certain self-healing in case of internal infection. Therefore, for sake of improving the properties of Ti-Cu alloy, the microstructure, mechanical properties, corrosion resistance and antibacterial properties of Ti-xCu alloy (x = 2, 5, 7 and 10 wt.%) prepared by Ar-arc melting followed by heat treatment were studied. The results show that the Ti-Cu alloy was mainly composed of α-Ti matrix and precipitated Ti2Cu phase. The Cu element mainly accumulates in the lamellar structure and forms the precipitated Ti2Cu phase. As the increase of Cu content, the lamellar Ti2Cu phase increases, the compressive strength and elastic modulus also were altered. The Ti-7Cu alloy exhibited the higher compressive strength (2169 MPa) and the lower elastic modulus (108 GPa) compared with other Ti-Cu alloys. The corrosion resistance of Ti-xCu alloys increases with the increase of Cu content. When the Cu content was greater than 5 wt.%, the value of corrosion current density for Ti-Cu alloy was less than 1 μAcenterdotcm−2, which is also significantly lower than that of CP-Ti. The antibacterial test revealed that only the Ti-Cu alloy with 5 wt.% or greater Cu content could display a strong antibacterial rate against E. coli and S. aureus. Therefore, the prepared Ti-7Cu alloy via heat treatment showed excellent mechanical properties, corrosion resistance, and antibacterial properties, which would meet the replacement of human hard tissue and clinical applications.
- ItemBio-inspired deposition of electrochemically exfoliated graphene layers for electrical resistance heating applications(Bristol : IOP Publishing, 2020-12-4) Utech, Toni; Pötschke, Petra; Simon, Frank; Janke, Andreas; Kettner, Hannes; Paiva, Maria; Zimmerer, CordeliaElectrochemically exfoliated graphene (eeG) layers possess a variety of potential applications, e.g. as susceptor material for contactless induction heating in dynamic electro-magnetic fields, and as flexible and transparent electrode or resistivity heating elements. Spray coating of eeG dispersions was investigated in detail as a simple and fast method to deposit both, thin conducting layers and ring structures on polycarbonate substrates. The spray coating process was examined by systematic variation of dispersion concentration and volume applied to heated substrates. Properties of the obtained layers were characterized by UV-VIS spectroscopy, SEM and Confocal Scanning Microscopy. Electrical conductivity of eeG ring structures was measured using micro-four-point measurements. Modification of eeG with poly(dopamine) and post-thermal treatment yields in the reduction of the oxidized graphene proportion, an increase in electrical conductivity, and mechanical stabilization of the deposited thin layers. The chemical composition of modified eeG layer was analyzed via x-ray photoelectron spectroscopy pointing to the reductive behavior of poly(dopamine). Application oriented experiments demonstrate the direct electric current heating (Joule-Heating) effect of spray-coated eeG layers.
- ItemNonlinear dynamical properties of frequency swept fiber-based semiconductor lasers(Bristol : IOP Publishing, 2021) Slepneva, Svetlana; Pimenov, AlexanderWe investigate dynamics of semiconductor lasers with fiber-based unidirectional ring cavity that can be used as frequency swept sources. We identify key factors behind the reach dynamical behavior of such lasers using state-of-the-art experimental and analytical methods. Experimentally, we study the laser in static, quasi-static and synchronization regimes. We apply experimental methods such as optical heterodyne or electric field reconstruction in order to characterize these regimes or study the mechanisms of transition between them. Using a delay differential equation model, we demonstrate that the presence of chromatic dispersion can lead to destabilization of the laser modes through modulational instability, which results in undesirable chaotic emission. We characterize the instability threshold both theoretically and experimentally, and demonstrate deterioration of the Fourier domain mode locking regime near the threshold.
- ItemSemi-Interpenetrating Polymer Networks Based on N-isopropylacrylamide and 2-acrylamido-2-methylpropane Sulfonic Acid for Intramolecular Force-Compensated Sensors(Bristol : IOP Publishing, 2021) Binder, Simon; Zschoche, Stefan; Voit, Brigitte; Gerlach, GeraldStimulus-responsive hydrogels are swellable polymers that take up a specific volume depending on a measured variable present in solution. Hydrogel-based chemical sensors make use of this ability by converting the resulting swelling pressure, which depends on the measured variable, into an electrical value. Due to the tedious swelling processes, the measuring method of intramolecular force compensation is used to suppress these swelling processes and, thus, significantly increase the sensor's response time. However, intramolecular force compensation requires a bisensitive hydrogel. In addition to the sensitivity of the measured variable the gel has to provide a second sensitivity for intrinsic compensation of the swelling pressure. At the same time, this hydrogel has to meet further requirements, e.g. high compressive strength. Until now, interpenetrating polymer networks (IPN) have been used for such a force-compensatory effective hydrogel, which are complex to manufacture. In order to significantly simplify the sensor design and production, a simpler synthesis of the bisensitive hydrogel is desirable. This paper presents a new bisensitive hydrogel based on semi-interpenetrating polymer networks. It is based on a copolymer network consisting of N-isopropylacrylamide (NiPAAm) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and long PAMPS strands that permeate it. Measurements show, that this hydrogel meets all essential requirements for intramolecular force compensation and is at the same time much easier to synthesize than previously used IPN hydrogels. © 2021 The Author(s).
- ItemThe influence of partial replacement of Cu with Ga on the corrosion behavior of Ti40Zr10Cu36PD14 metallic glasses(Bristol : IOP Publishing, 2019) Wei, Qi; Gostin, Petre Flaviu; Addison, Owen; Reed, Daniel; Calin, Mariana; Bera, Supriya; Ramasamy, Parthiban; Davenport, AlisonTiZrCuPdGa metallic glasses are under consideration for small dental biomedical implants. There is interest in replacing some of the Cu with Ga to improve the glass-forming ability and biocompatibility. Ti40Zr10Cu36-xPd14Gax (x = 0, 1, 2, 4, 8 and 10 at.%) metallic glasses in rod and ribbon forms were fabricated by mould casting and melt spinning, respectively, and electrochemically tested in a 0.9wt.% NaCl (0.154 M) solution. It has been shown that for both rod and ribbon samples Ga levels up to 8% have no significant effect on passive current density, pitting potential or cathodic reactivity in 0.9% NaCl at 37°C. Different pitting potential and corrosion potential values were found when ribbon and rod samples of the same composition were compared for all compositions apart from the one containing the highest Ga level (10%). This was attributed to structural relaxation occurring as a result of the slower cooling rates during casting rods compared with melt-spinning ribbons. Substitution of Ga for Cu in these metallic glasses therefore expected to have no significant effect on corrosion susceptibility. © The Author(s) 2019.
- ItemModeling Polycrystalline Electrode-electrolyte Interfaces: The Differential Capacitance(Bristol : IOP Publishing, 2020) Müller, Rüdiger; Fuhrmann, Jürgen; Landstorfer, ManuelWe present and analyze a model for polycrystalline electrode surfaces based on an improved continuum model that takes finite ion size and solvation into account. The numerical simulation of finite size facet patterns allows to study two limiting cases: While for facet size diameter dfacet →0 we get the typical capacitance of a spatially homogeneous but possible amorphous or liquid surface, in the limit 1[nm] < dfacet, an ensemble of non-interacting single crystal surfaces is approached. Already for moderate size of the facet diameters, the capacitance is remarkably well approximated by the classical approach of adding the single crystal capacities of the contributing facets weighted by their respective surface fraction. As a consequence, the potential of zero charge is not necessarily attained at a local minimum of capacitance, but might be located at a local capacitance maximum instead. Moreover, the results show that surface roughness can be accurately taken into account by multiplication of the ideally flat polycrystalline surface capacitance with a single factor. In particular, we find that the influence of the actual geometry of the facet pattern in negligible and our theory opens the way to a stochastic description of complex real polycrystal surfaces. © 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
- ItemA discussion of the cell voltage during discharge of an intercalation electrode for various C-rates based on non-equilibrium thermodynamics and numerical simulations(Bristol : IOP Publishing, 2020) Landstorfer, ManuelIn this work we discuss the modeling procedure and validation of a non-porous intercalation half-cell during galvanostatic discharge. The modeling is based on continuum thermodynamics with non-equilibrium processes in the active intercalation particle, the electrolyte, and the common interface where the intercalation reaction Li+ + e- ↔ Li occurs. The model is in detail investigated and discussed in terms of scalings of the non-equilibrium parameters, i.e. the diffusion coefficients DA and DE of the active phase and the electrolyte, conductivity sA and sE of both phases, and the exchange current density e0L, with numerical solutions of the underlying PDE system. The current density i as well as all non-equilibrium parameters are scaled s with respect to the 1-C current density iC A of the intercalation electrode. We compute then numerically the cell voltage E as function of the capacity Q and the C-rate Ch. Within a hierarchy of approximations we provide computations of E(Q) for various scalings of the diffusion coefficients, the conductivities and the exchange current density. For the later we provide finally a discussion for possible concentration dependencies. © The Author(s) 2019. Published by ECS.
- ItemBoundary conditions for electrochemical interfaces(Bristol : IOP Publishing, 2017) Landstorfer, ManuelConsistent boundary conditions for electrochemical interfaces, which cover double layer charging, pseudo-capacitive effects and transfer reactions, are of high demand in electrochemistry and adjacent disciplines. Mathematical modeling and optimization of electrochemical systems is a strongly emerging approach to reduce cost and increase efficiency of super-capacitors, batteries, fuel cells, and electro-catalysis. However, many mathematical models which are used to describe such systems lack a real predictive value. Origin of this shortcoming is the usage of oversimplified boundary conditions. In this work we derive the boundary conditions for some general electrode-electrolyte interface based on non-equilibrium thermodynamics for volumes and surfaces. The resulting equations are widely applicable and cover also tangential transport. The general framework is then applied to a specific material model which allows the deduction of a current-voltage relation and thus a comparison to experimental data. Some simplified 1D examples show the range of applicability of the new approach.
- ItemForce microscopy of layering and friction in an ionic liquid(Bristol : IOP Publishing, 2014) Hoth, Judith; Hausen, Florian; Müser, Martin H.; Bennewitz, RolandThe mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4][FAP]) in confinement between a SiOx and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip–sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface.