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Semi-Interpenetrating Polymer Networks Based on N-isopropylacrylamide and 2-acrylamido-2-methylpropane Sulfonic Acid for Intramolecular Force-Compensated Sensors
Stimulus-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).
Modeling Polycrystalline Electrode-electrolyte Interfaces: The Differential Capacitance
We 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.
On the Impact of Strained PECVD Nitride Layers on Oxide Precipitate Nucleation in Silicon
PECVD nitride layers with different layer stress ranging from about 315 MPa to −1735 MPa were deposited on silicon wafers with similar concentration of interstitial oxygen. After a thermal treatment consisting of nucleation at 650°C for 4 h or 8 h followed annealing 780°C 3 h + 1000°C 16 h in nitrogen, the profiles of the oxide precipitate density were investigated. The binding states of hydrogen in the layers was investigated by FTIR. There is a clear effect of the layer stress on oxide precipitate nucleation. The higher the compressive layer stress is the higher is a BMD peak below the front surface. If the nitride layer is removed after the nucleation anneal the BMD peak below the front surface becomes lower. It is possible to model the BMD peak below the surface by vacancy in-diffusion from the silicon/nitride interface. With increasing duration of the nucleation anneal the vacancy injection from the silicon/nitride interface decreases and with increasing compressive layer stress it increases. © The Author(s) 2019.
On the Impact of Strained PECVD Oxide Layers on Oxide Precipitation in Silicon
PECVD oxide layers with different layer stress ranging from about −305.2 MPa to 39.9 MPa were deposited on silicon wafers with similar concentration of interstitial oxygen. After a thermal treatment consisting of rapid thermal annealing (RTA) and furnace annealing 780°C 3 h + 1000°C 16 h in nitrogen the profiles of the oxide precipitate density were investigated. Supersaturations of self-interstitials as function of layer stress were determined by adjusting modelling results to measured depth profiles of bulk microdefects. The self-interstitial supersaturation generated by RTA at 1250°C and 1175°C at the silicon/oxide interface is increasing linearly with increasing layer stress. Values for self-interstitial supersaturation determined on deposited oxide layers after RTA at 1250°C and 1175°C are very similar to values published for RTO by Sudo et al. An RTA at 1175°C with a PECVD oxide on top of the wafer is a method to effectively suppress oxygen precipitation in silicon wafers. Nucleation anneals carried out at 650°C for 4 h and 8 h did not show any effect of PECVD oxide layers on oxide precipitate nucleation. © The Author(s) 2019.
Lithium metal penetration induced by electrodeposition through solid electrolytes: Example in single-crystal Li6La3ZrTaO12 garnet
Solid electrolytes potentially enable rechargeable batteries with lithium metal anodes possessing higher energy densities than today’s lithium ion batteries. To do so the solid electrolyte must suppress instabilities that lead to poor coulombic efficiency and short circuits. In this work, lithium electrodeposition was performed on single-crystal Li6La3ZrTaO12 garnets to investigate factors governing lithium penetration through brittle electrolytes. In single crystals, grain boundaries are excluded as paths for lithium metal propagation. Vickers microindentation was used to introduce surface flaws of known size. However, operando optical microscopy revealed that lithium metal penetration propagates preferentially from a different, second class of flaws. At the perimeter of surface current collectors smaller in size than the lithium source electrode, an enhanced electrodeposition current density causes lithium filled cracks to initiate and grow to penetration, even when large Vickers defects are in proximity. Modeling the electric field distribution in the experimental cell revealed that a 5-fold enhancement in field occurs within 10 micrometers of the electrode edge and generates high local electrochemomechanical stress. This may determine the initiation sites for lithium propagation, overriding the presence of larger defects elsewhere.
A discussion of the cell voltage during discharge of an intercalation electrode for various C-rates based on non-equilibrium thermodynamics and numerical simulations
In 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.
Lateral Selective SiGe Growth for Local Dislocation-Free SiGe-on-Insulator Virtual Substrate Fabrication
Dislocation free local SiGe-on-insulator (SGOI) virtual substrate is fabricated using lateral selective SiGe growth by reduced pressure chemical vapor deposition. The lateral selective SiGe growth is performed around a ∼1.25 μm square Si (001) pillar in a cavity formed by HCl vapor phase etching of Si at 850 °C from side of SiO2/Si mesa structure on buried oxide. Smooth root mean square roughness of SiGe surface of 0.14 nm, which is determined by interface roughness between the sacrificially etched Si and the SiO2 cap, is obtained. Uniform Ge content of ∼40% in the laterally grown SiGe is observed. In the Si pillar, tensile strain of ∼0.65% is found which could be due to thermal expansion difference between SiO2 and Si. In the SiGe, tensile strain of ∼1.4% along 〈010〉 direction, which is higher compared to that along 〈110〉 direction, is observed. The tensile strain is induced from both [110] and [−110] directions. Threading dislocations in the SiGe are located only ∼400 nm from Si pillar and stacking faults are running towards 〈110〉 directions, resulting in the formation of a wide dislocation-free area in SiGe along 〈010〉 due to horizontal aspect ratio trapping.
The influence of partial replacement of Cu with Ga on the corrosion behavior of Ti40Zr10Cu36PD14 metallic glasses
TiZrCuPdGa 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.
Boundary conditions for electrochemical interfaces
Consistent 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.
Static Dielectric Constant of β-Ga2O3 Perpendicular to the Principal Planes (100), (010), and (001)
The relative static dielectric constant ℇr of β-Ga2O3 perpendicular to the planes (100), (010), and (001) is determined in the temperature range from 25 K to 500 K by measuring the AC capacitance of correspondingly oriented plate capacitor structures using test frequencies of up to 1 MHz. This allows a direct quantification of the static dielectric constant and a unique direction assignment of the obtained values. At room temperature, ℇr perpendicular to the planes (100), (010), and (001) amounts to 10.2 ± 0.2, 10.87 ± 0.08, and 12.4 ± 0.4, respectively, which clearly evidence the anisotropy expected for β-Ga2O3 due to its monoclinic crystal structure. An increase of ℇr by about 0.5 with increasing temperature from 25 K to 450 K was found for all orientations. Our ℇr data resolve the inconsistencies in the previously available literature data with regard to absolute values and their directional assignment and therefore provide a reliable basis for the simulation and design of devices. © The Author(s) 2019.