Reversible sodiation of electrochemically deposited binder- and conducting additive-free Si-O-C composite layers

Binder- and conducting additive-free Si-O-C composite layers are deposited electrochemically under potentiostatic conditions from sulfolane-based organic electrolyte. Quartz crystal microbalance with damping monitoring is used for evaluation of the layer growth and its physical properties. The sodiation-desodiation performance of the material is afterward explored in Na-ion electrolyte. In terms of specific capacity, rate capability, and long-term electrochemical stability, the experiments confirm the advantages of applying the electrochemically formed Si-O-C structure as anode for Na-ion batteries. The material displays high (722 mAh g^-1) initial reversible capacity at j = 70 mA g^-1 and preserves stable long-term capacity of 540 mAh g^-1 for at least 400 galvanostatic cycles, measured at j = 150 mA g^-1. The observed high performance can be attributed to its improved mechanical stability and accelerated Na-ion transport in the porous anode structure. The origin of the material electroactivity is revealed based on X-Ray photoelectron spectroscopic analysis of pristine (as deposited), sodiated, and desodiated Si-O-C layers. The evaluation of the spectroscopic data indicates reversible activity of the material due to the complex contribution of carbon and silicon redox centers

Automated parameter extraction of ScAlN MEMS devices using an extended Euler-Bernoulli beam theory

Magnetoelectric sensors provide the ability to measure magnetic fields down to the pico tesla range and are currently the subject of intense research. Such sensors usually combine a piezoelectric and a magnetostrictive material, so that magnetically induced stresses can be measured electrically. Scandium aluminium nitride gained a lot of attraction in the last few years due to its enhanced piezoelectric properties. Its usage as resonantly driven microelectromechanical system (MEMS) in such sensors is accompanied by a manifold of influences from crystal growth leading to impacts on the electrical and mechanical parameters. Usual investigations via nanoindentation allow a fast determination of mechanical properties with the disadvantage of lacking the access to the anisotropy of specific properties. Such anisotropy effects are investigated in this work in terms of the Young’s modulus and the strain on basis of a MEMS structures through a newly developed fully automated procedure of eigenfrequency fitting based on a new non-Lorentzian fit function and subsequent analysis using an extended Euler–Bernoulli theory. The introduced procedure is able to increase the resolution of the derived parameters compared to the common nanoindentation technique and hence allows detailed investigations of the behavior of magnetoelectric sensors, especially of the magnetic field dependent Young‘s modulus of the magnetostrictive layer

Anisotropy of the ΔE effect in Ni-based magnetoelectric cantilevers: a finite element method analysis

In recent investigations of magnetoelectric sensors based on microelectromechanical cantilevers made of TiN/AlN/Ni, a complex eigenfrequency behavior arising from the anisotropic ΔE effect was demonstrated. Within this work, a FEM simulation model based on this material system is presented to allow an investigation of the vibrational properties of cantilever-based sensors derived from magnetocrystalline anisotropy while avoiding other anisotropic contributions. Using the magnetocrystalline ΔE effect, a magnetic hardening of Nickel is demonstrated for the (110) as well as the (111) orientation. The sensitivity is extracted from the field-dependent eigenfrequency curves. It is found, that the transitions of the individual magnetic domain states in the magnetization process are the dominant influencing factor on the sensitivity for all crystal orientations. It is shown, that Nickel layers in the sensor aligned along the medium or hard axis yield a higher sensitivity than layers along the easy axis. The peak sensitivity was determined to 41.3 T −1 for (110) in-plane-oriented Nickel at a magnetic bias flux of 1.78 mT. The results achieved by FEM simulations are compared to the results calculated by the Euler–Bernoulli theory

Development of low-gain avalanche detectors in the frame of the acceptor removal phenomenon

Low-gain avalanche detectors (LGAD) suffer from an acceptor removal phenomenon due to irradiation. This acceptor removal phenomenon is investigated in boron, gallium, and indium implanted samples by 4-point-probe (4pp) measurements, low-temperature photoluminescence spectroscopy (LTPL), and secondary ion mass spectrometry (SIMS) before and after irradiation with electrons and protons. Different co-implantation species are evaluated with respect to their ability to reduce the acceptor removal phenomenon. In case of boron, the beneficial effect is found to be most pronounced for the low-dose fluorine and high-dose nitrogen co-implantation. In case of gallium, the low-dose implantations of carbon and oxygen are found to be beneficial. For indium, the different co-implantation species have no beneficial effect. SIMS boron concentration depth profiles measured before and after irradiation show no indication of a fast movement of boron at room temperature. Hence, the discussed BSi-Sii-defect explanation approach of the acceptor removal phenomenon seems to be more likely than the other discussed Bi-Oi-defect explanation approach

ASi-Sii defect model of light-induced degradation (LID) in silicon: a discussion and review

The ASi-Sii defect model as one possible explanation for light-induced degradation (LID) in typically boron-doped silicon solar cells, detectors, and related systems is discussed and reviewed. Starting from the basic experiments which led to the ASi-Sii defect model, the ASi-Sii defect model (A: boron, or indium) is explained and contrasted to the assumption of a fast-diffusing so-called “boron interstitial.” An LID cycle of illumination and annealing is discussed within the conceptual frame of the ASi-Sii defect model. The dependence of the LID defect density on the interstitial oxygen concentration is explained within the ASi-Sii defect picture. By comparison of electron paramagnetic resonance data and minority carrier lifetime data related to the assumed fast diffusion of the “boron interstitial” and the annihilation of the fast LID component, respectively, the characteristic EPR signal Si-G28 in boron-doped silicon is related to a specific ASi-Sii defect state. Several other LID-related experiments are found to be consistent with an interpretation by an ASi-Sii defect

The two-dimensional electron gas of the In2O3 surface: Enhanced thermopower, electrical transport properties, and its reduction by adsorbates or compensating acceptor doping

In2O3 is an n-type transparent semiconducting oxide possessing a surface electron accumulation layer (SEAL) like several other relevant semiconductors, such as InAs, InN, SnO2, and ZnO. Even though the SEAL is within the core of the application of In2O3 in conductometric gas sensors, a consistent set of transport properties of this two-dimensional electron gas (2DEG) is missing in the present literature. To this end, we investigate high quality single-crystalline as well as textured doped and undoped In2O3(111) films grown by plasma-assisted molecular beam epitaxy to extract transport properties of the SEAL by means of Hall effect measurements at room temperature while controlling the oxygen adsorbate coverage via illumination. The resulting sheet electron concentration and mobility of the SEAL are 1.5E13 cm^-2 and 150 cm^2/Vs, respectively, both of which get strongly reduced by oxygen-related surface adsorbates from the ambient air. Our transport measurements further demonstrate a systematic reduction of the SEAL by doping In2O3 with the deep compensating bulk acceptors Ni or Mg. This finding is supported by X-ray photoelectron spectroscopy measurements of the surface band bending and SEAL electron emission. Quantitative analyses of these XPS results using self-consistent, coupled Schroedinger-Poisson calculations indicate the simultaneous formation of compensating bulk donor defects (likely oxygen vacancies) which almost completely compensate the bulk acceptors. Finally, an enhancement of the thermopower by reduced dimensionality is demonstrated in In2O3: Seebeck coefficient measurements of the surface 2DEG with partially reduced sheet electron concentrations between 3E12 and 7E12 cm^-2 (corresponding average volume electron concentration between 1E19 and 2E19 cm^-3 indicate a value enhanced by 80% compared to that of bulk Sn-doped In2O3 with comparable volume electron concentration.Comment: Main article: 11 pages, 7 figures Supplement: 4 pages, 2 figures To be submitted in Physical Review

Nanometer precise adjustment of the silver shell thickness during automated Au-Ag core-shell nanoparticle synthesis in micro fluid segment sequences

In this work, a wet-chemical synthesis method for gold–silver core–shell particles with nanometer precise adjustable silver shell thicknesses is presented. Typically wet-chemical syntheses lead to relatively large diameter size distributions and losses in the yield of the desired particle structure due to thermodynamical effects. With the here explained synthesis method in micro fluidic segment sequences, a combinatorial in situ parameter screening of the reactant concentration ratios by programmed flow rate shifts in conjunction with efficient segment internal mixing conditions is possible. The highly increased mixing rates ensure a homogeneous shell deposition on all presented gold core particles while the amount of available silver ions was adjusted by automated flow rate courses, from which the synthesis conditions for exactly tunable shell thicknesses between 1.1 and 6.1 nm could be derived. The findings according to the homogeneity of size and particle structure were confirmed by differential centrifugal sedimentation (DCS), scanning and transmission electron microscopy (SEM, TEM) and X-ray photoelectron spectroscopy (XPS) measurements. In UV-Vis measurements, a significant contribution of the core metal was found in the shape of the extinction spectra in the case of thin shells. These results were confirmed by theoretical calculations

Electrochemical deposition of silicon from a sulfolane-based electrolyte: effect of applied potential

As a low-cost, non-volatile, highly polar and chemically stable solvent, sulfolane has a high implementation potential for electroplating in organic media. This is the first report of the electrodeposition of silicon from sulfolane-based electrolytes. Voltammetric and chronoamperometric techniques, coupled with a quartz crystal microbalance, have been used to perform and characterize the process. Resonance frequency, f, damping, w, and apparent molar mass, Mapp are used as sensitive parameters for the evaluation of the silicon layer formation. Si electrodeposition displays a strong dependence on the applied potential. Close to theoretical values for Mapp and minimal w are observed at low deposition overpotentials, which allow an in situ quantitative mass evaluation. At higher overpotentials the process efficiency decreases due to simultaneous electrolyte decomposition. The electrodeposition of elemental Si (approx. 60% of the entire Si content) is evidenced by X-ray photoelectron spectroscopy. Additionally, the formation of a binary metal compound with the Cu substrate might be a key factor in the very good adhesion and mechanical stability of the layer

Effect of dislocations on electrical and electron transport properties of InN thin films. I. Strain relief and formation of a dislocation network

The strain-relaxation phenomena and the formation of a dislocation network in 2H-InN epilayers during molecular beam epitaxy are reported. Plastic and elastic strain relaxations were studied by reflection high-energy electron diffraction, transmission electron microscopy, and high resolution x-ray diffraction. Characterization of the surface properties has been performed using atomic force microscopy and photoelectron spectroscopy. In the framework of the growth model the following stages of the strain relief have been proposed: plastic relaxation of strain by the introduction of geometric misfit dislocations, elastic strain relief during island growth, formation of threading dislocations induced by the coalescence of the islands, and relaxation of elastic strain by the introduction of secondary misfit dislocations. The model emphasizes the determining role of the coalescence process in the formation of a dislocation network in heteroepitaxially grown 2H-InN. Edge-type threading dislocations and dislocations of mixed character have been found to be dominating defects in the wurtzite InN layers. It has been shown that the threading dislocation density decreases exponentially during the film growth due to recombination and, hence, annihilation of dislocations, reaching 109 cm−2 for 2200 nm thick InN films.Unión Europea NMP4-CT2003-505614Unión Europea NMP4-CT-2004-500101Comisión Interministerial de Ciencia y Tecnología MAT2004-01234 Españ