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Item type:Publication, Access status: with files , Surface acoustic wave induced transport and strain phenomena in van der Waals materialsSurface acoustic waves, the microcosmic cousins of seismic waves, can be generated and precisely controlled on a microscopic scale by applying a periodic electrical signal to a piezoelectric substrate. Harnessing and exploring their interactions with two-dimensional van der Waals (vdW) systems opens new frontiers in materials science and engineering. As part of a special issue on these guided elastic waves for hybrid nano- and quantum technologies, our review highlights work focusing on acoustically-induced transport phenomena at low temperatures that arise from the interaction between the surface acoustic waves in a piezoelectric substrate and a vdW material on its surface. A main focus is on technological methods to control the carrier concentration in transport and strain-related effects that can act on the carrier motion as an effective magnetic field.Publicationtype: Review Article9 29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nonlinear diffusion potential induced anti-ohmic effect(IOP Publishing, 2020-04-29); 10 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , An enhanced lumped element electrical model of a double barrier memristive device(IOP Publishing, 2017-04-13); ; ; ; The massive parallel approach of neuromorphic circuits leads to effective methods for solving complex problems. It has turned out that resistive switching devices with a continuous resistance range are potential candidates for such applications. These devices are memristive systems - nonlinear resistors with memory. They are fabricated in nanotechnology and hence parameter spread during fabrication may aggravate reproducible analyses. This issue makes simulation models of memristive devices worthwhile. Kinetic Monte-Carlo simulations based on a distributed model of the device can be used to understand the underlying physical and chemical phenomena. However, such simulations are very time-consuming and neither convenient for investigations of whole circuits nor for real-time applications, e.g. emulation purposes. Instead, a concentrated model of the device can be used for both fast simulations and real-time applications, respectively. We introduce an enhanced electrical model of a valence change mechanism (VCM) based double barrier memristive device (DBMD) with a continuous resistance range. This device consists of an ultra-thin memristive layer sandwiched between a tunnel barrier and a Schottky-contact. The introduced model leads to very fast simulations by using usual circuit simulation tools while maintaining physically meaningful parameters. Kinetic Monte-Carlo simulations based on a distributed model and experimental data have been utilized as references to verify the concentrated model.Publicationtype: Journal ArticleScopus© Citations 17 277 364 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Changes in contact angle providing evidence for surface alteration in multi-component solid foods(2015-10-15); ; ; ; Chocolate blooming, one of the major problems in the confectionery industry, is the formation of visible white spots or a greyish haze on the surface of chocolate products due to large sugar or fat crystals on the surface. This leads to aesthetic changes and deterioration of taste and thus large sales losses for the confectionery industry due to consumer complaints. Chocolate blooming is often related to migration of lipids or sugar molecules to the chocolate surface, where they recrystallize with an associated polymorphic change of crystal structure on the surface. The wetting behaviour from contact angle measurements gives further insight into surface properties and is needed to determine surface energies and to evaluate possible migration mechanisms and preferred pathways. Therefore, an equilibrium contact angle is needed which is not directly accessible and is influenced by surface texture and interaction between solid and test liquid. In this study, the surface of cocoa butter and conventional chocolates was characterized by measuring the contact angle with the sessile drop protocol. The influence of roughness, test liquid and pre-crystallization of the samples as well as the storage temperature were investigated. In case of no pre-crystallization, a change in surface properties due to storage at 20 °C was detected, whereas samples stored at 30 °C showed the same wetting behaviour as fresh samples. This is associated with polymorphic transformation from thermodynamically less stable crystals to more stable configurations.Publicationtype: Journal Article64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Prediction of cavitation erosion for marine applicationsThe paper presents the development of a cavitation erosion prediction method. The approach is tailored to marine applications and embedded into a VoF-based procedure for the simulation of turbulent flows. Supplementary to the frequently employed Euler-Euler models, Euler-Lagrange approaches are employed to simulate cavitation. The study aims to convey the merits of an Euler-Lagrange approach for erosion simulations. Accordingly, the erosion model is able to separate different damage mechanisms, e.g. micro-jets, single and collective bubble collapse, and also quantifies their contribution to the total damage. Emphasis is devoted to the prediction of the cavitation extend, the influence of compressible effects and the performance of the material damage model in practical applications. Examples included refer to 2D validation test cases and reveal a fair predictive accuracy.Publicationtype: Journal ArticleScopus© Citations 1 278 310 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combined strengthening of multi-phase and graded interface in laser additive manufactured TiC/Inconel 718 compositesLaser metal deposition (LMD) additive manufacturing of TiC particle reinforced Inconel 718 composite parts was performed. The influence of laser energy density (LED) on densification, microstructures and wear behaviour of LMD-processed composites was studied. It showed that using a LED of 280 J mm-3 produced ∼5% porosity in LMD-processed composites, caused by the aggregation of reinforcing particles. A further increase in LED above 350 J mm-3 yielded near-full densification. Two categories of reinforcing phases, i.e. the substoichiometric TiCx particles and the in situ (Ti,M)C (M = Mo, Nb and Cr) carbide having 7-10 at% Nb and Mo contents, were formed in the matrix of LMD-processed composites. The TiCx reinforcing particles changed from an irregular poly-angular shape to a smoothened and refined structure as the LED increased. An increase in LED resulted in a larger amount of phase formation and an enhanced degree of crystal growth of the in situ (Ti,M)C reinforcement. The interfacial graded layer with thickness of 0.2-1.2 μm, which was identified as (Ti,M)C (M = Mo, Nb and Cr) carbide with 5-6 at% Mo and Nb contents, was tailored between the TiC x particles and the matrix. At an optimal LED of 420 J mm -3, a considerably low coefficient of friction of 0.38 and resultant low wear rate of 1.8 × 10-4 mm3 N-1 m-1 were obtained in sliding tests, due to the combined strengthening of the interfacial graded layer and the multiple reinforcing phases. The wear resistance decreased at an excessive LED because of the coarsening of reinforcement crystals and the decrease in microstructural uniformity of composites.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nucleation and growth of copper on mesoporous silicon by immersion platingCopper deposition was investigated on electrochemically etched mesoporous silicon epilayers of pore diameter 7 nm, porosity 45% and surface area 500 m2 cm-3 by immersion plating in an aqueous solution containing Cu2+ ions. When the layers were immersed in a 0.1 M CuSO4 5H2O aqueous solution for different time-periods ranging from 1 to 60 min, elemental copper was deposited on the surface. Fourier transform infrared (FTIR) spectroscopy in transmittance mode was carried out on copper deposited porous silicon (PS) samples to infer the changes in the surface bonding of the PS. It was clearly observed from x-ray diffraction patterns and FTIR spectra that the reduction of copper ion on PS was accompanied by gradual and finally complete oxidation of the PS epilayers surface. Scanning electron microscopy has been used to study the morphology of the copper aggregates at the PS epilayers surface.Publicationtype: Journal Article13