Silicon carbide - graphene nano-gratings on 4H and 6H semi-insulating SiC. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 170-174
A technical methodology of fabrication of hierarchically scaled multitude graphene nanogratings with varying pitches ranging from the micrometer down to sub 40 nm scale combined with sub 10 nm step heights on 4H and 6H semi-insulating SiC for length scale measurements is proposed. The nanogratings were fabricated using electron-beam lithography combined with dry etching of graphene, incorporating a standard semiconductor processing technology. A scientific evaluation of critical dimension, etching step heights, and surface characterization of graphene nanograting on both polytypes were compared and evaluated.
https://doi.org/10.4028/p-wn4zya
Reversible sodiation of electrochemically deposited binder- and conducting additive-free Si-O-C composite layers. - In: Energy technology, ISSN 2194-4296, Bd. 10 (2022), 5, 2101164, S. 1-9
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.
https://doi.org/10.1002/ente.202101164
Nanoscale surface morphology modulation of graphene - i-SiC heterostructures. - In: Materials today, ISSN 2214-7853, Bd. 53 (2022), 2, S. 289-292
A multitude gratings design consists of gratings with different pitches ranging from the micrometre down to sub 40 nm scale combined with sub 10 nm step heights modulating the surface morphology for length scale measurements is proposed. The surface morphology modulation was performed using electron beam lithography incorporating a standard semiconductor processing technology. The critical dimension, edge roughness, step heights and line morphology in dependence on the grating pitch is studied.
https://doi.org/10.1016/j.matpr.2021.06.427
Analysis of temperature-dependent and time-resolved ellipsometry spectra of Ge. - In: 2021 IEEE Photonics Society Summer Topicals Meeting Series (SUM), (2021), insges. 2 S.
https://doi.org/10.1109/SUM48717.2021.9505707
Determination of piezo-resistive coefficient π44 in p-type silicon by comparing simulation and measurement of pressure sensors. - In: AIP Advances, ISSN 2158-3226, Bd. 11 (2021), 8, 085005, insges. 6 S.
https://doi.org/10.1063/5.0060034
Chemical changes of float glass surfaces induced by different sand particles and mineralogical phases. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 566 (2021), 120868
Particles play an important role in the storage, transportation and natural weathering of glasses, but their influence on glass degradation is little studied. In this work, the influence of main sand components is investigated. Feldspar exhibits the strongest leaching rate for the network former Na, while quartz has the lowest. The leaching rate of natural sands is in between. Based on these findings, a model describing the leaching mechanism was developed: Hereby, hydroxyl groups adhering on sand grains adsorb network modifiers by substituting their hydrogen by network formers from the glass surface. The amount of available hydroxyl groups determines the leaching rate. This model is supported by loss on ignition performed for the sands, which might be a suitable method to roughly estimate their leaching rates. The adsorption of network modifiers suppresses carbonate formation, dendritic growth and Mg diffusion in the glass surface region. Pimple-like crystal growth is observed.
https://doi.org/10.1016/j.jnoncrysol.2021.120868
Broadband femtosecond spectroscopic ellipsometry. - In: Review of scientific instruments, ISSN 1089-7623, Bd. 92 (2021), 3, S. 033104-1-033104-14
We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.
https://doi.org/10.1063/5.0027219
Enhanced cycling performance of binder free silicon-based anode by application of electrochemically formed microporous substrate. - In: Electrochimica acta, ISSN 1873-3859, Bd. 380 (2021), 138216, S. 1-9
In this work, an electrochemically formed porous Cu current collector (p-Cu) is utilized for the development of a high-performance binder-free silicon anode. Two electrolyte compositions based on sulfolane (SL) and [BMP][TFSI] ionic liquid (IL) are implemented for silicon deposition. The electrochemical experiments confirm the advantages of applying the p-Cu structure in terms of specific capacity, rate capability, and long-term cycling, where the best electrochemical properties have been observed for the Si deposited from SL electrolyte. The Si-based p-Cu anodes formed in SL display stable 2500 mAh g^-1 reversible capacity during the first 250 cycles and promising capacity retention. Compared to this result, the cycling performance of the same type of material deposited on flat Cu foil (f-Cu) showed significantly reduced capacity (1400 mAh g^-1) and inferior cycling performance. The positive effect can be attributed to the improved mechanical stability of the active material and accelerated ionic transport in the porous structure of the anode. The improved functional properties of the electrochemically deposited Si from SL electrolyte in p-Cu samples compared to those obtained in IL can be ascribed to differences in the chemical composition. While the layers deposited in SL electrolyte involve Si domains incorporated in a matrix containing C and O that offer high mechanical stability, the Si material obtained in IL is additionally influenced by N and F chemical species, resulting from active IL decomposition. These differences in the chemical surrounding of the Si domains are the primary reason for the inferior electrochemical performance of the material deposited from [BMP][TFSI] electrolyte. XPS analysis shows that the initial composition of the as deposited layers, containing a considerable amount of elemental Si, is changed after lithiation and that the electrochemical activity of the anode is governed by switching between the intermediate redox states of Si, where the carbon-oxygen matrix is also involved.
https://doi.org/10.1016/j.electacta.2021.138216
Transient birefringence and dichroism in ZnO studied with fs-time-resolved spectroscopic ellipsometry. - In: Physical review research, ISSN 2643-1564, Bd. 3 (2021), 1, S. 013246-1-013246-12
The full transient dielectric-function (DF) tensor of ZnO after UV-laser excitation in the spectral range 1.4-3.6 eV is obtained by measuring an m-plane-oriented ZnO thin film with femtosecond (fs)-time-resolved spectroscopic ellipsometry. From the merits of the method, we can distinguish between changes in the real and the imaginary part of the DF as well as changes in birefringence and dichroism, respectively. We find pump-induced switching from positive to negative birefringence in almost the entire measured spectral range for about 1 ps. Simultaneously, weak dichroism in the spectral range below 3.0 eV hints at contributions of inter-valence-band transitions. Line-shape analysis of the DF above the band gap based on discrete exciton, exciton-continuum, and exciton-phonon-complex contributions shows a maximal dynamic increase in the transient exciton energy by 80 meV. The absorption coefficient below the band gap reveals an exponential line shape attributed to Urbach-rule absorption mediated by exciton-longitudinal-optic-phonon interaction. The transient DF is supported by first-principles calculations for 1020cm^-3 excited electron-hole pairs in ideal bulk ZnO.
https://doi.org/10.1103/PhysRevResearch.3.013246
Electrochemical nucleation of silicon in ionic liquid-based electrolytes. - In: Meeting abstracts, ISSN 2151-2043, Bd. MA2020-01 (2020), 19, 1181
https://doi.org/10.1149/MA2020-01191181mtgabs