Tip- and laser-based 3D nanofabrication in extended macroscopic working areas. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 4 (2021), 3, S. 132-148
The field of optical lithography is subject to intense research and has gained enormous improvement. However, the effort necessary for creating structures at the size of 20 nm and below is considerable using conventional technologies. This effort and the resulting financial requirements can only be tackled by few global companies and thus a paradigm change for the semiconductor industry is conceivable: custom design and solutions for specific applications will dominate future development (Fritze in: Panning EM, Liddle JA (eds) Novel patterning technologies. International society for optics and photonics. SPIE, Bellingham, 2021. https://doi.org/10.1117/12.2593229). For this reason, new aspects arise for future lithography, which is why enormous effort has been directed to the development of alternative fabrication technologies. Yet, the technologies emerging from this process, which are promising for coping with the current resolution and accuracy challenges, are only demonstrated as a proof-of-concept on a lab scale of several square micrometers. Such scale is not adequate for the requirements of modern lithography; therefore, there is the need for new and alternative cross-scale solutions to further advance the possibilities of unconventional nanotechnologies. Similar challenges arise because of the technical progress in various other fields, realizing new and unique functionalities based on nanoscale effects, e.g., in nanophotonics, quantum computing, energy harvesting, and life sciences. Experimental platforms for basic research in the field of scale-spanning nanomeasuring and nanofabrication are necessary for these tasks, which are available at the Technische Universität Ilmenau in the form of nanopositioning and nanomeasuring (NPM) machines. With this equipment, the limits of technical structurability are explored for high-performance tip-based and laser-based processes for enabling real 3D nanofabrication with the highest precision in an adequate working range of several thousand cubic millimeters.
https://doi.org/10.1007/s41871-021-00110-w
AES and EDX surface analysis of weathered float glass exposed in different environmental conditions. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 572 (2021), 121083
To characterize the influence of environmental conditions on glass weathering, two different float glasses were subjected to a six-month outdoor experiment that took place in Durres (seacoast, Albania), Ilmenau (rural, Germany) and Pristina (urban, Kosovo), three sites with largely different environmental conditions. Atmospheric deposits and meteorological conditions led this study to receive information about different weathering behaviour of two types of float glasses. Typical glass degradation effects and reaction products at the glass surface are shown and the impact of weathering and air quality parameters on the formation of reaction products and degradation is discussed. Surface changes have been localized using optical microscopy. Further investigations for receiving chemical information on the contaminations include Auger electron spectroscopy (AES) and scanning electron microscopy (SEM/EDX). Surface analyses indicate a high amount of weathering products such as chlorides, sulphates and carbonates followed by severe delamination effects for both types of glass exposed in Durres and Pristina. In contrast to this, low levels of soiling and degradation for the samples exposed in Ilmenau were detected.
https://doi.org/10.1016/j.jnoncrysol.2021.121083
Band bending at heterovalent interfaces: hard X-ray photoelectron spectroscopy of GaP/Si(0 0 1) heterostructures. - In: Applied surface science, Bd. 565 (2021), 150514
https://doi.org/10.1016/j.apsusc.2021.150514
Atomic surface control of Ge(100) in MOCVD reactors coated with (Ga)As residuals. - In: Applied surface science, Bd. 565 (2021), 150513
Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge(100) surfaces. Ga and As are commonly omnipresent, when applying metalorganic chemical vapor deposition (MOCVD), either directly supplied by precursors, in the form of MOCVD reactor residuals, or both. We study the impact of the growth conditions on the Ge(100) surface formation in situ, in dependence on the reactor pre-conditioning, the type of As supply, and/or temperature, utilizing surface-sensitive reflection anisotropy spectroscopy. We benchmark the in situ spectra to in system X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We find that interaction of tertiarybutylarsine (TBAs) with a coating of the inner MOCVD reactor walls by GaAs residuals favors desorption of As from reactor parts resulting in As-dimers on the Ge(100) surface, which are rotated by 90˚ compared to preparation routes employing TBAs in Ga-free ambience. The optical in situ control enables precise adjustment and switching between distinct Ge(100) surface reconstructions for subsequent III-V heteroepitaxy.
https://doi.org/10.1016/j.apsusc.2021.150513
The structure of Gd3+-doped Li2O and K2O containing aluminosilicate glasses from molecular dynamics simulations. - In: Materials, ISSN 1996-1944, Bd. 14 (2021), 12, 3265, insges. 18 S.
Im Titel sind "3+" hochgestellt und "2" tiefgestellt
Understanding the atomic structure of glasses is critical for developing new generations of materials with important technical applications. In particular, the local environment of rare-earth ions and their distribution and clustering is of great relevance for applications of rare earth-containing glasses in photonic devices. In this work, the structure of Gd2O3 doped lithium and potassium aluminosilicate glasses is investigated as a function of their network modifier oxide (NMO-Li2O, K2O) to aluminum oxide ratio using molecular dynamics simulations. The applied simulation procedure yields a set of configurations, the so-called inherent structures, of the liquid state slightly above the glass transition temperature. The generation of a large set of inherent structures allows a statistical sampling of the medium-range order of the Gd3+ ions with less computational effort compared to other simulation methods. The resulting medium-range atomic structures of network former and modifier ions are in good agreement with experimental results and simulations of similar glasses. It was found that increasing NMO/Al ratio increases the network modifier coordination number with non-bridging oxygen sites and reduces the overall stability of the network structure. The fraction of non-bridging oxygen sites in the vicinity of Gd3+ ions increases considerably with decreasing field strength and increasing concentration of the network modifier ions. These correlations could be confirmed even if the simulation results of alkaline earth aluminosilicate glasses are added to the analysis. In addition, the structure predictions generally indicate a low driving force for the clustering of Gd3+. Here, network modifier ions of large ionic radii reduce the probability of Gd-O-Gd contacts.
https://doi.org/10.3390/ma14123265
Formation and evolution of Au-SiOx heterostructures: from nanoflowers to nanosprouts. - In: Materials and design, ISSN 1873-4197, Bd. 209 (2021), 109956, insges. 11 S.
This work reports the formation of circular cavities and Au-SiOx nanoflowers after annealing of thin Au film deposited on SiO2/Si substrates, and the transformation of nanoflowers to nanosprouts with increasing the annealing time. Two reference experiments indicate that both H2 and Si are indispensable for the above structures. The formation of cavities can be attributed to the SiO2 layer decomposition and the product, volatile SiO, provides a Si source for the formation of nanoflowers at the early stage. A model is proposed to indicate that SiO gas produced at the Si/SiO2 interface can diffuse to the surface assisted by the defects in the SiO2 layer before the decomposed cavities are exposed. Then the exposing of those cavities introduces another volatile SiO from the active oxidation of Si substrate, provoking a change in the direction of the main Si source, which in turn makes the one nanoparticle of the nanoflower split in two and finally form the nanosprout. The model about the escape of SiO further details SiO2 decomposition process, and the transformation mechanism from nanoflowers to nanosprout sheds light on a feasible nanofabrication method to design tunable size and shape of nanoparticles.
https://doi.org/10.1016/j.matdes.2021.109956
Preface on laser material interactions: from basic science to industrial applications (LaserMaterInter2020). - In: Applied surface science advances, ISSN 2666-5239, Bd. 6 (2021), 100133, insges. 1 S.
https://doi.org/10.1016/j.apsadv.2021.100133
Highly anisotropic fluorine-based plasma etching of ultralow expansion glass. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 23 (2021), 6, 2001336, insges. 10 S.
Deep etching of glass and glass ceramics is far more challenging than silicon etching. For thermally insensitive microelectromechanical and microoptical systems, zero-expansion materials such as Zerodur or ultralow expansion (ULE) glass are intriguing. In contrast to Zerodur that exhibits a complex glass network composition, ULE glass consists of only two components, namely, TiO2 and SiO2. This fact is highly beneficial for plasma etching. Herein, a deep fluorine-based etching process for ULE 7972 glass is shown for the first time that yields an etch rate of up to 425 nm min^-1 while still achieving vertical sidewall angles of 87˚. The process offers a selectivity of almost 20 with respect to a nickel hard mask and is overall comparable with fused silica. The chemical surface composition is additionally investigated to elucidate the etching process and the impact of the tool configuration in comparison with previously published etching results achieved in Zerodur. Therefore, deep and narrow trenches can be etched in ULE glass with high anisotropy, which supports a prospective implementation of ULE glass microstructures, for instance, in metrology and miniaturized precision applications.
https://doi.org/10.1002/adem.202001336
Effects of module stiffness and initial compression on lithium-ion cell aging. - In: Journal of power sources, ISSN 1873-2755, Bd. 506 (2021), 230163
The effects of automotive-related lithium-ion module design, i.e. module stiffness and initial compression during module assembly on cell aging, swelling and pressure evolution are still largely unknown. This paper presents the results of a long-term aging study of 12 large-format automotive graphite/NMC 622 pouch cells, cycled for different module stiffnesses and initial compressions using design of experiments. Statistical analysis of mechanical and aging data revealed significant nonlinear (interaction) effects of both factors on pressure evolution, capacity loss and increase in internal resistance of the cells. Pressure dependent cell aging is observed over 1000 cycles, which was related to loss of active material at the cathode from differential voltage analysis. Post-mortem analysis confirmed a cathode active material loss via half- and full-cell measurements of harvested electrodes. Cross-section SEM micrographs revealed increasing NMC-particle cracking with higher pressure. Based on this, a fatigue-based aging model was developed to describe the capacity loss due to pressure dependent particle cracking. The presented approach enables both improved modeling of pressure dependent aging and lifetime optimized module design
https://doi.org/10.1016/j.jpowsour.2021.230163
Microstructure investigation and fluorescence properties of europium-doped scheelite crystals in glass-ceramics made under different synthesis conditions. - In: Journal of luminescence, ISSN 0022-2313, Bd. 238 (2021), 118244, S. 1-8
https://doi.org/10.1016/j.jlumin.2021.118244