Fundamental investigations in the design of five-axis nanopositioning machines for measurement and fabrication purposes. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 4 (2021), 3, S. 156-164
The majority of nanopositioning and nanomeasuring machines (NPMMs) are based on three independent linear movements in a Cartesian coordinate system. This in combination with the specific nature of sensors and tools limits the addressable part geometries. An enhancement of an NPMM is introduced by the implementation of rotational movements while keeping the precision in the nanometer range. For this purpose, a parameter-based dynamic evaluation system with quantifiable technological parameters has been set up and employed to identify and assess general solution concepts and adequate substructures. Evaluations taken show high potential for three linear movements of the object in combination with two angular movements of the tool. The influence of the additional rotation systems on the existing structure of NPMMs has been investigated further on. Test series on the repeatability of an NPMM enhanced by a chosen combination of a rotary stage and a goniometer setup are realized. As a result of these test series, the necessity of in situ position determination of the tool became very clear. The tool position is measured in situ in relation to a hemispherical reference mirror by three Fabry-Pérot interferometers. FEA optimization has been used to enhance the overall system structure with regard to reproducibility and long-term stability. Results have been experimentally investigated by use of a retroreflector as a tool and the various laser interferometers of the NPMM. The knowledge gained has been formed into general rules for the verification and optimization of design solutions for multiaxial nanopositioning machines.
https://doi.org/10.1007/s41871-021-00102-w
Exploring nanowire regrowth for the integration of bottom-up grown silicon nanowires into AFM scanning probes. - In: Journal of micromechanics and microengineering, ISSN 1361-6439, Bd. 31 (2021), 5, 055010, S. 1-11
https://doi.org/10.1088/1361-6439/abf332
Long-time experimental investigation of turbulent superstructures in Rayleigh-Bénard convection by noninvasive simultaneous measurements of temperature and velocity fields. - In: Experiments in fluids, ISSN 1432-1114, Bd. 62 (2021), 4, 64, S. 1-18
Large-scale mean patterns in Rayleigh-Bénard convection, also referred to as turbulent superstructures, have mainly been studied by means of numerical simulations so far, but experimental investigations are still rare. However, the analysis of turbulent superstructures, which are of great importance due to their effect on the local transport of heat and momentum, require both numerical and experimental data. Therefore, within the scope of this study measurements were performed in the horizontal mid plane and in a horizontal plane closer to the top of a Rayleigh-Bénard cell with an aspect ratio of [Gamma]=l/h=25, thereby showing the initial formation of turbulent superstructures and their long-time rearrangement. The turbulent superstructures are investigated experimentally by noninvasive simultaneous measurements of temperature and velocity fields, using the color signal of thermochromic liquid crystals (TLCs) for the evaluation of the temperature and their temporal displacement for the determination of all three velocity components in the measurement planes via stereoscopic particle image velocimetry (stereo-PIV). Applying this measuring technique it is demonstrated that the time-averaging of instantaneous temperature and velocity fields uncovers the turbulent superstructures in both fields. Furthermore, the combination of the temperature and velocity data is used to characterize the local heat flux quantified by the local Nusselt number, which confirms that the turbulent superstructures strongly enhance the heat transfer in Rayleigh-Bénard convection.
https://doi.org/10.1007/s00348-020-03107-1
Incorporating ultra-small N-doped Mo2C nanoparticles onto 3D N-doped flower-like carbon nanospheres for robust electrocatalytic hydrogen evolution. - In: Nano energy, ISSN 2211-2855, Bd. 86 (2021), 106047
Im Titel ist "2" tiefgestellt
Developing highly-efficient and stable hydrogen evolution reaction (HER) electrocatalysts plays a crucial role in realizing the hydrogen production from electrocatalytic water splitting. Herein, ultra-small and nitrogen-doped molybdenum carbide (N-Mo2C) nanoparticles with oxidized surfaces are facilely synthesized with the assistance of cationic surfactants and simultaneously anchored onto three-dimensional nitrogen-doped flower-like carbon nanospheres (NFCNS), and the N-Mo2C/NFCNS composites are further investigated as HER electrocatalysts. Analysis results reveal that nitrogen atoms are doped into both the lattice and the carbon framework of Mo2C, resulting in low desorption energy of Mo-H bond for the easy evolution of hydrogen gas. Moreover, the high specific area of NFCNS enables enrichment of N-Mo2C nanoparticles, and its open framework facilitates fast ion diffusion. As a result, the N-Mo2C/NFCNS composites exhibit impressive HER activities with low overpotential, small Tafel slope, and excellent durability in both acidic and alkaline media, which outperform most of the reported Mo-based HER catalysts and are also highly comparable to the commercial Pt/C catalyst. Not limited to HER electrocatalysts, this work should open a new avenue for tailoring highly-efficient carbon/metal compounds-based electrocatalysts for oxygen reduction reaction, oxygen evolution reaction, nitrogen reduction reaction, etc.
https://doi.org/10.1016/j.nanoen.2021.106047
Morphological and compositional mapping of supersaturated AuNi alloy nanoparticles fabricated by solid state dewetting. - In: Applied surface science advances, ISSN 2666-5239, Bd. 4 (2021), 100082, insges. 6 S.
The solid state dewetting (SSD) of metallic bilayers is a straightforward method for the fabrication of alloy nanoparticles. In particular, alloys that present a gap of miscibility offer a rich phenomenology regarding not only the particle formation but also the composition of their phases. In the present work, AuNi precursor bilayers have been annealed at different temperatures and times to produce AuNi alloy nanoparticles. The evolution of the shape, size, and interparticle distance as well as the composition of the different phases formed in the nanoparticles, allow to unravel the role of the annealing temperatures and times for the fabrication of AuNi supersaturated alloys. Furthermore, the results offer a morphological and compositional map for the fabrication of AuNi alloys nanoparticles of different shapes, sizes, and compositions. Therefore, this map is a useful tool for the tailored design of supersaturated or decomposed nanoparticles by SSD.
https://doi.org/10.1016/j.apsadv.2021.100082
Nanostructured arrays for metal-ion battery and metal-air battery applications. - In: Journal of power sources, ISSN 1873-2755, Bd. 493 (2021), 229722
Rechargeable battery technology has been the research focus due to the largely increased global energy demand, while metal-ion batteries (MIBs) and metal-air batteries (MABs) are two major representatives. In addition to lithium-ion batteries, other MIBs such as sodium-ion batteries and aluminum-ion batteries have been drawn great attention. Regarding MABs, considerable research effort has been devoted to lithium-, zinc-, and sodium-air batteries. So far, significant progress in the performance improvement of both MIBs and MABs has been achieved through the material design and electrode design. Particularly, free-standing nanoarrays (NAs) directly grown on current collectors have been regarded as promising electrodes of both MIBs and MABs for improving the energy storage capability. In this review, recent advances in design, fabrication and application of NAs for MIBs and MABs have been summarized. Firstly, the motivation of employing NAs electrodes for MIBs and MABs is outlined. The principles and categories of MIBs and MABs, the construction, structural features, and resulting superiorities are also briefly reviewed. Secondly, the relationship of the conductive substrates, the structural features, and electrochemical performance of NAs electrodes is analyzed in depth. Finally, the future design focuses of NAs as advanced electrodes for MIBs and MABs are emphasized.
https://doi.org/10.1016/j.jpowsour.2021.229722
Achieving very high cycle fatigue performance of Au thin films for flexible electronic applications. - In: Journal of materials science & technology, ISSN 1941-1162, Bd. 89 (2021), S. 107-113
https://doi.org/10.1016/j.jmst.2021.02.025
Spinocerebellar ataxia type 14 : refining clinicogenetic diagnosis in a rare adult-onset disorder. - In: Annals of Clinical and Translational Neurology, ISSN 2328-9503, Bd. 8 (2021), 4, S. 774-789
Objectives Genetic variant classification is a challenge in rare adult-onset disorders as in SCA-PRKCG (prior spinocerebellar ataxia type 14) with mostly private conventional mutations and nonspecific phenotype. We here propose a refined approach for clinicogenetic diagnosis by including protein modeling and provide for confirmed SCA-PRKCG a comprehensive phenotype description from a German multi-center cohort, including standardized 3D MR imaging. Methods This cross-sectional study prospectively obtained neurological, neuropsychological, and brain imaging data in 33 PRKCG variant carriers. Protein modeling was added as a classification criterion in variants of uncertain significance (VUS). Results Our sample included 25 cases confirmed as SCA-PRKCG (14 variants, thereof seven novel variants) and eight carriers of variants assigned as VUS (four variants) or benign/likely benign (two variants). Phenotype in SCA-PRKCG included slowly progressive ataxia (onset at 4-50 years), preceded in some by early-onset nonprogressive symptoms. Ataxia was often combined with action myoclonus, dystonia, or mild cognitive-affective disturbance. Inspection of brain MRI revealed nonprogressive cerebellar atrophy. As a novel finding, a previously not described T2 hyperintense dentate nucleus was seen in all SCA-PRKCG cases but in none of the controls. Interpretation In this largest cohort to date, SCA-PRKCG was characterized as a slowly progressive cerebellar syndrome with some clinical and imaging features suggestive of a developmental disorder. The observed non-ataxia movement disorders and cognitive-affective disturbance may well be attributed to cerebellar pathology. Protein modeling emerged as a valuable diagnostic tool for variant classification and the newly described T2 hyperintense dentate sign could serve as a supportive diagnostic marker of SCA-PRKCG.
https://doi.org/10.1002/acn3.51315
In-depth microscopic characterisation of the weld faying interface revealing stress-induced metallurgical transformations during friction stir spot welding. - In: International journal of machine tools & manufacture, Bd. 164 (2021), 103716, insges. 14 S.
Friction stir spot welding (FSSW) is a solid-state welding process, wherein the properties of a weld joint are influenced by the state of friction and localised thermodynamic conditions at the tool-workpiece interface. An issue well-known about FSSW joints is their lack of reliability since they abruptly delaminate at the weld-faying interface (WFI). This study explores the origins of the delamination of multiple lap welded aluminium alloy (AA 5754-H111) sheets joined by FSSW at different rotational speeds typically used in industry. Experimental techniques such as the small punch test (SPT), Vickers hardness test, Scanning Electron Microscopy (SEM), Scanning Acoustic Microscope (SAM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and Frequency-Modulated Kelvin Probe Force Microscopy (FM-KPFM) were employed. The experimental results revealed that a complex interplay of stress-assisted metallurgical transformations at the intersection of WFI and the recrystallised stir zone (RSZ) can trigger dynamic precipitation leading to the formation of Al3Mg2 intermetallic phase, while metallic oxides and nanopits remain entrapped in the WFI. These metallurgical transformations surrounded by pits, precipitates and oxides induces process instability which in turn paves way for fast fracture to become responsible for delamination.
https://doi.org/10.1016/j.ijmachtools.2021.103716
Phase-modulated standing wave interferometer. - In: Micromachines, ISSN 2072-666X, Bd. 12 (2021), 4, 357, insges. 15 S.
The actual technical implementation of conventional interferometers is quite complex and requires manual manufacturing. In combination with the required construction space defined by the optical setup, their applications are limited to selected measuring tasks. In contrast, Standing Wave Interferometers (SWIs) offer an enormous potential for miniaturisation because of their simple linear optical setup, consisting only of a laser source, a measuring mirror and two transparent standing wave sensors for obtaining quadrature signals. The two sensors are located inside the measuring beam and therefore directly influence the length measurement. To reduce optical influences on the standing wave and avoid the need for an exact and long-term stable sensor-to-sensor-distance, a single sensor configuration was developed. There, a phase modulation is superimposed to the sensor signal by a forced oscillation of the measuring mirror. When the correct modulation stroke is applied, the resulting harmonics in the sensor signal are 90˚ phase-shifted to each other and can hence be used for obtaining quadrature signals for phase demodulation and direction discrimination by an arctan-algorithm.
https://doi.org/10.3390/mi12040357