Quantifying force and energy in single-molecule metalation. - In: Journal of the American Chemical Society, ISSN 1520-5126, Bd. 144 (2022), 16, S. 7054-7057
An atomic force microscope is used to determine the attractive interaction at the verge of adding a Ag atom from the probe to a single free-base phthalocyanine molecule adsorbed on Ag(111). The experimentally extracted energy for the spontaneous atom transfer can be compared to the energy profile determined by density functional theory using the nudged-elastic-band method at a defined probe-sample distance.
Lichtschichtfluoreszenzmikroskopische Untersuchung von Silikatmaterialien :
Light-sheet fluorescence microscopic probing of silicate materials. - In: Technisches Messen, ISSN 2196-7113, Bd. 0 (2022), 0, S. 1-8
Light-sheet fluorescence microscopy (LSFM) is a powerful method for 3D characterization of fluorescent samples. In this contribution we introduce the technique for the application in material analytics by demonstrating the 3D imaging of Ce 3+ -doped YAG (Y 3 Al 5 O 12 ) crystals isolated in a glass matrix. When excited with short wavelength laser radiation, the Ce 3+ doping enables fluorescence in the wavelength range between about 450 nm and 680 nm. Since the excitation wavelengths of Ce 3+ in the YAG and glass phases of the glass ceramic differ substantially, a suitable laser wavelength can be used to excite only the YAG phase. Thus, an imaging contrast to the surrounding glass matrix is generated. We exploit the crystal dendrites for monitoring the image contrast and improve it by a deconvolution operation of the images. This field of application of LSFM offers great potential, e. g. for fundamental understanding of the microstructuring processes in silicate glasses.
Aerostatically sealed chamber as a robust aerostatic bearing. - In: Tribology international, ISSN 0301-679X, Bd. 173 (2022), 107614, S. 1-10
Aerostatic bearings are typically used in ultra precision and high speed applications in controlled environments. The present study expands this operating domain. The present study experimentally investigates the performance and feasibility of a novel design for a robust air bearing consisting of an aerostatically sealed pressurized volume. A suitable operating domain for the bearing system was characterized based on measurements of the load capacity, friction moment, chamber flow, and seal flow rate at various opposing surface run-outs and supply pressures. The highest measured load capacity was 18.86 kN at 0.330 mm run-out, and decreased to 12.22 kN load at 3.804 mm run-out. The study provided corroborative evidence on the feasibility of the proposed chamber based bearing design.
Einfluss von Formabweichungen auf die Radius und Rundheitsmessung von Mikrokugeln :
Influence of form deviations on the radius and roundness measurement of micro spheres. - In: Technisches Messen, ISSN 2196-7113, Bd. 0 (2022), 0, S. 1-10
Micro and nano coordinate measuring machines (CMMs) require small and well characterized micro spheres as probing elements. However, established strategies and instruments have mostly been designed for and applied to the characterization of larger spheres in the range of millimetres or above. That is why we have recently focused our attention towards a novel strategy which is based on a set of atomic force microscope (AFM) surface scans in conjunction with a stitching algorithm. Initial experimental results are promising, but point to several influences which require further attention. We have, therefore, begun to model the measurement strategy and applied it on simulated spheres, in order to investigate and reduce some of these influences. The model is currently limited to effects which are related to the radius and form of the sphere. Other influences, like the AFM tip, are being ignored. In this paper, we introduce the essential parts of this model and apply it on spheres of different mean radii (60 [my]m, 100 [my]m and 150 [my]m) and of different qualities (Grade 3 and Grade 5). The investigations illustrate that the measurement object can have a significant influence on the measurement result and needs to be considered.
Perception thresholds and qualitative perceptions for electrocutaneous stimulation. - In: Scientific reports, ISSN 2045-2322, Bd. 12 (2022), 7335, S. 1-12
Our long-term goal is the development of a wearable warning system that uses electrocutaneous stimulation. To find appropriate stimulation parameters and electrode configurations, we investigate perception amplitude thresholds and qualitative perceptions of electrocutaneous stimulation for varying pulse widths, electrode sizes, and electrode positions. The upper right arm was stimulated in 81 healthy volunteers with biphasic rectangular current pulses varying between 20 and 2000 [my]s. We determined perception, attention, and intolerance thresholds and the corresponding qualitative perceptions for 8 electrode pairs distributed around the upper arm. For a pulse width of 150 [my]s, we find median values of 3.5, 6.9, and 13.8 mA for perception, attention, and intolerance thresholds, respectively. All thresholds decrease with increasing pulse width. Lateral electrode positions have higher intolerance thresholds than medial electrode positions, but perception and attention threshold are not significantly different across electrode positions. Electrode size between 15 × 15 mm^2 and 40 × 40 mm^2 has no significant influence on the thresholds. Knocking is the prevailing perception for perception and attention thresholds while mostly muscle twitching, pinching, and stinging are reported at the intolerance threshold. Biphasic stimulation pulse widths between 150 [my]s and 250 [my]s are suitable for electric warning wearables. Within the given practical limits at the upper arm, electrode size, inter-electrode distance, and electrode position are flexible parameters of electric warning wearables. Our investigations provide the basis for electric warning wearables.
Influence of rotational speed on the electrical and mechanical properties of the friction stir spot welded aluminium alloy sheets. - In: Welding in the world, ISSN 1878-6669, Bd. 66 (2022), 6, S. 1179-1190
An efficient and productive joining technique to weld aluminium has become a priority challenge for promoting the use of aluminium in the electrical industry. One of the challenges is to obtain welds with superior mechanical properties with the consistent quality of weld surface as well as low electrical resistance. In this paper, the influence of rotational speed during the friction stir spot welding of AA 5754-H111 was studied to analyse the mechanical and electrical properties of the welds. The results from two rotational speeds (1000 rpm and 4500 rpm) are presented and compared to the base material. It was observed that the samples welded at 1000 rpm showed a higher average shear failure load (˜ 1.1 kN) compared to the samples welded at 4500 rpm (˜ 0.94 kN). The microhardness of the samples welded at 1000 rpm was higher than that of the base material, while the microhardness of samples welded at 4500 rpm was lower. It was also found that the friction welded sheets, regardless of the rotational speed used, showed increased electrical resistance compared to the base material, albeit this increase for the samples welded at 1000 rpm was about 42%, compared to samples welded at 4500 rpm where this increase was just 14%.
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.
Nanostructured metal selenides as anodes for potassium-ion batteries. - In: Sustainable energy & fuels, ISSN 2398-4902, Bd. 6 (2022), 9, S. 2087-2112
In next-generation rechargeable batteries, potassium-ion batteries (KIBs) have been deemed to be one of the most promising candidates as a complement for lithium-ion batteries. Anodes as a component of ion batteries have a great effect on the safety and electrochemical performance. Among various developed anode materials, metal selenides (MSs) have been a popular option by merits of their superior material properties and high specific capacities. However, they are restricted by some intrinsic problems, such as large volume expansion and severe side reactions during electrochemical reactions, which limit their application to a certain degree. The strategy of structural design can endow MSs with superior material and electrochemical properties, making MSs exhibit better electrochemical performance. In this review, we summarize the recent advances in nanostructured MCs as KIB anodes. Meanwhile, their electrochemical reaction mechanisms and material synthesis methods are introduced briefly. Finally, the present challenges and future research directions are discussed.
KOH activated nitrogen and oxygen co-doped tubular carbon clusters as anode material for boosted potassium-ion storage capability. - In: Nanotechnology, ISSN 1361-6528, Bd. 33 (2022), 29, 295403, S. 1-9
Carbon nanomaterials have become a promising anode material for potassium-ion batteries (KIBs) due to their abundant resources, low cost, and excellent conductivity. However, among carbon materials, the sluggish reaction kinetics and inferior cycle life severely restrict their commercial development as KIBs anodes. It is still a huge challenge to develop carbon materials with various structural advantages and ideal electrochemical properties. Therefore, it is imperative to find a carbon material with heteroatom doping and suitable nanostructure to achieve excellent electrochemical performance. Benefiting from a Na2SO4 template-assisted method and KOH activation process, the KOH activated nitrogen and oxygen co-doped tubular carbon (KNOCTC) material with a porous structure exhibits an impressive reversible capacity of 343 mAh g^-1 at 50 mA g^-1 and an improved cyclability of 137 mAh g^-1 at 2 A g^-1 after 3000 cycles with almost no capacity decay. The kinetic analysis indicates that the storage mechanism in KNOCTC is attributed to the pseudocapacitive process during cycling. Furthermore, the new synthesis route of KNOCTC provides a new opportunity to explore carbon-based potassium storage anode materials with high capacity and cycling performance.
Metrologische Nanopositionierung kombiniert mit Zwei-Photonen-Laserdirektschreiben :
Metrological nanopositioning combined with two-photon direct laser writing. - In: Technisches Messen, ISSN 2196-7113, (2022), S. 1-8
The extension of nanopositioning and nanomeasuring machines (NPM-machines) to fabrication machines by using a femtosecond laser for the implementation of direct laser writing by means of two-photon absorption (2PA) is a promising approach for cross-scale metrological fabrication in the field of lithographic techniques . To this end, a concept for integrating two-photon technology into an NPM machine was developed and implemented, followed by a characterization of the system and targeted investigations to provide evidence for the synergy of the two techniques. On this basis, a new approach to high-throughput micro- and nano-fabrication was developed and investigated, demonstrating new possibilities in cross-scale, high-precision manufacturing . This mix-and-match approach is based on a combination of 2PA laser writing with field emission lithography to fabricate masters for subsequent nanoimprint lithography. Not only the advantages of the large positioning range of the NMM-1 could be highlighted, but also the advantages resulting from the highly accurate positioning. A systematic reduction of the distance between two adjacent lines resulted in a minimum photoresist width of less than 30 nm , which can be classified among the smallest distances between two laser-written lines described in the literature , , . The center-to-center distance of the lines of about 1.695 [my]m at a numerical aperture of 0.16 and a wavelength of 801 nm is only about 56% of the Rayleigh diffraction limit extended for the two-photon process. Thus, for the first time, a resist width far below the diffraction limit could be realized with conventional two-photon laser writing in positive photoresist.