Impact of sample preparation approach on transmission electron microscopy investigation of sputtered AlNi multilayers used for reactive soldering. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302215, S. 1-12
This work presents studies of sputtered Al/Ni reactive multilayers by transmission electron microscopy. They are prepared for these analyses by three methods (both Ga- and Xe-based focused ion beam, FIB, and tripod polishing plus Ar+ ion milling in precision ion polishing system, PIPS) to check their impact on these materials. Every sample shows polycrystalline and mostly chemically pure Al/Ni layers. They also hint existence of intermetallic compounds, especially the tripod-prepared sample. These intermetallics first originate from the sputtering process. The layers are increasingly rough along the growth direction. Other remarkable findings can be highlighted. First, the heating operations applied during the tripod polishing preparation lead to recrystallization and blurred Al/Ni interfaces due to increased metals reactions, although additional contributions by roughness and preparation thickness to the current compositional uncertainties must be distinguished by optimizing future sample fabrications and preparations. Second, Xe-based FIB leads to lamellae with seemingly low contamination, although Ga-FIB is a potentially good alternative. Finally, FIB is better to study cross-section preparations of pristine Al/Ni multilayers, whereas the present tripod polishing procedures are unsuitable for this purpose but allow to observe the beginning of Al/Ni transformations upon heating, which is interesting for the technological optimization of these materials.
https://doi.org/10.1002/adem.202302215
Exploring crystal-phase molecular dynamics of the low-viscous mesogen 6CHBT: a combined FFC and high-field NMR relaxometry investigation. - In: The journal of physical chemistry, ISSN 1520-5207, Bd. 128 (2024), 16, S. 3997-4007
The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.
https://doi.org/10.1021/acs.jpcb.3c08259
Broadband DRA with uniform angular dependent delay for indoor localization. - In: IEEE access, ISSN 2169-3536, Bd. 12 (2024), S. 63644-63654
Estimating the Time Difference of Arrival (TDoA), is a simple yet reliable technique to accurately perform an indoor monostatic localization. To implement TDoA estimation, one approach is to utilize a broadband radar system equipped with multiple receiving antenna elements. To obtain the Time of Arrival (ToA) at each antenna element, the round-trip time is required. However, the round-trip time does not only consist of the propagation delay in free space but the propagation delay within the antenna as well. To perform the localization precisely, it is desired that an antenna element introduces a uniform delay in all directions. To this end, a compact rectangular dielectric resonator antenna is designed for the operating frequency of 6.5 GHz with a fractional bandwidth of 20%. Al2O3 with a dielectric constant of 9.8 is used for the substrate as well as the dielectric resonator. The antenna is designed to provide a high correlation between the input and the output pulses. To investigate the correlation, the antenna is excited with a modulated Gaussian pulse and the radiated pulses are studied. The antenna possesses an excellent behavior in terms of pulse preservation for the upper hemisphere. Therefore, when incoming pulses from the same distance but different directions impinge on the antenna, they reach the port of the antenna at a similar time. It is shown that this feature of the proposed antenna allows the utilization of TDoA estimation without the need for a calibration step. The characteristics of the antenna are verified by simulation and measurement.
https://doi.org/10.1109/ACCESS.2024.3395124
Vergleich von vollständig fasergekoppelten Interferometersystemen unter Vakuumbedingungen :
Comparison of full fiber coupled interferometer systems under vacuum conditions. - In: Technisches Messen, ISSN 2196-7113, Bd. 91 (2024), 5, S. 281-289
The PTB built a comparator setup for testing length measuring systems under vacuum conditions. The setup is equipped with a linear stage which is operated in a closed loop using the feedback of a 1.5D encoder system with three encoder heads for length and vertical rotation angle and exhibits a movement range of 150 mm. The main measurement system is a heterodyne interferometer with periodic nonlinearities with amplitudes below 10 pm. The comparator setup was characterized using a mirror mounted on the stage reflecting the measurement as well as the reference beams. By these means, the resolution, the stability of the setup as well as the influence of guiding errors on position-dependent measurement deviations of the fully fiber coupled interferometer were investigated. A position-depending error was observed which was resulting from the variation of the performance of the coupling into the multi-mode fibers used to transfer the superposed beams to the photoreceivers. The measured deviations were 1.5 nm or 0.2 nm over 70 mm travel range depending on the core diameter of the multi-mode fibers of 50 µm and 200 µm, respectively. Three different commercial fiber interferometer systems were analysed under vacuum conditions with the comparator setup. All tested systems are working with light sources with a wavelength of approximately 1535 nm but differ in the amplitude of their periodic nonlinearities in the range between 10 pm and 29 nm. The tests of their resolution and stability were limited by vibrations in the comparator setup and the lack of adequate synchronization capabilities of the data acquisition of these systems.
https://doi.org/10.1515/teme-2024-0011
Experimental investigation and numerical analysis of convective heat and mass transport processes in salt melts affected by magnetic fields and thermal radiation :
Experimentelle Untersuchung und numerische Analyse konvektiver Wärme- und Stofftransportprozesse in Salzschmelzen unter Wirkung von Magnetfeldern und Wärmestrahlung. - In: Technisches Messen, ISSN 2196-7113, Bd. 0 (2024), 0, insges. 20 S.
In dieser Arbeit werden mit numerischen und experimentellen Methoden thermisch getriebene Konvektionsprozesse in Flüssigsalzen analysiert. Die Besonderheiten der Untersuchungen liegen darin, dass die in der Salzschmelze auftretenden Wärme- und Stofftransportprozesse zum einen aufgrund der elektrischen Leitfähigkeit des Arbeitsmediums von den Wechselwirkungen mit Magnetfeldern sowie zum anderen aufgrund der Semi-Transparenz des Mediums und der vorliegenden hohen Arbeitstemperaturen von thermischen Strahlungsvorgängen beeinflusst werden. Die genaue Kenntnis der Geschwindigkeits- und Temperaturfelder bei Vorliegen dieser zusätzlichen Effekte ist beispielweise von Wichtigkeit für den sicheren und effizienten Betrieb von thermischen Energiespeichern und Flüssigmetall-Batterien, in denen Salzschmelzen als gängige Arbeitsstoffe eingesetzt werden. Bei der numerischen Analyse wird eine zweidimensionale Rayleigh-Bénard-Anordnung betrachtet, bei welcher der thermische Antrieb der Konvektion in der Salzschmelze durch Heizung von unten und Kühlung von oben erfolgt. Der Magnetfeldeinfluss wird in der quasi-statischen Näherung und der Strahlungseinfluss mittels der Rosseland-Approximation für optisch dicke Medien in Grenzschicht-Näherung modelliert. Die mittels eines Spektrale-Elemente-Verfahrens erzielten Simulationsergebnisse zeigen, dass es unter der Wirkung der zusätzlichen Effekte tendenziell zu einer deutlichen Verringerung des konvektiven Wärmetransport kommt. Dies ist die Folge der strömungsdämpfenden Wirkung der unter Magnetfeldeinfluss induzierten Lorentz-Kräfte und der zusätzlichen thermischen Diffusion durch den Strahlungseinfluss. Im experimentellen Teil der Arbeit wird berichtet, wie ein entsprechender Versuchsstand aufgebaut und instrumentiert wird, um die von der numerischen Analyse vorhergesagten Wirkungen in Modellexperimenten zu verifizieren. Des Weiteren werden Ergebnisse von ersten Testmessungen in Salzschmelzen vorgestellt, durch die erstmalig der Nachweis geführt wird, dass die optischen Verfahren der Particle-Image-Velocimetry und der Laser-Doppler-Anemometrie auch zur räumlich und zeitlich hochaufgelösten Geschwindigkeitsmessung in Salzschmelzen angewandt werden können.
https://doi.org/10.1515/teme-2024-0018
Composite materials with nanoscale multilayer architecture based on cathodic-arc evaporated WN/NbN coatings. - In: ACS omega, ISSN 2470-1343, Bd. 9 (2024), 15, S. 17247-17265
Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: β-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from −50 to −200 V, the wear mechanisms change as follows: oxidative &flech; fatigue and oxidative &flech; adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.
https://doi.org/10.1021/acsomega.3c10242
Association of genetic risk for age-related macular degeneration with morphological features of the retinal microvascular network. - In: Diagnostics, ISSN 2075-4418, Bd. 14 (2024), 7, 770, S. 1-13
Background: Age-related macular degeneration (AMD) is a multifactorial disease encompassing a complex interaction between aging, environmental risk factors, and genetic susceptibility. The study aimed to determine whether there is a relationship between the polygenic risk score (PRS) in patients with AMD and the characteristics of the retinal vascular network visualized by optical coherence tomography angiography (OCTA). Methods: 235 patients with AMD and 97 healthy controls were included. We used data from a previous AMD PRS study with the same group. The vascular features from different retina layers were compared between the control group and the patients with AMD. The association between features and PRS was then analyzed using univariate and multivariate approaches. Results: Significant differences between the control group and AMD patients were found in the vessel diameter distribution (variance: p = 0.0193, skewness: p = 0.0457) and fractal dimension distribution (mean: p = 0.0024, variance: p = 0.0123). Both univariate and multivariate analyses showed no direct and significant association between the characteristics of the vascular network and AMD PRS. Conclusions: The vascular features of the retina do not constitute a biomarker of the risk of AMD. We have not identified a genotype-phenotype relationship, and the expression of AMD-related genes is perhaps not associated with the characteristics of the retinal vascular network.
https://doi.org/10.3390/diagnostics14070770
A new kind of atomic force microscopy scan control enabled by artificial intelligence: concept for achieving tip and sample safety through asymmetric control. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 7 (2024), 1, 11, S. 1-10
This paper introduces a paradigm shift in atomic force microscope (AFM) scan control, leveraging an artificial intelligence (AI)-based controller. In contrast to conventional control methods, which either show a limited performance, such as proportional integral differential (PID) control, or which purely focus on mathematical optimality as classical optimal control approaches, our proposed AI approach redefines the objective of control for achieving practical optimality. This presented AI controller minimizes the root-mean-square control deviations in routine scans by a factor of about 4 compared to PID control in the presented setup and also showcases a distinctive asymmetric response in complex situations, prioritizing the safety of the AFM tip and sample instead of the lowest possible control deviations. The development and testing of the AI control concept are performed on simulated AFM scans, demonstrating its huge potential.
https://doi.org/10.1007/s41871-024-00229-6
Dynamic characterization of Fiber Bragg Grating temperature sensors. - In: Experimental thermal and fluid science, Bd. 156 (2024), 111222, S. 1-10
To reliably characterize fast dynamic heat transfer mechanisms, fast-response temperature sensors are crucial, including knowledge about the temporal response. In this paper, the dynamic behavior of a Fiber Bragg Grating temperature sensor is investigated and compared to different types of fast-response thermocouples using two different experimental dynamic characterization methods. A temperature step is generated by either plunging the sensor into a fluid or exposing it to a fluid droplet at different temperatures. The step response is evaluated to determine the sensor response time. Calibration runs are performed for a silica-based 0.1 mm FBG sensor, as well as for 0.16 mm and 0.8 mm exposed tip and 0.25 mm sheathed tip type K thermocouples. Water, glycerin, oil and GaInSn were used to cover a broad range of applications regarding different thermal diffusivities and viscosities. The FBG sensor showed the shortest response times compared to the thermocouples, ranging from 60 ms in oil down to 3 ms in liquid metal, which is 20% up to 70% faster compared to a 0.25 mm sheathed tip type K thermocouple. Additional plunging calibration runs of the FBG sensor were performed in a ternary nitrate molten salt mixture (HITEC) to determine its overall and dynamic behavior in corrosive fluids at elevated temperatures. It turns out that the FBG sensor is not affected by the molten salt and shows similar response times to those measured in water. Regarding the characterization methods, both techniques show reproducible results, even though the droplet method is inapplicable for sensors with higher heat capacity or lower thermal conductivity than the calibration fluid. Furthermore, splashing effects for fluids with low viscosity reduce the reliability of the droplet method. The results also show that a dynamic characterization is indispensable for temperature measurements with high temporal resolution because the response time depends on the sensor size and the heat transfer coefficient between sensor and surrounding, which in turn depends on the sensor type, fluid properties and the flow parameters.
https://doi.org/10.1016/j.expthermflusci.2024.111222
Hot-pressing enhances mechanical strength of PEO solid polymer electrolyte for all-solid-state sodium metal batteries. - In: Small Methods, ISSN 2366-9608, Bd. 0 (2024), 0, 2301579, S. 1-9
Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are widely utilized in all-solid-state sodium metal batteries (ASSSMBs) due to their excellent flexibility and safety. However, poor ionic conductivity and mechanical strength limit its development. In this work, an emerging solvent-free hot-pressing method is used to prepare mechanically robust PEO-based SPE, while sodium superionic conductors Na3Zr2Si2PO12 (NZSP) and NaClO4 are introduced to improve ionic conductivity. The as-prepared electrolyte exhibits a high ionic conductivity of 4.42 × 10−4 S cm−1 and a suitable electrochemical stability window (4.5 V vs Na/Na+). Furthermore, the SPE enables intimate contact with the electrode. The Na||Na3V2(PO4)3C ASSSMB delivers a high-capacity retention of 97.1% after 100 cycles at 0.5 C and 60 ˚C, and exhibits excellent Coulombic efficiency (CE) (close to 100%). The ASSSMB with the 20 µm thick electrolyte also demonstrates excellent cyclic stability. This study provides a promising strategy for designing stable polymer-ceramic composite electrolyte membranes through hot-pressing to realize high-energy-density sodium metal batteries.
https://doi.org/10.1002/smtd.202301579