Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy. - In: Journal of magnesium and alloys, ISSN 2213-9567, Bd. 12 (2024), 2, S. 516-529
In order to obtain Mg alloys with fine microstructures and high mechanical performances, a novel friction-based processing method, name as “constrained friction processing (CFP)”, was investigated. Via CFP, defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced. Compared to the previous as-cast microstructure, the grain size was reduced from more than 1 mm to around 4 µm within 3 s by a single process cycle. The compressive yield strength was increased by 350% while the ultimate compressive strength by 53%. According to the established material flow behaviors by “tracer material”, the plastic material was transported by shear deformation. From the base material to the rod, the material experienced three stages, i.e. deformation by the tool, upward flow with additional tilt, followed by upward transportation. The microstructural evolution was revealed by “stop-action” technique. The microstructural development at regions adjacent to the rod is mainly controlled by twinning, dynamic recrystallization (DRX) as well as particle stimulated nucleation, while that within the rod is related to DRX combined with grain growth.
https://doi.org/10.1016/j.jma.2023.10.007
An improved GPU-optimized fictitious surface charge method for transcranial magnetic stimulation. - In: IEEE transactions on magnetics, ISSN 1941-0069, Bd. 60 (2024), 3, 5100104, insges. 4 S.
The fictitious surface charge method (FSCM) is used for the calculation of the induced electrical field in magnetic stimulation. The method was embedded and optimized in Python. It was designed to allow for the computation of large problems. An element-wise Jacobi method was combined with vectorized matrix operations to increase the parallelization capabilities and enable GPU computing. The induced fields are compared against an analytical solution for a homogeneous sphere and a FEM solution on a realistic head model. The results for both cases show that the normalized root mean square error of less than 0.5% can be achieved with the integral-free FSCM even on low-performance computer hardware.
https://doi.org/10.1109/TMAG.2023.3334747
Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors. - In: Chinese chemical letters, ISSN 1878-5964, Bd. 35 (2024), 2, 108796
The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport. However, it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors, especially vacuum-deposited small molecules. Here, interfacial molecular screening of polyimide (Kapton) dielectric in organic field-effect transistors (OFETs) is comprehensively studied. It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide (PI) dielectrics compared with the molecules without alkyl side chains. On this basis, the fabricated transistors could reach the mobility of 1.2 cm2 V−1 s−1 the molecule with alkyl side chains on bare PI dielectric. What is more, the compatible semiconductor and dielectric would further produce a low activation energy (EA) of 3.01 meV towards efficient charge transport even at low temperature (e.g., 100K, 0.9 cm2 V−1 s−1). Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.
https://doi.org/10.1016/j.cclet.2023.108796
Phototactic photocatalysis enabled by functionalizing active microorganisms with photocatalyst. - In: Advanced sustainable systems, ISSN 2366-7486, Bd. 8 (2024), 2, 2300302, S. 1-10
Positive phototropism enables plants to take advantage of sunlight more efficiently. However, positive phototropism of plant-like photocatalyst has not been reported yet, which cause people's limited understanding on it. Therefore, developing new photocatalysts that can move toward the light source and thus speed up the photocatalytic process, is a great challenge. Herein, a biologically active photocatalyst (graphitic carbon nitride combined with algae microorganisms, g-C3N4/alga) is reported first that can behave like green plants and move toward light source, leading to a great enhancement in photocatalysis. The photocatalytic degradation efficiency of the phototactic g-C3N4/alga is improved up to 570% than that of pure g-C3N4. The phototactic g-C3N4/alga photocatalyst can effectively utilize the synergy of phototaxis of microalgae and photocatalytic activity of g-C3N4 to promote the pollutant decomposition using sunlight. Imparting photocatalyst with positive phototropism will open a new door in photocatalysis field for clean energy production, pollutant treatment, and biomass conversion.
https://doi.org/10.1002/adsu.202300302
Precisely controlled batch-fabrication of highly sensitive co-resonant cantilever sensors from silicon-nitride. - In: Journal of micromechanics and microengineering, ISSN 1361-6439, Bd. 34 (2024), 1, 015005, S. 1-14
Dynamic-mode cantilever sensors are based on the principle of a one-side clamped beam being excited to oscillate at or close to its resonance frequency. An external interaction on the cantilever alters its oscillatory state, and this change can be detected and used for quantification of the external influence (e.g. a force or mass load). A very promising approach to significantly improve sensitivity without modifying the established laser-based oscillation transduction is the co-resonant coupling of a micro- and a nanocantilever. Thereby, each resonator is optimized for a specific purpose, i.e. the microcantilever for reliable oscillation detection and the nanocantilever for highest sensitivity through low rigidity and mass. To achieve the co-resonant state, the eigenfrequencies of micro- and nanocantilever need to be adjusted so that they differ by less than approximately 20%. This can either be realized by mass deposition or trimming of the nanocantilever, or by choice of dimensions. While the former is a manual and error-prone process, the latter would enable reproducible batch fabrication of coupled systems with predefined eigenfrequency matching states and therefore sensor properties. However, the approach is very challenging as it requires a precisely controlled fabrication process. Here, for the first time, such a process for batch fabrication of inherently geometrically eigenfrequency matched co-resonant cantilever structures is presented and characterized. It is based on conventional microfabrication techniques and the structures are made from 1 µm thick low-stress silicon nitride. They comprise the microcantilever and high aspect ratio nanocantilever (width 2 µm, thickness about 100 nm, lengths up to 80 µm) which are successfully realized with only minimal bending. An average yield of % of intact complete sensor structures per wafer is achieved. Desired geometric dimensions can be realized within ±1% variation for length and width of the microcantilever and nanocantilever length, ±10% and ±20% for the nanocantilever width and thickness, respectively, resulting in an average variation of its eigenfrequency by 11%. Furthermore, the dynamic oscillation properties are verified by vibration experiments in a scanning electron microscope. The developed process allows for the first time the batch fabrication of co-resonantly coupled systems with predefined properties and controlled matching states. This is an important step and crucial foundation for a broader applicability of the co-resonant approach for sensitivity enhancement of dynamic-mode cantilever sensors.
https://doi.org/10.1088/1361-6439/ad0d80
Hardness and tribological behaviour of annealed electroless nickel phosphorus composite layers with incorporated boron particles. - In: Surface and coatings technology, ISSN 1879-3347, Bd. 476 (2024), 130261, S. 1-17
In this study, a possible alternative to hard chromium coatings is investigated. Amorphous boron particles have been incorporated in electroless nickel‑phosphorus (NiP) deposits, yielding a dispersion coating. The distribution of the particles is homogenous and the maximum mass fraction of particles embedded in the coating is 6.2 ± 0.2 wt%. Measurements of the zeta potential and particle size of amorphous boron particles in a diluted electrolyte showed that the particles withstood agglomeration until 120 days. Primary and secondary hardness maxima are observed after thermal annealing at 400 ˚C and 860 ˚C due to the formation of nickel phosphide, nickel boride and nickel boride phosphide phases. X-ray diffractometry shows an increase in nickel and nickel phosphide crystal size at 400 ˚C before levelling off at 600 ˚C. The annealing duration should be kept between 30 and 60 min for optimal hardness. The wear resistance increases when the coating is annealed at 400 ˚C. DSC measurements on nickel phosphorus incorporated with boron particles, Ni-P-B, bulk material with P-content (9.6 ± 0,6 wt%) and B-content (4.5 ± 0.8 wt%) showed that the solidus line lies at 926 ˚C, which is why a maximum annealing temperature of 860 ˚C was chosen to avoid melting of the material. The relative texture and phase coefficients, RTC and RPC, showed that the nickel phase is preferred in the NiP system at 400 ˚C and 600 ˚C while the Ni3P phase is preferred in the Ni-P-B system at the same annealing temperature. REM and EDX area analyses are used to show the areal distribution of nickel, phosphorus, and boron before and after the annealing process along the thickness of the coating. A diffusion layer between substrate and coating that contains iron nickel boride and iron nickel phosphide lamellar structure is observed.
https://doi.org/10.1016/j.surfcoat.2023.130261
A magnetoelastic twist on magnetic noise: the connection with intrinsic nonlinearities. - In: Advanced functional materials, ISSN 1616-3028, Bd. 34 (2024), 9, 2309867, S. 1-11
Intrinsic magnetic noise limits the functionality of all magnetic field sensors and related devices using magnetic films as sensing elements. A novel origin of magnetic noise due to ferromagnetic material's magnetostriction is revealed by implementing a comprehensive multi-level signal-noise model and thoroughly validating it experimentally on magnetoelectric composite ΔE-effect sensors. From electrical measurements and operando magnetic domain visualization, magnetic contributions are shown to dominate the noise floor and limit the overall performance of multi-domain magnetoelastic sensors. The newly introduced noise contribution is correlated with the nonlinearity of the magnetostrictive properties. The effect on sensor output is particularly pronounced in magnetoelastic and magnetoelectric composite devices, but the results generally apply to all sensor devices incorporating magnetic materials. Therefore, the identified magnetic noise source makes a significant contribution to understanding the limitations of magnetic sensors and provides important guidelines for optimizing future magnetic sensors for low detectivity.
https://doi.org/10.1002/adfm.202309867
Electron spin finds a fresh excitation. - In: Nature physics, ISSN 1745-2481, Bd. 20 (2024), 1, S. 4-5
The Kondo effect - the screening of an impurity spin by conduction electrons - is a fundamental many-body effect. However, recent experiments combined with simulations have caused a long-standing model system for the single-atom Kondo effect to fail.
https://doi.org/10.1038/s41567-023-02265-3
Adaptation of metrology-grade ac current source in velocity mode of Planck-Balance 2: direct referencing induced voltages with ac quantum voltage standard. - In: Measurement science and technology, ISSN 1361-6501, Bd. 35 (2024), 1, 015026, S. 1-11
The adaptation of developed metrology-grade ac current source (MCS) to the velocity mode of measurements of the Planck-Balance 2 as a means for generating ac mechanical oscillations is presented. The universality in operating with the MCS unit especially practical for the Planck-Balance setup for frequencies of 0.1 Hz-20 Hz (including but not limited to the negligence of a broader range of 0.01 Hz up to several hundred Hz) and for amplitudes of up to 10 mA with 16 (offset with 14)-bit effective resolution is demonstrated. MCS allows generating complex ac waveform signals as waveform synthesizers by adding to the original signal an extra five independent harmonic components, each of which with an adjustable resolution of 10 ns for phase and 16-bit for amplitude. Additionally, the MCS is supported by an external clock at 10 MHz frequency which serves also as a common reference time base for the comparison between the direct output signal of MCS, or of the induced voltage in the coil of the Planck-Balance resulting due to the applied current by MCS, with the ac quantum voltage standard at the required accuracy levels.
https://doi.org/10.1088/1361-6501/ad006c
Electrochemical reduction of tantalum and titanium halides in 1-butyl-1-methylpyrrolidinium bis (trifluoromethyl-sulfonyl)imide and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ionic liquids. - In: Journal of solid state electrochemistry, ISSN 1433-0768, Bd. 0 (2023), 0, insges. 14 S.
The electrodeposition of tantalum-titanium–based films using different tantalum and titanium halides was investigated in two ionic liquids, namely, 1-butyl-1-methylpyrrolidinium bis (trifluoromethyl-sulfonyl)imide ([BMP][TFSI]) and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][OTf]). Cyclic voltammetry was used to analyse the electrochemistry of the electrolytes and potentiostatic deposition was performed to evaluate the feasibility of electrodepositing tantalum-titanium–based layers. Both the metal salts and the ionic liquid influenced the electrochemical reduction of the tantalum and titanium halides significantly. While titanium halides considerably retarded the reduction of tantalum pentahalides and inhibited electrodeposition in many electrolytes, an electrolyte composition from which tantalum and titanium-containing layers could be deposited was identified. Specifically, in TaBr5 and TiBr4 in [BMP][TFSI], TiBr4 did not inhibit the deposition of tantalum and titanium was co-deposited itself by a three-step reduction mechanism as confirmed by cyclic voltammetry and energy-dispersive X-ray spectroscopy. Furthermore, [BMP][TFSI] led to smoother and more compact deposits.
https://doi.org/10.1007/s10008-023-05773-7