Search

Tailoring thermoelectric properties of ScN-based materials is of vital importance for their application, particularly at high operating temperatures. Here, we report on the thermoelectric properties of the ScN layers deposited on MgO (001) substrates by the DC reactive magnetron sputtering. The microstructure of the produced thin films is examined by X-ray diffraction and atomic force microscopy, while their chemical composition and contamination by defects are determined by X-ray photoelectron spectroscopy. The effect of temperature on the phonon properties of ScN layers, having implications for their thermoelectric properties, is explored by Raman spectroscopy. The results of our experiments are confronted with those following from the first-principles studies. We find that the ScN/MgO(001) layers with twin-domain structure reveal enhanced thermoelectric properties at elevated temperature as compared to those measured for almost defect- and domain-free layers, namely, enlarged Seebeck coefficient by about 30% and over two and a half times increased figure of merit at 800 K. Therefore, structural twin domains in thin ScN film appear to be a simple and rather stable solution for the improvement of its thermoelectric properties at elevated temperatures.

The paper presents the results of a comprehensive study of yttrium gallium borate (YGa3(BO3)4) crystals low-doped (0.2 wt%) with erbium (Er3+) ions by in-situ X-ray diffraction (XRD), radioluminescence (RL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. Structural and elastic properties of YGa3(BO3)4: Er3+ crystals measured by the XRD method in the temperature range from 300 K to 1073 K have revealed the temperature variation of the volume thermal expansion coefficient. The analysis of RL spectra allowed us to assume the existence of the characteristic Er3+-related emission band located in the near-infrared region. The TSL spectra revealed strong peaks at low temperatures due to shallow traps and much less intense bands located above room temperature. Measurements of heat capacity in a wide temperature range allowed us to determine the Debye temperature θD ≈ 332 K. From the detailed analysis of the strongly anisotropic EPR spectra measured in YGa3(BO3)4:Er3+ crystals, the parameters of the spin Hamiltonian of Er3+ ions were determined: g⊥ = 9.34; g∥ = 1.269; A⊥ = 320.9 MHz; A∥ = 47.7 MHz. The temperature dependence of the spin-lattice relaxation rate of Er3+ ions was described well by the Orbach-Aminov process. It was proposed that Er3+ ions reside yttrium ions in YGa3(BO3)4 crystal lattice and are located in a slightly distorted prism made of six oxygen ions.

The properties of MXene flakes, a new class of two-dimensional materials, are strictly determined by their surface termination. The most common termination groups are oxygen-containing (=O or -OH) and fluorine (-F), and their relative ratio is closely related to flake stability and catalytic activity. The surface termination can vary significantly among MXene flakes depending on the preparation route and is commonly determined after flake preparation by using X-ray photoelectron spectroscopy (XPS). In this paper, as an alternative approach, we propose the combination of surface-enhanced Raman spectroscopy (SERS) and artificial neural networks (ANN) for the precise and reliable determination of MXene flakes' (Ti 3 C 2 T x ) surface chemistry. Ti 3 C 2 T x flakes were independently prepared by three scientific groups and subsequently measured using three different Raman spectrometers, employing resonant excitation wavelengths. Manual analysis of the SERS spectra did not enable accurate determination of the flake surface termination. However, the combined SERS-ANN approach allowed us to determine the surface termination with a high accuracy. The reliability of the method was verified by using a series of independently prepared samples. We also paid special attention to how the results of the SERS-ANN method are affected by the flake stability and differences in the conditions of flake preparation and Raman measurements. This way, we have developed a universal technique that is independent of the above-mentioned parameters, providing the results with accuracy similar to XPS, but enhanced in terms of analysis time and simplicity., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Humidity sensors play a critical role in monitoring human activities, environmental health, food processing and storage, and many other fields. Recently, some 2D materials, particularly MXenes, have been considered as promising candidates for creating humidity sensors because of their high surface area, surface-to-bulk ratio, and excellent conductivity, arising from the high concentration and mobility of free electrons. In this work, we propose the plasmon-assisted surface modification and termination tuning of common MXene (Ti 3 C 2 T x ) to enhance their response to humidity and increase their stability against oxidation. Hydrophobic (-C 6 H 4 -CF 3 ) and hydrophilic (-C 6 H 4 -COOH) chemical moieties were covalently grafted to the Ti 3 C 2 T x surface using plasmon-mediated diazonium chemistry. In situ Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements, performed at different humidity levels indicate that surface modification significantly affects penetration of water molecules in Ti 3 C 2 T x films. As a result, the sensitivity of the flakes to the presence of water molecules was significantly altered. Additionally, proposed surface grafting commonly proceeds on the less stable MXene surface sites, where flake oxidation commonly initiates. As a result of the modification, such "weak" and more chemically active sites were blocked and Ti 3 C 2 T x stability was significantly enhanced., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The recent advancements in pulsed laser deposition (PLD) control via plasma diagnostics techniques have been positive and raised questions on the limitation of some techniques, such as the Langmuir probe (LP). The particularities of laser-produced plasma can lead to incorrect interpretation of collected electrical signal. In this paper, we explored the limitations of LP as a technique for in situ PLD control by performing investigations on several metallic plasmas, expanding in various Ar atmosphere conditions. Sub-microsecond modulation was seen in the reconstructed IV characteristics attributed to non-equilibrium dynamics of the ejected charges. A perturbative regime was recorded for Ar pressures higher than 2 Pa, where ionic bursts were observed in the electron saturation region. This perturbation was identified as a plasma fireball. A non-linear multifractal model was developed here to explore these new regimes of the LP. The strange attractors characterizing each fireball were reconstructed, and their evolution with the Ar pressure is discussed. Both short- and long-time non-linear behavior were correlated via probe bias, and the pressure effect on the strange attractor's defining the fireball-like behavior was investigated. A good correlation was noticed between the simulated data and experimental findings.

The dynamics of transient plasma generated by UV ns-laser ablation of selected metals (Co, Cu, Ag, Bi) were investigated by the Langmuir Probe method in angle- and time-resolved modes. Multiple ionic and electronic structures were seen for all plasmas with some corresponding to anions or nanoparticle-dominated structures. The addition of an Ar atmosphere energetically confined the plasma and increased the charge density by several orders of magnitude. For pressure ranges exceeding 0.5 Pa fast ions were generated in the plasma as a result of Ar ionization and acceleration in the double layer defining the front of the plasma plume. Several correlations between the target nature plasma properties were attempted. The individual plasma structure expansion velocity increases with the melting point and decreases with the atomic mass while the corresponding charged particle densities decrease with the melting point, evidencing the relationship between the volatility of the sample and the overall abated mass.

Combined laser ablation and pulse modulated radio-frequency (RF) discharge for deposition of CNalpha films was studied by the use of optical emission spectroscopy. Chemically active nitrogen was produced by RF discharge, concentrated between two small electrodes. Influence of RF power, nitrogen pressure, modulation frequency and pulse rate on nitrogen species production was researched. For the same system plasma expansion rate, kinetic energy and concentration of carbon ions emitted by laser from graphite target were determined by Langmuir probes measurement.