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In this paper, we present the preparation of few-layer MoS2 films on single-crystal sapphire, as well as on heteroepitaxial GaN templates on sapphire substrates, using the pulsed laser deposition (PLD) technique. Detailed structural and chemical characterization of the films were performed using Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurements, and high-resolution transmission electron microscopy. According to X-ray diffraction studies, the films exhibit epitaxial growth, indicating a good in-plane alignment. Furthermore, the films demonstrate uniform thickness on large areas, as confirmed by Raman spectroscopy. The lateral electrical current transport of the MoS2 grown on sapphire was investigated by temperature (T)-dependent sheet resistance and Hall effect measurements, showing a high n-type doping of the semiconducting films (ns from ~1 × 1013 to ~3.4 × 1013 cm-2 from T = 300 K to 500 K), with a donor ionization energy of Ei = 93 ± 8 meV and a mobility decreasing with T. Finally, the vertical current injection across the MoS2/GaN heterojunction was investigated by means of conductive atomic force microscopy, showing the rectifying behavior of the I-V characteristics with a Schottky barrier height of ϕB ≈ 0.36 eV. The obtained results pave the way for the scalable application of PLD-grown MoS2 on GaN in electronics/optoelectronics.

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Magneto-transport characteristics of 2D and 3D superconducting layers, in particular, temperature and angular dependences of the upper critical field Hc2, are usually considered to be fundamentally different. In the work, using non-local resistance measurements at temperatures near the normal-to-superconducting transition, we probed an effective dimensionality of nm-thick NbN films. It was found that in relatively thick NbN layers, the thicknesses of which varied from 50 to 100 nm, the temperature effect on Hc2 certainly pointed to the three-dimensionality of the samples, while the angular dependence of Hc2 revealed behavior typical for 2D samples. The seeming contradiction is explained by an intriguing interplay of three length scales in the dimensionally confined superconducting films: the thickness, the Ginzburg-Landau coherence length, and the magnetic-field penetration depth. Our results provide new insights into the physics of superconducting films with an extremely large ratio of the London penetration depth to the Ginzburg-Landau coherence length exhibiting simultaneously 3D isotropic superconducting properties and the 2D transport regime.

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MXene is an innovative multilayered material that has been prepared by an acid-salt (HCl + NH4F) etching route and tested for the removal of 133Ba and 137Cs in radioactive conditions for the first time. MXene has exhibited high uptake capacity of about 154.9 and 121.5 mg g-1 for 133Ba and 137Cs, respectively, in 0.01 mol L-1 solution and using 5 g L-1 of adsorbent at natural pH.

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A simple noninvasive measurement method which allows one to determine the trapped charge in a biocompatible hydroxyapatite dielectric is developed. The hydroxyapatite samples are charged by electron beam with energy 30 keV and total irradiated charge ranging from 2 × 10-9 C to 2 × 10-7 C. The value of the trapped charge is determined by analyzing the shape change of a liquid droplet hanging from a needle in proximity of the charged sample surface. The shape change of the pendant drop in the field of gravity is commonly utilized in the measurements of the surface free tension (SFT) of liquids. The external electric field leads to a further modification of the droplet shape and to an effective change of the SFT. The change of the SFT as a function of distance between the droplet and sample and the critical distance at which the droplet detaches from the needle are measured for various values of the irradiated charge. These two quantities are also derived theoretically by considering the trapped charge as a single fitting parameter. We can thus determine the trapped charge in two independent noninvasive ways. It is noteworthy that our method is easily implementable into the standard pendant drop setups. As a practical application of the method, a long-term charge stability of the charged hydroxyapatite is demonstrated, thus paving the way toward quantitative studies of its bioactivity in dependence on the value of the trapped charge.

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TiO2 nanotube (TNT) layers are generally prepared in fluoride-based electrolytes via electrochemical anodization that relies on the field-assisted dissolution of Ti metal forming nanoporous/nanotubular structures. However, the usage of fluoride ions is considered hazardous to the environment. Therefore, we present an environmentally friendly synthesis and application of TNT layers prepared in fluoride-free nitrate-based electrolytes. A well-defined nanotubular structure with thickness up to 1.5 µm and an inner tube diameter of ∼55 nm was obtained within 5 min using aqueous X(NO3)Y electrolytes (X = Na+, K+, Sr2+, Ag+). For the first time, we show the photocatalytic performance (using a model organic pollutant), HO˙ radical production, and thorough characterization of TNT layers prepared in such electrolytes. The highest degradation efficiency (k = 0.0113 min-1) and HO˙ radical production rate were obtained using TNT layers prepared in AgNO3 (Ag-NT). The intrinsic properties of Ag-NT such as the valence band maximum of ∼2.9 eV, surface roughness of ∼6 nm, and suitable morphological features and crystal structure were obtained. These results have the potential to pave the way for a more environmentally friendly synthesis of anodic TNT layers in the future using the next generation of fluoride-free nitrate-based electrolytes.

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In the present work, nanotwin structured TiO2 nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 µm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H2O2, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.

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Owing to their excellent hydrogen surface susceptibility, TiO2 thin films have been proven worthy of sensing hydrogen. However, these sensors work best at temperatures of 150-400 °C, with poor selectivity and a low response at room temperature. In this context, the novelty of this paper includes an investigation of the critical role of electrode fabrication that is found to significantly define the surface as well as the performance of a sensor. Sensors prepared with optimized conditions showed the best sensor response (SR) of ∼1.58 × 107 toward 10 000 ppm H2 with excellent linearity (R-square ∼ 0.98 for 300-10 000 ppm) at room temperature (∼20 °C). In addition, the said sensor showed a response time of ∼125 s with full baseline recovery and a selectivity factors (SF) of ∼1754, 2456, and 4723 to 1000 ppm of interfering reducing gases CH4, CO, and NH3, respectively, at 100 °C. At room temperature, the selectivity factor (for 300 ppm H2) of the sensor is ∼3.41 to 90% RH and ∼37.35 to 250 ppm oxygen, 200 ppm CO, and 1600 ppm CO2. Last but not least, our X-ray diffraction, X-ray photoelectron spectroscopy, and electrical transport characteristics enabled us to explain the high sensing mechanism on the basis of the estimated grain size, the quantitative atomic composition, the barrier at the Pt/TiO2 interface, and the thermal activation energy (also known as the intergranular barrier height) of the thin films.

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The surface properties of hydroxyapatite, including electric charge, can influence the biological response, tissue compatibility, and adhesion of biological cells and biomolecules. Results reported here help in understanding this influence by creating charged domains on hydroxyapatite thin films deposited on silicon using electron beam irradiation and investigating their shape, properties, and carbon contamination for different doses of incident injected charge by two methods. Photoluminescence laser scanning microscopy was used to image electrostatic charge trapped at pre-existing and irradiation-induced defects within these domains, while phase imaging in atomic force microscopy was used to image the carbon contamination. Scanning Auger electron spectroscopy and Kelvin probe force microscopy were used as a reference for the atomic force microscopy phase contrast and photoluminescence laser scanning microscopy measurements. Our experiment shows that by combining the two imaging techniques the effects of trapped charge and carbon contamination can be separated. Such separation yields new possibilities for advancing the current understanding of how surface charge influences mediation of cellular and protein interactions in biomaterials.

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Micro-domains of modified surface potential (SP) were created on hydroxyapatite films by direct patterning by mid-energy focused electron beam, typically available as a microprobe of Scanning Electron Microscopes. The SP distribution of these patterns has been studied on sub-micrometer scale by the Kelvin Probe Force Microscopy method as well as lysozyme adsorption. Since the lysozyme is positively charged at physiological pH, it allows us to track positively and negatively charged areas of the SP patterns. Distribution of the adsorbed proteins over the domains was in good agreement with the observed SP patterns.

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The understanding and the precise control of protein adsorption is extremely important for the development and optimization of biomaterials. The challenge resides in controlling the different surface properties, such as surface chemistry, roughness, wettability, or surface charge, independently, as modification of one property generally affects the other. We demonstrate the creation of electrically modified patterns on hydroxyapatite by using scanning electron beam to tailor the spatial regulation of protein adsorption via electrostatic interactions without affecting other surface properties of the material. We show that domains, presenting modulated surface potential, can be created to precisely promote or reduce protein adsorption.

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