[en] The features of platinum film formation on n-6H-SiC substrates were experimentally studied for different methods of pulsed laser deposition, i.e., by both the conventional method in vacuum and in an inert gas atmosphere. In the latter case, a disk screen was placed on the plume expansion axis between the laser target and substrate to protect the latter from micrometer and submicrometer particles. A numerical model of such a process was developed, which makes it possible to predict the deposited film distribution over the substrate surface, energy and angular parameters of the atomic flow as laser plume properties, inert gas pressure, and screen position are varied. Simulation results were used to explain electrical properties of Pt/n-6H-SiC thin-film structures fabricated by different methods.

[en] Diode structures with ideality factors of 1.28-2.14 and potential barriers from 0.58 to 0.62 eV on the semiconductor side were formed by pulsed laser deposition of Au, Ag, Cu, Pd, Pt, W, and Zr metal films on n-6H-SiC crystal without epitaxial layer preparation. A high density of surface acceptor and donor states was formed at the metal-semiconductor interface during deposition of the laser-induced atomic flux, which violated the correlation between the potential barrier height and metal work function. The barrier heights determined from characteristic currents and capacitance measurements were in quite good agreement. For the used low-resistance semiconductor and contact elements, the sizes of majority carrier (electron) depletion regions were determined as 26-60 nm.

[en] The method of deposition from the gas phase is applied to the synthesis of thin films of molybdenum disulfide. It was established that varying the rate of temperature rise in the course of the synthesis affects the character of growth and the structure of the layers formed. With a decrease in the rate of temperature rise, a transition from standard two-dimensional to screw growth of MoS₂ films is observed. MoS₂ films produced as a result of screw growth have a high density of edge states, which makes them promising for use in catalysis.

[en] A comparative analysis of the abilities of several novel methods to produce ultrathin molybdenum disulphide (MoS₂) films containing from 1 to 10 molecular layers was carried out. To deposit MoS_x films and MoO_x precursor films, the atomic flux was formed by laser ablation of Mo, MoS₂, and MoO₃ targets. Saturation with sulphur of the deposited layers was performed using a reactive gas (hydrogen sulphide) or by thermally activated treatment of thin-film precursors in a sulphur vapor. It has been established that the use of hydrogen sulphide makes it possible to obtain ultrathin MoS₂ films at relatively low temperatures ∼ 350 °C. However, these films contained local defects which were absent in the films prepared by the treatment of thin film MoO_x precursors in sulphur vapours at higher temperatures (≥ 650°C). (paper)

[en] Thin-film structures based on gas-sensitive tungsten oxide and catalytic platinum are fabricated by room-temperature deposition on a silicon carbide wafer using pulsed laser and ion-plasma methods. Oxide layer annealing in air to 600°C caused the formation of microstructured and nanostructured crystalline states depending on the deposition conditions. Structural differences affect the electrical parameters and the stability of characteristics. The maximum response to hydrogen is detected in the structure fabricated by depositing a low-energy laser-induced flow of tungsten atoms in oxygen. The voltage shift of the currentvoltage curves for 2% H₂ in air at 350°C was 4.6 V at a current of ∼10 μA. The grown structures’ metastability caused a significant decrease in the shift after long-term cyclic testing. The most stable shifts of ∼2 V at positive bias on the Pt contact were detected for oxide films deposited by ion-plasma sputtering.

[en] The ability to increase the efficiency of electrochemical H₂ and O₂ evolution reactions in an alkaline solution using nickel-foam-based electrodes has been studied. To improve the catalytic properties of the foam, it was subjected to complex modification via sulfurizing in sulfur-containing gaseous media and the additional formation of amorphous or crystalline MoS_x nanolayers. The foam was sulfidized in hydrogen sulfide or sulfur vapor at a temperature of 400°C. Amorphous MoS_x films were produced via pulsed laser deposition from a MoS₂ target in an H₂S atmosphere. To obtain nanocrystalline catalytic MoS_x layers, thin-film Mo precursors were preliminarily applied to the foam pre-sulfurized in sulfur vapor at 400°C. The deposition of precursors was carried out in vacuum at 22°C. After deposition, the foam with precursors was oxidized in air at 600°C. The modified samples were probed via scanning electron microscopy involving microanalysis and Raman spectroscopy. The effect of the precursor layer thickness on the sulfurizing efficiency and phase composition of the modified layers was established. The amorphous layer deposition was found to have a strong impact on only the O₂ evolution. The crystalline layers obtained via sulfidizing of Mo-containing precursors exerted influence on both the cathodic and anodic reactions. The hydrogen overvoltage at a current density of 10 mA/cm² was −160 mV, and the oxygen overvoltage was below 150 mV, which corresponded to the best electrocatalysts on the nickel foam after the volume modification via conventional chemical treatment (hydro- and solvothermal synthesis).

[en] Novel nanostructured thin-film coatings containing WSe₂ and WO₃ nanosheets were prepared through a simple and highly reproducible method. Pulsed laser pre-deposition of W- Se-O films on a microcrystalline graphite substrate by ablation of WSe₂ target in a mixture of Ar and O₂ gases was followed by thermal post-treatment. The influence of pre-deposition and post-treatment conditions on the structure, morphology and chemical composition of the W-Se- O films was studied. Thermal annealing at appropriate conditions of pre-deposited amorphous W-Se-O films resulted in the formation of crystalline structure consisted of nanocrystals of WSe₂ and WO₃ phases. Such structural modification significantly altered the electrochemical properties of the thin-film coatings with consequences, in particular, on their catalytic activity toward hydrogen evolution reaction in an acid solution. (paper)

[en] Nanocomposite a-C(Mo/MoSe_x) thin films containing amorphous carbon matrix a-C, nano-Mo and MoSe_{x ≥2} clusters were obtained by pulsed laser co-deposition of carbon and MoSe₂. The deposition was carried out at room temperature onto a graphite substrate. Atomic content of the MoSe_x≥2 phase did not exceed 25%. The use of a buffer gas at a pressure of 10 Pa allowed to obtain the maximum Se/Mo ratio in the films and to increase the concentration of sp²-hybridized C atoms for high conductivity realization. The formation of MoSe_x≥2 cluster inclusions was the essential factor for activation of hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ aqueous solution. These clusters also promoted cathodic deposition of Pt nanoparticles on the surface of a-C(Mo/MoSe_x) in a H₂SO₄/KCl solution when a Pt anode was used as a source of Pt. Hybrid Pt/a-C(Mo/MoSe_x) thin-film coatings with a low Pt loading (∼6 μg/cm²) exhibit excellent HER property, which noticeably exceeds that of relatively thick Pt coating prepared on a graphite substrate by pulsed laser deposition. (paper)

[en] The films of tungsten oxides were prepared by pulsed laser ablation of W target in a reactive gas atmosphere (air of laboratory humidity). Optical analysis and ion signal measurements for the laser plume allowed to recognise a threshold gas pressure that suppresses the deposition of non-scattered atomic flux from the plume. When the pressure exceeds about 40 Pa, the films grow due to the deposition of species that could be formed in collisions of W atoms with reactive molecules (e.g., O₂). Kinetic Monte Carlo method was used for modelling film growth. Comparison of the model structures with the experimentally prepared films has shown that the growth mechanism of ballistic deposition at a pressure of 40 Pa could be changed on the diffusion limited aggregation at a pressure of ∼100 Pa. Thus, a cauliflower structure of the film transformed to a web-like structure. For good correlation of experimental and model structures of WO_x, a dimension of structural elements in the model should coincide with W-O cluster size. (paper)

[en] The influence of pulsed laser deposition conditions in the geometry “off-axis” on the catalytic properties of MoS_x films in the hydrogen evolution reaction is investigated. For the deposition of MoS_x films from MoS₂ target, pulsed laser radiation from the IR and UV wavelength ranges was used. The angle of incidence of the laser-induced plume on the surface of the substrate in a buffer gas was varied to check the influence of large in-size Mo-enriched particles. The efficiency of the catalyst was estimated from the results of the turnover frequency (TOF) measurement, which made it possible to minimize the influence of the “loading” of the catalyst on its characteristics. The effects of the chemical composition, local structure, and properties of the catalyst–substrate interface on the efficiency of the hydrogen evolution reaction are analysed. The regime of pulsed laser deposition of more effective thin-film MoS_x catalysts is determined. (paper)