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The thermochemical treatment of tungsten trioxide (WO3) nanostructured films in hydrogen sulfide to obtain tungsten disulfide (WS2) layers in the WS2/WO3 hybrid structure is studied. The temperature and treatment time influence the structural-phase state, morphology, optical properties of a WS2/WO3/FTO photocathode (on fluorinated tin oxide (FTO) substrates), and its photoelectrocatalytic activity in the hydrogen evolution reaction in acidic solution is established. The sulfidation of WO3 nanoneedle films leads to the formation of a WS2/WO3 nanocrystalline hybrid structure under optimal conditions, which provides the separation of photogenerated carriers (electrons and holes) at the interphase boundaries (heterojunctions) necessary for the efficient photoactivated hydrogen evolution reaction according to Z scheme. The calculations of thermodynamic properties of the WS2/WO3 hybrid nanocatalyst show that synergistic effect of nanophases is possible in it to increase the catalytic activity of hydrogen evolution both on the basal planes of WS2 nanoclusters and on the surface of metal oxide nanoclusters.

The influence of the chemical state of a WOy thin-film precursor on formation of WSe2 nanofilms under rapid selenization on a glassy carbon substrate at 900°C is studied. A nanolayer of amorphous molybdenum sulfide (MoSx ~ 3), which has high catalytic activity in the electrochemical reaction of hydrogen evolution, is applied onto the surface of the obtained WSe2 films by pulsed laser deposition. It is shown that the composition of the WOy thin-film precursor has a significant effect on the morphology of the WSe2 nanolayers, and this characteristic largely determines the efficiency of hydrogen evolution by the MoS3/WSe2 heterostructure upon photoactivated water splitting. The most efficient hydrogen evolution is found for the MoS3/WSe2 photocathode heterostructure containing WSe2 in the form of crystal petals of ~50 nm in thickness, with these crystals oriented perpendicular to the substrate surface. A theoretical analysis of the possible effect of synergistic interaction at the MoS3/WSe2 interface on the efficiency of hydrogen evolution is carried out. Density functional theory calculations have shown that MoS3 clusters can increase the efficiency of the hydrogen evolution reaction upon contact with surface regions of WSe2 nanocrystals different in atomic packing.

Features of thermochemical treatment of nanostructured tungsten trioxide (WO3) films in hydrogen sulfide aimed at the formation of tungsten disulfide (WS2) nanolayers in the hybrid WS2/WO3 structure are investigated. The effect of temperature and treatment time on the structure, chemical state, morphology, and optical properties of the WS2/WO3/FTO photocathode (on the fluorinated tin oxide substrate), as well as on its photoelectrocatalytic activity in the reaction of hydrogen evolution in an acidic solution has been established. It is shown that sulfurization of nano-needle WO3 films under optimal conditions leads to the formation of a nanocrystalline hybrid WS2/WO3 structure that ensures the separation of photogenerated carriers (electrons and holes) at interphase boundaries (heterojunctions). This facilitates the efficient photo-activated hydrogen evolution reaction according to the Z-scheme. First-principal calculations of the thermodynamic properties of the hybrid WS2/WO3 nanocatalyst showed that a synergistic effect of nanophases is possible. This increases the catalytic activity of hydrogen evolution on both the basal planes of WS2 nanoclusters and the surface of metal oxide nanoclusters.

MoS2 nanofilms were created by thermochemical processing (sulfurization) of thin-film Мо and МоОу precursors in S vapor. The precursor films were created by pulsed laser deposition. The obtained molybdenum disulfide films consisted of 2H-MoS2 nanocrystals with laminar packing of basal planes oriented perpendicular to the film surface. The increase in the sulfurization temperature from 500°C to 800°C provided better quality of local packing and, as a consequence, reduction of electric resistance, higher concentration of carriers (electrons) and their mobility. The application of metal oxide precursor МоОу resulted in higher efficiency of synthesis of high quality MoS2 nanofilms. The efficiency of activation of the electrochemical processes of hydrogen production in an acidic solution was lower with crystalline MoS2 nanofilms than with amorphous MoSx films. Nanocrystalline MoS2 films, however, manifested improved photo- and electrocatalytic characteristics in activation of reactions of hydrogen and oxygen evolution in an alkaline solution.

The mechanisms of film formation during pulsed laser ablation of a MoS2 target were studied. The conditions for the deposition of laser erosion plume were determined. This made it possible to obtain coatings with a porous structure consisting of round Mo nanoparticles coated with a thin shell of amorphous molybdenum sulfide MoSx > 2. Due to its hybrid structure, the MoSx > 2/Mo nanomaterial can be effectively used for electro- and photocatalysis of water splitting. The MoSx > 2/Mo films deposited on a glassy carbon substrate are characterized by good current transport and high active surface area. When the film thickness increased due to the increased deposition time, the overvoltage of hydrogen evolution in an acid solution monotonically decreased to 142.5 mV, which was necessary in order to obtain current density of hydrogen evolution of 10 mA/cm2. The catalyst loading was 230 μg/cm2. Further increase in the loading did not significantly reduce the overvoltage. The results indicate that it is promising to use Mo nanoparticles as an ultrafine support for the catalytic nanolayers of amorphous molybdenum sulfide.

The possibility of using physicochemical methods for treating a nickel foam to increase its electrocatalytic activity in hydrogen and oxygen evolution reactions in an aqueous alkaline solution was studied. The modification of a 1-mm-thick sheet of the foam was carried out through its surface and included physical deposition of pulsed laser plasma for the formation of catalytic MoSx and MoSxSey films, followed by their annealing. The effect of foam pretreatment by sulfurization in H2S under varying conditions and formation of catalytic layers with different structures and compositions was studied. The best improvement in the electrocatalytic performance of the foam was exerted by thin-film coatings of molybdenum sulfide and sulfide/selenide with a nanocrystalline structure formed on the surface of a foam with a Ni3S2 underlayer. The possibility of a synergetic effect of the formed phases was analyzed by DFT calculations. For the optimum composition of the modified layers, the overvoltage of H2 evolution (for a current density of 10 mA/cm2) decreased to 155 mV, and the overvoltage of O2 evolution did not exceed 160 mV. The electrocatalytic characteristics obtained by this treatment are not inferior to those for the best modern electrocatalysts created on nickel foam by widely used methods of hydrothermal synthesis or electrodeposition.

To obtain Mo–S–C thin-film coatings on steel substrates with varying structural and chemical states, pulsed laser codeposition method was used at room temperature, including the first ever use of reactive codeposition of Mo and C in H2S. The conditions are determined for obtaining sufficiently smooth layers with optimal local packing of atoms in amorphous MoSx and diamond-like carbon nanophases, which yielded relatively high wear resistance and a low sliding friction coefficient (~0.1) in air without a long running-in phase.

We present the results of a comparative investigation of the friction and wear characteristics of MoSx and MoSex coatings in an oxidizing medium (argon–air mixture) at a temperature of –100°C. Thin films of these solid lubricants were manufactured by pulsed laser deposition using MoS2, MoSe2, and Mo targets in vacuum and H2S. It was established that S-containing coatings ensured a friction coefficient of ~0.09 and were much superior to S-containing coatings in respect of wear. The properties of MoSx coatings depended on the concentration of S that determined the local atomic packing in the amorphous structure of the film. The friction coefficient of MoS3 coating after running-in was half as small as that of MoS2 and amounted to 0.08.

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 MoSx nanolayers. The foam was sulfidized in hydrogen sulfide or sulfur vapor at a temperature of 400°C. Amorphous MoSx films were produced via pulsed laser deposition from a MoS2 target in an H2S atmosphere. To obtain nanocrystalline catalytic MoSx 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).

The morphology, chemical composition, microstructure, and electrical properties of BC3 thin films subjected to melting by a nanosecond laser pulse are investigated. The original films have been created by pulsed laser codeposition of B and C onto a sapphire substrate at 150 and 350°C. Morphological changes in the films depended on their initial structural state. However, a “frozen” structure of both films after irradiation corresponded to the B-saturated graphite-like phase, the local composition of which varied due to the formation of inclusions of amorphous boron carbide. Before and after irradiation, the films exhibited a slightly decreasing dependence of the surface resistance with increasing temperature from 4.2 to 330 K. After laser irradiation, the films resistance has decreased by a factor of ~2.6.

Relatively low and high deposition rates of BCх films were realized by pulsed laser ablation of mixed B–diamond and dual B–graphite targets, respectively. Deposition was performed at 500 °C and the rate of film deposition was determined with respect to the number of atomic monolayers (obviously less or more than one monolayer) grown for one laser pulse. In the case of BCх films formation with a low deposition rate, doping with B facilitated the growth of the nanocomposite structure, which possessed an increased fraction of sp3 bonds, a very low electrical resistance, and an improved mechanical performance. The change of the sheet resistance of these films as the temperature was reduced from 300 to 65 K had a metallic character. For about 95-nm-thick films with bulk compositions of BC1.7 and BC0.6, the resistivity at room temperature were approximately equal to 1.5 mΩ·cm, and the lowest resistivity of 0.23 mΩ·cm was detected for B-enriched film at 85 K. With an increase in the B atom concentration in such films, the charge carrier (holes) concentration decreased, and their mobility increased from 180 to 10,500 cm2·V−1·s−1 due to samples cooling. The application of a higher deposition rate from the dual B–graphite target activated surface migration of condensed atoms, which caused the development of granular morphology, the B segregation and the reduction of the sp3 bond fraction. The hardness and electrical conductivity of such films were obviously inferior to those of the films obtained by PLD with a low deposition rate.

Structural features of CBx films obtained by pulsed laser ablation of targets made of pressed diamond powder with boron-powder additions at B/C atomic ratio of x = 0.33 have been studied. The films were deposited on heated substrates, so that diffusion processes involving C and B atoms on the surface and in the volume of films were possible. Selected conditions of film deposition ensured their effective doping with boron (0.4 ≤ x ≤ 0.6). The incorporation of B atoms was accompanied by the formation of B–C chemical bonds, whereas the formation of sp2 graphite bonds and their ordering in clusters with laminar packing was suppressed. The films possessed very low resistivity (~1.4 mΩ cm) at room temperature and exhibited metallic type of conductance on decreasing the temperature to 77 K.

Pulsed laser ablation of a MoS2 target causes enhanced splashing of the material. So, for MoSx films obtained by pulsed laser deposition (PLD) in the conventional normal incidence (NI) configuration, their typical morphology is characterized by an underlying granular structure with an overlayer of widely dispersed spherical Mo and MoSx particles possessing micro-, sub-micro- and nanometer sizes. We investigated the possibility of using high surface roughness, which occurs due to particle deposition, as a support with a large exposed surface area for thin MoSx catalytic layers for the hydrogen evolution reaction (HER). For comparison, the HER performance of MoSx layers formed by grazing incidence (GI) PLD was studied. During GI-PLD, a substrate was placed along the direction of laser plume transport and few large particles loaded the substrate. The local structure and composition of thin MoSx layers formed by the deposition of the vapor component of the laser plume were varied by changing the pressure of the buffer gas (argon, Ar). In the case of NI-PLD, an increase in Ar pressure caused the formation of quasi-amorphous MoSx (x ≥ 2) films that possessed highly active catalytic sites on the edges of the layered MoS2 nanophase. At the same time, a decrease in the deposition rate of the MoSx film appeared due to the scattering of the vapor flux by Ar molecules during flux transport from the target to the substrate. This effect prevented uniform deposition of the MoSx catalytic film on the surface of most particles, whose deposition rate was independent of Ar pressure. The scattered vapor flux containing Mo and S atoms was a dominant source for MoSx film growth during GI-PLD. The thickness and composition distribution of the MoSx film on the substrate depended on both the pressure of the buffer gas and the distance from the target. For 1.0–2.5 cm from the target, the deposition rate was quite sufficient to form S-enriched quasi-amorphous MoSx (2.5

To fabricate an electrocatalyst containing nanostructured layers of WOy and MoS x , a sequential formation of tungsten oxide and molybdenum sulfide thin films is performed by means of the pulsed laser deposition of W and Mo in low-pressure air and hydrogen sulfide media, respectively. The reactive medium pressure and the substrate (glassy carbon) temperature are varied during and after the deposition. WOy thin films of various morphologies and structures determining certain differences in their catalytic properties in the reaction of hydrogen evolution in acidic solutions are obtained. However, the catalytic efficiency of the obtained WO y nanoelements (spheres, needles, and sheets) with amorphous and crystalline structures appears to be insufficient. Additional deposition of MoS x with an amorphous structure results in a significant improvement of the catalytic properties. Sulfur atoms in the MoSx amorphous matrix cause the formation of catalytically active sites, while the developed surface of the WO y stimulates an increase in the catalyst total active area. Penetration of hydrogen effectively formed on MoS x into the bulk of thin films of WO y provides a crucial electrocatalysis condition—low current resistance in the support layer with a large exposed surface area.

The peculiarities of pulsed laser ablation of MoSe2 targets which caused the formation of a complex plume containing atoms (Mo and Se) and Mo nanoparticles (Mo-NPs) have been studied. Investigations of the composition, structure, and catalytic activity toward the hydrogen evolution reaction (HER) for MoSex/Mo-NPs films prepared by pulsed laser deposition (PLD) in a vacuum and in a buffer He gas were carried out. For He pressure of 30 Pa, a shock wave could be the dominant mechanism of material transport, resulting in the deposition of an Se-enriched flux of chemically active atoms and leading to the growth of amorphous films with an increased Se content. Mo nanoparticles allowed for a larger surface area of the MoSex∼3.1/Mo-NPs catalyst deposited 5 cm from the target. However, for deposition in He at 10 cm, the amount of Mo NPs in the film appreciably decreased. Factors that could impact on the transport of nanoparticles through a buffer gas were considered. The amorphous MoSex∼3.1/Mo-NPs films prepared by PLD in He gas exhibited excellent HER performance. Quasicrystal MoSex

We report the preparation of MoS x thin films with reactive pulsed laser deposition (RPLD), an original technique that allows us to investigate the correlation between key MoS x properties, such as the composition, morphology, and local structure, and the catalytic performance in the hydrogen evolution reaction (HER). The use of two geometries of normal angle (NA) and sliding angle (SA) for the deposition by laser plume from a Mo target on a glassy carbon substrate made it possible to regulate the characteristics of MoS x films (1.5 ≤ x ≤ 10) by varying the H 2 S pressure and thus to circumvent the limitations inherent in traditional pulsed laser deposition. Amorphous MoS x , quasi-crystalline layered MoS 2 , disordered as well as rather perfect Mo 3 –S clusters, and sulfur clusters were formed. The films containing locally ordered clusters with a higher content of bridging S 2 2 − and apical S 2 − ligands could be prepared by SA RPLD. This film was demonstrated to be the most efficient electrocatalyst, possessing a lower overpotential of − 130 mV at a current density of − 1 mA/cm 2 , a Tafel slope of 44 mV/dec, and a quite high exchange current density of ~ 1.2 μA/cm 2 . The preparation of a low-resistance MoS x underlayer by NA RPLD made it possible to increase the catalytic performance of a bilayer coating by 10%.

The possibility of detecting H2 by registering the thermal electromotive force signal, which arises between the surfaces of 6H-SiC plates with a thickness of 400 μm, is established. The working surface of the plates is modified by deposition of a WO x film and catalytic Pt. An ohmic contact (Ni/Pt) is created on the rear surface of the plate, and this surface is maintained at a stabilized temperature of 350°C. The temperature gradient through the plate thickness arises due to the cooling of the working surface with the air medium. The delivery of H2 into this medium up to a concentration of 2% gives rise to a 15-fold increase in the electric signal, which considerably exceeds the Pt/WO x /SiC/Ni/Pt system’s response registered in the usual way by measuring the current–voltage dependence. In this case, an additional power source for the registration of the thermal electromotive force is not required.

We have studied the characteristics of the structure, composition, and electrocatalytic properties of thin MoS x films obtained by pulsed laser deposition using an Mo target ablated in H2S reactive-gas medium. The laser plume during deposition was directed tangentially and normally to the substrate, which allowed amorphous films to be obtained with different local atomic packings in an amorphous matrix consisting of Mo3–S clusters. It is established that the orientation of Mo3–S clusters influences charge transport in the catalyst and determines the type and surface density of catalytically active sites in the reaction of hydrogen evolution. For small, approximately equal amounts of Mo and Pt (~4 μg/cm2) laser-deposited on glassy carbon substrates, the MoS x films were inferior to a Pt film with respect to hydrogen overvoltage (by about 90 mV) in acid solution, but the efficiency of thin-film MoS x catalysts at elevated cathode potentials exceeded that of a thin Pt film.

The effect of pulsed laser annealing (PLA, i.e., action of nanosecond laser pulses in air atmosphere) on surface morphology, structure, chemical state, and electrical properties of thin films consisting of boron and carbon atoms was studied. The nanolayered В/С and mixed ВСx~3 thin film precursors (with a thickness ~110–140 nm) were created on sapphire substrates by using the pulsed laser deposition. Scanning electron microscopy and Raman scattering measurements indicate that the process of stratification of the multilayer B/C films dominated during PLA of the films. The outer layers were removed, and closer to the substrate, the B and C layers were preserved, and they were not mixed. For the mixed ВСх films deposited at elevated temperatures, the PLA treatment enhances ordering of initially amorphous film structure. At the stage of melting of these films, oxygen (from surrounded air) penetrated inside the top layer of the film leading to the formation of a multiphase structure from g-BCx and B-doped GO/rGO after solidification. Studies of the chemical state of elements in the irradiated film have shown that О atoms, which penetrated the under-surface layers of the film, facilitated the formation of new chemical bonds in the B–C–O system. The concentration of O atoms in the depth of the film could reach 8%. The preferential oxidation of boron in a homogeneous mixture of B–C–O atoms indicated that intercalation of carbon matrix could be due to the incorporation of not only O atoms, but also B–O molecules. The laser irradiated ВСх films have a relatively low resistivity (~1.6 mΩ·cm) and semi-metallic dependence on temperature in the range 4.2–300 К. The spatial distribution of conductivity zones after PLA has an irregular structure, and its pattern looks like sand dunes, indicating that the PLA treatment leads to mixing zones of high with those of lower conductivity. The contact-tip resistivity inside the areas of high conductivity of the ВСx/Al2O3 samples may be significantly lower than that of pure graphite.

The results of structural and electrochemical studies of thin Mo-S-P films obtained by pulsed laser deposition at various conditions from a target made of mixture of MoS2 and P powders are presented. For variation of S/P ratio and modification structure of the catalytic films, the deposition of the laser plume was conducted in vacuum, in Ar and H2S gas. The highest electrocatalytic properties for activating the hydrogen evolution reaction in an acid solution were found for composite amorphous/nanocrystalline MoS6P/nc-Mo films. In the chemical stateof S 2p, the high binding energy dominated. The doping of the films with phosphorus increased the efficiency of the reaction compared with that of MoS x /nc-Mo films. The analysis of the synergistic effect of phosphorus on the performance of amorphous MoS x P y films in H2 evolution was carried out using the density functional theory.

It has been found that the pulsed laser deposition of a thin tungsten selenide film, followed by thermal treatment at 550°C in an Ar + O2 mixture of gases, results in the formation of a hybrid structure that is made up of ultrathin WSe2 and WO3–y platelets. The structural and size characteristics of the nanoplatelets deposited on microcrystalline graphite provide the effective hydrogen evolution reaction in a 0.5 M H2SO4 solution, with the cathode current made about seven times higher at a potential of–100 mV and the slope of the Tafel characteristic reduced from 340 to 90 mV/dec.

We demonstrate the possibility of fabricating high-efficiency semiconductor hydrogen detectors based on tangsten-oxide thin films deposited onto silicon-carbide crystals by reactive pulsed-laser deposition. The obtained WO3/SiC structures ensure a noticeable voltage shift ΔU on the reverse branch of the I−V characteristics without commonly used catalyst layers of platinum-group metals. The ΔU value reached 2.1 V at a detected hydrogen concentration of 0.2% in air at 350°C. The response times to hydrogen inlet and recovery of the WO3/SiC structure after hydrogen outlet are found to be much shorter than those for the Pt/WO3/SiC structure. The high performances of the fabricated WO3/SiC sensor are due to the layered structure of the orthorhombic phase of tungsten oxide, which consists of loosely packed microcrystalline plates containing nanocrystals smaller than 100 nm.

The introduction of molybdenum nanoparticles in MoSe x thin films formed by pulsed laser deposition led to changes in the film structure. The base planes of the layered atomic packing of the MoSe х matrix around Mo nanoparticles rotated; as a consequence, the edge sites that formed during the “breaking” of the Se–Mo–Se layered atomic packing came out to the film surface. At high nanoparticle concentrations, this effect led to high density of edge sites possessing increased catalytic activity (compared with that of the base planes) for initiating the electrochemical evolution of hydrogen in a 0.5 M H2SO4 solution. Voltammetric measurements at room temperature showed that when the carbon cathode was coated with MoSe x thin films under optimum conditions, the hydrogen overvoltage considerably decreased, and the cathodic current increased. The results indicate that developments in the field of preparation of nanostructured electrodes based on layered transition metal dichalcogenides show promise as an alternative to expensive electrodes based on platinum group metals for electrocatalysts of hydrogen evolution.

The possibility of obtaining new relatively inexpensive electrode materials to provide enhanced efficiency of hydrogen evolution reaction (HER) in an aqueous acid solution was investigated. For this purpose, the surface properties of cathodes made of microcrystalline graphite were modified by pulsed laser deposition of thin films of WSe x . The structure, morphology, and chemical composition of the thin film coatings were varied by changing the deposition conditions and subsequent heat treatment. The compact and dense structure of the film in an amorphous and crystalline state did not result in a marked positive impact on the character of the HER process, which was investigated in 0.5 M H2SO4 solution at room temperature. Formation of thin layers consisting of nanocrystalline “petals” WSe2 caused an increase in cathodic current by more than 6 times (at a voltage of–150 mV), and the Tafel slope of the voltage vs. current curve was reduced by about 80 mV/dec. The conditions were determined to produce on the surface of the graphite cathode a high density of new catalytically active sites that formed on edges of molecular planes forming a layered structure characteristic of WSe2 nanocrystals.

Features of the expansion of a pulsed laser-initiated plasma-vapor plume containing Se and Watoms in buffer gases of different chemical compositions (Ar and He) is investigated. It is found that gas pressure influences the structure and chemical state of the deposited WSex layers. The conditions for preparing coatings with low coefficients of sliding friction and high wear resistance are determined.

The effect of the nanostructure and chemical composition of thin Mo–Se–C films on the run-in of the diamond-like carbon coating (a-C) and the steel counterbody during ball-on-disk sliding test is studied. At the final stage of the deposition of the a-C coating on the steel substrate, a flow of atoms from the MoSe2 target was added to the flow of atoms being deposited. The influence of the air humidity on the selection of optimum structure and chemical composition of the film, which provide a fairly low (

Pulsed laser irradiation (wavelength 1.06 μm) of a molybdenum diselenide target in vacuum caused the formation of Mo-enriched particles on the surface of the target. Nanoparticles ~ 5–50 nm in size were torn from the target and deposited on the substrate. The use of a buffer gas (argon, pressure 5 Pa) increased the thickness of the shells formed around the nanoparticles and modified the chemical composition of the films. Heating the substrate caused the crystallization of the matrix, such that the basal planes were oriented in a direction parallel to the film surface. The orientation of the planes changed in the shells. The edge sites occurred at the film surface, exhibiting the enhanced catalytic activity in hydrogen evolution reaction. The deposition of MoSex/Mo films in a nanocrystalline state on the carbon electrode caused a decrease in the overvoltage of more than 270 mV, and the lowest Tafel slope was 86 mV/dec.

A method of shadow-masked pulsed laser deposition was applied to obtain W–Se and W–Se–C films using pure argon (Ar) gas and a mixture of Ar and methane, respectively. The gas pressure was varied in a range of 2–10 Pa. The deposition in Ar caused the formation of Se-enriched W–Se films (Se/W ∼ 5) with pronounced surface roughness because of an effective nanoparticle growth. Heating or DC/RF biasing the substrate modified the film composition (Se/W ∼ 1.7–4) and surface smoothing. The use of methane resulted in a doping of W–Se–C films with carbon, and the C concentration was increased to ∼67 at.% under RF biasing of the substrate. The films with smooth surface had high coefficients (∼30%) of light reflection. The formation of nanoparticles and density-graded surface texture decreased the reflectance to 3.8%. Antireflective properties and high area of the rough surface may play an essential role in enhancing the photovoltaic and catalytic properties of W–Se films. Dense structure, smooth surface, optimal Se/W ratio, and preferential sp2-bonding of C atoms promote the high tribological performance of nanocomposite W–Se–C coatings.

The formation conditions of the Pt/WOx/SiC thin-film system on a silicon carbide (6H-SiC) single crystal are optimized. The prepared system possesses stable characteristics and makes it possible to effectively record hydrogen at low concentrations in air at a temperature of ∼350°C, as well as to hold hydrogen in the WOx lattice at room temperature for a long time. The voltage shift of reverse portions of the current–voltage characteristics at a hydrogen concentration of ∼0.2% reach 6.5 V at a current of 0.4 µA because of large series resistance, which is defined by space-charge regions in WOx and SiC. Structural-phase investigations of the oxide layer are performed under various effect modes of the hydrogen-containing medium on the Pt/WOx/SiC system. A correlation in the variations of its electrical properties (ability to accumulate charge and vary the resistivity) and structural state of the oxide layer is revealed. An explanation for the variation in the current transport through the Pt/WOx/SiC and its contact regions (barrier layers) under the effect of hydrogen is proposed.

The requirements are formulated for a new type of nanomaterials based on transition metal dichalcogenides (TMD), which are promising to create relatively cheap and effective catalysts for electrochemical hydrogen evolution reaction. The possibility of implementation of some important requirements for the structure of these materials is investigated by the example of thin-film coatings containing tungsten diselenide and carbon. WSe x /C coatings are prepared via pulsed laser deposition in an inert and reactive (CH4) gas in a standard configuration and using an antidroplet screen. In some cases, low DC voltage or pulsed high-voltage bias are applied to the substrate, initiating ion bombardment of the coatings. Factors exerting an important influence on the chemical composition, morphology, and surface topography of the coatings are established. Modes of formation of a rough coating surface with a high density of WSe2 edges are determined, which is essential for high catalytic activity and performance of TMD-containing nanocatalysts. The carbon phase with a high concentration of sp2 bonds is needed for effective current transport in the formed layers.

Thin-filmed dichalcogenides of transition metals, in particular, MoSe2, are considered as potentially active materials in the hydrogen evolution reaction, which can compete with expensive platinum. It has been established that the laser deposition technique ensures the formation of nanocomposite films containing a high density of Mo nanoparticles in the MoSex shell. Deposition of Mo nanoparticles increase roughness and induce activation of a surface. This manifests itself in formation of “edge” sites in the MoSex shell and on edges of the basis planes in MoSex nanocrystals oriented normally to the film surface. In a 0.5 M H2SO4 solution, on carbon cathodes coated with MoSex films, the hydrogen overvoltage dropped to −0.17 V and the current density doubled.

Shadow-masked pulsed laser deposition (SMPLD) enables the preparation of films that contain none of the droplets that are normally formed in laser irradiation of the target. The platinum (Pt) film produced by SMPLD was studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford backscattering spectroscopy (RBS) of helium ions. The film thickness distribution across the substrate surface took the shape of a simple crater, and the film thickness on the crated “bottom” (center of the shadow area) was approximately 5 times less than that on the “mound” (edge of the shadow area). Monte Carlo collision (MCC) modeling of the laser plume movement during SMPLD was performed to clarify the role of the mask in the formation of the Pt films. The dynamics of the Pt atoms in the laser plume was studied using the vacuum deposition method through a narrow slit onto a rapidly displaced substrate, augmented by RBS measurements of the deposited film thickness along the substrate movement direction. The ionic flux was specifically measured using an ion probe. MСС simulation allowed the changes in the basic parameters of the deposited atom stream to be evaluated with the use of a mask. Comparison of the experimental and calculated distribution of the Pt film indicated that the best correlation was observed using the interpenetration model of the plume and buffer gas (argon, Ar) accompanied by elastic collisions of Pt atoms with the Ar atoms using the variable hard sphere model. Atomic flux models were utilized to imitate the growth of individual Pt crystals using the kinetic Monte Carlo method. In the SMPLD case, the root mean square roughness of the model crystal surface increased by ∼10% and the concentration of vacancies increased by ∼4% compared with the model crystal obtained by pulsed laser deposition (PLD). The surface topography of the experimental Pt films was defined by the nanocrystal nature of their structure. The use of a mask promoted the growth of relatively large nanocrystals and, thus, an increase in the surface roughness in AFM scans on the submicron scale.

The bilayer film Pt/WO x was deposited by pulsed laser ablation on a silicon carbide monocrystal plate (6 H -SiC) to form an H 2 sensor for high temperature application. The study demonstrates high sensitivity of the Pt/WO x /SiC structure to a low H 2 concentration. For 0.2 H 2 % in air at 350 °C, the shift of voltage on the reverse branch of the current-voltage characteristic reached 6.5 V at a current of 0.4 μA. After the high temperature interaction with H 2 , the sample can confine hydrogen atoms in the WO х layer at room temperature for a long time. The study explores the influence of operation conditions as well as the H 2 action on the structure and electrical characteristics of the layers in the system. Phase transformation of the crystalline structure of the WO x film due to hydrogen penetration was detected and this process initiated pronounced electrical properties changes.

To obtain diamond-like carbon (DLC) coatings, a graphite target was exposed to pulsed Nd:YAG laser radiation (1064 nm wavelength) at an energy of 30 mJ. The laser fluence was selected so as to initiate either effective plume ionization (80 J/cm2) or the greatest deposition rate (9 J/cm2). The properties of the coatings at 9 J/cm2 were modified through co-deposition of Ti and W atoms. A time-of-flight method was used to study the laser plume. The deposition rate, density, surface morphology, structure and chemical state of the coatings were studied using Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, micro-Raman spectroscopy, atomic force microscopy, and profilometry. The mechanical and tribological properties of coatings were also studied. Loads of 1 N or 5 N were applied to a steel ball (diameter 3 mm) during ball-on-disk sliding tests; only the greater load caused noticeable wear of the coatings. While an increase in the laser fluence decreased the deposition rate by a factor of approximately 18, it also enhanced the maximum energy of ions and the average energy of atoms. As a result, the DLC coating at 80 J/cm2 had a density (2.45 g/cm3), sp3 content (46%), and hardness (25.4 GPa) 1.1–1.2 times greater than the pure DLC coating at 9 J/cm2. Moreover, the coating at 9 J/cm2 had a rougher surface and microcracks that resulted in pronounced wear of the coating and the counterbody. However, accumulation of wear debris provided for the formation of a low friction tribolayer, so the friction coefficient for this coating was 0.06 or less compared to 0.1 for sliding against the coating obtained at 80 J/cm2. Co-deposition of Ti and W suppressed cracking and provided smooth surface coatings. Both elements caused a decrease in the sp3 content and formed chemical bonds with C atoms. However, the increase in wear resistance was evident only with Ti co-deposition.

We have studied the possibility of controlling important structural characteristics of WSex films, which belong to the class of layered materials and have good prospects for application in modern nano- and optoelectronic devices. It is established that, by using thermal treatment and ion irradiation during pulsed laser deposition (PLD) in the shadow of an antidroplet shield, it is possible to vary the Se/W atomic ratio from 5 to 1.5, change the character of atomic packing, and obtain films with either smooth or rough surfaces. An increase in the height of parabolic protrusions on the surface up to 200–500 nm leads to a decrease in the optical reflection coefficient in a broad wavelength range from 30% (typical of smooth films) to 6%, which can favor a significant increase in the efficiency of solar cells based on semiconductor films of this type.

Nanocomposite thin C-Ti-WSe x coatings, which contain antifriction (WSe x and amorphous carbon a-C) and hard (β-WC and TiC) components, are produced by pulsed laser deposition. In order to improve the tribological characteristics of the WSe x phase and to transform the structural state of the a-C matrix, alloying with titanium is used. The characteristics of the coatings are determined using the sliding of a steel ball at an increased humidity. A comparison of the characteristics of a composite C-Ti-WSe x coating and a carbon coating alloyed with titanium (a-C(Ti)) shows that the modification of the a-C matrix by introducing the WSe x phase leads to an increase in the coefficient of friction from 0.05 to 0.2; the wear of the composite coating is approximately six times higher than that of the a-C(Ti) coating. Possible solutions for improving the tribological characteristics of the composite C-Ti-WSe x coating in humid air are considered.

The results of a comparative study of the electrical properties of gas-sensitive semiconductor structures grown by the pulsed laser deposition of platinum, platinum ion implantation, and a combined method of platinum implantation and deposition onto an n-6H-SiC substrate are presented. Double-layer structures show a stronger response to hydrogen gas with a more pronounced diode behavior of the currentvoltage characteristics at high temperatures of ∼500°C than single-layer ion-implanted structures. Furthermore, double-layer structures exhibit higher reproducibility of the current-voltage characteristic parameters during thermal cycling in a hydrogen-containing medium than ordinary thin-film structures on SiC substrates. The chemical state of ion-implanted platinum and the structure of thin-film layers after long-term testing are studied under harsh conditions. Possible mechanisms of the effect of platinum on the current flow in the ion-implanted layer and its dependence on the composition of the surrounding gaseous medium are considered.

Solid lubricant films were obtained by pulsed laser deposition (PLD) on steel substrates in such a way as to form an underlayer of diamond-like carbon film, and then the concentration of carbon was gradually reduced in Mo–Se–Ni–C films to obtain a pure MoSex(Ni) top layer. The use of a shadow mask configuration (SMPLD) avoids the deposition of micron- and nanometre-sized metallic particles (Ni, Mo), but the SMPLD films were characterised by relatively high Se content, reduced density and low hardness. The tribological properties of the films were evaluated using a ball-on-disk sliding test in humid air after long-term storage in laboratory conditions. For the PLD films, a relatively high friction coefficient was measured during running-in (~ 0.08). The friction coefficient decreased to 0.06 and did not change during the deepening of the wear track. The micro- and nano-particles were embedded into the film matrix during initial running-in and did not cause any apparent acceleration of the wear that was inhibited by the formation of a thick MoSe2 tribolayer on the surface of the wear track. However, an increased wear rate of the counterpart was detected. The smooth surface of SMPLD films provides a low friction at the beginning of the test; then the friction coefficient increased gradually from 0.05 to 0.2 during the film wear, and sufficiently thick low-friction tribolayer was not found. The improved ability of the PLD films to form tribolayers could be due to their structure peculiarity and the relatively low concentration gradient of carbon in these films.

Thin-film precursors of BC x were formed by pulsed laser codeposition of boron and carbon. Targets made of pressed boron and carbon powders with an equal element content (B/C = 1/1) and an increased carbon content (B/C = 1/3) were used. The films were deposited on sapphire substrates at elevated temperature (700°C) which determined the initial properties of the precursor BC x films. Irradiation of the films was carried out by laser pulses of nanosecond duration with varying intensity. The films obtained by laser annealing of BC x (Q-BC x ) were studied by scanning electron microscopy and micro-Raman spectroscopy. Irradiation under optimal conditions made allowed to realize pulsed melting of the films and partial preservation of their continuity on the substrate. The local structure of Q-BC x films and the nature of the changes in their electrophysical properties depended on the composition of the precursor films and the laser irradiation regimes.

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 MoSxfilms and MoOxprecursor films, the atomic flux was formed by laser ablation of Mo, MoS2, and MoO3targets. 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 MoS2films 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 MoOxprecursors in sulphur vapours at higher temperatures (≥ 650°C).

Pulsed laser deposition of WSex films was carried out in a buffer gas (Ar). The mask was placed between a WSe2 target and a substrate in order to prevent the deposition of micro- and nanoparticles. At Ar pressure of 2 Pa the laser plume was effectively scattered by the gas into a shadow area, and the ion bombardment of the film was the most intense. The radial distribution of the W and Se atoms on the substrate was measured, and a significant enrichment of the film by selenium at the center of the shadow area was found. The experimental results were compared with the results of Monte Carlo simulations. A model described the inertial motion of laser-initiated atomic flux bypassing the mask due to collisions of atoms with gas molecules. Model distribution of deposited atoms agreed qualitatively with the experimental data quite well. Some discrepancy could be due to sputtering, re-deposition, and segregation processes. Rutherford backscattering spectroscopy of helium ions, atomic force microscopy, and micro-Raman spectroscopy studies showed that selenium segregated to the surface and formed amorphous nanoparticles. The model predicted an effective bombardment by atoms with energies up to 150 eV which, together with the ion, could stimulate the transport processes in a subsurface layer and on the surface of the films.

A pulsed plasma plume obtained by pulsed laser irradiation of a Pt target was used to fabricate a hydrogen sensor on a 6H–SiC single crystal by means of ion implantation followed by thin film deposition. To realize the ion implantation, high voltage pulses with positive polarity were applied to the Pt target when the laser plasma expanded from the target to the SiC substrate. Experimental diagnostics of pulsed ion beams extracted from laser-produced plasma were performed and the structure of the SiC crystal after high-temperature (500 °C) ion implantation was studied by Rutherford backscattering spectroscopy of 4He+ ions. At the same time, a one-dimensional model of the plasma movement in a pulsed electric field was developed and simulations were carried out using the particle-in-cell method. Modeling allowed determination of the ion energy distribution depending on the delay time of the high voltage pulse after the laser pulse. The calculated energy distribution of Pt ions was used to predict the depth profile of implanted Pt ions in the SiC substrate. The predicted profile agreed sufficiently well with the experimentally measured depth distribution of Pt in the SiC substrate. To characterize the fabricated SiC sensor, the current flow through a barrier structure was studied. The volt–ampere characteristics of the structure were measured in air and in a mixture of air and hydrogen (2%) at a temperature of 500 °C. The characteristic value of the change in voltage exceeded 2 V at the bias current of 1 mA when hydrogen was added to the air. The response of the sensor to the hydrogen was stable after long-term tests while the structure of the Pt film was disturbed. The ion-implanted layer operated as a series resistance, which had a significant effect on the current flow through the barrier structure. The resistance decreased under the influence of hydrogen and persisted during long-term tests.

Thin film, solid lubricating WSex coatings were deposited at room temperature on a steel substrate with a titanium underlayer by pulsed laser deposition (PLD). Two modes of PLD were investigated, i.e., the PLD under vacuum conditions and the PLD in a buffer gas (helium) at a pressure of 2–10 Pa. Gas was used to slow down the laser-induced atomic flux and to modify thus the conditions of the coatings growth. At a pressure ∼8 Pa, gas reduced the effectiveness of Se preferential sputtering by atomic flux, which resulted in the formation of coatings with a stoichiometric composition (x ≈ 2). The structure of the coatings was characterized by a greater degree of the perfect organization of atoms in the nanophase laminar packaging and reduced internal stresses. Studies by the ball-on-disk tests in humid air showed that the modification of the structure and the chemical composition of the coatings had a significant effect on their tribological behavior. Vacuum-deposited coatings fractured relatively quickly due to the cracking and delamination from the substrate surface along the sliding track. When the coatings deposited in helium were tested, wear by layer-by-layer removal was dominant, so the adhesive fracture was only observed in the local parts of the track. The simulation of the laser vapor deposition in the vacuum and in the buffer gas was performed. Likely factors that improve the tribological properties of the coating during deposition in the buffer gas were disclosed.

A multilayer WSe 1.7 / 57 Fe/ 54 Fe structure was created by sequential pulsed laser deposition on a Si substrate of 54 Fe-rich, 57 Fe-rich, and WSe 1.7 thin films subjected to laser plasma ion implantation (LPII). Electric pulses of negative polarity with amplitude 45 kV were applied to the 54 Fe laser target. The turn-on time of the pulse, with a duration of ~10 μs, was varied in the range of 0–9 μs after the laser pulse. Modeling of the LPII was carried out using the particle in the cell method in a one-dimensional approximation. The initial input characteristics of the plasma (velocity, temperature, concentrations of ions) were measured experimentally. The model adequately describes the ion pulses and results in terms of energy distribution of the ions. The LPII regime, providing an efficient implantation of 54 Fe +2 ions with energies up to 90 keV, was used. Before and after LPII the structure was studied by Rutherford backscattering spectroscopy of 4 He + ions and conversion-electron Mossbauer spectroscopy. LPII treatment induced mixing of W, Se and 57 Fe atoms. 57 Fe–Se phases and non-equilibrium 57 Fe–W compound were detected in a local structure of the interface layer. Thus, LPII may be considered as a promising method in combined laser technology, allowing deposition of coatings and modification of the interface, which may provide an enhanced adhesion and improved tribological properties

We have studied factors influencing the formation of particles with the structure of a spherical metal W core inside a WSe2 shell during pulsed laser deposition (PLD) of thin films of tungsten diselenide under variable conditions (buffer gas (Ar) pressure, substrate temperature). It is established that the metal core is formed at the stage of laser ablation of a synthesized WSe2 target, while the shell grows as a result of condensation, migration, and redistribution of atoms during deposition of a laser-initiated atomic flow on the surface of a growing film. Retardation of the atomic flow by a buffer gas at pressures within 2–10 Pa does not ensure activation of the shell condensation process on the metal core in the gas phase. Increasing the substrate temperature from room temperature up to 250°C leads to transformation of the shell structure from amorphous into laminar.