Search

Bi-layer W–Se–C/diamond-like carbon (DLC) and WSex/DLC coatings were obtained by standard and shadow-masked pulsed laser co-deposition from WSe2 and graphite targets. W–Se–C coatings appeared as nanocomposites containing quasi-amorphous WSe2, WC, spherical β-W nanocrystalline particles encapsulated in WSe2 amorphous shell, and amorphous carbon phases. In WSex/DLC coatings, the formation of chemical bonds between W and C atoms was noticed at the interface. An increase of the C concentration over 40 at.% increases hardness and elasticity (up to 2 times at ~ 60 at.%C), and the Se/W ratio was always close to 1.4. The use of shadow-masked configuration avoids the deposition of micro- and nanoparticles. However, this method leads to a substantial increase of the Se content (Se/W ≥ 4), and the coatings became softer.

Thin film Mo–Se–Ni–C coatings for tribologycal applications were prepared by pulsed laser co-deposition from two targets — MoSe 2 (Ni) and graphite. Two methods of deposition from the MoSe 2 (Ni) target were used: deposition with unhindered expansion of the laser plume (standard PLD) and deposition of a plume scattered in collisions with Ar gas (pressure 2 Pa) in the shadow of a mask (shadow-masked PLD — SMPLD). Doping with carbon by PLD was used in all cases, and carbon content in the composite Mo–Se–Ni–C coatings was varied in the range 35–85.5 at.%. Pure MoSe x (Ni) coatings were also prepared by PLD and SMPLD. Rutherford backscattering spectroscopy of helium ions, scanning electron and atomic force microscopy, electron probe microanalysis, transmission electron microscopy and micro-diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy and hardness evaluation were all used for comparative studies of the coatings obtained by PLD and SMPLD/PLD. In the PLD coatings, micron-sized particles were found, consisting of pure Ni or MoSe 2 , as well as nanometre-sized particles of monocrystalline Mo. The nanoparticles were distributed on the surface and in an amorphous matrix in all PLD coatings. Within the amorphous matrix of the Mo–Se–Ni–C coatings, local ordering of atoms was detected, causing the formation of a mixture of amorphous carbon, Mo–C, and Mo–Se phases. Increasing the carbon content caused an increase in the content of sp 3 bonds in the carbon phase, and an increase in the hardness of the coatings. SMPLD/PLD coatings had no micro- and nanoparticles, but these coatings were characterized by high selenium content and reduced density. Doping with carbon in the SMPLD/PLD configuration caused the formation of composite coatings containing Mo–Se and amorphous carbon phases as in the PLD coatings, but the hardness of the composite SMPLD/PLD coatings was significantly lower than even the hardness of the pure PLD MoSe x (Ni) coatings.

WSe x thin films were obtained by pulsed laser deposition in vacuum and at various Ar gas pressures up to 10 Pa. Stoichiometry and chemical state of the WSe x films were studied by means of Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. In the case of pulsed laser deposition of WSe x films in vacuum the value of stoichiometric coefficient x was 1.3. During the deposition in argon at pressures of 2–10 Pa the value of x varied from 1.5 to 2.2. To explain the influence of the buffer gas, a model was used that takes into account the following processes: (1) congruent pulsed laser evaporation of the WSe 2.2 target; (2) scattering of laser-evaporated W and Se atoms in Ar; (3) sputtering of the deposited film by high-energy atoms from the laser plume. Experimentally, the velocity distributions of laser-evaporated W and Se atoms in vacuum were determined by the time-of-flight measurements. Collision Monte Carlo simulations were used to quantify the impact of the buffer gas on the energy and the incidence angle distributions of the deposited W and Se atoms. Model distributions were used to determine the chemical composition of the WSe x films, depending on the efficiency of the preferential sputtering of Se atoms.

The formation of the chemical composition of dichalcogenide films at pulsed laser deposition in vacuum and in rarefied gases (Ar, H2 ) is investigated with MoSe x thinfilm coatings. It is found that deposi� tion in gases increases the selenium concentration and somewhat flattens the composition over the substrate surface. To elucidate the mechanisms underlying the MoSex film formation, a computer model is used that simulates the motion of a pulsed laserinitiated atomic flux through a rarefied gaseous medium. Using this model, the energy and angular parameters of atomic Mo and Se fluxes toward the substrate are calculated. It is shown that the expansion dynamics of laser plume components (Mo and Se) and the selective sputtering of selenium are the main factors governing the formation of the chemical composition and its distribution over the substrate. The influence of the sort of gas on the efficiency of atomic flux slowdown and scattering and on material losses during deposition is considered.

The chemical composition and tribological properties of the thin-film diselenide molybdenum coatings deposited by pulsed laser deposition in vacuum and a rarefied inert gas (argon) atmosphere are studied. Upon deposition in a gas at a pressure of ∼2 Pa, stoichiometric coatings with improved antifriction properties as compared vacuum-deposited coatings form. However, a too strong increase in the argon pressure (to ∼10 Pa) degrades the tribological properties of the coating. Structure formation in the MoSe x coatings grown by pulsed laser deposition on an unheated substrate is investigated. Deposition in vacuum or argon at a pressure of 2 Pa leads to formation of rather smooth coatings with a dense amorphous structure containing molybdenum nanoinclusions. Deposition at a high argon pressure results in a developed surface relief and a loose coating structure. A mathematical model is developed using the kinetic Monte Carlo method in order to describe structure formation in the coatings that grow during physical deposition of an atomic flux. A comparative analysis demonstrates satisfactory agreement between the simulated and experimentally studied structures in the coatings created by pulsed laser deposition at various gas pressures.

The present work considers simulation of contact area formation using the contact models of Hertz, DMT and JKR. The purpose of this work was to study development of real contact between rough surfaces taking into account the action of adhesion. The model of the Winkler foundation is used to describe the elastic properties of the rough surface. Solids with thin hard coatings were used as test specimens. The surface topography was measured with typical AFM at different scale levels. The data on the specific surface energy of specimens are obtained with contact adhesion meter developed in MPRI (Gomel, Belarus). The obtained value of specific surface energy was used in computer simulations of real contact using the AFM images.

MoSex coatings were obtained by pulsed laser deposition in vacuum at the pressure of background Ar gas up to 10 Pa. The deposition temperature was 200 °С. The films were studied by means of X-ray diffraction, scanning and transmission electron spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy of helium ions. The tribological properties of thin-film coatings were investigated by pin-on-disk testing in air with 50% relative humidity. In addition, wear tracks were studied by micro-Raman spectroscopy. Chemical composition, structure, and tribological properties of the coatings were found to be sensitive to the presence of the inert gas. Thus, increasing the gas pressure from 10− 4 to 10 Pa changes the chemical composition, so that the ratio of the atomic concentrations of Se and Mo (x = Se/Mo) increases from 1.5 to 2.4 in the principal deposition zone. The changing of the structure concerns the accumulation of distortions in the lattice of MoSex nano-crystals as increasing the distance between the basal planes and intensive formation of nano-sized inclusions of the amorphous phase and Mo nano-crystals in the volume of the coatings. At the optimal gas pressure (∼ 2 Pa), the composition of the coating was close to the stoichiometric one, and the layer adjacent to the substrate consisted of MoSex nano-crystals with the basal planes parallel to the substrate surface or oriented at small angles to the surface. The thickness of the oriented layer in such coatings was greater than the thickness of the similar layer in the coatings deposited in vacuum (10− 4 Pa). The tribological properties of MoSex coatings deposited on substrates of stainless steel type 95 × 18 (18 at.% Cr) depend on the gas pressure. The friction coefficient in air decreases from 0.08 for deposition at the background pressure of 10− 4 Pa to 0.04 for deposition at the optimal pressure. This change in the deposition conditions has only a marginal effect on the coating durability. Means to increase the durability are also considered.

Experiments on pulsed laser deposition of Fe films on Si substrates were performed with the aim to analyze the role of factors determining the formation of an energy spectrum and a dose of ions bombarding the film in strong pulsed electric fields. The amplitude of the high-voltage pulse (−40kV) applied to the substrate and the laser fluence at the Fe target were fixed during the deposition. Owing to the high laser fluence (8J∕cm2) at a relatively low power (20mJ), the ionization of the laser plume was high, but the Fe vapor pressure near the substrate was low enough to avoid arcing. Electric signals from a target exposed to laser radiation were measured under different conditions (at different delay times) of application of electric pulses. The Si(100) substrates were analyzed using Rutherford ion backscattering∕channeling spectrometry. The ion implantation dose occurred to be the highest if the high-voltage pulse was applied at a moment of time when the ion component of the plume approached the substrate...

The tribological performance and tribochemistry of both single-layer WSex(Ni) and bilayer WSex(Ni)/diamond-like carbon coatings formed on steel substrates by pulsed laser deposition are evaluated. The ball-on-disk tests of the coatings in air show that at a laser fluence of ∼100 J cm−2 and a partial pressure of argon ∼2 Pa, the endurance of the top WSex(Ni) film in the bilayer coating is nearly four times greater than for single-layer WSex(Ni) film. For the top WSe2(Ni) layer 170 nm thick, deposited onto DLC coating 200 nm, the coating friction coefficient was kept 0.03–0.09 during nearly 2 × 104 cycles.

WSe x coatings were obtained by pulsed laser deposition (PLD) and ion-assisted PLD. The films were studied by means of X-ray diffraction, scanning and transmission electron microscopy, Auger electron spectroscopy and energy-dispersive X-ray spectroscopy. The WSe x films were also characterized in terms of their hardness, elastic modulus, surface topography and wear performance. The structure of WSe x films was shown to consist of various nanocrystalline mixtures of WSe 2 and W 3 O phases in an amorphous WSe x matrix. Depending on deposition conditions, the WSe 2 crystallites were oriented with their basal planes either parallel or perpendicular to the substrate surface. A correlation between an amount of W 3 O phase and c -axis-oriented WSe 2 phase was outlined. The incorporation of oxygen atoms between the basal planes was shown to cause lattice distortion and resulted in anisotropy of the lattice parameter. Improved endurance of WSe x coatings was due to their composite structure. The presence of hard underlayer, such as TiC, TiCN or TiSiN, was shown to be essential for extremely low friction coefficients down to 0.015–0.03. The WSe x /TiC films showed low friction from the very start of the tests without initial maximum. The superior performance of WSe x /TiSiN coatings both in air and under water suggests that the double-layer coatings are suitable for use in terrestrial tribological applications.

A thorough study was made of the processes determining the formation of metastable surface alloys in a film–substrate system [using Au(110 nm)–Ni and Sn(40 nm)–Cr systems as an example] irradiated by laser pulses of nanosecond duration. The irradiation was performed in conventional conditions (in air) and, following the applied method, through a transparent overlay. Scanning/transmission electron microscopy and Rutherford backscattering spectroscopy investigations of alloys were complemented by the measurements of acoustic signals initiated by laser pulses in the substrate. It has been ascertained that the alloy formation in air is accompanied by two competitive processes: laser sputtering of the film substance and its diffusion into the molten substrate layer. As the irradiation intensity goes up, the hydrodynamical sputtering mechanism is replaced by the atomic vaporization. As a result, sufficiently high vapor pressure (up to 102 bar) is generated above the film surface, the film is pressed to the subs...

The thickness profiles and compositional distributions of MoSx films deposited from a plume generated by pulsed laser irradiation of the MoS2 target were investigated at a varying fluence and constant laser pulse energy. It was shown that films with stoichiometric composition were formed at sufficiently low fluence (near the ionization threshold), and increasing fluence caused intricate nonmonotonic variations of the compositional distribution. A substantial deviation of the film composition from stoichiometric and a significant radial gradient of the sulfur concentration over the substrate surface (1

The work deals with the study of the influence of combined action of thermomechanical and laser treatments of rapidly quenched TiNiCu thin ribbons on the properties of two-way shape memory effect. It was shown that increasing of the energy density of the laser radiation and the external mechanical stress leads to growth of the reversible strain of the received amorphous-crystalline composite in the interval of martensitic transformation.

A combination of low-pressure mercury lamp radiation-assisted processes for removal of carbon contaminants from the silicon substrate, SiO 2 chemical vapor deposition (CVD) from an Si 2 H 6 /O 2 mixture, and annealing of the deposited layers has been employed to fabricate dielectric-semiconductor structures with sufficiently good properties at low temperature (250°C) using gas-phase techniques only.

The influence of a buffer (inert) gas atmosphere on structure, composition and tribological properties of MoSx films formed by pulsed laser deposition with various laser influence was investigated. The films were deposited at room temperature from an MoS1.8 target under vacuum conditions (4 × 10-4 Pa) and in Ar atmosphere at a gas pressure varying from 0.7 Pa to 4 Pa. Ablation under vacuum conditions using a relatively low laser fluence resulted in the deposition of amorphous films with conservation of stoichiometry. According to XPS analysis data, such films may contain many defects of chemical nature. Deposition at higher laser fluences resulted in substantial sulphur depletion and, under certain conditions, crystallization of the films. These microcrystalline films exhibited a lower friction coefficient than amorphous ones. Ablation at high laser fluences in Ar atmosphere allowed us to deposit MoSx films with various stoichiometries (x ⩽ 2.2) and tribological properties superior to those of the films deposited under vacuum conditions. These films have the amorphous structure and chemistry (according to XPS measurements) inherent in perfect MoS2.

A relatively simple technique of high-energy ion implantation of the pulsed laser plasma under the influence of an external pulsed electric field is suggested. The developed mathematical model allows forecasting depth distribution of implanted atoms on the basis of experimental measurements of fundamental physical characteristics of the pulsed laser plasma and the technical parameters of high-voltage system. The possibility of implantation of platinum ions from laser plasma to create on-chip n-SiC hydrogen sensor for use in complicated conditions is demonstrated.

Peculiarities of WO x films fabrication by reactive pulsed laser deposition for high temperature Pt-oxide-SiC devices formation were investigated. Deposition of the oxide film was also carried out in such a way as to prevent deposition of droplet fraction (deposition with anti-droplet screen). Direct Simulation Monte Carlo and Kinetic Monte Carlo methods were performed for the deposition processes modeling. The response of the SiC-based devices to hydrogen-containing gases depends on the conditions of deposition of the oxide layer. The best properties were found in the sensor obtained by depositing the scattered flux of W atoms in a shady area on SiC substrate at an oxygen pressure of 10 Pa.

Physical, chemical and tribological properties of the MoSex and MoSe x C y coatings for micromechanical applications grown by pulsed laser deposition in vacuum and in a rarefied inert gas (argon) atmosphere are studied. In a number of experiments a disk-shaped screen was used that is placed on the path of the expansion of laser plume in order to trap the droplet fraction. Upon deposition in a gas at a pressure of ~2 Pa, stoichiometric MoSe 2 coatings with improved antifriction properties as compared vacuum-deposited MoSe x (x

The effect of pulsed laser radiation (λ = 248 nm, τ = 20 ns) on structural properties and shape memory behavior of the rapidly quenched Ti50Ni25Cu25 alloy ribbon was studied. The radiation energy density was varied from 2 to 20 mJ mm−2. The samples were characterized by means of scanning electron microscopy, x-ray diffraction, microhardness measurements and shape memory bending tests. It was ascertained that the action of the laser radiation leads to the formation of a structural composite material due to amorphization or martensite modification in the surface layer of the ribbon. Two methods are proposed which allow one to generate the pronounced two-way shape memory effect (TWSME) in a local area of the ribbon by using only a single pulse of the laser radiation. With increasing energy density of laser treatment, the magnitude of the reversible angular displacement with realization of the TWSME increases. The developed techniques can be used for the creation of various micromechanical devices.

Using in situ x‐ray photoelectron spectroscopy we have investigated the possibility of photochemical organic contaminant removal from a silicon surface at room temperature in oxygen and fluorine containing atmospheres (O2, NF3/H 2, O2/NF3/H2). In contrast to UV irradiation in O2 and NF3/H2 reagents, the possibility of complete organic contaminant removal has been observed in O2/NF3/H2 gas mixture.