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A thorough study was made of the processes determining the formation of metastable surface alloys in a film-substrate system irradiated by laser pulses of nanosecond duration. The experiments of irradiation of the same systems through transparent overlays have demonstrated a marked change in the pattern of processes that are alloying atoms efficiently penetrate from the film into the substrate, the depth of alloying increases to 400 nm, and defects are formed in deep layers of the substrate.

Abstract: MoSe x 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 MoSe x 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 MoSe x 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 MoSe x 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. [Copyright &y& Elsevier]

Highlights: [•] WSe x films (x >2) were prepared by pulsed laser deposition using shadow mask. [•] Excess selenium segregated to the surface and formed amorphous nanoparticles. [•] Distributions of W and Se atoms over the substrate were measured and simulated. [•] Model and experimental discrepancies could be due to Se redeposition and segregation. [•] Effective bombardment of a shadow substrate area by high energy atoms was predicted. [Copyright &y& Elsevier]

Highlights: [•] WSe1.7/57Fe/54Fe multilayer structure was created by laser plasma ion implantation. [•] Experimental diagnostics and modeling of ion treatment were performed. [•] Modeling was carried out using a particle-in-cell method in 1D approximation. [•] Mossbauer studies indicated formation of Fe–Se, and Fe–W phases after treatment. [ABSTRACT FROM AUTHOR]

Abstract: WSe x thin films were obtained by pulsed laser deposition in vacuum and at various Ar gas pressures up to 10Pa. 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 2–10Pa 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 WSe2.2 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. [Copyright &y& Elsevier]