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This review summarizes results of our study of the application of ion-beam assisted deposition (IBAD) technology for creation of nanoporous thin-film structures that can absorb more than 6 wt.% of hydrogen. Data of mathematical modeling are presented highlighting the structure formation and component creation of the films during their deposition at the time of simultaneous bombardment by mixed beam of nitrogen and helium ions with energy of 30 keV. Results of high-resolution transmission electron microscopy revealed that VNxfilms consist of 150–200 nm particles, boundaries of which contain nanopores of 10–15 nm diameters. Particles themselves consist of randomly oriented 10–20 nm nanograins. Grain boundaries also contain nanopores (3–8 nm). Examination of the absorption characteristics of VNx, TiNx, and(V,Ti)Nxfilms showed that the amount of absorbed hydrogen depends very little on the chemical composition of films, but it is determined by the structure pore. The amount of absorbed hydrogen at 0.3 MPa and 20°C is 6-7 wt.%, whereas the bulk of hydrogen is accumulated in the grain boundaries and pores. Films begin to release hydrogen even at 50°C, and it is desorbed completely at the temperature range of 50–250°C. It was found that the electrical resistance of films during the hydrogen desorption increases 104times.

Abstract. Vanadium and its alloy-based hydrides are extensively studied with regard to their use as hydrogen absorbents. The ion beam-assisted deposition method (IBAD) used for nanocrystalline VN x -H y thin-film hydrogen storages production is analyzed. The data of transmission and scanning electron microscopic studies of all stages of the film formation are considered. The main mechanisms of intergranular pores formation in nanograin structures have been established. The relation between the parameters of the ion beam-assisted deposition and those of film structure has been shown. The obtained data provide the explanation of the mechanisms of hydrogen absorption and desorption by thin films. It was suggested that the availability of branched network of intergranular pores allows accumulating the hydrogen by VN x -H y nano structures in large quantities and release it at the temperatures less than 275°C.Keywords: Nanocrystalline structures; hydrogen; storage; thin films; ion-beam assisted deposition. IntroductionVacuum deposition techniques, such as magnetron sputtering, physical and chemical vapor deposition, have been successfully used for thin films deposition for a long time. A characteristic feature of these techniques is that the resulting structures are formed under less than equilibrium conditions allowing the creation of materials with unique properties. B. Movchan and A.Dymchishin in 1969 [1] have shown the substrate temperature influence on the structure of Ti, Ni, W, ZrO 2 , and Al 2 O 3 films. Evaporation of the substances was carried out by the electron beam heating of the crucible. Three temperature zones with boundary temperatures T 1 and T 2 , that are respectively equal to 0.3 and 0.45 ... 0.5 of T m for metals, 0.22 ...0.26 and 0.45 ... 0.5 of T m for oxides were determined. The films with certain structure and properties have been formed inside each of these zones. These studies marked the beginning of the so-called structure zone model (SZM). Later J. Thornton [2] took into account the effect of the gas environment on the film structure additionally to the influence of the substrate temperature. It was shown that the film formation mechanism during ion bombardment was fundamentally changed not only by substrate temperature but also by pressure of the working gas (argon). Effect of the reactive gas (oxygen) on the formation of the microstructure of thermally evaporated metal (in that case, aluminum) has been studied in detail by P. Barna and M. Adamik [3]. Oxygen adsorbed on the surface during deposition reduces the mobility of grain nucleating centers and inhibits their coalescence. It results in the breaking of the columnar structure and nucleation of the grains with different texture. Eventually, at a high concentration of oxygen molecules, formation of aluminum oxide matrix with metallic inclusions is observed.The substrate temperature and gas concentration influence the formation of the film structure only at the initial stage. At this stage, the density of nucleation centers is determ...

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