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The initial stages of formation of VN-Ar/He nanocrystalline thin films that were obtained using ion beamassisted deposition technology have been investigated. It has been shown that the vanadium deposition accompanied by mixed inert and reactive gas beam bombardment leads to the formation of a nanoporous structure. The electron microscopic data and computer simulation results prove that many different processes take place during film structure nucleation, in particular, metal atom deposition, gas-vacancy cluster formation, and their migration, growth and collapse with gas release. As a result, vacant and gas-filled pores with a diameter of 5-50 nm were created.

Vanadium or its alloy-based hydrides are intensively studied at the moment with regard to their use as hydrogen absorbents. Most experiments were carried out using "bulk" materials. This paper uses ion beam-assisted deposition technology (IBAD) to create thin-film nanocrystalline VNx-Hy hydrogen storages. The transmission electron microscopy and scanning electron microscopy were used to study the initial stages of the film formation. The main mechanisms of the formation of intergranular pores in nanogranular structures have been established. The interrelation of the parameters of the IBAD and those of film structure has been shown. The obtained data allowed for the explanation of the mechanisms of hydrogen absorption and desorption by thin films. It was shown that the availability of branched network of intergranular pores allows VNx-Hy structures to accumulate hydrogen within a few minutes at a pressure of 0.5 MPa. Hydrogen in amount of up to 2.55 wt% is retained in the films of 3 μm thick at room temperature and atmospheric pressure. The hydrogen desorption starts at 100˚C.

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