Beryllium thin films deposited by thermionic vacuum arc for nuclear applications

Abstract

The aim of this paper is to investigate the influence of the thermionic vacuum arc (TVA) operation parameters (arc current, arc voltage and thermo-emission filament current) on the Be ion energy and plasma ionization degree, as well as on the topological, structural and mechanical properties of Be thin films.For this purpose, nanocrystalline Be thin films, with thickness of approximately 1 μm, were deposited by TVA on not intentionally heated silicon and stainless steel substrates by varying the arc voltage from 0.8 to 2.0 kV. Topological, structural and mechanical (hardness, Young's modulus, adhesion critical loads, and friction coefficient) properties of Be thin films were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), nanoindentation and scratch tests.The mechanical behaviour and structural changes are discussed based on TVA plasma diagnostics results. Be ion energy and plasma ionization degree were measured using cold and emissive probes, energy-resolved mass spectrometer and a quartz crystal microbalance.The preferential crystallographic orientation, morphology and packing density are sensitive to the selected processing parameters which, in turn, control, over a wide range, the plasma ionization degree and Be ion energy. The film deposited using an arc voltage value of 1.5 kV exhibits dense structure with low lattice defect density, high hardness, low coefficient of friction, good wear-resistance, fracture toughness and adhesion to the substrate.