Formation of a surface alloy in the beryllium–tungsten system

The interaction of beryllium and tungsten is investigated by deposition of thin beryllium layers (several nanometers) from the vapor phase onto polycrystalline tungsten substrates and analysis by means of X-ray photoelectron spectroscopy (XPS). Already after room temperature deposition we observe formation of a surface alloy, limited to the interface between the layer and the substrate. The alloy intensity increases continuously between 670 K and 1070 K. The alloy formation is restricted to a depth of 1.2 nm in maximum. Be in excess to this layer thickness desorbs from the sample surface. No Be diffusion or dissolution in the W bulk is observed. Sputter depth profiles before and after annealing experiments in combination with TRIDYN calculations demonstrate that Be is limited to the near-surface area of the tungsten substrate.