Tungsten oxide thin film exposed to low energy He plasma: Evidence for a thermal enhancement of the erosion yield

Nanocrystalline tungsten oxide thin films (about 75 nm in thickness) produced by thermal oxidation of tungsten substrates were exposed to low energy He plasma (≈ 20 eV/He) with a flux of 2.5×10 18 m-2 s-1 at two temperatures: room temperature and 673 K. The structure and morphology modifications which occur after this He bombardment and annealing treatments was studied using Raman spectroscopy and transmission electron microscopy. Due to the low fluence (4×10 21 m-2) and low ion energy, we have observed only few morphology modifications after He plasma exposure at room temperature. On the contrary, at 673 K, a change in the layer color is observed associated to an important erosion. Detailed analyses before/after exposure and before/after annealing allow us to describe the He interaction with the oxide layer, its erosion and structural modification at the atomic and micrometer scale.