Effective depth of electronic sputtering of WO3 films by high-energy ions

We have measured the electronic sputtering yields of WO3 as a function of the film thickness. WO3 films have been prepared by thermal oxidation of W deposited on MgO substrate and the film thickness is obtained by Rutherford backscattering spectrometry (RBS). It is found that the electronic sputtering yields by 100 MeV Xe and 90 MeV Ni ions steeply increase with increasing the film thickness and the yields reach the maximum value of 2.4 × 104 and 4.7 × 103 at the film thickness (effective depth contributing to the sputtering) of 40 nm for both ions. Assuming that cylindrical volume is eroded, the effective radius is obtained to be 1.6 and 0.7 nm, respectively. One of the mechanisms for the electronic excitation effect, the exciton model will be examined.