Investigation of the physical and chemical interaction of a low energy oxygen ion beam with oxide superconducting films

The mono-valent O+ ion is chemically highly reactive and when accelerated to 10s of electron volts it gains significant kinetic energy. We investigated the effect this species has on the surface of superconducting thin films in ultra high vacuum. We followed the interactions using an atomic force microscope, reflection high energy electron diffraction and X-ray diffraction. Using acceleration energies between 20 and 200 eV and comparing the effect of O+ and Ar+ ion beams, we were able to differentiate the chemical and physical effects induced by the O+ ion. We found that O+ improves the smoothness of the surface, but degrades the bulk properties of the films. Above 50 eV physical sputtering leading to a reduction in surface roughness was found to dominate. In the absence of the ion beam at 400°C, rectangular precipitates up to 50A˚in height were found to grow on the surface of these films. The O+ ion beam inhibits the chemical reaction causing these precipitates. Also the O+ ion beam caused significant expansion of thec-axislattice parameter of the films, greater then that expected for just oxygen loss. In all these cases the superconducting properties were lost.