Optimal conditions for gas cluster ion beams in studying inorganic interface species: improved chemical information at a ZnO interface

We have observed for the first time a subtle chemical change in the oxidation state of Zn at the interface between a ZnO thin film and a glass substrate using gas cluster ion beam (GCIB) depth-profiling. A combination of monoatomic and gas clusters was used for etching, allowing the removal of the surface rapidly using the monoatomic ion beam yet still yield a less damaged surface by removing the damaged layer using the argon GCIB as a final step. With this combined method, the depth-profile shows the transition of Zn from oxide to metal at the interface, which the monoatomic ion source if used alone would damage. This data indicates that the initial layers of the film did not undergo as much oxidation during the deposition compared with the rest of the film; therefore, metallic zinc resulted at the interface. We also examined the ZnO thin film under a range of conditions of argon ion profiling from monoatomic to cluster ions to study the most efficient method for depth-profiling of multiple layers of inorganic materials. The monoatomic ion beam does not show the transition phenomena at the interface, which was observed in cluster depth-profiling, probably because of atomic mixing effects. This suggests that care be taken in selection of etch parameters when studying interfaces. We recommend the combination of monoatomic sputtering followed by GCIB etching as the most efficient method for looking at interfaces of inorganic thin layers from the point of view of time taken and minimising damage at interface. Copyright © 2016 John Wiley & Sons, Ltd.