Nanoscale copper oxide ring structure on an SrTiO₃ substrate

Abstract

Nanoscale rings with diameters ranging from 70 to 120 nm and densities of up to 10 ⁹ cm⁻² have been observed on the surface of a thin copper film during processing by oxygen plasma at temperatures in the range from 600 to 700°C. The copper film was deposited on SrTiO₃ under ultra-high-vacuum conditions at room temperature. The structural and chemical behaviours of the surface have been investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS showed that cupric oxide formed and that the amount of copper left on the surface decreased significantly. AFM showed that self-assembled rings formed at later stages of the process. Theoretical analysis of the initial growth stage showed that the ring morphology arose owing to surface diffusion induced by the elastic strain gradient at the film surface. Analysis of the ring growth dynamics also revealed that sublimation suppresses the growth of the ring morphology except within a finite-wavelength band of growing perturbations.

Acknowledgements

This work was supported by laboratory-directed research and development funding at the Pacific Northwest National Laboratory. The work was performed in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the US Department of Energy's Office of Biological and Environmental Research. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. The authors wish to thank Scott Lee and Don Baer for a useful discussion of the data.

Notes

‡ Email: [email protected].

Additional information

Notes on contributors

Yong Liang‡

‡ Email: [email protected].