Nanoscale ring with diameter ranging from 70 nm 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 of 600 $^{\circ}$C to 700 $^{\circ}$C. The copper film was deposited on SrTiO$_3$ under ultra-high vacuum condition at room temperature. X-ray photoelectron spectroscopy measurements showed that cupric CuO oxide formed and that the amount of copper left on the surface decreased significantly due to the lack of thermodynamic stability of CuO. Atomic force microscopy showed that the surface morphological state changes significantly during plasma exposure and that, in addition to rings, dots have also formed at later stages of film exposure to the plasma. Theoretical analysis of the initial growth stage showed that the ring morphology arised due to stress-driven surface diffusion induced by gradients of strain associated with localized random perturbation arising due to nonuniform evaporation. Analysis of the ring growth dynamics also revealed that sublimation suppresses the growth of ring morphology except within a finite band of wavelength of growing surface perturbations.
Revised: June 29, 2011 |
Published: November 1, 2003
Citation
El-Azab A., and Y. Liang. 2003.Nanoscale copper oxide ring structure on a SrTiO3 substrate.Philosophical Magazine. Structure and Properties of Condensed Matter 83, no. 31-34:3847-3869.PNNL-SA-37154.