Wafer-scale development, characterization, and high temperature stabilization of epitaxial Cr2O3 films grown on Ru(0001).

This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5-20 nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4 mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru-Cr2O3-Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions.

Experimental and Computational Study of the Orientation Dependence of Single-Crystal Ruthenium Nanowire Stability.

Single-crystal nanowires are of broad interest for applications in nanotechnology. However, such wires are subject to both the Rayleigh-Plateau instability and an ovulation process that are expected to lead to their break up into particle arrays. Single crystal Ru nanowires were fabricated with axes lying along different crystallographic orientations. Wires bound by equilibrium facets along their length did not break up through either a Rayleigh-Plateau or ovulation process, while wires with other orientations broke up through a combination of both. Mechanistic insight is provided using a level-set simulation that accounts for strongly anisotropic surface energies, providing a framework for design of morphologically stable nanostructures.