Epitaxial (111) Films of Cu, Ni, and Cu$_xNi$_y$ on {\alpha}-Al$_2$O$_3$(0001) for Graphene Growth by Chemical Vapor Deposition

TL;DR

This study evaluates epitaxial (111) textured Cu, Ni, and CuNi films on Al2O3 substrates as substrates for graphene growth via chemical vapor deposition, analyzing their structure, orientation, and impact on graphene quality.

Contribution

It demonstrates the epitaxial growth of (111) textured Cu, Ni, and CuNi films on Al2O3 and investigates their effects on the uniformity of graphene produced.

Findings

All films exhibited (111) texture with 60° in-plane grain orientation differences.

Reactive sputtering of Al improved Ni film orientation significantly.

Graphene on Ni(111) films was more uniform than on polycrystalline Ni/SiO2.

Abstract

Films of (111)-textured Cu, Ni, and Cu$_x$Ni$_y$ were evaluated as substrates for chemical vapor deposition of graphene. A metal thickness of 400 nm to 700 nm was sputtered onto a substrate of $\alpha-$Al$_2$O$_3$(0001) at temperatures of 250 C to 650 C. The films were then annealed at 1000 C in a tube furnace. X-ray and electron backscatter diffraction measurements showed all films have (111) texture but have grains with in-plane orientations differing by $60^{\circ}$. The in-plane epitaxial relationship for all films was $[110]_{metal}$||$[10\bar{1}0]_{{Al}_{2}{O}_{3}}$. Reactive sputtering of Al in O$_2$ before metal deposition resulted in a single in-plane orientation over 97 % of the Ni film but had no significant effect on the Cu grain structure. Transmission electron microscopy showed a clean Ni/Al$_2$O$_3$ interface, confirmed the epitaxial relationship, and showed that formation of the $60^{\circ}$ twin grains was associated with features on the Al$_2$O$_3$ surface. Increasing total pressure and Cu vapor pressure during annealing decreased the roughness of Cu and and Cu$_x$Ni$_y$ films. Graphene grown on the Ni(111) films was more uniform than that grown on polycrystalline Ni/SiO$_2$ films, but still showed thickness variations on a much smaller length scale than the distance between grains.