Giant Secondary Grain Growth in Cu Films on Sapphire

TL;DR

This paper presents a novel method for producing large single-crystal copper films on sapphire substrates through sputter deposition and annealing, enabling high-quality graphene growth.

Contribution

It introduces a new approach combining sputter deposition and annealing to achieve giant grain growth in copper films on sapphire, differing from traditional high-temperature epitaxial methods.

Findings

Polycrystalline Cu can be transformed into large-grain Cu(111) films.

Giant grains of centimeter size are achieved after annealing.

Epitaxial graphene with 0.2 mm grains is grown on these films.

Abstract

Single crystal metal films on insulating substrates are attractive for microelectronics and other applications, but they are difficult to achieve on macroscopic length scales. The conventional approach to obtaining such films is epitaxial growth at high temperature using slow deposition in ultrahigh vacuum conditions. Here we describe a different approach: sputter deposition at modest temperatures followed by annealing to induce secondary grain growth. We show that polycrystalline as-deposited Cu on \alpha-Al2O3(0001) can be transformed into Cu(111) with centimeter-sized grains. Employing optical microscopy, x-ray diffraction, and electron backscatter diffraction to characterize the films before and after annealing, we find a particular as-deposited grain structure that promotes the growth of giant grains upon annealing. To demonstrate one potential application of such films, we grow graphene by chemical vapor deposition on wafers of annealed Cu and obtain epitaxial graphene grains of 0.2 mm diameter.