Oxygen-mediated selection of Cu crystallographic orientation for growth of single-crystalline graphene

Abstract

Grains of a polycrystalline Cu foil (CF) can be recrystallized into Cu(100) or Cu(111) by adequate thermal annealing near the surface melting temperature. However, the thermally driven recrystallization mechanism of CF remains elusive, which is connected to the uncontrollability of the orientation of recrystallized Cu surface. In this study, we ascertained that the unintentional presence of oxygen in CF grains acts a crucial role in determining the crystal orientation of CF. Comprehensive spectroscopic analysis coupled with density functional theory calculation was implemented to explore the correlation between the surface phase transition and the oxygen content of the surface of CFs. After annealing, oxygen-free Cu grains were explicitly recrystallized in the (111) crystal plane by minimizing their surface energy, whereas oxygen-contained Cu grains were recrystallized in the (100) orientation due to the elastic strain energy induced by oxygen. Notably, we arguably accomplished the recrystallized CF with (111) crystal plane can be transformed into a single crystal (111) CF by utilizing rationally designed cyclic heat treatment (CHT), however Cu(100) grains were not merged into a single crystal (100) CF presumably due to the presence of residual oxygen. We accomplished the synthesis of defect-less, continuous monolayer graphene on a single crystal (111) CF.