The influence of copper substrate orientation on graphene growth.

摘要

This dissertation is focused on determining the influence of the copper substrate on graphene grown by CVD. Graphene, which can be grown in single atomic layers on copper substrates, has potential applications in future electronic devices. One of the key issues for the use of graphene grown by chemical vapor deposition for device applications is the influence of defects on the transport properties of the graphene. For instance, growth on metal foil substrates results in multi-domain graphene growth because the foil substrates themselves have a variety of different surface terminations. Therefore, they don't serve as a very good template for low defect density graphene growth.;In order to determine whether epitaxial graphene growth by CVD is possible, initial experiments were conducted on a Cu(111) single crystal that was prepared in ultra high vacuum (UHV). The Cu(111) was then transferred to a tube furnace for graphene growth, and characterized with a variety of different techniques. Low Energy Electron Diffraction (LEED) measurements showed that a majority of the graphene domains were in rotational alignment with the underlying Cu(111), suggesting epitaxial growth could be possible. However, the presence of other rotational domains, as well as > 60 nm of topography on the surface, indicated that several unknown factors could be influencing the graphene growth process, possibly during the transfer from UHV to the tube furnace.;To control these unknowns, a custom UHV chamber designed to achieve the growth conditions needed for graphene growth was built. In addition, the chamber was equipped with a LEED so that in-situ characterization could be done. Initial attempts to grow graphene on Cu(100) by first raising the temperature as high as 900 °C and then backfilling the chamber with ethylene pressures up to 5 mTorr resulted in almost no observable graphene growth. However, backfilling the chamber with ethylene before heating the crystal resulted in 2-domain, epitaxial growth on the surface of Cu(100). In addition, the effect of oxygen on the graphene growth process was found to disrupt the nucleation and result in significant amounts of rotational disorder in the graphene. On Cu(111), the growth conditions that led to epitaxial graphene growth on Cu(100) resulted in no observable graphene growth. It was found that annealing the crystal in an ethylene-argon mixture resulted in rotationally aligned epitaxial graphene. Our results indicate that suppressing Cu sublimation is necessary for epitaxial graphene growth on Cu(111).