| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Monday Sessions |
| Session GR+EM+NS+PS+SS+TF-MoM |
| Session: | Growth of 2D Materials |
| Presenter: | Z. Robinson, U.S. Naval Research Laboratory |
| Authors: | Z. Robinson, U.S. Naval Research Laboratory G.G. Jernigan, U.S. Naval Research Laboratory K. Bussmann, U.S. Naval Research Laboratory R.L. Myers-Ward, U.S. Naval Research Laboratory V.D. Wheeler, U.S. Naval Research Laboratory L.O. Nyakiti, U.S. Naval Research Laboratory S. Oida, IBM T.J. Watson Research Center J. Hannon, IBM T.J. Watson Research Center M. Currie, U.S. Naval Research Laboratory C. Eddy, U.S. Naval Research Laboratory D.K. Gaskill, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
Graphene growth on Si-face SiC has been shown to have improved uniformity when synthesized in an argon environment instead of in UHV. For C-face growth, which is expected to yield graphene with superior electronic properties due to the absence of the interfacial layer, similar progress has not yet been achieved. It has been shown that growth by confinement controlled sublimation, where the C-face SiC is put in a graphite pillbox during growth, can result in improved quality graphene films. However, it remains unclear whether growth by low pressure sublimation (LPS) in a conventional furnace with an argon overpressure can achieve uniformity and thickness control similar to the Si-face. Therefore, a systematic study of SiC surface preparation by hydrogen etching and subsequent graphene growth in argon has been carried out for C-face SiC substrates in a commercially available Aixtron CVD reactor that has been modified for LPS. This reactor exhibits laminar Ar flow and a uniform temperature profile. In this system, which has the advantage of being able to subject different substrates to identical growth conditions simultaneously, it has been found that relatively small differences in the substrate, such as polytype, can have a drastic effect on the resulting graphene film. In fact, growth conditions that result in complete coverage of at least a single layer of graphene on a nominally on-axis 4H substrate have been shown to result in 60% coverage for a nominally on-axis 6H substrate. Therefore, it has been found that optimizing the growth conditions for a particular substrate is crucial if graphene thickness and uniformity are to be controlled. Additionally, it has been suggested that unintentional oxidation of the SiC substrate during growth in high pressures of argon is a potential cause for the non-uniform growth that is observed on the C-face [1]. Several experiments in which LPS grown C-face graphene was transferred to a UHV system equipped with in situ XPS have been conducted, and it has been found that UHV anneals of up to 1200 °C were necessary in order to desorb the oxygen. Following the anneal, exposure to atmospheric conditions resulted in the return of only ~20% of the original oxygen concentration. This suggests that a robust oxide which is stable at high temperature may be influencing the graphene growth process. A detailed LEED, LEEM and STM study has been initiated to determine the effect that this oxygen has on the graphene film’s properties and new results will be presented.
References:
[1] L. Srivastava, G. He et al., Phys. Rev. B 82, 235406 (2010)