| AVS 58th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Tuesday Sessions |
| Session GR-TuP |
| Session: | Graphene and Related Materials Focus Topic Poster Session |
| Presenter: | Mi Zhou, University of North Texas |
| Authors: | M. Zhou, University of North Texas F. Pasquale, University of North Texas J. Kelber, University of North Texas A. Boosalis, University of Nebraska - Lincoln M. Schubert, University of Nebraska - Lincoln P.A. Dowben, University of Nebraska - Lincoln |
| Correspondent: | Click to Email |
We report layer-by-layer growth of macroscopically continuous and uniform graphene sheets on Co3O4(111) at 1000 K by carbon molecular beam epitaxy (MBE) from a graphite rod source. The direct growth of graphene on dielectric substrates is an essential step in the practical and scalable production of graphene-based devices. Co3O4(111) films 3 monolayers (ML) thick were formed from surface segregation of dissolved oxygen after deposition ~ 40 Å Co grown on Al2O3(0001) substrates at 750 K in UHV. Epitaxial Co3O4(111) films, as characterized by Auger spectroscopy and LEED, were formed by subsequent annealing to 1000 K in UHV, and exhibit th a O-O surface nearest neighbor distance of 2.8 Å, in good agreement with literature. The evolution of the Auger electron C(KVV) lineshape during carbon MBE indicates sp2 hybridization, and layer-by-layer growth up to at least 3 ML average thickness. LEED spectra indicate that the sp2 (111) graphene overlayer is incommensurate with the Co3O4(111) substrate. The graphene-related diffraction spots remain sharp from a coverage of 0.4 ML up to 3 ML, indicating that the graphene sheets are azimuthally in registry with each other. Exposure of the 3 ML graphene/Co3O4(111)/Co(111) sample to ambient results in no observable change in Auger or LEED spectra, indicating macroscopically continuous graphene sheets. Subsequent acquisition of XPS spectra in a separate chamber yields a graphite-characteristic asymmetric C(1s) peak at 284.9 eV binding energy, indicating graphene → oxide charge transfer, as observed for graphene/SiC and graphene/MgO. A π → π* satellite feature is also observed. Spectroscopic ellipsometry measurements carried out in a separate system confirm the presence of a π → π* resonance, and similarities with the optical absorption of graphene/SiC are observed. Raman spectra acquired at different, macroscopically separated sample areas indicate a uniform 3ML graphene film thickness. These results also strongly suggest that other non-polar (111) transition metal oxide surfaces with similar O-O nearest neighbor distances may act as suitable substrates for graphene growth at moderate temperatures, opening the way to controlled direct growth of high quality graphene on a variety of dielectric substrates, with materials and processing temperatures readily compatible with Si CMOS integration.