| AVS 56th International Symposium & Exhibition | |
| Graphene Topical Conference | Tuesday Sessions |
| Session GR+EM+MS-TuM |
| Session: | Graphene and Carbon-based Electronics |
| Presenter: | H. Hirayama, Tokyo Institute of Technology, Japan |
| Authors: | Y. Aoki, Tokyo Institute of Technology, Japan H. Hirayama, Tokyo Institute of Technology, Japan |
| Correspondent: | Click to Email |
Recently, adsorption of a small amount of atomic hydrogen was reported to transform the exfoliated graphene from highly conductive semimetal into an insulator [1]. In this case, the C-atom is only the site for hydrogen adsorption. However, at the epitaxial graphene on the SiC(0001) substrate, hydrogen could adsorb on both C- and Si-site. Furthermore, the surface structure changes by stages from Si-rich 3x3, √3x√3 to C-rich 6√3x6√3 phase in the epitaxial growth of graphene on SiC substrates [2]. In this study, we investigated the hydrogen adsorption at these surfaces appeared in the way of epitaxial growth of graphene on the Si-terminated 6H-SiC(0001) surfaces.
Experiments were carried out in an ultra-high vacuum apparatus equipped with a Si dozer, a LEED/AES, a TPD (Temperature Programmed Desorption), a hydrogen gas inlet, and a hot W-filament. We prepared the 3x3, √3x√3, and 6√3x6√3 surfaces by heating the sample at 850°C under the Si flux, heating at 1150°C for 3min, and heating at 1250°C for 3min, respectively. We exposed these surfaces to atomic hydrogen, and measured their TPD spectra. Our TPD indicated that the saturation coverage of H was ≈0.1 monolayer (ML) at these surfaces independent of the surface structure. However, the TPD spectrum changed drastically at the stage from 3x3 to √3x√3. The 3x3 surface showed a shoulder at ≈500K, and a dominant peak at 700K, while the √3x√3 and the 6√3x6√3 surface had a single peak at 400K. Comparing to the previous TPD studies at graphite [3], we attributed to the single peak at 400K to the hydrogen desorption from the graphene layer. Meanwhile, the peak at 700K of the 3x3 surface is very close to the hydrogen desorption peak from the Si(111) surface. Both TPD and AES suggests that the π-bonded C-induced benzene ring structure started to grow at the appearance of the √3x√3 surface structure. This interpretation is supported by our electron energy loss spectroscopy (EELS) measurements in which the π-plasmon loss peak of the benzene ring started to evolve at the √3x√3 surface.
[1] Science 323,610(2009), [2]JPC,B208,19912(2004), [3]JCP117,8486(2002)