| AVS 59th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Tuesday Sessions |
| Session GR+AS+NS+SP+SS-TuA |
| Session: | Graphene Characterization Including Microscopy and Spectroscopy |
| Presenter: | G. He, Carnegie Mellon University |
| Authors: | G. He, Carnegie Mellon University N. Srivastava, Carnegie Mellon University R. Feenstra, Carnegie Mellon University |
| Correspondent: | Click to Email |
We have prepared graphene on the SiC(000-1) surface (the so-called C-face of the {0001} surfaces), by heating the SiC in a Si-rich environment produced either by using disilane (≈10-4 Torr) or cryogenically-purified neon (1 atm). With the Si-rich environments, we obtain considerably better uniformity in the thickness for thin, ≈ML-thick graphene on the C-face compared to that observed in samples prepared in vacuum or in an argon environment. We also find that different interface structures occur in these environments. In particular, we find a graphene-like buffer layer forming at the interface, analogous to the well known behavior of the SiC(0001) surface (the Si-face).
Studies are performed using atomic force microscopy (AFM), low-energy electron diffraction (LEED), and low-energy electron microscopy (LEEM). For graphene prepared in vacuum, LEED patterns show a characteristic 3X3 pattern together with graphene streaks. In contrast, for the graphene produced in either the disilane environment (≈10-4 Torr) or 1 atm of neon, LEED patterns reveals a complex √43X√43-R±7.6° arrangement along with graphene spots. This structure is somewhat similar to the well known 6√3X6√3-R30° “buffer layer” of the Si-face, with satellite spots surrounding the primary Si spots, and is interpreted as arising from a C-rich buffer layer on the SiC. Selected area diffraction on those surface areas reveals a wavevector magnitude precisely equal to that of graphene, thus proving that the buffer layer does indeed have structure very close to that of graphene (the pattern is interpreted as a distortion of the buffer-layer graphene due to bonding to the underlying SiC). Using LEEM, measurements from the buffer layer of the reflected intensity of the electrons as a function of their energy reveal a new characteristic reflectivity curve, not seen for vacuum-prepared graphene.
After oxidation of the samples, the √43X√43-R±7.6° spots disappear and √3X√3-R30° spots appear on the surface. This latter behavior is interpreted as oxidation of the SiC surface beneath the buffer layer. Selected area diffraction on portions of the surface that were previously identified as buffer layer still reveal a wavevector magnitude precisely equal to that of graphene. However, LEEM reflectivity curves on those areas reveal a completely new spectrum, indicative of a "decoupling" of the buffer from the SiC. This decoupling is consistent with our interpretation of this new interface structure as being a graphene buffer layer on C-face SiC.
This work is supported by NSF.