Chariya Virojanadara

Large homogeneous mono-/bi-layer graphene on 6H-SiC(0001) and buffer layer elimination

In this paper we discuss and review results of recent studies of epitaxial growth of graphene on silicon carbide. The presentation is focused on high quality, large and uniform layer graphene growth on the SiC(0 0 0 1) surface and the results of using different growth techniques and parameters are compared. This is an important subject because access to high-quality graphene sheets on a suitable substrate plays a crucial role for future electronics applications involving patterning. Different techniques used to characterize the graphene grown are summarized. We moreover show that atomic hydrogen exposures can convert a monolayer graphene sample on SiC(0 0 0 1) to bi-layer graphene without the carbon buffer layer. Thus, a new process to prepare large, homogeneous stable bi-layer graphene sheets on SiC(0 0 0 1) is presented. The process is shown to be reversible and should be very attractive for various applications, including hydrogen storage.

Analysis of the Formation Conditions for Large Area Epitaxial Graphene on SiC Substrates

We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.

Interfacial investigation of in situ oxidation of 4H-SiC

An in situ oxidation study of v3 × v3 R30° reconstructed 4H-SiC(001) surfaces is reported. An intermediate oxidation state (interpreted to be Si+1) is revealed in core level photoemission spectra r ...

The influence of substrate morphology on thickness uniformity and unintentional doping of epitaxial graphene on SiC

A pivotal issue for the fabrication of electronic devices on epitaxial graphene on SiC is controlling the number of layers and reducing localized thickness inhomogeneities. Of equal importance is to understand what governs the unintentional doping of the graphene from the substrate. The influence of substrate surface topography on these two issues was studied by work function measurements and local surface potential mapping. The carrier concentration and the uniformity of epitaxial graphene samples grown under identical conditions and on substrates of nominally identical orientation were both found to depend strongly on the terrace width of the SiC substrate after growth.

Studies of oxidized hexagonal SiC surfaces and the SiC/SiO2 interface using photoemission and synchrotron radiation

Oxidation of hexagonal SiC surfaces and SiO2/SiC interfaces were analyzed using photoemission and synchrotron radiation. The existence of carbon clusters or carbon-containing by-products and the ex ...

Changes in structural and electronic properties of graphene grown on 6H-SiC(0001) induced by Na deposition

The effects of Na deposited on monolayer graphene on SiC(001) were investigated by synchrotron-based photoelectron spectroscopy and angle resolved photoelectron spectroscopy. The experimental resul ...

Oxidation studies of 4H-SiC(0001) and (0001)

Abstract The results of a photoemission study of Si- and C-terminated 4H–SiC surfaces after different oxygen exposures are presented and discussed. The surfaces were oxidized gradually from 1 to 1.2×10 6 L at both room temperature and at 800 °C. Recorded Si 2p and C 1s spectra show at both temperatures only two oxidations states, Si 1+ and Si 4+ for the Si-terminated surface and Si 2+ and Si 4+ for the C-terminated surface. For the Si-terminated surface, no carbon containing by-product can be detected at the interface or at the surface after the largest exposure investigated. For the C-terminated surface, oxygen exposures are shown to affect the surface related carbon components quite strongly and the Si 2+ oxidation state is interpreted to originate from a mixture of Si–O–C bonding. The surface/interface related carbon decreases dramatically after the largest exposure investigated but is not eliminated as on the Si-terminated surface. For the latter, a clean and well ordered 3 surface is shown to be possible to re-create by in situ heating even after the largest oxygen exposures made.

Surface studies of hydrogen etched 3C-SiC(001) on Si(001)

The morphology and structure of 3C-SiC(001) surfaces, grown on Si(001) and prepared via hydrogen etching, are studied using atomic force microscopy (AFM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). On the etched samples, flat surfaces with large terraces and atomic steps are revealed by AFM. In ultrahigh vacuum a sharp LEED pattern with an approximate (5×1) periodicity is observed. AES studies reveal a “bulklike” composition up to the near surface region and indicate that an overlayer consisting of a weakly bound silicon oxide monolayer is present.

Multiple π-bands and Bernal stacking of multilayer graphene on C-face SiC, revealed by nano-Angle Resolved Photoemission.

Only a single linearly dispersing π-band cone, characteristic of monolayer graphene, has so far been observed in Angle Resolved Photoemission (ARPES) experiments on multilayer graphene grown on C-face SiC. A rotational disorder that effectively decouples adjacent layers has been suggested to explain this. However, the coexistence of μm-sized grains of single and multilayer graphene with different azimuthal orientations and no rotational disorder within the grains was recently revealed for C-face graphene, but conventional ARPES still resolved only a single π-band. Here we report detailed nano-ARPES band mappings of individual graphene grains that unambiguously show that multilayer C-face graphene exhibits multiple π-bands. The band dispersions obtained close to the moreover clearly indicate, when compared to theoretical band dispersion calculated in the framework of the density functional method, Bernal (AB) stacking within the grains. Thus, contrary to earlier claims, our findings imply a similar interaction between graphene layers on C-face and Si-face SiC.

A low-energy electron microscopy and x-ray photo-emission electron microscopy study of Li intercalated into graphene on SiC(0001)

The effects induced by the deposition of Li on 1 and 0 ML graphene grown on SiC(0001) and after subsequent heating were investigated using low-energy electron microscopy (LEEM) and x-ray photo-emis ...