We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the (0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full (6√3×6√3)-R30° unit cell, based on a van der Waals corrected exchange correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments, a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and the lowest known adsorption energy per atom for graphene on any substrate. A structural comparison to other graphenes suggests that hydrogen-intercalated graphene on 6H-SiC(0001) approaches ideal graphene.

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This research explores the surface chemistry of halogen based plasmas on silicon carbide and is aimed at the synthesis of large area graphene-on-insulator films. In these studies, 6H-SiC (0001) substrates were etched using either CF4 and Cl2 based plasmas and then thermally annealed. The resulting surfaces were analyzed using x-ray photoelectron spectroscopy, reflection high energy electron diffraction, atomic force microscopy, and Raman spectroscopy. The analyses showed that the etching process selectively etched silicon to produce carbon rich surface layers on the silicon carbide substrate, and when annealed, these carbon rich layers formed graphene films with halogen-and oxygen-based defects. The thickness of the graphene was controlled by the plasma etch parameters. Two point current-voltage measurements were used to characterize the electrical properties of the films. The current-voltage plots exhibited back-to-back Schottky behavior which suggests that the defects open a band gap in these films. Current-voltage data were used to determine the Schottky barrier height, carrier density, and the upper limit for the film resistivity.

Silicon Carbide possesses a combination of properties that make it ideal for use in electronics.

Halogen based (CF4 and Cl2) inductively coupled reactive ion etching (ICP-RIE) has been used to selectively etch silicon from 6H-SiC to produce a controlled number of carbon layers. After annealing at temperatures in the range of 550 °C to 1100 °C to reconstruct the near surface layers, x-ray photoelectron spectroscopy has been used to characterize the composition of the films. For the Cl2 based ICP-RIE, two carbon species are observed. One is due to carbon bound as SiC in the substrate and a second which can be attributed to graphene. In the case of CF4 based etching the situation is similar except the second peak is most closely aligned with p-type graphene. This is most likely due to electron transfer from the graphene to the trace levels of fluorine remaining on the surface after annealing.