The formation of continuous interfaces between graphene and dielectric materials, as required for fabrication of various integrated devices, is problematic due to dewetting and thermal instability; most materials do not wet graphene because it has a low-energy surface. Recently, however, M. Batzill and co-researchers from the University of South Florida grew a complete monolayer of yttria (Y2O3), which displays a high dielectric constant, on Pt-supported graphene. The researchers showed that even though the Y2O3 monolayer interacts weakly with graphene, it is stable at high temperatures. Furthermore, their procedure is consistent with the growth of graphene on metal surfaces, so it holds the potential for large-scale heterostructure fabrication.
Batzill and co-researchers report in the December 23, 2012 issue of Nature Nanotechnology (DOI: 10.1038/NNANO.2012.217) that a uniform, two-dimensional, yttria monolayer was grown on graphene supported on a clean Pt(111) single crystal, using reactive vapor deposition at room temperature. Ordered structures appeared only after annealing above 550°C but characterization by LEED, STM, x-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES) was presented for samples annealed up to 700°C. The researchers showed that the graphene layer remains intact with no formation of covalent bonds between graphene and yttria. However, the yttria layer maintains rotational registry with the graphene, indicating a preferential alignment with respect to each rotational domain.
In order to test their expectation that yttria growth on other metal-supported graphene substrates is similar to that on Pt(111)-graphene, the researchers grew yttria films on graphene supported on Ni(111) and Ir(111) substrates. Measurement of the oxygen to carbon ratios as functions of deposition time gave values identical to those observed for yttria/graphene/Pt(111), demonstrating monolayer growth. Commenting on their results, the researchers said that “yttria functionalization of graphene may be incorporated into the formation of large-scale graphene wafers on various metal supports. Such yttria monolayers may act as an atomic buffer or nucleation layers between graphene and other materials in subsequent processing steps.”