Atomically resolved electronic properties in single layer graphene on α-Al2O3 (0001) by chemical vapor deposition

Abstract

Metal-free chemical vapor deposition (CVD) of single-layer graphene (SLG) on c-plane sapphire has recently been demonstrated for wafer diameters of up to 300 mm, and the high quality of the SLG layers is generally characterized by integral methods. By applying a comprehensive analysis approach, distinct interactions at the graphene-sapphire interface and local variations caused by the substrate topography are revealed. Regions near the sapphire step edges show tiny wrinkles with a height of about 0.2 nm, framed by delaminated graphene as identified by the typical Dirac cone of free graphene. In contrast, adsorption of CVD SLG on the hydroxyl-terminated α-Al2O3 (0001) terraces results in a superstructure with a periodicity of (2.66 ± 0.03) nm. Weak hydrogen bonds formed between the hydroxylated sapphire surface and the π-electron system of SLG result in a clean interface. The charge injection induces a band gap in the adsorbed graphene layer of about (73 ± 3) meV at the Dirac point. The good agreement with the predictions of a theoretical analysis underlines the potential of this hybrid system for emerging electronic applications.

The MoS2-Graphene-Sapphire Heterostructure: Influence of Substrate Properties on the MoS2 Band Structure

“…Another obvious difference between the substrate regions G bond /S and G free /S is that the latter exhibits charge inhomogeneities, also described as electron and hole puddles, originating from π−π orbital mixing due to the presence of ripples in free-standing SLG (Figure 7a,b). 32,58 Consequently, MoS 2 /G free /S scanned with STM displays charge fluctuations caused by G free on all images. These electron and hole puddles can be observed best with V bias inside the MoS 2 bandgap due to the lack of MoS 2 states under these conditions (Supporting Information, Figure S7).…”

“…The darker and brighter regions on the substrate, see also the left inset of Figure , are due to variations in the coupling between SLG and H 2 -etched sapphire. Details are described in our recent study . The reduced SLG/S interlayer coupling, predominantly provoked by sapphire step edges, leads to nearly free-standing, highly conducting SLG regions (Figure c), while weakly bonded SLG regions (Figure b) are observed on sapphire terraces.…”

“…The reduced SLG/S interlayer coupling, predominantly provoked by sapphire step edges, leads to nearly free-standing, highly conducting SLG regions (Figure c), while weakly bonded SLG regions (Figure b) are observed on sapphire terraces. The latter exhibit a reduced conductivity by a factor of 4, discernible by the different contrast in SEM images . The nucleation and growth of MoS 2 nanosheets take place similarly on both substrate regions, G free and on G bond .…”

“…The vertical stacking of the heterostructures MoS 2 /G bond /S and MoS 2 /G free /S is displayed in Figure b,c, respectively, to illustrate the inherent differences in interlayer spacing of G bond and G free to the H 2 -etched sapphire substrate. G bond and G free are located at minimum distances of 0.26 and 0.38 nm to α-Al 2 O 3 (0001), respectively, as deduced in ref . Since the distance of 0.38 nm is considerably larger than the graphite interlayer distance (0.334 nm), only minor vdW interactions between G free and the supporting sapphire can be expected.…”

“…In this connection, we focus especially on the influence of local variations, that is, the specific topography and the different electronic properties of the two substrate regions, G free /S and G bond /S. The results are gained with well-established STM and STS methods revealing electronic properties at well-defined positions on the 2D material surface. ,− These insights are additionally supported by scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM).…”