Abstract
The transfer process of graphene onto the surface of oxide substrates is well known. However, for many devices, we require high quality oxide thin films on the surface of graphene. This step is not understood. It is not clear why the oxide should adopt the epitaxy of the underlying oxide layer when it is deposited on graphene where there is no lattice match. To date there has been no explanation or suggestion of mechanisms which clarify this step. Here we show a mechanism, supported by first principles simulation and structural characterisation results, for the growth of oxide thin films on graphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a graphene and show that local defects in the graphene layer (e.g. grain boundaries) act as bridge-pillar spots that enable the epitaxial growth of STO thin films on the surface of the graphene layer. This study, and in particular the suggestion of a mechanism for epitaxial growth of oxides on graphene, offers new directions to exploit the development of oxide/graphene multilayer structures and devices.
Highlights
It exhibits extraordinarily high electronic quality which is usually characterized by mobility of its charge carriers
The charge carriers in such thin graphitic films are confined to two dimensions
We propose a growth mechanism that explains the formation of epitaxial SrTiO3 (STO) thin films on graphene, which were prepared by chemical vapour deposition (CVD) and subsequently transferred onto STO
Summary
Films on Graphene received: 08 April 2016 accepted: 21 July 2016 Published: 12 August 2016. Defects in the sheet introduced during the graphene growth or transfer provide reaction centres for the adsorbing oxide and may allow bridge structures to form between the substrate and the oxide overlayer In this scenario, an oriented single crystal STO film on a graphene layer might be supported by epitaxial pillars grown through the defects in the graphene layer (e.g. grain boundaries) (Fig. 1.b). The shear strain forces outplay the week interaction between the STO film, STO substrate and the sandwiched graphene layer, squeezing and folding the latter between two pillars These results are in perfect agreement with the Raman spectroscopy analysis and the growth mechanism discussed above. The evidence provided suggests that it is possible to grow epitaxial oxide films on graphene
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