Remote epitaxy of SrTiO₃ films on wet-transferred graphene using hybrid molecular beam epitaxy

Lattice mismatch between a crystalline film and substrate is often a key limitation in engineering heterostructures. If the mismatch is sufficiently large, defects such as dislocations can form when lattice mismatch-induced strain relaxes, resulting in often-undesirable consequences for the physical properties. The ability to accommodate strain relaxation without forming such defects can therefore have a significant impact on the synthesis science of epitaxial films. In this talk, we will present our results using a “remote” epitaxy approach to achieve defect-free relaxation by inserting a monolayer/bilayer of wet-transfer graphene between the SrTiO₃ (STO) film and the substrates. By using hybrid molecular beam epitaxy that employs a metal-organic precursor, titanium isopropoxide, to supply both Ti and oxygen (without the need for additional oxygen), oxidation of the graphene layer can be avoided. Phase-pure, epitaxial STO films were grown on substrates, and were then successfully exfoliated and transferred onto other substrates. We confirmed that the transferred STO membrane is single-crystalline and that the graphene layer remained on the substrate after exfoliation. We will discuss how pinholes or wrinkles in graphene can influence the growth and surface morphology of the STO film in addition to discussing strain relaxation mechanisms.