In situ X-ray studies of epitaxial growth of LaTiO₃ (001) on graphene by molecular beam epitaxy

Remote epitaxy is a novel synthesis technique that allows the fabrication of ultrathin, flexible, and highly unique heterostructures that cannot be created by other methods. The technique was recently applied to construct freestanding, complex oxide membranes [1]. By inserting graphene between the film and substrate during thin film growth, the van der Waals interactions between graphene and other materials are strong enough to enable epitaxial growth but weak enough to allow the rapid release the thin film. The technique may eventually be exploited to create novel, single crystal heterostructures, as each film can be “stacked” atop another, regardless of degradation due to misfit strain or incompatibilities due to high temperature reactions. However, details regarding how remote epitaxy actually occurs remains unknown as this requires an in situ investigation of the remote epitaxy process. Here we describe the results of in situ synchrotron X-ray measurements conducted during the epitaxial growth of LaTiO₃ on SrTiO₃ (001) both with and without bilayer graphene as an intermediate layer. Crystal Truncation Rods (CTRs) were measured during the growth, and COherent Bragg Rod Analysis (COBRA) was used to reconstruct the electron density. Intensity oscillations at 001/2 (HKL) of each layer were observed during deposition, demonstrating the layer-by-layer growth mode. Raman spectroscopy was used to confirm the presence of the graphene after the deposition. The results will be compared to those from SrTiO₃ / graphene / SrTiO₃ (001).