Atomistic mechanism and interface-structure-energetics of van der Waals epitaxy demonstrated by layered alpha-MoO3 growth on mica
Unlike conventional epitaxy, van der Waals epitaxy (vdWE) allows nearly stress-free growth of thick films with highly oriented crystals without dislocations even for large film-substrate lattice mismatches. Despite reports of vdWE in numerous materials systems, an atomistic understanding of film/substrate interface structure that explains and predicts vdWE has remained elusive. Here, we address this knowledge gap by unveiling atomistic interface mechanisms for vdWE of alpha-MoO3(0k0) on mica(001). X-ray diffraction and electron microscopy reveal alpha-MoO3(0k0) epilayers with large columnar crystals in three non-equivalent in-plane orientations. These results, together with negligible strain buildup in continuous epilayers, confirm vdWE. Ab initio computations showing interface energy minima for these orientations correlate with high cross-interface proximity between Mo atoms in alpha-MoO3 and K in mica conducive for maximal vdW attraction. These atomistic insights on interface structure and energetics provide a crucial framework for predicting vdWE for different film/substrate combinations and designing of stress-free and/or standalone epitaxial films of layered materials such as MoO3 on layered substrates such as f-mica.