Atomistic mechanism and interface-structure-energetics of van der Waals epitaxy demonstrated by layered alpha-MoO3 growth on mica

TL;DR

This study uncovers atomistic interface mechanisms behind van der Waals epitaxy of alpha-MoO3 on mica, explaining how stress-free, highly oriented films form despite lattice mismatches.

Contribution

It provides the first atomistic understanding of vdWE interface structures and energetics, enabling prediction and design of stress-free epitaxial layered films.

Findings

Alpha-MoO3 forms large columnar crystals in three orientations on mica.

Negligible strain buildup confirms van der Waals epitaxy.

Interface energy minima correlate with atomistic proximity and vdW attraction.

Abstract

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.