Iso-oriented monolayer {\alpha}-MoO3(010) films epitaxially grown on SrTiO3(001)

TL;DR

This study demonstrates the reproducible epitaxial growth of monolayer { extalpha}-MoO3 films on SrTiO3(001) substrates using molecular beam epitaxy, revealing insights into their structural properties and growth conditions.

Contribution

It introduces a method for growing iso-oriented monolayer { extalpha}-MoO3 films with controlled thickness and crystallinity via molecular beam epitaxy.

Findings

Successful epitaxial growth of monolayer { extalpha}-MoO3 on SrTiO3(001)

Optimal growth temperature range identified for monolayer formation

Layer thickness is limited by thermal desorption, not deposition time

Abstract

The ability to synthesis well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in-situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented {\alpha}-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) (STO) substrates by molecular beam epitaxy ( (010)MoO3 || (001)STO, [100]MoO3 || [100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 {\AA}, aSTO = 3.905 {\AA}), the lattice mismatch along other direction is large (~5%, cMoO3 = 3.70 {\AA}), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer {\alpha}-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between {\alpha}-MoO3 layers. Lowering growth temperature after the initial iso-oriented {\alpha}-MoO3 monolayer leads to thicker {\alpha}-MoO3(010) films with excellent crystallinity.