title: Iso-oriented monolayer α-MoO3(010) films epitaxially grown on SrTiO3(001).
abstract: The ability to synthesize 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 α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) 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 (a(MoO3) = 3.96 Å, a(STO) = 3.905 Å), the lattice mismatch along other direction is large (∼5%, c(MoO3) = 3.70 Å), 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 α-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 α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352 USA. Yingge.Du@pnnl.gov.
authors.forename: Yingge
authors.initials: Y
authors.lastname: Du
authors.affiliation: Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352 USA and Key Laboratory of Photovoltaic Materials of Henan Province, School of Physics & Electronics, Henan University, Kaifeng, 475004 P. R. China.
authors.forename: Guoqiang
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of Wyoming, Laramie, WY 82072 USA.
authors.forename: Erik W
authors.initials: EW
authors.lastname: Peterson
authors.affiliation: Department of Chemistry, University of Wyoming, Laramie, WY 82072 USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352 USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352 USA.
authors.forename: Rentao
authors.initials: R
authors.lastname: Mu
authors.affiliation: Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352 USA.
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Dohnálek
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352 USA. Yingge.Du@pnnl.gov.
authors.forename: Mark
authors.initials: M
authors.lastname: Bowden
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352 USA. Yingge.Du@pnnl.gov.
authors.forename: Igor
authors.initials: I
authors.lastname: Lyubinetsky
authors.affiliation: Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352 USA.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Chambers