Molecular beam epitaxy growth of thin films of SnS2 and SnSe2 on cleaved mica and the basal planes of single-crystal layered semiconductors: Reflection high-energy electron diffraction, low-energy electron diffraction, photoemission, and scanning tunneling microscopy/atomic force microscopy characterization

Abstract

SnS2 and SnSe2 thin films were deposited by molecular beam epitaxy (MBE) methods on a variety of layered semiconductor substrates (freshly cleaved SnS2, SnSe2, WSe2, MoS2, MoTe2, GaSe, InSe) and cleaved mica, for investigation of the interfaces formed as a result of MBE growth. These ultrathin films were characterized in situ by x-ray photoelectron spectroscopy and surface reflection high energy and low energy electron diffraction techniques. The growth modes were verified ex situ by scanning tunneling microscopy and/or atomic force microscopy [scanning probe microscopies (SPM)]. Despite the chemical and structural similarities between SnS2 and SnSe2, SPM measurements show that the two materials as ultrathin films have different growth morphologies in the first few monolayers. Photoelectron spectroscopy (PES) measurements lead to the conclusion that both materials grow on the basal planes of most layered substrates in an epitaxial, layer-by-layer mode. Small deviations from ideal Frank–van der Merwe growth for these thin films could be determined from PES intensity ratios versus coverage. Deposition of both materials on freshly cleaved mica, where the lattice mismatch between the substrate and the overlayer surface unit cell dimension exceeds 40%, yields exclusively 500–1000 Å diameter epitaxial islands with threefold symmetry.