Epitaxial Growth of Monolayer MoS2 on SrTiO3 Single Crystal Substrates for Applications in Nanoelectronics

Monolayer molybdenum disulfide (MoS2) crystals grown on amorphous substrates such as SiO2 are randomly oriented. However, when MoS2 is grown on crystalline substrates, the crystal shapes and orientations are also influenced by their epitaxial interaction with the substrate. In this paper, we present the results from chemical vapor deposition growth of MoS2 on three different terminations of single crystal strontium titanate (SrTiO3) substrates. On SrTiO3(111), the monolayer MoS2 crystals form equilateral triangles with two main orientations, in which they align their < 2 (1) over bar(1) over bar0 >-type directions (i.e., the sulfur-terminated edge directions) with the (110)-type directions on SrTiO3. This arrangement allows near-perfect coincidence epitaxy between seven MoS2 unit cells and four SrTiO3 unit cells. On SrTiO3(110), the MoS2 crystals tend to align their edges with both the < 1 (1) over bar0 > and < 1 (1) over bar(2) over bar > directions on SrTiO3 because these both provide favorable coincidence lattice registry. This distorts the crystal shapes and introduces an additional strain detectable by photoluminescence. When triangular MoS2 crystals are grown on SrTiO3(001), they again show a preference to align their edges with the < 1 (1) over bar0 > directions on SrTiO3. Our observations can be explained if the interfacial van der Waals (vdW) bonding between MoS2 monolayers and SrTiO3 is greatest when maximum commensuration between the lattices is achieved. Therefore, a key finding of this paper is that the vdW interaction between MoS2 and SrTiO3 substrates determines the supported crystal shapes and orientations by epitaxial relations. Controlled crystal orientations make the growth of large sheets of MoS2 possible when there are multiple nucleation sites. This minimizes the number of grain boundaries and optimizes the electronic properties of the material, e.g., charge mobility, which is crucial for the application of monolayer MoS, in next-generation nanoelectronic devices.