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

Abstract

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 ⟨21̅1̅0⟩-type directions (i.e., the sulfur-terminated edge directions) with the ⟨11̅0⟩-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 ⟨11̅0⟩ and ⟨11̅2̅⟩ 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 ⟨11̅0⟩ 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 MoS2 in next-generation nanoelectronic devices.

Thermodynamics driving the strong metal–support interaction: Titanate encapsulation of supported Pd nanocrystals

“…The crystals tend to align one of their {111} edge facets with the <100> substrate directions on both substrates, so the interfacial crystallography can be described as (111 strain in Pd. Such favorable coincidence lattice registry has been confirmed to be a powerful driver in determining the epitaxial alignment of supported crystals on crystalline substrates [32][33][34]. Also, we expect the misfit strain levels here (+1.4% and -1.8%) to be accommodated elastically on both substrates.…”

Molecular Nanowire Bonding to Epitaxial Single‐Layer MoS2 by an On‐Surface Ullmann Coupling Reaction

“…The case of connecting both ends of a poly‐DBT wire to MoS 2 islands is much rarer than connecting one end; however, we believe a more suitable organic molecule might increase the success rate in connecting multiple MoS 2 islands. Obviously, device production requires the use of insulating substrates, and it will be an interesting topic to study if well‐defined MoS 2 grown by CVD methods on SiO 2 , Al 2 O 3 or other oxides can be used for this purpose 48–50. We note that the role of Au surface may be an important factor here, as metal atoms are needed to initiate the Ullmann coupling during the chain growth, but we speculate that addition of trace amounts of metals species (as in solution phase Ullmann coupling) can help overcome this problem.…”

Spectroscopic view of ultrafast charge carrier dynamics in single- and bilayer transition metal dichalcogenide semiconductors

“…In the future, we hope to extend this work to TMDC samples on insulating substrates such as metal oxides [67,68], as well as TMDC-based heterostructures [58,69]. Indeed, TR-ARPES studies on SL semiconducting TMDCs have until recently been limited by flake sizes that are small (on the order of 10 µm) compared to the typical XUV beam size.…”

“…Indeed, TR-ARPES studies on SL semiconducting TMDCs have until recently been limited by flake sizes that are small (on the order of 10 µm) compared to the typical XUV beam size. As the TMDC growth technology is maturing, synthesis of large, single-orientation MoS 2 and WS 2 flakes has become possible on a range of substrates [50,68,70], and a variety of sample infrastructures can be engineered by van der Waals pick-up transfer methods [71]. Furthermore, the application of photoemission electron microscopes to pump-probe experiments [72,73] allows for the combination of time-and momentum-resolved spectra with imagining at the microscale.…”