The interface of in-situ grown single-layer epitaxial MoS 2 on SrTiO 3 (001) and (111).

SrTiO 3 (STO) is a versatile substrate with a high dielectric constant, which may be used in heterostructures with 2D materials, such as MoS 2 , to induce interesting changes to the electronic structure. STO single crystal substrates have previously been shown to support the growth of well-defined epitaxial single-layer (SL) MoS 2 crystals. The STO substrate is already known to renormalize the electronic bandgap of SL MoS 2 , but the electronic nature of the interface and its dependence on epitaxy are still unclear. Herein, we have investigated an in-situ physical vapor deposition (PVD) method, which could eliminate the need for ambient transfer between substrate preparation, subsequent MoS 2 growth and surface characterization. Based on this, we then investigate the structure and epitaxial alignment of pristine SL MoS 2 in various surface coverages grown on two STO substrates with a different initial surface lattice, the STO(001)(4 × 2) and STO(111)-(9/5 × 9/5) reconstructed surfaces, respectively. Scanning tunneling microscopy shows that epitaxial alignment of the SL MoS 2 is present for both systems, reflected by orientation of MoS 2 edges and a distinct moiré pattern visible on the MoS 2 (0001) basal place. Upon increasing the SL MoS 2 coverage, the presence of four distinct rotational domains on the STO(001) substrate, whilst only two on STO(111), is seen to control the possibilities for the formation of coherent MoS 2 domains with the same orientation. The presented methodology relies on standard PVD in ultra-high vacuum and it may be extended to other systems to help explore pristine two-dimensional transition metal dichalcogenide/STO systems in general.