Single-oriented epitaxial MoS2

Transition metal dichalcogenides (TMDCs) are a rising star among other two-dimensional materials, in view of a possible usage in building new electronic devices.
In particular, the employment of single layer (SL) MoS₂, the prototypical TMDC, for electronic devices, demands a controllable growth of highly crystalline layers featuring large area with a low concentration of defects to preserve its outstanding electronic properties. Moreover, given the peculiar electronic structure, new degrees of freedom are accessible allowing for spin- and valley-dependent phenomena, that can be retained in devices only through singly-oriented domains.
Current chemical vapor deposition methods have not been able to achieve this and have produced mirror twin domains leading to the formation of domain boundaries and dislocations in the layer.

We present a protocol to synthesize a singly-oriented SL MoS₂ on Au(111) based on the physical vapor deposition technique where the ideal growth conditions were determined by monitoring the growth by fast-XPS.

We investigated the structural properties using a combination of surface science techniques, including scanning tunneling microscopy (STM) and x-ray photoelectron diffraction (XPD). In particular, the latter was pivotal in determining the single-orientation of the grown MoS₂ layer. Moreover, Angular resolved photoemission measurements (ARPES), confirmed the single layer character and the high structural quality of MoS₂ while the single domain orientation allowed the measurement, through spin-resolved ARPES of the complete spin polarization with spin reversal of the states near K and -K points of the MoS₂ Brillouin zone.