Modification of monolayer 1T-VSe2 by selective deposition of vanadium and tellurium

Hetero-structures of transition metal dichalcogenide (TMD) layers offer vast possibilities of new materials properties. The growth behaviors of such TMD hetero-structures can be complex. In this study, we report the structure modification of a VSe2 monolayer by the molecular beam deposition of Te, V, or both. With a typical growth temperature of 300 degrees C and a nominal flux rate, we found that Te deposition leaves the VSe2 intact. Vanadium deposition, in contrast, leads to small clusters ordered in stripes along well-defined directions. The charge density wave symmetry of monolayer VSe2 surprisingly changes in small regions enclosed by such vanadium stripes. With V and Te co-deposition, a dramatic change of the monolayer surface structure to a (2 x 1) ordered phase is observed. This study illustrates the unexpected complexities involved in preparing even a simple bilayer TMD hetero-structure, such as VTe2/VSe2.