Formation of monolayer V5Se8 from multilayer VSe2 films via V- and Se-desorption

Two-dimensional van der Waals vanadium selenide compounds are expected to be a key platform for searching the new emergent phenomena by forming the artificial heterostructures. Here, we systematically investigated the electronic properties of monolayer and multilayer vanadium selenide films grown with different conditions using in situ angle-resolved photoemission spectroscopy and first-principles calculations. We observed the band dispersions of pristine ${\mathrm{VSe}}_{2}$ in a sample grown at substrate temperature (${T}_{\mathrm{sub}}$) of $250{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, whereas the significant modulations of the Se-derived bands can be seen at ${T}_{\mathrm{sub}}$ = $380{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. For ${T}_{\mathrm{sub}}=420{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, we found that the V self-intercalated ${\mathrm{V}}_{5}{\mathrm{Se}}_{8}$ was formed. As a simple and convenient way, we also demonstrate that the monolayer ${\mathrm{V}}_{5}{\mathrm{Se}}_{8}$ can be fabricated by annealing from the multilayer ${\mathrm{VSe}}_{2}$ film, and the possible formation mechanism is discussed. The establishment of the growth methods of the ${\mathrm{V}}_{5}{\mathrm{Se}}_{8}$ film and verifying its electronic properties provide the substantial step for the creation of the two-dimensional van der Waals heterostructures.