Low-defect-density SnSe2 films nucleated via thin layer crystallization

We have studied the structural and morphological features of SnSe₂ films grown on Si(111) and Bi₂Se₃(0001) surfaces in an in situ reflection electron microscope. On both substrates, the SnSe₂ growth started at 100 °C as an amorphous layer, and when thickness reached 1 nm, crystallized by raising the growth temperature to 250 °C without interruption of Sn and Se fluxes. The introduction of this growth-initiating stage has decreased the concentration of screw dislocations on films’ surfaces to ∼18 and ∼2 μm⁻² for the Si(111) and Bi₂Se₃(0001) substrates, respectively. High-resolution transmission electron microscopy investigation has shown that the layered SnSe₂ film has a hexagonal lattice structure corresponding to the space group $\text{P}\overline{3}\text{m}1$ (no. 164) with lattice parameters a = 0.38 nm and c = 0.62 nm. Raman spectroscopy has shown vibrational modes corresponding to the 1T-SnSe₂ phase. We have shown that the decrease in Se:Sn flux ratio switches growth mode from Frank—van der Merwe type SnSe₂ epitaxy to Volmer—Weber type nucleation of SnSe 3D islands.