Molecular beam epitaxy synthesis of In₂Se₃ films

The effects of substrate choice, substrate temperature, Se/In flux ratio, and cooling rate after deposition on the phase composition, surface morphology, and stoichiometry of indium selenide films synthesized via molecular beam epitaxy are presented. In₂Se₃ films were synthesized on sapphire, Si(111) and highly oriented, pyrolytic graphite (HOPG) substrates. The phase composition, stoichiometry, and surface morphology of the films were characterized via Raman spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy, respectively. Higher substrate temperature combined with higher Se/In ratio promoted formation of β-In₂Se₃ over γ and/or κ-In₂Se₃ on all substrates. Higher Se/In ratio also independently promoted β-In₂Se₃ over γ and/or κ-In₂Se₃ on all substrates at 673 K. The lateral dimensions of In₂Se₃ flakes increased as the substrate temperature increased on all substrates, and the largest lateral dimensions were observed for β-In₂Se₃ flakes on HOPG at 973 K. No evidence of α-In₂Se₃ was observed in the Raman spectra of any of the films at any of the synthesis conditions in this study. β-In₂Se₃ films on HOPG were cooled at 1200, 120, and 12 K/h and no evidence of a β to α-In₂Se₃ phase transition was observed. Some evidence of β to α-In₂Se₃ phase transition was observed in temperature-dependent XRD of In₂Se₃ powders, suggesting that another parameter besides cooling rate is locking the In₂Se₃ films into the β-phase.