Microscopy and spectroscopy study of nanostructural phase transformation from β-MoO3 to Mo under UHV - MBE conditions
Abstract
We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400 °C and MoO2 to Mo at 750 °C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750 °C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750 °C.
- Publication:
-
Surface Science
- Pub Date:
- April 2019
- DOI:
- 10.1016/j.susc.2018.12.008
- Bibcode:
- 2019SurSc.682...64M
- Keywords:
-
- β-MoO<SUB>3</SUB> nanoribbons;
- Mo nanoparticles;
- Molecular beam epitaxy (MBE);
- Phase transition;
- In-situ XPS;
- KPFM