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Microscopy and spectroscopy study of nanostructural phase transformation from β-moo3 to mo under uhv – mbe conditions

DOI: 10.1016/j.susc.2018.12.008 DOI Help

Authors: Paramita Maiti (Institute of Physics, Bhubaneswar; Homi Bhabha National Institute) , Puspendu Guha (Institute of Physics, Bhubaneswar; Homi Bhabha National Institute) , Hadeel Hussain (Diamond Light Source) , Ranveer Singh (Institute of Physics, Bhubaneswar; Homi Bhabha National Institute) , Chris Nicklin (Diamond Light Source) , Parlapalli V. Satyam (Institute of Physics, Bhubaneswar; Homi Bhabha National Institute)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Surface Science

State: Published (Approved)
Published: January 2019

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.

Journal Keywords: β-MoO3 nanoribbons; Mo nanoparticles; Molecular beam epitaxy (MBE); Phase transition; In-situ XPS; KPFM

Subject Areas: Materials, Chemistry

Instruments: I07-Surface & interface diffraction