Post-deposition Annealing Controlled Structural And Optical Properties Of RF Magnetron Sputtered MoO3 Films

Department of Physics, Sri Venkateswara University, Tirupati 517502, India

Adv. Mater. Lett., 2013, Current Issue, 4 (8), pp 637-642

DOI: 10.5185/amlett.2012.11466

Publication Date (Web): Jul 13, 2013

Copyright © IAAM-VBRI Press

E-mail: srsuguru.phy@gmail.com

Abstract

MoO₃ films were deposited on Corning glass and silicon substrates held at room temperature (303 K) by RF magnetron sputtering of metallic molybdenum target at a fixed oxygen partial pressure of 4x10^-4 mbar and sputter pressure of 4x10^-2 mbar. The as deposited films were annealed in air at different temperatures in the range 473 – 673 K. X-ray diffraction studies suggest that the as-deposited and the films annealed at 473 K were amorphous in nature, while those annealed at 573 and 673 K were polycrystalline with mixed phases of α- orthorhombic and β- monoclinic MoO₃. Scanning electron microscope images of the films annealed at 573 and 673 K exhibited nanoflower like and nanodisk like structures due to improvement in the crystallinity. Fourier transform infrared studies showed the characteristic vibrations of MoO₃ with shift in the vibrational modes of Mo = O and Mo – O – Mo with increase of annealing temperature. The optical absorption edge of the films shifted towards lower wavelengths side with increase of annealing temperature. Optical band gap of as-deposited films was 2.98 eV with refractive index 2.01, while those annealed at 673 K showed the optical band gap of 3.15 eV and refractive index of 2.08. The MoO₃ films annealed at 673 K were of nanocrystalline with crystallite size of 39 nm with optical band gap of 3.15 eV and refractive index of 2.08 were favorable for electron blocking and hole-selective layers in bulk-heterojuction solar cells.

Keywords

RF sputtering, molybdenum oxide, post-annealing, structural,optical properties.