Spatially resolved imaging of inhomogeneous charge transfer behavior in polymorphous molybdenum oxide. I. Correlation of localized structural, electronic, and chemical properties using conductive probe atomic force microscopy and Raman microprobe spectroscopy

Todd M. McEvoy, Keith J. Stevenson

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)

Abstract

A detailed study of electrochemically deposited molybdenum oxide thin films has been carried out after they were sintered at 250°C. Conductive probe atomic force microscopy (CP-AFM), Raman microscopy, and X-ray photoelectron spectroscopy (XPS) techniques were employed to assess the complex structural, electronic, and compositional properties of these films. Spatially resolved Raman microprobe spectroscopy studies reveal that sintered molybdenum oxide is polymorphous and phase segregated with three types of domains observed comprising orthorhombic α-MoO 3, monoclinic β-MoO 3, and intermixed α-/β-MoO 3. CP-AFM studies conducted in concert with Raman microprobe spectroscopy allowed for correlation between specific compositional regions and localized electronic properties. Single point tunneling spectroscopy studies of chemically distinct regions show semiconducting current-voltage (I-V) behavior with the β-MoO 3 polymorph exhibiting higher electronic conductivity than intermixed α-/β-MoO 3 or microcrystalline α-MoO 3 domains. XPS valence level spectra of β-MoOs films display a small structured band near the Fermi level, indicative of an increased concentration of oxygen vacancies. This accounts for the greatly enhanced electronic conductivity of β-MoO 3 as these positively charged cationic defects (anion vacancies) act to trap excess electrons. Connections between structural features, electronic properties, and chemical composition are established and discussed. Importantly, this work highlights the value of using spatially resolved techniques for correlating structural and compositional features with electrochemical behaviors of disordered, mixed-phase lithium insertion oxides.

Original languageEnglish
Pages (from-to)3521-3528
Number of pages8
JournalLangmuir
Volume21
Issue number8
DOIs
Publication statusPublished - 12 Apr 2005
Externally publishedYes

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