AVS 62nd International Symposium & Exhibition
    Applied Surface Science Thursday Sessions
       Session AS-ThM

Paper AS-ThM12
Correlation between Chemistry, Optical Properties, and Environmental Stability of DC Sputtered Rhenium Oxides

Thursday, October 22, 2015, 11:40 am, Room 212D

Session: Practical Surface Analysis III: Multiple-technique Problem-solving and Structure-property Correlations
Presenter: Neil Murphy, Air Force Research Laboratory
Authors: N.R. Murphy, Air Force Research Laboratory
L. Sun, General Dynamics Information Technology
J.G. Jones, Air Force Research Laboratory
J.T. Grant, General Dynamics Information Technology
Correspondent: Click to Email
Thin films of rhenium oxide (<150 nm) are deposited using magnetron sputtering employing a rhenium cathode within an argon-oxygen atmosphere. Throughout the deposition process, the working pressure is maintained at a constant level of 1.33 Pa as the oxygen content is varied from 0% to 80% in increments of 10%. As the oxygen content is varied, the extinction coefficient, k, of the deposited layers is monitored via in situ­ ellipsometry. In situ ellipsometry is used to identify absorption features specific to ReO3, including the characteristic reduction of k brought on by the optical band gap at 310 nm as well as the onset of intraband absorption above 540 nm. In situ ellipsometry results indicate that films deposited at oxygen levels of 50% and 60% have resepective k450 values of 0.6 and 0.25, characteristic of ReO3. Chemical analysis via x-ray photoelectron spectroscopy confirmed that films individually deposited at oxygen levels of 50% and 60% are mixed-valent, consisting largely of ReO3 (Re6+), with contributions from ReO2 (Re4+) and Re2O7 (Re7+). Note that films deposited at 50% oxygen content also contained up to 15% Re2O3 (Re3+). Further monitoring of the films’ valence states, after an environmental exposure time of 30 days, indicates a correlation between structural instability and the presence of both Re2O3 and Re2O7. Analyses via XPS and ex situ spectroscopic ellipsometry indicate that films deposited within an atmosphere of 60%oxygen do not contain Re3+ and demonstrate stable surface chemistry and optical behavior throughout the 30 day period, while those deposited at 50% oxygen experience significant degradation. Increasing the stability of mixed-valent Re-O films could give rise to more widespread use of rhenium in optics and catalysis, especially in applications where mild moisture exposure is unavoidable.