Factors Influencing the Stability of Au-Incorporated Metal-Oxide Supported Thin Films for Optical Gas Sensing

• Published in: Journal of the Electrochemical Society Vol. 164; no. 4; pp. B159 - B167
• Main Authors: Baltrus, John P., Holcomb, Gordon R., Tylczak, Joseph H., Ohodnicki, Paul R.
• Format: Journal Article
• Language: English
• Published: United States The Electrochemical Society 01.01.2017
• Subjects: Au Nanoparticle; Fuel Gas; Hydrogen; MATERIALS SCIENCE; Optical Gas Sensing; Thin Films; X-ray Photoelectron Spectroscopy
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.1451704jes

There is interest in using Au-nanoparticle incorporated oxide films as functional sensor layers for high-temperature applications in optical-based sensors for measurements in both highly-oxidizing and highly-reducing atmospheres at temperatures approaching 900°C-1000°C because of a relatively high melting temperature combined with the inert nature of Au nanoparticles. This study includes a systematic series of experiments and theoretical calculations targeted at further understanding stability of Au-nanoparticle incorporated TiO2 films as archetype sensing materials. A combination of thermodynamic modeling and long-term exposure tests were utilized to unambiguously determine that gas stream composition-dependent reactive evaporation of Au (to form predominately Au(g) or AuH(g), depending upon the environment) at the surface of the nanoparticles is the dominant mechanism for mass loss of Au. Primary factors dictating the rate of reactive evaporation, and hence the associated film stability, were determined to be the gas stream temperature and the concentration of H2, with the former playing a more significant role over the ranges of temperatures (700°C-800°C) and H2 concentrations (1% to 29% H2 by volume) explored. The mitigation of Au-mass loss through reactive evaporation was also successfully demonstrated by depositing a SiO2 overlayer on the Au-nanoparticle embedded films to prevent direct Au-nanoparticle/vapor-phase contact.