MTL Annual Report

Figure 1. (a-c) Top and (d) cross-sectional views of 25-nm-thick microsphere templated SnO₂ film, enhanced with co-deposited Pt nanoparticles.

Gas sensors play a vital role in public health and safety, industrial process control, and reduction of toxic emissions into the environment ^[1].  Conductometric gas sensors based on semiconducting metal oxide (SMO, e.g., ZnO, TiO₂, and SnO₂) thin films are of high interest in many applications due to high sensitivity, small size, and simplicity of measurement ^[2] [3].  However, a number of limitations exist in conventional approaches to this technology, including poor control over SMO/substrate interactions and high temperatures (300-400°C) required for device operation. To overcome the first challenge, the microsphere templating technique has been developed, and it greatly reduces SMO film contact with the substrate and increases film interaction with the environment ^[4].  In the past year, microsphere templated SMO films have been used as a highly reproducible and sensitive model system for the study of gas sensor performance.  Noble metal (Pt) nanoparticles have been co-deposited with microsphere templated SMO films to catalyze surface reactions with the environment.  These films exhibit higher sensitivity and faster response time at reduced operating temperatures. In addition, the devices exhibited significantly improved temperature stability, and further optimization shows promise for improvements in selectivity of sensor operation.

1. F. Rock et al., “Electronic Nose: Current Status and Future Trends,” Chemical Reviews, vol. 108, no. 2, pp. 705-725, Jan, 2008. [↩]
2. K.J. Albert et al., “Cross-Reactive Chemical Sensor Arrays,” Chemical Reviews, vol. 100, no. 7, pp. 2595-2626, Jun., 2000. [↩]
3. K. Wiesner et al., “Working mechanism of an ethanol filter for selective high-temperature methane gas sensors,” IEEE Sensors Journal, vol. 2, no. 4, pp. 354-359, Aug., 2002. [↩]
4. I.D. Kim et al., “Microsphere Templating as Means of Enhancing Surface Activity and Gas Sensitivity of CaCu₃Ti₄O₁₂ Thin Films,” Nano Letters, vol. 6, no. 2, pp. 193-198, Jan., 2006. [↩]