Microsphere templating as means of enhancing the sensitivity of thin film metal-oxide gas sensors
A. Rothschild, I-D Kim, T. Hyodo and H.L. Tuller
Massachusetts Institute of Technology, US
microsphere templates, macroporous structures, thin film, gas sensors
Chemical and physical synthesis routes were combined to prepare macroporous thin films of semiconducting metal-oxides such as SnO2, TiO2, ZnO, and CaCu3Ti4O12 by reactive sputtering or pulsed laser deposition onto polymethylmethacrylate and polystyrene microsphere templated substrates. Subsequently, the organic microspheres were removed by thermal decomposition. The remaining inorganic films comprised a monolayer of hollow hemispheres with diameter commensurate with that of the organic microspheres (100…800 nm). The wall thickness and grain size were typically about 100 nm.
A network of voids between the film and substrate, formed as a result of the microsphere decomposition during the calcination step, provides easy accesses for gas molecules to the internal surfaces of the hemispheres. This unique morphology increases the surface area and reduces the interface area between film and substrate. Consequently, the surface activity is markedly enhanced while deleterious interfacial effects between film and substrate are significantly reduced. Both effects are highly advantageous for gas sensing applications. Indeed, microsphere templated films showed remarkably enhanced gas sensitivity compared with control films deposited onto untreated substrates. Sensors fabricated by this method exhibit notable advantages in terms of reproducibility and compatibility with microfabrication process compared to conventional thick film processes such as screen printing and spraying.
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Nanotech 2006 Conference Program Abstract