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O: Fachverband Oberflächenphysik

O 35: Poster Session II (Polymeric biomolecular films; Nanostructures; Electronic structure; Spin-orbit interaction; Phase transitions; Surface chemical reactions; Heterogeneous catalysis; Particles and clusters; Surface magnetism; Electron and spin dynamics; Surface dynamics; Methods; Electronic structure theory; Functional molecules)

O 35.51: Poster

Dienstag, 27. März 2012, 18:15–21:45, Poster B

Flame-Synthesis of Tailored Metal-Oxide Nanoparticle Surfaces for Highly Selective and Reactive Gas Sensors — •Antonio Tricoli — Particle Technology Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

Metal-oxide nanoparticles such as SnO₂ and TiO₂ are state-of-the-art materials for the assembly of solid-state chemical gas sensors. The remarkable chemical and temperature stability of these wide band-gap semiconductors allows operation in very harsh environments as for exhaust oxygen sensors in modern fuel control feedback loop. The high reactivity of their surface with simple and complex gaseous compounds allows detection of important analytes down to particle per billion concentrations (ppb). However, this is usually achieved by exploitation of spill-over effects on noble-metal clusters post-deposited (e.g. by impregnation) on their surface. This drastically limits the stability of their sensing performance at the elevated operation temperatures (250−600 ^∘C) of these metal-oxides and considerably increases the cost for their production. Additionally, such gas sensing metal-oxides suffer of very poor selectivity confining their application to relatively simple gas mixtures. This is a main limitation to their utilization as gas sensors in novel applications such as non-invasive medical diagnostics by breath analysis. Development of noble-metal-free metal-oxide nanoparticles with high selectivity to trace concentrations (ppb) of the target analyte is a key-step toward the fabrication of portable and wearable gas sensing technology with numerous applications. Here, the one-step flame-synthesis of tailored multi-oxide nanoparticles is presented as a tool for the production of very selective and sensitive gas sensors. In particular, the synthesis of highly reactive SnO₂−SiO₂ nanocomposites with limit of detection (LOD) in the ppb range is demonstrated as a valid alternative to the utilization of noble-metals leading to considerably higher sensitivity and stability. In particular, the thermal stabilization of very fine SnO₂ nanocrystals with size below twice their Debye length up to very high temperatures (900 ^∘C) is shown as a reliable method for the synthesis of wide band-gap semiconductors with surface states-controlled conductivity and thus very high sensitivity. Additionally, the flame-synthesis of SnO₂−TiO₂ solid solutions with rutile crystal structure is presented as a powerful approach to control the selectivity of such metal-oxide surfaces against disturbing agents such as water vapor, an omnipresent and varying component in gas sensing.