Newly developed metal oxide nanobelts and nanorings are potential candidates for fabrication of nanoscale devices. Their extraordinary sensing properties have been recently shown for ultra sensitive gas and DNA detection The finite size of the metal oxide wires confines the electrons wave functions, leading to quantized energy levels and to a huge modification of the transport and optical properties of the material. The hugely enhanced surface/volume ratio augments the role of surface states in the sensor response.
Worldwide most recent research in the field of quasi one-dimensional inorganic structures for gas sensing and some promising results achieved at Sensor Lab in Brescia Italy in conductometric and visible photoluminescence quenching will be discussed.
Gas sensors based on the SnO2 and ZnO nanobelts, synthesized by thermal evaporation of oxide powders under controlled conditions, have been fabricated. Electrical characterization showed that these nanobelts were very sensitive to the surrounding atmosphere. The results show the experimental feasibility of fabricating nano-size sensors using the integrity of individual nanobelts.
The visible photoluminescence (PL) of tin oxide nanobelts is quenched by nitrogen dioxide at ppm level in a fast (time scale order of seconds) and reversible way. Besides the response seems highly selective towards humidity and other polluting species like CO and NH3. Adsorbed gaseous species that create surface states can quench PL by creating competitive non-radiative paths. PL change produced by the gaseous environment depends on: nanostructure size and shape, crystalline face exposed to the surrounding environment, surface oxygen vacancies and sample pre-treatment in oxidizing or reducing atmosphere.
A comparison between conductometric and PL response suggests that the two response are ascribable to different adsorption processes.

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