Tailoring Microstructure to Optimise the Electrical Resistance and Gas Sensing Properties of Tin Dioxide Films

A systematic study of the influence of deposition conditions on microstructure has been carried out in tin dioxide films produced by a pulsed laser deposition technique, with the aim of better understanding the influence of the microstructure on resistivity and improving their gas sensing properties. Gas detection is based on physicochemical reactions between gas molecules and oxygen species adsorbed on the surface: modification of the height of the grain boundary potential barrier occurs due to chemisorption, thus changing the electrical resistivity of the film. Sensor performance is related to the grain diameter, which determines the specific surface area available for absorption, and the density of lattice defects, such as oxygen vacancies and crystallographic shear planes that affect the electrical conductivity. The mean grain diameter and film composition are dependent on deposition temperature, oxygen partial pressure and subsequent annealing treatment. Films produced under a low oxygen partial pressure consist entirely of stoichiometric nanocrystalline SnO2, while those deposited in vacuum were non-stoichiometric and contained a mixture of amorphous SnO and nanocrystalline SnO2. Both the electrical resistance and gas sensing response depend on the surface oxidation state and the presence of oxygen deficient crystallographic shear planes. The sensitivity of films deposited at elevated temperature was higher than that of those synthesised at room temperature.

RICKERBY David;  SERVENTI Alessandra;  SKOULOUDIS Andreas; 

2011-01-03

Fraunhofer IWS

JRC58974