Preparation And Oxygen Sensing Performance Research Of Nb-doped TiO₂Thin Film With Porous Structure

Metal oxide semiconductor materials appear to be one of the best candidates forgas-sensing due to the strong dependence of electrical conductivity on the ambient gascomposition. Among all the conventional semiconducting metal oxides, TiO2has beendemonstrated to hold a substantial promise for oxygen sensor devices due to its goodchemical stability even at high temperatures. Also, TiO2-based oxygen sensors havesuperior durability against lead poisoning compared with ZrO2-based oxygen sensors. Atpresent, Niobium acting as a dopant to improve the oxygen sensing properties has notreceived much attention for use in the field of TiO2-based thin film oxygen sensor In thispaper, we have prepared the crack-free TiO2porous thin film and measured the oxygensensing properties of both the undoped and doped TiO2thin film. In addition, therelationship between microstructure of thin film samples and their oxygen sensingproperties have also been studied. The mechanism for reponse to O2is discussed. Theresults are listed below:1. Nb-doped titanium dioxide thin films were fabricated via the sol-gel method from astarting solution of TiCl4dissolved in ethanol. Dip-coating was used to deposit the solon the aluminum oxide substrates. The materials had been structurally characterizedby means of X-ray diffraction,field-emission scanning electron microscopy.Thecompositions of the films were determined by energy dispersive spectroscopy(EDS)using an field-emission scanning electron microscopy. The results demonstrate thatthe TiO2porous thin film with no crack can be prepared via sol-gel process andmanifest that Nb main partially fill the cation sites that would normally occupied byTi atoms owing to the similarly in ionic radius between Ti4+(0.68) and Nb5+(0.70).2. Both the anatase and the rutile exist in the pristine and Nb-doped TiO2porous thinfilms annealed at800℃. The intensity of the (110) diffraction peaks becomes smaller with the increase of the Nb doping manifesting that the introduction of the Nballows the retarding the anatase to rutile transformation.3. All the thin films show porous wormlike structure constructed by continuouslyconnected nanoparticles possessing a uniform size and shape. Nb doping can impedesgrain growth and improve the special surface area of the thin film which are favorablefor the sensor signal. It can be found that TiO2thin film with6%Nb doping shows themaximal S values of11.3and11.9times higher than those of the undoped TiO2thinfilm at operating temperature of700℃at the concentration of2%and20.9%,respectively.4. The reaction between the target gas and the surface of material controls the responsetime for the thin film sensor. Nb doping is beneficial to the adsorption anddissociative adsorption reacting on TiO2porous thin film surface. Compared to theundoped TiO2thin film oxygen sensor,6%and8%doped ones show significantlyshort response time.