Structure and properties of TiO/sub 2/:Fe thin films prepared by the sol-gel technique

Abstract

TiOz thin films doped with Fe have been prepared by using the sol-gel process on silicon substrates. A metal-organic precursor solution for coating silicon substrates was synthesized using a Ti alkoXide derivative iron salt and isopropanol as a solvent. Acetylacetone was used as an inhibitor of derivative iron hydrolysis-condensation reactions. The structure of the fIlms was investigated by X-ray diffraction and Raman scattering analysis. The electrical characterization of the fIlms is reported. A. IntroductionThe phenomenon of a conductive film sensitive to the presence of gases has been known and studied for many decades. Ti02 has been mainly studied in bulk or thick film form as a material for sensing 02 gas at temperatures as high as 800°C. However, there have been few trials to develop Ti02-based thin films to detect gases at low temperature. We have previously suggested [1] that the use of a metal-organic precursor as a starting material is an effective way to improve gas sensitivity and selectivity at low temperature. With this method it is possible to form films with controlled microstructure on the nanoscale since each element in the precursor, including the hetero component, is homogeneously dispersed and bonded at the molecular level.In order to improve the sensing properties of Ti02 thin films, several metal nanoparticles such as: Nd, pi [1], Y, Ce, Sr, Tb [2] have been embedded in titanium oxide matrices. Experimental results indicated that the doped Ti02 thin films were sensitive to methanol and insensitive to CO, N02 and C6H6 at low operating temperature [1]. To improve the gas sensitivity and selectivity at low temperature, we tried to dope some other elements into Ti02 matrix. In this study, trivalent iron (Fe3+) has been used to improve the sensing characteristics. The ionic size of Fe3+ ( O.58A) and Ti 4 + (O.61A) are very close to each other.Therefore, Fe ions can go into the lattice as substitutional metal dopants. The trivalent Fe acts as an acceptor type impurity and by addition of a trivalent dopant the concentration of oxygen vacancies increases in the titanium lattice.In this paper, we have used the sol-gel technique for the preparation of Ti02 doped with Fe. The role of the Fe metal ion in Ti02 has been discussed on the basis of results obtained from thermal analysis (DSC, TGA) and Raman spectra. B. ExperimentalThe precursor solution was prepared by using starting materials of titanium butoxide (TBOT) (Ti(OC4H9) 4 ) and iron salt Fe(N03)3.9H20 with a purity of 99.9% and 99%, respectively. Analytical purity isopropanol (lPA) was used as the solvent. RN03 (2N) was used as the catalyst and acetylacetone (ACT) was used as an inhibitor of hydrolysis-0-7803-6698-0/00/$10.00