A Modified Chemical Route for Synthesis of Zirconia Thin Films Having Tunable Porosity
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1074-I10-34
A Modified Chemical Route for Synthesis of Zirconia Thin Films Having Tunable Porosity Manish Kumar and G. B. Reddy Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India ABSTRACT A modified chemical synthesis route is reported for deposition of zirconia thin films having tunable porosity with average pore size in nanometer range. Deposition method is simply a sol-gel dip coating in which HCl is used as catalyst. TEM and FTIR studies of deposited films show porous microstructure, which depends critically on ageing of sol used. The shift in binding energy of Zr 3d5/2 (at 182.4 eV) attributes the formation of zirconia. Optical results show high transmittance (> 80%) in VIS-NIR region and effective refractive indices values (neff) tend to decrease for films prepared with higher aged sol. Porosity enhancement from 15-52% is observed by neff comparing with refractive index of non porous films (nz). INTRODUCTION Porous thin films of dielectric oxides have been finding more and more applications in various areas such as optics, microelectronics, membranes and sensors [1-4]. Average pore size and their distribution influence the diffusion and equilibrium of molecules adsorbed in the structure. Controlled porosity provides filling of variable amounts of reinforcement of dielectric oxides /semiconductors /metals, which in turn modify optical, electronic, mechanical, chemical and magnetic properties. This demands finely tuning of the pore size and porosity of the thin films. Among the dielectric oxides, zirconia having large band gap (>5.7 eV), excellent transmittance in visible region and high refractive index (>2) is emerging as a multipurpose material. It is reported in literature that zirconia films can be used to prevent chemical corrosion and oxidation in metals [4], to minimize thermal losses [2], and to sense oxygen [5]. Many deposition methods have been adopted to prepare zirconia films, which include atomic layer deposition [6], r.f. magnetron/reactive sputtering [7], chemical vapor deposition [8], pulsed laser deposition and sol-gel dip coating/spin coating [9]. Among these techniques, sol-gel is the most suitable technique for controlling the porosity (p) and to deposit on any geometrical shapes required for practical applications. Variety of additives like yttria, ceria, β-diketone and acetic acid, have been used to control the gelation process, which influences both pore size and porosity. In this paper, we attempted HCl as choice of additive to control the gelation process in the sol and examined the feasibility of obtaining zirconia thin films having pore size in nanometer size.
EXPERIMENTAL DETAILS Sol of 0.1 M was prepared by mixing zirconium n-iso propoxide (M/s STREM chemicals) precursor in iso-propanol solvent and stirred for 6 h. HCl was mixed in the appropriate quantity for controlling the hydrolysis rate. This solution was stirred for 18 h keeping temperature constant at 35°C and humidity between 40% and 50%. Films were depos
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