Sol-Gel Technology

SOL-GEL TECHNOLOGY

the sol-gel process is a versatile solution process for making ceramic and glass materials. In general, the sol-gel process involves the transition of a system from a liquid sol" (mostly colloidal) into a solid "gel" phase. Applying the sol-gel process, it is possible to fabricate ceramic or glass materials in a wide variety of forms: ultra-fine or spherical shaped powders,thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramic anda glasses, or extremely porous aerogel materials. An overview of the sol-gel process is presented in a simple graphic below.
The starting materials used in the preparation of the "sol" are usually inorganic metal salts or metal organic compounds such as metal alkoxides. In a typical sol-gel process, theprecursor is subjected to a series of hydrolysis anda polymeration reactions to form a colloidal suspension, or a "sol". Further processing of the ""sol" enables one to make ceramic materials in different forms. Thin films can be produced on a piece of substrate by spin-coating or dip-coating. When the sol" is cast into a mold, a wet "gel" will form. With further drying and heat-treatment, the "gel"is converted into dense ceramic or glass articles. If the liquid in a wet gel is removed under a supercritical condition, a highly porous and extremely low density material called "aerogel" is obtained. As the viscosity of a sol" is adjusted into a proper viscosity range, ceramic fibers can be drawn from the "sol". ultra-fine anda uniform ceramic powders are formed by precipitation, spraypyrolysis, or emulsion techniques.

INTRODUCTION

Thin films of ZnO have been an active area of research for nearly half a century due to the diverse technological of ZnO uniquely suited. It is an excellent material for a variety of photonic applications when doped with suitable dopant. Al or in, ZnO films are used as a transparent conducting electrode for display devices and amorphous silicon solarcells. Due to their piezoelectric and semi-conducting properties, thin films of ZnO are extensively used in surface acoustic waves (SAW) components and various MEMS-based sensors. The properties of ZnO films depend upon the method of their preparation. Characterization of ZnO films becomes important in deciding their device worthiness in the light of the cost effectiveness, consistency andreliability of the sensor . It, thus, becomes important to investigate the crystalline features of these films for any preferred orientation during growth. Nanostructured zinc oxide materials are of current importance in electronic, optic and photonic applications and form the basis of nano-technology applications in sensors and molecular electronics. The nanostructures exhibit novel electrical,mechanical, chemical and properties which are believed to be due to the surface confinement effects of nanostructures in one dimension (1D). These 1D objects are of great importance in understanding some basic physics related phenomena in the low dimension systems to anodevices.
The current initiatives in nanotechnology research have led to discovery of a variety of nanostructures of ZnO such asnanrods, nantubes, nanobelts nanorings, nanocombs, nanosaws, nanosprings, nanospirals, etc. Wang has recently presented an excellent survey of the growth, properties and applications of a variety of nanostructures of zinc oxide. Nanowires of ZnO are a promising candidate as probe for AFM cantilever due to their high mechanical stability. However, a sharp needle shaped structure would still be a betteroption for the tip of the AFM probe. The results on the films of ZnO grown by sol-gel method have been presented. This technique of film preparation is a low. cost process and is attractive as the film properties can be tailored conveniently for a given application. This process, thus, becomes a preferred option for exploratory studies where a large number of candidate materials and properties...