Thin Film Deposition By Sol-Gel and CVD Processing of Metal-Organic Precursors

Abstract

The application of metal-organic chemistry has played a major role in the development of thin film deposition by Chemical Vapour Deposition (CVD) and Sol-Gel techniques [1–2]. The success of chemical synthesis routes is largely attributed to the availability of molecular compounds that can be transformed via solution (Sol-Gel) [3–6] or gas phase (CVD) [7,8] reactions into high-purity coatings of desired ceramics or composites. In contrast to the solid-state reactions, the reactions in vapor or liquid phase allow a controlled interaction of atoms or molecules to form uniform films or particles. Further, the flexibility to combine different ligand or metal combinations allows the precursor designing to meet the demands of the target material. Assembling all the phase-forming elements in a single molecular source augments the advantages of chemical processing and simultaneously reduces the process parameters. In addition, the molecule-to-material transformation requires much lower temperatures than those required for the conventional (mixing, grinding and calcining) methods [9]. The clear practical implications of nanostructured materials [10,11] with a precise control over composition, size, size distribution and morphology has led to an upsurge of research activity in the synthesis and chemical processing of molecular precursors [12–17]. Among the various inorganic compounds—halides, nitrates, acetates, carboxylates, ß-diketonates, alkyls, alkoxides—used in the synthesis of metal oxides, metal alkoxides (M(0R)_n) are especially attractive as precursors [18–24]. Some of their salient features include high purity, easy transformation into oxides with formation of volatile byproducts, ability to form homogeneous solution in different solvents and conditions and more importantly the facile formation of heterometal species useful for the synthesis of multicomponent materials [25]. The present article is intended to provide a brief account of the recent developments in the field of heterometal alkoxide chemistry and their applications in obtaining nanocrystalline thin films.