Nanocomposite Films of Metal Oxides in a Plasma Polymer Matrix and Their Properties

Nanocomposite metal and metal oxide plasma polymers can be utilized for many applications such as optical coatings, protective films, biomedical materials etc. Mechanical, optical, electrical properties of such nanocomposites are shortly reviewed below. Particularly optical and electrical properties as a function of the filling factor are presented too. The experimental part of the paper describes the preparation procedure and recent results on studying SiOx/plasma polymers and TiOx/plasma polymers. Introduction It has been known for many years that an electrical discharge in organic vapours may lead to the formation of deposits on the surfaces in plasma. For some time these coatings have been considered as unwanted byproducts [1]. Since then the area of plasma polymerization has become well recognized as an important part of material science. Plasma polymers have been suggested for application in many fields of science, particularly chemistry, physics and in the recent years in biology. Furthermore, a new class of materials based on plasma polymers has emerged where an inorganic component is admixed to plasma polymer matrix during the deposition. Composite metal/plasma polymer films have been studied in detail with Ag, Ni, Mo, Cu and Ge used as inorganic fillers dispersed in a plasma polymer from a hydrocarbon precursor [3-8]. In the recent years, a research interest has moved to more complex composite systems, and metal oxide (SiO2 and TiO2)/plasma polymers have been considered [9-12, 18-20] Since the inorganic component in these materials is very often present as a separate phase in a form of inclusions with a nanometre scale the resulted films have been referred to as nanocomposites. The presented contribution is aimed to describe the main properties of nanocomposite plasma polymers, the deposition techniques and to review the recent results and progress in this field to set the perspective for the future research work. Plasma polymers Plasma polymer thin films can be prepared by using plasma polymerization processes. Such coatings have only distant similarity with conventional polymers, materials with regularly repeating structure. The structure of plasma polymers depends on the deposition parameters i.e. the monomer used, the pressure, the reactor geometry, the substrate and its position within plasma, its temperature, electrical bias etc. [for more details see Ref. 1 and 37] Various excitation, ionization and dissociation events running in plasma cause the formation of highly reactive carbon-based radicals which take part in polymerization reactions. In addition, the radicals can participate in polymerization reactions with precursor species provided that the latter contain unsaturated bonds. Such a complex ensemble of the possible reaction pathways results in deposition of plasma polymers which are not composed of regular repeating units. Their chains are branched and crosslinked (Fig. 1), and plasma polymers are usually amorphous.