Doping of Polymers with ZnO Nanostructures for Optoelectronic and Sensor Applications

The discovery of new materials with unique properties often leads to new technology. After discovery of conductive polymers at the end of the 1970s, it opened up a whole new research, which eventually led to a new technology of plastic electronics (Chiang et al., 1978). When interesting material properties are observed in the laboratory, efforts are made to understand their mechanisms, which leads to the fine control of the fabrication process of this new and potentially important material. If future applications are anticipated, optimization of material properties becomes a continuous and sometimes a lifelong process. Doping of materials is one of the ways of modifying their physical properties. For example, a pure silicon (Si), which has a very poor electrical conducting properties can be doped with boron or arsenic to make it a good hole or electron conductor respectively. This opened up a new class of doped-Si materials, which is now the basis of perhaps the largest global electronics industry. Polymers, which consist of large molecules linked together in repeated fashion to form long chains, have naturally existed for a long time. Examples are tortoise shell, tar and horns. Today synthetic polymers are finding important applications in many areas. Polyolefins, epoxies and engineering resins are crucial materials for construction, commerce, transportation and entertainment. They are very appealing alternative materials because of the simple processing they offer such as drop casting, spray painting and printing. In addition, they almost provide low cost large-area scalability. In most applications however, polymeric materials are multicomponent systems. The integration of fillers such as minerals, ceramics, metals or even air, can generate an infinite variety of new materials with unique physical properties and possibly reduced production cost. Typically, when the filler in these multicomponent systems, which represents a minor constituent, has at least one dimension below 100 nm, the resulting material is termed, “polymer nanocomposite“ (Winey & Vaia, 2007). Reseach in this area is very active and promising, mainly because of many different combinations of polymers and filler materials that can be explored. Few examples of fillers that were recently reported are SrTiO3 (Umeda et al., 2009), fluorinated single walled carbon nanotubes (Bennett et al., 2009) and ZnS-coated CdSe nanocrystals (Kim et al., 2009). The addition of a small amount of filler material into a host polymer can be considered a doping process if there is an intention of modifying the physical properties of the host. Some fillers, particularly with macroscopic dimensions, do not chemically react with the polymer so they cannot be regarded as dopants. Nanomaterials are attractive dopants to polymers