Ionization-Assisted Deposition of Large Molecular Weight Organic Materials and its Mass Analysis

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A new technique of depositing high-quality thin films of large-molecular weight organic materials is required for the development of functional organic thin film devices. A dry process, that forms thin films in the clean environment of vacuum, is especially favorable for the future development of micro devices. However, it has been difficult by the conventional vacuum evaporation technique to produce thin films of organic materials that have high molecular weight. This project aims to solve this problem by developing a new process technique, ionization-assisted deposition. The emphasis is to study the high molecular weight organic thin films from the standpoint of process technology. Its strategy is largely classified in two categories ; 1. Direct deposition of organic molecules, and 2. Film formation that accompanies polymerization process in the course of deposition. The latter category is subdivided into two methods according to the type of polymerization reaction ; stepwise reactio … More n and chain reaction.In the first sategory, we have deposited several monomer materials, including perylenetetracarboxylicdianhidride and 8-hydroxyquinoline aluminum. It has been found that the ionization-assisted deposition method was effective in controlling the semiconducting and light emitting properties of these materials. The technique can be applied for the development of thin film devices such as organic light-emitting diode. As a polymeric material, direct deposition of polytetrafluoroethylene was deposited by the ionization-assisted method. Thin polymeric films that have controlled molecular orientation and improved electrical insulation capability were obtained.In the second category, monomer source materials were evaporated to form polymeric thin film by the reaction on the substrate surface. Polyurea thin films were obtained by stepwise reaction of two codeposited monomers ; diisocyanate and dipiperidine. It was found that the ionization-assisted deposition can control the dipole orientation during the film formation by means of the bias voltage on the substrate and the ionic charge accumulated on the film surface. As a consequence, the as-deposited films showed optical nonlinearity and electro-optic effect without additional poling process. Some vinyl compounds were polymerized by chain reaction on the substrate surface. Although the simple evaporation technique does not yield polymeric films, the ionization-assisted deposition can excite the molecules during the deposition and can control the polymerization reaction by the ion current and ion acceleration voltage. Mass analysis of the deposition beam showed that the polymerizable molecules easily form fragments upon the ionization process. Less