The features of organic thin films are in the versatility of the molecular structures and the molecular aggregation states. A specialproject research on organic thin films for information conversion, which is supported by the Grant-in-Aid from the Ministry of Education, aims at the most efficient information conversion of the aggregated molecules in organized molecular environments. In this paper, the responses of the organic thin films to electrical and/or optical excitations are discussed in terms of the molecular structure and molecular alignments in thin films. Some problems to be solved are also pointed out.
Recently, there has been a wide range of interest in thin organic film fabrication technique. The Langmuir-Blodgett technique is one of the most promising techniques for fabricating ultra-thin organic films. In this paper, recent topics in LB films are summarized from the point of view of film fabrication technique. Particularly, insulating and conducting LB films are described. Polyimide LB films having a monolayer thickness of about 4Å, polybutadiene LB films, hetero structure LB films, and so on are briefly mentioned. LB technique is now rapidly progressing, and highly controlled LB films with excellent crystallity will be produced in the near future.
Thin oriented films of some organic compounds can be prepared by either the vacuum-deposition method or the Langmuir-Blodgett method. The characterization of the structure of thin films is carried out by electron microscopy. The orientation of thin films is determined by several experimental methods : electron diffraction, decoration and high resolution electron microscopy for the vacuum-deposited films, and shadowing and replica methods for L-B films.
Recent trends on the electrical properties of organic thin films are reviewed concerning the new development of functional molecules and the expansion of the fabrication for insulators, conductors, and their composites. They include evaporated films, electrically polymerized films, and Langmuir-Blodgett films. The orientation control by liquid crystal and epitaxyal growth were profitable for realizing the highly ordered structure of polymers for the improvement of conductivity. A variety of electrical devices are proposed, using conducting polymers for switches, memories, displays, and sensors. Thermal stable Langmuir-Blodgett films without long alkyl chains are fabricated.
Molecular superorganizates imply that the structures are designed and arranged in different organic molecules individually, with the result that they reveal a unique phenomenon, an excellent property and something new. LB technique would be useful for constructing molecular superorganizates. A review of the optical properties of organic thin films, such as non-linear optics, photoelectric effects, and photochromism, is presented with this in view. Furthermore, the possibility to control and modify polar structures, molecular interactions, molecular heterojunctions, and photochemical reactions by organizing molecules is discussed.
The efforts for preparing functional organic thin membranes are now being continued extensively. A novel stage of the organic thin layers with good separation properties was initiated by the successful preparation of asymmetric membranes for reverse osmosis by Loeb and Sourirajan. In these membranes the thin layers with active properties for separation are formed with the supporting layers by the phase-separation mechanism. In continual efforts to develop novel and high speciality functions, very thin organic membranes, such as monolayers and bilayers, have been prepared and made functional. These processes and future problems are briefly reviwed.
Electrochromic iridium oxide thin films have been investigated by a new method of electrodeposition. The transparent conductive glass was cathodically electrolyzed in an aqueous solution of 3wt% Ir(SO4)2·nH2O at a constant current density of ca. 30mA/cm2 at 32°C. After this procedure the thin films on transparent conductive glass were heat-treated in an electric furnace at 350°C for 30min. The cyclic voltammograms of electrodepositediridium oxide films (EIROF) shows 2 pairs of peaks at 0.25V (vs SCE) and at 0.7V (vs SCE), which are corresponding to oxidation state and reduction state respectively. Electrodeposited iridium oxide films have a strong adhesion to the transparent conductive glass. It is chemically very stable and showed a good reversibility of ECD. Life test of more than 105 cycles in 0.5M H2SO4 leads to no detectable deterioration.