The preparation and characterisation of novel organo-ruthenium Langmuir-Blodgett films
In recent years, there has been considerable interest in media which exhibit significant non-linear physical properties. The non-linear optical response of many materials has attracted a great deal of attention from the telecommunications industry owing to their possible use for signal processing applications. Also, applications such as thermal imaging depend ultimately upon the proficient operation of the active material within the device structure. Traditionally, inorganic materials such as lithium niobate and strontium barium niobate have been used for non-linear optics and infra-red detection. However, the last decade or so has exposed the potentially high efficiency offered by organic materials which, coupled to the ability to engineer their physical properties by subtle modifications at the molecular level, suggests an exciting and productive future. In order to maintain compatibility with existing integrated optics and display technologies, it is often useful to process the active compound in thin film form. The stringent symmetry requirements imposed upon the molecules and their organisation in the macroscopic structure necessitates the existence of non-centrosymmetric molecular structures for second-order non-linear applications such as those mentioned above. The Langmuir-Blodgett deposition technique enables such assemblies to be constructed by the sequential transfer of organic monomolecular layers from a liquid-air interface onto a solid substrate. The precise control of film thickness and molecular architecture afforded by the technique allow polar multilayer structures to be produced which possess the properties required for highly efficient second-order non-linear physical operation. This thesis describes the development of a series of novel organo-metallic complexes which possess the necessary molecular properties for LB deposition in addition to those required for the observation of a large non-linear response. The complexes offer substantially improved thermal stability over other LB materials, and are thus appealing to the industrial device engineer. Their physical properties have been systematically studied and related to their detailed molecular structure. In particular, optical second-harmonic generation studies have shown that they possess high molecular coefficients and have provided a launching stage for further development. Their high pyroelectric response has attracted much enthusiasm from both industry and academia because of their potential commercial exploitation in thermal imaging devices.