Polar Langmuir-Blodgett thin film layers for non-linear optical and pyroelectric applications

Advances in the synthesis of non-centrosymmetric molecules coupled with the recently acquired ability to incorporate them into stable three dimensional arrays with a high degree of order, holds out exciting possibilities for the development of high quality, low cost organic materials for a variety of applications. Langmuir-Blodgett (LB) films possessing a unique polar axis can be fabricated by depositing head to tail sequences of a specially designed molecule or better still by forming organic superlattices (alternate layers of different molecules) using purpose built equipment. Two device areas of particular interest that capitalize on this ability to form supermolecular assemblies are optoelectronics and pyroelectricity. This paper reviews the efforts that have been made in engineering molecules so as to optimize their non-linear properties. In the optics field, most attention has been placed on materials designed specifically for second harmonic generation applications. For thermal imaging purposes the emphasis is on molecular structures with low relative permittivity and dielectric loss that can be deposited on low thermal mass substrates. Considerable progress has been made during the past two years. Results are described confirming the great potential of LB films in these important areas of research.