Thin Film Photonics Research Group

The Thin Film Photonics Group WWW pages are at http://newton.ex.ac.uk/research/thinfilms/.
The Nonlinear Optics WWW pages are at http://newton.ex.ac.uk/research/nonlinear/.

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This is one of the largest research groups in the country working on the optical and other physical properties of thin films and interfaces.

The group, formed in 1983, has evolved into a cohesive unit in which individual success is promoted in an environment of co-operative team effort. Much of the work conducted is receiving international recognition and all of the members are expected to spend some of their time collaborating with scientists overseas.

At present the group of 23 personnel, led by Professor Roy Sambles, has four full time academic staff members, two technicians, seven research fellows and ten research students. Each student is encouraged to produce a minimum of four research papers in their three years in the group and presentations at conferences overseas is also given a high priority. Substantial funding from various organisations means that even though there are a large number of individuals little sharing of equipment occurs. This means that progress on a weekly basis is very rapid, thus the period from the germination of a new idea to the realisation of new results may be as little as a few days. With such rapid progress available this makes for a very lively research environment in which to work.

Rationale

The study of interfaces and the properties of thin films are crucial to the development of a satisfactory comprehension of many potential devices in the areas of optoelectronics, optical display systems, molecular and biological sensors.

Techniques involving the propagation of surface polaritons along interfaces and guided waves in thin layers and the excitation and characterisation of fluorescence in such structures have been developed at Exeter as tools to investigate the properties of multilayer structures and surfaces. These methods have proved extremely valuable in identifying, and enhancing our understanding of new phenomena. This work has been aided by the development of computer simulations which model the experimental situations allowing interactive comparison between experiment and theoretical analysis. From this many new avenues of research have been found and new areas for device potential have been uncovered, many of which we are now exploring as pioneers.

Primary Research Areas

The group is very active in the following areas of basic research, all of which are related to potentially exploitable devices and which are therefore of interest to industry as well as the general scientific community. A significant proportion of the research is sponsored by research establishments in the UK including DRA (Malvern), NPL, SHARP, Thorn EMI and DRA (Poole). There are also collaborations with other academics at Strathclyde, Hull, Bristol, Cranfield, East Anglia, Cambridge and elsewhere.

Photonic Surfaces

New developments in optical structures are being realised with parallel research into both the theory and the practical realisation of corrugated (grating) surfaces which support optical modes with novel properties. We have already produced original results on optical band gaps in grating systems, added fluorescent overlayers and exploring fluorescence lifetimes is now forming a new focus of research with very demanding theoretical modelling to complement experiment.

We have extended grating theory to bi gratings and to gratings containing uniaxial media and the incorporation of fluorescent entities in this modelling is the next step.

Surface Polaritons

The coupling of radiation to surface modes, including surface plasmons and surface excitons is being developed with grating surfaces. This not only allows fundamental studies of the surface modes but also gives opportunities for surface profile characterisation (of vital importance to various industrial colleagues), development of novel bio sensors (in collaboration with CSIRO, Australia) and novel optically probed electrochemistry.

Liquid Crystals

The understanding of the alignment of liquid crystals and the response of aligned layers to applied electric fields plays a vital role in the design of LC displays. An extensive program of research has led to a thorough understanding of the behaviour of nematic liquid crystals at both high and low fields. New results on ferroelectric liquid crystals are beginning to unravel the complex nature of these exciting new display materials. This field of research has great commercial interest as well as being exciting fundamental science. As yet there is no satisfactory continuum theory available to model the ferroelectric liquid crystal phase and our novel optical studies, combined with theoretical developments at Strathclyde, Sharp and DRA (Malvern) are leading this new area.

Control of Molecular Fluorescence

A new area of research for the group is to control the emission of fluorescent molecules by surface geometry. The optical properties of an ion or molecule depends not only on their immediate chemical environment but also on the geometry of their environment at the scale of the wavelength of light. Carefully controlled experimental conditions and sensitive optical techniques are being used to investigate this new branch of quantum optics.

Molecular Electronics

New techniques allow the deposition of organic molecules in a monolayer form into ordered structures offering the potential for producing microscopc molecular devices - so-called molecular electronics. To achieve this potential it is essential to fully understand the bonding of such layers to substrates and their structural characateristics as well as their conduction properties. Very careful experiments of this kind have led to the fabrication of the first metal/organic monolayer/metal capacitor and the prototype organic diode.

Experimental Facilities

1. Two ultra-clean rooms for Langmuir-Blodgett film deposition.
2. One semi-clean room for production of Liquid-crystal cells, surface acoustic wave devices and LB deposition.
3. Thin film deposition room equipped with four vacuum evaporators.
4. Ten dark rooms for optics experiments.
5. Fluorescence lifetime and time resolved spectroscopy equipment.
6. An Argon-ion laser for production of holographic gratings and for optical studies of Liquid crystals.
7. Three convergent beam, linear diode array or CCD optical systems for dynamic studies.
8. Five lathe bed optical bench systems, with computer controlled rotating tables for studies of guided and surface modes.
9. Two multi wavelength monochromator systems.
10. Two dye lasers pumped by Argon-ion lasers, for spectroscopy.
11. Two UV lasers for fluorescence studies.
12. Two silicon graphics workstations.

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