Cookies

We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Centre for Materials Physics

Research

The seeds of a new concept in interferometry

Integrated Optical Sensing

We invented a new integrated optical interferometer now commercialised as an optical biosensor. Simple end illumination of the device is all that is required for this interferometer to work, generating a Young's fringe interference pattern that can give real-time information on the thickness and density of biological films growing at the surface.

A microscope image showing birefringence within a nematic liquid crystal.

Liquid Crystals

The research activity is directed towards investigations of the guest-host effect in dye doped liquid crystals. We explore the possibilities to use these systems in display applications. There are several potential benefits with this approach, one being a way forward towards a flat, perhaps flexible full colour display with low power consumption. More fundamental questions are also addressed such as the strength and character in the interactions between guest and host (dye and liquid crystal) in these systems. We use a range of methods to investigate the materials but optical spectroscopy plays an important role in our investigations. Work is now underway to explore the structure of the layers of liquid crystal that lie adjacent to the substrate. Using dual polarisation interferometry (see "Integrated optical sensing" section) we have been exploring the growth of these layers by condensation from the vapour phase and monitoring the evolution of the average polar alignment during the layer densification.

Non-linear Optic Materials

Electro-optic effects in organic materials can be larger and show faster responses than those of inorganic materials. Our work targets new molecules and polymers that should bring high bandwidth and low drive voltage modulators and switches into wide deployment in the metro, as well as long haul, telecom network.

Quantum Tunnelling Metal Composites

A local high technology materials development company, Peratech, has invented a new type of metal-polymer, named "QTC" (Quantum Tunnelling Composite). This unique material displays very large changes in electrical conductivity when mechanically deformed in any way (ie: compressed, stretched etc). The reason for this unusual electrical behaviour is thought to be due to a quantum-mechanical tunnelling process, whereby conduction electrons tunnel from one metallic grain to another.

Top: The family of QTC fabrics & materials. Middle: Scanning Electron Microscope (SEM) images of metal powder used in QTC. Bottom: QTC fabric, 'roll-up' keyboard & a jacket sleeve featuring a control panel for the operation of a personal stereo.

Historical background to QTC

In 1996 David Lussey approached Prof. David Bloor via Knowledge House, which provided an interface between academia and industry in the North East, with an electrically conductive, metal-polymer composite that he had discovered and thought had unusual properties. Prof. Bloor's initial measurements revealed this was the case laying the foundation for on-going research collaboration. This research is unusual as it is the result of the "spinning-in" to the Department of a novel material, which did not conform to accepted physical models. The Department's role has, therefore, been one of providing scientific expertise and experimentation to provide a proper understanding of the physics of the material as a foundation for the development of parallel commercial activity. This has played an important part in the growth of the company (Peratech Ltd) founded by David Lussey to exploit the unique properties of the composite, which has applications in areas associated with touch sensitivity and human interaction with screens, keyboards, controls and switches as well as robotics, security and medicine. A percolation model was used to describe metal polymer composites with the conductivity rising at the percolation threshold when there are enough metal particles to form chains in intimate contact and provide conductive paths spanning the material. As metal content is increased the conductivity increases rapidly across a narrow concentration range as more percolation paths form until saturation is approached when the conductivity rises slowly to its maximum value. David Lussey's composite, loaded above the percolation threshold with Ni powder, should have been conductive but was insulating until deformed. It became conductive when not only when compressed but also when stretched or bent. Our studies revealed that the silicone elastomer matrix intimately coated the Ni particles, which retained sharp surface features with nanometre dimensions1. Electrical charge residing on the Ni particles produces very large electric fields at the tips of the surface features facilitating electron tunnelling through the relatively thick, adhering, insulating polymer. Deformation reduces the barrier thicknesses and gives rise to large changes in sample resistance, a reduction greater than 1014 has been observed in compression2. The underlying physics resulted in the material being called Quantum Tunnelling Composite (QTC). Peratech has grown strongly over the last five years and developed a variety of conductive composites tailored to clients' specific end uses. Recently Samsung and Nissha Printing have started using printable forms of the composites in mass-market products and this is providing licensing revenues to Peratech amounting to almost £1million in the first year. Research utilising the Department's state of the art facilities now focuses on the new generations of Peratech's composites. On its part Peratech participates in the Department's teaching providing materials and manpower to support B.Sc. Team Projects, M.Sci. final year experimental projects and giving lectures on the company's activities.