Dr Andrew Thomas, Research Fellow, Department of Physics

My main research interests lie in the adsorption of molecules on surfaces. The interaction of molecules at surfaces is important in a number of fields such as biomaterials and biosensors, TFT (molecular electronics) devices and catalysis. Understanding how molecular adsorption influences the electronic structure of the molecule and the substrate onto which the adsorb helps us to understand electron transport mechanisms in these layers and how overlapping bands allow electrons to move from the molecular layer to the substrate and vice-versa. For example in biosensors an ideal device would simply anchor molecules onto an electronic material and when this device detects a virus, protein or other biological molecule or organism would cause an electron transfer process between the electronic material and the molecular layer. This change in state would then allow us to determine the presence of our target. This is basically how the electronic detectors used for monitoring blood glucose levels in diabetic patients works. For these types of experiment we use photoemission spectroscopy and resonant photoemission spectroscopy which allows us to determine which atoms or ions in a system contribute to particular electronic states in the solid.

In addition we need to understand how the arrangement of molecules on the surface governs the transport of electrons through the molecular layer. Using the searchlight effect in NEXAFS (Near Edge X-ray Absorption Fine Structure) we are able to determine whether a molecule stands up or lies down on a surface. Other techniques such as LEED (Low energy electron diffraction) and STM (scanning tunnelling microscopy) help us see if the molecules form ordered overlayers on the surface.

The figure below illustrates the types of interaction we might expect at a biomaterial interface:

As can be seen water adsorption is thought to play an important role in governing the later adsorption processes