DAVID McCOMB

The chemistry of surfaces and interfaces plays a crucial part in almost every walk of life, from applying paint to car body parts to the bonding and adhesion of replacement hips with bone. Hence, it is important to develop fundamental understanding of chemical interactions at surfaces, and interactions at interfaces between surfaces. To this end, probes that can be used to analyse the chemistry, bonding and structure of surfaces and interfaces are essential. In my research I apply two complementary techniques to studies of chemical bonding at surfaces and interfaces: analytical electron microscopy and scanning tunneling microscopy.

The analytical electron microscope (AEM) can provide information on the structure of a specimen by high-resolution imaging and electron diffraction. Using suitably prepared specimens this allows identification of interfaces and structural characterisation. Use of analytical techniques in the electron microscope, e.g. energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy (EELS), permits the chemical identity and coordination chemistry to identified with high spatial resolution (5-10Å). Successful identification of an interfacial phase in SiC-reinforced Mg alloys was achieved recently using EELS by utilising the results of earlier EELS studies of silicate minerals.

Atomic resolution studies using scanning tunnelling microscopy (STM) have given unprecedented insights into the structure and bonding on surfaces, and with the development of variable temperature systems it is now possible to follow reactions on surfaces on the same scale. In the past I have used STM to follow in a stepwise fashion the reaction of Ag on Si(111) and have identified reaction intermediates which are formed due to the kinetics of the nucleation and growth process. STM has also been applied to the study of clusters on surfaces with the aim of providing insight into size-dependent properties of nanostructures with obvious relevance to catalysis as well as semiconductor devices. In more recent work I have applied cross-sectional techniques with both STM and AEM to characterise the local chemical fluctuations during growth of InGaAsP multilayer structures.