Academic Staff

Research Expertise

Surface Science

(see also the Research Centre for Materials and Surface Science)

Surface Science research is concerned with investigating (at the molecular level) the interaction of adsorbing atoms, molecules, or ions with the substrate surface. Some areas for which this is relevant, and in which work has been done at La Trobe, are heterogeneous catalysis, corrosion, ion-selective electrodes and microelectronic devices.

As an example of the former, consider the conversion of methanol (CH₃OH) to methanal (formaldehyde; H₂CO), which takes place over a copper catalyst. Surface science research over the past several years has positively identified CH₃O as the intermediate surface species, and indications are that it stands largely upright. What does this imply about the surface reaction mechanism? A reaction scheme as illustrated can be envisaged. Notice in particular that it could be expected that it would be necessary for the intermediate to be tilted in order for the second stage of the reaction to proceed.

A distinction needs to be made, though, between permanently and transiently tilted species. The latter could come about, as is indicated in the diagrams, by the intermediate having a 'wagging' vibration of substantial amplitude. However the situation is further complicated by the fact that the adsorption site may not lie entirely on   the surface. Instead the adsorbate may be partly incorporated into   the first substrate monolayer (as appears the case with the analogous CH₃S species). These systems form one of the 'new frontiers' of chemistry.

Some of the experimental techniques employed are Ultraviolet and X-ray Photoelectron Spectroscopies and Vibrational Electron Energy Loss Spectroscopy (all of which are energy-level-oriented), and Thermal Desorption Mass Spectrometry. These identify bonding interactions and surface species. Complimenting them are the structural techniques of Low Energy Electron Diffraction, Scanning Tunnelling Microscopy and X-ray Photoelectron Diffraction. Together, these enable the identification of adsorbate orientation, along with the actual sites at which surface reactions occur..

There are also similar investigations involving just solid materials. One line in particular concerns thin metal films on semiconductors, undertaken in conjunction with workers at RMIT and ANU. We have for some time been interested in several aspects of these systems, particularly the effect of various forms of radiation on interface properties, and recently have been studying III-V materials (eg GaAs) relevant to electro-optical devices. One matter of particular interest to us concerns the differences between metals which form either reactive, nonreactive but alloying, or inert films. The chemical identity and structure of the resulting interlayer is amenable to study by the above techniques.

Another program is concerned with ion-selective electrodes, such as the fluoride ISE (used to monitor added fluoride concentration in city tap water). Surface Science studies have revealed much about the processes which take place at the membrane surface (solution interface), including ageing and interference effects of hydroxide ions. Other studies include the growth and properties of alternative single-crystal ISE membrane materials.

Additional facets of work at La Trobe include theoretical modelling (of both free molecules and when adsorbed on substrate surfaces and clusters), instrumental development and computer interfacing, and data processing (including resolution enhancement of spectra via deconvolution ) [Comput-abs].