Professor David King FRS, Dr Heike Arnolds, Dr Stephen Driver and Dr Stephen Jenkins.
University of Cambridge.
If you were asked to describe what happens during a chemical reaction on a metal surface or substrate, you might look for a change in colour or temperature, or perhaps listen out for a bang. But chemists at the University of Cambridge have developed equipment that enables them to record chemical changes on surfaces at an extraordinary level of detail, by watching what happens to individual molecules and atoms, and recording the most fundamental steps in a reaction: how bonds between the atoms are made and broken.
Chemical reactions on metal surfaces are crucial to industrial processes that rely on catalysts to control the speed at which they happen, and the route that they take. For example, the catalytic converter that scrubs toxic gases out of car exhaust relies on a reaction that takes place on the catalyst surface. 'Our equipment means we can track changes in molecules, atoms and bonds on their own space and timescales to discover exactly what makes the best surface for a perfect reaction,' explains David King.
Individual molecules and atoms are tracked by a laser-heated, low temperature scanning tunnelling microscope (STM). This records where a molecule or atom sits in relation to the catalyst surface during a reaction, which helps us understand how it will react with the surface. STM pictures illustrate what surface features favour reactions; pulse-laser surface heating shows how atoms and molecules move across the surface.
Alterations in the bonds that bind the atoms are recorded by an ultrafast femtosecond laser, which detects the characteristic vibration connected with each bond. Data from the STM and laser are complemented by a third approach, theoretical modelling, which can 'try out' new surfaces more quickly than the experimental approaches and calculate what will happen under new reaction conditions.
Traditionally, our understanding of what goes on in a reaction has involved changing the initial conditions, such as temperature and pressure, recording the end products, and making an educated guess at what went on in between. The Cambridge group is now combining theory with practice to unpick this black box in the middle.
Web links
- Professor Sir Dave King
- Seeing is believing
- Surface science research group
See all exhibits from 2003