"But mass is such a fundamental unit that even this very small change is significant and the impact of a slight variation on a global scale is absolutely huge. There are cases of international trade in high-value materials - or waste - where every last microgram must be accounted for.
"What we have done at Newcastle is effectively give these surfaces a suntan. By exposing the surface to a mixture of UV and ozone we can remove the carbonaceous contamination and potentially bring prototype kilograms back to their ideal weight."
The kilogram is one of the seven SI base units from which all other units can be derived and is the only one which is measured against a physical object the IPK all others are standardised against known constants.
The Newcastle team are now moving on to study the addition of mercury from the atmosphere, something Professor Cumpson first identified while working at the NPL in the 1990's. But it is the development of techniques such as XPS which has allowed them to accurately measure how the build up of chemicals such as hydrocarbons can be most effectively removed.
Newcastle University hosts the 3million National XPS service funded by the Engineering and Physical Sciences Research Council (EPSRC).
Using a Theta-probe XPS machine the only one of its kind in the world - Professor Cumpson and Dr Sano showed how the UV/ozone wash could be used to remove contamination without damaging the platinum surface. "The Theta probe allows us to look at the composition of very thin layers by measuring the angle at which the electrons emerge from it," explains Professor Cumpson.
"Rather like an MRI scanner, it takes a cross section of the material but at an atomic level. The second part of the machine is the Argon cluster ion gun which fires charged 'droplets', each containing about a thousand
|Contact: Peter Cumpson|