Purer and smoother coatings to reduce friction between mechanical components could help the tooling, textiles and microelectronics industries.
Coatings are used in devices such as reading and writing heads on PC hard drives or machine tools.
But performance is determined by the way the coating is made. The purity, coverage and consistency of the film, which is sometimes only one molecule deep, are major factors in its ability to reduce friction.
German researchers claim their process overcomes a number of the problems of past coating techniques. Dr Peter Siemroth, a project manager at the Fraunhofer Institute for Material and Beam Technology in Dresden, said coatings made with a new discharge plasma technique are purer and more consistent.
‘We use an arc discharge plasma process that does not need a gas and accurately places our material, amorphous carbon. In this method an electric arc struck in a vacuum vaporises material off graphite electrodes, which then builds up as a super-hard coating in a controlled process.’
The lack of any gas means that the carbon molecules cannot be accidentally deposited on the target surface. Siemroth’s researchers use magnetic fields to direct the carbon-carrying plasma for a more consistent placing of the material. The magnetic fields also enable the filtering of large particles of carbon that may reduce a coating’s smoothness. Ensuring small particle placement will also better guarantee coatings that are just two to three nanometres thick.
Magnetron sputtering is the common method of laying down such films. But continuedminiaturisation in areas such as micro-electronics means a new method was required. Computer hard drives have presented a particular challenge for sputtering. As the capacity of hard drives increases the distance between read and write heads has become smaller, which requires a much smother and more consistent surface to be applied to the disk.
According to Siemroth, sputtering has two major problems. ‘Sputtering requires a gas, normally argon. The argon gas ions can be absorbed by the target area, which is one problem. Another is that it is a large target area process. Our process can be aimed at a small area ensuring smooth coverage.’
The work of Siemroth’s team has focused on hard drives, but he expects the new coating to have applications in three other areas. Copper deposition on silicon circuits could be improved, he said, as well as the coating of machine tools. The new method could also be useful in the textile industry where weaving machines must have low friction between the cloth and the machine itself.