Plasma enhanced CVD of materials for energy convertors: nano-silicon for solar cells and nano-diamond for fusion reactors

Our plasma materials research has been a significant influence in developing microwave plasma enhanced chemical vapour deposition (MPECVD) of diamond and in a similar process for nanocrystalline silicon. These contrasting materials will be presented, together with techniques for determining their structure and quality, including X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. For instance, Raman spectra clearly show the dependence on deposition parameters of the crystallinity of MPECVD Si films deposited at temperatures below 200 degrees C on to glass, aluminium and polyester. By using mixtures of silane with argon and/or hydrogen, these films are designed to have amorphous or nanocrystallinc structure. Photosensitive P-I-N diodes have been produced on conductor-coated, polyester fabric as a step towards manufacturing flexible solar cells on textiles.

In contrast, the higher temperature synthesis of diamond and its unique properties (e.g. resistance to high heat flux and chemical erosion) has led to the first experiments on microcrystalline and nanocrystalline CVD diamond as a candidate coating for plasma-facing components in tokamaks. Our exposure results show that diamond coatings do not delaminate, undergo only slight surface amorphisation, retain only small amounts of deuterium in the surface and erode in hydrogen or deuterium plasma similar to 40% slower than graphite.