X-ray photoelectron spectroscopy study on change of chemical state of diamond window by ion implantation

In the fusion reactors, windows made of diamond have been developed for the rf and torus windows. The torus window is the primary boundary of tritium and the vacuum confinement. The structure change of the diamond induced by energetic deuterium ion implantation was investigated using the X-ray Photoelectron Spectroscopy (XPS) technique. It was found that the diamond structure changed to the graphite structure by not only deuterium ion implantation but also heating. The heating before the implantation changed the sp3-bonding structure of diamond to the sp2-bonding. The deuterium ion implantation was also found to induce graphitization and then the implanted deuterium was chemically trapped by carbon. Heating after the implantation, namely thermal annealing, induced the complete graphitization of the diamond. The sputtered sample, which had a smaller amount of oxygen on the surface than the as-received sample, was graphitized with smaller ion fluence than that for the as-received sample.