Deuterium retention and near-surface modification of ion-irradiated diamond exposed to fusion-relevant plasma

Chemical vapour deposited diamond was irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. Ion-irradiated samples were then exposed to a deuterium plasma in MAGPIE with ion flux of ∼1.3 × 10²¹ ions m ^-2 s^-1. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the degree of disorder and sp²-bonding induced by the ion irradiation. The signals of sp²-bonded and disordered carbon were observed to decrease after exposure to the deuterium plasma, although sharp Raman peaks indicative of vacancy and interstitial defects induced by the MeV ions were less affected. Recovery of a diamond-like surface after plasma exposure was evident in the NEXAFS spectra. Elastic recoil detection analysis showed that the ion-damaged diamond retained more deuterium than diamond exposed only to deuterium plasma. For the case of unirradiated samples, diamond retained more deuterium than graphite. However, for the case of the ion-irradiated samples, diamond exhibited less deuterium retention than graphite.