Influence of deuterium implanted in materials surface on Balmer lines emission from backscattering deuterium

We have studied the influence of implanted deuterium (D) on Balmer lines emission from backscattering D atoms under Df irradiation of C, Al, Si, Mo and Pd for an incident energy ranging from 5 to 25 keV at a target temperature from RT to 600 K. For clean surface, D-alpha photon intensity is proportional to the backscattering coefficients calculated by the TRIM code for all incident energies. For 15 and 20 keV injection, the intensity stays constant with increasing fluence in accordance with the simulation that the backscattering coefficient is not influenced by implanted deuterium because the mass of D is much less than that of the targets. Significant D-alpha photon intensity increase is observed in Si with the injection of 5 keV or less energy D+. The intensity gradually increases with the fluence until saturation after prolonged irradiation. With increase in the target temperature, the intensity increment is reduced and disappears above 500 K. The decay of the D-alpha photon intensity accompanied by thermal release of implanted deuterium is also observed. Similar increment of the D-alpha intensity is observed in C and Pd under 3 keV D+ injection but not at higher energy. In non-hydride-forming materials as Al and Mo, no increment is observed at ail. It is concluded that only dynamically retained deuterium at the top surface layers in the hydride-forming materials given by lower energy incidence modifies the surface electronic structure and consequently enhances the electron capture process of the backscattering deuteron. In this paper, it is clearly shown that in recycling hydrogen from the wall highly energy excited hydrogen particles are produced. The rate of this production is influenced by the surface chemical state. If the amount of such excited hydrogen is significant, it should be taken into account for the energy recycling. (C) 1999 Elsevier Science B.V. All rights reserved.