Influence of target chemical activity on Balmer lines emission from backscattered hydrogen

We have investigated the influence of implanted hydrogen on Balmer lines emission from backscattered particles under D- irradiation to Si target for an incident energy ranging from 5 to 25 keV at a target temperature from room temperature (RT) to 600 K and the experimental results are compared with Monte Carlo simulation by the TRIM92 code. For clean Si surface, Dα photon intensity was proportional to the backscattering coefficients calculated by the TRIM92 code for all incident energies. The intensity stayed constant with increasing the fluence for incident energies of 15 and 25 keV in accordance with the simulation that the backscattering coefficient is not so much influenced by implanted deuterium because the mass of D is much less than that of Si. At 5 keV incidence, the Dα photon intensity gradually increased with the fluence until saturated after prolonged irradiation. The difference between the initial intensity and that after saturated was reduced with increasing the target temperature and disappeared above 600 K. The decay of the Dα photon intensity accompanied by the thermal release of implanted deuterium was also observed above 370 K. According to the TRIM92 calculation, the D/Si atomic ratio at the top surface for 5 keV incidence with the fluence of 4 x 1017 D-/cm2 exceeds 0.4 which is the maximum hydrogen concentration of amorphous hydrogenated Si (a:Si-H), whereas that for 15 keV incidence remains below 0.1 even over the 7 x 1017 D-/cm2 irradiation. All these results made us to conclude that the Dα intensity at 5 keV incidence is enhanced by retained deuterium near the top surface through modifying the electron capture process of backscattered deuteron. (orig.)