REEMISSION AND THERMAL-DESORPTION OF D-0, D-2, AND CD4, FROM GRAPHITE

The emission of atoms and molecules form ion-implanted graphite has been studied by means of line-of-sight quadrupole mass spectrometry. During the thermal desorption process, it was found that D-2 was the primary species released, while lesser amounts of D-0 and CD4 were observed. Compared to the temperature at which D-2 molecules were released (peak at similar to 1200 K), the peak temperature for atom release was similar to 100 K higher, while CD4 molecules were released at similar to 200 K lower temperature. For ion-loading fluences above implantation zone saturation (similar to 10(21) D/m(2) for 1 keV D+), < 20% of the hydrogen was released in the form of atoms. We have also measured the steady-state reemission levels of atoms and molecules for temperatures 300 to 1800 K using fluxes in the range 10(19) to 10(20) D/m(2) s and energies 1 and 3 keV/D+. Given the scatter in the experimental data, it is only possible to state that no major flux density dependence was observed, while a minor energy dependence was apparent.