Chemical sputtering of graphite by low temperature nitrogen plasmas at various substrate temperatures and ion flux densities

We report measurements of chemical sputtering yields of graphite exposed to low temperature nitrogen plasmas. The influence of surface temperature and incoming ion energy on the sputtering yields has been investigated in two distinct ion flux density regimes. Sputtering yields grow consistently with increasing temperatures in experiments with low flux density (Gamma(i) approximate to 10(20) m(-2)s(-1) - 10(21) m(-2)s(-1)) and high flux density (Gamma(i) approximate to 10(23) m(-2)s(-1)). Moreover, empirical fitting of the data suggests that the temperature of 670 degrees C is optimal for chemical sputtering at high flux density. Negative biasing of the samples was used to vary the ion energy in the low flux density regime. The sputtering yield in this case increases from 0.07 atoms/ion for E-i = 1.5eV to 0.19 atoms/ion for E-i = 35 eV. After taking into account the dependence of the yields on temperature and ion energy, we evidenced a flux dependence of sputtering, similar to that found for chemical sputtering of carbon by hydrogen.