SPUTTERING OF THIN CARBON FOILS BY 20 KEV AND 40 KEV AR+ BOMBARDMENT

Sputtering of nominal 2 mu g/cm(2) carbon foils by 20 keV and 40 keV A r+ bombardment has been measured using thickness measurements derived from the angular scatter distribution of 2 keV protons transiting the foils. The total sputtering yield is observed to reach a constant rate of 3.5 atoms removed per incident Ar+ and is independent of both the foil thickness and the incident energy. This is attributed to a nearly constant deposited energy density at the entrance and exit surfaces, which results from a nuclear stopping power that varies little over th e energy range of 6-40 keV. By extrapolating measured backsputtering y ield data to the energies used in this study, we obtain a transmission sputtering yield of approximately 1.7. Holes were also formed in the foil, and the fraction of holes created by Ar+ bombardment linearly in creases with increasing fluence above a threshold fluence of 4.5 x 10( 15) Ar+/cm(2).