SPUTTERING THRESHOLDS AND DISPLACEMENT ENERGIES

A spectroscopic method for the measurement of small numbers of atoms sputtered at low energies was developed; a strong emission line of the target material is monitored by a monochromator and measured by a photomultiplier detector. The plot of spectral line intensity vs. bombarding ion energy in most cases closely matches the yield plot obtained by absolute methods. The sensitivity of this method is 10/sup -4/ or more atoms per ion for many metals. Measurement of yields was made for about 20 metals sputtered by Ar/sup +/ and Hg/ sup +/ ions; one such yield curve is given for chromium. The results indicate that yields at very low ion energies (<50 ev) become sensitive to the anode voltage above a critical value and decrease with decreasing ion energy more rapidly than previous estimates. The threshold energy for sputtering appears to be 15 to 45 ev, with 25 ev as the approximate value for Ar/sup +/ ions; this is on the same order as the displacement threshold energy for radiation damage. (D. L.C.)