SPUTTER-INDUCED PITS ON (100)NICKEL SURFACES

Nickel (Ni+) ions of 180 keV energy impinging on {100} faces of nickel single crystals produce sputtered surfaces. Examination of these surf aces exposed to fluences up to 8 x 10(17) ions/cm(2) and at temperatur es between 25 degrees C and 750 degrees C reveals pits with facets par allel to the {111} and {100} crystallographic planes of the nickel. Su bsurface voids also form and, when intersected by the sputtered surfac e, become small pits which grow with further sputtering. The pits exhi bit facets that are direct extensions of facets present on the voids. The voids nucleate and grow during the initial stages of bombardment a t temperatures above 600 degrees C but shrink beyond fluences of simil ar to 3.5 x 10(17) ions/cm(2). Voids are not observed after bombardmen t at temperatures less than 600 degrees C. Sputtering at these lower t emperatures produces no pits unless the nickel is bombarded first at h igher temperatures to produce the requisite voids. Measuring the rate at which the {100} surface recedes due to sputtering provides the sput tering yield. This yield, near 3.8 atoms per Ni+ ion, is independent o f temperature from 25 degrees C to 750 degrees C. The growth rate of t he pits, i.e., the rate at which oppositely inclined {111} faces separ ate, is also measured. At temperatures below 350 degrees C, the measur ed growth rate matches that based on sputtering of these inclined surf aces. The rate increases with increasing temperature above 350 degrees C, reaching nearly tenfold its low-temperature value by 750 degrees C . The mechanisms causing this accelerated growth with increasing tempe rature are discussed and related to the migration of the point defects produced by the bombardment.