Isotope Fractionation in the Sputtering of ⁶³Cu-⁶⁵Cu

Under 2keV Xe ion bombardment of a ⁶³Cu_69.1⁶⁵Cu_30.9 isotope mixture, isotope fractionation difference between small and large polar emission angles, δ(15°)-δ(75°), was calculated by use of a dynamic Monte Carlo program. Calculation results show that δ(15°)-δ(75°) is large at both the zero fluence and the high fluence, then it minimizes at a low fluence of 1.6x 10¹⁵ ions/cm² between two fluence limits. An important cause of this minimum is that the surface composition gradient of ⁶³Cu maximiles at the fluence of 1.6x10¹⁵ ions /cm².