ARGON AND NEON TRAPPING NEAR COPPER SURFACES

The binding energies of argon and neon impurities trapped below copper surfaces have been studied using a two-component effective-medium the ory. The impurities are placed at various interstitial and substitutio nal sites and ht divacancies within the first few surface layers, and the local energy minima as well as diffusion paths have been calculate d taking into account full relaxation of the copper atoms. The results differ clearly from those obtained for hulk copper and are different for different surfaces. The results suggest that argon and neon are di ffusing out from copper via a vacancy mechanism, with the help of a di vacancy, or the impurity-vacancy pair dissociates clearly below the su rface layer.