Threshold Displacement Energies and Subthreshold Displacements in Copper and Gold Near 10°K

Abstract

These experiments were undertaken to determine more precisely the minimum energy T_d needed to displace an atom from its lattice position. The resistivity increase as a function of integrated flux was measured at various electron energies. The damage‐production curve, thus obtained, was the sum of two components. The first contribution is due to direct displacement processes. From a projection of this component to zero, we estimate T_d^Cu=16–19 eV and T_d^Au=33–36 eV. The second contribution, the subthreshold events, are due to various ``soft spots'' associated with unavoidable impurities in the nominally 99.999% pure copper and gold specimens. It has been shown that displacements near dislocations do not contribute in a significant manner. It has been further shown that the formation of light‐atom interstitials can contribute to subthreshold processes. While this does not conclusively prove that subthreshold processes in nominally pure copper and gold are due to the presence of light‐atom impurities, we believe this to be the most probable subthreshold mechanism.