The Plasticity of Silicon and Germanium

A qualitative analysis of Gallagher's measurements of plastic flow in germanium and silicon is made. It is reasonable to suppose the slip occurs by motion in {111} planes of dislocations having a Burger's vector equal to an allowed translation in the (11̄0) direction. It is suggested, following current thought, that the observed temperature-dependent incubation time for plastic flow is related to the freeing by thermal fluctuations of locking points of the Cottrell type associated with the broken bonds which occur along nearly pure screw dislocations that have a small edge component. It is proposed that foreign atoms reside at the broken bonds in normal materials. A discrepancy in the coefficient of the Boltzmann factor indicates, however, that these concepts cannot be applied in the most simple form. The analogy between Gallagher's measurement and those of Kramer and Maddin in β-brass is pointed out.