DAMAGE AND ANNEALING IN 2-DIMENSIONAL COULOMB CRYSTALS

Experiments have shown that the attenuation of shear modes in a 2D cla ssical Coulomb crystal, formed from helium ions trapped below the free surface of superfluid helium, is sensitive to damage in the crystal, and it can therefore be used to monitor the annealing process that fol lows deliberate damage to the crystal. The characteristic time require d for annealing in a circular crystal of radius 13 mm is found to be o f order 500 s, and it rises only slowly with decreasing temperature. I t is suggested that such behaviour requires the production of configur ations of dislocations that can disappear only through dislocation cli mb, which requires the absorption and emission of vacancies or interst itials, and that the relatively small temperature dependence implies t hat there must be some source of vacancies or interstitials within the crystal even at the lowest temperatures. (C) 1998 Elsevier Science B. V. All rights reserved.