Nanoindentation creep of single-crystal tungsten and gallium arsenide

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Abstract
An extensive study of indentation creep on the nanometre scale has been made on single-crystal indium, tungsten and gallium arsenide. We use the force modulation technique which gives a direct measure of contact stiffness and, being insensitive to thermal drift, allows the accurate observation of creep in small indents to be carried out over long time periods: We show that strain rate indices similar to those for macroscopic creep can be obtained for indium. Stress relaxation negative creep is also observed in a manner similar to macroscopic tests. Indentation of tungsten and gallium arsenide shows a distinct pop-in at a critical load, before which the deformation is essentially elastic and after which it is elastoplastic with significant dislocation multiplication. The creep behaviour is quite different before and after pop-in, clearly demonstrating the role of mobile dislocations in creep, even in nanometre-sized volumes of materials.