The kinetics and thermodynamics of structural rearrangements under mechanical stress depend strongly on particle size due to the influence of surface free energy. By suitable design of surface structure and stress environment it is possible, in principle, to prepare nanocrystals in structures inaccessible to bulk materials. Here we demonstrate this principle by example of two simulation studies: the irreversible shape change of gold nanoparticles under shock-wave compression, and the structural transformation of CdSe/ZnS core/shell nanocrystals under hydrostatic pressure. In the latter case, we show that the core high pressure structure can be made metastable under ambient conditions by tuning the thickness of the shell. In nanocrystalswith thick shells, we furthermore observe a wurtzite to NiAs transformation, which does not occur in the pure bulk materials. These phenomena are linked to a fundamental change in the atomistic transformation mechanism from heterogeneous nucleation at the surface to homogeneous nucleation in the crystal core.

Pressing matters: Structural rearrangments of nanocrystals under stress

244th National Meeting (2012)

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