Imaging small particles

This paper reviews recent results on multiply twinned particles, emphasising the interplay between experimental electron microscopy and theoretical modelling of the internal and surface structures. A wide range of particle structures can be understood through the use of a modified Wulff construction. Inhomogeneous elasticity is also useful in understanding defects in small particles. With respect to the energy balance between multiply twinned particles and single crystals, it is important to include the weakening of the (111) surface bonding for Ag and Au evidenced by recent experimental results on the longitudinal surface phonon frequencies. Theoretical models need to be extended to the atomic level, and there remain a number of unsolved structural problems.