Multiply twinned particles beyond the icosahedron

Multiply twinned particles with shapes beyond that of the complete icosahed ron have been observed in island layers obtained by physical vapour deposit ion on alkali halide substrate. Image analysis applied to lattice plane ima ges of one distinctive example of such particles by employing Fourier proce ssing routines allowed to set up a detailed model of MTPs composed of two i cosahedra stacked into each other. These icosahedra being in twin position share a central decahedron that does not exhibit external faces. So, the pa rticle comprises 35 tetrahedral subunits, but has only 30 outer faces. Comp arison of the image contrast calculated according to this model with the ex perimental electron microscopy image showed rather good agreement. The form ation of such particles is assumed to proceed via successive growth twinnin g. (C) 2000 Elsevier Science B.V. All rights reserved.