Formation of Multiply-Twinned Particles on Alkali Halide Crystals by Vacuum Evaporation and Their Structures

During studies on the epitaxy and film growth of metals evaporated onto alkali halide crystals curious particles causing anomalous 111 electron diffraction spots and showing unusual shapes and contrasts on electron micrographs have been found. They have mainly been studied for Au on NaCl. As a result of analysis it has become clear that they have multiply twinned structures and are divided into three kinds, i.e., a pentagonal decahedron particle composed of five distorted tetrahedral twins, an icosahedral particle composed of twenty distorted tetrahedral twins and a rhombic shape particle consisting of five distorted twins. Stability of these multiply-twinned particles that have inherently strained structures is discussed, the total energies of them being calculated and compared with those of a fcc tetrahedron and a fcc Wulff-polyhedron. There is a good agreement in sizes of multiply-twinned particles between calculation and observation. Behavior of the particles during film growth of various metals on NaCl and KCl is described. Finally, the origin of the particles is discussed, most of them being presumed to form by nucleation at the earliest stage of film growth