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We explain the atomistic processes involved in epitaxial growth of nanowires and nanotubes grown in a three phase system. The prevailing growth mechanism for 1-D growth, the vapor-liquid-solid (VLS) mechanism, is examined. We discuss that VLS and other similar mechanisms lack details about the atomistic processes involved in wire growth. When these atomistic processes are examined it is revealed that there are several different names describing what are proposed to be 'different' mechanisms that in reality rely on the same atomistic processes. We therefore present a detailed review of the atomistic processes involved in one dimensional (1-D) crystal growth of nanowires in a three phase system. The presence of the third phase acts to make the nucleation rate at one of the phase boundaries higher than at other phase boundaries. This preferential nucleation combined with other crystal growth modes, like step flow growth, account for 1-D crystal growth. This view of 1-D wire growth is relevant in any three phase growth system where the presence of the third phase produces a preferential nucleation site. Preferential nucleation at a phase boundary is motivated by reviewing and expanding the understanding of these interfaces. We also explore the effects of differences in the nucleation and step flow rates at different phase boundaries. This reveals that tubular structures, like nanotubes and nanotubular crystals, are also described by preferential phase-boundary nucleation. Experimental results that suggest that the mutual boundary between the three phases, the three phase boundary, is often the most preferred nucleation site are presented. Observed characteristics of nanowires, like preferred growth directions, morphology, side facet formation, and stacking fault formation are also discussed in the context of atomistic processes. Due to the similarities in atomistic processes in different three phase systems we suggest the name 'Preferential Phase-Boundary Nucleation' (PPBN) as a replacement for the many different names of this mechanism. Unlike previous names this name is relevant to the processes as well as emphasizing the importance of the phases. |