Chapter XII - Morphological Instability and Growth of Phases

Abstract

This chapter illustrates morphological instability and growth of phases. There are many manifestations of morphological instability, such as in solidification, where a planar growth front can degenerate into a dendritic growth morphology, in thin film deposition, where the thin film can decompose into an array of globules, and in chemical vapor deposition (CVD), where a planar front can degenerate into one containing whiskers. The instability of morphology occurs in the presence or absence of a reaction front. At a reaction front, instability is induced by composition or temperature gradients ahead of the interface between parent and product phases and it is observed that capillarity forces tend to restore stability in these situations. The chapter describes the morphological instability at a planar reaction front between a parent and a single product phase as treated by Mullins and Sekerka and the morphological instability at a reaction front between a single metastable parent phase and a duplex product denoted as Eckhaus instability. Transitions in morphology occur during growth, which are also a consequence of morphological instability essentially from a cellular pattern to a dendritic pattern. These transitions are also explored in the chapter.