The Origins of Epitaxial Orientations in thin Films

ABSTRACTWhen a continuous film is deposited on a planar, single crystal substrate, there is usually a single set of relative film-substrate orientations for which the free energy of the film-substrate interface is minimized. It is often assumed that epitaxial films have adopted the orientation which minimizes this energy. However, this is not necessarily the case. Orientation selection is also constrained by minimization of the energy of the/ree surface of a film, as well as by minimization of the strain energy. In systems in which films grow by an island mechanism, epitaxial orientations can be established during or after nucleation, and can change before or after formation of a continuous film. Interfacial and surface energy minimization is constrained differently for islands and films. Epitaxial grain growth is a process which occurs in continuous films, in which epitaxially-aligned, energy-minimizing grains grow at the expense of other grains. Recent experiments on epitaxial grain growth in polycrystalline Ag films on single crystal Ni is discussed to illustrate, the affects of surface, interface, and strain energy minimization on epitaxial orientation selection.