Published online by Cambridge University Press: 26 February 2011
Determination of the structure of the core of grain boundaries is the key to a fundamental understanding of properties such as grain boundary migration. Whilst theory, especially computer simulation, offered valuable insights, nothing can supplant experimental data. High resolution electron microscopy has been used to reveal the dislocation structure of high angle boundaries, some elements of the structural units which are thought to provide the characteristic building blocks of grain boundaries, rigid translations and a remarkable multiplicity of structure in neighboring regions of particular grain boundaries. The understanding which results from these studies gives an insight to the way in which polycrystalline and polyphase materials evolve towards a state where the excess energy due to the interface is minimized providing the necessary atomic mobility is possible. This evolution occurs at the nucleation and growth stages of microstructural development. In practice nucleation selects low energy orientations which may be perpetuated during growth. For the important case of thin films interfacial processes control (a) the formation of grain structure in single component films and (b) the development of preferred orientations in heteroepitaxial deposits.