Crystals are like people, it is their defects that make them interesting. On occasion a Materials Scientist might be tempted to replace interesting with frustrating! Nevertheless, without their defects most engineering materials would be useless. Defects facilitate common properties such as ductility in metals or remarkable properties such as zero resistance in superconductors. Yet our image of a solid at the atomic level is one of perfectly aligned rows of atoms. In only a few cases is this view accurate. Most real materials are full of defects: missing atoms, displaced atoms or even extra atoms arranged in long rows called dislocations. It is the objective of the Materials Scientist to control the spatial distribution of defects, that is, to perform atomic scale engineering.
During the lecture we shall use demonstrations to help us explore the world of crystal imperfections. Some defects will actually be visible. Others will be understood in terms of analogies. Historically, such demonstrations have played an important role in advancing our understanding of defect motion and stability. More recently the key has been to combine atomic scale computer simulation with experimental data. But the aim remains the same: to develop new material with enhanced or new properties. This requires us to understanding the role of defects.