Materials that are absolutely perfect—in other words, materials that contain no defect of any kind—are usually not very interesting. Imagine being married to a saint: you would quickly be bored out of your mind! Defects and impurities can considerably change many properties of materials in ways that allow a wide range of applications.
About stefankePhD in theoretical Physics from the U of Zurich (1982), now Paul Whitfield Horn Professor of Physics at Texas Tech University; Fellow of the APS (1997); Humboldt Research Award (2001); Fellow of the Institute of Physics (2006). About 200 publications - including a handful on the history of wine. Research interests: first-principles theory of defects in semiconductors.