This Festschrift is an outgrowth of a collection of papers presented as a conference in honor of Professor Heinz K. Henisch on his sixty-fifth birthday held at the Institute for Amorphous Studies. Bloomfield Hills. Michigan. It is our great pleasure to be editors of the Festschrift volume to honor Heinz and his work. Professor Henisch has a long and distinguished career and has many accomplishments in semiconductor materials and devices. He has made seminal contributions to the understanding of semiconductor switching devices and contact properties. He has an outstandin~ reputation as an expositor of science. His seminars and lectures are always deep. lucid and witty. He received his doctorate in Physics from the University of Reading and then joined the faculty. In 1963. he accepted a position in the Department of Physics at Pennsylvania State University. While at Penn State. Dr. Henisch broadened his research interest to include the History of Photography. At the present time. Dr. Henisch holds parallel appointments as a Professor of Physics and a Professor of the History of Photography at Pennsylvania State University. He is a Fellow of the American Physical Society. the Institute of Physics. London. the Royal Photographic society and is a Corresponding Member of the Deutsche Gesellschaft fur Photographie. In addition to his considerable publication in the fields of physics and the history of photography. Dr. Henisch is the founder and editor of the Journal of the History of Photography published quarterly by Taylor and Francis. Ltd .. London.

Twenty-four years ago, Hellmut Fritzsche came to our laboratory to evaluate our work in amorphous materials. He came many times, sometimes bringing his violin to play with our youngest son, to talk, to help, to discover, and to teach. The times with him were always exciting and rewarding. There was a camaraderie in the early years that has continued and a friendship that has deepened among Iris and me and Hellmut, Sybille and their children. The vision that Hellmut Fritzsche shared with me, the many important contributions he made, the science that he helped so firmly to establish, the courage he showed in the time of our adversity, and the potential that he recognized put all of us in the amorphous field, not only his close friends and collaborators, in his debt. He helped make a science out of intuition, and played an important role not only in the experimental field but also in the basic theoretical aspects. It has been an honor to work with Hellmut through the years.

Landmark contributions to science and mechanisms for the origin of the phenomena, and technology are rarely recognized at the time of reached important conclusions about the physical publication. Few people, even in technical areas, nature of the materials at equilibrium and their recogni zed the importance of developments such as electronic nonequilibrium properties. Many of these the transistor, the laser, or electrophotography ideas were condensed into a publication for Physical until well after their successful demonstration. Review Letters, paper 1 in this collection. This So-called experts, in fact, tend to resist new paper immediately attracted attention to the field, inventions, a natural instinct based on a combina and directly lead to the initiation of large research tion of fear of obsolescent expertise and jealousy efforts at both industrial laboratories and univer- arising from lack of active participation in the ties throughout the world. Inevitably, there was discovery. the usual amount of controversy, with many experts Denigration of new ideas is a relatively simultaneously taking positions (2) and (3) above. safe modus operandi, since the vast majority It has now been well over 20 years since eventually are abandoned well short of commerciality. the original publication date, and an objective view However, a successful device can be identified by can be taken in hindsight.