Crystals: Slim, slender, single

Some years ago I found it impossible to refute the irreverent comments of a colleague to the effect that thin films should be considered as belonging to the liquid state, such was their condition of disorder, rather than to the solid state. One had of necessity to admit that the grim reality of the early experimenters’ films, deposited at an uncertain rate, in a dirty vacuum (or sputtered), on a substrate of uncertain properties, bore but little resemblance to the theoretician’s concept, deftly represented by two parallel straight lines, of a homogeneous, isotropic, parallel‐sided slab of material with nice, well‐behaved physical properties. The development of the electron microscope soon enabled one to see just how different was the harsh reality, revealing a depressingly complex system, sensitive alike to method of preparation and nature of substrate, in which particle size, particle shape, crystallographic orientation, and form of gram boundaries represent but a few of the variable factors in the field. The phenomenon of epitaxy is by no means new, having been discussed as far back as 1836. Interest in the phenomenon received a fillip when electron diffraction was discovered in the late twenties. On my last count, as of some six months back, there were 674 distinct examples of epitaxy in films condensed from the vapor phase on to a monocrystalline substrate. Despite this large number, the detailed mechanism underlying the process remains unclear. Quite apart from the interest in epitaxy as a crystal‐growth phenomenon, the possibility arises of using the process (even though we may not understand it) as a means of producing films which more closely approach the theoretician’s delight of a well‐behaved, ordered film. It was to bring together those interested in this area of thin‐film physics—those dedicated to the belief that such systems can possess a state of order justifying their inclusion in the field of solidstate physics—that a meeting was held at the Philco Scientific Laboratory, Blue Bell, Pennsylvania, from May 13 through 15, 1963. Sponsored jointly by the Office of Naval Research, Philco Corporation, Princeton University, and the University of Pennsylvania, the conference, entitled “Single‐Crystal Films”, was held under the chairmanship of Roman Smoluchowski. The meeting was ably organized by Carlo Bocciarelli and Maurice Francombe in a manner that combined informality with efficiency. Some 150 people attended, thus obviating the need for parallel sessions (in which the two papers which you want to hear invariably coincide) and insuring a large enough collision cross section so that one had no difficulty in capturing anyone at some stage.