Furuduy Discuss., 1993, 95, 1-2 Introduction J. N. Sherwood Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, UK GI 1XL 1949 saw the publication of the seminal Faraday Discussion on Crystal Growth. At that time this scientific area, which can be regarded as one of the most ancient of scientific crafts, had seen some major theoretical developments and the subject served well as one of the opening series of the Faraday Discussions. Crystal growth was emerging from being lsquo;still in the alchemical stagersquo; (a quotation made in the closing remarks to the Discussion). It was beginning to see the initiation of that most essential blend of theoretical development and practical experience which leads to major scientific advances.Discussion No. 5 served to bring together the theorists and experimentalists to initiate the interaction between the two activities. Looking back at the published volume, one finds all the basic elements which are recognised as having underpinned the development of the subject. Stranskirsquo;s papers on equilibrium form show the relationship between the crystal structure and the morphology and surface structure of the material. The series of papers by Burton, Cabrera and Frank relate this well to the growth process and to the influence of sub-structural defects (notably screw dislocations) on the growth process. These contributions laid the essential foundation for the development of the modelling of the growth process and the expansion of all aspects of the theory of crystal growth which have developed to the present day.Additionally, we also see, possibly for the first time, the confrontation of theory and experiments on pure systems. The consideration of the growth process is important not only for the scientific development of crystal growth but also for its technological applications. Crystallisation is probably the most common unit process in the chemical industry. Its understanding and control to produce a well defined product have many ramifications in downstream processing. Industrial crystallisation processes take place in the less favourable environ- ment of synthetically impure solutions. The impurities influence both growth process and crystal habit.Experimental studies of these phenomena and their potential use in controlling habit were also represented in the original Discussion bringing the industrial community into contact with the fundamental scientists. The studies reported were devoted principally to inorganic systems and it was freely admitted that the processes are lsquo;imperfectly understoodrsquo;. The need for their better understanding was, however, signalled. Finally, the problems of mineral synthesis and the associated art of producing large single crystals for device production were addressed. The latter papers are devoted to what one might regard today as simple materials for optical and piezoelectric applications grown by relatively simple procedures. As we all know, industrial developmment of the growth of semiconductor and optical materials from this simple base was to become rapid and to have a phenomenal impact on both science and society.Thus the 1949 Discussion signalled the beginnings of what were to be major changes in the development of the understanding of the process ofcrystal growth, which were to have a major influence across the whole range of science and technology. The past forty years have seen many developments in the better understanding of the theoretical background to the crystal growth process both in a static and a dynamic sense. The development of the theories of intermolecular and interionic forces have enabled the better prediction of a whole range of phenomena associated with the equilibrium nature of 1 Introduction surfaces and surface processes.Based principally on the development of the Hartman- Perdok theory, these allow not only predictions of equilibrium morphology but also its modification in the presence of solvent and impurities. It has proved possible to extend this to consider the effect of kinetic factors and the development of important processes such as thermodynamic and kinetic surface roughening under extremes of operational conditions. Such variations become extremely important in the operation of industrial crystallisers where they have a marked influence on the nature and purity of the final crystalline product. The development and application of molecular dynamics calculations to the crystallisation process has also played a major role in theoretical development.A major contribution to these developments has been the full acceptance of the role of structural effects on the crystal growth process. This has led to a number of important contributions of which two are particularly worthy of note: first, the absolute identification of sub-structural defects such as screw dislocations and the definition of their role in the growth process. This gave considerable support to the early theoretical approaches and gave confidence as to their viability. Secondly, and more recently, the seminal studies of the group from the Weizmann Institute group on crystal habit modification and in which the influences noted by the earlier workers were explained and defined.These and other developments are of course aided and underpinned by the definition of new and improved experimental techniques which can be used to access data of increased detail and reliability and to examine the nature and development of the crystal surface under operational conditions. Foremost amongst these is of course the computer in all its manifestations. Unavailable to our colleagues of 1949 this instrument has played the greatest part in the development of the theory of crystal growth. In parallel, however, developments in interferometry and microscopy in all its forms from optical to electron, and now atomic force microscopy, allow us an in situ view of surfaces of size from 1 cm2 to 1 nm2. The development of synchrotron X-ray sources and imaging detectors have also opened the way for the detailed structural examination of interfaces. Using the combination of these techniques considerable advances have been made in the understanding of the crystal growth process.There remains, however, much to be done before we could claim to be at the stage where crystal growth could be said to be a predictable process, although we are in almost that position in some areas. Consequently, it seemed appropriate to take stock of the present situation and once more to bring together the principal exponents of the science and technology of crystal growth to discuss the present state of the art. In considering what had been achieved the organizing committee decided that the major outstanding problems requiring solution lay in the more detailed consideration of the lsquo;interfacersquo; including particularly, the solution phase, which has probably been the least addressed part of the whole process over the years. It was decided therefore to focus the present Discussion on lsquo;Crystal Growth-Equilibrium Structure, Interface Kinetics, Lattice Defects and their Interrelationshipsrsquo; and as in 1949 to bring together todayrsquo;s theoretical and experimental crystal growers to summarize the state of the art and to define future developments.
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