In recent years nanotechnology has become one of the most important and exciting forefront fields in Physics, Chemistry, Engineering and Biology. It shows great promise for providing us in the near future with many breakthroughs that will change the direction of technological advances in a wide range of applications. To facilitate the timely widespread utilization of this new technology it is important to have available an overall summary and commentary on this subject which is sufficiently detailed to provide a broad coverage and insight into the area, and at the same time is sufficiently readable and thorough so that it can reach a wide audience of those who have a need to know the nature and prospects for the field. The present book hopes to achieve these two aims.

The current widespread interest in nanotechnology dates back to the years 1996 to 1998 when a panel under the auspices of the World Technology Evaluation Center (WTEC), funded by the National Science Foundation and other federal agencies, undertook a world-wide study of research and development in the area of nanotechnology, with the purpose of assessing its potential for technological innovation. Nanotechnology is based on the recognition that particles less than the size of 100 nanometers (a nanometer is a billionth of a meter) impart to nanostructures built from them new properties and behavior. This happens because particles which are smaller than the characteristic lengths associated with particular phenomena often display new chemistry and physics, leading to new behavior which depends on the size. So, for example, the electronic structure, conductivity, reactivity, melting temperature, and mechanical properties have all been observed to change when particles become smaller than a critical size. The dependence of the behavior on the particle sizes can allow one to engineer their properties. The WTEC study concluded that this technology has enormous potential to contribute to significant advances over a wide and diverse range of technological areas ranging from producing stronger and lighter materials, to shortening the delivery time of nano structured pharmaceuticals to the body's circulatory system, increasing the storage capacity of magnetic tapes, and providing faster switches for computers. Recommendations made by this and subsequent panels have led to the appropriation of very high levels of funding in recent years. The research area of nanotechnology is interdisciplinary, covering a wide variety of subjects ranging from die chemistry of the catalysis of nanoparticles, to the physics of the quantum dot laser. As a result researchers in any one particular area need to reach beyond their expertise in order to appreciate the broader implications of nanotechnology, and learn how to contribute to this exciting new field. Technical managers, evaluators, and those who must make funding decisions will need to understand a wide variety of disciplines. Although this book was originally intended to be an introduction to nanotechnology, due to the nature of the field it has developed into an introduction to selected topics in nanotechnology, which are thought to be representative of the overall field. Because of the rapid pace of development of the subject, and its interdisciplinary nature, a truly comprehensive coverage does not seem feasible. The topics presented here were chosen based on the maturity of understanding of the subjects, their potential for applications, or the number of already existing applications. Many of the chapters discuss present and future possibilities. General references are included for those who wish to pursue further some of the areas in which this technology is moving ahead-

We have attempted to provide an introduction to the subject of nanotechnology written at a level such that researchers in different areas can obtain an appreciation of developments outside their present areas of expertise, and so that technical administrators and managers can obtain an overview of the subject It is possible that such a book could be used as a text for a graduate course on nanotechnology. Many of the chapters contain introductions to the basic physical and chemical principles of the subject area under discussion, hence the various chapters are self contained, and may be read independently of each other. Thus Chapter 2 begins with a brief overview of the properties of bulk materials that need to be understood if one is to appreciate how, and why, changes occur in these materials when their sizes approach a billionth of a meter. An important impetus that caused nanotechnology to advance so rapidly has been the development of instrumentation such as the scanning tunneling microscope that allows the visualization of the surfaces of nanometer sized materials. Hence Chapter 3 presents descriptions of important instrumentation systems, and provides illustrations of measurements on nano materials. The remaining chapters cover various aspects of the field.

One of us (CPP) would like to thank his son Michael for drawing several dozen of the figures that appear throughout the book, and his grandson Jude Jackson for helping with several of these figures. We appreciate the comments of Prof. Austin Hughes on the biology chapter. We have greatly benefited from the information found in the five volume Handbook of Nano structured Materials and Nanotechnology edited by H. S. Nahva, and in the book Advanced Catalysis and Nanostructured Materials edited by W. R. Moser, both from Academic Press.

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