This book deals with selected aspects of structural chemistry, concentrating particularly on molecular and Raman spectroscopy. The authors of the various chapters were chosen from friends, colleagues and past students of Len Woodward. It is our hope that the book will prove useful both to honours students and to research workers. We would like to thank all our contributors for their willing cooperation in this endeavour. We are also grateful to all those who have given permission for the reproduction of copyright material from other publica tions; specific acknowledgments are made in each chapter. We are par ticularly indebted to the Principal and Fellows of Jesus College, Oxford, and the artist, H. A. Freeth, R.A., for permission to reproduce the portrait of Len Woodward which forms the frontispiece. Our thanks are also due to Mrs. J. Stevenson, who undertook a great deal of the secretarial work associated with the organization of this volume, and to Mr. P. Espe who photographed the portrait. The royalties from the sale of this book will, in the first instance, go to Jesus College, Oxford, and will be used for the establishment of a prize to be associated with Len Woodward's name."

The correlation of spectroscopic and chemical investigations in recent years has been highly beneficial of many reasons. Around 1950, no valid explanation was available of the colours of compounds of the five tran sition groups. Later, it was possible to identify the excited levels with those expected for an electron configuration with adefinite number of electrons in the partly filled shell. I t is not generally recognized that this is equivalent to determining spectroscopic oxidation states related to the preponderant electron configuration and not to estimates of the fractional atomic charges. This brings in an entirely different type of description than the formal oxidation numbers used for characterizing compounds and reaction schemes. However, it must be realized that collectively oxidized ligands, formation of cluster-complexes and catenation may prevent the oxidation state from being well-defined. The writer would like to express his gratitude to many, but first of all to DR. CLAUS SCHAFFER, University of Copenhagen, who is the most efficient group-theoretical engineer known to the writer; his comments and discussions have been highly valuable. The writer's colleague, Pro fessor FAUSTO CALDERAZZO (now going to the University of Pisa) has been most helpful in metallo-organic questions. Thanks are also due to Professors E. RANcKE-MADsEN and K. A. JENSEN for correspondence and conversations about formal oxidation numbers."

Radiocarbon After Four Decades: An Interdisciplinary Perspective commemorates the 40th anniversary of radiocarbon dating. The volume presents discussions of every aspect of this dating technique, as well as chronicles of its development and views of future advancements and applications. All of the 64 authors played major roles in establishment, development or application of this revolutionary scientific tool. The 35 chapters provide a solid foundation in the essential topics of radiocarbon dating: Historical Perspectives; The Natural Carbon Cycle; Instrumentation and Sample Preparation; Hydrology; Old World Archaeology; New World Archaeology; Earth Sciences; and Biomedical Applications.

The field of gas phase inorganic ion chemistry is relatively new; the early studies date back approximately twenty years, but there has been intense interest and development in the field in the last ten years. As with much of modern chemistry, the growth in gas phase inorganic ion chemistry can be traced to the development of instrumentation and new experimental methods. Studies in this area require sophisticated instruments and sample introduc tion/ ionization methods, and often these processes are complicated by the need for state-selecting (or collisionally stabilizing) the reactive species in order to assign the chemistry unequivocally. At the present level of experimental development, a wide range of experiments on diverse ionic systems are possible and many detailed aspects of the chemistry can be studied. Gas Phase Inorganic Chemistry focuses on the reactions of metal ions and metal clusters, and on the study of these species using the available modern spectroscopic methods. Three of the twelve chapters cover the chemistry of ionic monometal transition metal ions and the chemistry of these species with small diatomics and model organics. Two of the chapters focus on the studies of the chemical and physical properties of (primarily) transition metal clusters, and these chapters review experimental methods and capabilities. Two chapters also deal with the chemistry of transition metal carbonyl clusters, and these chapters address issues important to cluster growth and activation as well as the characterization of such species."

In the last twenty years the literature on the processes of ionic polymerization has reached such a level that there is not a single question which is not covered by the information contained in the many monographs, reference books, and textbooks in this field. It is easy for the interested reader to find sources for in-depth study, for a superficial acquaintance with the fundamentals of the subject or with the general features of these processes. At the same time the field is being continually enriched by new facts which have not only broadened the data base but which influence existing concepts on the mechanisms of these reactions. Such influences often touch the very foundations of these concepts, i. e., they go beyond simple descriptions of the structure of the pre-reaction states or earlier schemes. It is therefore appropriate to attempt a critical appraisal of the modern views on the mechanisms of formation of macro molecules in ionic systems which envisages, so far as is possible, the differentiating of fundamental and hypothetical conclusions or concepts. With this in mind we have preferred to address ourselves to the reader who is already quite well acquainted with the general litera ture. This has allowed us to dispense with detailed introductions to the questions discussed and to limit ourselves to brief comments on the fundamentals of the subject."

This book is about compounds such as the boron hydrides and associated metal hydrides and alkyls which acquired the label 'electron deficient' when they were thought to contain too few valence electrons to hold together. Though they are now recognized as containing the numbers of bonding electrons appropriate for their structures, the term 'electron deficient' is still commonly applied to many substances that contain too few valence electrons to provide a pair for every pair of atoms close enough to be regarded as covalently bonded. The study of such substances has contributed much to chemistry. Techniques for the vacuum manipulation of volatile substances were devised specifically for their study; developments in valence theory resulted from considerations of their bonding; and the reactivity of several (for example, diborane and complex metal hydrides, lithium and aluminium alkyls) has made them valuable reagents. The purpose of this book is to provide an introduction to the chemistry of these fascinating compounds. The experimental and spectroscopic methods by which they can be studied are outlined, the various types of structure they adopt are described and profusely illustrated, and the relative merits of extended valence bond and simple molecular orbital treatments of their bonding are discussed, with as liberal use of diagrams and as limited recourse to the Greek alphabet as possible. A recurring theme is the importance attached to considerations of molecular sym metry. Their reactions are treated in sufficient detail to show whether these reflect any deficiency of electrons."

Biochemistry of Scandium and Yttrium gathers together existing knowledge about scandium and yttrium from a wide variety of disciplines. Part 2 addresses the biochemical aspects of these two elements, and the various medical and environmental applications. (Part 1 presents a comparative study of the physical and chemical properties of scandium and yttrium, looking at both their similarities and their differences.) While these elements are relatively rare in nature, these books will show that they have unusual physical and chemical properties, and a disproportionate number of important applications. Improved analytical techniques have revealed that scandium and yttrium are present throughout living matter, even though only a relatively limited number of species have been analyzed so far. This fact of course has far-ranging implications for biological and environmental concerns. The major impacts of scandium and yttrium in science, technology, and medicine will be of interest to a wide variety of researchers, including geochemists, inorganic and organic chemists, clinical biochemists, and those specializing in environmental protection.

Electronic Properties of Fullerenes and other Novel Materials gives an overview of the state-of-the-art research. It presents most recent results on preparation, experimental analysis by electron spectroscopy, infrared and Raman spectroscopy, luminescence, and nonlinear optical, as well as possible technological applications. Emphasis is also placed on the superconducting properties of Fullerenes. The introductory and advanced contributions provide a good survey of the current status of this rapidly developing field.

This is a textbook of what is often called magnetochemistry. We take the point of view that magnetic phenomena are interesting because of what they tell us about chemical systems. Yet, we believe it is no longer tenable to write only about such subjects as distinguishing stereochemistry from the measurement of a magnetic susceptibility over a restricted temper ature region; that is, paramagnetism is so well-understood that little remains to explore which is of fundamental interest. The major purpose of this book is to direct chemists to some of the recent work of physicists, and in particular to a lengthy exposition of magnetic ordering phenomena. Chemists have long been interested in magnetic interactions in clusters, but many have shied away from long-range ordering phenomena. Now however more people are investigating magnetic behavior at temperatures in the liquid helium region, where ordering phenomena can scarcely be avoided. The emphasis is on complexes of the iron-series ions, for this is where most of the recent work, both experimental and theoretical, has been done. The discussion therefore is limited to insulating crystals; the nature of magnetism in metals and such materials as semiconductors is sufficiently different that a discussion of these substances is beyond our purposes. The book is directed more at the practical experimentalist than at the theoretician."

NMR is better suited than any other experimental technique for the characterization of supramolecular systems in solution. The presentations included here can be broadly divided into three classes. The first class illustrates the state of the art in the design of supramolecular systems and includes examples of different classes of supramolecular complexes: catenanes, rotaxanes, hydrogen-bonded rosettes, tubes, capsules, dendrimers, and metal-containing hosts. The second class comprises contributions to NMR methods that can be applied to address the main structural problems that arise in supramolecular chemistry. The third class includes biological supramolecular systems studied by state-of-the-art NMR techniques.

217 2. COPOLYMERIZATION OF PROPENE OR HIGHER I-ALKENES WITH 218 CARBON MONOXIDE 2. 1. Ligands and polymerization conditions 218 2. 2. Spiroketal formation 221 2. 3. Enantioselectivity 222 2. 4. Higher I-Alkenes 226 3. COPOLYMERIZATION OF STYRENE OR ITS DERIVATIVES WITH 226 CARBON MONOXIDE 4. COPOLYMERIZATION OF OTHER OLEANS WITH CARBON MONOXIDE 230 5. ASYMMETRIC TERPOLYMERIZATION OF MORE THAN Two KINDS OF 232 OLEFINS WITH CARBON MONOXIDE 6. POLYKETONE CONFORMATION 233 7. CONCLUSION 234 Chapter 8. Chain Propagation Mechanisms 237 Ayusman Sen 1. INTRODUCTION 237 2. PALLADIUM (II) BASED SYSTEMS 238 3. NICKEL (II) BASED SYSTEMS 256 4. RHODIUM (I) BASED SYSTEMS 257 5. CONCLUSION 261 Chapter 9. Theoretical Studies on Copolymerization of Polar Monomers 265 Peter Margl, Artur Michalak, and Tom Ziegler 1. INTRODUCTION 265 2. COPOLYMERIZATION OF CARBON MONOXIDE WITH ETHYLENE 267 2. 1. Experimental and calculated rates for the insertion processes for 267 copolymerization catalysed by Pd(II) systems. 2. 2. A more detailed look at the productive and unproductive cycles 270 in copolymerization catalysed by Pd(II) complexes. 2. 2. 1. The productive cycle 270 2. 2. 2. C2H4 misinsertion into an ethylene terminated polyketone 275 chain 2. 3. Experimental and calculated rates for the insertion processes for 277 alternating copolymerization catalyzed by Ni(II) systems 3. COPOLYMERIZATION OF OLEFINS WITH POLAR MONOMERS OTHER 280 THAN CO 3. 1. Preferred binding mode of oxygen containing monomers 282 3. 2. Preferred binding mode of nitrogen containing monomers 285 3. 3.

The term "carbon-functional organosilicon compound" is used for organosilicon compounds in which a functional group is bonded to an organic moiety that is in turn con nected to silicon via a Si-C bond. Thus, only Si-Cn-Y com pounds (Y designates a functional group) will be discussed in this book 1 Si-O-Cn-Y compounds will in general not be considered, although the latter group does include a large number of natural substances containing silylated hydroxyl groups. (Because of the differing importance of various Y groups, the reader will find some deviation from this restriction). Finally, compounds containing a silyl group as the functional group are not considered. An overview of the field of organosilicon chemistry would show that in the last several decades the commercial synthesis of organosilicon products has increased substan tially, both in annual production and also in the increasing variety of compounds produced. This increase in the number of commercially available carbon-functional monomers and polymers (silicone polymers) is most remarkable and is occurring because new applications are continually being found for these compounds. As might be expected, the number of publications in this field is also increasing. The important position of silicon in the periodic table - between carbon, aluminum, and phosphorus - means that an understanding of the nature of the bonds in organosilicon compounds is quite important in order to understand the bonding in these other areas."

"Meditationis est perscrutari occulta; contemplationis est admirari perspicua . . . Admiratio generat qurestionem, qurestio investigationem, investigatio inventionem" once wrote HUGO DE S. VICTORE and possibly described best the life span of the rare earths since the Swedish Army Lieutenant, C. A. ARRHENIDS' discovery of an unusual black mineral at Ytterby in 1787. Since then the rare earths have passed through the machinery of various phases of physical science. Europium as a member of the rare earth family shows characteristics of the series as a whole as well as some typical behaviour of its own due to the presence of its six f electrons i. e. , one less than the half-filled shell. This present volume attempts to provide an understanding of the various aspects of its chemical and physical behaviour. In doing so, it is hoped to provide the reader with more than just a list of the complete bibliography on the subject, and I have tried to review the literature for it's interesting features, balancing the experimental facts with the help of the minimum amount of theory as far as possible. Experience has shown us that the trend of inorganic research has changed during the past years and one frequently needs some understanding of chemical spectroscopy and quantum mechanics to be able to appreciate the developments in this field and to interpret the wealth of experimental data. The reader is referred to B. G. WYBOURNE'S book: Spectroscopic Properties of Rare Earths (ref. [488]), and B. R.

A lively demonstration of the great vitality and the multidisciplinary character of cluster research and of the usefulness of synthesizing its various aspects was given at this symposium. This volume covers all aspects of the physical and chemical properties of free and supported clusters or small particles: static, dynamical, electronic, magnetic and optical properties, adsorption and chemical phenomena. It thus gives a complete overview of the status of the field and its development.

The renowned theoretical physicist Victor F. Weisskopf rightly pointed out that a real understanding of natural phenomena implies a clear distinction between the essential and the peripheral. Only when we reach such an understanding - that is to say when we are able to separate the relevant from the irrelevant, will the phenomena no longer appear complex, but intelectually transparent. This statement, which is generally valid, reflects the very essence ofmodelling in the quantum theory of matter, on the molecular level in particular. Indeed, without theoretical models one would be swamped by too many details embodied in intricate accurate molecular wavefunctions. Further, physically justified simplificqtions enable studies of the otherwise intractable systems and/or phenomena. Finally, a lack of appropriate models would leave myriads of raw experimental data totally unrelated and incomprehensible. The present series ofbooks dwells on the most important models of chemical bonding and on the variety of its manifestations. In this volume the electronic structure and properties of molecules are considered in depth. Particular attention is focused on the nature of intramolecular interactions which in turn are revealed by various types ofmolecular spectroscopy. Emphasis is put on the conceptual and interpretive aspects of the theory in line with the general philosophy adopted in the series."

This book contains the papers and discussions from the sympo , ium on "The Catalytic Chemistry of Nitrogen Oxides" held at the General Motors Research Laboratories on October 7-8, 1974. This symposium is the eighteenth in the annual series presented by the Research Laboratories. The topics for these symposiums have covered a broad range. Each topic was selected to be of intense current interest and of significant technical importance. There is no question that the subject of the 1974 Symposium satisfies these two criteria. The control of automotive nitrogen oxides has been perhaps the most difficult and controversial area of automotive emissions both in terms of what is necessary and in terms of what is technically feasible. This area has been a source of considerable discussion not only in the technical community but also in governments both in the U. S. and abroad. This meeting brought together scientists working in surface chemistry with engineers working on system design. It also brought together representatives of government, academia and industry. We feel that an important side benefit of the meeting was the improved understanding that was developed between these groups. Participants came from Europe and Japan as well as Canada and the United States. The technical papers spanned the range from fundamental interactions of NO on surfaces through bench scale kinetic and mechanistic studies and ended with catalytic applications. Although the emphasis was on automotive NO removal, stack gas NO x x control was also covered.

It is now some sixteen years since the author's first series of books on the analysis of organometallic compounds. Many developments in the subject have occurred since that time and a new book on the subject is now overdue. The present book aims to provide a comprehensive review of the subject. It covers not only all aspects of the analysis of organometallic compounds but also contains two additional chapters, dealing with environmental analysis and the use of chelates of metals in the determination of very low concentrations of organic metals. Whilst reviewing the literature for the present book, it was observed that whereas papers published prior to 1973 dealt almost exclusively with various forms of analysis, a high proportion of those published during the past ten years were concerned with the application of proven or newly developed methods to the determination of organometallic compounds in environmental samples such as water, air, soil, river and ocean sediments, fish life and biota samples. An increasing range of elements including mercury, lead, arsenic, tin, antimony, selenium and manganese are now being found in organically bound forms in the environment, some resulting from pollution, others formed in nature by bacterial processes. As many of these substances have appreciable implications to human and animal health and the ecosystem as a whole, it was considered that it would be timely to include a separate chapter in the book devoted entirely to this subject.

In every generation the achievements in science have served mankind. The progress accomplished by one generation stimulates the next generation to even greater achievements, which may take the form of increasing, crystallizing, or detailing existing theo- ries. Other forms, generally resulting from persistence and enlight- ened fortune, open new areas of investigation previously unimagined and have an impact that may be felt for many years. An example of this latter form of achievement was the prepara- tion and elucidation of the structures of dicyclopentadienyliron (ferrocene, reported in 1951) dibenzenechromium iodide, triphenyl- chromium tristetrahydrofuranate, and numerous olefin-metal -com- plexes which provided an introduction to new types of chemical bonds- the sigma carbon-transition metal bond and the metal -complex bond. Initial progress in the field of organotransition-metal chemis- try followed the lines of interest generated separately by organic and inorganic chemistry. However, it is becoming increasingly clear that organotransit10n-metal chemistry is not only bridging these two fields, but also crosslinking many other fields of science.

The three natural streams of present-day chemistry are Structure, Dynamics and Synthesis and all these three elements are essential for the study of materials, particularly in the solid state. The solid state provides challenging opportunities for illustrating and applying principles of chemistry to systems of academic interest and technological importance. There are several practising solid state chemists in universities and research laboratories, but the subject has not yet become part of the formal training program in chemistry. Being one of the new frontiers of chemistry, Solid State Chemistry has a tremendous future and undoubtedly demands the active involvement of many more chemists. A Winter School in Solid State Chemistry was organized at the Indian Institute of Technology, Kanpur, to promote this area and to develop curricular material. Solid State Chemistry being lighly interdisciplinary in nature, the lecturers and participants at the Winter School had widely different backgrounds and interests. It was my great desire that the lecture material from the Winter School should become available to a larger body of students, teachers and research workers interested in the solid state and hence this volume.

During the course of far-infrared investigations of inorganic and coordina tion compounds at Argonne National Laboratory in the years 1962-1966, it became apparent that no suitable book existed which correlated and dis cussed the important vibrations occurring in this region for these molecules. Early in 1967 the initial steps were taken to write such a book. Then, in 1968, an excellent text by Professor David M. Adams entitled Metal-Ligand and Related Vibrations was published. At this point serious consideration was given to discontinuing work on this book. However, upon examination of Adams' book, it became clear that the references covered only the period to 1966. This field of research is accelerating so tremendously, and the period 1966-1969 has seen so many new studies, that upon reconsideration it was decided to continue writing this text. The references in this book, particularly in the last several chapters, include many papers published in 1969. However, the proliferation of the far-infrared literature has made it impossible to present all the published material that has any bearing on the subject. Many titles do not pertain primarily to the far-infrared region as such, and some of this research has been omitted for this reason. Organometallic compounds have been neglected since the author feels that adequate reviews of that subject are available. Other studies may be missing simply because, owing to space limitations, only the more important researches could be considered. Of course, "importance" may, in this case, reflect the author's interest and prejudices."

V. I. MATKOVICH During the meeting of the International Symposium on Boron held in October, 1972 in Tbilisi, U.S.S.R., the idea was proposed to assemble a review of boron and refractory borides by the specialists present. The advantages of such a work were immediately apparent. Such diverse applications of borides as in protective armor, nuclear reactors, coat ings, reinforcement, etc. can hardly all be presented in sufficient detail by a single author. On the other hand it was also recognized that with so much specialization, some areas of interest may not be covered. Within the last decade or two a number of areas have been developed in which the use of refractory borides is growing and improvements are being actively explored. Thus, a number of borides have considerable potential as reinforcing material for plastics or light metals, though only boron fibers have been firmly established up to the present. Ap plication of flakes and films for two-dimensional reinforcement appears attractive, although the high cost of materials and development repre sents a considerable barrier. A number of borides have been used to manufacture lightweight protec tive armor. In this area relatively fast changes seem to be taking place as improvements in performance and weight are made. Boron carbide has found considerable use in this application and new developments exploit the light weight of beryllium borides."

Recent developments in various areas of chemistry have been decisively influenced by the principles of structure and mechanism and by the ideas of coordination chemistry, in particular by the donor-acceptor approach, A unified view of almost all kinds of molecular forces is provided by quantum mechanics, and for practical purposes have been classified according to model assumptions, namely, dispersion, polarization, electrostatic, and short-range forces. The latter are divided into two- and three-center covalent chemical bonds, metallic bonds, and exchange-repulsion forces. This approach allows statements of principle and systematic analysis. However, quantitative predictions on concrete large systems are virtually impossible, and there are no general rules that account for structural and chemical changes due to intermolecular interactions. Chemists are therefore left with qualitative descriptions in which the changes in electron densities are considered. Such models as the MO theory or the resonance concept unrealistically assume that the nuclei remain in fixed positions. Further difficulties are encountered in the attempted description on the "nature" of the chemical bond, e.g., the forces involved. In order to avoid these difficulties an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, will be presented in this book. In this way, changes in the positions of the nuclei can be taken into account and the question of the nature of the molecular forces is no longer important.

Humans have been "manually" extracting patterns from data for centuries, but the increasing volume of data in modern times has called for more automatic approaches. Early methods of identifying patterns in data include Bayes' theorem (1700s) and Regression analysis (1800s). The proliferation, ubiquity and incre- ing power of computer technology has increased data collection and storage. As data sets have grown in size and complexity, direct hands-on data analysis has - creasingly been augmented with indirect, automatic data processing. Data mining has been developed as the tool for extracting hidden patterns from data, by using computing power and applying new techniques and methodologies for knowledge discovery. This has been aided by other discoveries in computer science, such as Neural networks, Clustering, Genetic algorithms (1950s), Decision trees (1960s) and Support vector machines (1980s). Data mining commonlyinvolves four classes of tasks: * Classi cation: Arranges the data into prede ned groups. For example, an e-mail program might attempt to classify an e-mail as legitimate or spam. Common algorithmsinclude Nearest neighbor,Naive Bayes classi er and Neural network. * Clustering: Is like classi cation but the groups are not prede ned, so the algorithm will try to group similar items together. * Regression: Attempts to nd a function which models the data with the least error. A common method is to use Genetic Programming. * Association rule learning: Searches for relationships between variables. For example, a supermarket might gather data of what each customer buys.

For a long time, the properties of transition metal and rare earth compounds have fascinated chemists and physicists from a scientific view-point, and more recently also their enormous potential as new materials has been explored. Applications in different fields have already been realized or are under c- rent investigation, for example, new laser materials, IR to visible upconversion systems, compounds for photolithographic processes, systems involving pho- redox processes for solar energy conversion, new photovoltaic devices, chemical sensors, biosensors, electroluminescent devices (OLEDs) for flat panel display systems, supramolecular devices with wide-range definable photophysical properties, materials for energy harvesting, optical information and storage systems, etc. Metal complexes are also highly important in biology and me- cine. Most of the applications mentioned are directly related to the properties of the electronic ground state and the lower-lying excited states. Metal complexes with organic ligands or organometallic compounds exhibit outstanding features as compared to purely organic molecules. For instance, metal compounds can often be prepared and applied in different oxidation states. Furthermore, various types of low-lying electronic excitations can be induced by a suitable choice of ligands, for example, such as metal-centered transitions (MC, e. g. d-d* tran- tion), ligand-centered (LC, e. g. n-n*), metal-to-ligand-charge transfer (MLCT, e. g. d-7r*), intra-ligand-charge-transfer (ILCT) transitions, etc. In particular, the orbitals involved in the resulting lowest excited states determine the photoph- ical and photochemical properties and thus the specific use of the compoun

Micro Electro Mechanical Systems (MEMS) is already about a billion dollars a year industry and is growing rapidly. So far major emphasis has been placed on the fabrication processes for various devices. There are serious issues related to tribology, mechanics, surfacechemistry and materials science in the operationand manufacturingof many MEMS devices and these issues are preventing an even faster commercialization. Very little is understood about tribology and mechanical properties on micro- to nanoscales of the materials used in the construction of MEMS devices. The MEMS community needs to be exposed to the state-of-the-artoftribology and vice versa. Fundamental understanding of friction/stiction, wear and the role of surface contamination and environmental debris in micro devices is required. There are significantadhesion, friction and wear issues in manufacturing and actual use, facing the MEMS industry. Very little is understood about the tribology of bulk silicon and polysilicon films used in the construction ofthese microdevices. These issues are based on surface phenomenaand cannotbe scaled down linearly and these become increasingly important with the small size of the devices. Continuum theory breaks down in the analyses, e. g. in fluid flow of micro-scale devices. Mechanical properties ofpolysilicon and other films are not well characterized. Roughness optimization can help in tribological improvements. Monolayers of lubricants and other materials need to be developed for ultra-low friction and near zero wear. Hard coatings and ion implantation techniques hold promise.