Physics and Chemistry of Materials with Low-Dimensional Structures - Böcker

In the last two decades low-dimensional (low-d) physics has matured into a major branch of science. Quite generally we may define a system with restricted dimensionality d as an object that is infinite only in one or two spatial directions (d = 1 and 2). Such a definition comprises isolated single chains or layers, but also fibres and thin layers (films) of varying but finite thickness. Clearly, a multitude of physical phenomena, notably in solid state physics, fall into these categories. As examples, we may mention: • Magnetic chains or layers (thin-film technology). • Metallic films (homogeneous or heterogeneous, crystalline, amorphous or microcristalline, etc.). • I-d or 2-d conductors and superconductors. • Intercalated systems. • 2-d electron gases (electrons on helium, semiconductor interfaces). • Surface layer problems (2-d melting of monolayers of noble gases on a substrate, surface problems in general). • Superfluid films of ~He or 'He. • Polymer physics. • Organic and inorganic chain conductors, superionic conductors. • I-d or 2-d molecular crystals and liquid crystals. • I-d or 2-d ferro- and antiferro electrics.

This volume on the novelties in the electronic properties of solids appears in occasion of Franco Bassani sixtieth birthday, and is dedicated to honour a scientific activity which has contributed so much of the development of this very active area of research. It is re­ markable that this book can cover so large a part of the current research on electronic properties of solids by contributions from Bassani's former students, collaborators at different stages of his scientific life, and physicists from all over the world who have been in close scientific relationship with him. A personal flavour therefore accompanies a number of the papers of this volume, which are both up-to-date reports on present research and original recollections of the early events of modern solid state physics. The volume begins with a few contributions dealing with theoretical procedures for electronic energy levels, a primary step toward the interpretation of structural and optical properties of extended and confined systems. Other papers concern the interacting state of electrons with light (polaritons) and the effect of the coupling of electrons with lattice vibrations, with emphasis on the thermal behaviour of the electron levels and on such experimental procedures as piezospectroscopy. Electron-lattice interaction in external magnetic field and transport-related properties due to high light excitation are also con­ sidered. The impact of synchroton radiation on condensed matter spectroscopy is dis­ cussed in a topical contribution, and optical measurements are presented for extended and impurity levels.

Recent dramatic progress in solid state physics, as highlighted by novel phenomena in semiconductor heterostructures or intercalation compounds and by high Tc superconductivity, is a fascinating outcome of the interaction between the physicists and chemists in various fields working on low-dimensional systems. The strength of the present volume lies in the fact that it gives a survey of the frontier of various classes of low-dimensional systems with articles by leading scientists from the international community. The volume has been conceived as a tribute to Professor H. Kamimura to honour his accomplishments upon his retirement from the University of Tokyo. Reflecting his wide spectrum of interests, the topics covered here range from (i) intercalation compounds and layered materials, (ii) 2D systems and superlattices, (iii) high Tc compounds to (iv) surfaces, mesoscopic systems, quasi-1D systems and point defects, thus ranging from 2D down to 0D, from superconductors to insulators, and from physics to quantum chemistry.The remarkable richness of subjects and approaches treated here will enable the readers to discover intriguing common and distinct key concepts in different classes of systems. This addition to the series Physics and Chemistry of Materials with Low-Dimensional Structures will thus prove to be fundamental to an exploration of the new horizons in condensed-matter physics and chemistry in the 1990s.

This volume is devoted exclusively to the interfacial photoelectronic properties of the inorganic layered semiconductors investigated in solid state (Schottky and p-n) photovoltaic and photoelectrochemical (solid/electrolyte) cells. The results of extensive studies on the various interfacial and surface electronic characteristics, interfacial photoreactions and materials aspects of the layered semiconductors reported in the last 15 years have been reviewed. The layered transition metal dicharcogenides have served as model compounds for the investigation of the details of photoelectrochemical processes and related studies involving surfaces. The layered semiconducting materials have been found to be promising solar cell materials. Significant energy conversion efficiencies have been realized in photoelectrochemical solar cells and in solid state photovoltaic cells. Novel studies including quantum size effects in layered semiconductors have been reported. UHV spectroscopic studies of the surfaces of the important layered semiconductors have been given. Recent developments in the preparation of the layered materials have been summarized.New insights into the physical and chemical characteristics of this class of materials have been gained by the studies reported in this book.

Nuclear magenetic resonance (NMR), nuclear quadrupole resonance (NQR), time differential perturbed angular correlations (TDPAC) and the Mossbauer effect (ME) have been applied to the study of charge density wave (CDW) systems. These hyperfine techniques provide unique tools to probe the structure and symmetry of commensurate CDWs, give a clear fingerprint of incommensurate CDWs and are ideally suited for CDW dynamics. This book represents an attempt in the series "Physics and Chemistry of Materials with Low-dimensional Structures" to bring together a group of scientific results obtained by nuclear spectroscopy related to charge density wave (CDW) phenomena in pseudo one- and two-dimensional systems. The individual chapters contain: the theory of CDWs in chain-like transition metal tetrachalcogenides is one topic discussed; NMR, NQR, TDPAC and ME investigations of layered transition metal dichalcogenides; NMR studies of CDW-transport in chain-like NbSe 3 and molybdenum bronzes; mulitnuclear NMR of KCP, high resulution NMR of organic conductors.THis book should be of interest to graduate students and scientists who want to acquire a broader knowledge of nuclear spectroscopy techniques applied to CDW systems.

Layered crystals, characterized by a quasi-two-dimensional character of certain physical properties, play an interesting role in surface science. First of all they provide excellent inert substrates for epitaxial deposition and physisorption studies. The surfaces of layered crystals, however, are interesting in their own right because they make a relevant class of low-dimensional phenomena accessible to surface probes. Charge density waves, incommensurate structures, phonon anomalies and high T superconductivity are well known examples. This book collects a series of review articles written by outstanding specialists on the structural assessment and spectroscopy of layered structures with surface-sensitive probes such as scanning tunneling microscopy and helium atom scattering, the theoretical analysis of their electronic and vibrational surface states, and the investigation of physisorbed overlayers.

This volume reviews the work achieved in the field of intercalation compounds since the first volume on "Intercalated Layered Materials" was published in this series in 1979. Leading experts in a number of important fields of current research present a collection of contributions on materials, methods, models and applications. Various aspects such as new compounds, preparation and characterization techniques, reaction mechanisms, theory, structural and physical properties, are covered. Layered materials are most important, but one-dimensional and three-dimensional systems, polymers and related host structures are also considered. The book has an interdisciplinary character and addresses itself to chemists, physicists and materials scientists interested in intercalation research. It is a reference work suitable for all scientists and research students working in this field.

The study of clusters is one of the most exciting topics in the rapidly developing field of nanostructured materials. As discussed in this book, nanometer-sized metal particles can be obtained not only by evaporation methods, producing atomic or molecular beams, but also by the chemical synthesis of metal cluster compounds. These have a well-defined stoichiometry and are composed of metal clusters of a given, homogeneous size, each cluster being surrounded by a shell of ligand molecules. Accordingly, the compounds provide excellent model systems for macroscopic assemblies of small metal particles embedded in a dielectric solid. The underlying physical properties are described in terms of a three-dimensional matrix of mutually separated quantum wells. In going from one compound to another, the size and separation of the quantum wells may be varied. In this way, one may study such fundamental properties as the size-induced transition from metallic to molecular behaviour. At the same time, the electronic level structure may be changed in a controlled way, which should confer tunable optical, electrical or magnetic properties.This text is intended for physicists, chemists and materials scientists with an interest in metal-cluster compounds and their physical properties.

Recent studies on two-dimensional systems have led to new insights into the interplay between physical properties and dimensionality. Many of these ideas have emerged from work on electrons bound to the surface of a weakly polarizable substrate such as liquid helium or solid hydrogen. This book is a comprehensive overview of experimental and theoretical research in this field. It is intended to provide a coherent introduction for graduate students and non-experts, while at the same time serving as a reference source for active researchers in the field. The chapters are written by individuals in the field and cover a variety of specialized topics. These include the origin of the surface states, tunneling and magneto-tunneling out of these states, the phase diagram, collective excitations, transport and magneto-transport.

This text reviews the results obtained in the 1990s for layered copper-oxide high-temperature superconductors by neutron scattering techniques. The following topics are thoroughly introduced, methodically discussed and highlighted with the most important results by acknowledged experts in their respective fields: static and dynamical properties of the crystal lattice (oxygen site occupation, charge transfer, charge-stripe order, phonon dispersions and density-of-states), static and dynamical magnetic correlations (phase diagrams, 2D and 3D magnetic ordering, spin waves and spin fluctuations, crystal-field excitations) and the structure of the flux-line lattice (field and temperature dependence). The 2D features of the copper-oxide perovskites are found to be essential for achieving high-temperature superconductivity by doping. The book addresses an interdisciplinary audience, both specialists and those entering the field. Emphasis is put on the fundamental properties; however, technological applications are evidently emerging from these basics.

A collection of topical and mostly critical reviews written by professionals who are working or have been working in this and related fields, this book intends to provide a complete, ordered and concise summary of what is known (or not known) about carbyne at this date. The authors have tried to be critical of overstated results and expectations and have made an effort to provide a balanced approach to the controversial topic. The book provides a sound approach to this elusive carbon allotrope. This book will be of interest to research scientists (both experimentalists and theoreticians), postgraduate and graduate students working in the field of chemistry and physics of carbon (including diamond and diamond-like materials, graphite intercalation compounds, fullerenes, carbon nanotubes and related areas), conjugated and/or bio-polymers, and one-dimensional molecular systems.

Kratschmer and Huffman's revolutionary discovery of a new solid phase of carbon, solid C60, in 1990 opened the way to an entire new class of materials with physical properties so diverse that their richness has not yet been fully exploited. Moreover, as a by-product of fullerene research, carbon nanotubes were later identified, from which novel nanostructures originated that are currently fascinating materials scientists worldwide. Rivers of words have been written on both fullerenes and nanotubes, in the form of journal articles, conference proceedings and books. The present book offers, in a concise and self-contained manner, the basics of the science of these materials as well as detailed information on those aspects that have so far been better explored. Structural, electronic and dynamical properties are described as obtained from various measurements and state-of-the-art calculations. Their interrelation emerges as well as their possible dependence on, for example, preparation conditions or methods of investigation.By presenting and comparing data from different sources, experiment and theory, this text aims to help the reader to rapidly master the basic knowledge, to grasp important issues and critically discuss them.

The effect of reduced dimensionality, inherent at the crystallographic level, on the electronic properties of low dimensional materials can be dramatic, leading to structural and electronic instabilities—including supercond- tivity at high temperatures, charge density waves, and localisation—which continue to attract widespread interest. The layered transition metal dichalcogenides have engaged attention for many years, partly arising from the charge density wave effects which some show and the controlled way in which their properties can be modified by intercalation, while the development of epitaxial growth techniques has opened up promising areas based on dichalcogenide heterostructures and quantum wells. The discovery of high-temperature superconducting oxides, and the realisation that polymeric materials too can be exploited in a controlled way for various opto-electronic applications, have further sti- lated interest in the effects of structural dimensionality. It seems timely therefore to draw together some strands of recent research involving a range of disparate materials which share some common char- teristics of low dimensionality. This resulting volume is aimed at researchers with specialist interests in the particular materials discussed but who may also wish to examine the related phenomena observed in different systems, and at a more general solid state audience with broad interests in electronic properties and low dimensional phenomena. Space limitations have required us to be selective as regards particular materials, though we have managed to include those as dissimilar as polymeric semiconductors, superconducting oxides, bronzes and layered chalcogenides.

This book provides an attempt to convey the colorful facets of condensed matter systems with reduced dimensionality. Some of the specific features predicted for interacting one-dimensional electron systems, such as charge- and spin-density waves, have been observed in many quasi-one-dimensional materials. The two-dimensional world is even richer: besides d-wave superconductivity and the Quantum Hall Effect - perhaps the most spectacular phases explored during the last two decades - many collective charge and spin states have captured the interest of researchers, such as charge stripes or spontaneously generated circulating currents.Recent years have witnessed important progress in material preparation, measurement techniques and theoretical methods. Today larger and better samples, higher flux for neutron beams, advanced light sources, better resolution in electron spectroscopy, new computational algorithms, and the development of field-theoretical approaches allow an in-depth analysis of the complex many-body behaviour of low-dimensional materials. The epoch when simple mean-field arguments were sufficient for describing the gross features observed experimentally is definitely over.The Editors' aim is to thoroughly explain a number of selected topics: the application of dynamical probes, such as neutron scattering, optical absorption and photoemission, as well as transport studies, both electrical and thermal. Some of the more theoretical chapters are directly relevant for experiments, such as optical spectroscopy, transport in one-dimensional models, and the phenomenology of charge inhomogeneities in layered materials, while others discuss more general topics and methods, for example the concept of a Luttinger liquid and bosonization, or duality transformations, both promising tools for treating strongly interacting many-body systems.

This volume is devoted exclusively to the interfacial photoelectronic properties of the inorganic layered semiconductors investigated in solid state (Schottky and p-n) photovoltaic and photoelectrochemical (solid/electrolyte) cells. The results of extensive studies on the various interfacial and surface electronic characteristics, interfacial photoreactions and materials aspects of the layered semiconductors reported in the last fifteen years have been reviewed. The layered transition metal dichalcogenides have served as model compounds for the investigation of the details of photoelectrochemical processes and related studies involving surfaces. The layered semiconducting materials have been found to be promising solar cell materials. Significant energy conversion efficiencies have been realized in photoelectrochemical solar cells and in solid state photovoltaic cells. Novel studies including quantum size effects in layered semiconductors have been reported. UHV spectroscopic studies of the surfaces of important layered semiconductors have been given. Recent developments in the preparation of the layered materials have been summarized.New insights into the physical and chemical characteristics of this class of materials have been gained by the studies reported in this book. Highlights include: -- Data on optical and electronic properties of layered semiconductors; -- Solid state and semiconductor/electrolyte junction characteristics; -- Photovoltaic and photoelectrochemical solar cells based on layered materials; -- UHV spectroscopic studies of surfaces of layered semiconductors; -- Quantum size effects in layered semiconductor colloids; -- Novel layered material preparation techniques.

Nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), time differential perturbed angular correlations (TDPAC), and the Mössbauer effect (ME) have been applied to the study of charge density wave (CDW) systems. These hyperfine techniques provide unique tools to probe the structure and symmetry of commensurate CDWs, give a clear fingerprint of incommensurate CDWs, and are ideally suited for CDW dynamics. This book represents a new attempt in the series `Physics and Chemistry of Materials with Low-dimensional Structures' to bring together a consistent group of scientific results obtained by nuclear spectroscopy related to CDW phenomena in pseudo-one- and two-dimensional systems. The individual chapters contain: the theory of CDWs in chain-like transition metal tetrachalcogenides; NMR, NQR, TDPAC, and ME investigations of layered transition metal dichalcogenides; NMR studies of CDW-transport in chain-like NbSe3 and molybdenum bronzes; multinuclear NMR of KCP; high resolution NMR of organic conductors. This book is of interest to graduate students and all scientists who want to acquire a broader knowledge of nuclear spectroscopy techniques applied to CDW systems.

The study of clusters is one of the most exciting topics in the rapidly developing field of nanostructured materials. As discussed in this book, nanometer-sized metal particles can be obtained not only by evaporation methods, producing atomic or molecular beams, but also by the chemical synthesis of metal cluster compounds. These have a well-defined stoichiometry and are composed of metal clusters of a given, homogeneous size, each cluster being surrounded by a shell of ligand molecules. Accordingly, the compounds provide excellent model systems for macroscopic assemblies of small metal particles embedded in a dielectric solid. The underlying physical properties are described in terms of a three-dimensional matrix of mutually separated quantum wells. In going from one compound to another, the size and separation of the quantum wells may be varied. In this way, one may study such fundamental properties as the size-induced transition from metallic to molecular behaviour. At the same time, the electronic level structure may be changed in a controlled way, which should confer tunable optical, electrical or magnetic properties.This book summarizes physical experiments performed so far on this challenging new class of materials, as well as the basic aspects of their chemical synthesis. For physicists, chemists and materials scientists with an interest in metal-cluster compounds and their physical properties.

Recent studies on two-dimensional systems have led to new insights into the fascinating interplay between physical properties and dimensionality. Many of these ideas have emerged from work on electrons bound to the surface of a weakly polarizable substrate such as liquid helium or solid hydrogen. The research on this subject continues to be at the forefront of modern condensed matter physics because of its fundamental simplicity as well as its connection to technologically useful devices. This book is the first comprehensive overview of experimental and theoretical research in this exciting field. It is intended to provide a coherent introduction for graduate students and non-experts, while at the same time serving as a reference source for active researchers in the field. The chapters are written by individuals who made significant contributions and cover a variety of specialized topics. These include the origin of the surface states, tunneling and magneto-tunneling out of these states, the phase diagram, collective excitations, transport and magneto-transport.

This is the first book which reviews the most important results obtained in the past decade for layered copper-oxide high-temperature superconductors by neutron scattering techniques. The following topics are thoroughly introduced, methodically discussed and highlighted with the most important results by acknowledged experts in their respective fields: static and dynamical properties of the crystal lattice (oxygen site occupation, charge transfer, charge-stripe order, phonon dispersions and density-of-states), static and dynamical magnetic correlations (phase diagrams, 2D and 3D magnetic ordering, spin waves and spin fluctuations, crystal-field excitations) and the structure of the flux-line lattice (field and temperature dependence). The 2D features of the copper-oxide perovskites are found to be essential for achieving high-temperature superconductivity by doping. The book addresses an interdisciplinary audience, both specialists and those entering the field. Emphasis is put on the fundamental properties; however, technological applications are evidently emerging from these basics.

This book provides an attempt to convey the colorful facets of condensed matter systems with reduced dimensionality. Some of the specific features predicted for interacting one-dimensional electron systems, such as charge- and spin-density waves, have been observed in many quasi-one-dimensional materials. The two-dimensional world is even richer: besides d-wave superconductivity and the Quantum Hall Effect - perhaps the most spectacular phases explored during the last two decades - many collective charge and spin states have captured the interest of researchers, such as charge stripes or spontaneously generated circulating currents.Recent years have witnessed important progress in material preparation, measurement techniques and theoretical methods. Today larger and better samples, higher flux for neutron beams, advanced light sources, better resolution in electron spectroscopy, new computational algorithms, and the development of field-theoretical approaches allow an in-depth analysis of the complex many-body behaviour of low-dimensional materials. The epoch when simple mean-field arguments were sufficient for describing the gross features observed experimentally is definitely over.The Editors' aim is to thoroughly explain a number of selected topics: the application of dynamical probes, such as neutron scattering, optical absorption and photoemission, as well as transport studies, both electrical and thermal. Some of the more theoretical chapters are directly relevant for experiments, such as optical spectroscopy, transport in one-dimensional models, and the phenomenology of charge inhomogeneities in layered materials, while others discuss more general topics and methods, for example the concept of a Luttinger liquid and bosonization, or duality transformations, both promising tools for treating strongly interacting many-body systems.

The combination of solid materials of different structural dimensionality with atomic or molecular guest species via intercalation processes represents a unique and widely variable low temperature synthesis strategy for the design of solids with particular composition, structure and physical properties. In the last decade this field has experienced a rapid development and represents now an established specific domain of solid state research and materials science. Substantial progress has been made with respect to an understanding of the complex relationship between structure, bonding, physical properties and chemical reactivity since the first volume on the subject appeared in this series in 1979 (Intercalated Layered Materials, F. Levy, ed.). The purpose of this volume is to present a survey on progress and per­ spectives based on the treatment of a series of major areas of activities in this field. By the very nature of its subject this monograph has an interdisciplinary character and addresses itself to chemists, physicists and materials scien­ tists interested in intercalation research and related aspects such as design and characterization of complex materials, low temperature synthesis, solid state reaction mechanisms, electronic/ionic conductivity, control of electronic properties of solids with different structural dimensionality and application of intercalation systems. Several chapters have been devoted to specific groups of host lattices.

Layered crystals, characterized by a quasi-two-dimensional character of certain physical properties, play an interesting role in surface science. First of all they provide excellent inert substrates for epitaxial deposition and physisorption studies. The surfaces of layered crystals, however, are interesting in their own right because they make a relevant class of low-dimensional phenomena accessible to surface probes. Change density waves, incommensurate structures, phonon anomalies and high Tc superconductivity are well known examples. This book collects a series of review articles written by outstanding specialists on the structural assessment and spectroscopy of layered structures with surface-sensitive probes such as scanning microscopy and helium atom scattering, the theoretical analysis of their electronic and vibrational surface states, and the investigation of physisorbed overlayers.

In Bird of Passage by Rudolf Peierls, we find a paragraph in which he de­ scribes his Cambridge days in the 1930s: On these [relativistic field theory] problems my main contacts were Dirac, and the younger theoreticians. These included in particular Nevill (now Sir Nevill) Mott, perhaps the friendliest among many kind and friendly people we met then. Professor Kamimura became associated with Sir Rudolf Peierls in the 1950s, when he translated, with his colleagues, Peierls's 1955 textbook, Quantum Theory of Solids, into Japanese. This edition, to which Sir Rudolf himself contributed a preface, benefitted early generations of Japanese solid state physicists. Later in 1974/5, during a sabbatical year spent at the Cavendish Laboratory, Professor Kamimura met and began a long association with Sir Nevill Mott. In particular, they developed ideas for disordered systems. One of the outcomes is a paper coauthored by them on ESR-induced variable­ range hopping in doped semiconductors. A series of works on disordered systems, together with those on two-dimensional systems, have served as building blocks for Physics of Interacting Electrons in Disordered Systems, in the International Series of Monographs on Physics, coauthored by Aoki and published in 1989 by the Oxford University Press. Soon after Professor Kamimura obtained a D. Sc. in 1959 for the work on the ligand field theory under the supervision ofMasao Kotani, his strong con­ nections in the international physical community began when he worked at the Bell Telephone Laboratories in 1961/64.

Krätschmer and Huffman's revolutionary discovery of a new solid phase of carbon, solid C60, in 1990 opened the way to an entire new class of materials with physical properties so diverse that their richness has not yet been fully exploited. Moreover, as a by-product of fullerene research, carbon nanotubes were later identified, from which novel nanostructures originated that are currently fascinating materials scientists worldwide. Rivers of words have been written on both fullerenes and nanotubes, in the form of journal articles, conference proceedings and books. The present book offers, in a concise and self-contained manner, the basics of the science of these materials as well as detailed information on those aspects that have so far been better explored. Structural, electronic and dynamical properties are described as obtained from various measurements and state-of-the-art calculations. Their interrelation emerges as well as their possible dependence on, for example, preparation conditions or methods of investigation. By presenting and comparing data from different sources, experiment and theory, this book helps the reader to rapidly master the basic knowledge, to grasp important issues and critically discuss them. Ultimately, it aims to inspire him or her to find novel ways to approach still open questions. As such, this book is addressed to new researchers in the field as well as experts.

Modulated crystals have been intensively investigated over the past several years and it is now evident that an understanding of their crystallography and microstructure is fundamental to the elucidation of the physical properties and phase transitions in these materials. This book brings together for the first time the crystallographic descriptions and experimental methods for the structural and microstructural analysis of modulated crystals as described by well-known researchers in the various areas. The emphasis is on charge density wave modulations, and the detailed analysis of the prototypical NbTe4/TaTe4 system gives practical applications of the methods. Scanning Tunnelling Microscopy is a new technique providing significant new insights into atomic scale details of the modulations' structures and a chapter on this method is included.

1.1. THE DISCOVERY OF CARBYNE Yu.P. KUDRYA VTSEV A.N. Nesmeyanov Institute ofOrganoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russia Abstract - The history of the discovery of carbyne is briefly recalled. The existence of carbyne was first disclosed by Russian researchers in 1960. It was obtained for the first time via oxidative dehydropolycondensation of acetylene based on the Glaser coupling of ethynyl compounds. 1. Introduction The polymeric nature of carbon was first pointed out by Mendeleev. He wrote: "The molecules of coal, graphite, and diamond are very complicated, and carbon atoms exhibit the capability of binding one to another to form complex molecules in all compounds of carbon. None of the elements possesses an ability of complicating in such an extent as does carbon. There is still no basis to define the polymerization degree of the coal, graphite, or diamond molecules. One should believe, however that they contain en species, where 'n' is a large value" [IJ. Until the 1960s only two allotropic forms of carbon were known, viz., graphite and diamond, including their polymorphous modifications. For a long time 'amorphous carbon' was also included among the simple forms. Presently, however, the structure of amorphous and quasi-amorphous carbons (such as carbon blacks, soot, cokes, glassy carbon, etc.) is known to approach that of graphite to various degrees [2J.

The history of low dimensional conductors goes back to the prediction, more than forty years ago, by Peierls, of the instability of a one dimensional metallic chain, leading to what is known now as the charge density wave state. At the same time, Frohlich suggested that an "ideal" conductivity could be associated to the sliding of this charge density wave. Since then, several classes of compounds, including layered transition metal dichalcogenides, quasi one-dimensional organic conduc­ tors and transition metal tri- and tretrachalcogenides have been extensively studied. The molybdenum bronzes or oxides have been discovered or rediscovered as low dimensional conductors in this last decade. A considerable amount of work has now been performed on this subject and it was time to collect some review papers in a single book. Although this book is focused on the molybdenum bronzes and oxides, it has a far more general interest in the field of low dimensional conductors, since several of the molybdenum compounds provide, from our point of view, model systems. This is the case for the quasi one-dimensional blue bronze, especially due to the availability of good quality large single crystals. This book is intended for scientists belonging to the fields of solid state physics and chemistry as well as materials science. It should especially be useful to many graduate students involved in low dimensional oxides. It has been written by recognized specialists of low dimensional systems.

In the last two decades low-dimensional (low-d) physics has matured into a major branch of science. Quite generally we may define a system with restricted dimensionality d as an object that is infinite only in one or two spatial directions (d = 1 and 2). Such a definition comprises isolated single chains or layers, but also fibres and thin layers (films) of varying but finite thickness. Clearly, a multitude of physical phenomena, notably in solid state physics, fall into these categories. As examples, we may mention: • Magnetic chains or layers (thin-film technology). • Metallic films (homogeneous or heterogeneous, crystalline, amorphous or microcristalline, etc.). • I-d or 2-d conductors and superconductors. • Intercalated systems. • 2-d electron gases (electrons on helium, semiconductor interfaces). • Surface layer problems (2-d melting of monolayers of noble gases on a substrate, surface problems in general). • Superfluid films of ~He or 'He. • Polymer physics. • Organic and inorganic chain conductors, superionic conductors. • I-d or 2-d molecular crystals and liquid crystals. • I-d or 2-d ferro- and antiferro electrics.