Contribution of Clusters Physics to Materials Science and Technology : From Isolated Clusters to Aggregated Materials

During the last decade there has been an increasing interest in clusters and small particles because of the peculiar proper­ ties induced by their large area to volume ratio. For that reason small particles are often considered as an intermediate state of matter at the border between atomic (or molecular) chemistry, and physics of the condensed matter. The importance of the surface effect can explain the anomalous properties, for example the exis­ tence of the five fold symmetry observed in different circumstan­ ces '(beams of rare gas clusters, gold particles deposited on a substrate). However the question of the critical size at which the transition to bulk properties occurs cannot be simply answered, since the reply depends on the peculiar property which is studied. The importance of the size effect was emphasized in the last International Meetings. However the situation remains confused in most cases since the exact role of the cluster environment cannot be clearly elucidated and is a main difficulty, except in cluster beam experiments. In fact ideally free clusters constitute a labo­ ratory exception. In most applications small particles must be supported on a surface or embedded in a matrix, in order to be stabilized, which obviously shows the role of the environment.

Properties of Clusters in the Gas Phase.- 1. Introduction.- 2. Cluster production.- 3. Mass spectrometrie detection.- 4. Experiments on clusters in the gas phase.- 5. Laser spectroscopy of free clusters.- 6. Future developments.- Metal Cluster Beams and Electron Diffraction: Deviations from the Bulk States of Matter.- 1. Introduction.- 2. The cluster nucleation process.- 3. Cluster beams.- 4. Cluster electron diffraction.- 5. Metal cluster results.- Generation of Beams of Refractory Metal Clusters.- An Introduction to the Field of Catalysis by Molecular Clusters.- 1. An introduction to molecular clusters.- 1.1 Definition.- 1.2 Bonding in molecular clusters.- 1.3 Dynamic behaviour of molecular clusters.- 1.4 Reactivity of molecular clusters.- 1.5 Molecular clusters as structural models of intermediates or chemisorbed species in surface science.- 2. Catalysis by molecular clusters.- 2.1 The relationship between molecular clusters and small metal particles.- 2.2 Homogeneous cluster catalyzed reactions.- 2.3 Catalysis by supported molecular clusters.- 2.4 Supported clusters and heterogeneous catalysis: surface organometallic chemistry.- Quantum Chemistry for Metal Clusters.- 1. Generalities — cluster science.- 2. Quantum chemical methods.- 3. Comparisons of Hartree-Fock with X? (LSD) results.- 4. Electronic and magnetic structure of transition metal clusters.- 5. Concluding remarks — need for experiments on isolated clusters.- Electronic Structure of Metal Clusters.- 1. Introduction.- 2. Results.- 2.1 General considerations.- 2.2 Computational approaches.- 2.3 Geometry.- 2.4 Charge separation.- 2.5 Odd-even effects.- 2.6 Ionization potential.- 2.7 Density of states.- 2.8 Substrate effects.- 3. Experimental results.- Characterization of Supported Metal Particles in Heterogeneous Catalysts: I. Studies of high surface area materials.- 1. Introduction.- 2. Strategies for characterization of metal particles on on high surface area supports.- 3. X-ray diffraction and scattering.- 4. Extended X-ray absorption fine structure.- 5. Mossbauer spectroscopy.- 6. Magnetic susceptibility.- 7. Ferromagnetic resonance.- 8. Vibrational spectroscopy.- Characterization of Supported Metal Particles in Heterogeneous Catalysts: II. Studies of low surface area, model materials.- 1. Introduction.- 2. Strategies for characterization of metal particles on low surface area, model supports.- 3. Experimental techniques.- 4. Applications of studies using model supported metal samples.- 5. Concluding remarks.- Peculiar Aspects of Heterogeneous Nucleation and Growth Processes Related to Metal Supported Catalyst.- 1. Introduction.- 2. Kevnotes for heterogeneous nucleation.- 3. Mass transfer mechanisms.- 4. Epitaxy post nucleation phenomenon.- 5. Miscellaneous.- Formation, Action, and Properties of Clusters in the Photographic Process.- 1. Introduction.- 2. Basic principles of the photographic process.- 2.1 General description.- 2.2 Crystallography of the silver halides.- 2.3 The photographic process.- 2.4 Development.- 3. Theory of the photographic process.- 3.1 Experimental frame of the theories.- 3.2 Atomistic theories of the photographic process.- 3.3 The photographic process as an event of phase formation.- 4. Outlook.- Formation of Clusters in Bulk Materials.- 1. Introduction.- 2. Metal-excess alkali halides.- 3. Experimental methods for the study of colloids.- 4. Nucleation of colloids from F centres.- 5. Growth of colloids.- 6. Particle coarsening.- 7. Formation of clusters by irradiation.- 8. Summary.- Optical Properties of Small Particles in Insulating Matrices.- 1. Introduction.- 2. Optical material properties of small particles.- 2.1 Material functions of the bulk like matter.- 2.2 Material functions of small particles.- 2.3 Material functions of solid-state-clusters.- 3. Optical extinction and dispersion of one particle.- 3.1 Quasi-static case (ellipsoidal particles).- 3.2 General case (spherical particles).- 3.3 Physics behind the resonances.- 3.4 Volume plasmons in spherical metal particles.- 3.5. Optical properties of particles of various shapes.- 3.6. Summary of optical single particle polarizabilities.- 4. Optical properties of systems of many particles.- 4.1 Size distribution.- 4.2 Shape and orientation distribution.- 4.3 Multiple extinction effects.- 4.4 Interaction among particles.- 4.5 Summary.- to Percolation Theory.- 1. Two examples.- 2. Formal definition — Site percolation — Bond percolation.- 3. Definition and behaviour of the characteristic quantities.- 4. Thermodynamic analogy.- 5. Scaling laws.- 6. Exact results.- 7. Approximate results.- 8. The exponent of the conductivity.- 9. Percolation and macroscopic random media.- Electronic and Transport Properties of Granular Materials.- I. Effective medium theories of transport in inhomogeneous materials.- 1. Introduction.- 2. Effective medium theory for random resistor networks.- 3. The multiple scattering formalism.- 4. The hierarchy of effective medium approximations.- 5. EMA for continuous random systems.- 6. Effects of spatial correlation.- 7. EMA for other physical properties.- II. Specific inhomogeneous materials Morrel H. Cohen.- 1. Introduction.- 2. Macroscopically inhomogeneous materials.- 3. Microscopically inhomogeneous materials.- 4. Local electronic properties.- 5. The inhomogeneous metal-nonmetal transition.- 6. Porous media.- III. The origins of clustering Morrel H. Cohen.- 1. Introduction.- 2. Density fluctuations in expanded liquid Hg.- 3. Concentration fluctuations in metal-ammonia solutions.- 4. Valence fluctuations in Te, Se and SeTe alloys.- 5. Density fluctuations as clustering in glasses.- Optical Properties and Solar Selectivity of Metal-Insulator Composites.- 1. Introduction.- 2. Effective medium theories.- 3. Bounds on the effective dielectric permeability.- 4. Size limits for validity of effective medium theories.- 5. Case study one: optical properties and solar selectivity of coevaporated Co-Al2O3 films.- 6. Case study two: electrolytically coloured anodic Co-Al2O3 coatings.- 7. Summary and remarks.- Adhesion and Sintering of Small Particles.- 1. Introduction.- 2. Production of particles.- 3. General observations.- 4. Dynamics aspects of contact.- 5. Other aspects of adhesion.- 6. Sintering of small particles.- 7. Conclusion.- Physics on the Beach or the Theory of Windsurfing.