The Panel was charged with assessing the present scientific understanding of the size-dependent physical and chemical properties of clusters, the methods of synthesis of macroscopic amounts of size-selected clusters with desired properties, and most importantly, the possibility of their controlled assembly into new materials with novel properties. The Panel was composed of both academic and industrial scientists from the physics, chemistry, and materials science communities, and met in January 1988.

In materials (insulators, semiconductors, and metals) with strong chemical bonding, there is extensive spatial delocalization of valence electrons, and therefore the bulk physical properties which depend upon these electrons develop only gradually with cluster size. Recent research using supersonic-jet, gas-aggregation, colloidal, and chemical-synthetic methods indeed clearly establishes that intermediate size clusters have novel and hybrid properties, between the molecular and bulk solid-state limits. A scientific understanding of these transitions in properties has only been partially achieved, and the Panel believes that this interdisciplinary area of science is at the very heart of the basic nature of materials. In Sec. V (Future Challenges and Opportunities), a series of basic questions for future research are detailed. Each question has an obvious impact on our potential ability to create new materials.

Present methods for the synthesis of useful amounts of size-selected clusters, with surface chemical properties purposefully controlled and/or modified, are almost nonexistent, and these fundamentally limit our ability to explore the assembly of clusters into potentially novel materials. While elegant spectroscopic and chemisorption studies of size-selected clusters have been carried out using molecular-beam technologies, there are no demonstrated methods for recovery and accumulation of such samples. Within the past year, the first reports of the chemical synthesis of clusters with surfaces chemically modified have been reported for limited classes of materials. Apparatus for the accumulation and consolidation of nanophase materials have been developed, and the first promising studies of their physical properties are appearing. In both the chemical and nanophase synthesis areas, clusters with a distribution of sizes and shapes are being studied. Progress on macroscopic synthetic methods for size-selected clusters of controlled surface properties is the most important immediate goal recognized by the Panel. Simultaneous improvement in physical characterization will be necessary to guide synthesis research.

Assuming such progress will occur, the Panel suggests that self-assembly of clusters into new elemental polymorphs and new types of nanoscale heterogeneous materials offers an area of intriguing technological promise. The electrical and optical properties of such heterogeneous materials could be tailored in very specific ways. Such ideas are quite speculative at this time; their implementation critically depends upon controlled modification of cluster surfaces, and upon development of characterization and theoretical tools to guide experiments.

The Panel concluded that a number of genuinely novel ideas had been enunciated, and that in its opinion some would surely lead to exciting new science and important new materials.

A method has been developed for determining the equilibrium phase composition of multicomponent systems at subsolidus conditions and atmospheric pressure, based on the knowledge of binary phase compatibilities and on information concerning the existence and stoichiometry of ternary and higher order compounds. The method, combined with material balance, enables computation of the changes of equilibrium phase compositions of fired products dependent on the proportions of multicomponent raw materials; the procedure is useful for assessing the exploitability of industrial wastes for production of binding materials and ceramics. It is also possible to find the raw material mixture composition needed for the desired phase composition of the fired product.

The reactions of vacuum deposited thin films of lithium with various complex glasses have been explored using x-ray photoelectron spectroscopy (XPS). In contrast to lithium reactions with simple glasses such as silica or boron oxides, the reactions are predominantly those of the network modifiers such as sodium, potassium, and magnesium. XPS and x-ray induced Auger lineshapes indicate the migration of the network modifier to the near surface region followed by its reduction. In the case of magnesium, there is evidence for stable alloy formation with unreacted lithium following these migration and reduction steps.

The classical model of Chemical Vapor Infiltration (CVI) treats diffusion and surface reaction in a representative cylindrical pore. Two significant modifications to that approach are presented herein. One accounts for more complex chemistry by allowing for both gas-phase and surface reactions which lead to film growth. The other couples the pore model to a reactor model for the region external to the porous preform. The results demonstrate that it is possible to select chemical schemes that yield densification from the interior to the exterior of the preform, thus avoiding premature trapping of interior voids.

Mg–Ti–spinel formation has been observed by cross-sectional transmission electron microscopy at the interface of TiN(100) films and MgO(100) substrates for films grown at substrate temperatures higher than 800 °C and for samples post-annealed at 850 °C. The TiN films were deposited by reactive magnetron sputtering onto cleaved (100)-oriented MgO substrates. The spinel formed 5 nm epitaxial layers along the interface with occasional (111) wedges growing into the MgO. The orientational relationships were found to be TiN(100)|spinel(100)|MgO(100) and TiN[001]|spinel[001]|MgO[001]. The spinel composition is suggested to be Mg2TiO4.

Polyacrylonitrile (PAN) films have been fabricated by both spin and solvent casting techniques, and pyrolyzed to produce carbon films in the thickness range of 200–50000 Å. These films have higher electrical conductivities than carbon films produced from most other precursors at similar temperatures. The chemical structure of the films at different stages of processing was investigated by UV, IR, Raman, and XPS spectroscopies. An extra degree of control over the final electrical conductivity was obtained by varying the PAN content of copolymer precursors. Oxidation rates and an activation energy were determined. Finally, processing techniques are described which allow both dry and wet film transfer and lithographic patterning.

The freeze-fracture technique has been developed to study solid-liquid dispersions. In this technique, a sample of dispersion is frozen, then fractured. A replica of the fracture surface is made and observed using a scanning electron microscope. The physical form of the solid thickener in dispersion can be studied, and the structure of the thickener can be revealed as well as a combination of rupture properties of the solid and the frozen liquid. The application of this technique is on lubricant greases. Greases are two-phase dispersed systems composed of mineral oil gelled with solid particles of soap. Three lithium 12-hydroxystearate greases are examined. Two different kinds of washing of the replica are used, the first eliminating the liquid phase. The configuration of soap particles and the network formed by them are observed, and artifacts such as twisting soap fibers are avoided. The second washing eliminates the solid and liquid phase. Examination of the fracture surface of the soap provides information on crystalline arrangement. The observed structures by freeze fracture are related to the thermal treatments during grease manufacture. The results are compared with the observations obtained from an electron transmission microscope analysis after preparation by the usual dispersion technique.

Photon emission accompanying the fracture of an epoxy and single crystal MgO is examined for evidence of deterministic chaos by means of the autocorrelation function, the Fourier transform, the correlation integral of Grassberger and Procaccia, and the fractal box dimension. A positive Lyapunov exponent is also obtained from the epoxy phE data. Each of these measures is consistent with a significant degree of deterministic chaos associated with attractors of relatively low dimension. A typical epoxy fracture surface was analyzed for fractal character by means of the slit island technique, yielding a fractal dimension of 1.32 ± 0.03. The fractal dimensions of the fracture surface and the photon emission data (box dimension) of the epoxy are in good agreement. These observations suggest that fluctuations in photon emission intensity during fracture reflect the production of fractal surface features as they are being produced and thus provide important information on the process of dynamic crack growth.

The compound La2Ti2O7 was prepared by a liquid mix technique and examined at room temperature by x-ray diffraction, infrared absorption, and Raman spectroscopy. The examinations confirm and supplement the earlier observation by x-ray diffraction that La2Ti2O7 crystallizes in the monoclinic structure without an inversion symmetry. The energy-shifts (cm−1) that were observed in the vibrational spectra may be explained by a sixfold coordination for the titanium and a ninefold coordination for the lanthanum in the structure. This type of coordination satisfies Pauling's electrostatic valence rule regarding the electrostatic bond strengths at the shared anions.

Epitaxial crystallization of polyphenylene sulfide (PPS) from 1-chloronaphthalene solution on NaCl (001) surface has been studied using electron microscopy and electron diffraction techniques. Three different epitaxial morphologies were observed: (1) conventional rodlike structures (fold plane epitaxy); (2) platelet structures (fold surface epitaxy); and (3) roselike structures whose growth mechanism and molecular packing are not completely understood at present. Of primary importance is the fact that a possible new crystal structure β-phase) of PPS was formed in the fold surface epitaxy through a true two-dimensional lattice matching by lateral lattice dimensional adjustment of PPS. Lattice match criterion again shows its merit in explaining the formation of fold surface epitaxy and the new crystal structure of PPS. Solution concentration, crystallization temperature, and time have significant influence on crystal growths, orientations, molecular packing, and morphological arrangements.

The stress-displacement relation of the fiber is analyzed for fiber-reinforced ceramic composites during axial compressive loading (indentation) and unloading on the exposed end of an embedded fiber. An unbonded fiber/matrix interface subject to Coulomb friction and residual radial clamping stresses is considered in the present study. The results show that the stress-displacement curves during loading and unloading can be used to evaluate the magnitude of the clamping stress, the coefficient of friction, and the frictional stress distribution at the interface. Specifically, in the absence of Poisson's effect (i.e., when Poisson's ratio of the fiber is zero), the interfacial shear stress is constant, the loading curve is parabolic, and, after complete unloading, the residual fiber displacement equals half of the maximum fiber displacement at the peak loading stress. In the presence of Poisson's effect, the interfacial shear stress is not constant, and, after complete unloading, the residual fiber displacement is less than half of the maximum fiber displacement at the peak loading stress.

The investigation of dilute solution epitaxy of polyphenylene sulfide (PPS) has been carried out on a series of inorganic substrates, which cover a wide range of interatomic spacings, surface energies, and geometries. A variety of morphological arrangements of PPS on various substrates were observed. Both 〈100〉 and 〈110〉 epitaxial orientations were observed on monovalent alkali halides. While the 〈100〉 epitaxy is generally thought to grow upon nucleation on surface steps along the 〈100〉 direction, 〈110〉 epitaxy may also be nucleated on these surface steps. Changes in ionic lattice dimensions and ionic nature of the substrate have a substantial effect on the molecular packing of PPS and the resulting crystal orientations. Four new crystalline phases of PPS have resulted from the fold surface epitaxies on NaCl, KCl, KBr, and mica with favorable one- or two-dimensional lattice matching. This is a direct indication of the important role of lattice matching in inducing and defining the epitaxies and polymorphism of PPS.

Laser-driven synthesis of refractory powders from the organosilicon compounds ((CH3)3Si)2NH and ((CH3)3Si)2O has been studied as prototypical of powder syntheses from large molecules. A cw CO2 laser is used for powder syntheses and pulsed TEA CO2 laser-driven homogeneous pyrolysis is used to study the initiation chemistry. Initial decomposition of the organosilanes by Si–C bond cleavage initiates free radical chain reactions which produce organosilicon polymers and subsequent refractory phases. A qualitative model is proposed which provides a framework for understanding the parameters influencing powder synthesis from large molecules.

Transparent silica gel–polymer composites have been prepared by the impregnation of porous gels with organic monomer and polymerization in situ. The relative amount of each phase was adjusted by varying the porosity of the silica gel prior to impregnation. These materials constitute a new class of transparent composites. Properties, such as density, refractive index, modulus of rupture, compressive strength, abrasion rate, and Vickers hardness, have been measured over the compositional range of 100% silica to 100% polymethyl methacrylate (PMMA).

Our recent applications of the atom-probe field ion microscope to the study of physics and chemistry of materials at the atomic level are summarized. The materials applicability of field ion microscopy has recently been extended to silicon, silicide, graphite, high Tc superconductors, and other materials. Atom-probe field ion microscopy has been used for atomic layer by atomic layer chemical analysis of surfaces in alloy and impurity segregations, for analyzing the compositional changes across metal-semiconductor interfaces, and for studying formation of cluster ions in laser stimulated field desorption. The energetics of atoms in solids and on surfaces can be studied by a direct kinetic energy analysis of field desorbed ions using a high resolution pulsed-laser time-of-flight atom-probe and by other field ion microscope measurements. The site specific binding energy of surface atoms can be measured at low temperature, where the atomic structure of the surface is still perfectly defined, to an accuracy of about 0.1 to 0.3 eV.

The microstructures of carbon fibers prepared from coal tar mesophase pitch and heat-treated at 2500 °C were studied by transmission electron microscopy (TEM). The degree of preferred orientation of the carbon fibers along the fiber axis was not significantly changed: by spinning, while stirring the pitch above the capillary; by changing the viscosity of the pitch in spinning from 60 poise to 250 poise, keeping the diameter of the pitch precursor fiber about 11.5 μm, which is that of the as-spun fiber; and by controlling the diameter of the pitch fiber from 8 μm to 18 μm, keeping the viscosity of the pitch at about 250 poise. Such a weak dependency of the degree of preferred orientation of the carbon fibers on the spinning conditions is qualitatively consistent with the relationships between the degree of preferred orientation of a pitch precursor fiber and the spinning conditions. The graphite layers of the carbon fibers heat-treated at 2500 °C showed shrinkage in the transverse fiber cross section. The degree of shrinkage was significantly increased by stirring the pitch above the capillary while spinning, and the shrinkage also increased when the viscosity of the pitch was increased for spinning, and when the diameter of the fibers was decreased. Roughly speaking, the degree of shrinkage was proportional to the mean size of the mesophase domains in the transverse section of pitch precursor fibers.

The properties of graphite intercalation compounds (GIC's) are discussed with respect to possible applications. Five families of intercalates give high electrical conductivity to GIC's: pentafluorides leading to high conductivity, 108 S/m (higher than metallic copper); metal chlorides; fluorine and alkali metals with bismuth giving relatively high conductivity of the order of 107 S/m plus stability in air; and residual halogens showing extremely high stability under severe conditions, though the conductivity is only of the order of 106 S/m. Electrodes of different GIC's have been tried in primary and secondary batteries, where their characteristics are high electrical conductivity and easy diffusion of electrochemically active species between the graphite layers. Primary lithium batteries of a covalent graphite fluoride are now widely used commercially. Secondary batteries using different host graphites and intercalates give interesting results. Large amounts of hydrogen can be stored in the functional space in alkali metal-GIC's. The same GIC's show high coefficients of isotope separation of hydrogen at liquid nitrogen temperature. The structure and texture of the host graphite play a decisive role in the absorption and separation behaviors of GIC's. Exfoliated graphite prepared by rapid heating of GIC's or their residue compounds leads to flexible graphite sheets which have great industrial applications. Some problems connected with the production and use of these sheets are discussed.

The cells in living bone are embedded in a charged, organic-inorganic solid permeated by ionic fluids flowing through a complex network of channels (diameter ∼10−1–102 μm). The solid matrix, which has a high degree of composite material organization beginning at the macromolecular level, has even finer pores of diameter ≳10−3 μm containing extracellular fluids. Since bone cells are thus bathed in fluid environments of varying ionic composition and concentration, it is likely that the physiology of bone depends on its electrical and electromechanical properties. This hypothesis is supported by the known effects of externally applied mechanical and electrical signals on physiological functions. Contrary to the earlier perception of bone as an insulating material, it is now recognized that the fluid content of bone endows it with physiologically significant conductivity. Mechanoelectric transduction in bone, at low frequencies, is most likely an electrokinetic process associated with the solid-fluid interfaces in bone. Electromechanical properties of bone have been determined experimentally by measurements of stress-generated potentials and streaming potentials in wet bone specimens and electrophoretic mobility of bone particles. Interpretation of results has been difficult due to the complexity of the solid-fluid interfaces in bone and the often undefinable alterations of the pores and interfaces due to specimen preparation. This paper is a review of the present state of knowledge of mechanoelectric transduction in bone and its physiological significance.