This study explores the influence of the ball-milling process on A3Fe compound formation starting from three compositions of mixed elemental powders. It has been found that nanocrystalline structures of A3Fe can directly form by ball-milling of powders with composition Al-20%Fe and Al-25%Fe whilst for the composition Al-12.5%Fe the compound only forms after annealing the milled powders.

The miniaturization of electronic and optic devices has revolutionized response times, energy loss and transport efficiency. An additional bonus is that as one approaches the nanosize regime the presence or absence of a few atoms and the geometrical disposition of each atom can significantly modify electronic and photonic properties. This control can be further supplemented by “packaging” assemblies of atoms or molecules into thin film or nanocomposite bulk materials to define surface states, cluster environment and geometry, intercluster interactions, and consequently, a wide tunable range of optical and charge carrier responses.

The chemist is presented with an intriguing challenge. First the clusters must be unisized with identical geometries. Secondly, the atom or molecular assemblies should ideally have perfect periodicity in order to rigorously define optoelectronic densities and intercluster tunnelling. A third requirement is that the nanocomposite be processable, generally in the form of thin films or single crystals. Numerous approaches are being undertaken in achieve these goals, including molecular beam and atomic layer epitaxy, molecular sieve inclusion chemistry, molecular capping of inorganic clusters, porous glass and aerosol synthesis. This paper presents a brief review of the interface chemistry associated with nanophase confinement and packaging and some features of three dimensional surface confinement using molecular sieves and zeolites.

The formation of cluster-assembled materials using the sintering process is investigated. We present a model that describes the initial stages exactly using information derived from ab initio calculations of cluster behavior. Surface area, effective cross section and density of the cluster-assembled material, are calculated as functions of time for several implementations of the model.

We report here the use of nucleotides as stabilizers in the formation of quantum-confined (‘Q-size’) CdS, with the size and composition of the nucleotide exerting a significant effect on the resultant CdS structure. In general, CdS formed from equimolar Cd+2 and S2− (6 × 10−4 M) in the presence of a number of nucleotides yields clusters possessing similar absorption spectra but which differ significantly with respect to emissive behavior and overall physical stability. CdS/polynucleotide colloids (DNA, poly [A], poly[C]) exhibit strong trap luminescence and are stable on a timescale of months, but analogous CdS prepared from the mononucleotides ATP and AMP are virtually nonemissive and flocculate within hours, even upon stabilization at lower temperatures (5 to −60°C). In addition to their preparation and spectroscopic properties, the results of TEM, AFM, and computer modeling studies on these CdS/nucleotide colloids are discussed.

A preparation method for mixtures of chemically different kinds of crystals on a nanometer scale is described. The method is based on inert gas condensation followed by the consolidation by means of high pressure. Since the size of the crystals is in the range of 6–20 nm, an appreciable volume fraction of the material is made up by interphase boundaries between the different crystals. Investigations of the morphological homogeneity of compacted mixtures consisting of Fe crystals and Cu or Ag crystals respectively have been carried out by means of electron microscopy and small-angle X-ray scattering. The atomistic structure in the vicinity of the Fe atoms has been studied by Moessbauer spectroscopy; indications for the formation of alloy phases have been found even for the Ag-Fe system which exhibits no miscibility in the liquid state. Alloy formation is proposed to take place at the interphase boundaries due to the special thermodynamic conditions in the boundary regions. These conditions are attributed to the free volume of the boundaries as well as to the presence of stresses.

Controlled polymerization of iron leads to the synthesis of molecular clusters of ever-increasing size, tending to extended structures. Polymerization of oxo-bridged octahedrally coordinated iron leads to clusters with 3D magnetic interactions between iron ions, while sulfide- and selenide-bridged tetrahedrally coordinated iron ions produce clusters of lower magnetic dimensionality. The magnetic properties of the resulting large molecular clusters with N ≥ 17 (where N = the number of iron ions in the cluster) are being investigated for the presence of collective magnetic correlations associated with the solid state.

TiO2 has been fabricated using a modified alkoxide hydrolysis route; the process yields about 50 g/day of nanocrystalline powder on a laboratory scale, which can be used to make large (1–10 g) samples. Pore size distributions show the powder is non-agglomerated, and TEM and BET analyses confirm the nanocrystalline size of the particles at about 20 nm. The powder is extremely reactive, sintering at about half the temperatures required of commercial powders. The chemically produced powder compacts to only 62% of the density that can be achieved by compacting a gas phase condensation (GPC)-produced TiO2. Nevertheless, the reactivity of this less dense compact is such that it reaches final densities comparable to that of the GPC TiO2. The difficulties in compacting and sintering large nanocrystalline samples are discussed. It is hoped that an understanding of these problems will lead to more intelligent densification of ultrafine powders so that full densification can be accomplished while retaining a nanocrystalline grain size.

A new technique has been developed to condense nanoparticles (clusters) of SiC and other nonoxide materials in a nonthermal microwave plasma. The experimental rationale and approach is described. It utilises silane and acetylene precursors in an Ar diluent, with the synthesis carried out in a microwave plasma at a pressure of ∼1 torr. The plasma conditions have been characterised, as have the effect of important parameters (gas ratios, flow rates and pressure) on the product nanoparticles. The resultant nanoparticles have been characterised ex-situ by TEM, Auger, and XPS spectroscopy. SiC particles collected are ∼5nm in size, with cubic, hexagonal and rhombohedral polytypes observed. Silicon nitride has been synthesised similarly by using silane and nitrogen as the precursor gases. Implications of the new technique are discussed.

A new approach has been developed for the synthesis of nanoscale ceramic powder materials from liquid organosilazane precursors. This technique, by exploiting fast kinetic chemical and physical reactions, makes it possible to synthesize significant quantities of material in a relatively short time. In the current approach aerosols of a silazane monomer, (CH3SiHNH)n, (n = 3 or 4), of mol. wt. 280–320, are injected into the beam of a cw industrial CO2 laser to obtain nanoscale ceramic powders. Injection of the aerosol into the laser-beam results in a high-temperature plume. Rapid condensation of the molecular precursor species emerging from the laser plume results in the formation of preceramic polymer particles, with an average diameter of 62 nm. One attractive feature of this process is that 70 wt.% of the liquid precursor is converted into nanoscale powders. Another feature is that only a further 10 wt.% loss occurs during post thermal treatment to form the end-product.

Nanometer-scale iron oxide magnetic particles have been formed in the porous network of a cross-linked polymer matrix by ion exchange and subsequent hydrolysis. The oxide particles are uniform, well-dispersed and spherical with a diameter ranging between 30 and 1200 Å depending on the synthesis conditions. The DC magnetic susceptibility, measured between 4 and 300 K, continuously increases with decreasing temperature and tends to saturate at low temperatures. Composites containing iron oxide particles with an average diameter of 80 Å exhibit superparamagnetism while those on the order of 1000 Å undergo an antiferromagnetic-type transition at 33 K. The magnetic susceptibility is critically dependent upon the particle size and the strength of the magnetic field.

Nanocrystalline ceramics have been produced by the method of inert gas condensation of ultra-small particles and in situ consolidation. Sintering characteristics and microstructural parameter such as grain size, porosity and pore size distributions have been investigated by a variety of techniques, including: X-ray diffraction, gravimetry, nitrogen adsorption, scanning electron microscopy and small angle neutron scattering. In pure TiO2, the sintering temperatures are drastically lowered compared to conventional ceramics, however, extensive grain growth occurs before full densification is achieved. High density, nanocrystalline ceramics can be prepared by pressure assisted sintering, doping and additions of second phases. High temperature microhardness and creep deformation in compression were measured and it was found that creep processes occur at lower temperatures than in ceramics with larger grain sizes. Nanocrystalline TiO2 with densities > 99 % can be deformed plastically without fracture at temperatures below half the melting point. The total strains exceed 0.6 at strain rates as high as 10−3 s−1. The stress exponent of the strain rate, n, is approximately 3 and the grain size dependence is G-q with q in the range of 1 – 1.5. It is concluded that the creep deformation occurs by an interface reaction controlled mechanism.

Measurements of tensile strength and creep resistance have been made on bulk samples of nanocrystalline Cu, Pd and Ag consolidated from powders by cold compaction. Samples of Cu-Cu2O have also been tested. Yield strength for samples with mean grain sizes of 5–80 nm and bulk densities on the order of 95% of theoretical density are increased 2–5 times over that measured in pure, annealed samples of the same composition with micrometer grain sizes. Ductility in the nanocrystalline Cu has exceeded 6% true strain, however, nanocrystalline Pd samples were much less ductile. Constant load creep tests performed at room temperature at stresses of >100 MPa indicate logarithmic creep. The mechanical properties results are interpreted to be due to grain size-related strengthening and processing flaw-related weakening.

A universal, accurate and simple method is developed to describe the thermodynamic properties of disordered grain boundaries in nanocrystalline metals. Based on a free volume approach at negative pressure of the universal equation of state, the maximum free volume, bulk modulus, specific heat at constant pressure, thermal expansion coefficient, excess enthalpy, excess entropy and free energy of grain boundaries are derived from well-known thermodynamic relationships. Describing nanocrystalline metals as a bimodal material with a grain boundary component and a crystalline component, their thermodynamic properties can then be estimated by appropriate scaling of the boundary-to-volume ratio.

A High Resolution Electron Microscopy (HREM) study of grain boundaries in nanocrystalline copper produced by sliding wear and by inert gas condensation is described. The results in both cases are essentially the same and similar to those in conventional polycrystals. Contrary to reports in the literature, these results do not indicate the presence of a fundamentally different structure in nanocrystalline materials. Measurements of the mechanical properties (such as yield strength, elastic modulus and strain rate sensitivity) of these materials using nanoindentation are also presented. These are found to be in good agreement with values expected from a polycrystalline material with a very fine grain size.

In May of 1990, crystals of a new form of carbon were observed crystallizing from a solution of the newly-produced macroscopic quantities of fullerene molecules. This discovery followed many years of work we had done in producing and measuring the optical properties of small particles of graphitic carbon, a work which was aimed, in part, at a better understanding of the various spectral features of interstellar material. Among three distinctly different types of carbon particulates, distinguished by their differing ultraviolet and Raman spectra, was one that later proved to contain macroscopic quantities of C60 and C70. Evidence for fullerenes came from mass spectra, infrared spectra, and X-ray and electron diffraction. More, recent experiments with our collaborators have included scanning tunneling microscopy and gas phase emission spectroscopy in the infrared. At the moment, there is no obvious connection with interstellar spectral features.

It has taken almost exactly five years to prove that the buckminsterfullerene structure, originally proposed to account for the unexpected stability of the C60 molecule in cluster beam experiments, is actually correct. That an easily-produced, stable compound of pure carbon, the most studied of all the elements, could have been under our noses since time immemorial and have eluded detection for so long seems almost unbelievable. Although the existence of this molecule appears to have boundless prospects for the development of new materials with exciting and novel applications it is worth noting that it was serendipitously discovered during basic science programmes aimed at understanding the nature of processes in space rather than an applied programme aimed at understanding the intrinsic properties of carbon.

We recently demonstrated that C60 and C70, as well as other fullerenes, can be deposited and accumulated on surfaces using laser ablation of graphite in an Inert gas atmosphere. After learning of the work of Krätschmer et al. indicating the presence of C60 in carbon soot, we showed that samples consisting almost exclusively of C60 and C70 can be sublimed from such soot. Vibrational Raman spectra of C60 and C70 were obtained from these samples. The C60 spectrum Is consistent with the calculated spectrum of Buckmlnsterfullerene, and the strongest three lines can be assigned on the basis of frequency and polarization. The NMR spectrum of dissolved C60 was then obtained, and found to consist of a single resonance, establishing the icosahedral symmetry of this molecule. STM images of the C60 molecules on a Au(111) crystal face show that these clusters form hexagonal arrays with an intercluster spacing of 11.0 Å and are mobile at ambient temperature. Distinctly taller species evident in the arrays are believed to be C70 clusters. Vibrational Raman and infrared spectra have also been obtained for separated C60 and C70.

Generation of C60 at a rate of more than 10 grams per day has been accomplished by operation of a carbon arc in an atmosphere of helium. Optimum yield of 15% was found to occur near 100–200 torr, but yields greater than 3% were found throughout the range between 50 and 760 torr. A model is proposed to explain the observed behavior based on competition between annealing of graphitic sheets to curve so that they minimize dangling bonds, and further rapid growth of these sheets in the gas phase to form giant fullerenes. In agreement with predictions of this model, laser vaporization of graphite targets was found to produce macroscopic quantities of C60 only when performed in an oven above 1000 C.

A report is given on molecular carbon research in Los Angeles, starting with review of the molecular precursor approach to carbon materials.1 Regarding larger molecules, mixtures of carbon molecules, Cn, are extracted2 in 25–40 percent yield from graphite evaporated under helium. Gram quantities of the mixture are then separated into pure fractions – C60, C70, C76/C78, C84, and higher (n > 88),3,4 and characterized by mass spectrometry, liquid chromatography, and 13CNMR spectroscopy. Examination of the spectroscopic and photophysical5 properties of the molecules, with particular focus on C60 in solution, reveals: (i) the first transitions appear at high energy, are electronically forbidden (in C60, the homo-lumo hu - t1u transitions), and exhibit resolved vibronic structure; (ii) the spectra sharpen in cryogenic media, allowing vibronic assignment; and (iii) relaxation occurs with near-unity quantum yield to a long-lived triplet, which also transfers energy efficiently to acceptors including O2.

In this paper we will describe the production, separation and characterization of the new all carbon molecules, C60 and C70. High performance liquid chromatography HPLC is used to obtain purified samples of C60 and C70, which are subsequently characterized by electron impact and chemical ionization mass spectrometry, IR and UV-visible absorption spectroscopy, NMR, ESR, scanning tunnelling microscopy, transmission electron microscopy and x-ray absorption fine structure measurements.