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We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800 °C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500 °C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications.

This article introduces the November 2005 issue of MRS Bulletin on the life and works of Arthur Robert von Hippel, who pioneered the interdisciplinary approach to materials research. This issue of MRS Bulletin celebrates his long life, his large volume of work, and the overall impact he had on materials research as practiced today. This introductory article summarizes the start and progression of the various fields presented in this issue, and how many were inspired directly by von Hippel's work and ways, and how new fields continue to emerge based on the same foundations of interdisciplinarity. The articles in this issue cover research areas in which von Hippel was involved, namely, ferroelectrics and magnetism; fields that thrived on an interdisciplinary approach that von Hippel represented, such as semiconductors; and areas that reflect his own vision about materials research and interests later in life, including molecular design and biomaterials. Before the scientific work is presented, the issue begins with a personal sketch of von Hippel, contributed by his son Frank N. von Hippel.

High yields of graphitic conical nanofibres (5–70 nm OD; 5 μm long) are produced by pyrolysing palladium precursors under Ar at 850–1000°C. The fibres exhibit diamond-shaped Pd particles at their tips, which are responsible for the formation of stacked graphene cones (open, lampshade-type, or closed). The cones observed with apex angles of ca. 30°, 50° and 70° can be explained by an open cone approach, which considers different chiralities. Due to the presence of open edges (dangling bonds), we envisage that these novel nanofibres may find important applications in the fabrication of field emitters, gas storage components and composites.

A review of the structure and properties of fullerenes is presented. Emphasis is given to their behavior as molecular solids. The structure and property modifications produced by alkali-metal doping are summarized, including modification to the electronic structure, lattice modes, transport, and optical properties. Particular emphasis is given to the alkali-metal-doped fullerenes because of their importance as superconductors. A review of the structure and properties of fullerene-based graphene tubules is also given, including a model for their one-dimensional electronic band structure. Potential applications for fullerene-based materials are suggested.

Metrology is the science of measurement, applicable to any field of science and technology. The growing interest in applying nanomaterials to societal needs is now urging that increasing attention be given to the development of scientific and applied nanometrology. As it is impossible to give a broad coverage of all classes of nanomaterials, here we use sp 2 carbon nanostructures as an illustrative system for the development of nanometrology, with focus on carbon nanotubes and graphene, as prototypes for one- and two-dimensional nanostructures.

We present the first femtosecond pump-prove measurements of the room temperature optical properties of high-Tc superconductors. Three oriented superconducting thin-films were studied: YBa2Cu3O7−δ, Bi2Sr2CaCu2O8+z, and Bi2Sr2Ca2Cu3O10+y. The observed changes in e2 can be related to the dynamics of the Cu d to O p band charge transfer excitation occurring in the Cu  O planes. By depleting the YBa2Cu3O7−δ sample of oxygen, we simultaneously vary the Fermi level and the Tc. The sign of Δe2 is found to depend on the Fermi level position, while the recovery time is found to increase markedly with decreasing Tc.

Publisher Summary This chapter focuses on the structure and properties of the various forms of carbon, carbon clusters, and molecules. Carbon-based materials, clusters, and molecules arc unique in many ways. One distinction relates to the many forms that carbon based materials can assume. Under ambient conditions and in bulk form, the graphite phase with strong in-plane trigonal bonding is the stable phase under the application of high pressure and high temperature (both of which are somewhat reduced when catalyst particles like iron or nickel are used), transformation to the diamond structure takes place. Once the pressure is released, diamond remains essentially stable under ambient conditions although, in principle, it will very slowly transform back to the thermodynamically stable form of solid carbon, which is graphite. However, when exposed to various perturbations, such as irradiation and heat, diamond will quickly transform back to the equilibrium graphite phase. In the graphite phase, the structure is highly anisotropic, exhibiting semimetallic behavior in the basal (ab) plane and poor electrical conductivity.

Publisher Summary This chapter focuses on the experimental observations of superconductivity in various fullerene-related compounds. The first observation of superconductivity in a carbon-based material goes back to 1965, when superconductivity was observed in the first-stage alkali metal graphite intercalation compound. The early observation of superconductivity in a doped fullerene solid attracted interest because of its relatively high Tc. This work was soon followed by observations of superconductivity at even higher temperatures. It is interesting to note that if superconductivity had been found in these alkali metal-doped C60 compounds prior to the discovery of superconductivity in the cuprates, the alkali metaldoped fullerenes would have been the highest-Tc superconductors studied up to that time. At present, the highest-Tc organic superconductor is an alkali metal-doped fullerene, namely Cs3C60 under pressure with Tc ∼ 40 K, breaking a record previously held by the tetrathiafulvalene derivative.

Publisher Summary This chapter reviews the lattice mode structure for the isolated fullerene molecules and for the corresponding molecular solid. The major experimental techniques for studying the vibrational spectra include Raman and infrared spectroscopy, inelastic neutron scattering, and electron energy loss spectroscopy. Of these techniques, the most precise values for vibrational frequencies are obtained from Raman and infrared spectroscopies. In most crystalline solids, Raman and infrared spectroscopy measurements focus primarily on first-order spectra which are confined to zone-center (q = 0) phonons. Because of the molecular nature of fullerene solids, higher-order Raman and infrared spectra also give sharp spectral features. Analysis of the second-order Raman and infrared spectra for C60 provides a good determination of the 32 silent mode frequencies and their symmetries. If large single crystals are available, then the most general technique for studying solid-state phonon dispersion relations is inelastic neutron scattering. Unfortunately, large single crystals are not yet available even for C60, so that almost all the reported inelastic neutron scattering measurements have been done on polycrystalline samples. Much of the emphasis of the inelastic neutron scattering studies thus far has been on the lowest-energy intermolecular dispersion relations, which have been studied on both single-crystal and polycrystalline samples.

Publisher Summary Early synthesis of fullerenes was done using laser ablation of graphite targets in He gas to create fullerenes in the gas phase. An intense laser pulse was used to vaporize material from a graphite surface, thereby creating a hot carbon plasma. This hot plasma was quenched and entrained in a flowing inert gas (e.g., He) to form carbon clusters. The clustering was permitted to occur for 30–200μs, after which the gas stream was allowed to expand and cool, thereby terminating cluster growth. This laser ablation source was coupled to the front end of a time-of-flight mass spectrometer which allowed the mass spectrum of the clusters and molecules formed by the source to be measured. The mass spectrum above 40 carbon atoms shows a prominence for clusters of mass C60. This preponderance of the C60 line in the mass spectra was recognized by Kroto and Smalley at an early stage. By allowing the plasma to react for a longer time, they found that the C60 peak could be enhanced relative to the other peaks.

Publisher Summary The electronic structures of the crystalline phases are expected to be closely related to the electronic levels of the isolated fullerene molecules. The electronic structure for the solid is considered from both the standpoint of a highly correlated molecular solid and as a one-electron band solid. Theoretical work on the electronic structure of fullerenes had relied heavily on comparisons of these calculations with photoemission experiments, because, in principle, photoemission and inverse photoemission experiments are, respectively, sensitive to the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) electronic densities of states. Several models for the electronic structure of fullerene molecules have been developed, ranging from one-electron Hiickel calculations or tight-binding models to first principles models. While sophisticated models yield somewhat more quantitative agreement with optical, photoemission, and other experiments sensitive to the electronic structure, the simple Hiickel models lead to the same level ordering near the Fermi level and for this reason are often used for physical discussions of the electronic structure.

Publisher Summary This chapter discusses the optical response of fullerenes over a photon energy range from the near infrared (IR) through the ultraviolet (UV) region of the spectrum (1-6 eV). This region of the spectrum is used to explore the nature of the electronic states of fullerenes, whether they are studied in the gas phase, in solution, or assembled in the solid state. Results of experiments to obtain the linear, as well as the nonlinear, optical response are considered and compared, when possible, with theoretical models and calculations. Since the absorption and luminescence spectra of solid C60 resemble to a considerable degree the corresponding spectra observed for C60 in solution, it is believed that molecular states should be a good starting point for the description of the electronic bands in solid C60.

Publisher Summary The magnetic properties of fullerenes are interesting and surprising. Materials with closed-shell configurations are diamagnetic. There are several methods for introducing paramagnetic behavior into fullerenes, including methods for producing magnetically ordered phases. For example, the introduction of a magnetic dopant ion with an unfilled d or f shell (either endohedrally of exohedrally) is expected to lead to Curie paramagnetism. The large number of aromatic rings in fullerenes suggests that they might be highly diamagnetic, setting up shielding screening currents upon application of a magnetic field. More detailed analysis shows that the hexagonal rings contribute a diamagnetic term to the total susceptibility χ, while the pentagonal rings contribute a paramagnetic term of almost equal magnitude, thereby leading to an unusually small diamagnetic susceptibility for C60 in comparison with other ring compounds and with graphite itself, which has only hexagonal rings. This approach to the analysis of the magnetic susceptibility is in good agreement with χ measurements on both C60 and C70.

There is great current interest in layered anisotropic materials. Much of the interesi relates to the possibility of an approximate decoupling of 3-dimensional (3D) behavioi into ID properties perpendicular to the layer planes and 2D properties associated with the layer planes. Since this decoupling in layered materials is enhanced by intercalation, much attention has been given to intercalation compounds in recenl years as a means to study interesting questions of low dimensional physics. Since many deliberately structured materials also are prepared in layered sequences, there are many close connections between the properties of intercalated layered materials and deliberately structured materials. This article will focus on several important connections between intercalated layered materials and multilayered superlattice structures prepared by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD).Interest in intercalation compounds has led to three lively MRS symposia on this topic (Fall 1982, Fall 1984, Fall 1986) and a number of summer schools and workshops, one of which was held in July 1986 at Erice, Sicily, under the auspices of NATO and the European Physical Society. The published lecture notes1 from this summer school provide a useful introduction and reference for students and others interested in this field.

First- and second-order Raman scattering are described for EuSe near T N = 4.6 K. The second-order spectral features are interpreted using previous mode assignments for EuSe. Spin fluctuation effects are described for T ≳ T N and related to the phonon dispersion relations.

The first-order Raman scattering experiments in the europium chalcogenides are analyzed in terms of both the symmetries of the various magnetic phases and the resonant enhancements associated with the electronic structure. Both a one-electron band model and a localized magnetic exciton model are used for a calculation of the Raman scattering intensity. The parameters of these models are chosen to be consistent with the optical reflectivity and with the observed resonant Raman enhancement. Comparison with experiment is given in terms of a dimensionless plot of the frequency dependence of the Raman intensity for several europium chalcogenides in the ferromagnetic phase. Comparison with the experimental data suggests that the excitonic model for the electronic transitions is responsible for the observed resonant enhancement behavior.

Room temperature Raman microprobe, (00 l ) x-ray diffraction and electrical resistivity measurements have been performed on carbon/carbon composites made from mesophase pitch which were heat treated (T HT ) at 2680°C, 2820°C and 3015°C. Results of these measurements indicate that both the ex-pitch carbon fiber and mesophase pitch matrix constituents of the composites were highly graphitic, exhibiting in-plane crystallite dimensions (L a ) greater than 1000 A for this range of T HT values. The c-axis crystallite dimensions (L c ) were determined by analysis of x-ray diffraction peak widths to be ∼ 150 A . CuCl 2 was successfully reacted with T HT = 3020°C composites forming a stage 3 intercalation compound in both the fibers and the matrix, as determined by their Raman spectra.

Electron microscopy can be used to study structures and phase transitions occurring in graphite intercalations compounds. The fundamental symmetry in graphite intercalation compounds is the staging periodicity whereby each intercalate layer is separated by n graphite layers, n denoting the stage index. The currently accepted model for intercalation proposed by Herold and Daumas assumes that the sample contains equal amounts of intercalant between any two graphite layers and staged regions are confined to domains. Specifically, in a stage 2 compound, the Herold-Daumas domain wall model predicts a pleated lattice plane structure.