We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

http://science.sciencemag.org/content/sci/306/5696/666.full.pdf

Electric Field Effect in Atomically Thin Carbon Films

Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

The rise of graphene

There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m(-1)) and -690 Nm(-1), respectively. The breaking strength is 42 N m(-1) and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = -2.0 terapascals, and intrinsic strength of sigma(int) = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

/pdf/measurement-of-the-elastic-properties-and-intrinsic-strength-27nythtm75.pdf

Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene

CARBON nanotubes are predicted to have interesting mechanical properties—in particular, high stiffness and axial strength—as a result of their seamless cylindrical graphitic structure1–5. Their mechanical properties have so far eluded direct measurement, however, because of the very small dimensions of nanotubes. Here we estimate the Young's modulus of isolated nanotubes by measuring, in the transmission electron microscope, the amplitude of their intrinsic thermal vibrations. We find that carbon nanotubes have exceptionally high Young's moduli, in the terapascal (TPa) range. Their high stiffness, coupled with their low density, implies that nanotubes might be useful as nanoscale fibres in strong, lightweight composite materials.

Exceptionally high Young's modulus observed for individual carbon nanotubes

We estimate the stiffness of single-walled carbon nanotubes by observing their freestanding room-temperature vibrations in a transmission electron microscope. The nanotube dimensions and vibration amplitude are measured from electron micrographs, and it is assumed that the vibration modes are driven stochastically and are those of a clamped cantilever. Micrographs of 27 nanotubes in the diameter range 1.0--1.5 nm were measured to yield an average Young's modulus of $〈Y〉=1.25 \mathrm{TPa}.$ This value is consistent with previous measurements for multiwalled nanotubes, and is higher than the currently accepted value of the in-plane modulus of graphite.

Young’s modulus of single-walled nanotubes

Section Headings.Preface. Explanatory notes. Powder pattern identification table. Powder patterns. Powder patterns simulations of disordered intergrowths.

Collection of Simulated XRD Powder Patterns for Zeolites Fifth (5th) Revised Edition

Collection of Simulated Xrd Powder Patterns for Zeolites

The nucleation and growth of curved carbon structures, such asfullerenes, nanotubes and soot, are still not well understood. Avariety of models have been proposed1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17, and it seems clear that the occurrence of pentagons, which yield 60° disclination defects in the hexagonal graphitic network, is a key element in the puzzle. The problem of nucleation has been complicated by the great variety of structures observed in any one sample. Here we report an unusual carbon sample generated by pyrolysis of hydrocarbons, consisting entirely of graphitic microstructures with total disclinations that are multiples of +60°. The disclination of each structure corresponds to the presence of a given number of pentagons in the seed from which it grew: disks (no pentagons), five types of cones (one to five pentagons), of which only one was known previously18, and open tubes (six pentagons). Statistical analysis of these domains shows some unexpected features, which suggest that entropy plays a dominant role in the formation of disclinations. Furthermore, the total disclination of a domain is determined mainly at the nucleation stage.

/pdf/graphitic-cones-and-the-nucleation-of-curved-carbon-surfaces-2tbwpkz8ig.pdf

Michael Treacy

Papers

Exceptionally high Young's modulus observed for individual carbon nanotubes

Young’s modulus of single-walled nanotubes

Collection of Simulated XRD Powder Patterns for Zeolites Fifth (5th) Revised Edition

Collection of Simulated Xrd Powder Patterns for Zeolites

Graphitic cones and the nucleation of curved carbon surfaces