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

THE synthesis of molecular carbon structures in the form of C60 and other fullerenes1 has stimulated intense interest in the structures accessible to graphitic carbon sheets. Here I report the preparation of a new type of finite carbon structure consisting of needle-like tubes. Produced using an arc-discharge evaporation method similar to that used for fullerene synthesis, the needles grow at the negative end of the electrode used for the arc discharge. Electron microscopy reveals that each needle comprises coaxial tubes of graphitic sheets, ranging in number from 2 up to about 50. On each tube the carbon-atom hexagons are arranged in a helical fashion about the needle axis. The helical pitch varies from needle to needle and from tube to tube within a single needle. It appears that this helical structure may aid the growth process. The formation of these needles, ranging from a few to a few tens of nanometres in diameter, suggests that engineering of carbon structures should be possible on scales considerably greater than those relevant to the fullerenes. On 7 November 1991, Sumio Iijima announced in Nature the preparation of nanometre-size, needle-like tubes of carbon — now familiar as 'nanotubes'. Used in microelectronic circuitry and microscopy, and as a tool to test quantum mechanics and model biological systems, nanotubes seem to have unlimited potential.

Helical microtubules of graphitic carbon

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

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

This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

/pdf/the-electronic-properties-of-graphene-2siyzsnf5w.pdf

The electronic properties of graphene

The Hall effect and magnetoresistance were measured for stage-1 and -2 potassium-hydrogen-graphite ternary intercalation compounds (KH-GIC's) in the temperature range 1.4--250 K, in order to investigate their electronic structure and transport properties. The presence of two kinds of carriers was found: majority carriers in the graphitic ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ bands with electron character and minority hole carriers in the free-electron-like hydrogen 1s band. The hole carriers in the H 1s band are associated with the incomplete charge transfer to the hydrogen species. The Hall coefficient ${\mathit{R}}_{\mathit{H}}$ and conductivity tensor ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{y}}$ component exhibit large temperature dependences, which are considered to be due to the different in-plane scattering mechanisms for the two kinds of carriers. The hole carriers were found to have high mobilities, comparable to the mobilities of the graphitic \ensuremath{\pi} electrons. The scattering mechanism for the ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ bands can be explained in terms of an acoustic-phonon scattering process with small effective masses and a large deformation potential. On the other hand, that for the H 1s band is dominated by an acoustic-phonon scattering process, with a small deformation potential in the ionic ${\mathrm{K}}^{+}$${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ intercalate layers below 80 K, in addition to a low-energy optical-phonon scattering, which is operative mainly at higher temperatures.

https://pure.royalholloway.ac.uk/portal/services/downloadRegister/4720323/PhysRevB.46.16106.pdf

Hall effect in potassium-hydrogen-graphite intercalation compounds and their conduction mechanism.

In previous studies it was found that when highly oriented pyrolytic graphite (HOPG) is implanted at room temperature, the damage caused by the implantation could be completely annealed by heating the sample to temperatures higher than ∼ 2500°C. However at these high temperatures, the implanted species was found to diffuse out of the sample, as evidenced by the disappearance of the impurity peak in the Rutherford backscattering (RBS) spectrum. If, on the other hand, the HOPG crystal was held at a high temperature (≥ 600°C) during the implantation, partial annealing could be observed. The present work further shows that it is possible to anneal the radiation damage and simultaneously to retain the implants in the graphite lattice by means of high temperature implantation (T i ≥ 450°C) followed by annealing at 2300°C.

High Temperature Implantation in Graphite

Antidot arrays were formed in thin films of bismuth by the e-beam evaporation of the metal on the porous surface of porous anodic alumina templates. The magnetoresistance of the antidot array films was measured and compared to that of films deposited on glass slides. A significant difference in magnetoresistance behavior was observed, and this difference was attributed to the enhancement of the two dimensional weak antilocalization effect in the antidot arrays. Scattering rates were obtained by fitting the experimental results to the theoretical expression. The results indicate that the antidot morphology enhances the elastic scattering rate over the inelastic scattering rate.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400099565

Anomalous Magnetoresistance Behavior of Bismuth Antidot Arrays

Electronic structure of ion-implanted graphite

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-008749.pdf

Mildred S. Dresselhaus

Papers

Hall effect in potassium-hydrogen-graphite intercalation compounds and their conduction mechanism.

High Temperature Implantation in Graphite

Anomalous Magnetoresistance Behavior of Bismuth Antidot Arrays

Electronic structure of ion-implanted graphite

Vertical Graphene-base transistor on GaN substrate