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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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.

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The electronic properties of graphene

Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

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Two-dimensional gas of massless Dirac fermions in graphene

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Electrically switchable anisotropic polariton propagation in a ferroelectric van der Waals semiconductor

There has been enormous progress in the synthesis of large area graphene layers, with much of the focus in the use of a catalytic reaction on a metal surface during Chemical Vapor Deposition (CVD) [1-3] After the graphene is grown on a metal, it must be transferred to a dielectric substrate for its use in transport characterization and in devices This exfoliation process inevitably induces degradation and contamination of the graphene layers It would be desirable to be able to grow graphene layers directly on an insulating substrate allowing for high quality, transfer-free graphene devices We explore a molecular beam epitaxy (MBE) approach to this challenge that could lead, in the future, to further benefits such as the capability to fabricate doped graphene, multilayer heterostructures and high carrier mobility layers We present here initial results on the fabrication of ultrathin graphitic layers on several dielectric substrates using a carbon by a molecular beam deposition MBD technique [4] The samples have been characterized ex situ by: Raman spectroscopy, micro Raman spectroscopy, near-edge x-ray absorption fine structure (NEXAFS), AFM and STM These results have been obtained on three different dielectric substrates: hexagonal-BN micro flakes (h-BN), SiO2 and Mica The experimental growth set up (Figure 1) has been developed for this purpose that employs a UHV chamber with a carbon cell (figure 1, f) that can deposit sub-monolayer controlled graded amounts of carbon on a heated sample holder (s) The set-up allows in situ post growth high temperature annealing in a furnace as schematically shown in Figure 1 The micro-Raman spectra (shown in Figure 2) reveal the Raman features D and G that are characteristic of graphitic material On h-BN (red) an additional sharp and strong resonance is observed at ~1370 cm -1 that is from the underlying h-BN substrate The spectrum taken on SiO2 (black) shows also some structure around ~2700 cm -1 , which in graphene would be associated with a second-order Raman band Finally, a Mica substrate presents a similar spectrum (blue) Although these Raman features are far away from ideal graphene, they show that it is possible to fabricate graphitic materials directly on dielectric NEXAFS measurements confirm the predominant sp 2 bond that confirms the graphitic character of the grown carbon layers The NEXAFS analysis of a layer of carbon MBE-grown on Mica (figure 3) shows the following graphitic characteristics: an intense C=C * resonance at 285 eV (missing for sp 3 like diamond), a C=C * resonance at ~292 eV, and a strong polarization dependence of * and * resonances characteristic of an ordered 2-D bonding environment Finally a fine structure in the * region (photon energy > 290 eV) indicates long-range periodicity in the electronic structure This work is supported by ONR (N000140610138 and Graphene Muri), NSF (CHE-0117752 and CHE-0641523), NYSTAR, CSIC-PIF (200950I154), Spanish CAM (Q&C Light (S2009ESP-1503), Numancia 2 (S2009/ENE-1477)) and Spanish MICINN (NANINPHO-QD, TEC2008-06756-C03-01)

http://absimage.aps.org/image/MAR11/MWS_MAR11-2010-006881.pdf

Graphitic carbon molecular beam epitaxy on dielectric substrates

We have developed a device fabrication process to pattern graphene into nanostructures of arbitrary shape and control their electronic properties using local electrostatic gates. Electronic transport measurements have been used to characterize locally gated bipolar graphene $p$-$n$-$p$ junctions. We observe a series of fractional quantum Hall conductance plateaus at high magnetic fields as the local charge density is varied in the $p$ and $n$ regions. These fractional plateaus, originating from chiral edge states equilibration at the $p$-$n$ interfaces, exhibit sensitivity to inter-edge backscattering which is found to be strong for some of the plateuas and much weaker for other plateaus. We use this effect to explore the role of backscattering and estimate disorder strength in our graphene devices.

Local Gate Control of Electronic Transport in Graphene Nanostructures

Scanning tunneling microscopy (STM) is a powerful tool for nanoscale research since it can both create and probe the properties of nanostructures. We have used STM to create T-phase TaSe2 nanocrystals embedded in H-phase TaSe2 through a tip-induced solid-solid phase transition at liquid He temperature. Atomic-resolution images have been used to develop a structural model to understand this solid-solid phase transformation. Furthermore, STM studies of the charge density wave (CDW) state in the T-TaSe2 nanocrystals have been used to address CDW physics in finite dimensions.

Creation of Nanocrystals Via a Tip-Induced Solid-Solid Transformation

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Philip Kim

Papers

Electrically switchable anisotropic polariton propagation in a ferroelectric van der Waals semiconductor

Graphitic carbon molecular beam epitaxy on dielectric substrates

Local Gate Control of Electronic Transport in Graphene Nanostructures

Creation of Nanocrystals Via a Tip-Induced Solid-Solid Transformation

Quantum Hall drag of exciton condensation in bilayer graphene double layer