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

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

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

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.

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Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene

Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.

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Graphene: Status and Prospects

Thin film Carbon Nanotube (CNT) networks are used as a conductive, transparent and flexible electrode for electrochemically depositing a conducting polymer on it, polypyrrole or polyaniline in the present work. We analyse the properties of the device as an electrochemical sensor, measuring his pH dependence by recording the open circuit potential in various buffer solutions, ranging from pH 1 to 13. The results show a good sensitivity, linearity and stability in both cases. In the case of CNT/polyaniline, it can be used simply as an optical sensor, as the colour of polyaniline changes with pH. The CNT/polypyrrole and CNT/polyaniline devices could have applications as solid state gas sensor or biosensor deposited on any shape of surface that can be transparent and flexible.

Transparent and flexible carbon nanotube/polypyrrole and carbon nanotube/polyaniline pH sensors

We present the first direct observation of molecular rectification as a consequence of asymmetric tunnelling process through molecular quantum wells. In addition, single-electron tunnelling effects were observed which might be attributed to the charging of single molecules or molecular stacks. As molecular systems we used LB-film-based heterostructures consisting of an octasubstituted metallophthalocyanine and a perylene-3,4,9,10-tetracarboxyldiimide derivative sandwiched between two gold electrodes. By using a special thermal evaporation technique to deposit the top gold electrode, we have overcome the problem of short circuits and were able to fabricate highly reproducible devices.

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Organic Quantum Wells: Molecular Rectification and Single-Electron Tunnelling

We prepared symmetric sandwich structures of the sequence gold/Langmuir–Blodgett film/gold by employing a novel evaporation technique. As molecular systems, we used an octasubstituted palladiumphthalocyanine and a perylene‐3,4,9,10‐tetracarboxyldiimide derivative. Electronic transport measurements show a tunneling characteristic which arises from a direct tunneling process through molecular states. The current/voltage curves are symmetric for positive and negative bias proving the identical electronic behavior of the two organic/inorganic interfaces at the top and bottom electrode.

Microstructured gold/langmuir-blodgett film/gold tunneling junctions

The pressure dependence of the high-energy Raman modes in single- and multi-walled carbon nanotubes was measured in the range 0–10 GPa. We found the pressure coefficient to be linear in both materials but 25% smaller in MWNT. Given that the curvature effects on vibrational properties of the rolled-up graphene sheets are small, we can explain this difference simply with elasticity theory.

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S. Roth

Papers

Transparent and flexible carbon nanotube/polypyrrole and carbon nanotube/polyaniline pH sensors

Organic Quantum Wells: Molecular Rectification and Single-Electron Tunnelling

Microstructured gold/langmuir-blodgett film/gold tunneling junctions

Raman spectroscopy on single- and multi-walled nanotubes under high pressure

Chromatography of carbon nanotubes