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

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

We present the fabrication of a high optical quality single-walled carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite film. The composites demonstrate strong saturable absorption at ∼1.5 μm, the spectral range for optical communications. By measuring the nonlinear transmission of a sub-picosecond pump pulse through the film, we were able to deduce a saturation fluence of ∼13.9 μJ/cm2 and a modulation depth ∼16.9% (in absorption) at a high pulse fluence ∼200 μJ/cm2. Transient saturable absorption is investigated by measuring the transmitted autocorrelation traces at various incident power levels. Observed side-peak suppression indicates a fast recovery time on the scale of ∼1 ps for our saturable absorber devices. Furthermore, we use these SWNT-PVA composite saturable absorbers as mode-lockers in an Er3+ fiber ring laser and achieve ∼560 fs pulse generation with good jitter performance and long term stability. The laser performance is also associated with the parameters of our SWNT based saturable absorber.

Fabrication, characterization and mode locking application of single-walled carbon nanotube/polymer composite saturable absorbers

Laser scribing has been proposed as a fast and easy tool to reduce graphene oxide (GO) for a wide range of applications. Here, we investigate laser reduction of GO under a range of processing and material parameters, such as laser scan speed, number of laser passes, and material coverage. We use Raman spectroscopy for the characterization of the obtained materials. We demonstrate that laser scan speed is the most influential parameter, as a slower scan speed yields poor GO reduction. The number of laser passes is influential where the material coverage is higher, producing a significant improvement of GO reduction on a second pass. Material coverage is the least influential parameter, as it affects GO reduction only under restricted conditions.

https://www.mdpi.com/2311-5629/7/2/48/pdf

Raman Spectroscopy Investigation of Graphene Oxide Reduction by Laser Scribing

A droplet evaporation/stamping method was employed to fabricate closely packed arrays of Au nanorods aligned parallel or perpendicular to a support. The potential as SERS substrates was investigated using model molecule 4-aminobenzenethiol (4-ABT), for which enhanced signals where obtained compared to the signals of the bulk molecule. Enhancement factors of the order of 104 and 105 were calculated for parallel and perpendicular arrays, respectively. Quantitative Raman detection of 4-ABT was obtained with detection limits in the nM concentration range. Fabricated arrays displayed good stability and uniformity, showing their potential as sensing platforms for plasmon-induced optical molecular detection.

Surface-Enhanced Raman Scattering of 4-Aminobenzenethiol on Au Nanorod Ordered Arrays

The growth of multiwalled carbon nanotubes and carbon nanofibers by catalytic chemical vapor deposition at lower temperatures is found to be aided by a separate catalyst pretreatment step in which the catalyst thin film is restructured into a series of nanoparticles with a more active surface. The restructuring is particularly effective when carried out by an ammonia plasma. The nature of the restructuring is studied by atomic force microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and Raman. We find that as the growth temperature decreases, there is a limiting maximum catalyst thickness, which gives any nanotube growth. Plasmas are found to restructure the catalyst by a combination of physical etching and chemical modification. Large plasma powers can lead to complete etching of thin catalyst films, and hence loss of activity. Ni is found to be the better catalyst at low temperatures because it easily reduced from any oxide form to the catalytically active metallic state. On the other hand, Fe gives the largest nanotube length and density yield at moderate temperatures because it is less easy to reduce at low temperatures and it is more easily poisoned at high temperatures.

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Plasma restructuring of catalysts for chemical vapor deposition of carbon nanotubes

We present a technique for hysteresis suppression in single-wall nanotube field effect transistors (SWNT-FETs) using chemical functionalization. We selectively modify the electrode surfaces and the device channel area with self-assembled monolayers (SAMs) of octanethiol and aminopropyltriethoxysilane (APTES), respectively. These can efficiently prevent surface adsorption of water molecules. We show that hysteresis is suppressed, with a 15 times decrease in hysteresis gap compared to the conventional SWNT-FETs on bare SiO 2 /Si.

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Vittorio Scardaci

Papers

Fabrication, characterization and mode locking application of single-walled carbon nanotube/polymer composite saturable absorbers

Raman Spectroscopy Investigation of Graphene Oxide Reduction by Laser Scribing

Surface-Enhanced Raman Scattering of 4-Aminobenzenethiol on Au Nanorod Ordered Arrays

Plasma restructuring of catalysts for chemical vapor deposition of carbon nanotubes

Hysteresis suppression in self-assembled single-wall nanotube field effect transistors