Tunable synthesis of metal-graphene complex nanostructures and their catalytic ability for solvent-free cyclohexene oxidation in air

A one-step method was developed for the controllable construction of metal-graphene core-shell structures, hollow graphene nanospheres, and a high density of metal nanoparticles supported on graphene. The metal-graphene core-shell nanostructures as nanocatalysts show excellent catalytic ability for the selective oxidation of cyclohexene.     

Magnetic response of conductance peak structure in junction-confined graphene nanoribbons

We have numerically investigated the magnetic response of the conductance peak structures in the transport gap of graphene nanoribbons. It is shown that the magnetic field induces a number of new conductance peaks within the transport gap of graphene nanoribbons confined by structural junctions. In addition, the magnetic field causes a shift of the conductance peak position and broadening of the peak width. This behaviour is due to the disappearance of zero conductance dips at the junction as a result of breaking time-reversal symmetry. Such behaviour is, however, not observed in the electronic transport of graphene nanoribbons confined by potential barriers, i.e. p-n-junctions. Thus, the magnetic response of conductance peaks may be used to distinguish the origin of the conductance peak structure within the transport gap observed in the experiments.     

Analytical study of electronic quantum transport in carbon-based nanomaterials

We introduce a new method based on the tight-binding model and mode space (MS) renormalization approach to the study of quantum transport properties of carbon-based nanomaterials (CBNs) such as carbon nanotubes (CNTs), graphene nanoribbons (GNRs), superlattice structures and conducting polymers. The calculations are based on the Green's function method, in which the electrical conductance, density of states (DOS) and localization length of the systems are calculated, analytically. Our model and simple formulas are useful to study the impact of slice-like defects, to distinguish different regimes and reduce the computation time. The efficiency of our method in reducing the CPU time is tested in electrical conductance, where the computation time is reduced by up to a factor of 40 depending on the parameters of the problem. We demonstrate the power of this approach by studying the electronic transport in partially unzipped carbon nanotubes (UCNTs).     

Transport in suspended monolayer and bilayer graphene under strain: A new platform for material studies

We develop two types of graphene devices based on nanoelectromechanical systems (NEMS), that allows transport measurement in the presence of in situ strain modulation. Different mobility and conductance responses to strain were observed for single layer and bilayer samples. These types of devices can be extended to other 2D membranes such as MoS₂, providing transport, optical or other measurements with in situ strain.     

Conductance of Graphene Nanoribbon Junctions and the Tight Binding Model

Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Green's function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations.     

Edge effect on electronic transport properties of graphene nanoribbons and presence of perfectly conducting channel

Numerical calculations have been performed to elucidate unconventional electronic transport properties in disordered nanographene ribbons with zigzag edges (zigzag ribbons). The energy band structure of zigzag ribbons has two valleys that are well separated in momentum space, related to the two Dirac points of the graphene spectrum. The partial flat bands due to edge states make the imbalance between left- and right-going modes in each valley, i.e. appearance of a single chiral mode. This feature gives rise to a perfectly conducting channel in the disordered system, i.e. the average of conductance 〈g〉 converges exponentially to 1 conductance quantum per spin with increasing system length, provided impurity scattering does not connect the two valleys, as is the case for long-range impurity potentials. Ribbons with short-range impurity potentials, however, through inter-valley scattering, display ordinary localization behavior. Symmetry considerations lead to the classification of disordered zigzag ribbons into the unitary class for long-range impurities, and the orthogonal class for short-range impurities. The electronic states of graphene nanoribbons with general edge structures are also discussed, and it is demonstrated that chiral channels due to the edge states are realized even in more general edge structures except for armchair edges.     

Electromechanical properties of armchair graphene nanoribbons under local torsion

While graphene nanoribbons are prone to twist intrinsically, the effect of local twist on the electromechanical properties remains unexplored. By using the density functional theory in combination with the nonequilibrium Green’s function method, we investigate the responses of structural evolution and electrical transport of armchair graphene nanoribbons to local torsion. We show that local twist can alter their transport properties significantly. The current at a given bias can switch on/off or change many times with twist angle, which is related with twist-induced changes in electronic structures of graphene nanoribbons. Our results can provide a valuable guideline for design and implementation of graphene nanoribbons in nanoelectromechanical systems and devices.     

Heat conduction across metal and nonmetal interface containing imbedded graphene layers

Thermal conductance at the interface between metal and non-metal materials in the presence or absence of an inserted graphene layer is measured using a time domain transient thermoreflectance technique. The insertion of a single layer graphene between thermal evaporation Al film and Si substrate enhances the interfacial thermal conductance, because the graphene works as a mask to prevent the metal atoms diffusing into the substrate and causes the reduction of the intermixing layer thickness. Conversely, for the Al/Si interface with the Al film prepared by magnetron sputtering, the insertion of a single layer graphene increases the number of interface and leads to the decrease of the interfacial thermal conductance.     

Duality of the interfacial thermal conductance in graphene-based nanocomposites

The thermal conductance of graphene–matrix interfaces plays a key role in controlling the thermal properties of graphene-based nanocomposites. Using atomistic simulations, we found that the interfacial thermal conductance depends strongly on the mode of heat transfer at graphene–matrix interfaces: if heat enters graphene from one side of its basal plane and immediately leaves it through the other side, the corresponding interfacial thermal conductance, G_across, is large; if heat enters graphene from both sides of its basal plane and leaves it at a position far away on its basal plane, the corresponding interfacial thermal conductance, G_non-across, is small. For a single-layer graphene immersed in liquid octane, G_across is ∼150 MW/m²K while G_non-across is ∼5 MW/m²K. G_across decreases with increasing multi-layer graphene thickness (i.e., number of layers in graphene) and approaches an asymptotic value of 100 MW/m²K for 7-layer graphenes. G_non-across increases only marginally as the graphene sheet thickness increases. Such a duality of the interface thermal conductance for different probing methods and its dependence on graphene sheet thickness can be traced ultimately to the unique physical and chemical structure of graphene materials. The ramifications of these results in areas such as the optimal design of graphene-based thermal nanocomposites are discussed.     

Electrostatic transparency of graphene oxide sheets

The interaction of graphene oxide of varying reduction degrees with dielectric and metallic surfaces is probed in this study, in order to assess the influence that the supporting substrate has on the electronic properties of as-produced graphene oxide and its reduced form. Lateral inhomogeneities in the distribution of substrate trapped charged impurities are found to affect the electronic properties of reduced graphene oxide, giving rise to significant in-plane variations of the local electrostatic potential on reduced one-layer sheets supported on dielectric substrates. On the contrary, no such surface potential fluctuations are identified on as-produced graphene oxide sheets, or on graphene oxide layers deposited on a metallic substrate. Thicker, two-layer reduced graphene oxide sheets show effective screening of the electrostatic effects caused by charge impurities trapped in the substrate. The current study provides a useful account of the limitations that device performance could face when attempting to tune the electronic structure of graphene oxide via functionalization, highlighting the role of substrate-related disorder affecting the behaviour of nanodevices. The role of the substrate is particularly important for applications where electronic properties of graphene oxide are especially targeted, such as transparent conducting films, sensors and electrochemical devices.     

One-dimensional extended lines of divacancy defects in graphene

Since the outstanding transport properties of graphene originate from its specific structure, modification at the atomic level of the graphene lattice is needed in order to change its electronic properties. Thus, topological defects play an important role in graphene and related structures. In this work, one-dimensional (1D) arrangement of topological defects in graphene are investigated within a density functional theory framework. These 1D extended lines of pentagons, heptagons and octagons are found to arise either from the reconstruction of divacancies, or from the epitaxial growth of graphene. The energetic stability and the electronic structure of different ideal extended lines of defects are calculated using a first-principles approach. Ab initio scanning tunneling microscopy (STM) images are predicted and compared to recent experiments on epitaxial graphene. Finally, local density of states and quantum transport calculations reveal that these extended lines of defects behave as quasi-1D metallic wires, suggesting their possible role as reactive tracks to anchor molecules or atoms for chemical or sensing applications.     

Electronic states of disordered grain boundaries in graphene prepared by chemical vapor deposition

Perturbations of the two dimensional carbon lattice of graphene, such as grain boundaries, have significant influence on the charge transport and mechanical properties of this material. Scanning tunneling microscopy measurements presented here show that localized states near the Dirac point dominate the local density of states of grain boundaries in graphene grown by chemical vapor deposition. Such low energy states are not reproduced by theoretical models which treat the grain boundaries as periodic dislocation-cores composed of pentagonal–heptagonal carbon rings. Using ab initio calculations, we have extended this model to include disorder, by introducing vacancies into a grain boundary consisting of periodic dislocation-cores. Within the framework of this model we were able to reproduce the measured density of states features. We present evidence that grain boundaries in graphene grown on copper incorporate a significant amount of disorder in the form of two-coordinated carbon atoms.     

Electromechanical switching in graphene nanoribbons

We investigate the effect of twisting on the electronic, magnetic and transport properties of zigzag graphene nanoribbon (ZGNR) using density functional theory (DFT) calculations. We compare electronic and magnetic properties of ZGNR in both planar and 180°-twisted geometries. Furthermore, combining DFT with the nonequilibrium Green’s function method (NEGF), we examine the quantum conductance of twisted ZGNR in its antiferromagnetic and ferromagnetic states. Consequently, the structure of local magnetic moments in the region between electrodes of opposite magnetization behaves as a Bloch/Neel domain wall. Our calculations show that ZGNR in its ground state (antiferromagnetic) is insensitive to twisting, there is no band gap change, and the conductance of the twisted ZGNR is almost unchanged as well. We demonstrate that the electromechanical switching can be realized by twisting a ferromagnetic ZGNR, which is an ideal spin valve in case of oppositely polarized leads (after twisting).     

Chemical modification of graphene characterized by Raman and transport experiments

A chemical approach to modify the electronic transport of graphene is investigated by detailed transport and Raman spectroscopy measurements on Hall bar shaped samples. The functionalization of graphene with nitrobenzene diazonium ions results in a strong p-doping of the graphene samples and only slightly lower mobilities. Comparing Raman and transport data taken after each functionalization step allowed the conclusion that two preferential reactions take place on the graphene surface. In the beginning a few nitrobenzene molecules are directly attached to the graphene atoms creating defects. Afterwards these act as seeds for a polymer like growth not directly connected to the graphene atoms. The effects of solvents were excluded by thorough control measurements.     

石墨烯复合浆料应用于ABS塑料电镀前表面处理

采用石墨烯等碳纳米材料与溶剂及多种助剂混合研磨,制备了稳定的石墨烯复合导电浆料.将导电浆料喷涂于丙烯腈-丁二烯-苯乙烯共聚物(ABS)表面获得ABS/石墨烯材料,赋予ABS塑料优良的导电性能,继而进行电镀处理.为了提高石墨烯涂层与ABS塑料表面的结合力,对ABS塑料进行了不同的表面处理,包括磨砂、有机溶剂微腐蚀和化学粗...     

Band structure and transport properties of carbon nanotubes using a local pseudopotential and a transfer-matrix technique

In order to address the band-structure and transport properties of carbon nanotubes, we build a local pseudopotential from the requirement that results relevant to the π-bands of simple hexagonal graphite and isolated graphene sheets are reproduced. We then apply a transfer-matrix technique to compute the band structure and conductance of the (10,0), (5,5), (10,10), (15,15) and (10,10)@(15,15) carbon nanotubes. We also investigate how the conductance of a broken (10,10) nanotube is affected by a (15,15) tube placed around the gap. Our results show how fast band-structure and stationary-wave effects appear in finite-size nanotubes. They provide a complementary insight on the effects of the tubes' curvature and the transferability of parameters from graphite to carbon nanotubes.     

Redox-switchable devices based on functionalized graphene nanoribbons

The possibility of tuning the electronic properties of graphene by tailoring the morphology at the nanoscale or by chemical functionalization opens interesting perspectives towards the realization of devices for nanoelectronics. Indeed, the integration of the intrinsic high carrier mobilities of graphene with functionalities that are able to react to external stimuli allows in principle the realization of highly efficient nanostructured switches. In this paper, we report a novel approach to the design of reversible switches based on functionalized graphene nanoribbons, operating upon application of an external redox potential, which exhibit unprecedented ON/OFF ratios. The properties of the proposed systems are investigated by electronic structure and transport calculations based on density functional theory and rationalized in terms of valence-bond theory and Clar's sextet theory.     

二氧化钛/氧化石墨烯复合光催化剂的合成

采用水热法,以钛酸四正丁酯及氧化石墨烯（GO）为原料,在水性体系中合成了一系列具有不同GO质量分数的TiO2/GO复合光催化剂。FE-SEM分析结果表明,分散的钛酸四正丁酯以多分子层的形式吸附到氧化石墨烯的表面,最后在水热过程中转化为锐钛型TiO2粒子。当氧化石墨烯的质量分数低于3%时,产物中含有纯TiO2微球及TiO2/GO复合物;当氧化石墨烯质量分数大于5%时,产物为单纯的TiO2/GO复合物。电化学性能测试结果表明,GO复合后,TiO2电极中载流子的传输效率提高。氧化石墨烯复合量为10%时,复合光催化剂显示了对亚甲基蓝最佳的光催化活性。当复合氧化石墨烯转化为石墨烯后,其光催化活性可得到进一步大幅度的提高。     

The ultimate diamond slab: GraphAne versus graphEne

In this article, we present a comprehensive characterization of three carbon nanomaterials of technological interest: graphene, graphane, and fluorinated graphene. By means of first principles and tight-binding calculations in combination with analytical methods, we carried out detailed comparative studies of their structural, mechanical, thermal, and electronic properties. The calculated elastic properties of these materials confirm their high mechanical stability and stiffness, which in association with their low dimensionality, translates into a large ballistic thermal conductance. Furthermore, we show that while graphene is a zero gap semi-metal, graphane and fluorinated graphene are wide gap semiconductors. Finally, we discuss designed interfaces between these systems, and show that their physical properties have potential applications in nanoelectronic devices.     

Graphene oxide as dyestuffs for the creation of electrically conductive fabrics

Graphene oxide (GO) was immobilized on the surfaces of acrylic yarns through a conventional dyeing approach. The GO dyed yarns and/or the fabric were immersed in an aqueous sodium hydrosulfite solution at around 363 K for 30 min, which converted the GO into graphene. The graphene created a graphitic-coloured and electrically conductive thin layer over each yarn in the fabric. Data on the electrical conductance of the yarns versus temperature (30-300 K) fit well with the so-called fluctuation-induced tunneling model, which suggests that the graphene layer belongs to a continuously interconnected network. Values of the electrical resistivity ranged from 10² to 10¹⁰ Ohm/cm, as verified by the content of graphene in the conductive layer.