In the last 30 days

• Open/close Viscoelastic Acoustic Response of Layered Polymer Films at Fluid-Solid Interfaces: Continuum Mechanics Approach

  M V Voinova et al 1999 Phys. Scr. 59 391 Tag this article

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  We have derived the general solution of a wave equation describing the dynamics of two-layer viscoelastic polymer materials of arbitrary thickness deposited on solid (quartz) surfaces in a fluid environment. Within the Voight model of viscoelastic element, we calculate the acoustic response of the system to an applied shear stress, i.e. we find the shift of the quartz generator resonance frequency and of the dissipation factor, and show that it strongly depends on the viscous loading of the adsorbed layers and on the shear storage and loss moduli of the overlayers. These results can readily be applied to quartz crystal acoustical measurements of the viscoelasticity of polymers which conserve their shape under the shear deformations and do not flow, and layered structures such as protein films adsorbed from solution onto the surface of self-assembled monolayers.

• Open/close Towards industrial applications of graphene electrodes

  Sukang Bae et al 2012 Phys. Scr. 2012 014024 Tag this article

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  Since the first isolation of graphene in 2004 by mechanical exfoliation from graphite, many people have tried to synthesize large-scale graphene using various chemical methods. In particular, there has been a great number of advances in the synthesis of graphene using chemical vapor deposition (CVD) on metal substrates such as Ni and Cu. Recently, a method to synthesize ultra-large-scale (~30 inch) graphene films using roll-to-roll transfer and chemical doping processes was developed that shows excellent electrical and physical properties suitable for practical applications on a large scale. Considering the outstanding scalability/processibility of roll-to-roll and CVD methods as well as the extraordinary flexibility/conductivity of graphene films, we expect that transparent graphene electrodes can replace indium tin oxide in the near future.

• Open/close Fifty years in studying carbon-based materials

  Mildred S Dresselhaus 2012 Phys. Scr. 2012 014002 Tag this article

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  A review is presented based on our 50 year involvement in studying carbon materials physics and carbon-based nanostructures. The review topics include an early history of studies of graphene and graphite, graphite intercalation compounds, forerunners of nano-carbons, fullerenes, carbon nanotubes and, finally, graphene and graphene nanoribbons.

• Open/close Two-dimensional crystals-based heterostructures: materials with tailored properties

  K S Novoselov and A H Castro Neto 2012 Phys. Scr. 2012 014006 Tag this article

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  Graphene is just one example of a large class of two-dimensional crystals. These crystals can either be extracted from layered three-dimensional materials or grown artificially by several different methods. Furthermore, they present physical properties that are unique because of the low dimensionality and their special crystal structure. They have potential for semiconducting behavior, magnetism, superconductivity, and even more complex many-body phenomena. Two-dimensional crystals can also be assembled in three-dimensional heterostructures that do not exist in nature and have tailored properties, opening an entirely new chapter in condensed matter research.

• Open/close Graphene prehistory

  A K Geim 2012 Phys. Scr. 2012 014003 Tag this article

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  After the 2010 Nobel Prize recognized the research breakthrough reported by our group in a 2004 paper, I feel that, as my contribution to the proceedings of the Nobel symposium held earlier in 2010, it is both appropriate and important to review pre-2004 scientific literature and acknowledge early ideas. With the benefit of hindsight, I also try to analyze why our first graphene paper has attracted so much interest.

• Open/close Graphene for future electronics

  Pirjo Pasanen et al 2012 Phys. Scr. 2012 014025 Tag this article

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  We discuss some aspects of how graphene could be used in mainstream electronic devices. The main focus is on signal processing applications in high-volume, industrially manufactured battery-powered devices, e.g. mobile phones and laptop computers, but we will also discuss applicability to other components like interconnects, wireless communication antennae and camera sensors, as well as novel types of signal processing devices, based on the unique physical properties of graphene.

• Open/close Role of edges in the electronic and magnetic structures of nanographene

  Toshiaki Enoki 2012 Phys. Scr. 2012 014008 Tag this article

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  In graphene edges or nanographene, the presence of edges strongly affects the electronic structure depending on their edge shape (zigzag and armchair edges) as observed with the electron wave interference and the creation of non-bonding π-electron state (edge state). We investigate the edge-inherent electronic features and the magnetic properties of edge-sate spins in nanographene/graphene edges. Graphene nanostructures are fabricated by heat-induced conversion/fabrication of nanodiamond particles/graphite step edges; single-layer nanographene islands (mean size 10 nm) and armchair-edged nanographene ribbons (width 8 nm). Scanning tunneling microscopy (STM)/scanning tunneling spectroscopy observations demonstrate that edge states are created in zigzag edges in spite of the absence of such states in armchair edges. In addition, zigzag edges tend to be short and defective, whereas armchair edges are long and continuous in general. These findings suggest that a zigzag edge has lower aromatic stability than an armchair edge, consistent with Clar's aromatic sextet rule. The manner in which electron wave scattering takes place is different between zigzag and armchair edges. In the vicinity of an armchair edge, a honeycomb superlattice is observed in STM images together with a fine structure of threefold symmetry, in spite of the superlattice at a zigzag edge. The honeycomb lattice is a consequence of the intervalley K–K' transition that accompanies the electron wave interference taking place at the armchair edge. The Raman G-band is also affected by the interference, showing polarization angle dependence specifically at armchair edges. The magnetism of a three-dimensional disordered network of nanographene sheets is understood on the basis of the ferrimagnetic structure of the edge-state spins in individual constituent nanographene sheets. The strengthening of the inter-nanographene-sheet magnetic interaction brings about a spin glass state.

• Open/close Emergent electromagnetism in solids

  Naoto Nagaosa and Yoshinori Tokura 2012 Phys. Scr. 2012 014020 Tag this article

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  The electromagnetic field (EMF) is the most fundamental field in condensed-matter physics. Interaction between electrons, electron–ion interaction and ion–ion interaction are all of electromagnetic origin, while the other three fundamental forces, i.e. the gravitational force and weak and strong interactions, are irrelevant in the energy/length scales of condensed-matter physics. Also the physical properties of condensed matter, such as transport, optical, magnetic and dielectric properties, are almost described as their electromagnetic responses. In addition to this EMF, it often happens that the gauge fields appear as the emergent phenomenon in the low-energy sector due to the projection of the electronic wavefunctions onto the curved manifold of the Hilbert sub-space. These emergent EMFs play important roles in many places in condensed-matter physics including the quantum Hall effect, strongly correlated electrons and also in non-interacting electron systems. In this paper, we describe the fundamental idea behind it and some of its applications studied recently.

• Open/close Molecular interactions on epitaxial graphene

  Andrew T S Wee and Wei Chen 2012 Phys. Scr. 2012 014007 Tag this article

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  This paper reviews our recent work on molecular interactions on epitaxial graphene (EG) grown on 6H-SiC(0001). A major challenge in graphene-based devices is opening the energy band gap and doping. Molecular functionalization of graphene is one approach to modifying its electronic properties. Such surface transfer doping relies on charge separation at interfaces, and represents a valuable tool for the controlled and non-destructive doping of graphene, thereby facilitating the development of hybrid organic-graphene nanoelectronics. We have also demonstrated molecular self-assembly of bimolecular systems on EG and graphite.

• Open/close Synthesis and properties of ZnO nanorods as ethanol gas sensors

  K Mirabbaszadeh and M Mehrabian 2012 Phys. Scr. 85 035701 Tag this article

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  Uniform ZnO nanorods were synthesized via the sol–gel process under mild conditions in which different ZnO nanostructures have been prepared by changing the pH of growth solution. It was seen that the optimum nanorods were grown at pH 11.33. The prepared ZnO nanostructures and morphologies were characterized by x-ray diffraction and scanning electron microscopy measurements. The ZnO one-dimensional nanostructures were found to have a wurtzite hexagonal crystalline structure and grow along the [001] direction. The optimum nanorods were about 1 μm in length and less than 100 nm in diameter. The ZnO nanostructures have been tested for different concentrations and different operating temperatures for ethanol vapor in air and the surface resistance of the sensors has been evaluated as a function of different parameters. The gas sensor fabricated from ZnO nanorods grown in solution with a special pH exhibited good performance. The sensor response to 5000 ppm ethanol was up to about 2.5 at the operating temperature of 300 °C. The differences in gas-sensing performance between the sensors were analyzed based on the defects created in the nanorods during their fast growth. The correlations between material structures and the properties of the gas sensors are discussed.