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Two-dimensional networks made of metal nanowires are excellent paradigms for the experimental observation of electrical percolation caused by continuous jackstraw-like physical pathways. Such systems became very interesting as alternative material in transparent electrodes, which are fundamental components in display devices. This work presents the experimental characterization of low-haze and ultra-transparent electrodes based on silver nanowires. The films are created by dip-coating, a feasible and scalable liquid film coating technique. We have found dominant alignment of the silver nanowires in withdrawal direction. The impact of this structural anisotropy on electrical anisotropy becomes more pronounced for low area coverage. The rod alignment does not influence the technical usability of the films as significant electrical anisotropy occurs only at optical transmission higher than 99 %. For films with lower transmission, electrical anisotropy becomes negligible. In addition to the experimental work, we have carried out computational studies in order to explain our findings further and compare them to our experiments and previous literature. This paper presents the first experimental observation of electrical anisotropy in two-dimensional silver nanowire networks close at the percolation threshold.

In this work, graphene field effect transistors (FETs) were fabricated on a trench structure made by carbonized poly(methylmethacrylate) to modify the graphene surface. The trench-structured devices showed different characteristics depending on the channel orientation and the pitch size of the trenches as well as channel area in the FETs. Periodic corrugations and barriers of suspended graphene on the trench structure were measured by atomic force microscopy and electrostatic force microscopy. Regular barriers of 160 mV were observed for the trench structure with graphene. To confirm the transfer mechanism in the FETs depending on the channel orientation, the ratio of experimental mobility (3.6-3.74) was extracted from the current-voltage characteristics using equivalent circuit simulation. It is shown that the number of barriers increases as the pitch size decreases because the number of corrugations increases from different trench pitches. The noise for the 140 nm pitch trench is 1 order of magnitude higher than that for the 200 nm pitch trench.

The fabrication and characterization of highly flexible textiles are reported. These textiles can harvest thermal energy from temperature gradients in the desirable through-thickness direction. The tiger yarns containing n- and p-type segments are woven to provide textiles containing n-p junctions. A high power output of up to 8.6 W m(-2) is obtained for a temperature difference of 200 °C., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Synchrotron radiation circular dichroism (SRCD) is a rapidly growing technique for structure analysis of proteins and other chiral biomaterials. UV-CD12 is a high-flux SRCD beamline installed at the ANKA synchrotron, to which it had been transferred after the closure of the SRS Daresbury. The beamline covers an extended vacuum-UV to near-UV spectral range and has been open for users since October 2011. The current end-station allows for temperature-controlled steady-state SRCD spectroscopy, including routine automated thermal scans of microlitre volumes of water-soluble proteins down to 170 nm. It offers an excellent signal-to-noise ratio over the whole accessible spectral range. The technique of oriented circular dichroism (OCD) was recently implemented for determining the membrane alignment of α-helical peptides and proteins in macroscopically oriented lipid bilayers as mimics of cellular membranes. It offers improved spectral quality <200 nm compared with an OCD setup adapted to a bench-top instrument, and accelerated data collection by a factor of ∼3. In addition, it permits investigations of low hydrated protein films down to 130 nm using a rotatable sample cell that avoids linear dichroism artifacts.

A periodically modulated graphene (PMG) generated by nanopatterned surfaces is reported to profoundly modify the intrinsic electronic properties of graphene. The temperature dependence of the sheet resistivity and gate response measurements clearly show a semiconductor-like behavior. Raman spectroscopy reveals significant shifts of the G and the 2D modes induced by the interaction with the underlying grid-like nanostructure. The influence of the periodic, alternating contact with the substrate surface was studied in terms of strain caused by bending of graphene and doping through chemical interactions with underlying substrate atoms. Electronic structure calculations performed on a model of PMG reveals that it is possible to tune a band gap within 0.14-0.19 eV by considering both the periodic mechanical bending and the surface coordination chemistry. Therefore, the PMG can be regarded as a further step toward band gap engineering of graphene devices.

We prepare thin single-walled carbon nanotube networks on a transparent and flexible substrate with different densities, using a very simple spray method. We measure the electric impedance at different frequencies Z(f) in the frequency range of 40 Hz to 20 GHz using two different methods: a two-probe method in the range up to 110 MHz and a coaxial (Corbino) method in the range of 10 MHz to 20 GHz. We measure the optical absorption and electrical conductivity in order to optimize the conditions for obtaining optimum performance films with both high electrical conductivity and transparency. We observe a square resistance of 1 to 8.5 kΩ for samples showing 65% to 85% optical transmittance, respectively. For some applications, we need flexibility and not transparency: for this purpose, we deposit a thick film of single-walled carbon nanotubes on a flexible silicone substrate by spray method from an aqueous suspension of carbon nanotubes in a surfactant (sodium dodecyl sulphate), thereby obtaining a flexible conducting electrode showing an electrical resistance as low as 200 Ω/sq. When stretching up to 10% and 20%, the electrical resistance increases slightly, recovering the initial value for small elongations up to 10%. We analyze the stretched and unstretched samples by Raman spectroscopy and observe that the breathing mode on the Raman spectra is highly sensitive to stretching. The high-energy Raman modes do not change, which indicates that no defects are introduced when stretching. Using this method, flexible conducting films that may be transparent are obtained just by employing a very simple spray method and can be deposited on any type or shape of surface.

We present an accurate measurement and a quantitative analysis of electron-beam-induced displacements of carbon atoms in single-layer graphene. We directly measure the atomic displacement ("knock-on") cross section by counting the lost atoms as a function of the electron-beam energy and applied dose. Further, we separate knock-on damage (originating from the collision of the beam electrons with the nucleus of the target atom) from other radiation damage mechanisms (e.g., ionization damage or chemical etching) by the comparison of ordinary (12C) and heavy (13C) graphene. Our analysis shows that a static lattice approximation is not sufficient to describe knock-on damage in this material, while a very good agreement between calculated and experimental cross sections is obtained if lattice vibrations are taken into account.

Thermoelectrics are materials capable of the solid-state conversion between thermal and electrical energy. Carbon nanotube/polymer composite thin films are known to exhibit thermoelectric effects, however, have a low figure of merit (ZT) of 0.02. In this work, we demonstrate individual composite films of multiwalled carbon nanotubes (MWNT)/polyvinylidene fluoride (PVDF) that are layered into multiple element modules that resemble a felt fabric. The thermoelectric voltage generated by these fabrics is the sum of contributions from each layer, resulting in increased power output. Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics., (© 2012 American Chemical Society)

The electronic charge density distribution or the electrostatic atomic potential of a solid or molecule contains information not only on the atomic structure, but also on the electronic properties, such as the nature of the chemical bonds or the degree of ionization of atoms. However, the redistribution of charge due to chemical bonding is small compared with the total charge density, and therefore difficult to measure. Here, we demonstrate an experimental analysis of charge redistribution due to chemical bonding by means of high-resolution transmission electron microscopy (HRTEM). We analyse charge transfer on the single-atom level for nitrogen-substitution point defects in graphene, and confirm the ionicity of single-layer hexagonal boron nitride. Our combination of HRTEM experiments and first-principles electronic structure calculations opens a new way to investigate electronic configurations of point defects, other non-periodic arrangements or nanoscale objects that cannot be studied by an electron or X-ray diffraction analysis.

A novel single electron pump based on individual molecules (a single wall carbon nanotube) is discussed in terms of the hybrid superconducting-normal conducting pumping principle. A concept demonstration device has been built based on a carbon nanotube contacted by Nb-Ti leads. Charge current quantization is achieved through rf modulation of the back gate voltage. The device is able to transfer a given number of electrons per pumping cycle. Single electron pumping is achieved for pumping frequencies up to 80 MHz.

This tutorial review discusses the contradictory material properties of electrical conductivity and optical transparency for the examples of graphene films and carbon nanotube networks. It is argued that for homogeneous films both properties are linked by basic laws of physics and that for perfect monoatomic layers conductivity and transparency can be calculated from the fine structure constant. To beat these limitations, inhomogeneous films are required, such as graphene with an array of holes or nanotube networks. An overview is given on literature values of transparency and conductivity, both for graphene films and for nanotube networks.

The improved field emission stability of thin multiwalled carbon nanotube (thin-MWCNT) emitters using a tip sonication process has been investigated. The thin-MWCNTs showed short lengths and many open tips after the tip sonication treatment. The field emission properties of the thin-MWCNT emitters were investigated. Field emission stability dramatically increased as the tip sonication time increased. In particular, field emission current at an acceleration condition was quite stable and showed no degradation for over 19 h after tip sonication treatment of 30 min. Tip sonication could effectively cut CNTs short and regulate the length of CNTs. Therefore, field emission stability was significantly improved during a long period of operation because many shortened thin-MWCNTs could participate in field emission after the treatment.

The twin arginine translocation (Tat) system can transport fully folded proteins, including their cofactors, across bacterial and thylakoid membranes. The Tat system of Bacillus subtilis that serves to export the phosphodiesterase (PhoD) consists of only two membrane proteins, TatA(d) and TatC(d). The larger component TatC(d) has a molecular weight of 28 kDa and several membrane-spanning segments. This protein has been expressed in Escherichia coli and purified in sufficient amounts for structure analysis by circular dichroism (CD) and NMR spectroscopy. TatC(d) was reconstituted in detergent micelles and in lipid bilayers for CD analysis in solution and in macroscopically oriented samples, to examine the stability of the protein. Suitable protocols and model membrane systems have been established, by which TatC(d) maintains the level of helicity close to theoretically predicted, and its transmembrane alignment could been verified.

We applied Raman spectroscopy to investigate the response to electrochemical doping of the second-order D* band in single-walled carbon nanotube (SWNT) bundles. Our study reveals a dramatic increase of the D* band sensitivity to doping upon moving the laser excitation to the red end of the visible spectrum and beyond. Using the double-resonance scattering model, we show that this phenomenon evidences a second Kohn anomaly in metallic SWNTs, located in the K-point-derived region of the Brillouin zone (BZ), which stems from the Kohn anomaly at the K-point of graphene. Our results will be compared to recent doping experiments on graphene with field-effect gating and can be used to investigate the wave-vector dependent electron-phonon coupling in the bulk of the BZ of metallic SWNTs.

We fabricated point emitters using a multiwalled carbon nanotube (MWCNT) yarn which was treated by ethylene glycol. The point emitter showed a very high emission current of 3.01 mA (current density of 1.1 x 10(8) A cm(-2)) and good emission stability of over 20 h. We attributed the excellent field emission properties to a large field enhancement factor caused by the large aspect ratio of the sharp tip of the point emitter and the tight bonding of neighboring MWCNTs due to the ethylene glycol treatment. We investigated the field enhancement factor according to the gap between the anode and the emitter tip at a macroscopic gap regime. The measured field enhancement factor of the MWCNT point emitter was in good agreement with theoretical models.

Atomic force microscopy (AFM) has become a versatile and powerful method for imaging both insulating and conducting objects down to the atomic scale. By extending the high spatial resolution and sensitivity of AFM to the force spectroscopy dimension, oscillations of individual molecules can be studied with atomic resolution. Using three-dimensional mapping of the force and damping fields we address individual Dy@C(82) metallofullerene molecules confined inside single-walled carbon nanotubes (so-called metallofullerene peapods) and reveal their oscillatory behaviour via attractive interactions with the AFM probe tip. The damping energy DeltaE signals, generated in very close proximity of the tip and nanotube peapod, show a close relationship with hysteresis in the short-range forces, thereby indicating that a soft vibrational (phonon) mode is site-specifically (i.e., atom-by-atom) induced by the AFM tip.

Uniform zinc oxide coated single-walled nanotubes (SWNTs) were fabricated by ultrasonic irradiation with acid-treated SWNTs, zinc acetate, and triethanolamine at low temperature in aqueous phase processing. The ZnO coating process did not decrease the dark current of the SWNTs, but a real decrease in the steady state negative photocurrent was observed after ZnO coating, suggesting a clear photosensitization effect. Transport measurements reveal that the negative photocurrent in s (semiconducting)-SWNTs@ZnO could be described by electron-hole compensation behavior attributed to the ZnO layer under ultraviolet excitation. This simple coating method for one-dimensional material can open up new possibilities for multifunctional nanodevices.

The position and width of the Raman G-line was analyzed for unintentionally doped single-layered graphene samples. Results indicate a significant heating of the monolayer by the laser beam. Moreover, a weak additional component was resolved in the G-band. The position of the line is independent of the level of doping of the sample. We conclude that this new component is due to the phonons coupled to the intraband electronic transitions.

Oriented circular dichroism (OCD) was used to characterize and compare in a quantitative manner the secondary structure and concentration dependent realignment of the antimicrobial peptides PGLa and MSI-103, and of the structurally related cell-penetrating peptide MAP in aligned phospholipid bilayers. All these peptides adopt an amphiphilic alpha-helical conformation, and from solid-state NMR analysis they are known to bind to membranes in two distinct orientations depending on their concentration. At low peptide/lipid (P/L) ratio the helices are aligned parallel to membrane surface (S-state), but with increasing concentration they realign to a tilted orientation (T-state), getting immersed into the membrane with an oblique angle supposedly as a result of dimer-formation. In macroscopically aligned liquid crystalline 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine bilayers the two limiting states are represented by distinct OCD spectra, and all spectra at intermediate peptide concentrations can be described by a linear combination of these two line shapes. The corresponding fraction of molecules occupying the T-state was determined by fitting the intermediate spectra with a superposition of the two extreme line shapes. By plotting this fraction versus 1/(P/L), the threshold P/L* ratio for realignment was extracted for each of the three related peptides. Despite their structural similarity distinctly different thresholds were obtained, namely for MSI-103 realignment starts already at a low P/L of approximately 1:236, for a MAP derivative (using a nonaggregating analog containing a D-amino acid) the transition begins at P/L approximately 1:156, whereas PGLa needs the highest concentration to flip into T-state at P/L approximately 1:85. Analysis of the original MAP sequence (containing only L-amino acids) gave OCD spectra compatible with beta-pleated conformation, suggesting that this peptide starts to aggregate with increasing concentration, unlike the other helical peptides. All these changes in peptide conformation and membrane alignment observed here by OCD seem to be functionally relevant, as they can be correlated with the membrane perturbing activities of the three antimicrobial and cell-penetrating sequences.

Heterojunctions consisting of nanotubes and an industrialized semiconductor-GaAs have been produced, and their transport properties were studied. We found that the p-doped GaAs forms an ohmic contact with a nanotube but the n-doped GaAs/nanotube heterojunction is rectifying. Analysis of measurement results at various temperatures shows that tunneling transport plays an important role. We also observed photovoltaic effects in n-GaAs/nanotube junction with the illumination of a green laser or desk lamp.

The two-terminal magnetotransport of a single graphene layer was investigated up to a field of 55 T. The dependence of the electron transmission probability at the organo-metallic interface between the graphene and the metal electrodes was studied as a function of filling factor and electron density. A resistance-plateau spanning several tens of tesla width was observed. We argue that this plateau originates from an augmented sublattice spin-splitting due to the high surface-impurity concentration of the graphene layer. At electron densities close to the Dirac point, fingerprints of a thermally activated energy gap were observed.

The hollow core inside a carbon nanotube can be used to confine single molecules and it is now possible to image the movement of such molecules inside nanotubes. To date, however, it has not been possible to control this motion, nor to detect the forces moving the molecules, despite experimental and theoretical evidence suggesting that almost friction-free motion might be possible inside the nanotubes. Here, we report on precise measurements of the mechanical responses of individual metallofullerene molecules (Dy@C82) confined inside single-walled carbon nanotubes to the atom at the tip of an atomic force microscope operated in dynamic mode. Using three-dimensional force mapping with atomic resolution, we addressed the molecules from the exterior of the nanotube and measured their elastic and inelastic behaviour by simultaneously detecting the attractive forces and energy losses with three-dimensional, atomic-scale resolution.

We studied the transition from the electrochemical double-layer charging regime to intercalative doping of bundled single-walled carbon nanotubes (SWNT) in KCl and HCl aqueous solution. For this purpose we used high doping levels by applying constant potentials above 1000 mV approaching and slightly exceeding the oxidation potential for Cl(-) ions. At each potential in situ Raman measurements of the radial breathing mode (RBM), the high-energy tangential mode (HEM), and the disorder-induced (D) mode were performed. Furthermore, the conductivity and reflectivity of a set of SWNT samples were measured as a function of doping and subsequently the samples were examined by X-ray photoelectron spectroscopy (XPS). From a comparative analysis of the results we conclude that above 1000 mV a significant penetration of chlorine species into the interstitial channels of the SWNT bundles and possible covalent functionalization take place.

The self-assembly of amphiphilic molecules in aqueous solution into lyotropic liquid crystals (LCs), characterised by soft yet long-range ordered nanoscale structures, constitutes a fascinating phenomenon at the heart of soft matter science which can be employed in a manifold of creative ways. Particularly interesting structures may arise as a result of functionalisation of the LC with appropriate guest molecules, adopting the order of their host. Here we combine cat- and anionic surfactants to form a liquid-crystalline colloidal suspension of carbon nanotubes (CNTs), which by virtue of the spontaneously formed hexagonal columnar LC structure are uniaxially aligned over macroscopic areas. The nanotube concentration can be so high, with sufficiently uniform alignment, that the mixture becomes a fluid linear polariser, the anisotropic optical properties of CNTs having been transferred to macroscopic scale by the LC. Moreover, thin and highly aligned filaments can be drawn and deposited in selected directions on arbitrary surfaces, after which the LC template can be rinsed away. Combined with recently developed methods for CNT fractionation according to chirality, the technique would yield an unprecedented degree of control in the practical realisation of carbon nanotube-based devices and materials.

The urgent need for toxicological studies on carbon nanotubes (CNTs) has arisen from the rapidly emerging applications of CNTs well beyond material science and engineering. In order to provide a basis for comparison to existing epidemiological data, we have investigated CNTs at various degrees of agglomeration using an in vitro cytotoxicity study with human MSTO-211H cells. Non-cytotoxic polyoxyethylene sorbitan monooleate was found to well-disperse CNT. In the present study, the cytotoxic effects of well-dispersed CNT were compared with that of conventionally purified rope-like agglomerated CNTs and asbestos as a reference. While suspended CNT-bundles were less cytotoxic than asbestos, rope-like agglomerates induced more pronounced cytotoxic effects than asbestos fibres at the same concentrations. The study underlines the need for thorough materials characterization prior to toxicological studies and corroborates the role of agglomeration in the cytotoxic effect of nanomaterials.

Raman and in situ Raman spectroelectrochemical studies of Dy3N@C80@SWCNT peapods have been carried out for the first time. The formation of peapods by the encapsulation of gaseous Dy3N@C80 has been confirmed by HR-TEM microscopy and by the successful transformation of Dy3N@C80@SWCNT into double-walled carbon nanotubes. The Raman spectra of the endohedral fullerene cluster changed dramatically in the interior of the single-walled carbon nanotube (SWCNT). The electrochemical charging of the peapod indicates a slight reversible attenuation of the Raman intensities of fullerene features during anodic doping. The results support the assignment of Raman bands to the Dy3N@C80 moiety inside a SWCNT.

Much effort has been directed at the fabrication of carbon nanotubes (CNTs)/polymer composites and the characterization of their physical properties. Among them, composites comprising CNTs and the biocompatible polymers are of special interest due to their potential for specific biomedical applications. we report the preparation of the MWCNT/poly(L-lactide) composite and the corresponding spectroscopic (Raman) and the microscopic (SEM, TEM) characterization. The electronic transport, thermal properties, and biocompatibility of this composite have also been investigated. The Raman spectroscopic analysis suggests the interaction between PLLA and MWCNT occurs mainly through the hydrophobic C-CH3 functional groups. The DC conductivity of the composite increases as the MWCNT loading is increased. Such behavior can be described by a percolation mechanism in which a percolation threshold at about 14 wt % MWCNT loading is observed with the maximum end conductivity of 0.1 S x cm(-1). The DSC study of the PLLA/MWCNT composite reveals that the MWCNTs in the composite have the effect of inducing crystallization and plasticizing the polymer matrix. The results from the cell culture test suggest that the presence of MWCNT in the composite inhibits the growth of the fibroblast cells.

We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects.

Using electron diffraction on freestanding single-walled carbon nanotubes, we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3 nm. On the same freestanding tubes, we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7 nm), these measurements confirm previously established radial breathing mode frequency versus diameter relations and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.

We have built a torsional pendulum based on an individual single-walled carbon nanotube, which is used as a torsional spring and mechanical support for the moving part. The moving part can be rotated by an electric field, resulting in large but fully elastic torsional deformations of the nanotube. As a result of the extremely small restoring force associated with the torsional deformation of a single molecule, unusually large oscillations are excited by the thermal energy of the pendulum. By diffraction analysis, we are able to determine the handedness of the molecule in our device. Mechanical devices with molecular-scale components are potential building blocks for nanoelectromechanical systems and may also serve as sensors or actuators.

Chemical modification by SOCl2 of an entangled network of purified single-wall carbon nanotubes, also known as 'bucky paper', is reported to profoundly change the electrical and mechanical properties of this system. Four-probe measurements indicate a conductivity increase by up to a factor of 5 at room temperature and an even more pronounced increase at lower temperatures. This chemical modification also improves the mechanical properties of SWNT networks. Whereas the pristine sample shows an overall semiconducting character, the modified material behaves as a metal. The effect of SOCl2 is studied in terms of chemical doping of the nanotube network. We identified the microscopic origin of these changes using SEM, XPS, NEXAFS, EDX, and Raman spectroscopy measurements and ab initio calculations. We interpret the SOCl2-induced conductivity increase by p-type doping of the pristine material. This conclusion is reached by electronic structure calculations, which indicate a Fermi level shift into the valence band, and is consistent with the temperature dependence of the thermopower.

We show that the band structure of metallic carbon nanotubes can be dramatically altered by the local electrostatic field. This is realized by coupling chemically functionalized nanotubes to form T junctions. The bar of the T is the conducting channel and the leg of the T is used for local gating. Transport measurements reveal that an energy gap develops upon application of a local electric field in both devices with or without linker molecules at the junction. We propose that the mechanism of the band gap modulation in the T junctions without linker molecules is the field effect, with the linker molecules introducing additional electromechanical and chemical effects.

Vanadium oxides, such as V2O5, are promising for lithium-ion batteries, catalysis, electrochromic devices and sensors. Vanadium oxides were proposed more than a decade ago for another redox-dependent application: the direct conversion of electrical energy to mechanical energy in actuators (artificial muscles). Although related conducting polymer and carbon nanotube actuators have been demonstrated, electromechanical actuators based on vanadium oxides have not be realized. V2O5 nanofibres and nanotubes provide the potential advantages of low-cost synthesis by sol-gel routes and high charging capacity and long cycle life. Here, we demonstrate electromechanical actuation for obtained high modulus V2O5 sheets comprising entangled V2O5 nanofibres. The high surface area of these V2O5 sheets facilitates electrochemical charge injection and intercalation that causes the electromechanical actuation. We show that the V2O5 sheets provide high Young's modulus, high actuator-generated stress, and high actuator stroke at low applied voltage.