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Designing advanced electrocatalysts for hydrogen evolution reaction is of far-reaching significance. Active sites and conductivity play vital roles in such a process. Herein, we demonstrate a heteronanostructure for hydrogen evolution reaction, which consists of metallic 1T-MoS2 nanopatches grown on the surface of flexible single-walled carbon nanotube (1T-MoS2/SWNT) films. The simulated deformation charge density of the interface shows that 0.924 electron can be transferred from SWNT to 1T-MoS2, which weakens the absorption energy of H atom on electron-doped 1T-MoS2, resulting in superior electrocatalytic performance. The electron doping effect via interface engineering renders this heteronanostructure material outstanding hydrogen evolution reaction (HER) activity with initial overpotential as small as approximately 40 mV, a low Tafel slope of 36 mV/dec, 108 mV for 10 mA/cm2, and excellent stability. We propose that such interface engineering could be widely used to develop new catalysts for energy conv...

The recent ExecutiveOrder by President Trump attempting to ban temporarily the citizens of seven countries (Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen) from entering the United States is having significant consequences within the country and around the world. The Order poses a threat to the health and vitality of science, barring students and scientists from these countries from traveling to the United States to study or to attend conferences. In preventing those members of the international scientific community from traveling beyond U.S. borders without guaranteed safe return, the Executive Order demeans them; in so doing, it demeans us all. Universities and research communities are especially impacted, as major universities have students and often faculty holding passports from one of these seven countries. This temporary ban would affect refugees fleeing war-torn areas, challenging the long-standing notion that the United States is a safe haven for those fleeing persecution and war in addition to being a magnet for talent from every corner of the world. The pages of this journal reflect the geographic, ethnic, and cultural diversity that underpins great science. The ban impacts domestic and global scientific efforts and communities. Science succeeds through the cooperation between collections of individuals and teams around the world discovering and learning from each other. To ensure rapid scientific progress, open communication and exchange between scientists are essential. As scientists, engineers, and clinicians, we have benefited from open interactions and collaborations with visitors and students from all parts of the world as well as through scientific publications and discussions at scientific meetings.

Guest editors Hua Zhang, Manish Chhowalla and Zhongfan Liu introduce the 2D nanomaterials: graphene and transition metal dichalcogenides themed issue of Chemical Society Reviews.

Significant interest has grown in the development of earth-abundant and efficient catalytic materials for hydrogen generation. Layered transition metal dichalcogenides present opportunities for efficient electrocatalytic systems. Here, we report the modification of 1D MoOx/MoS2 core–shell nanostructures by lithium intercalation and the corresponding changes in morphology, structure, and mechanism of H2 evolution. The 1D nanowires exhibit significant improvement in H2 evolution properties after lithiation, reducing the hydrogen evolution reaction (HER) onset potential by ∼50 mV and increasing the generated current density by ∼600%. The high electrochemical activity in the nanowires results from disruption of MoS2 layers in the outer shell, leading to increased activity and concentration of defect sites. This is in contrast to the typical mechanism of improved catalysis following lithium exfoliation, i.e., crystal phase transformation. These structural changes are verified by a combination of Raman and X-ra...

Low-dimensional materials and their hybrids have emerged as promising candidates for electrocatalytic and photocatalytic hydrogen evolution and CO2 conversion into useful molecules. Progress in synthetic methods for the production of catalysts coupled with a better understanding of the fundamental catalytic mechanisms has enabled the rational design of catalytic nanomaterials with improved performance and selectivity. In this Review, we analyse the state of the art in the implementation of low-dimensional nanomaterials and their van der Waals heterostructures for hydrogen evolution and CO2 reduction by electrocatalysis and photocatalysis. We explore the mechanisms involved in both reactions and the different strategies to further optimize the activity, efficiency and selectivity of low-dimensional catalysts. The electrochemical oxidation and reduction of water and carbon dioxide are associated with the release or storage of energy. This Review reports the latest developments in the design and use of low-dimensional materials and their van der Waals heterostructures for electrocatalytic and photocatalytic hydrogen evolution and CO2 conversion.

Graphene oxide (GO) has emerged as a multifunctional material that can be synthesized in bulk quantities and can be solution processed to form large-area atomic layered photoactive, flexible thin films for optoelectronic devices. This is largely due to the potential ability to tune electrical and optical properties of GO using functional groups. For the successful application of GO, it is key to understand the evolution of its optoelectronic properties as the GO undergoes a phase transition from its insulating and optically active state to the electrically conducting state with progressive reduction. In this paper, we use a combination of electrostatic force microscopy (EFM) and optical spectroscopy to monitor the emergence of the optoelectronic properties of GO with progressive reduction. EFM measurements enable, for the first time, direct visualization of charge propagation along the conducting pathways that emerge on progressively reduced graphene oxide (rGO) and demonstrate that with the increasing degree of reduction, injected charges can rapidly migrate over a distance of several micrometers, irrespective of their polarities. Direct imaging reveals the presence of an insurmountable potential barrier between reduced GO (rGO) and GO, which plays the decisive role in the charge transport. We complement charge imaging with theoretical modeling using quantum chemistry calculations that further demonstrate that the role of barrier in regulating the charge transport. Furthermore, by correlating the EFM measurements with photoluminescence imaging and electrical conductivity studies, we identify a bifunctional state in GO, where the optical properties are preserved along with good electrical conductivity, providing design principles for the development of GO-based, low-cost, thin-film optoelectronic applications.

Hybrid nanostructured materials comprised of amorphous carbon nanoneedles (CNN)-supported Co3O4 nanoparticles (Co3O4-CNN) were synthesized. The synthesis involved layer-by-layer nanocasting of cellulose nanowhiskers with precursors of cobalt oxide and silica, followed by pyrolysis of the core–shell–shell composite materials and etching of the outer silica shells from the carbonized materials. Notably, cotton-derived cellulose nanowhiskers were used as the carbon precursors, and also as the hard templates for needle-shaped carbons, in the synthesis. The effectiveness of the core–shell–shell nanoreactors, possessing the silica shell-entrapped cellulose nanowhiskers and Co(II) ions, in generating organized carbon nanomaterials with metal oxide nanoparticles, or otherwise, as a function of the loading of Co(II) ions was evaluated. Details of the synthetic method and the different materials in terms of composition and morphology it results in as a function of the relative amount of metal ions have also been discussed. The materials showed promising supercapacitive properties and electrocatalytic activity for the oxygen reduction reaction (ORR). The materials' double layer capacitance and performance for ORR electrocatalysis as a function of their Co3O4 content and particles size have also been discussed. The results indicated that the electrochemical properties of these hybrid materials are strongly related to the morphology of their carbon nanostructures. The synthetic method demonstrated here can potentially serve as a facile route to produce other metal oxide/carbon nanomaterials, with different morphologies and similar or better properties, using other carbon precursors.

Composite materials of Sn-doped TiO 2 nanoparticles (4–6 nm) uniformly anchored onto reduced graphene oxide (RGO) sheets were fabricated by a hydrothermal process. When compared with an undoped TiO 2 /RGO composite material, the partial substitution of Sn 4+ for Ti 4+ in TiO 2 /RGO in different doping concentrations not only increased the specific surface area, but also narrowed the band gap energy of the material. It also resulted in a shift in the photoresponse of the material into the visible light region, an increase in the relative intensity of its Raman (D/G) band, and changes in its X-ray photoelectron spectra; these results implied strong interactions between the Sn species and nanosized TiO 2 as well as between the TiO 2 and RGO layers. The presence of RGO led to enhanced adsorptivity of methyl orange onto the material compared with that of either pure TiO 2 or Sn-doped TiO 2 . Increasing the Sn dopant content to optimal value facilitated photoactivity under both UV and visible light irradiation. The incorporation of both RGO and Sn dopants significantly modified the electronic structure of TiO 2 , altering the electron transfer direction and efficiently prohibiting the recombination of photo-induced charge carriers.

We report a facile, nanocasting synthetic method that results in nitrogen-doped mesoporous carbons with tailorable density of N-dopants and high charge storage capacity. The key step in the synthesis of the materials is the preparation of different nitrogen-functionalized SBA-15 mesoporous silicas with tunable density of organoamine groups using a simple solvent-assisted post-grafting method, and the use of the resulting materials both as hard templates as well as N-doping agents for the carbon materials forming inside the pores of SBA-15 via nanocasting. Accordingly, the carbonization of common carbon sources within the organoamine-functionalized SBA-15 produces mesostructured carbons containing different densities of nitrogen dopant atoms. Specifically, a polar protic solvent (ethanol) and a non-polar solvent (toluene) are used for grafting the organoamine groups, ultimately producing two different nitrogen-doped mesoporous carbons, labelled here as N-MC-E and N-MC-T, respectively. These materials possess not only different amounts of nitrogen dopant atoms (0.6 and 2.4 atomic%, respectively) but also distinct electrochemical and charge storage properties. Nitrogen sorption measurements indicate that both materials have mesoporous structures with a high surface area (typically, ∼800 m2 g−1) and nanometer pores with an average pore size of ∼5 nm. Electrochemical measurements at 0.5 A g−1 reveal that the N-MC-E and N-MC-T exhibit high capacitance (152.4 F g−1 and 190.2 F g−1, respectively). These values are either better or comparable to some of the highest capacitance values recently reported for related materials synthesized via other methods. In addition, N-MC-E and N-MC-T retain up to 98% of their stored charges or initial capacitance after 1,000 charge–discharge cycles at a current density of 2.0 A g−1. These results clearly show N-MCs' good electrochemical stability as well as potential application in energy storage.

We report chemically exfoliated MoS2 nanosheets with a very high concentration of metallic 1T phase using a solvent free intercalation method. After removing the excess of negative charges from the surface of the nanosheets, highly conducting 1T phase MoS2 nanosheets exhibit excellent catalytic activity toward the evolution of hydrogen with a notably low Tafel slope of 40 mV/dec. By partially oxidizing MoS2, we found that the activity of 2H MoS2 is significantly reduced after oxidation, consistent with edge oxidation. On the other hand, 1T MoS2 remains unaffected after oxidation, suggesting that edges of the nanosheets are not the main active sites. The importance of electrical conductivity of the two phases on the hydrogen evolution reaction activity has been further confirmed by using carbon nanotubes to increase the conductivity of 2H MoS2.

Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

Graphene films are grown in open-atmosphere on metal substrates using a multiple inverse-diffusion flame burner with methane as fuel. Substrate material (i.e. copper, nickel, cobalt, iron, and copper–nickel alloy), along with its temperature and hydrogen treatment, strongly impacts the quality and uniformity of the graphene films. The growth of few-layer graphene (FLG) occurs in the temperature range 750–950 °C for copper and 600–850 °C for nickel and cobalt. For iron, the growth of graphene is not exclusively observed. The variation of graphene quality for different substrates is believed to be due primarily to the difference in carbon solubility between the metals.

In the quest for higher performance, the dimensions of field-effect transistors (FETs) continue to decrease. However, the reduction in size of FETs comprising 3D semiconductors is limited by the rate at which heat, generated from static power, is dissipated. The increase in static power and the leakage of current between the source and drain electrodes that causes this increase, are referred to as short-channel effects. In FETs with channels made from 2D semiconductors, leakage current is almost eliminated because all electrons are confined in atomically thin channels and, hence, are uniformly influenced by the gate voltage. In this Review, we provide a mathematical framework to evaluate the performance of FETs and describe the challenges for improving the performances of short-channel FETs in relation to the properties of 2D materials, including graphene, transition metal dichalcogenides, phosphorene and silicene. We also describe tunnelling FETs that possess extremely low-power switching behaviour and explain how they can be realized using heterostructures of 2D semiconductors. Field-effect transistors (FETs) with semiconducting channels made from 2D materials are known to have fewer problems with short-channel effects than devices comprising 3D semiconductors. In this Review, a mathematical framework to evaluate the performance of FETs is outlined with a focus on the properties of 2D materials, such as graphene, transition metal dichalcogenides, phosphorene and silicene.

Graphene-based electronics show much promise due to the potential high charge-carrier mobility of the material as well as its flexibility in preparation on different substrates. Recently there has been much evidence suggesting that the wrinkle structures found in pristine graphene inhibit electron transport, reducing device performance. In this study the inhibiting role of standing wrinkles within chemically derived graphene are studied quantitatively using Kelvin force microscopy. Samples were evaluated before and after annealing at 250 C to observe changes in the channel's surface potential dependence on the state of reduction. Annealed samples were found to have inter-flake and intra-flake contribution to the potential drop and that for the latter a correlation between the potential drop magnitude and wrinkle density is found, although there is no correlation with wrinkle height. Statistical averaging across many images demonstrated that the average lower limit of wrinkle resistance in these devices is approximately 4.5 kΩ. Such high resistance demonstrate definitively that elimination of wrinkles within graphene oxide based devices is essential in order to obtain optimum performance. © 2013 Elsevier Ltd. All rights reserved.

We demonstrate low operating voltage (

A two-dimensional crystal of molybdenum disulfide (MoS2) monolayer is a photoluminescent direct gap semiconductor in striking contrast to its bulk counterpart. Exfoliation of bulk MoS2 via Li intercalation is an attractive route to large-scale synthesis of monolayer crystals. However, this method results in loss of pristine semiconducting properties of MoS2 due to structural changes that occur during Li intercalation. Here, we report structural and electronic properties of chemically exfoliated MoS2. The metastable metallic phase that emerges from Li intercalation was found to dominate the properties of as-exfoliated material, but mild annealing leads to gradual restoration of the semiconducting phase. Above an annealing temperature of 300 °C, chemically exfoliated MoS2 exhibit prominent band gap photoluminescence, similar to mechanically exfoliated monolayers, indicating that their semiconducting properties are largely restored.

Boron carbide is characterized by a unique combination of properties that make it a material of choice for a wide range of engineering applications. Boron carbide is used in refractory applications due to its high melting point and thermal stability; it is used as abrasive powders and coatings due to its extreme abrasion resistance; it excels in ballistic performance due to its high hardness and low density; and it is commonly used in nuclear applications as neutron radiation absorbent. In addition, boron carbide is a high temperature semiconductor that can potentially be used for novel electronic applications. This paper provides a comprehensive review of the recent advances in understanding of structural and chemical variations in boron carbide and their influence on electronic, optical, vibrational, mechanical, and ballistic properties. Structural instability of boron carbide under high stresses associated with external loading and the nature of the resulting disordered phase are also discussed.

CdO nanowires were produced by calcination process using Cd(OH)2 nanowires as precursors. The Cd(OH)2 nanowires were synthesized via arc discharge method submerged in de-ionized water. Transmission electron microscopy (TEM) analysis of the as-synthesized Cd(OH)2 nanowires revealed that nanowire morphology was abundant form with the diameters range from 5 to 40 nm. In addition to the nanowire morphology, Cd(OH)2 nanospheres and hexagonal shaped nanoparticles were also displayed. The Cd(OH)2 nanostructures were used as precursors to produce CdO nanowires and calcinated in air at 400 °C for four hours. After calcination, the structural, morphological and optical properties of the as-synthesized CdO nanowires were characterized by means of TEM, selected area electron diffraction (SAED), X-ray diffraction (XRD) and UVvis spectroscopy. The XRD and SAED techniques showed that the as-synthesized Cd(OH)2 nanostructures could be transformed into CdO nanostructures after the calcination process. TEM results revealed that the assynthesized CdO nanowires were 5–30 nm in diameter and shorter than corresponding Cd(OH)2 nanowires. In addition, the diameters of the spherical or irregular CdO nanoparticles ranged from 20 nm to 50 nm. UV-vis spectroscopy analysis was showed that the direct gap of the CdO nanowires were found to be 2.60 eV which is slightly higher than the earlier reported values of the bulk CdO for direct band gaps (2.3 eV) due to quantum size effect.

A detailed in situ infrared spectroscopy analysis of single layer and multilayered graphene oxide (GO) thin films reveals that the normalized infrared absorption in the carbonyl region is substantially higher in multilayered GO upon mild annealing. These results highlight the fact that the reduction chemistry of multilayered GO is dramatically different from the single layer GO due to the presence of water molecules confined in the ∼1 nm spacing between sheets. IR spectroscopy, XPS analysis, and DFT calculations all confirm that the water molecules play a significant role interacting with basal plane etch holes through passivation, via evolution of CO(2) leading to the formation of ketone and ester carbonyl groups. Displacement of water from intersheet spacing with alcohol significantly changes the chemistry of carbonyl formation with temperature.

A detailed description of the electronic properties, chemical state, and structure of uniform single and few-layered graphene oxide (GO) thin films at different stages of reduction is reported. The residual oxygen content and structure of GO are monitored and these chemical and structural characteristics are correlated to electronic properties of the thin films at various stages of reduction. It is found that the electrical characteristics of reduced GO do not approach those of intrinsic graphene obtained by mechanical cleaving because the material remains significantly oxidized. The residual oxygen forms sp3 bonds with carbon atoms in the basal plane such that the carbon sp2 bonding fraction in fully reduced GO is ∼0.80. The minority sp3 bonds disrupt the transport of carriers delocalized in the sp2 network, limiting the mobility, and conductivity of reduced GO thin films. Extrapolation of electrical conductivity data as a function of oxygen content reveals that complete removal of oxygen should lead to properties that are comparable to graphene.

B–C and B–C:Si films were deposited by r.f. magnetron sputtering from a hot-pressed B4C polycrystalline target with Si pieces placed on the preferentially eroded zone. The effect of Si content, ranging from 2 to 6 at.-%, on the B–C films was studied at a fixed substrate bias of −70 V. Preliminary depositions with different substrate bias showed that with −70 V the deposition of free carbon was avoided. All deposited films were X-ray diffraction (XRD) amorphous, and the result was confirmed by Fourier transform infrared spectroscopy (FTIR). Si-containing films were harder than Si-free ones, reaching 30 GPa for compositions up to 4.5 at.-% Si. After thermal annealing of the B–C:Si films up to 700 °C, an increase of the hardness was observed. The maximum hardness of 37 GPa was obtained for 2 at.-% Si film annealed at 600 °C, which corresponds to an increase of ∼23% in relation to the as-deposited conditions. No vestiges of crystallinity were found either by XRD or FTIR analysis suggesting that the structure of the Si-containing films consisted of a local order arrangement of boron-rich icosahedral units.

In this paper, we report on the synthesis and applications of semiconducting nanostructures. Nanostructures of interest were zinc oxide (ZnO) nanowires and tungsten disulfide (WS2) nanotubes where transistors/phototransistors and photovoltaic (PV) energy conversion cells have been fabricated. ZnO nanowires were grown with both high- and low-temperature approaches, depending on the application. Individual ZnO nanowire side-gated transistors revealed excellent performance with a field-effect mobility of 928 cm2/V middots. ZnO networks were proposed for large-area macroelectronic devices as a less lithographically intense alternative to individual nanowire transistors where mobility values in excess of 20 cm2/V middots have been achieved. Flexible PV devices utilizing ZnO nanowires as electron acceptors and for photoinduced charge separation and transport have been presented. Phototransistors were fabricated using individual WS2 nanotubes, where clear sensitivity to visible light has been observed. The results presented here simply reveal the potential use of inorganic nanowires/tubes for various optoelectronic devices.

Improvement of the photovoltaic efficiency via exposure of organic poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) devices to solvent vapor at room temperature is reported. In situ photoluminescence (PL) and Raman spectroscopy, in conjunction with ex situ optical absorption and atomic force microscopy, have been used to provide insight into the nanoscale morphological changes occurring during solvent vapor annealing. We found that in 1 : 1 composites of P3HT : PCBM, suppression of PL, narrowing in line-width of the 1442 cm−1 P3HT Raman peak, and strong modifications in the optical absorption spectra were observed during solvent vapor annealing, while minimal changes occurred in pure P3HT films. We attribute these spectral modifications to de-mixing of PCBM and subsequent stacking of P3HT in coplanar conjugated segments, similar to what is observed during thermal annealing.

Conventional analysis of nanoindentation data considers only the unloading curve, but this may be misleading for materials that are very elastic. An alternative method that considers the loading and unloading curve may be more appropriate. Results for a carbonaceous material with a high hardness (or yield stress) relative to its elastic modulus are presented. An analysis considering the whole nanoindentation cycle gives a ratio of H/E that is significantly higher than that obtained from just the loading or unloading curve.

A detailed parametric study of single-walled carbon nanotubes (SWNTs) synthesized in powder form and on substrates using the alcohol catalytic chemical vapour deposition (ACCVD) method is reported. As-grown SWNTs were analysed using transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and UV-vis-NIR spectroscopy to obtain structural and electronic information. We found that nucleation and growth of SWNTs occurs within seconds after introduction of the alcohol vapour and that high quality SWNTs with a narrow diameter distribution without amorphous carbon can be grown using Co acetate catalyst doped with Fe acetate above 750 degrees C. Defective multiwalled nanotubes were observed at lower temperatures, with the optimum temperature being 850 degrees C. These and other results reported in this paper allow the basis for optimizing the ACCVD process for the synthesis of large numbers of SWNTs.

We present a detailed study of the growth of multiwall and single-wall carbon nanotubes (SWCNTs) by chemical-vapor deposition using a thin-film triple metal (Al∕Fe∕Mo) catalyst. Using Nanoauger spectroscopy, a full map of the metals in the sample surface is constructed and their evolution followed at different deposition temperatures. During the formation of SWCNTs at high temperatures (∼1000°C), the initial iron layer (∼1nm) is transformed into nanosized particles at the surface. In addition, the Al layer also plays a critical role during the annealing process by being altered into AlxOy particles. These particles act as a suitable underlayer to stabilize the nanosized Fe catalyst for nanotube growth. We also show that it is possible to resolve SWCNTs by mapping the areal intensity of carbon KVV Auger electrons.

Vertically aligned carbon nanotubes were synthesized by plasma enhanced chemical vapor deposition using nickel as a metal catalyst. High resolution transmission electron microscopy analysis of the particle found at the tip of the tubes reveals the presence of a metastable carbide Ni3C. Since the carbide is found to decompose upon annealing at 600 °C, we suggest that Ni3C is formed after the growth is stopped due to the rapid cooling of the Ni-C interstitial solid solution. A detailed description of the tip growth mechanism is given, that accounts for the composite structure of the tube walls. The shape and size of the catalytic particle determine the concentration gradient that drives the diffusion of C atoms across and though the metal.

The effect of the plasma on heating the growth substrate in plasma enhanced chemical vapor deposition (PECVD) of carbon nanotubes is characterized for the first time. This effect, which is commonly ignored in the nanotube/nanofiber literature, is the sole heating mechanism in this work for catalyst pretreatment and growth of straight and vertically aligned multiwalled carbon nanofibers. Significant temperatures, as high as 700 °C, are induced from a C2H2:NH3 direct current (dc) plasma with no other heat source present. To model the behavior of the plasma-heated substrate platform, we have developed a 1-D dc discharge model that incorporates a cathode platform energy balance, including ion bombardment, thermal radiation, and solid and gas conduction. The predicted gas-phase species present are correlated with the morphology of nanofibers grown by exclusive plasma heating as well as by heating from plasma in combination with a conventional resistive heater. The understanding of plasma heating and its accurate modeling are essential for reactor design for wafer scale production of vertically aligned nanofibers.

A novel nanocarbon structure, carbon nanohorns (CNHs) particle which includes one Ni-contained carbon nanocapsule (CNC) in its center, is produced by submerged arc in liquid nitrogen using Ni-contained (0.7 mol%) graphite anode. Transmission electron microscopy revealed that each CNHs particle in nearly spherical shape of diameter around 50–100 nm has one Ni nanoparticle of diameter 5–20 nm encapsulated by graphitic shells as CNC.

We report on a study into electrode fabrication for the gate control of carbon nanotubes partially suspended above an oxidised silicon substrate. A fabrication technique has been developed that allows self-aligned side-gate electrodes to be placed with respect to an individual nanotube with a spacing of less than 10 nm. The suspended multi-walled carbon nanotube (MWCNT) is used as an evaporation mask during metal deposition. The metal forms an island on the nanotube, with increasing width as the metal is deposited, forming a wedge shape, so that even thick deposited layers yield islands that remain separated from the metal deposited on the substrate due to shadowing of the evaporation. The island can be removed during lift-off to leave a set of self-aligned electrodes on the substrate. Results show that Cr yields self-aligned side gates with around 90% effectiveness.

Characteristics of the Raman spectrum from carbon onions have been identified in terms of the position of the G peak and appearance of the transverse optic phonon peaks. Five new peaks were observed in the low wavenumber region, at about 1100, 861, 700, 450 and 250 cm−1. The origins of these peaks are discussed in terms of the phonon density of states (PDOS) and phonon dispersion curves of graphite. The curvature of the graphene planes is invoked to explain the relaxation of the Raman selection rules and the appearance of the new peaks. The Raman spectrum of carbon onions is compared with that of highly oriented pyrolytic graphite (HOPG). The strain of graphene planes due to curvature has been estimated analytically and is used to account for the downward shift of the G peak.

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1–10 kΩ/μm length (resistivity 10 −6 to 10 −5 Ω m) and have a maximum current carrying capability of 0.2–2 mA (current density 10 7 –10 8 A/cm 2 ). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼10 μA were obtained. The failure of nanotubes under field emission is also discussed.

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

The overall aim of this work is to produce arrays of field emitting microguns, based on carbon nanotubes, which can be utilised in the manufacture of large area field emitting displays, parallel e-beam lithography systems and electron sources for high frequency amplifiers. This paper will describe the work carried out to produce patterned arrays of aligned multiwall carbon nanotubes (MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/fibres can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the Ni catalyst to precisely define the position of each nanotube/fibre. Details of the field emission behaviour of the different arrays of MWCNTS will also be presented.

We report the incorporation of graphene-oxide quantum dots (GOQDs) into films, diluted solutions, and light-emitting diodes (LEDs) as part of a water-soluble derivative of poly(p-phenylene vinylene), or PDV.Li, to investigate their impact on the light-emission properties of this model conjugated polymer. Despite the well-known ability of graphene and graphene oxide to quench the photoluminescence of nearby emitters, we find that the addition of GOQDs to diluted solutions of PDV.Li does not significantly affect the photoluminescence (PL) dynamics of PDV.Li, bringing about only a modest quenching of the PL. However, loading the polymer with GOQDs led to a substantial decrease in the turn-on voltage of LEDs based on GOQD–PDV.Li composites. This effect can be attributed to either the improved morphology of the host polymer, resulting in an increase in the charge mobility, or the enhanced injection through GOQDs near the electrodes.

Molybdenum disulfide (MoS2) multilayers with functional polyelectrolyte nanospacing layers are presented. Taking advantage of the facile method of layer-by-layer (LbL) assembly, individual chemically exfoliated MoS2 layers are not only effectively isolated from interlayer coupling but also doped by functional polymeric layers. It is clearly demonstrated that MoS2 nanosheets separated by polymeric trilayers exhibit a much larger increase in photoluminescence (PL) as the number of layers is increased. The enhanced PL has been correlated to the ratio of excitons to trions with the type of polymeric spacers. Because uniform heterogeneous interfaces can be formed between various transition metal dichalcogenides and other soft materials, LbL assembly offers possibilities for further development in the solution-processable assemblies of two-dimensional materials.

We report the effect of diameter on the composition, optical, and electronic properties of the BiFeO 3 (BFO) nanofibers. Bismuth ferrite nanofibers with different diameter (20 to 150nm) have been fabricated by a sol gel based electrospinning route. The effect of quantum confinement has been found to influence the photoconductivity, grain size and optical properties of the nanofibers. A shift in the band gap to 2.1 eV was observed as a result of the variation on the nanofiber diameter. The position and intensity of the Raman peaks in the low wavenumber are found to shift depending on the diameter due to local stress in the nanofiber. Transmission electron microscopy revealed the nanocrystalline morphology. The composition analysis through energy dispersive detector and electron energy loss spectroscopy revealed the heterogeneous nature of the composition with Bi-rich and Fe-rich regions. X-ray photoelectron spectroscopy results confirmed the combination of Fe3+ and Fe2+ valence state in the nanofibers with a major contribution from Fe3+ which varies with the nanofiber diameter. Photoconductivity measurements show a considerable increase in the current flowing through the nanofibers when measured under illumination. The photoresponse of the nanofibers is increased considerably with decreasing the diameter. This effect is described by a size dependent surface recombination mechanism.

We have investigated the effects of seven sputtering control factors on the hardness of carbon nitride (CNx) thin films by design of experiments and the analysis of variance (ANOVA) to synthesize hard CNxthin films. It was determined statistically that the substrate temperature, the sputtering pressure and the target to substrate distance are significant control factors for the hardness of the CNxthin films within the experimental range of this study. Especially, the distance is the most important control factor of the seven factors; the hardest films are obtained at the distance of 4.5 cm. On the other hand, the effects of the substrate treatment, the dc power, the nitrogen concentration and the sputtering time are not statistically significant. It is suggested that these statistical methods are effective to compare the importance of many sputtering control factors. The CNxthin films deposited under the optimized sputtering conditions exhibit a relatively high hardness value of 55 ± 11 GPa, Young's modulus of 228 ± 21 GPa and an elastic recovery (%R) of 98%. The compressive stress in the films is a low value of 0.3 GPa.

Electronic properties of nitrogen doped hydrogenated amorphous carbon films deposited in an inductively coupled plasma enhanced chemical vapour deposition process by decomposition of methane (CH4) and nitrogen (N2) are reported. In particular, the relation of these properties to the overall field emission performance of an a-C:H:N/Si heterojunction is considered. The heterojunctions have forward to backward rectifying current ratios of 3–4 orders of magnitude. The capacitance as a function of voltage (C–V) characteristics show negligible hysteresis, zero flat band voltage and response up to 13 MHz without loss of the typical depletion transition. The current as a function of voltage (I–V) of the metal (Au)/a-C:H:N/Si are consistent with Fowler–Nordheim type tunnelling of carriers from Si into a-C:H:N. The transition barrier is found to be ∼0.07 eV. Which is very close to the previously reported electron emission barrier into vacuum from a-C:H:N. Correlation between the electron emission properties of a-C:H:N/Si heterojunctions and the electronic properties are presented.

The electronic and optical properties of nitrogen doped tetrahedral amorphous carbon (ta-C:N) are compared with those of a new form of carbon ta-C film in which nanotube regions are included (ta-C:(NT)). It is found that nanotubes in ta-C inhibit the N doping effect in ta-C and leads to a reduction in conductivity. The results point to the nanotube regions acting as electronically isolated graphitic regions in ta-C. The refractive index in ta-C:(NT) is found to have the opposite dependency on wavelength to that of ta-C. It is proposed that the refractive index can be used as a signature for the presence of nanotubes and other large graphitic regions in ta-C.

The plasma characteristics of a new arc mode on carbon referred to as the ‘‘stationary cathodic arc’’ are reported. Particularly, optical emission spectroscopy, probe and ion energy distribution measurements are used to compare the properties of the stationary arc with the normal ‘‘random cathodic arc’’ on carbon. The measurements revealed that the plasma properties of both arc modes are similar. In addition, we have correlated the plasma characteristics to the film properties. Carbon films deposited using the stationary arc were found to have a surface particle density equivalent to those deposited using the filtered cathodic vacuum arc. The macro‐particle free films were found to be highly tetrahedral and compressively stressed. Both the sp3 fraction and stress values were strongly dependent on the ion energy with maximum values of 85% and 9.4 GPa, respectively, occurring at ≊50 eV.

Curved magnetic ducts are frequently used to remove macroscopic-sized droplets from the plasma stream of cathodic vacuum arcs. The plasma of a cathodic vacuum arc in a magnetic filter is characterized by a strongly directional ion velocity (corresponding to 20-100 eV) and magnetized electrons. In the first section of this paper the effects of these features on the I-V characteristic curves of planar probes are identified and explained using a simple model. This is then used to interpret the interaction of the plasma with the walls of a biased quarter torus duct. Two small electrodes placed on the outer and inner sections of the curved duct wall show that the I-V characteristic is determined primarily by the electron-ion current balance at the wall on the outside of the curve. The application of a bias to a planar electrode on the outer wall section was found to give the same increase in throughput as a positive bias applied to the entire duct with the advantage of a much smaller electron current being drawn by the biasing power supply. The improvement in duct throughput achievable with positive-biasing of the duct wall was found to depend on both the configuration and strength of the magnetic field in the quarter torus filter. The plasma density profile and potential were unaffected by the application of the bias.

The charge states and ion energy distributions (IEDs) of cathodic arc zirconium (Zr) plasma in vacuum and in nitrogen are reported. The dominant charge states in vacuum and in nitrogen were found to be Zr4+ and Zr2+, respectively. In addition to Zrn+, N2+ and N+ species along with ionized zirconium nitride (ZrNn+) were also detected. The peak ion energies of all Zrn+ species in vacuum were found to be slightly higher (∼19 eV) than in nitrogen (∼15 eV). The IEDs of N2+ species exhibited two peaks, one at 2–4 eV and the other at ∼15 eV. The dual peaks in the N2+ IEDs indicate that some species are ionized in the plasma and others are emitted from, or near, the surface of the cathode. The peak energies of ZrN2+ and ZrN+ species were found to be ∼15 eV, indicating that they are emitted from the nitrided (“poisoned”) surface of the cathode or the from the dense plasma region above the arc spot.

Chemically derived graphene oxide (GO) is an atomically thin sheet of graphite that has traditionally served as a precursor for graphene, but is increasingly attracting chemists for its own characteristics. It is covalently decorated with oxygen-containing functional groups - either on the basal plane or at the edges - so that it contains a mixture of sp(2)- and sp(3)-hybridized carbon atoms. In particular, manipulation of the size, shape and relative fraction of the sp(2)-hybridized domains of GO by reduction chemistry provides opportunities for tailoring its optoelectronic properties. For example, as-synthesized GO is insulating but controlled deoxidation leads to an electrically and optically active material that is transparent and conducting. Furthermore, in contrast to pure graphene, GO is fluorescent over a broad range of wavelengths, owing to its heterogeneous electronic structure. In this Review, we highlight the recent advances in optical properties of chemically derived GO, as well as new physical and biological applications.

Summary form only given. In this talk, we would like to present the applications of graphene-based materials on large-area photovoltaic and optoelectronic devices. Chemically derived graphene-oxide (GO) from solution processes or epitaxial graphene obtained from chemical vapor deposition (CVD) have been demonstrated to replace the ITO electrode. GO could be also a simple solution processable alternative to PEDOT:PSS as the effective hole transport and electron blocking layer in polymer photovoltaics, suggesting that future polymer solar-cell devices could be "all-carbon". In addition, photoluminescence of GO and reduced-GO will be demonstrated. The tunablity of PL emission from red to blue colors offers a potential to use graphene-based materials on solution-processable optoelectronic devices for full-color display and lighting applications.

Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large-area thin-film deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO-based thin-film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO-based thin films are discussed in relation to their potential applications in electronics and optoelectronics.

The emerging field of "organic" or "plastic" electronics has brought low-voltage, ultrathin, and energy-efficient lighting and displays to market as organic light-emitting diode (OLED) televisions and displays in cameras and mobile phones. Despite using carbon-based materials as the light-emitting layer, previous efficient organic electronic light-emitting devices have required at least one metal electrode. Here, we utilize chemically derived graphene for the transparent cathode in an all-plastic sandwich-structure device, similar to an OLED, called a light-emitting electrochemical cell (LEC). Using a screen-printable conducting polymer as a partially transparent anode and a micrometer-thick active layer solution-deposited from a blend of a light-emitting polymer and a polymer electrolyte, we demonstrate a light-emitting device based solely on solution-processable carbon-based materials. Our results demonstrate that low-voltage, inexpensive, and efficient light-emitting devices can be made without using metals. In other words, electronics can truly be "organic".

The authors have reported the structure of the nanoclusters in carbon nitride thin films before [D. Roy et al., Phys. Rev. B 70, 035406 (2004)]. In this work, effects of the addition of hydrogen in the deposition gas mixture on the structures of carbon nitride thin films prepared by magnetron sputtering were investigated using Raman spectroscopy. Raman measurements showed that the structures of carbon nanoclusters remained unaffected by the addition of hydrogen in the carbon nitride films. On the other hand, the structures of amorphous thin films were affected by the addition of hydrogen in the deposition gas mixture. These are explained in terms of changes in the ratios of the D-peak to the G-peak intensities and shifts in the G-peak centers.

Field emission measurements on individual carbon nanotubes grown by dc plasma CVD at 700/spl deg/C have been performed with a high resolution scanning anode field emission microscope. I-V characteristics of as-grown CNs show a saturation for currents above 1 /spl mu/A and the maximum emission current is in the range 5-10 /spl mu/A. This saturation is attributed to a bad CN/substrate contact. By improving this electric contact by thermal annealing at 950/spl deg/C, the saturation is suppressed. To improve emission current density, the effect of CN density on maximum emission current is studied. For this purpose, 0.5 /spl times/ 0.5 mm/sup 2/ arrays of vertically aligned CNs with a 1.5 /spl mu/m height, a 15 nm diameter and a 3 /spl mu/m spacing are grown. The CN density is 10/sup 7/ cm/sup -2/. CNs exhibit almost the same aspect ratio [200] but the CN density is increased by a factor of 10. From such an array, an emission current of 10 mA corresponding to a current density of 4 A cm/sup -2/ is measured.