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Field emission properties of various carbon nanostructures, including carbon nanotube (CNT) films, graphene, amorphous graphene and CNT/graphene composite films are investigated and compared. The crystallinity and surface morphology both play important role in field emission of nano-carbon materials.

Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure–Si heterojunction structures.

A method for the preparation of highly oxidized nitrogen-doped carbon nanotubes (N-CNTs) from KMnO4C H2SO4 solution is described. The atomic ratio of C=O in oxidized N-CNTs is as low as 1.2. The x-ray photoelectron spectroscopy results show that about 75% of the carbon atoms are oxidized and bound to oxygen-containing functional groups. The oxidation reaction mainly occurs at the outer sidewalls, which destroys the graphene stack to an sp 3 -rich structure and helps to preserve the tubular structure of the inner N-CNTs. The oxidized N-CNTs show an energy gap of 2.1 eV. (Some figures may appear in colour only in the online journal)

Spring-like carbon nanotube ropes consisting of perfectly arranged loops are fabricated by spinning single-walled nanotube films, and can sustain tensile strains as high as 285%.

Previous fiber-shaped solar cells are based on polymeric materials or dye-sensitized wide band-gap oxides. Here, we show that efficient fiber solar cells can be made from semiconducting nanostructures (e.g. CdSe) with smaller band-gap as the light absorption material. We directly grow a vertical array of CdSe nanowires uniformly around a core metal wire and make the device by covering the top of nanowires with a carbon nanotube (CNT) film as the porous transparent electrode. The CdSe-CNT fiber solar cells show power conversion efficiencies of 1-2% under AM 1.5 illumination after the nanowires are infiltrated with redox electrolyte. We do not use a secondary metal wire (e.g. Pt) as in conventional fiber-shaped devices, instead, the end part of the CNT film is condensed into a conductive yarn to serve as the secondary electrode. In addition, our CdSe nanowire-based photoelectrochemical fiber solar cells maintain good flexibility and stable performance upon rotation and bending to large angles.

We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 μm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 10(5) S m(-1) and over 1 × 10(5) A cm(-2) in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.

We present the photovoltaic properties of heterojunctions made from single-walled carbon nanotube (SWNT) fibers and n-type silicon wafers. The use of the opaque SWNT fiber allows photo-generated holes to transport along the axis direction of the fiber. The heterojunction solar cells show conversion efficiencies of up to 3.1% (actual) and 10.6% (nominal) at AM1.5 condition. In addition, the use of strong, environmentally benign carbon nanotube fibers provides excellent structural stability of the photovoltaic devices.

Creating highly electrically conducting cables from macroscopic aggregates of carbon nanotubes, to replace metallic wires, is still a dream. Here we report the fabrication of iodine-doped, double-walled nanotube cables having electrical resistivity reaching ∼10⁻⁷ Ω.m. Due to the low density, their specific conductivity (conductivity/weight) is higher than copper and aluminum and is only just below that of the highest specific conductivity metal, sodium. The cables exhibit high current-carrying capacity of 10⁴∼10⁵ A/cm² and can be joined together into arbitrary length and diameter, without degradation of their electrical properties. The application of such nanotube cables is demonstrated by partly replacing metal wires in a household light bulb circuit. The conductivity variation as a function of temperature for the cables is five times smaller than that for copper. The high conductivity nanotube cables could find a range of applications, from low dimensional interconnects to transmission lines.

Integration of graphene into macroscopic architectures represents the first step toward creating a new class of graphene-based nanodevices. We report a novel yet simple approach to fabricate graphene fibers, a porous and monolithic macrostructure, from chemical vapor deposition grown graphene films. Graphene is first self-assembled from a 2D film to a 1D fiberlike structure in an organic solvent (e.g., ethanol, acetone) and then dried to give the porous and crumpled structure. The method developed here is scalable and controllable, delivering tunable morphology and pore structure by controlling the evaporation of solvents with suitable surface tension. The fibers are 20-50 μm thick, with a typical electrical conductivity of ∼1000 S/m. The cyclic voltammetric studies show typical capacitive behavior for the porous graphene fibers with good rate stability and capacitance values ranging from 0.6 to 1.4 mF/cm(2). Decorated with only 1-3 wt % MnO(2), the graphene/MnO(2) composites exhibit remarkable enhancement of combined performance both with respect to discharge capacitance (up to 12.4 mF/cm(2)) and cycling stability. This special structure could facilitate chemical doping and electrochemical energy storage and find applications in catalyst supports, sensors, supercapacitors, Li ion batteries, etc.

This paper reports the light emission from aligned multiwalled carbon nanotubes (MWNTs) under continuous wave CO(2) laser (λ = 10.6 µm) irradiation. Results indicate that the light emission is dependent on the angle θ between the laser incident direction and the nanotube axis. The relative intensity of the light emission at certain wavelengths shows a Lorentzian feature when θ varies from 0° to 90°. The Lorentzian fitting curve displays a distinct tendency between shorter (λ600 nm) and longer wavelength (λ700 nm). A minimum intensity was observed at θ(m) close to 67° under shorter wavelength, whereas a maximum intensity was shown at θ(m) of about 60° at longer wavelength. These results show the anisotropic property of aligned MWNTs.

We report large-scale self-assembly of suspended, straightened, single-walled carbon nanotubes (SWNTs) across regular TiO(2) gel islands. By coating a SWNT network on top of a pool of the TiO(2) colloid and inducing a rapid drying and chapping process, initially curled, random SWNTs can be straightened into aligned arrays and suspended across the island gaps. The suspended SWNT arrays were grafted by semiconducting or metallic nanoparticles, resulting in hybrid structures with tailored and neat morphology, and enhanced photoresponse. We further demonstrate these suspended SWNTs can sustain high speed gas blowing (up to 20 m per second) reversibly for hundreds of cycles, and detect gas velocity by the resistance change.

Carbon nanotube sponges show effective filtration for nanoparticles and dye molecules with different sizes and concentrations from water. The three-dimensional interconnected porous structure formed by entangled nanotubes can trap nanoparticles and molecules by physisorption without the need for chemical functionalization. The sponge filters are potential environmental materials for water treatment.

www.MaterialsViews.com C O M Graphene-On-Silicon Schottky Junction Solar Cells M U N I By Xinming Li , Hongwei Zhu , * Kunlin Wang , * Anyuan Cao , Jinquan Wei , Chunyan Li , Yi Jia , Zhen Li , Xiao Li , and Dehai Wu C A IO N Graphene, a single atomic layer of carbon hexagons, has stimulated a lot of research interest owing to its unique structure and fascinating properties. [ 1 ] Graphene has been produced in the form of ultrathin sheets consisting of one or a few atomic layers by chemical vapor deposition (CVD) [ 2–4 ] or solution processing [ 5 , 6 ] and can be transferred to various substrates. The two-dimensionality and structural fl atness make graphene sheets ideal candidates for thin-fi lm devices and combination with other semiconductor materials such as silicon. These fi lms typically show sheet resistances on the order of several hundred ohm per square at about 80% optical transparency. [ 7 ] With modifi cation on the electronic properties and improvement of processing techniques, graphene fi lms show potential for use in conductive, fl exible electrodes, as an alternative for indium tin oxide (ITO). Graphene applications are just starting, and current investigations are on a number of areas such as fi llers for composites, nanoelectronics, and transparent electrodes. [ 8 ] For applications related to solar cells, graphene microsheets were dispersed into conjugated polymers to improve exciton dissociation and charge transport. [ 9–11 ] Also, solution-processed thin fi lms were used as conductive and transparent electrodes for organic [ 12 ] and dyesensitized [ 13 ] solar cells, although the cell effi ciency is still lower than those with ITO and fl uorine tin oxide (FTO) electrodes. Compared with carbon nanotube fi lms that have been extensively studied, graphene fi lms may have several advantages. A continuous single-layer graphene fi lm could retain high conductivity at very low (atomic) thickness, and avoid contact resistance that occurs in a carbon nanotube fi lm between interconnected nanotube bundles. In addition, graphene fi lms have minimum porosity and, in small areas, can provide an extremely fl at surface for molecule assembly and device integration. There are many opportunities in utilizing distinct properties of graphene and exploring novel applications. Bulk heterojunction structures based on carbon materials have attracted a great deal of interest for both scientifi c fundamentals and potential applications in various new optoelectronic devices

Carbon nanotubes show great potential in developing solar cells with enhanced power conversion efficiency, yet the device stability has not been thoroughly studied. Here, we show how the interaction between components in a nanotube-based hybrid solar cell could cause a significant change in output voltage and fill factor, resulting in photoinduced degradation in device performance. We functionalized carbon nanotubes with CdS nanoparticles to make hybrid films and deposited these films onto silicon substrates to construct solar cells with efficiencies up to 1.4%. The I-V characteristics show reversible change in response to light illumination, suggesting potential applications as visible-light sensors. The fill factor and open-circuit voltage gradually decrease under continuous illumination, inversely proportional to the incident light energy within a considerable range up to 60 J. The unique photoresponse is attributed to a charge-transfer process between nanotubes and nanoparticles under excitation and to change in series resistance in the solar cells.

The paper describes the combination of conductive, semi-transparent graphene films with a n-type silicon wafers to make solar cells with power conversion efficiencies up to 1.5% at AM 1.5G. The Schottky junction solar cells reported here can be extended to other semiconducting materials instead of silicon, in which graphene serves multiple functions as an active junction layer, charge transport path and transparent electrode.

High-yield bamboo-shaped carbon nanotubes (BCNTs) have been produced by using cresol as the precursor, for the first time and there are almost no straight CNTs or amorphous carbon found in the product: the role of cresol in promoting the growth of BCNTs is discussed; improved cycle stability and electric conductivity of the BCNTs as an anode additive in a lithium ion battery are achieved.

Carbon nanotubes (CNTs) filled with ferromagnetic metals have potential applications of microwave absorption and electromagnetic interference shielding due to their high aspect-ratio of nanostructures that promises low percolation threshold and their inner cavities which could incorporate magnetic materials to improve the permeability and magnetic loss of composites. It has been reported that CNTs have high permittivity [1, 2]. And it could be used as dielectric microwave absorbers due to their high permittivity [3, 4]. Excellent microwave absorption should have better electromagnetic match of magnetic loss and dielectric loss. The microwave absorption could be significantly improved by matching the dielectric and magnetic contribution from respective components (e.g. CNTs and Fe) [5]. For CNTs, only dielectric loss contributes to the energy loss of microwave, while for ferromagnetic nanowires, the effect of magnetic loss becomes dominant over the dielectric loss. Either only the dielectric loss or magnetic loss may induce weak microwave absorption due to the imbalance of the electromagnetic match. Here we directly fabricated the microwave absorber by as-grown Fe-filled CNTs, which have the dielectric properties of CNTs and magnetic properties of the filled iron nanowires.Copyright © 2008 by ASME

Double-walled carbon nanotube (DWNT) film is a potential alternative of ITO, due to its excellent electrical and optical properties. In this paper, laser treatment with appropriate power density is introduced to improve the optical transmission of the DWNT film by removing the adsorbates (H2O, O2) in the film, without any structural change. The enhancement of the optical properties makes the DWNT solar cell a higher conversion efficiency.Double-walled carbon nanotube (DWNT) film is a potential alternative of ITO, due to its excellent electrical and optical properties. In this paper, laser treatment with appropriate power density is introduced to improve the optical transmission of the DWNT film by removing the adsorbates (H2O, O2) in the film, without any structural change. The enhancement of the optical properties makes the DWNT solar cell a higher conversion efficiency.

In this paper, we developed a new technique to fabricate a large number of interconnections between double-walled carbon nanotube (DWNT) bundles, and even between DWNT bundles and multi-walled carbon nanotubes (MWNTs) by current-assisted laser irradiation. Although most of the junctions were induced by amorphous carbon deposition, some graphitized interconnections were directly formed without any other treatments. The formation of these junctions can be considered as a result of decomposition of hydrocarbons molecules into amorphous carbon and partial transformation from amorphous carbon into graphitized structures at the contact points, under the combined energy input of both current-induced heat accumulation and laser irradiation.In this paper, we developed a new technique to fabricate a large number of interconnections between double-walled carbon nanotube (DWNT) bundles, and even between DWNT bundles and multi-walled carbon nanotubes (MWNTs) by current-assisted laser irradiation. Although most of the junctions were induced by amorphous carbon deposition, some graphitized interconnections were directly formed without any other treatments. The formation of these junctions can be considered as a result of decomposition of hydrocarbons molecules into amorphous carbon and partial transformation from amorphous carbon into graphitized structures at the contact points, under the combined energy input of both current-induced heat accumulation and laser irradiation.

We directly configured double-walled carbon nanotubes as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and a charge carriers collecting/transport layer. The solar cells consist of a semitransparent thin film of nanotubes conformally coated on a n-type crystalline silicon substrate to create high-density p-n heterojunctions between nanotubes and n-Si to favor charge separation and extract electrons (through n-Si) and holes (through nanotubes). Initial tests have shown a power conversion efficiency of >1%, proving that DWNTs-on-Si is a potentially suitable configuration for making solar cells. Our devices are distinct from previously reported organic solar cells based on blends of polymers and nanomaterials, where conjugate polymers generate excitons and nanotubes only serve as a transport path.

Carbon nanotubes (CNTs) have great potential for use as electrical wires because of their outstanding electrical and mechanical properties. Here, we fabricate lightweight CNT fibers with electrical conductivity as high as that of stainless steel from macroscopic CNT films by drawing them through diamond wire-drawing dies. The entangled CNT bundles are straightened by suffering tension, which improves the alignment of the fibers. The loose fibers are squeezed by the diamond wire-drawing dies, which reduces the intertube space and contact resistance. The CNT fibers prepared by drawing have an electrical conductivity as high as 1.6 × 106 s m−1. The fibers are very stable when kept in the air and under cyclic tensile test. A prototype of CNT motor is demonstrated by replacing the copper wires with the CNT fibers.

Large-area (e.g. centimeter size) graphene sheets are usually synthesized via pyrolysis of gaseous carbon precursors (e.g. methane) on metal substrates like Cu using chemical vapor deposition (CVD), but the presence of grain boundaries and the residual polymers during transfer deteriorates significantly the properties of the CVD graphene. If carbon nanotubes (CNTs) can be covalently bonded to graphene, the hybrid system could possess excellent electrical conductivity, transparency and mechanical strength. In this work, conducting and transparent CNT–graphene hybrid films were synthesized by a facile solid precursor pyrolysis method. Furthermore, the synthesized CNT–graphene hybrid films display enhanced photovoltaic conversion efficiency when compared to devices based on CNT membranes or graphene sheets. Upon chemical doping, the graphene–CNT/Si solar cells reveal power conversion efficiencies up to 8.50%.

We report on the characterization of a terahertz (THz) photodetector with an extremely simple structure consisting of only a macroscopic bundle of double-walled carbon nanotubes (DWCNTs) suspended between two metal electrodes. Polarization-sensitive, broadband, and significant photoresponse occurring at the DWCNT-metal contacts under THz illumination are observed with room-temperature photocurrent and photovoltage responsivities up to ∼16 mA/W and ∼0.2 V/W at 2.52 THz, respectively. Scanning photocurrent measurements provide evidence that the photothermoelectric mechanism dominates the detector response. The simple geometry and compact nature of our device make it suitable for integration and show promising applications for THz detection.

By intercalating monolayer titania (TO) nanosheets into graphene oxide (GO) laminates with mild ultraviolet (UV) reduction, the as-prepared RGO/TO hybrid membranes exhibit excellent water desalination performances. Without external hydrostatic pressures, the ion permeations through the RGO/TO hybrid membranes can be reduced to

All carbon coaxial supercapacitors based on hollow carbon nanotube (CNT) sleeve structure are assembled and tested. The key advantage of the structure is that the inner core electrode is variable from CNT sleeve sponges, to CNT fibers, reduced graphene oxide fibers, and graphene woven fabrics. By changing core electrodes from sleeve sponges to CNT fibers, the electrochemical performance has been significantly enhanced. The capacitance based on sleeve sponge + CNT fiber double the capacitances of double-sleeve sponge supercapacitors thanks to reduction of the series and internal resistances. Besides, the coaxial sleeve structure possesses many other features, including high rate capacitance, long cycle life, and good flexibility.

We explore the transport properties of mixed ionic-electronic conductors made of carbon nanotube/RbAg4I5 film composite nanostructures in the presence of optical fields. The formation of ion-electron bound states (IEBSs) due to Coulomb interactions results in significant conductance decrease. The wavelength-dependent and power-dependent dynamic responses show that the effect of photo-induced dissociation of IEBSs is pronounced in the visible region and negligible in near-infrared region. Our results lead to a deeper understanding of the impact of ion-electron interactions (IEIs) on transport and are expected to open up a way for designing new-type photodetectors based on IEIs.

A hybrid heterojunction and solid-state photoelectrochemical solar cell based on graphene woven fabrics (GWFs) and silicon is designed and fabricated. The GWFs are transferred onto n-Si to form a Schottky junction with an embedded polyvinyl alcohol based solid electrolyte. In the hybrid solar cell, solid electrolyte serves three purposes simutaneously; it is an anti-reflection layer, a chemical modification carrier, and a photoelectrochemical channel. The open-circuit voltage, short-circuit current density, and fill factor are all significantly improved, achieving an impressive power conversion efficiency of 11%. Solar cell models are constructed to confirm the hybrid working mechanism, with the heterojunction junction and photoelectrochemical effect functioning synergistically.

We investigate the optoelectronic properties of a carbon nanotube (CNT)-metal heterostructure in the terahertz range. On the basis of terahertz time-domain spectroscopy characterization of a double-walled CNT (DWNT) film, we present and analyze the photocurrent measurement for a DWNT-nickel heterojunction illuminated by continuous-wave terahertz radiation. A significant current across the junction directly induced by terahertz excitation is observed and a negative photoconductivity behavior is found to occur in the device. The photocurrent shows a linear response to the bias voltage and the illumination power within the examined range. These phenomena support the feasibility of using CNT-metal heterojunctions as novel terahertz detectors.

We have explored the ion-modulated electronic transport properties of mixed ionic-electronic conductor (MIEC) composite nanostructures made of superionic conductor RbAg4I5 films and carbon nanotube (CNT) bundle spiderwebs. Our experimental and theoretical studies indicate that the formation of ion-electron bound states (IEBSs) leads to strong ion-electron interference effect and interesting electronic transport of CNT, such as nonlinear current-voltage (I–V) characteristics and novel temperature dependence of the current. With increasing temperature, the hybrid nanostructures show rich phases with different dependence of current on temperature, which is related to the structural phase transition of RbAg4I5 and the transition of dissociation of IEBSs. The ion-modulation of the electric conductivity in such MIEC composite nanostructures with great tunability has been used to design new ionic-electronic composite nano-devices with function like field effect transistor.

Very less attention has been paid recently to the electrochemical properties of graphene films with intrinsic flat structure prepared by chemical vapor deposition (CVD). In this work, button supercapacitors were fabricated using ionic liquid as electrolytes and layer-by-layer graphene structures as electrodes. The specific capacitances of the supercapacitors increased with the increase of layer number. The areal specific capacitance of ten-layer graphene supercapacitor was 0.29 mF/cm2 at the scan rate of 50 mV/s, which was about three times of that of monolayer graphene supercapacitor (0.1 mF/cm2). The sandwiched multi-layer structures with oxide deposition further improved the device performance. However, the polycrystalline nature of CVD-grown graphene films introduced structural instability during charge-discharge process, resulting in degraded capacitive performance and cycling stability. Our results suggest that graphene films with intrinsic “in-plane” structure might not be ideal candidates for electrode materials.

Cu2O/Si radial nanowire array heterojunctions were prepared by depositing Cu2O nanoparticles via surfactant-assisted chemical bath deposition on n-Si nanowire arrays that were fabricated by metal-assisted electroless etching. After 20 cycles of deposition, large numbers of Cu2O nanoparticles with diameters of around 70 nm form shells that wrap the upper segment of each Si nanowire. Using the rectifying effect of the Cu2O/Si pn junctions, high photodetection sensitivity under illumination at 405, 532 and 1064 nm is exhibited, with a maximal photoresponsivity of 13.05 mA W−1 at 532 nm. The photocurrents are superior to those of Cu2O/Si planar heterojunctions.

Traditional TiO2 based photodetectors (PDs) suffer from high dark resistance, which increases loss of photoexcited charge carriers. Here, we report a new and simple way to improve the performance of PDs based on double-walled carbon nanotube (DWCNT)/TiO2 nanotube heterojunctions. Highly ordered TiO2 nanotube arrays were fabricated using a two-step anodic oxidation method, and coated with a DWCNT film, which functioned as a semitransparent electrode and a photoactive layer. Via pre-electroforming, the device was switched from a high resistance state (HRS) to a low resistance state (LRS). At an applied bias of 1 V, the dark resistance was reduced from 926 to 0.67 kΩ, as a result of the formation of oxygen vacancy related conducting filaments. The photoresponse (ΔI = Ip - Id, where Ip and Id represents photocurrent and dark current, respectively) of the PD in LRS reached 816.76 μA W(-1) under 532 nm laser illumination and 802.89 μA W(-1) under 1064 nm laser irradiation, which is 965 and 3980 times higher, respectively, than those obtained from the HRS device under the same conditions. This strategy for enhancing the photoresponse of TiO2 based PDs may have applications in further improving the power conversion efficiency of dye-sensitized solar cells.

Graphene woven fabric (GWF) prepared from chemical vapor deposition was used as smart self-sensing element to assemble piezoresistor through directly transferring onto the flexible substrate poly(dimethylsiloxane) (PDMS) with the deposited Ti/Au electrodes. A rational strategy was proposed to fabricate flexible touch sensors easily and effectively with the full usage of the mechanical and electrical properties of GWF, whose resistance is highly sensitive to macro-deformation or micro-defect. Compared to commercial and traditional touch sensing, the GWF-on-PDMS piezoresistor is structurally flexible that is demanded under special conditions and meanwhile makes the piezoresistor to have excellent durability.

We study the influence of gas absorption on the photovoltaic properties of carbon nanotube/Si solar cells (CSSCs). The power efficiency of CSSCs changes evidently when exposed in gas, resulting from the resistance change of carbon nanotube (CNT) by gas absorption. The performances of CSSCs degrade when they are long time exposed in air, which results mainly from excessive gas absorption. Gas desorption on CNTs is accelerated by applying a current through the cells, making recovery of efficiency. By applying a current through the cells before light illumination, CSSCs show stable efficiency at ∼10% in one month.

A T-type method is developed to comprehensively evaluate the thermoelectric properties of materials. The thermoelectric properties, including thermal conductivity, thermopower, and electrical conductivity of an ultralong double-walled carbon nanotube bundle are studied from 240 K to 340 K by applying the T-type method. The determined figure of merit achieves 10−3 which is significantly larger than that reported for carbon nanotubes samples. The bundle consists of thousands of nanotubes aligned along the long axis with low levels of impurities, and the thermal conductivity is significantly reduced compared to that of individual double-walled nanotube, while the electrical conductivity is superior to most of the carbon nanotubes samples.

We demonstrated the p-type chemical doping by chlorine and nitrate anions to enhance the Schottky junction in the solar cell. Nitrate ions were found to be more effective for reducing the sheet resistance and enlarging the work function of graphene for effective charge separation and transport, and the efficiency was increased to 9.2% by a factor of 1.68 under AM 1.5 illumination.

We demonstrate an improved low-pressure chemical vapor deposition method to fabricate hexagonal boron nitride (h-BN) domains of a few layers (one-four layers) from ammonia borane by adding a small quartz tube to stabilize the gas flow over the copper substrate and reducing the growing rate of h-BN. The h-BN grows freely and spontaneously to form triangular domains on the Cu (100) plane. The triangular domains are prone to be parallel to each other on the copper substrate. The h-BN domains grow by extending in the normal direction of the triangle and form a large thin film by joining together. Both the size and coverage rate on Cu foils are well controlled by tuning the amount of ammonia borane.

We explore the photoconductive properties of double-walled carbon nanotube film under laser illumination at different wavelengths in both ambient air and vacuum. In our experimental measurements, the photoconductivity of the film shows a strong dependence on the wavelength of light and can be changed from negative to positive by fully removing oxygen. We propose that competition among photoexcitation, photodesorption, and surface plasmon polaritons is responsible for these interesting phenomena. Our results are expected to provide potential applications in the field of nano-optoelectronic sensors based on carbon nanotubes.

Photoinduced molecular desorption from solid surfaces will modify the electrical transporting properties of matter and result in significant change in resistance. The UV induced resistive response of graphene films prepared by chemical vapor deposition was investigated. The resistance of graphene increased exponentially upon UV irradiation and decreased also in an exponential form when the UV light was turned off. Both processes exhibited large time constants of hundreds of seconds. UV-induced molecular desorption mechanisms for graphene, carbon nanotubes, and reduced graphene oxides were compared and discussed.

Hetrodimensional contacts were fabricated by coating double-walled carbon nanotube (CNT) films on CuO nanowire arrays. Wavelength dependent photovoltaic effects by irradiating the devices with 405, 532, and 1064 nm lasers were observed. Two possible mechanisms responsible for the observed results were discussed. Photoexcitations within CuO nanowires and Schottky barriers in the heterojunctions dominate the photovoltaics in the 405 and 532 nm cases. For the 1064 nm case, the photovoltaic is the result of the excitation within the CNTs and of the heterodimensionality effect. Control experiments on CNT film/CuO granular film hetrodimensional contacts further show the relationship between these two mechanisms.

A structure for visible photosensors based on double-walled carbon nanotube (DWCNT) film/Cu2O nanoparticle (NP) film/TiO2 nanotube array (TNA) heterojunctions has been fabricated. Cu2O nanoparticles reduce dark current and enhance photoresponse of the heterojunctions. Consequently, the optoelectric performance is significantly enhanced compared to that of the heterojunctions without Cu2O nanoparticles. The photocurrent-to-dark current ratio reaches ∼1 × 104 under illumination at 405 nm and ∼3 × 104 under illumination at 532 nm, which is two orders of magnitude higher than the results of double-walled carbon nanotube film/TiO2 nanotube array heterojunctions under the same illumination density. Moreover, the response speed of the heterojunctions is greatly improved.

Morphology control of thin film relies on understanding multiple ongoing processes during deposition and growth. To reveal the shape evolution of graphene domains on copper surfaces in chemical vapor deposition (CVD), a combinative study is performed on the CVD growth of graphene on copper surfaces. To identify the factors that influence the adsorption and diffusion of carbon atoms and further determine the domain shape, simulations based on kinetic Monte Carlo techniques are carried out. The results reveal the dependence of the graphene domain shapes on the crystalline orientation of the underlying copper substrate surfaces. S Online supplementary data available from stacks.iop.org/Nano/23/115605/mmedia (Some figures may appear in colour only in the online journal) Crystal growth has been of great technological importance for many years, and the morphology control of thin films relies on a good understanding of multiple ongoing processes during the deposition, surface diffusion and growth. In particular, the 2D diffusion of atoms on surfaces plays a critical role in thin film growth, especially in the early stages. Recently, more understanding of graphene synthesis has been gained from advances in the areas of crystal and thin film growth and surface science. The advances of techniques such as epitaxy [1‐3] and chemical vapor deposition (CVD) [4‐6] for growing large-area and high-quality graphene films have permitted the development of a host of useful devices and materials, and also hold the promise of many others— electronics, optoelectronics, magnetics, and biosensing [7‐9]. On the other hand, shape evolution and control of graphene

Controlled assembly of nanoparticles can lead to a variety of interesting structures and also is an important step in exploring potential applications. Here, we report a solution process for the self-assembly of macroporous, single-layer to hierarchical Ag2S nanoparticle membranes at the air–liquid interface, in which the trapping and releasing of air bubbles leads to the formation of a three-dimensional porous structure without the need to use a template. The resulting membranes contain close-arranged arrays of polygonal holes (mostly pentagons and hexagons) of a few micrometers in size, which are unanimously open upwards and are surrounded by thin nanoparticle walls. Energy and environmental-related applications are demonstrated based on these multifunctional Ag2S membranes, including photo-sensing, photocatalysis and photoelectrochemical solar cells. The porous nanoparticle membranes are distinct from other extensively studied structures such as densely packed crystal-like films and superlattices.

Ultrathin hybrid films of graphene oxide (GO) and monolayer titania (TO) were assembled by layer-by-layer and drop-casting methods. The photo-induced wettability modulation of the hybrid films with different configurations was systematically studied. Due to the photocatalytic reduction of GO by TO, GO sheets in the hybrid films exhibited a tendency to undergo photo-induced conversion from hydrophilic to hydrophobic upon UV irradiation. On the contrary, TO nanosheets showed the reverse trend. Both surfaces of the hybrid film showed opposite yet tunable hydrophilicity under UV irradiation, demonstrating the potential for future application in liquid transport engineering.

We study the gas flow assisted photovoltaic behaviour of the carbon/Si Schottky solar cells and reveal a hybrid effect with a flow-induced enhancement in cell efficiency. Gas flow sensing using the carbon/Si solar cells is proposed and tested.

Nanostructures such as carbon nanotubes (CNTs) and semiconducting nanowires are promising candidates for developing next-generation photovoltaics. Here, we report solar cells using individual single-walled or double-walled CNTs and CdSe nanobelts arranged in simple cross-junction configurations. The CNT and CdSe nanobelts form reliable line contacts at their intersections, resulting in efficient heterojunction solar cells with power conversion efficiencies up to 1.87% and stable performance in air over long periods. Both semiconducting and metallic CNTs can form solar cells with CdSe nanobelts, with similar open-circuit voltages but different short-circuit current densities. We can integrate multiple CNTs in parallel with a single nanobelt to construct an array of cross-junction solar cells simultaneously, with scaled current output, indicating the possibility of parallel device connection and large-scale production. Our results show the potential of utilizing one-dimensional nanostructures to design and fabricate high performance photovoltaic devices with well-defined and scalable structures.

Electrical and thermal properties of a carbon nanotube (CNT)/multiferroic BiFeO(3) (BFO)/Pt photovoltaic heterojunction are investigated for the first time. Enhanced photovoltaic properties (J(sc)≈ 2.1 μA cm(-2) and V(oc)≈ 0.47 V), as compared to the traditional polycrystalline BFO with indium tin oxide (ITO) as the top electrode, are observed due to the unique properties of CNT. An equivalent electrical and thermal model is constructed based on the energy band diagram of the CNT/BFO/Pt heterojunction for the first time and the carriers' transportation behavior is depicted theoretically. The influence of CdSe quantum dots (QDs) sensitization on the photovoltaic properties is presented, and a clear improvement of ~4 fold in photocurrent density is observed.