Integration of carbon nanotubes as hole transport electrode in polymer/fullerene bulk heterojunction solar cells

Transparent and conductive single-walled carbon nanotube (SWNT) thin films were fabricated onto glass substrates and their optical and electrical properties were evaluated. Particular attention was given to the dependence of the conductivity and optical transparency on the thickness of the films. Furthermore, the SWNT thin films were integrated in organic photovoltaic devices as the hole transport electrode. The best photovoltaic performance was observed for the devices utilizing 80 nm SWNT films with a sheet resistance of 362 Ω/sq, and a transmittance of 64% at 520 nm. The experiments reveal that SWNTs films can be used as transparent electrodes for efficient, flexible organic photovoltaic devices.     

Growth and characterization of GaAs nanowires on carbon nanotube composite films: toward flexible nanodevices

Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter between 20 to 200 nm, with heights up to 2.5 microm. Transmission electron microscopy analysis of the NW-SWNT interface indicated that NW growth was initiated upon the surface of the nanotube composite films. Photoluminescence characterization of a single NW specimen showed high optical quality. Rectifying asymmetric current-voltage behavior was observed from contacted NW ensembles and attributed to the core-shell pn-junction within the NWs. Potential applications of such novel hybrid architectures include flexible solar cells, displays, and sensors.     

Templating of self-alignment patterns of anisotropic gold nanoparticles on ordered SWNT macrostructures

We report a simple and versatile technique for oriented assembly of gold nanorods on aligned single-walled carbon nanotube (SWNT) macrostructures, such as thin nanotube films and nanotube fibers. The deposition and assembly is accomplished via drop drying of dilute gold nanorod suspensions on SWNT macrostructures under ambient conditions. Guided by anisotropic interactions, gold nanorods, and polygonal platelets spontaneously align with SWNTs, resulting in macroscopic arrays of locally ordered nanorods supported on aligned SWNT substrates. SEM reveals that the scalar order parameter of rods relative to the local average SWNT alignment is 0.7 for rods on SWNT films and 0.9 for rods on SWNT fibers. This self-alignment is enabled by anisotropic gold nanoparticle-SWNT interactions and is observed for a wide range of nanoparticles, including nanorods with aspect ratios ranging from 2-35, thin gold triangular and other polygonal platelets. The plasmonic properties of aligned gold nanorods together with superior electronic, chemical and mechanical properties of SWNTs make these hybrid nanocomposites valuable for the design of self-assembled multifunctional optoelectronic materials and optical metamaterials.     

Micro orientation and anisotropy of conductivity in liquid crystalline polymer films filled with carbon nanotubes

In this communication we report the preferential orientation of single wall carbon nanotubes (SWNT) in a nematic liquid crystalline (LC) polymer matrix. The alignment of the nanotubes was characterized through anisotropy of electrical conductivity of the composite measured in directions parallel and perpendicular to the nematic director. The anisotropy of the nanocomposite films strongly depends on the nanotube concentration in the range from 1 to 10% and vanished at higher loads. The electrical conductivity of nanocomposites is related to their structural features revealed by atomic force microscopy and Raman spectroscopy experiments and is explained by a strong coupling between the nanotubes and the polymer matrix.     

Single-walled carbon nanotube thin film emitter-detector integrated optoelectronic device

We use the suspended single-walled carbon nanotube (SWNT) thin film technology to assemble the first prototype of an integrated optoelectronic SWNT device, a SWNT optocoupler in which a SWNT emitter and a SWNT detector couple two electrical circuits by the transmission of a signal through the optical channel. Our experiments show that the integrated SWNT emitter/SWNT detector is an ideal couple in which the broadband wavelength character of the emission matches the broadband detection capabilities.     

Large third-order optical nonlinearity in directly synthesized single-walled carbon nanotube films

Large third-order optical nonlinearity is observed in single-walled carbon nanotube (SWNT) films that are directly synthesized by CVD method rather than post-deposited from solution. Through z-scan method, the third-order nonlinear susceptibility (chi(3)) is measured, and the |Im chi(3)| is 1.8 x 10(-7) esu at 1064 nm, which is among the highest reported values for optical nonlinear materials. Combined with their transparent morphology and ultrafast carrier relaxation time, our results indicate the promising prospect of directly synthesized SWNT films as saturable absorbers using in mode-lock lasers or ultrafast switching materials in optical telecommunications.     

The effect of the environment on the electronic properties of single-walled carbon nanotubes

We present optical absorption spectra of single-walled carbon nanotube (SWNT) films obtained after 1-year-long film storage in air and upon heating up to 250°C. The results of the investigation show that long-term storage of the SWNTs in normal atmosphere leads to a substantial drop in intensity of optical absorption caused by electronic excitation, which recovers after film heating. The mechanism of changes in the electronic properties of the SWNTs under the influence of environment is discussed.     

Thin films of single-walled carbon nanotubes promote human osteoblastic cells (Saos-2) proliferation in low serum concentrations

One strategy used for the regeneration of bone is the development of cell culture substrates and scaffolds that can control osteoblast proliferation and differentiation. In recent investigations, carbon nanotubes (CNTs) have been utilized as scaffolds for osteoblastic cell cultures; however, there are only a few reports describing the proliferation of osteoblastic cells on thin CNT films; in particular, the effects of serum concentration on cell proliferation have not been studied. In the present study, we prepared culture dishes with homogeneous thin or thick films of non-modified CNTs and examined the effect of serum concentrations on human osteoblastic cells (Saos-2) proliferation in these culture dishes. We demonstrated that the ratio of cell proliferation was strongly affected by the concentration of serum. Interestingly, single-walled carbon nanotube (SWNT) thin films were found to be the most effective substrate for the proliferation of Saos-2 cells in low concentrations of serum. Thus, thin SWNT films may be used as an effective biomaterial for the culture of Saos-2 cells in low serum concentrations.     

Improving the Electrical Contact Property of Single-Walled Carbon Nanotube Arrays by Electrodeposition

Nano-Micro Letters - A parallel method for the fabrication of metal contacts on single-walled carbon nanotube (SWNT) arrays was presented and the electrical contact property was evaluated by a...     

Broad Microwave Dielectric Property of Single-walled Carbon Nanotube Composites

Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes （SWNT） embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompa- nied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.     

DNA-linker-induced surface assembly of ultra dense parallel single walled carbon nanotube arrays

Ultrathin film preparations of single-walled carbon nanotube (SWNT) allow economical utilization of nanotube properties in electronics applications. Recent advances have enabled production of micrometer scale SWNT transistors and sensors but scaling these devices down to the nanoscale, and improving the coupling of SWNTs to other nanoscale components, may require techniques that can generate a greater degree of nanoscale geometric order than has thus far been achieved. Here, we introduce linker-induced surface assembly, a new technique that uses small structured DNA linkers to assemble solution dispersed nanotubes into parallel arrays on charged surfaces. Parts of our linkers act as spacers to precisely control the internanotube separation distance down to <3 nm and can serve as scaffolds to position components such as proteins between adjacent parallel nanotubes. The resulting arrays can then be stamped onto other substrates. Our results demonstrate a new paradigm for the self-assembly of anisotropic colloidal nanomaterials into ordered structures and provide a potentially simple, low cost, and scalable route for preparation of exquisitely structured parallel SWNT films with applications in high-performance nanoscale switches, sensors, and meta-materials.     

Processing and performance improvements of SWNT paper reinforced PEEK nanocomposites

In this letter, the sandwich-like single-walled carbon nanotube (SWNT) paper/polyetheretherketone (PEEK) composites were successfully prepared by using a hot-compress method. Based on SEM observation, it was found that the PEEK macromolecules could diffuse into the voids of SWNT paper and were able to form very good bonding to the nanotube bundles, which ensure effective stress transfer between two phases. Some typical problems in preparing conventional carbon nanotube/polymer composites, e.g. the difficulty to obtain well-dispersed high-loading nanotubes into polymer matrices, were successfully overcome. Moreover, the compact networks of SWNTs were not destroyed at the appropriate processing condition. Correspondingly, the resulting composite (with one layer of SWNT paper) exhibited about 40% increased in Young’s modulus and 4% enhanced in failure strength when comparing with that of neat PEEK, respectively. According to rule-of-mixtures of the special sandwich-like structure, the estimated Young’s modulus can reach up to about 8 GPa, which was nearly three times of that of neat matrix. Moreover, the surface electric conductivity and thermal conductivity of the PEEK films were also increased after the addition of SWNT paper. The preliminary results suggest that the SWNT paper has great potential for being used to reinforce polymers.     

Anisotropic properties of aligned SWNT modified poly (methyl methacrylate) nanocomposites

The poly (methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites with good uniformity, dispersion and alignment of SWNT were fabricated in an improved figuration process. The semidried mixture was stretched along one direction at a drawing ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The transmission electron microscopic (TEM) observation demonstrated that SWNT in the PMMA/SWNT composite tends to align in the stretching direction owing to a torque exerting on it in the stretching process. The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of composite rise with the increase of SWNT concentration, and that composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The thermogravimetric analysis (TGA) revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

Transparent boron-doped carbon nanotube films

We report results of studies on the sheet resistance and optical transmission of thin films of boron-doped single-walled carbon nanotubes (SWNTs). Boron doping was carried out by exposure of SWNTs to B 2O 3 and NH 3 at 900 degrees C and 1-3 atom % boron was found in the SWNT bundles via electron energy loss spectroscopy (EELS). Boron doping was found to downshift the positions of the optical absorption bands associated with the van Hove singularities (E 11 (s) E 22 (s) and E 11 (m)) by approximately 30 meV relative to their positions in acid-treated and annealed SWNTs. Raman spectroscopy, EELS, and optical data are consistent with the picture that a few atom % boron has been substituted for carbon in the sp (2) framework of SWNTs. Finally, our results show that boron doping does not significantly affect the optical transmittance in the visible region. However, boron doping lowers the sheet resistance by approximately 30% relative to pristine SWNT films from the same batch. Boron-doped SWNT may provide a better approach to touch-screen technology.     

Transport phenomena and conduction mechanism of single-walled carbon nanotubes (SWNTs) at Y- and crossed-junctions

This letter illustrates the transport phenomena associated with single-walled carbon nanotube (SWNT) junctions of Y- and cross-configurations. Localized gating effect exhibited by Y- and crossed-junctions suggests the resemblance of their electrical characteristics with ambipolar and unipolar p-type FETs, respectively. Temperature dependence of the I-V characteristics reveals that the conduction mechanism in the said SWNT junctions is governed by thermionic emission at temperatures above 100 K and by tunneling at T < 100 K. In-depth analysis of current transport through the crossed- and Y-junction SWNTs is significant in view of their predominant influence on the electrical performance of carbon nanotube networks (CNT-mat).     

Experimental and theoretical studies of transport through large scale, partially aligned arrays of single-walled carbon nanotubes in thin film type transistors

Gate-modulated transport through partially aligned films of single-walled carbon nanotubes (SWNTs) in thin film type transistor structures are studied experimentally and theoretically. Measurements are reported on SWNTs grown by chemical vapor deposition with systematically varying degrees of alignment and coverage in transistors with a range of channel lengths and orientations perpendicular and parallel to the direction of alignment. A first principles stick-percolation-based transport model provides a simple, yet quantitative framework to interpret the sometimes counterintuitive transport parameters measured in these devices. The results highlight, for example, the dramatic influence of small degrees of SWNT misalignment on transistor performance and imply that coverage and alignment are correlated phenomena and therefore should be simultaneously optimized. The transport characteristics reflect heterogeneity in the underlying anisotropic metal-semiconductor stick-percolating network and cannot be reproduced by classical transport models.     

Single-walled carbon nanotubes under the influence of dynamic coordination and supramolecular chemistry

A dynamic coordinative-directed solubilization of single-walled carbon nanotubes (SWNTs) in aqueous solutions has been achieved through a combination of a Zn(II) metalloporphyrin complex and a cis-protected Pd(II) complex, which are believed to form charged acyclic and/or cyclic adducts on or around the side walls of SWNTs. The solubilization of SWNTs in aqueous solution only occurs when these acyclic and/or cyclic complexes are allowed to enter simultaneously into a self-assembly process with SWNTs under mild conditions. The aqueous solubility properties that these dynamic complexes confer upon SWNTs are believed to involve noncovalent bonding interactions between the two entities. They have been probed in solution using ultraviolet and visible absorption spectroscopy and in thin films using high-resolution transmission electron microscopy. The supramolecular electronic effects that the individual components of their acyclic and/or cyclic complexes impart upon a single semiconducting SWNT have been probed within a nanotube field-effect transistor device.     

Rational design of amorphous indium zinc oxide/carbon nanotube hybrid film for unique performance transistors

Here we report unique performance transistors based on sol-gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0-2 wt % have been investigated with the field effect mobility reaching as high as 140 cm(2)/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ～10(7). Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications.     

Carbon nanotube based transparent conductive thin films

Carbon nanotube (CNT) based optically transparent and electrically conductive thin films are fabricated on plastic substrates in this study. Single-walled carbon nanotubes (SWNTs) are chemically treated with a mixture of concentrated sulfuric acid and nitric acid before being dispersed in aqueous surfactant-contained solutions. SWNT thin films are prepared from the stable SWNT solutions using wet coating techniques. The 100 nm thick SWNT thin film exhibits a surface resistivity of 6 kohms/square nanometer with an average transmittance of 88% on the visible light range, which is three times better than the films prepared from the high purity as-received SWNTs.     

Launching propagating surface plasmon polaritons by a single carbon nanotube dipolar emitter

We report on the excitation of propagating surface plasmon polaritons in thin metal films by a single emitter. Upon excitation in the visible regime, individual semiconducting single-walled carbon nanotubes are shown to act as directional near-infrared point dipole sources launching propagating surface plasmons mainly along the direction of the nanotube axis. Plasmon excitation and propagation is monitored in Fourier and real space by leakage radiation microscopy and is modeled by rigorous theoretical calculations. Coupling to plasmons almost completely reshapes the emission of nanotubes both spatially and with respect to polarization as compared to photoluminescence on a dielectric substrate.