Polyaniline/carbon nanotube composite Schottky contacts

Schottky contacts were fabricated on composites of high molecular weight polyaniline and pristine multiwalled carbon nanotubes. Physical and electrical characteristics of these organic composite materials were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical measurements. The RMS surface roughness of the composite films was found to be 4 nm. From the IV characteristics of these composite devices, it appears that the current follows Ohm's law at lower voltages and Child's law at higher voltages, indicating a space‐charge‐limited emission mechanism in the presence of a distribution of shallow traps.     

Possibility of driving water molecules along a single-walled carbon nanotube using methane molecules

Molecular dynamics simulation is used to study the transport behavior of water molecules along an open-ended single-walled carbon nanotube (SWCNT) under the driving force of methane molecules. The methane molecules pull the water molecules from the inside of a SWCNT along the axial direction. The transport velocity of water molecules increases with increasing number of methane molecules, but decreases with increasing diameter of the SWCNT.     

Fabrication and characterization of single-walled carbon nanotube fiber for electronics applications

We present a customized technique to spin fiber from unique single-wall carbon nanotube (SWCNT) films utilizing a motorized pulling/twisting stage. The manufactured SWCNT fibers’ diameter ranged from 30 to 130 μm. Electrical measurements show fusing current of 1–200 mA – depending on the spun fiber’s diameter – which is close to the values known for copper wires with similar diameter. These results reveal that the fiber spinning process could retain most of the advantageous electrical properties of original nanotubes, and also indicate a good possibility for using these low cost, sustainable SWCNT fibers in electrical wiring applications.     

Fabrication and distribution characteristics of polyurethane/single-walled carbon nanotube composite with anisotropic structure

A polyurethane/single-walled carbon nanotube (SWCNT) composite with anisotropic structure is synthesized by two-step process. The effects of external force during the curing process of the composite as well as the tensile stress on the distribution of the SWCNTs in the matrix have been examined by using field-emission scanning electron microscope. The microstructure analysis results indicate that the different distributions of the SWCNTs in the matrix have appeared along two orthogonal directions for the composite samples.     

Comparison of double-walled with single-walled carbon nanotube electrodes by electrochemistry

Double-walled carbon nanotubes (DWCNTs) were selectively functionalised by treatment with concentrated nitric and sulphuric acid, resulting in carboxylated outer and pristine inner tube constituents. The functionalised DWCNTs were then incorporated into two types of pre-existing carbon nanotube (CNT) electrode platforms, and the performance of each was compared to single-walled carbon nanotubes (SWCNTs). To make the CNT electrode platforms DWCNTs were covalently bound to fluorinated tin oxide glass (FTO) or electrografted aminophenyl tether layers on silicon. The performance of single- compared to double-walled CNTs on FTO or silicon supported electrodes was then determined through electrochemical methods, using the redox probes, ferrocene and ruthenium hexaamine, respectively. The DWCNTs showed an improved heterogeneous rate constant. This improvement was attributed to the protection of the electronic properties of the inner wall of the DWCNT during the chemical modification and suggests that DWCNTs may offer a useful alternative to SWCNTs in future electronic devices.     

Micropatterning of single-walled carbon nanotube forest

In this work, high-aligned single-walled carbon nanotube (SWCNT) forest have been grown using a high-density plasma chemical vapor deposition technique (at room temperature) and patterned into micro-structures by photolithographic techniques, that are commonly used for silicon integrated circuit fabrication. The SWCNTs were obtained using pure methane plasma and iron as precursor material (seed). For the growth carbon SWCNT forest the process pressure was 15 mTorr, the RF power was 250 W and the total time of the deposition process was 3 h. The micropatterning processes of the SWCNT forest included conventional photolithography and magnetron sputtering for growing an iron layer (precursor material). In this situation, the iron layer is patterned and high-aligned SWCNTs are grown in the where iron is present, and DLC is formed in the regions where the iron precursor is not present. The results can be proven by Scanning Electronic Microscopy and Raman Spectroscopy. Thus, it is possible to fabricate SWCNT forest-based electronic and optoelectronic devices.     

Fabrication of single-walled carbon nanotube three-dimensional networks inside the pores of a porous silicon structure

Single-walled carbon nanotube (SWCNT) three-dimensional (3-D) networks were first fabricated in the pores of a porous silicon substrate using thermal decomposition of C₂H₂ at 800 °C. Catalyst nanoparticles were uniformly distributed on the inner wall surfaces of the pores using a dipping method combined with ultrasonication. SWCNTs were synthesized along the inner wall surface of the pores, and spanned it. The suspended SWCNTs inside the pores formed 3-D networks in the results of the chaotic overgrowth of SWCNTs in a confined space under thermal vibration, and van der Waals interactions between SWCNTs.     

Hybrid carbon source for single-walled carbon nanotube synthesis by aerosol CVD method

The conductivity enhancement of single-walled carbon nanotube (SWCNT) films was achieved by increasing the bundle length in an aerosol CVD synthesis method with the help of two carbon sources. Carbon monoxide provides carbon at temperatures below 900 °C, while ethylene takes over at higher temperatures. The significant decrease in the sheet resistance at the 90% transmittance was observed from 3500 to 7500 Ω/sq. for pure CO system via 1909 and 1709 Ω/sq. for CO–H₂ system to 291 and 358 Ω/sq. in the presence of C₂H₄ at 900 and 1100 °C, respectively. Doping the film with a gold chloride solution in acetonitrile allowed us to create the transparent conductive films with the sheet resistance as low as 73 Ω/sq. at a transmittance of 90%.     

Electrochemical capacitance of well-coated single-walled carbon nanotube with polyaniline composites

Well-coated single-walled carbon nanotube (SWNT) with polyaniline (PANI) composite electrodes with good uniformity for electrochemical capacitors are prepared by the polymerization of aniline containing well-dissolved SWNTs. The capacitance properties are investigated with cyclic voltammetry, charge-discharge tests and ac impedance spectroscopy. The composite electrode shows much higher specific capacitance, better power characteristics and is more promising for application in capacitor than pure PANI electrode. The effect and role of SWNT in the composite electrode are also discussed in detail.     

Surface oxidation of single-walled carbon nanotube paper with oxygen atoms

Single-walled carbon nanotube paper was surface oxidized with gaseous oxygen atoms produced by low-pressure: (1) vacuum UV (λ?=?104.8 and 106.7?nm) photo-oxidation and (2) downstream microwave plasma discharge of an Ar–O₂ mixture. X-ray photoelectron spectroscopy was used to detect the carbon- and oxygen-containing functional groups in the top 2–5?nm of the sample’s surface. Both methods produced a saturation level of ca. 12 at.% oxygen with the predominant formation of the epoxide/ether groups.     

Resist-assisted assembly of single-walled carbon nanotube devices with nanoscale precision

We report a novel resist-assisted dielectrophoresis method for single-walled carbon nanotube (SWCNT) assembly. It provides nanoscale control of the location, density, orientation and shape of individual SWCNTs. Sub-50 nm accuracy and a yield higher than 85% have been achieved. Using the method, we demonstrate suspended-body SWCNT field-effect transistors (FETs) with back-gate and sub-100 nm air-gap lateral-gate configurations. The suspended-body SWCNT FETs show excellent electrical characteristics with I_on/I_off ～ 10⁷, ultra-low off currents ～10^?14 A and small subthreshold swings. The technique contributes to the ultimate solution for bottom-up fabrication of a broad field of CNT-based devices, such as: complementary metal–oxide-semiconductor and nano-electrical–mechanical-system devices for sensing and radio-frequency applications. Moreover, the versatile method could be applied to the assembly of many other promising materials, such as: nanowires and graphene flakes.     

High-performance biosensors based on enzyme precipitate coating in gold nanoparticle-conjugated single-walled carbon nanotube network films

Single-walled carbon nanotube (SWCNT) network films with high network density were prepared by vacuum-filtering a suspension of SWCNTs, and used as a host of enzyme precipitate coating of glucose oxidase (EPC-GOx). EPC-GOx was fabricated into the SWCNT network films in a two-step process of enzyme precipitation and crosslinking. High GOx loading in a form of EPC expedited the generation of electrons while the good connectivity of conductive SWCNTs in the network structure increased the electron transfer rate. According to amperometric measurements, the sensitivities of GOx/SWCNT electrodes, governed by both generation and transfer of electrons, were significantly enhanced by filling up the open pores of SWCNT films with the EPC-GOx when compared to the approaches of covalent-attachment (CA) and enzyme coating (EC) with no step of enzyme precipitation. For example, the sensitivities of CA, EC and EPC-GOx were 0.039, 0.140, and 5.72 μA mM⁻¹, respectively. High sensitivity of EPC-GOx was maintained under iterative uses for 10 days. The deposition of gold nanoparticles into SWCNT films has resulted in high-performance glucose sensors with a remarkable sensitivity of 24.5 μA mM⁻¹, which can be explained by further expedited electron transfer due to deposited gold nanoparticles.     

Modification of fluorinated single-walled carbon nanotubes with aminosilane molecules

Single-walled carbon nanotubes (SWCNTs) modified with amino groups were prepared via chemical addition of fluorine on the carbon nanotube surface by plasma treatment. The amino termination makes possible to realize hybrid nanostructures made out of SWCNTs and alkoxy-silane (3′-(aminopropyl)tri-ethoxysilane (APTES)) molecules. The functionalization of the SWCNTs was evidenced by transmission electron microscopy, infrared spectroscopy and thermogravimetric measurements. It was found that the application of a dc electric field enhances the assembly of APTES modified SWCNTs into ordered films with rectifying diode behavior.     

Surfactant-free assembling of functionalized single-walled carbon nanotube buckypapers

The electrical and textural properties of single-walled carbon nanotube buckypapers were tunned through chemical functionalization processes. Single-walled carbon nanotubes (SWCNTs) were covalently functionalized with three different chemical groups: Carboxylic acids (-COOH), benzylamine (-Ph-CH₂-NH₂), and perfluorooctylaniline (-Ph-(CF₂)₇-CF₃). Functionalized SWCNTs were dispersed in water or dimethylformamide (DMF) by sonication treatments without the addition of surfactants or polymers. Carbon nanotube sheets (buckypapers) were prepared by vacuum filtration of the functionalized SWCNT dispersions. The electrical conductivity, textural properties, and processability of the functionalized buckypapers were studied in terms of SWCNT purity, functionalization, and assembling conditions. Carboxylated buckypapers demonstrated very low specific surface areas (< 1 m²/g) and roughness factor (R_a = 14 nm), while aminated and fluorinated buckypapers exhibited roughness factors of around 70 nm and specific surface areas of 160-180 m²/g. Electrical conductivity for carboxylated buckypapers was higher than for as-grown SWCNTs, but for aminated and fluorinated SWCNTs it was lower than for as-grown SWCNTs. This could be interpreted as a chemical inhibition of metallic SWCNTs due to the specificity of the diazonium salts reaction used to prepare the aminated and fluorinated SWCNTs. The utilization of high purity as-grown SWCNTs positively influenced the mechanical characteristics and the electrical conductivity of functionalized buckypapers.     

Improvement of the mechanical properties of single-walled carbon nanotube networks by carbon plasma coatings

Carbon vacuum arc was used to deposit 5–25 nm thick carbon coatings on single-walled carbon nanotube (SWCNT) networks. The SWCNT bundles thus embedded in conformal coatings maintained their optical transparency and electrical conductivity. Sheet resistances of the networks were measured during the vacuum arc deposition, revealing initially a 100-fold increase, followed by significant recovery after exposing the samples to an ambient atmosphere. Nanoindentation measurements revealed improved elasticity of the network after applying the carbon coating. Pristine SWCNT networks were easily deformed permanently, but a 20 nm carbon coating strengthened the nanostructure, resulting in a fully elastic recovery from a 20 μN load applied with a Berkovich tip. In nano-wear tests on selected areas, the coated SWCNT maintained its networking integrity after two passes raster scan at loads up to 25 μN. On the other hand, the pristine networks were badly damaged under a 10 μN scan load and completely displaced under 25 μN. Raman and electron energy loss spectroscopies indicated the carbon coating on bundles to be mainly sp² bonded. Finite element modeling suggests that the low content of sp³ bonds may be due to heating by the intense ion flux during the plasma pulse.     

Growth of novel carbon phases by methane infiltration of free-standing single-walled carbon nanotube films

High-temperature methane infiltration of thin, free-standing films of acid-treated single-walled carbon nanotubes (SWCNT) has been studied by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. In the early stages of infiltration, carbon nuclei form predominantly at SWCNT bundle intersections. Further growth proceeds via the formation of graphite nanosheets - without further influence of the nanotube support. Both sheet edges and their structural imperfections act as reaction centers for subsequent deposition, likely giving rise to autocatalytic deposition kinetics. In contrast, infiltration with a H₂:CH₄ (24:1) mixture leads to the reductive activation of residual Ni/Co impurities embedded in the precursor SWCNT-felt. This is associated with a different predominant carbon deposition mode in which multiwalled carbon nanotubes grow out from the substrate.     

聚砜/改性碳纳米管复合膜的制备及亲水性能

利用浸没沉淀相转化法,以聚砜(PSF)为膜材料,羧基化碳纳米管(MWCNTs-COOH)为添加剂,聚乙烯吡咯烷酮(PVP)为致孔剂,N,N-二甲基乙酰胺(DMAc)为溶剂,制备了聚砜/多壁碳纳米管复合膜,系统研究了制备复合膜时碳纳米管的添加量、预挥发时间以及凝固浴组成对其结构和性能的影响。实验结果表明,添加MWCNTs-COOH后,复合膜的亲水性能和抗污性能显著提高,同时复合膜的力学性能也明显增强。复合膜的 SEM 照片显示,随预挥发时间的延长和凝固浴中DMAc 质量分数的增加,复合膜断面由指状孔结构向海绵状孔结构过渡;复合膜的水通量下降,截留率上升。