Super-durable ultralong carbon nanotubes

Fatigue resistance is a key property of the service lifetime of structural materials. Carbon nanotubes (CNTs) are one of the strongest materials ever discovered, but measuring their fatigue resistance is a challenge because of their size and the lack of effective measurement methods for such small samples. We developed a noncontact acoustic resonance test system for investigating the fatigue behavior of centimeter-long individual CNTs. We found that CNTs have excellent fatigue resistance, which is dependent on temperature, and that the time to fatigue fracture of CNTs is dominated by the time to creation of the first defect.

A New Route to Enhance the Packing Density of Buckypaper for Superior Piezoresistive Sensor Characteristics

Transforming individual carbon nanotubes (CNTs) into bulk form is necessary for the utilization of the extraordinary properties of CNTs in sensor applications. Individual CNTs are randomly arranged when transformed into the bulk structure in the form of buckypaper. The random arrangement has many pores among individual CNTs, which can be treated as gaps or defects contributing to the degradation of CNT properties in the bulk form. A novel technique of filling these gaps is successfully developed in this study and termed as a gap-filling technique (GFT). The GFT is implemented on SWCNT-based buckypaper in which the pores are filled through small-size MWCNTs, resulting in a ~45.9% improvement in packing density. The GFT is validated through the analysis of packing density along with characterization and surface morphological study of buckypaper using Raman spectrum, particle size analysis, scanning electron microscopy, atomic force microscopy and optical microscopy. The sensor characteristics parameters of buckypaper are investigated using a dynamic mechanical analyzer attached with a digital multimeter. The percentage improvement in the electrical conductivity, tensile gauge factor, tensile strength and failure strain of a GFT-implemented buckypaper sensor are calculated as 4.11 ± 0.61, 44.81 ± 1.72, 49.82 ± 8.21 and 113.36 ± 28.74, respectively.

Dynamic Conductivity and Two-Dimensional Plasmons in Lateral CNT Networks

We study theoretically the carrier transport and the plasmonic phenomena in the gated structures with dense lateral carbon nanotube (CNT) networks (CNT “felt”) placed between the highly-conducting slot line electrodes. The CNT networks under consideration consist of a mixture of semiconducting and metallic CNTs. We find the dispersion relations for the two-dimensional plasmons, associated with the collective self-consisted motion of electrons in the individual CNTs, propagating along the electrodes as functions of the net electron density (gate voltage), relative fraction of the semiconducting and metallic CNTs, and the spacing between the electrodes. In a wide range of parameters, the characteristic plasmonic frequencies can fall in the terahertz (THz) range. The structures with lateral CNT networks can used in different THz devices.

On Adhesive and Buckling Instabilities in the Mechanics of Carbon Nanotubes Bundles

Many recently synthesized materials feature aligned arrays or bundles of carbon nanotubes (CNTs) whose mechanical properties are partially determined by the van der Waals interactions between adjacent tubes. Of particular interest in this paper are instances where the resulting interaction between a pair of CNTs often produces a forklike structure. The mechanical properties of this structure are noticeably different from those for isolated individual CNTs. In particular, while one anticipates buckling phenomena in the forked structure, an adhesion instability may also be present. New criteria for buckling and adhesion instabilities in forklike structures are presented in this paper. The criteria are illuminated with a bifurcation analyses of the response of the forklike structure to applied compressive and shear loadings.

Fabrication and Properties of Macroscopic Carbon Nanotube Assemblies Transforming from Aligned Nanotubes

Macroscale assemblies of well-aligned carbon nanotubes (CNTs) can inherit intrinsic properties from individual CNTs and at the same time ease handling difficulties that occur at nanometer scale when dealing with individual CNTs. Herein, simple fabrication processes are introduced to produce a variety of macroscale CNT assemblies, including well-aligned CNT bundles, CNT films, and CNT fibers, from the same starting material: spinnable CNT arrays. The electrical and mechanical properties of the as-prepared CNT assemblies have been investigated and compared. It is found that CNT films show an electrical conductivity of 145~250 S cm−1which is comparable to CNT fibers, but two orders magnitude higher than that of conventional Bucky paper. CNT fibers exhibit diameter dependent tensile strength which is mainly attributed to the nonuniform twisting along the radial direction of fibers.

Characterization of Si–C Covalent Bonding Fabricated between Single Carbon Nanotube and Si Substrate

The SiC covalent bonding between Carbon nanotube and Si substrate was fabricated by thermal vapor deposition using photolithography and gas blowing technology. Scanning electron microscopy, micro-Raman imaging and spectroscopy were used to investigate the interaction of individual CNTs and Si substrate. The characterization results showed that covalent bonds were formed between certain CNTs and Si substrate. Moreover, the reasons for the fabrication of SiC covalent bonding between CNTs and Si substrate were also proposed.

The Carbon Nanotube Fibers for Optoelectric Conversion and Energy Storage

This review summarizes recent studies on carbon nanotube (CNT) fibers for weavable device of optoelectric conversion and energy storage. The intrinsic properties of individual CNTs make the CNT fibers ideal candidates for optoelectric conversion and energy storage. Many potential applications such as solar cell, supercapacitor, and lithium ion battery have been envisaged. The recent advancement in CNT fibers for optoelectric conversion and energy storage and the current challenge including low energy conversion efficiency and low stability and future direction of the energy fiber have been finally summarized in this paper.

Nickel Oxide Coated on Pretreated MWCNTs as an Electrode for Supercapacitor

Nickel oxide/carbon nanotubes (NiO/CNTs) composite materials for supercapacitor are prepared by chemically depositing of nickel hydroxide onto CNTs pretreated by ultrasonication and followed by thermal annealing at 200-300°C. A series of NiO/CNTs composites with different weight ratios of CNTs and different annealing temperature are synthesized via the same route. The scanning electron microscope (SEM) images show that the nucleation of the nickel hydroxide formed on the outer walls of CNTs due to ultrasonic cavitations, and then nickel oxide coated uniformly on the outer surface of the individual CNTs after thermal annealing. The NiO/CNTs electrode presents a maximum specific capacitance of 254 F/g as well as a good cycle life in 2 M KOH electrolyte. The good electrochemical characteristics of NiO/CNTs composite can be attributed to the three-dimensionally interconnected nanotubular structure with a thin film of electroactive materials.

Fabrication of Microscale Carbon Nanotube Fibers

Carbon nanotubes (CNTs) have excellent mechanical, chemical, and electronic properties, but realizing these excellences in practical applications needs to assemble individual CNTs into larger-scale products. Recently, CNT fibers demonstrate the potential of retaining CNT's superior properties at macroscale level. High-performance CNT fibers have been widely obtained by several fabrication approaches. Here in this paper, we review several key spinning techniques including surfactant-based coagulation spinning, liquid-crystal-based solution spinning, spinning from vertical-aligned CNT arrays, and spinning from CNT aerogel. The method, principle, limitations, and recent progress of each technique have been addressed, and the fiber properties and their dependences on spinning parameters are also discussed.

ELECTRON BEAM INDUCED CARBONACEOUS DEPOSITION AS A LOCAL DIELECTRIC FOR CNT CIRCUITS

Evaluating the electrical nature of carbon nanotubes (CNTs) from a collection requires establishing electrical contacts across individual CNTs lying on a dielectric layer. In this work, it is shown how a dielectric layer may be inserted underneath a chosen CNT. This has been accomplished by the electron beam induced carbonaceous deposition process in the presence of moisture and residual hydrocarbons present in the SEM chamber. When performed at a CNT location on a Si substrate, the CNT instead of getting buried underneath is found to be lifted on top of the carbonaceous platform, as if due to nonwetting nature of CNT surface. By fixing one end of the CNT on the Ag/Si substrate using a Pt deposit and lifting rest of the length to lie on a carbonaceous platform, the I–V data from nanotubes of varying resistances have been collected using conducting AFM. The chosen nanotubes have also been examined by Raman measurements. The method is particularly useful while working with a random collection of nanotubes resulting from a chemical process.