Synthesis of large arrays of well-aligned carbon nanotubes on glass

Effects of the electrical conductivity and orientation of silicon substrate on the synthesis of multi-walled carbon nanotubes by thermal chemical vapor deposition

We studied the effects of the electrical conductivity and orientation of silicon substrate on both catalytic Fe thin film and the structure and morphology of multi-walled carbon nanotube (MWNT) grown by low-pressure chemical vapor deposition. Both p-type Si(100) and Si(111) substrates with three different doping concentrations (high, low, undoped) were used to evaluate the formation of catalytic nanoparticles and the growth of MWNTs. The morphology of catalytic nanoparticles such as size and density was characterized by field-emission scanning electron microscopy, Cs-corrected energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Structural characteristics of MWNTs grown on different combinations of silicon substrate orientation and electrical conductivities (σ) were also systematically analyzed. Based on the experimental results, growth modes of MWNTs could be controlled by choosing an appropriate combination of σ and orientation of Si substrates.

Functionalization of vertically aligned carbon nanotubes

This review focuses and summarizes recent studies on the functionalization of carbon nanotubes oriented perpendicularly to their substrate, so-called vertically aligned carbon nanotubes (VA-CNTs). The intrinsic properties of individual nanotubes make the VA-CNTs ideal candidates for integration in a wide range of devices, and many potential applications have been envisaged. These applications can benefit from the unidirectional alignment of the nanotubes, the large surface area, the high carbon purity, the outstanding electrical conductivity, and the uniformly long length. However, practical uses of VA-CNTs are limited by their surface characteristics, which must be often modified in order to meet the specificity of each particular application. The proposed approaches are based on the chemical modifications of the surface by functionalization (grafting of functional chemical groups, decoration with metal particles or wrapping of polymers) to bring new properties or to improve the interactions between the VA-CNTs and their environment while maintaining the alignment of CNTs.

Supramolecular glucose oxidase-SWNT conjugates formed by ultrasonication: effect of tube length, functionalization and processing time

BACKGROUND

Generation-3 (Gen-3) biosensors and advanced enzyme biofuel cells will benefit from direct electron transfer to oxidoreductases facilitated by single-walled carbon nanotubes (SWNTs).

METHODS

Supramolecular conjugates of SWNT-glucose oxidase (GOx-SWNT) were produced via ultrasonic processing. Using a Plackett-Burman experimental design to investigate the process of tip ultrasonication (23 kHz), conjugate formation was investigated as a function of ultrasonication times (0, 5, 60 min) and functionalized SWNTs of various tube lengths (SWNT-X-L), (X = -OH or -COOH and L = 3.0 μm, 7.5 μm).

RESULTS

Enzyme activity (KM, kcat, kcat/KM, vmax and n (the Hill parameter)) of pGOx (pristine), sGOx (sonicated) and GOx-SWNT-X-L revealed that sonication of any duration increased both KM and kcat of GOx but did not change kcat/KM. Functionalized tubes had the most dramatic effect, reducing both KM and kcat and reducing kcat/KM. UV-vis spectra over the range of 300 to 550 nm of native enzyme-bound FAD (λmax at 381 and 452 nm) or the blue-shifted solvated FAD of the denatured enzyme (λmax at 377 and 448 nm) revealed that ultrasonication up to 60 minutes had no influence on spectral characteristics of FAD but that the longer SWNTs caused some partial denaturation leading to egress of FAD. Circular dichroism spectral analysis of the 2° structure showed that sonication of any duration caused enrichment in the α-helical content at the sacrifice of the unordered sequences in GOx while the presence of SWNTs, regardless of length and/or functionality, reduced the β-sheet content of pristine GOx. Surface profiling by white light interferometry revealed that ultrasonication produced some aggregation of GOx and that GOx effectively debundled the SWNT.

CONCLUSIONS

Supramolecular conjugates formed from shorter, -OH functionalized SWNTs using longer sonication times (60 min) gave the most favored combination for forming bioactive conjugates.

Scalable nano-bioprobes with sub-cellular resolution for cell detection

Here we present a carbon nanotube based device to noninvasively and quickly detect mobile single cells with the potential to maintain a high degree of spatial resolution. The device utilizes standard complementary metal oxide semiconductor (CMOS) technologies for fabrication, allowing it to be easily scalable (down to a few nanometers). Nanotubes are deposited using electrophoresis after fabrication in order to maintain CMOS compatibility. The devices are spaced by 6 μm which is the same size or smaller than a single cell. To demonstrate its capability to detect cells, we performed impedance spectroscopy on mobile human embryonic kidney (HEK) cells, neurons cells from mice, and yeast cells (S. pombe). Measurements were performed with and without cells and with and without nanotubes. Nanotubes were found to be crucial to successfully detect the presence of cells. The devices are also able to distinguish between cells with different characteristics.

Carbon Nanotubes: A Review on Structure and Their Interaction with Proteins

Carbon nanotubes (CNTs) are allotropes of carbon with a nanostructure that can have a length-to-diameter ratio greater than 1,000,000. Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, and chemical vapor deposition. Developments in the past few years have illustrated the potentially revolutionizing impact of nanomaterials, especially in biomedical imaging, drug delivery, biosensing, and the design of functional nanocomposites. Methods to effectively interface proteins with nanomaterials for realizing these applications continue to evolve. The high surface-to-volume ratio offered by nanoparticles resulted in the concentration of the immobilized entity being considerably higher than that afforded by other materials. There has also been an increasing interest in understanding the influence of nanomaterials on the structure and function of proteins. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. With the growing attention paid to cascade enzymatic reaction, it is possible that multienzyme coimmobilization would be one of the next goals in the future. In this paper, we focus on advances in methodology for enzyme immobilization on carbon nanotubes.

Carbon nanotube based high resolution holograms

Carbon nanotubes are used as the smallest possible scattering element for diffracting light in a highly controlled manner to produce a 2D image. An array of carbon nanotubes is elegantly patterned to produce a high resolution hologram. In response to incident light on the hologram, a high contrast and wide field of view CAMBRIDGE image is produced.

Electronic and optoelectronic nano-devices based on carbon nanotubes

The discovery and understanding of nanoscale phenomena and the assembly of nanostructures into different devices are among the most promising fields of material science research. In this scenario, carbon nanostructures have a special role since, in having only one chemical element, they allow physical properties to be calculated with high precision for comparison with experiment. Carbon nanostructures, and carbon nanotubes (CNTs) in particular, have such remarkable electronic and structural properties that they are used as active building blocks for a large variety of nanoscale devices. We review here the latest advances in research involving carbon nanotubes as active components in electronic and optoelectronic nano-devices. Opportunities for future research are also identified.

Formation of gradient multiwalled carbon nanotube stripe patterns by using evaporation-induced self-assembly

Gradient stripe patterns of multiwalled carbon nanotubes (MWCNTs) with remarkable regularity over large areas were fabricated by using evaporation-induced self-assembly technique. In this method, a glass coverslip was inclinedly immersed into a suspension of MWCNTs in dichloroethane. By controlling the solvent evaporation temperature, well-defined gradient stripes were formed at the air-solvent-substrate contact line. The effects of several experimental parameters, such as the substrate tilt angle, concentration of MWCNTs, and evaporation temperature, on the regularity of stripes were discussed. A possible stripe formation process was described as a negative feedback of MWCNT concentration caused by a concavely curved shape of the meniscus. Additionally, the strips of MWCNTs on Si/SiO(2) substrate were directly used to fabricate field-effect transistor (FET) devices. The electrical properties of the MWCNT-FET devices were also investigated.

Variety of Bio-Hydrocarbon Precursors for the Synthesis of Carbon Nanotubes

In this work, we have synthesized carbon nanotubes (CNT) using different bio-hydrocarbon precursors namely palm, olive, coconut, corn and sesame oils. Prior to the synthesis process, thermogravimetric analysis (TGA) characterization was performed on the carbon precursors to facilitate the optimization procedures of CNT and reach maximum yield and higher quality CNT. The CNT arrays were deposited on a silicon substrate by thermal catalytic decomposition of the precursor using 5.33 wt% ferrocene. The synthesis was carried out at 750 °C for 60 min under argon ambient. The samples were characterized using field emission scanning electron microscopy, micro-Raman spectroscopy and TGA analysis. The difference in oil density resulted in different quality and tube diameter of CNT produced. Among all, the CNT synthesized from coconut oil can be considered as the best bio-hydrocarbon precursor for higher quality (ID/IG ~0.62) and good purity (81.95 %) CNT.

A critical review of glucose biosensors based on carbon nanomaterials: carbon nanotubes and graphene

There has been an explosion of research into the physical and chemical properties of carbon-based nanomaterials, since the discovery of carbon nanotubes (CNTs) by Iijima in 1991. Carbon nanomaterials offer unique advantages in several areas, like high surface-volume ratio, high electrical conductivity, chemical stability and strong mechanical strength, and are thus frequently being incorporated into sensing elements. Carbon nanomaterial-based sensors generally have higher sensitivities and a lower detection limit than conventional ones. In this review, a brief history of glucose biosensors is firstly presented. The carbon nanotube and grapheme-based biosensors, are introduced in Sections 3 and 4, respectively, which cover synthesis methods, up-to-date sensing approaches and nonenzymatic hybrid sensors. Finally, we briefly outline the current status and future direction for carbon nanomaterials to be used in the sensing area.

Ultrasensitive chemical detection using a nanocoax sensor

We report on the design, fabrication, and performance of a nanoporous, coaxial array capacitive detector for highly sensitive chemical detection. Composed of an array of vertically aligned nanoscale coaxial electrodes constructed with porous dielectric coax annuli around carbon nanotube cores, this sensor is shown to achieve parts per billion level detection sensitivity, at room temperature, to a broad class of organic molecules. The nanoscale, 3D architecture and microscale array pitch of the sensor enable rapid access of target molecules and chip-based multiplexing capabilities, respectively.

Carbon nanomaterials for advanced energy conversion and storage

It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Influence of Dispersion and Alignment of Nanotubes on the Strength and Elasticity of Carbon Nanotubes Reinforced Composites

In this paper, the effective strength and elastic properties of carbon nanotube reinforced composites are evaluated using a representative volume element with a number of carbon nanotubes embedded in the matrix. This concept is used to predict the mechanical properties of multiple, unidirectional, aligned, and also randomly dispersed carbon nanotube reinforced composites. To characterize these nanocomposites, a continuum model has been developed for large-scale analysis. The effective Young’s and shear moduli of the composites are determined using finite element analysis under the effect of elastic deformation. The role of design parameters like length and volume fraction of carbon nanotubes, tensile and shear strength as well as type of loading conditions are analyzed for multiple carbon nanotubes based composites. The discontinuous and continuous types of carbon nanotubes, with aligned and random distribution, are evaluated. The results show that the continuous and aligned carbon nanotubes produce the largest tensile modulus, compared to the discontinuous and aligned as well as discontinuous and randomly oriented carbon nanotubes along the longitudinal direction.

Effect of iron concentration on the growth of carbon nanotubes on clay surface

The successful growth of carbon nanotubes (CNTs) on montmorillonite (MMT) precursors treated with different concentrations of ferric nitrate at 50 °C (MMT(Fe)-50) and 100 °C (MMT(Fe)-100) was achieved via the in situ chemical vapor deposition (CVD) of acetylene. The as-obtained MMT-CNTs composites were characterized using X-ray diffraction, inductively coupled plasma emission spectrometry, scanning electron microscopy, and transmission electron microscopy. All Fe(3+) ions were intercalated into the MMT interlayers at either 50 or 100 °C in the case of [Fe(3+)]/[clay] = 1. However, the iron content in MMT(Fe)-100 increased rapidly with the amount of ferric nitrate added, whereas the iron content in MMT(Fe)-50 did not exhibit significant changes. On the other hand, the physical and chemical adsorption of Fe(3+) onto the MMT surface was believed to be responsible for the great diversity of iron contents in MMT(Fe)-50 and MMT(Fe)-100 at the same [Fe(3+)]/[clay] ratios. Moreover, the CNT yield showed variation similar to the iron content because the CNTs yield depends primarily on the amount of catalyst available. The CNTs embedded onto MMT(Fe)-100 exhibited narrower diameter distributions than those on the MMT(Fe)-50 precursors, with more CNTs with diameters less than 50 nm on the former. It is suggested that a porous structure with many pores formed by iron species and MMT laminas is related to the morphology and structure of CNTs embedded on the surface of MMT.

High Voltage Electrophoretic Deposition of Aligned Nanoforests for Scalable Nanomanufacturing of Electrochemical Energy Storage Devices

High voltage electrophoretic deposition (HVEPD) has been used to obtain forests of aligned multi-walled carbon nanotubes (MWCNTs) on long strips of flexible, conductive substrates. Successful design and integration of a continuous HVEPD setup has enabled scalable fabrication of electrodes for electrochemical energy storage. The mechanism of continuous HVEPD has been investigated to ensure appropriate alignment. Well-aligned forests of MWCNTs were obtained using a conductive holding layer which helped reduce internal resistance and enhance the electrochemical performance of the electrodes.

A new ultrahigh-speed method for the preparation of nanofibers containing living cells: a bridge towards industrial bioengineering applications

A novel method is reported of producing nanofibers/nanotubes (measuring from tens of nanometres to several hundreds of nanometres) containing living cells, mechanically and with ultrahigh speed and at low cost. High-pressure gas was used to extrude viscous precursors through a spray with micron-sized holes into air. The sprayed micro-sized droplets had high velocity and were continuously elongated into uniform nanofibers/nanotubes in a temperature field during their flight. We demonstrated that the throughput of this spinning method to fabricate nanofibers/nanotubes from an individual setup could be as high as 10 g s(-1). A possible mechanism for this extrusion method was proposed based on flow mechanics and the experimental results. Additionally, it was shown that the new method could be used to directly prepare nanofibers containing living cells. It was demonstrated that the living cells with high survival rate can be used in bioengineering.

Carbon Nanofiber Synthesis within 3-Dimensional Sintered Nickel Microfibrous Matrices: Optimization of Synthesis Conditions

This study focuses on the process of optimization for carbon nanofiber synthesis at the exterior and the interior of 3-dimensional sintered nickel microfibrous networks. Synthesis of carbon nanofibers (CNF) by catalytic decomposition of acetylene (ethyne) was conducted at atmospheric pressure and short reaction times (10 min). Two factors evaluated during the study were (a) CNF quality (observed by SEM and Raman spectroscopy) and (b) rate of reaction (gravimetrically measured carbon yield). Independent optimization variables included redox faceting pretreatment of nickel, synthesis temperature, and gas composition. Faceting resulted in an 8-fold increase in the carbon yield compared to an untreated substrate. Synthesis with varying levels of hydrogen maximized the carbon yield (9.31 mg C/cm2catalyst). The quality of CNF was enhanced via a reduction in amorphous carbon that resulted from the addition of 20% ammonia. Optimized growth conditions that led to high rates of CNF deposition preferentially deposited this carbon at the exterior layer of the nickel microfibrous networks (570°C, 78% H2, 20% NH3, 2% C2H2, faceted Ni.). CNF growth within the 3-dimensional nickel networks was accomplished at the conditions selected to lower the gravimetric reaction rate (470°C, 10% H2, 88% N2, 2% C2H2, nonfaceted Ni).

ENHANCED GROWTH OF CARBON NANOTUBES ON SELECTED AREA USING AN AQUEOUS CATALYST

This paper describes the work carried out to produce patterned arrays of multi-wall carbon nanotubes (MWCNTs) using a liquid catalyst and a microwave plasma technique. By this method we can control the CNT growth on selective sites by engineering the substrate surface and yet maintain a very high CNT growth rate (~10 μm per minute). The catalyst is made by hydrochloric acid solution which contains high concentration of ferromagnetic metal ions. Upon dispersing the liquid catalyst on a silicon nitride substrate containing exposed silicon patterns, the catalyst only precipitates on the hydrophilic sites (i.e. silicon surface). After performing the CNT growth in a microwave reactor with CH 4/ N 2 mixture plasma, nanotubes can only be found to grow on exposed silicon surface instead of the main area covered by silicon nitride. This method allows us to produce multi-wall carbon nanotubes on the selective area as in the silicon trenches, concavities and thin film edges.

SYNTHESIS OF 2D QUASI-ALIGNED MULTIWALLED CARBON NANOTUBES BY CATALYTIC CHEMICAL VAPOR DEPOSITION METHOD

Alignment or patterning of carbon nanotubes (CNTs) is particularly important for fabricating functional devices such as field emitters, nanophotonics, nanoelectronics, and ultrahydrophobic materials. This work reports on the synthesis of 2D quasi-aligned carbon nanotube bundles by catalytic chemical vapor deposition (CCVD) method using a series of catalysts and a study of their performance in a nutshell.

The evolution of carbon nanotubes during their growth by plasma enhanced chemical vapor deposition

During the growth of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD), plasma etching is the crucial factor that determines the growth mode and alignment of the CNTs. Focusing on a thin catalyst coating (Ni = 5 nm), this study finds that the CNT growth by PECVD goes through three stages from randomly entangled (I-CNTs) to partially aligned (II-CNTs) to fully aligned (III-CNTs). The I-CNTs and II-CNTs are mostly etched away by the plasma as time goes by ending up with III-CNTs as the only product when growth time is long enough. However, with a thickness of the catalyst coating of 10 nm or more, neither I-CNTs nor II-CNTs are produced, but III-CNTs are the only type of CNTs grown during the whole growth process. During the growth of III-CNTs, the catalyst particles (Ni) stay on the tips of each of the aligned CNTs and act as a 'safety helmet' to protect the CNTs from plasma ion bombardment. On the other hand, it is also the plasma that limits the growth of III-CNTs, since the plasma eventually etches all the catalytic particles out and stops the growth.

Applications of nanoscale carbon-based materials in heavy metal sensing and detection

This article reviews applications of nanoscale carbon-based materials in heavy metal sensing and detection. These materials, including single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanofibers among others, have unique and tunable properties enabling applications in various fields spanning from health, electronics and the environment sector. Specifically, we highlight the unique properties of these materials that enable their applications in the sorption and preconcentration of heavy metals ions prior to detection by spectroscopic, chromatographic and electrochemical techniques. We also discuss their distinct properties that enable them to be used as novel electrode materials in sensing and detection. The fabrication and modification of these electrodes is discussed in detail and their applications in various electrochemical techniques such as voltammetric stripping analysis, potentiometric stripping analysis, field effect transistor-based devices and electrical impedance are critically reviewed. Perspectives and futures trends in the use of these materials in heavy metal sensing and detection will also be highlighted.

Role of ion flux on alignment of carbon nanofibers synthesized by DC plasma on transparent insulating substrates

A key factor to the implementation of devices with vertically aligned carbon nanofibers (VACNFs) is fundamental understanding of how to control fluctuations in the growth direction of the fibers. Here we demonstrate synthesis of VACNF on transparent and insulating substrates by continuous direct current (DC) plasma for realization of cellular interface suitable for transmission optical microscopy. To maintain continuous glow discharge above the substrate, a metal grid electrode layer (Cr) was deposited over silica with windows of exposed silica ranging in size from 200 μm to 1 mm. This electrode geometry allows for synthesis of VACNFs even within an insulating window. This observation and the observed trends in the alignment of nanofibers in the vicinity of grid electrodes have indicated that the alignment does not correspond to the direction of the electric field at the substrate level, contrary to previously proposed alignment mechanism. Computational modeling of the plasma with this grid cathode geometry has shown that nanofiber alignment trends follow calculated ion flux direction rather than electrical field. The new proposed alignment mechanism is that ion sputtering of the carbon film on a catalyst particle defines the growth direction of the nanofibers. With this development, fiber growth direction can be better manipulated through changes in ionic flux direction, opening the possibility for growth of nanofibers on substrates with unique geometries.

Carbon nanostructures for orthopedic medical applications

Carbon nanostructures (including carbon nanofibers, nanostructured diamond, fullerene materials and so forth) possess extraordinary physiochemical, mechanical and electrical properties attractive to bioengineers and medical researchers. In the past decade, numerous developments towards the fabrication and biological studies of carbon nanostructures have provided opportunities to improve orthopedic applications. Therefore, the aim of this article is to provide an up-to-date review on carbon nanostructure advances in orthopedic research. Orthopedic medical device applications of carbon nanotubes/carbon nanofibers and nanostructured diamond (including particulate nanodiamond and nanocrystalline diamond coatings) are emphasized here along with other carbon nanostructures that have promising potential. In addition, widely used fabrication techniques for producing carbon nanostructures in both the laboratory and in industry are briefly introduced. In conclusion, carbon nanostructures have demonstrated tremendous promise for orthopedic medical device applications to date, and although some safety, reliability and durability issues related to the manufacturing and implantation of carbon nanomaterials remain, their future is bright.

Carbon diffusion from methane into walls of carbon nanotube through structurally and compositionally modified iron catalyst

To understand diffusion processes occurring inside Fe catalysts during multiwall carbon nanotube (MWCNT) growth, catalysts were studied using atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Nanotube walls emanate from structurally modified and chemically complex catalysts that consist of cementite and a 5 nm amorphous FeOx cap separated by a 2-3 nm thick carbon-rich region that also contains Fe and O (a-C:FexOy). Nonuniform distribution of carbon atoms throughout the catalyst base reveals that carbon molecules from the gas phase decompose near the catalyst multisection junction, where the MWCNT walls terminate. Formation of the a-C:FexOy region provides the essential carbon source for MWCNT growth. Two different carbon diffusion mechanisms are responsible for the growth of the inner and outer walls of each MWCNT.

Time-dependent contact behavior between diamond and a CNT turf

The elastic and adhesive properties of nominally vertically aligned carbon nanotube (CNT) turfs have been measured using nanoindentation. The perceived stiffness of a CNT turf is dependent on the unloading rate, which decreases at slower unloading rates. Depth-controlled nanoindentation was used to examine adhesion effects. Adhesive loads between the turf and the probe tip increased as the time the tip is in contact with the turf increased. As these effects could be from either more tubes coming into contact with the tip due to relaxation and motion of CNTs relative to one another or each tube in contact increasing its adhesive behavior and sub-contact stiffness due to tube-tube interactions within the turf, electrical resistance measurements during nanoindentation were carried out. When the tip is held at a fixed nominal depth, the current remains constant while the contact load decreases, suggesting the number of tubes in contact with the tip stays constant with time while the relaxation mechanisms in the turf occur at positions lower than the contact surface. These observations, in conjunction with in situ TEM compression test of CNT arrays, are used to describe the relative effects the various length and time scales may have on the perceived properties measured during experiments, including elastic modulus and adhesion for gecko-like dry adhesives.

Carbon nanotube mass production: principles and processes

Our society requires new materials for a sustainable future, and carbon nanotubes (CNTs) are among the most important advanced materials. This Review describes the state-of-the-art of CNT synthesis, with a focus on their mass-production in industry. At the nanoscale, the production of CNTs involves the self-assembly of carbon atoms into a one-dimensional tubular structure. We describe how this synthesis can be achieved on the macroscopic scale in processes akin to the continuous tonne-scale mass production of chemical products in the modern chemical industry. Our overview includes discussions on processing methods for high-purity CNTs, and the handling of heat and mass transfer problems. Manufacturing strategies for agglomerated and aligned single-/multiwalled CNTs are used as examples of the engineering science of CNT production, which includes an understanding of their growth mechanism, agglomeration mechanism, reactor design, and process intensification. We aim to provide guidelines for the production and commercialization of CNTs. Although CNTs can now be produced on the tonne scale, knowledge of the growth mechanism at the atomic scale, the relationship between CNT structure and application, and scale-up of the production of CNTs with specific chirality are still inadequate. A multidisciplinary approach is a prerequisite for the sustainable development of the CNT industry.

Enhanced Electron Transfer Rates by AC Voltammetry for Ferrocenes Attached to the End of Embedded Carbon Nanofiber Nanoelectrode Arrays

The effect of the interior structure of carbon nanomaterials on their electrochemical properties is not well understood. We report here the electron transfer rate (ETR) of ferrocene (Fc) molecules covalently attached to the exposed end of carbon nanofibers (CNFs) in an embedded nanoelectrode array. The ETR in normal DC voltammetry was found to be limited by the conical graphitic stacking structure interior of CNFs. AC voltammetry, however, can cope with this intrinsic materials property and provide over 100 times higher ETR, likely by a new capacitive pathway. This provides a new method for high-performance electroanalysis using CNF nanoelectrodes.