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Directly growing vertically aligned carbon nanotube arrays (VACNTs) on conductive substrates has shown great potential in a wide variety of applications. Among the various substrates, stainless steel (SS) possesses the advantageous features of wide availability, diverse compositions, and Fe containing, all of which are favorable for direct use as a low-cost and efficient catalytic substrate for VACNT growth. However, it is still unachieved to grow high-density VACNTs on SS in a facile way due to the lack of effective engineering strategies on the SS surface. Herein, we demonstrate a facile but efficient method to grow dense and highly VACNTs on an SS mesh by simply etching the SS mesh with an optimized HCl solution. Experimental results show that the etching can remove the chromium-rich passive layer and create highly active sites for chemical vapor deposition. In addition, it is revealed that the presence of the high-melting element of Mo in SS 316 is essential for prolonging the lifetime of active sites. Compared to the case on the SS 304 without Mo element, the VACNTs grown on SS 316 exhibit a higher purity, better alignment, higher degree of graphitization, and more importantly, large height of 80 μm. [ABSTRACT FROM AUTHOR]

A simple chemical vapor deposition technique at atmospheric pressure (APCVD) is adopted to synthesize the aligned arrays of functionalized multi-walled carbon nanotubes (AMWCNTs) without using any carrier gas, at 230◦C, 750◦C and 850 ◦C. Camphor (C10H16O) is used as carbon source because this botanical hydrocarbon is chip and abundant which convert the CVD technique to a green method for production of carbon nanotubes (CNTs). The oxygen atoms in camphor oxidize the amorphous carbons and create hydroxyl functional groups in AMWCNTs. The molecular structure of camphor lead to form hexagonal and pentagonal carbon rings which increase the growth rate and alignment of MWCNTs. In this work, AMWCNTs are grown on silicon substrate, copper, and quartz. The synthesized AMWCNTs are characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). The SEM results show that the deposited CNTs are formed in vertical aligned arrays and each has a functional OH group which is seen in FTIR spectroscopy results.

Abstract: The fabrication of functionalized 1D oxide fibers with accurate control of orientation, location, and number is highly demanded and challengeable based on current techniques, which hinder their practical application in opto/electronic devices. Herein, a rapid and simple method is developed to directly draw the oxide fibers from its polymer solution over large area. The draw‐spinning method enables the accurate positioning of individual fiber and the construction of complex patterns, holding great potentials in fiber‐based electronics. The assembled field‐effect transistors (FETs) based on single indium oxide (In2O3) fiber exhibit excellent current modulation capability with a high on/off current ratio of 106. Adjusting the number of fibers within the channel, the device performance can be modulated. Moreover, the draw‐spinning technique is applied to fabricate highly aligned fiber arrays by using brush pen. The FETs based on aligned In2O3 fiber arrays exhibit superior current‐driven capability compared with the devices with limited number of fibers. Their further integrations on high‐permittivity dielectric layer show improved device performance at an operating voltage of 4 V. This method is scalable and can be implemented easily to fabricate various functional fibers in both laboratory and industrial manufacturing. [ABSTRACT FROM AUTHOR]

Axial polydisperse carbon microstructures composed of vertically aligned arrays of multiwalled carbon nanotubes (MWCNTs) are synthesized via chemical vapor deposition (CVD) of cyclohexane with ferrocene onto a single-crystal silicon substrate. Their structural peculiarities are examined via scanning electron microscopy on a Tescan Lyra3 FEG system, atomic force microscopy on an Ntegra Spectra NT-MDT probe microscopy, by Raman spectroscopy. The abilities to purify synthesized carbon structures from amorphous carbon through oxidation with atomic oxygen and ozone are studied in order to achieve significant enlargement of specific surface area of nanotubes. The routes of application of polydisperse structures as catalyst supports, solid electrolytes, and chemical sensor supports, as well as absorption techniques of gas and liquid storage, are proposed. [ABSTRACT FROM AUTHOR]

Flexible lead-free piezoelectric nanofibers, based on BNT-ST (0.78Bi0.5Na0.5TiO3-0.22SrTiO3) ceramic and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymers, were fabricated by an electrospinning method and the effects of the degree of alignment in the nanofibers on the piezoelectric characteristics were investigated. The microstructure of the lead-free piezoelectric nanofibers was observed by field emission scanning electron microscope (FE-SEM) and the orientation was analyzed by fast Fourier transform (FFT) images. X-ray diffraction (XRD) analysis confirmed that the phase was not changed by the electrospinning process and maintained a perovskite phase. Polarization-electric field (P-E) loops and piezoresponse force microscopy (PFM) were used to investigate the piezoelectric properties of the piezoelectric nanofibers, according to the degree of alignment—the well aligned piezoelectric nanofibers had higher piezoelectric properties. Furthermore, the output voltage of the aligned lead-free piezoelectric nanofibers was measured according to the vibration frequency and the bending motion and the aligned piezoelectric nanofibers with a collector rotation speed of 1500 rpm performed the best.

Naturally existing materials often acquire unique functions by adopting a gradient structure with gradual change in their microstructure and related properties. Imparting such an elegant structural control into synthetic materials has been a grand challenge in the fi eld. Here, the concept of gradient structure into macroscopic carbon nanotube (CNT) fi lms is employed and the CNT arrangement from well-aligned array to completely random distribution, in a continuous and smooth way, is changed. Gradient films with tailored alignedto- random transition rate or multilevel hierarchical structures with repeated transition have been fabricated. Local deformation and mechanical properties are directly related to the arrangement of CNTs and can be tailored by Herman's orientation factor; in particular, the elastic modulus and stiffness span over several orders of magnitude from aligned to random regions within a single monolithic film. Controlled synthesis of macroscopic CNT gradient structures with tunable mechanical properties opens a potential route toward manufacturing biomimetic functional materials with locally optimized design. [ABSTRACT FROM AUTHOR]

Electrospinning (e-spinning) is a versatile technique to fabricate ultrathin fibers from a rich variety of functional materials. In this paper, a modified e-spinning setup with two-frame collector is proposed for the fabrication of highly aligned arrays of polystyrene (PS) and polyvinylidene fluoride (PVDF) nanofibers, as well as PVDF/carbon nanotube (PVDF/CNT) composite fibers. Especially, it is capable of producing fibrous arrays with excellent orientation over a large area (more than 14 cm × 12 cm). The as-spun fibers are suspended and can be easily transferred to other rigid or flexible substrates. Based on the aligned fibrous arrays, twisted long ropes are also prepared. Compared with the aligned arrays, twisted PVDF/CNT fiber ropes show enhanced mechanical and electrical properties and have potential application in microscale strain sensors. [ABSTRACT FROM AUTHOR]

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single-walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as-grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of metallic-single-walled nanotube (SWNT) shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to 10 μm. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that an aligned multi-walled carbon nanotube array can immobilize Hela cells through insertion of the nanotube tips into the cell. The cells were immobilized by pressing onto the nanotube array with the aid of mild centrifugal force. The nanotube array fixed a much larger number of cells compared with the flat surface of a Si substrate, indicating strong binding force of the aligned nanotubes toward the cell. This is the first example of mechanical cell immobilization, which offers future applications of the nanotube array for cellular biology, tissue engineering, and biomolecular devices. [Copyright &y& Elsevier]

Separation of electronically pure, narrowly dispersed, pristine, semiconducting single-walled carbon nanotubes (CNTs) from a heterogeneous as-synthesized mixture is essential for various semiconducting technologies and biomedical applications. Although conjugated polymer wrappers are often utilized to facilitate electronic-type sorting, it is highly desirable to remove organic residues from the resulting devices. We report here the design and synthesis of a mild acid-degradable π-conjugated polyimine polymer, poly[(9,9-di-n-octyl-2,7-fluoren-dinitrilomethine)-alt-co-(6,6'-{2,2'-bipyridyl-dimethine})] (PFO-N-BPy), that is structurally analogous to the commonly used and commercially available poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6'-(2,2'-bipyridine))] (PFO-BPy). An acid cleavable imine link (-HC═N-) was introduced in the PFO-N-BPy backbone to impart degradability, which is absent in PFO-BPy. PFO-N-BPy was synthesized via a metal catalyst-free aza-Wittig reaction in high yields. PFO-N-BPy with a degree of polymerization of just ∼10 showed excellent (>99% electronic purity) selectivity for both large-diameter (1.3-1.7 nm) arc-discharge semiconducting CNTs (S-CNTs) and smaller diameter (0.8-1.2 nm) high-pressure carbon monoxide disproportionation reaction S-CNTs. Overall, the selectivity for the semiconducting species is similar to that of PFO-BPy but with an advantage of complete depolymerization under mild acidic conditions into recyclable monomers. We further show by ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy that the PFO-N-BPy-wrapped S-CNTs can be aligned into a monolayer array on gate dielectrics using a floating evaporative self-assembly process from which the polymer can be completely removed. Short channel field effect transistors were fabricated from the polymer-stripped aligned S-CNT arrays, which further confirmed the semiconducting purity on the order of 99.9% or higher.

Sheets of graphene and arrays of single-walled carbon nanotubes (SWNTs) are formed separately using chemical vapor deposition techniques onto different optimized growth substrates. Techniques of transfer printing provide a route to integration, yielding two terminal devices and transistors in which patterned structures of graphene form the electrodes and the SWNTs arrays serve as the semiconducting channels., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)