Encapsulated Carbon Nanotubes Research Articles

Formation, Structure, and Polymorphism of Novel Lowest‐Dimensional AgI Nanoaggregates by Encapsulation in Carbon Nanotubes

Formation, Structure, and Polymorphism of Novel Lowest‐Dimensional AgI Nanoaggregates by Encapsulation in Carbon Nanotubes

Molecularly Imprinted Polypyrrole Encapsulated Carbon Nanotubes in Stainless Steel Frit for Micro Solid Phase Extraction of Estrogenic Compounds

A novel micro-solid phase extraction (microSPE) device was prepared by electrochemically adhering molecularly imprinted polypyrrole encapsulated carbon nanotubes (MIPPy/CNTs) onto a stainless steel frit. It was found that the use of CNTs increased the total binding capacity without compromising the porosity of the frit. Three templates, 17alpha-ethynyl estradiol (EE2), 17beta-estradiol (E2), and ochratoxin A (OTA) were imprinted individually to make their respective MIPPy/CNTs-modified frits. The binding properties of these microSPE devices were characterized by high performance liquid chromatography (HPLC) with fluorescence detection (FLD). In comparison with non-imprinted polypyrrole encapsulated carbon nanotubes (PPy/CNTs), the molecular imprinting technique enhanced the selective binding towards the imprint molecules. MIPPy/CNTs-microSPE-HPLC-FLD results demonstrated the selectivity of MIPPy had been tailored by imprinting with different templates. This is the first report on how versatile pyrrole can be as a functional monomer for the molecular imprinting of target compounds with a broad range of high to low pKa values.

Energetics of ice nanotubes and their encapsulation in carbon nanotubes from density-functional theory

We have performed total-energy electronic-structure calculations based on the density-functional theory that clarify atomic and electronic structures of ice nanotubes encapsulated in carbon nanotubes. We have found that three tubular structures of ice are stable in carbon nanotubes. The structural characteristics of these ice nanotubes is a straight stacking or helical arrangement of polygonal units consisting of water molecules. In these stable ice nanotubes, each water molecule is fourfold coordinated with neighboring water molecules through hydrogen bonds. The energy gain upon encapsulation of ice nanotubes in carbon nanotubes is found to be an order of $10\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ per water molecule, whereas the energy gain to form ice nanotubes from isolated water molecules is about a half eV per molecule. Carbon nanotubes act as a template to form the new polymorph of ice. Detailed structural analysis has revealed a role of hydrogen-bond angles in determining energetics of the ice nanotubes. We have also clarified that energy gaps of ice nanotubes are comparable with the gap of the most stable ice polymorph Ih and that the electronic structure of ice nanotubes encapsulated in carbon nanotubes is a superposition of the energy bands of the constituents.

Energy dispersion in graphene and carbon nanotubes and molecular encapsulation in nanotubes

Density-functional calculations of electronic and vibrational dispersion energies for pristine graphite monolayer graphene and single-walled carbon nanotubes SWCNTs are presented. Optimized parameters for nonlocal norm-preserving pseudopotentials which replace the potential field due to core electrons are given. Comparison with observations, where available, is made. The effect of encapsulation of carbon nanotubes with an alkali-halide matrix is numerically investigated. The electronic band structure of encapsulated SWCNT is noticeably modified, as is its charge density, and hence its optical properties.

Embedded vertically grown carbon nanotubes for field emission applications

Vertically aligned carbon nanotubes, embedded in titanium oxide, have been fabricated and their electron emission behavior has been characterized. The growth of carbon nanotubes was achieved using a dc plasma enhanced chemical vapor deposition method with a mixture of acetylene and hydrogen, and nickel was used as the catalyst layer. Titanium oxide, deposited using an atmospheric pressure chemical vapor deposition, was used to encapsulate the grown carbon nanotubes and the physical properties of the as-grown carbon nanotubes as well as the encapsulated structures have been investigated using scanning electron microscopy. By a sequential polishing and plasma ashing, it is possible to open up the top side of the encapsulated carbon nanotubes. Also by means of a reactive ion etching, carbon nanotubes are exposed with an inherent gate surrounding each one. This technique allows the evolution of individually processed nanotubes with no need of nanolithography. The emission of electrons from carbon nanotubes was examined and a preliminary field emission display was prepared.

DNA Encapsulation Inside Carbon Nanotubes Using Micro Electrolyte Plasmas

AbstractDNA encapsulated carbon nanotubes are formed using a plasma ion irradiation method in electrolyte solutions with DNA, which can be regarded as electrolyte plasmas from the view point that the electrolyte solutions consist of positive and negative ions, and neutral particles in the same way as gas phase plasmas. When both the direct current (DC) and radio frequency (RF) electric fields are applied to the DNA electrolyte plasmas through micro gap electrodes, DNA which is negatively charged in solutions tends to change its conformation from random‐coil to stretched‐form by the RF field and be irradiated to the carbon‐nanotube coated anodeelectrode by the DC field. Based on Raman spectroscopy and transmission electron microscopy analyses, DNA is confirmed to be inserted into the carbon nanotubes. The creation of DNA encapsulated carbon nanotubes using the micro electrolyte plasmas supports the validity of the plasma concept extended from gas to liquid phase, which could pioneer novel applications in such nanoelectronics and biomedical fields. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transfer of Flexible Arrays of Vertically Aligned Carbon Nanofiber Electrodes to Temperature‐Sensitive Substrates

The unique physical, chemical, and mechanical properties of vertically aligned carbon nanotubes (VACNTs) and nanofibers (VACNFs) have led to their use in a variety of applications. VACNTs and VACNFs have demonstrated viability as field electron emitters, electrochemical probes, and biosensors. These demonstrations have been enabled by the ability to deterministically synthesize vertically aligned nanostructures using catalytically directed plasma-enhanced chemical vapor deposition (PECVD) processes, where a carbonaceous source gas is decomposed and precipitated on catalyst nanoparticles at elevated temperatures. Catalyst activation in plasma requires substrate temperatures usually in the range 600–700 °C. There have been several recent reports on carbon nanofibers grown at lower substrate temperatures. However, it still remains an open question whether the graphitization quality of such nanofibers is sacrificed. The impact of low-temperature synthesis on the resultant structure’s chemical, electrochemical, and mechanical properties also requires further exploration. In addition, the actual growth temperatures due to plasma heating could be considerably higher than those measured at the substrate heater. These temperatures still impose restrictions on the types of substrates that can be used, with silicon and fused silica often being the substrates of choice owing to their compatibility with relatively high-temperature processes. Substrates sensitive to high temperatures, plasmas, or certain gases, including most polymers, glasses, and conventional microelectronics (i.e., complementary metal-oxide semiconductors, CMOSs), are degraded and sometimes destroyed by the harsh growth conditions of vertically aligned carbon nanostructures. As an alternative, in a recent report, carbon nanotubes encapsulated within an epoxy polymer were released from their growth substrate and aligned, using micromanipulators, on a receptor substrate in a lowtemperature process. This technique offers the advantage of preserving receptor substrates from the harsh growth conditions of carbon nanotubes. However, the spatial dimensions defined by the deterministic growth of nanotubes from photolithographically defined catalyst sites are lost. The necessity of realigning the encapsulated carbon nanotubes on the receptor substrate by micromanipulators also reduces the efficiency of the process. We report on a method for growing VACNFs in a high-temperature (630 °C) direct-current PECVD process and subsequently transferring these nanofibers to new substrates. In brief, following high-temperature growth on silicon substrates, carbon nanofibers were partially embedded in a UV-crosslinked epoxy membrane and peeled from their original growth substrate. The membrane, featuring embedded highaspect-ratio nanofibers, was then aligned and mated with an array of individually addressable contact pads. This process provides intact nanofibers that can be transferred to essentially any planar surface, including those that would otherwise be destroyed by the harsh conditions imposed on the substrate during nanofiber synthesis. Transferred carbon nanofibers were shown to retain their high-aspect-ratio morphology and their viability as electrodes, as demonstrated by electrochemical analysis and gold electrodeposition. Nanofiber arrays were grown on silicon wafers from photolithographically defined nickel catalyst sites as previously described (Fig. 1C, process steps 1,2). Following growth, nanofibers were inspected in a Hitachi 4700S scanning electron microscope at an acceleration voltage of 10 kV using a mixed-detector mode. Figure 1A presents a representative reC O M M U N IC A IO N S

Electrically triggered insertion of single-stranded DNA into single-walled carbon nanotubes

The formation of DNA encapsulated carbon nanotubes, which are expected to modify electronic properties of carbon nanotubes, is for the first time demonstrated using a modified electrophoresis method. Radio-frequency and direct-current electric fields are applied to the DNA solution in order to stretch random-coil-shaped DNA and irradiate DNA to carbon nanotubes that are coated onto electrodes immersed in the DNA solution, respectively. Transmission electron microscopy and Raman scattering spectroscopy analyses reveal that DNA can be encapsulated into the carbon nanotubes. In this procedure, the key for the formation of DNA encapsulated carbon nanotubes is found to irradiate the stretched-shaped DNA to the carbon nanotubes.

Control of injected carriers in tetracyano-p-quinodimethane encapsulated carbon nanotube transistors

We examined transistor characteristics of tetracyano-p-quinodimethane encapsulated single-walled carbon nanotubes (TCNQ@SWNTs). In device operations, a clear conversion to a p-type character was observed and the stability of carriers, previously doped into SWNTs, were simultaneously clarified. Because of an energy band shift, between the electrodes and the doped SWNTs induced by the doping, electron injection was achieved only by application of a high source-drain voltage, while holes were easily injected because of decrease in hole barrier height.

Encapsulation of Carbon Nanotubes by Self-Assembling Peptide Amphiphiles

We demonstrate the dispersion and noncovalent functionalization of carbon nanotubes in water using peptide amphiphiles each consisting of a short hydrophobic alkyl tail coupled to a more hydrophilic peptide sequence. The assembly of peptide amphiphile molecules on the surfaces of carbon nanotubes adds biofunctionality to these one-dimensional conductors and simultaneously eliminates the hydrophobic nanotube-water interface, thus dispersing them in the aqueous medium. This should occur without the degradation of their structural, electronic, and optical properties caused by covalent functionalization and without the need for specific peptide sequences designed to bind with nanotube surfaces. The encapsulation by peptide amphiphiles is confirmed using transmission electron microscopy and optical absorbance spectroscopy and may have significant future applications in biosensing or medicine.

Naturally produced carbon nanotubes

Carbon nanotubes represent an impressive kind of materials with diverse unexpected properties, and different methods to artificially produce them have been developed. Recently, they have also been synthesized at low temperatures, demonstrating that these materials might exist in fluids or carbon rocks of the Earth’s crust. A new type of natural encapsulated carbon nanotubes found in a coal–petroleum mix is presented. These findings show that all allotropic carbon forms known up to date can be produced in Nature, where pressure, catalysts particles, shear stress and parameters other than exclusively very high temperature, seem to play an important role for producing nanotubes.