Single Nanotubes Research Articles

Theoretical studies of urea adsorption on single wall boron-nitride nanotubes

Surface modification of a boron nitride nanotube (BNNT) with urea molecule was investigated in terms of its energetic, geometric, and electronic properties using B3LYP and PW91 density functionals. In this investigation, various armchair (n,n) nanotubes, where n=5, 6, 7 have been used. Two different interaction modes, including interaction with outer layer and inner layer of tube were studied. The results indicated that the adsorption of single urea molecule in all of its configurations is observed to be exothermic and physical in nature. Interestingly, the adsorption energy for the most stable configuration of urea was observed when the molecule located inside of the nanotube. Besides, the adsorption of urea on BNNTs changes the conductivity of nanotube.

MoS2 nanotube field effect transistors

We report on electric field effects on electron transport in multi-walled MoS2 nanotubes (NTs), fabricated using a two-step synthesis method from Mo6SxI9-x nanowire bundle precursors. Transport properties were measured on 20 single nanotube field effect transistor (FET) devices, and compared with MoS2 layered crystal devices prepared using identical fabrication techniques. The NTs exhibited mobilities of up to 0.014 cm2V−1s−1 and an on/off ratio of up to 60. As such they are comparable with previously reported WS2 nanotube FETs, but materials defects and imperfections apparently limit their performance compared with multilayer MoS2 FETs with similar number of layers.

Controllable growth of single crystalline CdS nanotubes by thermal evaporation

CdS nanotubes have been successfully prepared by thermal evaporation of CdS powder. The TEM measurements demonstrate that the CdS nanotubes are single crystalline wurtzite and grow along the [0001] direction. The nanotubes nucleate and grow from catalytic Au islands on a silicon substrate, with both their diameter and morphology dependent on size of catalyst islands. A model is presented to explain the nucleation and growth of nanotubes. By optimizing their diameter and morphology, the CdS nanotubes with high optical quality were obtained, and only free-exciton-related emission peaks are observed in their PL spectra.

Generation of low-frequency radiation under focused laser irradiation of a semiconductor

The excitation of the nonlinear medium based on the zigzag nanotubes is analyzed. The terahertz emission is demonstrated under excitation in spite of an equidistant spectrum of a single nanotube. The system exhibits relatively high absorbance in the absence of pumping due to a relatively large oscillator strength.

Inherent carbonaceous impurities on arc-discharge multiwalled carbon nanotubes and their implications for nanoscale interfaces

This paper presents evidence that strongly adhered carbonaceous surface impurities, intrinsic impurities that accompany multiwall carbon nanotubes (MWCNTs) synthesized by arc-discharge, are a component that cannot be ignored in experiments involving single nanotubes and their interfaces with a second surface. At the interface that forms between a carbon nanotube and a graphitic surface, these impurities can significantly alter the adhesion properties of the underlying nanotube and can cause over 30% scatter in computed interaction energies, similar in magnitude to the scatter reported in experimental measurements involving individual CNTs. Also presented is high-resolution TEM evidence that commonly used purification techniques that are effective at removing larger impurity particles from as-produced arc-discharge MWCNT samples do not remove these strongly adhered carbonaceous surface impurities.

Poly(3-hexylthiophene) Nanotubes with Tunable Aspect Ratios and Charge Transport Properties

Regioregular poly(3-hexylthiophene) (RR-P3HT) nanotubes (200 nm in diameter) with tunable aspect ratios from 25 to 300 were prepared using a polymer melt wetting technique. Aspect-ratio tunability was achieved by controlling the wetting behavior of RR-P3HT melts in a template. The crystallinity and chain orientation of RR-P3HT were studied by grazing incidence X-ray diffraction, wide-angle X-ray diffraction, and polarized photoluminescence spectroscopy. Results suggest that RR-P3HT chains in the lamellar structure prefer to be perpendicular to the axis of the RR-P3HT nanotubes, forming a face-on conformation in the RR-P3HT nanotubes that leads to increased carrier mobility of RR-P3HT. Field-effect transistors were fabricated based on a single RR-P3HT nanotube and showed a carrier mobility of 0.14 ± 0.02 cm(2)/V·s.

Single Crystalline-Like TiO2 Nanotube Fabrication with Dominant (001) Facets Using Poly(vinylpyrrolidone) for High Efficiency Solar Cells

The single crystalline-like TiO2 nanotubes (SC-TiO2 NTs) are prepared in the anodization process containing poly(vinylpyrrolidone) (PVP). The PVP in the electrolyte solution functions as a surfactant and controller of the crystal growth. The PVP is favorably adsorbed onto the (001) surfaces rather than onto the (101) facet during the TiO2 nanotube (TiO2 NTs) synthesis because of the high absorption energy (81.1 kcal/mol) on the (001) facets. PVP adsorbed (001) facets are protected during the synthesis, and a single crystalline anatase that primarily exposes the (001) plane is prepared. Furthermore, the overall synthetic mechanism of the fabricated crystalline anatase is clarified using computational calculations. It is clear that there is a difference in the binding interactions between the PVP and TiO2 facets depending on the type of surface. It is concluded that the differences in the binding energies might cause the generation of the SC-TiO2 NTs with exposed (001) facets. In the photovoltaic performance results, the dye-sensitized solar cells (DSSCs) based on the SC-TiO2 NTs show higher photocurrent density because of the large amount of adsorbed dye and the high crystallinity in comparison with that of TiO2 NTs. Because most of the crystalline SC-TiO2 NTs with the active (001) facets have low recombination sites, this results in the effective charge separation and electron transport in the SC-TiO2 NTs DSSCs, leading to the high efficiency solar cell devices.

Inclined slit-based pullout method for determining interfacial strength of multi-walled carbon nanotube–alumina composites

Abstract This paper describes a testing method which enables us to determine experimentally the interfacial strength between multi-walled carbon nanotube (MWCNT) and ceramic matrix in MWCNT/ceramic composites. The testing method developed in this research, named “Inclined slit-based pullout method”, includes a single nanotube pullout technique and a focused ion beam (FIB) technique, which enables MWCNTs to be pulled out from the ceramic matrix during the pullout tests. Single MWCNTs embedded in a fracture surface of an alumina matrix composite are pulled out using a nanomanipulator system in a scanning electron microscope. Embedded lengths of the MWCNTs are controlled by using the FIB technique, i.e., by making an inclined through-slit near the fracture surface of the composite. The average interfacial strength between the MWCNTs and alumina matrix is evaluated to be 19.2 ± 6.6 MPa for 3 MWCNTs tested in this research. This value is found to be approximately close to that estimated from pullout lengths of the MWCNTs on the fracture surface of the composite, supporting the validity of the testing methods developed in this research.

Investigation of multiwalled carbon nanotube interconnection geometry and electrical characteristics of an CNT-filled aluminum microgap

In recent years a very large amount of data has been collected regarding devices formed by multiwalled carbon nanotubes (MWCNTs) in polymer matrix as well as single nanotubes. Conversely, very little investigation exists of nanotube networks composed of a small number of MWCNTs. A detailed investigation of the long time stability, adhesion to the surface, and topological structure of the interconnections between MWCNTs is reported here. Three different microscopy techniques, focused ion beam (FIB), scanning electron microscope (SEM), and atomic force microscope (AFM), were used to investigate the interconnection of MWCNTs deposited by electrophoresis on a thermally oxidized silicon wafer with aluminum microgap structures. SEM, AFM, and FIB imaging revealed an interesting interconnection morphology between the drop casted MWCNTs. In particular it was found that in some cases the MWCNTs were connected to each other in a geometry similar to a twisted structure. Furthermore a good stability of the sample in time has been found, proving a strong adhesion of the nanotubes to the oxide surface. Despite the fact that electrical contacts with aluminum to carbon nanotube - based devices are in general not very reliable, using the dielectrophoresis deposition technique with an adequate subsequent annealing procedure, long-term stable temperature sensors with carbon nanotube networks in the aluminum contact microgap were realized. Their temperature dependence can be explained by modeling the internanotube contact resistance.

Observation of defect state in highly ordered titanium dioxide nanotube arrays

For the first time, a conductive-substrate induced electro-deposition approach is employed to achieve highly ordered TiO2 nanotube arrays based on an anodic aluminum oxide template. Different from other methods, the morphology and parameters of arrays can be adjusted easily through changing the exposure area of a conductive layer. All these arrays are used as matrixes to explore the defect state emission by photoluminescence (PL) spectra. Interestingly, we find that the emission from blue edge to red edge (∼450 nm–600 nm) are apparently quenched in the ordered nanotube arrays, especially when compared to the PL spectra of nanowire arrays, single nanotube and nanoparticles. This distinct result originates from passivation of oxygen vacancies residing along the tube walls when the tubes are interconnected, which is further evidenced by the observation of PL spectra with crystalline phase and sintering. The passivation of defects suggests valuable charge transport perpendicular to the long axis of the tubes in the ordered arrays. This point is particularly significant to the design of highly efficient devices and the applications in various energy-related fields.

The excitonic effects in single and double-walled boron nitride nanotubes.

The electronic structures and excitonic optical properties of single- and double-walled armchair boron nitride nanotubes (BNNTs) [e.g., (5,5) and (10,10), and (5,5)@(10,10)] are investigated within many-body Green's function and Bethe-Salpeter equation formalism. The first absorption peak of the double-walled nanotube has almost no shift compared with the single-walled (5,5) tube due to the strong optical transition in the double-walled tube that occurs within the inner (5,5) one. Dark and semi-dark excitonic states are detected in the lower energy region, stemming from the charge transfer between inner and outer tubes in the double-walled structure. Most interestingly, the charge transfer makes the electron and the hole reside in different tubes. Moreover, the excited electrons in the double-walled BNNT are able to transfer from the outer tube to the inner one, opposite to that which has been observed in double-walled carbon nanotubes.

Tensile behavior of single crystalline GaN nanotube bundles: An atomistic-level study

The tensile behavior of single crystalline GaN nanotube bundles was studied using classical molecular dynamics. Stillinger–Weber potential was used to describe the atom–atom interactions. The GaN bundles consisted of several individual GaN nanotubes with {100} side planes. The simulation results show that the nanotube bundles show a brittle to ductile transition (BDT) by changing the temperatures. The fracture of GaN nanotube bundles is ruled by a thermal activated process, higher temperature will lead to the decrease of the critical stress. At high temperatures the individual nanotube in the bundles interact with each other, which induces the increase of the critical stress of bundles.

A unified analytical model of the junction electrostatics in nanowire and nanotube arrays

We establish the unity underlying the junction electrostatics of nanowire and nanotube arrays, and develop a simple analytical model for both based on a common set of approximations of the field/potential distributions. The model predicts large depletion widths accurately, and reveals that, the depletion width in an array of nanowire and nanotube junctions varies as 1/charge per unit length of wire/tube multiplied by inter-wire/tube separation, where charge per unit length includes the effects of wire/tube radius and doping. This is much different from the exponential form derived in literature for a single nanowire or nanotube junction. The model satisfies all the limiting conditions, matches with numerical simulations and is extendible to nanofilms. Hence, it should be quite useful for nanodevice design.

Atomic monolayer deposition on the surface of nanotube mechanical resonators.

We study monolayers of noble gas atoms (Xe, Kr, Ar, and Ne) deposited on individual ultraclean suspended nanotubes. For this, we record the resonance frequency of the mechanical motion of the nanotube, since it provides a direct measure of the coverage. The latter is the number of adsorbed atoms divided by the number of the carbon atoms of the suspended nanotube. Monolayers form when the temperature is lowered in a constant pressure of noble gas atoms. The coverage of Xe monolayers remains constant at 1/6 over a large temperature range. This finding reveals that Xe monolayers are solid phases with a triangular atomic arrangement, and are commensurate with the underlying carbon nanotube. By comparing our measurements to theoretical calculations, we identify the phases of Ar and Ne monolayers as fluids, and we tentatively describe Kr monolayers as solid phases. These results underscore that mechanical resonators made from single nanotubes are excellent probes for surface science.

Simulation and Experimental Study of Nanowire Assembly by Dielectrophoresis

Although dielectrophoretic (DEP) assembly has been demonstrated to be an efficient way to align nanowires or nanotubes for making nanodevices based on one-dimensional nanostructures, misalignment is often observed in experimental implementation. This unfavorable observation discourages researchers’ enthusiasm in making devices by DEP. To make DEP assembly in a controllable fashion, theoretical and simulation studies are indispensable. However, traditional analysis on DEP is based on a zero-dimensional model derived from the interaction between a nonuniform electric field and dielectric particles, which might not be directly applicable to nanowires or nanotubes. In this paper, we propose an approach similar to finite element method to calculate the total DEP force and torque on the one-dimensional nanostructure by considering the dimensional effect. It is shown from the simulation that the magnitude of DEP force is related to the conductivity of the nanostructure and the frequency of the electric field, which provides feasibility on controllable and selective assembly of the nanowires or nanotubes. To study the trajectory of single nanowire or nanotube assembled by DEP, a comprehensive model involving DEP force, DEP torque, drag force, drag torque, and Brownian motion is proposed. The one-dimensional nanostructure is predicted from the simulation to either attach one electrode and align at certain direction or bridge the electrodes. The theoretical and simulation study indicate that the alignment of one-dimensional nanostructure is mainly related to its length, the gap size of the electrodes as well as the initial contact position of the nanowire or nanotube onto the electrode. The predication from the simulation has been confirmed by assembled zinc oxide nanowires and carbon nanotubes using DEP.

Effects of preparing conditions on controllable one-step electrodeposition of ZnO nanotube arrays

By using a one-step electrodeposition method, well oriented single crystalline ZnO nanotube arrays (ZNTAs) with average diameter less than 200nm were synthesized on FTO substrate under different conditions. The effects of preparing conditions such as pretreatment of substrate, pH value of electrolyte, electrodeposition potential, concentration of electrolyte, reaction temperature and growth time on the electrodeposition of ZNTAs were systematically investigated by scanning electron microscopy (SEM), and ultraviolet visible absorbance spectroscopy to make the formation mechanism clear. It is indicated that the electrodeposition parameters have significant influence on the morphology, average diameter and growth density of as-prepared ZNTAs. The aligned ZNTAs can be only obtained on the FTO substrate pre-treated with acid solution when the applied potential is controlled from -0.8 to -1.0V and the pH value of electrolyte is from 3.10 to 3.90, simultaneously. The growth temperature and the electrolyte pH value have great impact on the morphology of as-prepared ZnO nanostructure. The tube diameters can be monitored to some extent only by changing the concentration of the zinc precursors or growth time, in addition, the growth time is closely related to the band gap energy (Eg) of as-prepared ZNTAs.

Nanotubes for Osmotic Energy Harvesting

New paradigms for fluid transport are expected to emerge from the confinement of liquids at the nanoscales [1- 3], with potential breakthroughs in ultra-filtration, desalination, and energy conversion [4]. Nevertheless, advancing the fundamental understanding of fluid transport at the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores.To this end, a major challenge for nanofluidics consists in building distinctive and well-controlled nano-channels, amenable for systematic exploration of their properties. In this work [5] we describe the elaboration and exploitation of a new hierarchical nanofluidic device, made of a unique boron-nitride (BN) nanotube that transpierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the versatile exploration of fluidic transport through a single nanotube under diverse forcing, including electric fields, pressure drops, and chemical gradients.Using this device, we discover huge osmotically-induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates from the anomalously high surface charge carried by the BN internal surface in water at large pH, which was independently quantified from conductance measurements. The nano-assembling route using nanostructures as building blocks opens new perspectives to explore fluid, ionic and molecule transport at nanoscales, paving the way towards biomimetic functionalities. Our results furthermore suggests that boron-nitride nanotubes could be advantageously exploited as membranes for osmotic power harvesting under salinity gradients, making it a prime renewable source of energy.[1] W. Sparreboom, et al., Nature Nano, 4, 713-720 (2009).[2] L. Bocquet and E. Charlaix, Chem. Soc. Rev. 39, 1073-1095 (2010).[3] J. C. Rasaih, et al., Annu. Rev. Phys. Chem. 59 713-740 (2008).[4] B. E. Logan and M. Elimelech, Nature, 488 313-319 (2012).[5] A. Siria, et al. Nature, 494, 455-458, (2013).

Room temperature carrier transport through large diameter bundles of semiconducting single-walled carbon nanotube

In this work, we purify semiconducting SWNTs (S-SWNTs) using the density gradient method being already developed and compare carrier transport in dielectrophoretically formed bundles at 298K to unseparated counterparts. We find that for a 36-nm-diameter S-SWNTs bundle produced in this work, resistance values ranging 0.4–1.6MΩ are consistent with previously reported values for smaller diameter bundles (3nm), where it was assumed that only the circumferential SWNT contributes to conduction from the electrode. Estimated transmission probabilities of 0.004 and 0.017, which are calculated in this work, are approximately 1–2 orders of magnitude lower than single nanotube counterparts, suggesting a significant amount of carrier scatterings in the bundled state. This is also reflected in the corresponding room temperature mean free paths of 18.6 and 4.3 nm, respectively, which are comparable to Ar+ ion damaged bundles of smaller size. We note that theses values are consistent with a value of 22nm predicted from a semi-classical transport model for the elastic scattering length for carriers in an idealized (6, 5) SWNT.

Gold Nanoparticle Silica Nanopeapods

A subnanometer gap-separated linear chain gold nanoparticle (AuNP) silica nanotube peapod (SNTP) was fabricated by self-assembly. The geometrical configurations of the AuNPs inside the SNTPs were managed in order to pose either a single-line or a double-line nanostructure by controlling the diameters of the AuNPs and the orifice in the silica nanotubes (SNTs). The AuNPs were internalized and self-assembled linearly inside the SNTs by capillary force using a repeated wet-dry process on a rocking plate. Transmission electron microscopy (TEM) images clearly indicated that numerous nanogap junctions with sub-1-nm distances were formed among AuNPs inside SNTs. Finite-dimension time domain (FDTD) calculations were performed to estimate the electric field enhancements. Polarization-dependent surface-enhanced Raman scattering (SERS) spectra of bifunctional aromatic linker p-mercaptobenzoic acid (p-MBA)-coated AuNP-embedded SNTs supported the linearly aligned nanogaps. We could demonstrate a silica wall-protected nanopeapod sensor with single nanotube sensitivity. SNTPs have potential application to intracellular pH sensors after endocytosis in mammalian cells for practical purposes. The TEM images indicated that the nanogaps were preserved inside the cellular constituents. SNTPs exhibited superior quality SERS spectra in vivo due to well-sustained nanogap junctions inside the SNTs, when compared to simply using AuNPs without any silica encapsulation. By using these SNTPs, a robust intracellular optical pH sensor could be developed with the advantage of the sustained nanogaps, due to silica wall-protection.

Self-assembly of monodisperse CdS nanocylinders with an axial pore.

We present our conclusions of the investigation of the self-assembly and growth of an array of CdS nanotubes: a consequence of a fine balance of directed motion, diffusion, and aggregation of reacting Cd(+2) and S(-2) ions. In a previous communication [Kiruthiga and Chatterji, J. Chem. Phys. 138, 024905 (2013)], we identified the mechanism of an unexpected growth of a CdS nanocylinder of uniform radial cross section from the end of a nanochannel. Furthermore, the cylinder had a pore along the axis but was closed at one end. This unique phenomenon of self-assembly of very monodisperse CdS nanocylinders had been observed in a rather simple experiment where two chambers containing 0.1M CdCl(2) and 0.1M Na(2)S solutions were joined by an array of anodized aluminium oxide (AAO) nanochannels [Varghese and Datta, Phys. Rev. E 85, 056104 (2012)]. Interestingly, the growth of CdS nanotubes was observed only in the Na(2)S chamber. The primary focus of our previous study was on identifying the principles governing the growth of a single nanotube at the exit point of a single AAO nanochannel. In this communication, we identify factors affecting the self-assembly of a nanotube in the presence of other similar neighboring nanotubes growing out from an array of closely spaced AAO nanochannel exit points, a scenario closer to the experimental situation. Our model is not Cd(+2) or S(-2) specific, thus our conclusions suggest that the experimental scheme can be extended to the self-assembly of a general class of reacting-diffusing A and B ions with A (in this case Cd(+2) ions) selectively migrating out from a nanochannel. In particular, we note that after the initial growth of nanotubes for a period of time, there can arise a severe deficiency of B ions (S(-2)) near the AAO-nanochannel exits. The low concentration of B near the nanochannel exits impedes further growth of uniform CdS nanotubes. We further identify the parameters which can be tuned to obtain an improved crop of monodisperse nanotubes. Thereby we predict the necessary characteristics of reacting systems which can be self-assembled using suitable adaptations of experiments used to grow CdS cylinders.