Multiwalled Carbon Nanotube Tip Research Articles

Encapsulation of Fullerenes: A Versatile Approach for the Confinement and Release of Materials Within Open-Ended Multiwalled Carbon Nanotubes.

We have employed fullerenes as versatile agents to “cork” the open tips of multiwalled carbon nanotubes (MWCNTs), and as promoting species for the release of the inorganic material filled within the nanotubes’ cavities. High Z element compounds, namely, PbI2, ZnI2, and CeI3, were chosen to easily determine the presence of the filler inside the hosting nanotubes by transmission electron microscopy (TEM). Fullerenes can isolate inorganic nanostructures confined within the hollow cavities of MWCNTs, which allows the removal of the external material remnant after the filling. Otherwise, taking advantage of the affinity of fullerenes with selected solvents, we have confirmed the ability of the C60 molecules to promote the displacement of the inorganic guest from the host. We propose two different strategies to trigger the release, employing vapor and liquid phase treatments. The first protocol involves annealing filled MWCNTs in presence of fullerenes (to obtain C60PbI2@MWCNTs) and the subsequent washing of the sample in ethanol under mild conditions. On the other hand, the simultaneous introduction of the C60 molecules and the liberation of the guest are produced by a single step wet procedure; the latter being potentially useful when materials that are not stable at high temperatures are employed for filling.

Functionalized multi-walled carbon nanotubes with strong fluorescence emission

Multi-walled carbon nanotubes (MWCNTs) with strong visible fluorescence were synthesized via oxidation and amination. A large number of oxygen-containing surface functional groups contributing to fluorescence emission have been found, and the novel structure of carbon nanoclusters with the diameter of 20–30 nm are formed at the tips of MWCNTs. The fluorescent MWCNTs exhibit distinct excitation-wavelength dependence and pH response. Furthermore, the temperature sensitivity of fluorescence has been described carefully. The fluorescence intensity first increases and then decreases upon increasing temperature, and the maximum emission is achieved when the functionalized MWCNTs are dried at 150 °C.

Electron beam-induced changes in tips of multi-walled carbon nanotubes with/without Au nanoparticles

Tips of multi-walled carbon nanotube of dissimilar shapes with/without gold nanoparticles are irradiated under electron beam. The tips become meta-stable and cause reduction in lengths of tubes under a high intense uniform electron beam by their smaller radius of curvature when the diffusion and evaporation of carbon atoms are activated. Meanwhile, normal-tube-tips and volcano-tube-tips with/without gold nanoparticles present dissimilar changes in their diameters. The gold nanoparticles with size ≥ 3 nm not only slow down length reduction process in the normal-tube-tips and increase tips diameters but also increase their size on the normal-tube-tip by the interaction and growth, while gold nanoparticles with size ≤ 1.5 nm retard the length reduction process in volcano-tube-tips without any change in the tips diameters. Furthermore, they also activate formation of carbon shells over their surface and keep their positions fixed on the volcano-tube-tip. This abnormal interaction of gold nanoparticles with the unstable tips is elucidated in terms of irradiation-induced activation of the graphitic layers, diffusion of Au atoms and bonding between adjacent large (≥ 3 nm) Au NPs, and catalytic effects of small (≤ 1.5 nm) Au NPs. The method can be employed to modify nanotubes with almost atomic precision and to create a predefined pattern of metal nanoparticles on tube tips and surface.

Tip and Inner Wall Modification of 4.9 nm Diameter Multi-Walled Carbon Nanotubes and Its Nanocomposite Polyamide Reverse Osmosis Membrane.

The tip and inner surface of large diameter multi-walled carbon nanotubes (MWCNTs) (4.9 nm diameter) were functionalized on the tip and inner surface to improve the rate of desalination and maintain high water flux. The modified MWCNTs-doped reverse osmosis membranes were fabricated by interfacial polymerization using trimesoyl chloride (TMC) solution in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized MWCNTs. The functionalized MWCNTs were analyzed by X-ray photoelectron spectroscopy (XPS), thermal gravity analysis (TGA), high resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy and other techniques. The obtained results showed that changes occurred in the structure of the carbon nanotubes with the inner diameter becoming smaller, and the dispersibility and stability were improved. Carboxyl, acyl chloride, amide and amino groups were successfully grafted on the tip and interior of MWCNTs. The surface characteristics of the prepared membranes were studied by scanning electron microscopy (SEM) and contact angle analysis. The desalination performance of the membranes was investigated in terms of water flux and salt rejection. The experimental results revealed that the incorporation of the modified MWCNTs (especially containing hydrophilic groups such as carboxyl groups) into the polyamide layer of RO membranes led to a significantly increase of the water flux and salt rejection.

Atomic-level Sharpening of a Carbon Nanotube Tip for High-resolution Scanning Tunneling Microscopy

Using a multi-walled carbon nanotube (MW-CNT) tip, we have observed the honeycomb lattice of highly oriented pyrolytic graphite (HOPG) via scanning tunneling microscopy (STM). This observation was made after acquiring typical STM images of HOPG, i.e., showing the triangular lattice. We consider this change is due to atomic reconfiguration at the apex of the MW-CNT tip induced by continuous STM scanning. The atomic-level sharpening of CNT tips will be useful to image samples with small lattice constants or to obtain orbital information from samples with an orbital ordering such as manganites.

Field emission properties of a DWCNT bundle and a single MWCNT

The field emission properties of a bundle of double-walled carbon nanotubes (DWCNTs) and a single multiwalled carbon nanotube (MWCNT) were investigated. A DWCNT bundle or a single MWCNT was attached to the head of sharpened tip of tungsten by electrophoresis; the tungsten tip was dipped into a drop of a carbon nanotube/1,2-dichloroethane suspension on a stainless plate, and a high-frequency AC voltage (20 V peak to peak with a frequency of 15 MHz) was applied between the tungsten tip and the stainless steel plate. The turn-on fields of the DWCNT and MWCNT tips for 1 nA/cm2 were 0.05 and 0.48 V/μm, respectively. From the Fowler-Nordheim plots, the field enhancement factor (β) of the tips was estimated to be 109,600 (DWCNT) and 6780 (MWCNT). The present DWCNT emitter is characterized by a very small turn-on field and large β. The field emission performance is discussed in terms of the sizes of the bundle of DWCNTs and a single MWCNT.

Measurements of the work function of single-walled carbon nanotubes encapsulated by AgI, AgCl, and CuBr using kelvin probe technique with different kinds of probes

We report the results on the measurements of the work function of single-walled carbon nanotubes encapsulated by Agl (AgI@SWCNT), AgCl (AgCl@SWCNT), and CuBr (CuBr@SWCNT) by the local Kelvin probe technique. We found the values of the work function of tubes encapsulated with AgI and AgCl (Φ(AgI@SWCNT) = 5.08 ± 0.02, Φ(AgCl@SWCNT) = 5.10 ± 0.02 eV) to exceed substantially that of pristine carbon nanotubes, and the value of the work function of carbon nanotubes encapsulated with CuBr is Φ(CuBr@SWCNT) = 4.89 ± 0.03 (eV). The measurements are carried out using different kinds of microscope probes including multi-walled carbon nanotube tips.

Nanoscale Bubble Valves on MWCNT Membranes for Chemical Energy Storage

Nanoscale Bubble Valves on MWCNT Membranes for Chemical Energy Storage

Scanning MWCNT-Nanopipette and Probe Microscopy: Li Patterning and Transport Studies.

A carbon-nanotube-enabling scanning probe technique/nanotechnology for manipulating and measuring lithium at the nano/mesoscale is introduced. Scanning Li-nanopipette and probe microscopy (SLi-NPM) is based on a conductive atomic force microscope (AFM) cantilever with an open-ended multi-walled carbon nanotube (MWCNT) affixed to its apex. SLi-NPM operation is demonstrated with a model system consisting of a Li thin film on a Si(111) substrate. By control of bias, separation distance, and contact time, attograms of Li can be controllably pipetted to or from the MWCNT tip. Patterned surface Li features are then directly probed via noncontact AFM measurements with the MWCNT tip. The subsequent decay of Li features is simulated with a mesoscale continuum model, developed here. The Li surface diffusion coefficient for a four (two) Li layer thick film is measured as D=8(±1.2)×10(-15) cm(2) s(-1) (D=1.75(±0.15)×10(-15) cm(2) s(-1)). Dual-Li pipetting/measuring with SLi-NPM enables a broad range of time-dependent Li and nanoelectrode characterization studies of fundamental importance to energy-storage research.

Super-hydrophobic multi-walled carbon nanotube coatings for stainless steel

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to directly grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature () without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values () and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films with scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling, but also could provide low friction and drag reduction.

Microfluidic integrated multi-walled carbon nanotube (MWCNT) sensor for electrochemical nucleic acid concentration measurement

A microfluidic assisted electrochemical (EC) biosensing platform based on vertically aligned multi-walled carbon nanotubes (MWCNTs) embedded in SiO2 was developed using multi-scale manufacturing techniques. The MWCNT-EC sensor was fabricated using electron beam (E-beam) nanolithography, thin-film metal deposition and reactive/electrochemical etching. The MWCNT-EC sensor was integrated with a microfluidic EC cartridge including the counter and reference electrodes and a PDMS microfluidic channel on a glass substrate. After packaging the MWCNT chip and microfluidic EC cartridge into a manifold which included sample inlet/outlet, electrical connectors and a miniaturized potentiostat, the platform was characterized with differential pulse voltammetry (DPV) using ferrocyanide and ruthenium(II) solutions. The DPV measurement results are consistent with commercial EC systems. Microfluidic nucleic acid hybridization was demonstrated using the MWCNT chip on which the MWCNT tips were functionalized with single stranded DNA (ssDNA) probes. The synthetic complementary ssDNA targets were input through the microfluidic channel and hybridized with the functionalized ssDNA probes. The relative DPV peak magnitude linearly correlated with the target DNA concentration. This platform provides a simple way to integrate a MWCNT biosensor with microfluidics as an electronic system for a variety of possible nucleic acid analyses.

Magnetic property of FePt nanoparticles encaged in carbon nanotubes

Encapsulation of FePt nanoparticles in carbon nanotubes (CNTs) was attempted using a thermal chemical vapor deposition technique with a Fe/Pt bilayer catalyst. The metal nanoparticles were encapsulated at the tip of multi-walled CNTs. A selected area electron diffraction measurement of the nanoparticles at CNT tips indicated that diffraction spots attributed to an ordered L10 phase. Magnetic hysteresis loops indicated existence of magnetic nanoparticles having various coercivities. From numerical fittings assuming that high and low coercivity components contributed to the hysteresis loops, the high coercivity component was estimated to reach 11.3 kOe (902 kA/m).

Microstructural evolution of multi-walled carbon nanotubes in the presence of mixture of silicon and silica powders at high temperatures

Microstructural evolution of multi-walled carbon nanotubes (MWCNTs) in the presence of mixture of silicon and silica powders in a coke bed is studied in the temperature range of 1000–1500°C by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and thermogravimetry–differential scanning calorimetry (TG–DSC). The results showed that a thin amorphous SiO2 coating was formed on the surface of MWCNTs at the temperature below 1300°C. With the increase of the treated temperature, the coating became thicker, 3–7nm in thickness at 1400°C and a maximum of 10nm at 1500°C. Meanwhile, SiC nanowires and SiC nanocrystals around Ni catalyst at the tip of MWCNTs were formed at 1400°C and 1500°C, which were related to the vapor–vapor (V–V) and vapor–liquid–solid (V–L–S) reactions between SiO (g) and CO (g) or C (s), respectively. The oxidation resistance of all the treated MWCNTs was better than that of as-received ones. The oxidation peak temperature reached 804.2°C for the treated MWCNTs, much higher than 652.2°C for as-received ones.

In situ TEM study on the improvement of contact resistance between a carbon nanotube and metal electrodes by local melting

Contact resistance between a multiwalled carbon nanotube (MWNT) and a metal electrode is governed by the contact structure. The relationship between the contact structure and electrical resistance was examined by in situ transmission electron microscopy using a nickel electrode and MWNTs with two kinds of tip structure; close‐capped and open‐ended. When the current density through the contact region reached a threshold value about 7.6 × 108 A/cm2, the MWNT tip was embedded below the nickel surface by local melting of the metal, and the contact resistance was reduced. In the case of the open‐ended MWNT, significant reduction of the contact resistance was observed, because inner shells of the MWNT with open cap can connect directly with the electrode. Copyright © 2011 John Wiley & Sons, Ltd.

High Throughput Nanofabrication of Silicon Nanowire and Carbon Nanotube Tips on AFM Probes by Stencil-Deposited Catalysts

A new and versatile technique for the wafer scale nanofabrication of silicon nanowire (SiNW) and multiwalled carbon nanotube (MWNT) tips on atomic force microscope (AFM) probes is presented. Catalyst material for the SiNW and MWNT growth was deposited on prefabricated AFM probes using aligned wafer scale nanostencil lithography. Individual vertical SiNWs were grown epitaxially by a catalytic vapor-liquid-solid (VLS) process and MWNTs were grown by a plasma-enhanced chemical vapor (PECVD) process on the AFM probes. The AFM probes were tested for imaging micrometers-deep trenches, where they demonstrated a significantly better performance than commercial high aspect ratio tips. Our method demonstrates a reliable and cost-efficient route toward wafer scale manufacturing of SiNW and MWNT AFM probes.

A new solution on the buckling and stable length of multi wall carbon nanotube probes near graphite sheets

In this paper, a power series solution is used to study effect of intermolecular forces on the instability of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. A power series method basis on symbolic computation is introduced to obtain an analytical solution for the distributed parameter model. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. Minimum nanotube-graphite initial gap and stable length of freestanding carbon nanotube are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers. The obtained results are compared with the Adomian decomposition and Green's function as well as numerical results. The obtained results in compare with numerical results represent remarkable accuracy rather than the Adomian decomposition method and Green's function.

Modification of interface structure and contact resistance between a carbon nanotube and a gold electrode by local melting

The electrical connection between a multiwalled carbon nanotube (MWNT) and a gold electrode on applying an electric current was studied by performing in situ transmission electron microscopy observations while simultaneous measuring the bias voltage and the electric current. The tip of the MWNT was brought into contact with the gold surface. When a current density of ∼108A/cm2 flowed through the contact, the gold surface started to melt along the surface of the MWNT tip due to Joule heating. At about twice the current density, a drastic change was observed in the structure of the gold surface in the contact region. This structural change increased the contact area between the MWNT tip and gold, which reduced the electrical contact resistance.

New approach to model the buckling and stable length of multi walled carbon nanotube probes near graphite sheets

Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out for the first time via two analytical approximation methods as well as a numerical one. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. In addition, minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.

Field emission of carbon-nanotube point electron source

Carbon nanotube (CNT)-based point electron emitter was fabricated using a cavity-confined dielectrophoresis. The emission current of an individual multi-walled CNT (MWCNT) was stable up to 10 μA and reached ~ 2 mA (1.7 × 10 8 A/cm 2), about three orders of magnitude higher than the threshold current of the existing single MWCNT tip. At low electric field, the current fluctuated in a stepwise manner. On the other hand, above critical field, CNT point emitter started to disintegrate so that the current fluctuated rapidly and gradually diminished. These anomalous behaviors were explained from the cap opening and field-induced unraveling of tip edges.

Behaviors of single CO2molecule on pentagon at carbon nanotube tip observed by field emission microscopy

AbstractBehaviors of a single CO2 molecule on a clean pentagon at a tip of multiwall carbon nanotube (MWNT) were investigated by field emission microscopy (FEM). A CO2 admolecule was recognized as a gourd‐shaped bright spot in an FEM image similar to the nitrogen admolecule previously reported. The shape of bright spot reflected an adsorption state that the molecular axis was parallel to substrate pentagon. The CO2 admolecule moved between five steady adsorption sites which were reflected in the geometrical five‐fold symmetry of pentagon. From these experimental results, we propose an adsorption site model for a CO2 admolecule on a clean pentagon. By an Nd:YAG pulse laser irradiation, the CO2 admolecule successfully desorbed without any damage of the substrate pentagon whereas the end‐atoms are oxygen. This suggests that a CO2 molecule on a pentagon is physisorbed and chemically inert for surfaces of MWNT. Copyright © 2008 John Wiley & Sons, Ltd.