Multiwalled Carbon Nanotube Arrays Research Articles

Hydrogen Plasma Treatment of Aligned Multi-Walled Carbon Nanotube Arrays for Improvement of Field Emission Properties.

Vertically aligned carbon nanotube (CNT) arrays show potential for the development of planar low-voltage emission cathodes. The characteristics of cathodes can be improved by modifying their surface, e.g., by hydrogen plasma treatment, as was performed in this work. The surface of multi-walled CNT arrays grown on silicon substrates from toluene and ferrocene using catalytic chemical vapor deposition was treated in a high-pressure (~104 Pa) microwave reactor. The structure, composition, and current-voltage characteristics of the arrays were studied before and after hydrogen plasma treatment at various power values and durations. CNT tips were destroyed and catalytic iron was released from the CNT channels. The etching rate was influenced by iron particles that formed on the array surface. The lower emission threshold in the plasma-treated arrays than in the initial sample is explained by the amplification factor of the local electric field increasing due to graphene structures of unfolded nanotube layers that formed at the CNT tips.

Metal-decorated carbon nanotubes-based sensor array for simultaneous detection of toxic gases

Herein, we report a toxic gas detector based on an array of metal-decorated multiwalled carbon nanotubes (M-MWCNTs) sensors. The room temperature (20 °C) response of the sensors array towards NO2, H2S, NH3, and CO gases was investigated. The MWCNTs were decorated with transition metals, Pt, Ti, Ag, Ru, and Cu to enhance the sensitivity and selectivity of the carbon nanotubes to the toxic gases. The M-MWCNTs powders were deposited on gold electrodes and printed on flexible Kapton sheets to form the sensors array. CO exhibited the lowest resistance change response for all six sensors (five transition metal-decorated MWCNTs sensors and one pristine MWCNTs-based sensor), with the Ag-MWCNTs sensor exhibiting the highest response of 0.047–100 ppm CO. The Ag-MWCNTs also revealed the relatively highest sensitivity of 0.944 upon exposure to 100 ppm NH3. The Cu-MWCNTs sensor showed the highest sensitivity of 1.75 upon exposure to 10 ppm H2S, while the Pt-MWCNTs sensor showed the highest response of 1.96 upon exposure to 10 ppm NO2. A unique response pattern was generated for each gas that can be used for its identification. The experimental results were also compared to our previously reported density functional theory (DFT) calculations, revealing the same order of resistance change, thereby validating the use of DFT as a tool to predict the interaction properties and providing an in-depth understanding of the reducing/oxidizing gas electron transfer mechanisms.

Hydrogen-modulated Ar/CH4 HWP-CVD for fast preparation of multi-wall carbon nanotube arrays with high specific capacitance

Two-dimensional Multiwalled Carbon Nanotube arrays (MWCNTs) were prepared by a novel high-density helicon wave plasma chemical vapor deposition (HWP-CVD) at room temperature. Preliminary studies show that the MWCNTs prepared by this method has strong orientation and is perpendicular to the substrate surface, and exhibit a highly ordered array distribution. The addition of hydrogen can effectively improve the growth rate of MWCNTs and increase the aspect ratio. The height and aspect ratio of MWCNTs can be effectively increased with the increase of growth time. Electrochemical investigation indicated that MWCNTs have high specific capacitance (1.96 mF/cm−2) and excellent rate capability (81.6%).

A new-structured nanocarbon cushion with highly impact-resistant properties

Compared with traditional impact-resistant materials, nanocarbon materials have the advantages such as light weight, large specific volume for energy dissipation and their exceptional thermal stability for the extreme-environmental working potentials. However, based on the commonly used fabrication method, the general nanocarbon structures (e.g. carbon nanotube (CNT) array) are always constructed with the weak interaction between units. Therefore, when they are subjected to impact, the impact energy cannot be transferred throughout the whole loose and discontinuous structure efficiently, which results in the degradation of their impact-resistant capabilities. To address the above issue, we fabricated a nanocarbon “cushion” with the combination of a diamond like carbon (DLC) film and multi-wall CNT (MWCNT) array. The DLC film was deposited successfully onto the as-grown MWCNT array through enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) method to form a continuous upper layer which is vital to distribute and transfer the impact energy loading. The new nanocarbon system has high specific dissipated energy up to ∼2.22 kJ/m3, which is almost twice as much as that of the commercial polyurethane sponge. We anticipate that this study will provide new insights to develop novel nanocarbon materials for impact resistance in high-tech edge applications.

Development of CNT Film Alignment and Geometries for Neuronal Attachment and Efficient Signal Transfer between Neurons and Electrodes

Carbon nanotubes (CNTs) are widely used in neuroscience research for its excellent properties such as high conductivity, electrochemical stability, biocompatibility, mechanical compatibility with tissues, tunable mechanical and chemical properties. CNTs are investigating for its performance as neuronal scaffolds to support neural tissues, neuron growth and differentiation as well as neural stimulating and recording electrodes to control and monitor neural activity in both vitro and in vivo environments. Surprisingly neurons show a better interaction with CNTs when neurons are grown on CNT substrates. Previous research has shown neuronal differentiation on pristine CNT and CNT composites and the alignment of neurites on CNT substrates. Current research focus on interaction of neurons at the interface of pristine CNT films with aligned and cross hatch patterned CNT layers prepared from multi-walled CNT arrays. CNTs have nano scale surface roughness and contribution of alignment of CNTs can retain and adhere neurons without any adhesive proteins. As an initial step to study the interaction of neurons with CNT films, the effect of different CNT alignment on neuron adhesion and neurite development was chosen. PC12 cell line was used to study neuron adhesion and neurite alignment on CNT substrates. It is a commonly used neuronal cell model due to its ability to attain sympathetic neurons characteristics in the presence of nerve growth factor (NGF) in low serum medium. For the study, CNT films were prepared as aligned and in cross hatch pattern on PET sheets. After sterilization with UV irradiation, PC12 cells were seeded and cultured at a density of 20 000 cells/mL on CNT films and allowed to differentiate in NGF medium. For comparison poly l lysine (PLL) coated CNT films were used. Fig 1(Left) shows SEM image of a differentiating PC12 cell on PLL coated film of aligned CNTs and Fig 1(Right) shows SEM image of a differentiating PC12 cell on a crosshatch patterned CNT film with no adhesive coating. While neurites of PC12 cells align with the CNTs on aligned CNT film as states in the literature, pristine CNTs in crosshatch pattern were also able to hold the cells without any surface adhesive coating and allow differentiation of cells. Also PC12 cells tend to show random alignment on crosshatch patterned CNTs and adhere well due to higher degree of porosity and surface roughness. As pristine CNT films were able to hold PC12 cells, the interface properties will be further evaluated by impedance spectroscopy. Figure 1

Creation of metasurface from vertically aligned carbon nanotubes as versatile platform for ultra-light THz components

Here a simple and reproducible method for obtaining terahertz metasurfaces formed from multiwall carbon nanotubes (MWCNTs) is presented. The metasurfaces were obtained from a vertically aligned array of MWCNTs using a laser engraving technique followed by polymer covering. The structures under study demonstrate frequency-selective reflection in terahertz range following the Huygens–Fresnel formalism. For a normal incidence of the electromagnetic wave, the model for numerical calculation of backscattering from the metasurfaces was proposed. Lightweight and compact MWCNT-based metasurfaces are capable to replace conventional pyramidal absorbers and could serve as a versatile platform for scalable cost-efficient production of ultra-light electromagnetic components for THz applications.

The Effect of Laser Structuring of Carbon Nanotubes on the Proliferation of Chondroblasts and Mesenchymal Stem Cells

The density of cartilage cells (chondroblasts) proliferating on a silicon substrate coated with vertically oriented arrays of multi-walled carbon nanotubes (MWCNTs) was shown to be higher than on a pure silicon substrate. Electron microscopy showed that the cells in a nutrient medium affected the vertical position of the nanotubes in the array. A method for structuring the MWCNT arrays by 100-ns laser pulse scanning and abrasive water processing on planar substrates was developed. As a result of the structuring of the MWCNTs, the arrays become resistant to bending under the influence of the nutrient medium with mesenchymal stem cells. Structured MWCNT arrays were shown to have no toxic or pathological effect on the viability and morphology of stem cells. Thus, such materials can be suggested for use in cell-adhesive components of biomedical devices.

Self-Catalyzed Vertically Aligned Carbon Nanotube-Silicon Core-Shell Array for Highly Stable, High-Capacity Lithium-Ion Batteries.

Here, we report on the simple, catalyst-free preparation and application of carbon nanotube-silicon core-shell composite anodes on stainless steel. The stainless steel mesh structure acts as a self-catalyzing agent for the plasma-enhanced chemical vapor deposition (PECVD) growth of vertically aligned, dense, multiwalled carbon nanotube arrays. The carbon nanotube array then serves as a bed for silicon deposition by the decomposition of silane through chemical vapor deposition (CVD). This approach leads to the formation of highly conductive and stable composite anodes. Silicon deposition on the substrate is controlled in terms of the optimal silicon shell thickness, thus enhancing the performance of the cell. These extremely stable, binder-free composite electrodes were characterized as potential anodes in Li-ion batteries, exhibiting long cycle life (>700 cycles), high gravimetric capacity (>4000 mAh/gSi), low irreversible capacity (<10%), and high Coulombic efficiency (>99.5%). These composite anodes meet the requirements of Li-ion batteries for future portable electronics and electric vehicle applications.

Memory Effect and Fractional Differential Dynamics in Planar Microsupercapacitors Based on Multiwalled Carbon Nanotube Arrays

The development of portable electronic devices has greatly stimulated the need for miniaturized power sources. Planar supercapacitors are micro-scale electrochemical energy storage devices that can be integrated with other microelectronic devices on a chip. In this paper, we study the behavior of microsupercapacitors with in-plane interdigital electrodes of carbon nanotube array under sinusoidal excitation, step voltage input and sawlike voltage input. Considering the anomalous diffusion of ions in the array and interelectrode space, we propose a fractional-order equivalent circuit model that successfully describes the measured impedance spectra. We demonstrate that the response of the investigated micro-supercapacitors is linear and the system is time-invariant. The numerical inversion of the Laplace transforms for electric current response in an equivalent circuit with a given impedance leads to results consistent with potentiostatic measurements and cyclic voltammograms. The use of electrodes based on an ordered array of nanotubes reduces the role of nonlinear effects in the behavior of a supercapacitor. The effect of the disordering of nanotubes with increasing array height on supercapacitor impedance is considered in the framework of a distributed-order subdiffusion model.

Effective surface emissivity and heat dissipation among integrated bamboo-like super-black vertical carbon nanotube array electrodes in silicon via holes

Recently, carbon nanotube (CNT)-based micro-devices have attracted extensive attention at the frontiers of intelligent electronics, but the practical application of these devices are seriously limited by the low CNT package rates, poor heat dissipation, and intricate in-situ growth processes. Here, microelectrodes with low impedance based on in-situ-grown super-black vertical bamboo-like multi-walled CNT arrays (∼70 μm) were fabricated inside silicon via holes using face-down catalytic plasma enhanced chemical vapor deposition. Interestingly, the unique CNT array exhibited uniformly high absorption efficiency with a broad range of wavelength (exceeding 99.65% in the UV-NIR band and 99% in the mid-infrared region). Moreover, the excellent cooling performance of CNT array microelectrodes based on in-situ-grown bamboo-like CNT arrays within silicon via holes was demonstrated. Our study highlights the benefits of CNT-based micro functional devices, which indicates the integrated in-situ-grown bamboo-like CNT arrays will have potential applications in advanced microelectrodes, CNT-based field-effect transistors, and portable terahertz inspection devices.

Ullmann Reactions of Carbon Nanotubes-Advantageous and Unexplored Functionalization toward Tunable Surface Chemistry.

We demonstrate Ullmann-type reactions as novel and advantageous functionalization of carbon nanotubes (CNTs) toward tunable surface chemistry. The functionalization routes comprise O-, N-, and C-arylation of chlorinated CNTs. We confirm the versatility and efficiency of the reaction allowing functionalization degrees up to 3.5 mmol g−1 by applying both various nanotube substrates, i.e., single-wall (SWCNTs) and multi-wall CNTs (MWCNTs) of various chirality, geometry, and morphology as well as diverse Ullmann-type reagents: phenol, aniline, and iodobenzene. The reactivity of nanotubes was correlatable with the nanotube diameter and morphology revealing SWCNTs as the most reactive representatives. We have determined the optimized conditions of this two-step synthetic protocol as: (1) chlorination using iodine trichloride (ICl3), and (2) Ullmann-type reaction in the presence of: copper(I) iodide (CuI), 1,10-phenanthroline as chelating agent and caesium carbonate (Cs2CO3) as base. We have analyzed functionalized CNTs using a variety of techniques, i.e., scanning and transmission electron microscopy, energy dispersive spectroscopy, thermogravimetry, comprehensive Raman spectroscopy, and X-ray photoelectron spectroscopy. The analyses confirmed the purely covalent nature of those modifications at all stages. Eventually, we have proved the elaborated protocol as exceptionally tunable since it enabled us: (a) to synthesize superhydrophilic films from—the intrinsically hydrophobic—vertically aligned MWCNT arrays and (b) to produce printable highly electroconductive pastes of enhanced characteristics—as compared for non-modified and otherwise modified MWCNTs—for textronics.

Optical Rectenna Arrays Using Carbon Nanotubes: From Fundamental Understanding to Next Generation Devices

Optical rectennas have emerged as promising devices for high frequency optoelectronic applications such as infrared and optical sensing and energy conversion. We achieve optical rectification using vertical multiwall carbon nanotube (CNT) arrays. The CNT nanoantennas absorb electromagnetic waves and ultrafast metal-insulator-metal tunnel diodes fabricated at the CNT tips convert the resulting terahertz AC current into DC electricity. Since the first demonstration in 2015, considerable progress to CNT optical rectennas has been made. The latest generation of CNT rectenna uses an innovative multi-insulator structure to provide exceptional diode properties and enable air stable materials. We applied photon-assisted tunneling theory to model our device’s optical-frequency behavior. Comparing the rectenna model to our optical experiments through a range of wavelengths (404–1064 nm) has yielded a better fundamental understanding that will guide future device design. The model provides strong evidence that the CNT antennas behave as dipole antennas and implicates a 780 THz diode cutoff frequency that reveals room for performance improvement. We report ongoing research developing a novel flexible CNT rectenna device structure. We use polydimethylsiloxane (PDMS) to infiltrate the CNT array and create a mechanically flexible substrate and planarized diode surface. This structure enables transparent, conductive top electrodes with PEDOT:PSS. Our recent efforts greatly enhance the commercial development of efficient, low cost, and application tunable CNT rectennas.

Carbon nanotube based dielectric spectroscopy of tumor secretion; electrochemical lipidomics for cancer diagnosis

Cell free diagnosis of cancer is one of the crucial fields in new generation of medical technology. In this regard, cancer detection based on coastal fluids secreted from the tissues (named as secretome) has attracted a lot of attention. Lipids are important macromolecules could be found with much higher concentrations in secretome of cancer tissues vs. normal ones. On the other hand, lipids are the main dielectric components of the secretome with respect to proteins and ions. Here for the first time we introduced an electrochemical lipidomics based on electrical impedance spectroscopy (EIS) of the secretomes to detect the cancerous samples due to the lipidic content of their secretions. The EIS sensor was fabricated by multiwall carbon nanotube (MWCNT) arrays as conductive and super hydrophobic materials to have great interactive surface with the lipidic content of the solution. Results of the tests on the secretions of more than 100 human biopsied breast tissues showed the promising match between the charge transfer resistance (RCT) of samples’ secretions and pathological states of the tissues with meaningful boundary (up to 8 kΩ for normal and more than 13 kΩ for cancer samples). Mass spectroscopic analyses confirmed the higher content of lipids in cancer secretomes. Electrical lipidomics of the secretome shed new lights in cell free cancer diagnosis and could be applied as a complementary clinical approach in all of biopsy based diagnoses in future.

Effect of Functionalization on the Conductivity and Noise Characteristics of Arrays of Multiwall Carbon Nanotubes

Effect of Functionalization on the Conductivity and Noise Characteristics of Arrays of Multiwall Carbon Nanotubes

Enhanced hydrophobicity of stainless-steel mesh surface by carbon nanotube arrays from flame

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays were synthesized directly on the stainless-steel (SS) mesh with grooves by flame method. The results from comprehensive characterizations confirmed the MWCNTs were prepared as array structures with good hydrophobicity on the surface of the SS mesh and were connected into a complete layer. The static contact angle of surface of the MWCNTs hydrophobicity coating was increased from the 113° to 141° as the growth of MWCNT arrays. The scalability from the hydrophobicity of the MWCNT arrays have been also verified when MWCNTs were anchored on another flexible substrate by the static contact angle test and water droplet rolling experiment. At the same time, the lipophilicity of MWCNTs was verified by dynamic contact angle test and oil-water separation experiment.

Влияние функционализации на электропроводность и шумовые характеристики массивов многостенных углеродных нанотрубок

AbstractThe electrophysical and noise characteristics of arrays of multiwall carbon nanotubes (MWCNTs) functionalized in various ways were studied. It is demonstrated that the as-prepared and annealed MWCNT arrays have semiconductor-type resistivities and temperature dependences of resistivity, while the arrays of annealed MWCNTs functionalized with acids have metallic properties. Low-frequency 1/ f noise in the 0.2‒20 kHz range was observed for all MWCNT arrays. Simple thermal annealing raised the noise level severalfold and annealing with acid treatment resulted in noise reduction and a change in the index of power in its current dependence. The normal amplitude distribution of noise spikes transformed to a lognormal one as the density of as-prepared MWCNT arrays increased. The duration distribution of these spikes became narrower at higher densities.

Arrays of vertically aligned multi-walled carbon nanotubes grown on silicon and copper substrates by thermal decomposition of ferrocene-toluene aerosol

Arrays of multi-walled carbon nanotubes (MWCNTs) were grown vertically on the surfaces of SiO2/Si substrates using aerosol-assisted catalytic chemical vapour deposition (CCVD) method. Aerosol was produced by injecting a solution of ferrocene (catalyst source) in toluene (carbon source) into a hot zone of a horizontal CVD reactor. Dependences of the height and density of the MWCNT array on the synthesis temperature and ferrocene concentration were determined. The found optimal parameters were used for the MWCNT growth on copper substrates. For this purpose, a copper foil was covered by alumina layer and we showed that the thickness of this layer should be not less than 17 nm to provide the MWCNT growth over the entire foil surface. The vertically aligned MWCNT array tightly bonded with copper substrate can be used as a heat-exchange surface in various micro and nano heat-transfer devices.

Chlorine-assisted synthesis of Fe3C-filled mm-long vertically aligned arrays of multiwall carbon nanotubes

Recent reports have shown that chlorine-radicals can be beneficial for the growth of Fe3C filled carbon nanotubes (CNTs) and the control of their filling-ratio. Here we use such chlorine-assisted approach to demonstrate the controlled synthesis of vertically aligned arrays of mm-long multiwall CNTs filled with large quantities of ferromagnetic Fe3C. CNTs-lengths up to 2 mm can be achieved through the control of the ferrocene concentration and the thickness of the SiO2 layer of the substrate for a fixed dichlorobenzene concentration.

Channelling and induced defects at ion-bombarded aligned multiwall carbon nanotubes

A detailed investigation of ion channelling and defect production for a highly-ordered array of multi-wall carbon nanotubes is presented. The effects of argon ion bombardment (0.25–5 keV) carried out either parallel (top) or perpendicular (side) to their axis, have been studied by Raman, X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy. Raman spectra provided evidence of channelling of the Ar+ ions observed for top bombardment along the whole 180 μm carbon nanotube length, while the penetration length is limited to the first 10 μm when the ions impinge from the side. The nature of defects, determined through the spectral fingerprints of the C 1s core level as a function of energy and flux, unveils a distorted sp3-like bonding increase and the π-excitation decrease till quenching. Dangling bond states due to displaced carbon atoms become significant only at beam energies higher than 0.25 keV and high flux. These results on anisotropic channelling and selective defects creation open new perspectives in the application of highly-ordered arrays of multi-wall carbon nanotubes as anisotropic detectors.

Hyaluronic acid-grafted three-dimensional MWCNT array as biosensing interface for chronocoulometric detection and fluorometric imaging of CD44-overexpressing cancer cells.

A sandwich-type electrochemical cytosensor is described for quantitative determination of CD44-overexpressing HeLa cells. Hyaluronic acid (HA) acts as a targeting molecule that was in-situ incorporated into the sensor based on the use of an indium tin oxide (ITO) electrode modified with multi-walled carbon nanotubes (MWCNTs). The 3D-MWCNT structure is shown to strongly improve the electronic properties and surface chemical reactivities. The HA-modified sensor exhibits a highly sensitive response to HeLa cells. A sandwiched hybridization protocol was then established using BIO [an N-butyl-4-(6'-aminohexyl)amino-1,8-naphthalimide probe modified with HA] as the tracing labels of the fluorescent probes for targeting CD44-positive tumor cells. The signal amplification was thereby maximized and measured by chronocoulometry. The binding ofCD44-positive HeLa cells to the HA modified sensing layer causes a decrease in chronocoulometric response. The signal decreases linearly in the 2.1 × 102 to 2.1 × 107 HeLa cells·mL-1 concentration range with a detection limit of 70 cells·mL-1. Such a sandwich-type assay may be tailored as a sensitive candidate for detecting low levels of tumor cells. Graphical abstract Schematic of a sandwich cytosensor based on hyaluronic acid-grafted 3D-MWCNT as biosensing interface and BIO as fluorescent probe. This biosensor possessed excellent electrochemical activity, high sensitivity and selectivity, providing a dynamical tracking and detecting platform for CD44-positive tumor cells.