Carbon Nanotube Arrays Research Articles

Vertical carbon nanotubes arrays with controlled morphology on silicon carbide fibers for electromagnetic wave absorption

Silicon carbide fiber-Carbon nanotubes arrays (SiCf-CNTs) hybrids with controllable morphologies were successfully synthesized by a floating catalyst chemical vapor deposition method (CVD). As the reaction duration prolonged from 2 min to 15 min, the length of CNTs was elongated from 2 μm to 50 μm, and moreover the content of CNTs in the hybrids increased from 1.5 wt% to 3.7 wt%. By filling this chopped SiCf-CNTs (20 wt%) hybrids into paraffin, the composite with 3 mm in thickness presented the minimum reflection loss (RLmin = −56.2 dB) and the maximum effective absorption wideband (EAB, RL ≤ −10 dB) of 4.3 GHz (8.5–12.8 GHz). The dielectric performance of this hybrid synthesized by optimized CNT's length and growth density has presented high potential in the application of electromagnetic wave absorption.

Flexible and waterproof nitrogen-doped carbon nanotube arrays on cotton-derived carbon fiber for electromagnetic wave absorption and electric-thermal conversion

• Flexible and waterproof NCNT arrays on carbon fiber (NCNT@CF) were fabricated. • NCNT@CF exhibited excellent EMW absorption performances. • The R L,min value and EAB 10 of NCNT@CF are − 57.8 dB and 4.5 GHz, respectively. • RCS values of the materials were simulated under real far field conditions. • NCNT@CF had flexible, waterproof, and electric-thermal conversion functions. It is highly desirable, but challenging to develop multi-functional electromagnetic wave (EMW) absorbing material for practical applications in some special environments. Herein, we successfully fabricated cobalt-nanoparticle-embedded N-doped carbon nanotube arrays on the carbonized cotton fiber cloth as multifunctional material with an excellent EMW absorption, flexibility, hydrophobicity, and electric-thermal performance. The excellent multifunction benefits from high conductivity, large specific surface area, abundant N dopants, and three-dimensional open porous features. Minimal reflection loss and efficient absorption bandwidth of the optimized material as EMW absorbers can reach − 57.8 dB and 4.5 GHz, respectively, which are better than most reported carbon-based absorbers. Meanwhile, theoretical simulations of the radar cross-sectional (RCS) further confirm that the multifunctional material has excellent EMW attenuation performance and potential in practical application. Moreover, the materials possess strong hydrophobicity and high electrical conductivity, endowing them with other attractive functions of self-cleaning and good electric thermal performance, which expand the potential applications range of EMW absorption materials. Our present method can be extended to design next-generation EMW absorbing materials with multifunctionalities for practical applications in harsh environments.

Topologically Tuned Obliquity of Klein-Tunnelling Charged Currents Through Graphene Electrostatically-Confined p - n Junctions

Problem of control over Klein-tunnelling states from electrostatically-confined graphene p - n junctions has been discussed. The lack of quasi-bound states, being the states with a finite life time, in a pseudo-Dirac-fermion model for the graphene quantum dot (GQD) is theoretically predicted as inapplicability of the so-called "resonance condition" leading to an inconsistent linear system corresponding to matching conditions. Within a pseudo-Dirac-Weyl fermion model GQD, the graphene charge carriers are topologically nontrivial and can be confined by a staircase-type potential due to competition between Zak curvature and centrifugal-force actions. The predicted topological effects elucidate experimentally observed resonances created by electron beam and laser pulse in crystalline arrays of single-walled carbon nanotubes as the Klein-tunnelling resonant states in the p - n graphene junctions. We present a robust approach to fabricate stable graphene p - n junctions by fine-tuning the topological effects.

The Fowler–Nordheim plot behaviour from virtual field emitters arrays of zinc oxide nanorods mixed with carbon nanotubes

ABSTRACT The Fowler–Nordheim plot behaviour is investigated for large area field emitters arrays composed of mixtures of ZnO nanorods and single-wall carbon nanotubes (CNTs). The field emission current–voltage characteristics are calculated using the Murphy-Good equation based on the Fowler–Nordheim model. The influencing factors taken into consideration are the radii of the ZnO rods, the heights of the CNTs, the variation of the onset voltage of the saturation of the ZnO conduction band (CB) emission current and the degradation of the CNTs at high applied voltages. The results show that the FN plots of the mixed arrays exhibit nonlinear behaviour near the high-field region which could be related to the FN plot behaviour of the constituting emitters arrays. The distribution of the emitters geometrical parameters and the onset of saturation of the ZnO CB current are found to affect the FN plot behaviour of the pure ZnO, CNTs arrays as well as mixed arrays. The comparisons between the FN plots from the present work and those measured experimentally are found useful to shed light on the field emission mechanism. This may in turn aid the development of complex field emission arrays for future technological applications. The work also shows the possibility to apply the standard FN model to complex large area field emitters arrays.

Impact of Impure Gas on CO2 Capture from Flue Gas Using Carbon Nanotubes: A Molecular Simulation Study.

We used a grand canonical Monte Carlo simulation to study the influence of impurities including water vapor, SO2, and O2 in the flue gas on the adsorption of CO2/N2 mixture in carbon nanotubes (CNTs) and carboxyl doped CNT arrays. In the presence of single impure gas, SO2 yielded the most inhibitions on CO2 adsorption, while the influence of water only occurred at low pressure limit (0.1 bar), where a one-dimensional chain of hydrogen-bonded molecules was formed. Further, O2 was found to hardly affect the adsorption and separation of CO2. With three impurities in flue gas, SO2 still played a major role to suppress the adsorption of CO2 by reducing the adsorption amount significantly. This was mainly because SO2 had a stronger interaction with carbon walls in comparison with CO2. The presence of three impurities in flue gas enhanced the adsorption complexity due to the interactions between different species. Modified by hydrophilic carboxyl groups, a large amount of H2O occupied the adsorption space outside the tube in the carbon nanotube arrays, and SO2 produced competitive adsorption for CO2 in the tube. Both of the two effects inhibited the adsorption of CO2, but improved the selectivity of CO2/N2, and the competition between the two determined the adsorption distribution of CO2 inside and outside the tube. In addition, it was found that (7, 7) CNT always maintained the best CO2/N2 adsorption and separation performance in the presence of impurity gas, for both the cases of single CNT and CNT array.

Detection of ovarian cancer via the spectral fingerprinting of quantum-defect-modified carbon nanotubes in serum by machine learning.

Serum biomarkers are often insufficiently sensitive or specific to facilitate cancer screening or diagnostic testing. In ovarian cancer, the few established serum biomarkers are highly specific, yet insufficiently sensitive to detect early-stage disease and to impact the mortality rates of patients with this cancer. Here we show that a 'disease fingerprint' acquired via machine learning from the spectra of near-infrared fluorescence emissions of an array of carbon nanotubes functionalized with quantum defects detects high-grade serous ovarian carcinoma in serum samples from symptomatic individuals with 87% sensitivity at 98% specificity (compared with 84% sensitivity at 98% specificity for the current best clinical screening test, which uses measurements of cancer antigen 125 and transvaginal ultrasonography). We used 269 serum samples to train and validate several machine-learning classifiers for the discrimination of patients with ovarian cancer from those with other diseases and from healthy individuals. The predictive values of the best classifier could not be attained via known protein biomarkers, suggesting that the array of nanotube sensors responds to unidentified serum biomarkers.

Resonant terahertz generation by cross-focusing of Gaussian laser beams in the array of vertically aligned anharmonic and magnetized CNTs

In this novel scheme of terahertz (THz) generation, the effect of cross-focusing of Gaussian laser beams in the array of vertically aligned anharmonic carbon nanotubes (CNTs) has been studied. The static magnetic field is applied transverse to the axis of CNTs to magnetize the CNTs. The nonlinearity in the system arises due to the ponderomotive force exerted by the laser beams on the electrons of CNTs. The plasma in the CNTs rearranges itself due to this ponderomotive nonlinearity, which gives rise to the cross-focusing of both laser beams. The nonlinear current at THz frequency appears in the array of CNTs on account of the ponderomotive nonlinearity and anharmonicity of the system. The anharmonicity plays a pivotal role in the enhancement of THz generation. The normalized amplitude of THz radiation shows a notable enhancement with the increase of the externally applied static magnetic field 90kG to330kG, dimensions of CNTs, and inter-tube separation. The cross-focusing of two laser beams in the magnetized collisional plasma makes a significant enhancement in the THz generation with the help of anharmonicity.

Electrochemical Microfluidic Multiplexed Bioanalysis by a Highly Active Bottlebrush-like Nanocarbon Microelectrode.

We present a highly efficient multichannel microfluidic electrochemical sensor integrated with an electroactive nanocarbon microelectrode for sensitive and selective detection of multiple biomarkers in different biological samples. Our results have shown that ionic liquid-assisted wet spinning followed by tailored growth of metal-organic frameworks and pyrolysis treatment led to structural and molecular engineering of mechanically robust all-carbon microfibers for excellent electrochemical activities. The flexible bottlebrush-like nanocarbon microelectrode features a "stem" of freestanding N, B-codoped graphene fiber and high-density "bristles" of Co, N-codoped carbon nanotube arrays, leading to promoted electrocatalytic mechanism that has been substantiated by density functional theory calculations. The structural characteristics, high catalytic activities, and favorable biocompatibility of the bottlebrush nanocarbon electrodes provide opportunities for multichannel, microfluidic detection of redox-active biomolecules, including hydrogen sulfide (H2S), dopamine (DA), uric acid (UA), and ascorbic acid (AA), and have been applied to on-chip monitoring of H2S and DA released from live cancer cells or neuroblastoma cells and DA, UA, and AA in trace amounts of body fluids such as sweat, finger blood, tears, saliva, and urine, which is of great significance for clinical diagnosis and prognosis in point-of-care testing.

A Hydrogen-Free Approach for Activating an Fe Catalyst Using Trace Amounts of Noble Metals and Confinement into Nanoparticles.

Metallic iron (Fe) represents an exceptionally active catalyst, as shown in its use in the Haber-Bosch process to dissociate nitrogen molecules; however, the ease of corrosion by oxidation limits its usage. Hence, in most applications using metallic Fe catalysts, hydrogen is a necessary reactant. We report a novel hydrogen-free approach to fabricating reduced, highly active, and corrosion-resistive Fe-based catalysts using trace levels of noble metals (NMs) such as Ir, Rh, and Pt confined in the nanoparticle (NP). X-ray photoelectron spectroscopy (XPS) revealed that as little as ∼0.3 atom % was sufficient to induce the reduction of Fe. Extensive XPS analysis showed that the reduced NM atoms segregated to the NP surface and reduced the surrounding Fe atoms. We demonstrated the catalytic activity of the nanoparticles by the efficient synthesis of submillimeter tall, vertically aligned, and mainly double-walled carbon nanotube arrays using a completely hydrogen-free chemical vapor deposition process.

A Flexible and Ultra‐Wideband Terahertz Wave Absorber Based on Pyramid‐Shaped Carbon Nanotube Array via Femtosecond‐Laser Microprocessing and Two‐Step Transfer Technique

AbstractHigh and uniform absorption capabilities of terahertz (THz) waves in an ultra‐broadband range is desirable for many THz functional devices. Nowadays, it is still challenging to fabricate flexible THz absorbers with a uniformly high absorptance across the entire THz band merely based on traditional bulk materials. Engineered metamaterials absorbers utilize impedance matching to reduce the surface reflection at a single frequency, and can achieve near‐unity power absorption within a relatively narrow bandwidth. In this work, a fabrication strategy combining a femtosecond‐laser microprocessing process and a two‐step‐transfer technique is demonstrated for the realization of vertically‐aligned carbon nanotube (VACNT) arrays with pyramid‐shaped unit cells for THz wave absorptions. To transfer the structured VACNT array from the silicon to the flexible PDMS/Cu/PET substrate, the temperature and pressure dependences of the transfer process are systematically investigated. The fabricated THz absorber demonstrates an average power absorptance over 98.9% from 0.1 to 2.5 THz, and can function well in bended states and after 300 times bending cycles. The proposed fabrication strategy is expected to be used for the patterning of VACNTs and other nanomaterials, and advance the development of novel THz devices for various applications.

Highly flexible all-solid-state microsupercapacitors for on chip applications using a transfer-free fabrication process

Recent research efforts in flexible electronics focus on developing lightweight, thin, and flexible micro scale supercapacitor devices integratable on a chip as power source devices. The key requirements for such devices are high performance, 2D form factor, and compatibility with thin-chip technology. We report the fabrication of an ultra-thin flexible microsupercapacitor (fMSC) based on a highly aligned horizontal array of carbon nanotube (HACNT) sheet with in-plane interdigitated configuration using a facile, single-step and scalable fabrication process. The devices exhibited, excellent flexibility under various bending states, and outstanding bending durability up to 10,000 cycles under bending angle of 180°. A representative fMSC with resolution of 40 μm showed a high peak energy density of 54 mWh cm−3. It was observed that the electrolyte deposition technique (drop-cast vs. spin-coating) affects the performance of fMSC devices. Drop-cast devices showed a higher specific capacitance (almost double) compared to spin-coated devices, but at the expense of flexibility. To demonstrate on-board integration, an array of these fMSCs was used as an energy storage unit in a vibrational energy-harvesting device, powered by a piezoelectric disk. This work demonstrates the potential of HACNT sheet based fMSCs with spin-coat electrolytes as ultra-thin microsupercapacitor devices for portable and wearable electronics.

Feasibility of a prototype carbon nanotube enabled stationary digital chest tomosynthesis system for identification of pulmonary nodules by pulmonologists.

BackgroundScreen detected and incidental pulmonary nodules are increasingly common. Current guidelines recommend tissue sampling of solid nodules >8 mm. Bronchoscopic biopsy poses the lowest risk but is paired with the lowest diagnostic yield when compared to CT-guided biopsy or surgery. A need exists for a safe, mobile, low radiation dose, intra-procedural method to localize biopsy instruments within target nodules. This retrospective cross sectional reader feasibility study evaluates the ability of clinicians to identify pulmonary nodules using a prototype carbon nanotube radiation enabled stationary digital chest tomosynthesis system.MethodsPatients with pulmonary nodules on prior CT imaging were recruited and consented for imaging with stationary digital chest tomosynthesis. Five pulmonologists of varying training levels participated as readers. Following review of patient CT and a thoracic radiologist’s interpretation of nodule size and location the readers were tasked with interpreting the corresponding tomosynthesis scan to identify the same nodule found on CT.ResultsFifty-five patients were scanned with stationary digital chest tomosynthesis. The median nodule size was 6 mm (IQR =4–13 mm). Twenty nodules (37%) were greater than 8 mm. The radiation entrance dose for s-DCT was 0.6 mGy. A significant difference in identification of nodules using s-DCT was seen for nodules <8 vs. ≥8 mm in size (57.7% vs. 90.9%, CI: −0.375, −0.024; P<0.001). Inter-reader agreement was fair, and better for nodules ≥8 mm [0.278 (SE =0.043)].ConclusionsWith system and carbon nanotube array optimization, we hypothesize the detection rate for nodules will improve. Additional study is needed to evaluate its use in target and tool co-localization and target biopsy.

Synthesis of carbon nanotube arrays on quartz-based fibrous materials and their morphological characterization

Carbon nanotubes (CNTs) were synthesized on quartz-based fibrous materials via chemical vapor deposition using camphor. Quartz wool with two different fiber diameters, and quartz filter paper were used as the substrate materials for the synthesis. Quartz wool produced a high yield of CNTs, and the arrays on the fibers had characteristic plate-shaped aligned structures. In addition, CNTs were grown on the quartz filter paper fibers; however, most of these CNTs were not aligned. The effects of the fiber diameter and interfiber distance of the substrate materials on the yield and morphology of the resulting CNTs are discussed.

Excitation of Ultraslow High‐q Surface Plasmon Polariton Modes in Dense Arrays of Double‐Walled Carbon Nanotubes

AbstractThis work explores the plasmonic properties of parallel double‐walled carbon nanotube arrays. It is shown that ultraslow surface plasmon polariton (SPP) modes possessing a phase velocity some orders of magnitude lower than the speed of light in vacuum and high Q‐factor can be generated in such arrays. It is demonstrated that nonrelativistic electron beams with the velocity less than 106 m s−1 can be used to excite SPPs in arrays of double‐walled carbon nanotubes. For the SPP modes excited by an electron beam, the frequency range of SPP waves and electron beam velocities corresponding to the phase matching within a wide frequency range are determined. It opens the way to design slow‐wave structures based on the dense arrays of multiwalled carbon nanotubes employing an efficient energy transfer from the pump to the SPPs.

Soft-lock drawing of super-aligned carbon nanotube bundles for nanometre electrical contacts.

The assembly of single-walled carbon nanotubes (CNTs) into high-density horizontal arrays is strongly desired for practical applications, but challenges remain despite myriads of research efforts. Herein, we developed a non-destructive soft-lock drawing method to achieve ultraclean single-walled CNT arrays with a very high degree of alignment (angle standard deviation of ~0.03°). These arrays contained a large portion of nanometre-sized CNT bundles, yielding a high packing density (~400 µm-1) and high current carrying capacity (∼1.8 × 108 A cm-2). This alignment strategy can be generally extended to diverse substrates or sources of raw single-walled CNTs. Significantly, the assembled CNT bundles were used as nanometre electrical contacts of high-density monolayer molybdenum disulfide (MoS2) transistors, exhibiting high current density (~38 µA µm-1), low contact resistance (~1.6 kΩ µm), excellent device-to-device uniformity and highly reduced device areas (0.06 µm2 per device), demonstrating their potential for future electronic devices and advanced integration technologies.

High Efficiency and Anomalous Photoacoustic Behavior in Vertical CNTs Array

Miniaturized sound generators are attractive to realize intriguing functions. Thermoacoustic device's application is seriously limited due to the frequency‐doubling phenomenon. To address this issue, photoacoustic sound generator is considered as a promising alternative. Here, based on vertical single‐wall carbon nanotubes (CNTs) array, we introduce a photoacoustic sound generator with internal nano‐Helmholtz cavity. Different from traditional device that generates sound by periodically heating up the open space air around material, this sound generator produces an audio signal by forming a forced vibration of the air inside the CNTs. Interestingly, anomalous photoacoustic behavior is observed that the sound pressure level (SPL) curve has a resonance peak, the corresponding frequency of which is inversely proportional to the CNTs array’s height. Furthermore, the energy conversion efficiency of this photoacoustic device is 1.64 times as large as that of a graphene sponge‐based photoacoustic device. Most importantly, this device can be employed for music playing, bringing a new clew for the development of musical instruments in the future.

Propagation of few cycle pulses in the array of carbon nanotubes with polymers under the constant magnetic field

The effect of a constant magnetic field on the behavior of few cycle optical pulses in an array of carbon nanotubes with polymers was studied in this research. The main equation describing the propagation of an electromagnetic field in the medium under consideration was obtained on the basis of Maxwell's equations. The dependences of the optical pulse shape on the concentration of the polymer in the medium are obtained. Keywords: few cycle pulse, cafbon nanotube, magnetic field, polymer.

The change in the thermal conductivity of a multilayer array of carbon nanotubes during its lateral compression

Numerical simulation of thermal conductivity across a multilayer array of single-walled carbon nanotubes is carried out. The effect of transverse compression of the array on thermal conductivity has been studied. It is shown that the compression of the array can occur uniformly when all the nanotubes of the array are compressed equally, and it can occur inhomogeneously when a part of the nanotubes is strongly compressed, and the other part is weakly compressed. With homogeneous compression, the thermal conductivity of the array increases, but with inhomogeneous compression, it does not change and may even decrease in case of a large number of layers. This effect is especially pronounced for arrays of nanotubes of small diameter (D&amp;lt;2 nm). Keywords: carbon nanotubes, nanotube arrays, transverse compression, heat conductivity.

Dynamics of a colloid-in-tube host-guest system.

Originated from supramolecular chemistry, the host-guest concept is generalized and appreciated across the fields of enzyme catalysis, biological channel conduction, and carbon nanotube transport, to name a few. Despite the extensive study of host-guest thermodynamics, it is still a fundamental challenge to directly measure its dynamics in real-space and real-time. Herein we approach such dynamics by direct imaging and tracking in a colloid-in-tube system, where self-assembled tubes are the hosts and sphere particles are the guests. The key difference from a previously reported static 1D confinement is that the present tubes are thermally actuated and capable of translations and rotations. It is the host tube thermal motions that impose a number of anomalies to guest particle dynamics including broadened distribution perpendicular to the tube, enhanced diffusion parallel to the tube phenomenologically resembling the rapid flow in ion channels or carbon nanotubes, and induced long-range particle-particle attraction analogous to capillary condensation. This work in the colloidal system is of wide implications for host-guest systems that are naturally embedded in thermal fluctuations such as transmembrane ion channels and carbon nanotube arrays in a soft matrix.

Three-Dimensional Mathieu and Bessel Pulses in an Array of Impurity Carbon Nanotubes

Three-Dimensional Mathieu and Bessel Pulses in an Array of Impurity Carbon Nanotubes