Well-aligned Carbon Nanotube Arrays Research Articles

Direct growth of vertically well-aligned carbon nanotube arrays on atomic layer deposition of ZnO films

Plasma-enhanced chemical vapor deposition (PECVD) was used to prepare vertically well-aligned carbon nanotube arrays on atomic layer deposition (ALD) of zinc oxide (ZnO) films with acetylene (C2H2) and ammonia (NH3). The mechanisms of their nucleation and initial growth were analyzed on ZnO films, and the activation energy was also calculated to be about 60.7 kJ/mol. Generally, the reactivity of NH2 radicals was higher than that of H2 molecules and H radicals, so the activation energy was lower for the nucleation and initial growth of vertically aligned carbon nanotube arrays (VACNTs) with NH2 radicals, compared with H radicals and H2 molecules.

An Ingenious Strategy to Integrate Multiple Electrocatalytically Active Components within a Well-Aligned Nitrogen-Doped Carbon Nanotube Array Electrode for Electrocatalysis

In this paper, an ingenious strategy was developed to construct a well-aligned nitrogen-doped carbon nanotube (NCNT) array electrode integrated with multiple electrocatalytically active components ...

Aligning dense carbon nanotube arrays

Device Technology Although semiconducting carbon nanotubes (CNTs) are promising candidates to replace silicon in transistors at extremely small dimensions, their purity, density, and alignment must be improved. Liu et al. combined a multiple dispersion sorting process, which improves purity, and a dimension-limited self-alignment process to produce well-aligned CNT arrays on a 10-centimeter silicon wafer. The density is sufficiently high (100 to 200 CNTs per micrometer) that large-scale integrated circuits could be fabricated. With ionic liquid gating, the performance metrics exceeded those of conventional silicon transistors with similar dimensions. Science , this issue p. [850][1] [1]: /lookup/doi/10.1126/science.aba5980

Aligned, high-density semiconducting carbon nanotube arrays for high-performance electronics.

Single-walled carbon nanotubes (CNTs) may enable the fabrication of integrated circuits smaller than 10 nanometers, but this would require scalable production of dense and electronically pure semiconducting nanotube arrays on wafers. We developed a multiple dispersion and sorting process that resulted in extremely high semiconducting purity and a dimension-limited self-alignment (DLSA) procedure for preparing well-aligned CNT arrays (within alignment of 9 degrees) with a tunable density of 100 to 200 CNTs per micrometer on a 10-centimeter silicon wafer. Top-gate field-effect transistors (FETs) fabricated on the CNT array show better performance than that of commercial silicon metal oxide-semiconductor FETs with similar gate length, in particular an on-state current of 1.3 milliamperes per micrometer and a recorded transconductance of 0.9 millisiemens per micrometer for a power supply of 1 volt, while maintaining a low room-temperature subthreshold swing of <90 millivolts per decade using an ionic-liquid gate. Batch-fabricated top-gate five-stage ring oscillators exhibited a highest maximum oscillating frequency of >8 gigahertz.

Realizing Controllable Carbon Nanotube Arrays for Soft Devices by Asymmetric Langmuir–Blodgett and Hydrophilization Process

Well-aligned Carbon nanotube (CNT) arrays are expected by flexible and stretchable devices. In this paper, an asymmetric Langmuir-Blodgett (LB) method and inorganic hydrophilization method have been proposed, with which well-aligned CNT arrays on soft substrates like polyethylene naphthalate, polyimide and polydimethylsiloxane have been realized. After depositing 50 nm SiO2 for hydrophilization, the water contact angle has been significantly reduced for different substrates. The surface roughness and flexibility have also been characterized to analyze their effect on device performance. The nanotube density in the arrays can be controlled to 10-25 tubes/μm 2 , 25-35 tubes/μm 2 or 35-45 tubes/μm 2 by tuning the surface pressure during the LB process. With aligned semiconducting CNT arrays as channel and anisotropic metallic CNT network as gate/source/drain electrodes, all-carbon nanotube transistors on PI substrate have been fabricated for demonstration. The fabricated devices show a subthreshold swing of 92.9 mV/dec, a carrier mobility of 15.32 cm 2 /Vs, and an on/off current ratio of 4.51 × 10 2 . More importantly, with 50 nm thick gate dielectrics, the changes of threshold voltage and carrier mobility are within 16.62% and 28.78%, respectively, even after bending 1000 times under a curvature radius of 3.66 mm.

Facile active control of a pulsed erbium-doped fiber laser using modulation depth tunable carbon nanotubes

Short pulsed fiber lasers have been widely made using single-walled carbon nanotubes as a saturable absorber (SA). However, most of the currently used devices can only operate in one determined operation state with an unchangeable modulation SA depth in the cavity, which significantly limits their application in photonic devices. In this paper, well-aligned carbon nanotube arrays are synthesized using zeolite AlPO4-5 as a template, which features anisotropic optical absorption. The linear optical absorption of the as-synthesized carbon nanotube arrays can easily be tuned by adjusting a polarization controller, thus providing a tunable modulation depth for the carbon nanotube SA. By exploiting this SA in an erbium-doped fiber laser cavity, both Q-switched and mode-locked pulsed lasers are achieved by simply adjusting a polarization controller under a fixed pump power of 330 mW. In addition, the repetition rate of the Q-switching and pulse duration of the mode-locking can be tuned according to the variation of modulation depth. Moreover, soliton molecules can be obtained when the modulation depth of the SA is 4.5%.

A New Mitigation Method for Space Robot Charging Effect Based on CNTs

Autonomous space robot will be widely used to complete various space missions in future. Unfortunately electrostatic surface discharge (ESD) induced by space plasma environment may produce one of the most common anomaly in space robots. Liquid Metal Ion Source (LMIS) is one of the effective mitigation methods for space robot charging effect. But as a devices for space-robots charging mitigation equipment, has strict requirements to its weight and volume. The present LMIS can only work at a very high voltage, so the weight and volume of LMIS isn’t suitable for space robot. Here we propose that carbon nanotubes (CNTs) can be used as capillary-type emitters in LMIS to meet the challenge. Well-aligned CNT arrays are synthesized on self-ordered hexagonal porous anodic aluminum oxide (AAO) template using chemical vapor deposition (CVD) method. The CNTs obtained are monodispersed and have open tip, which indicates that they have the similar geometry to the present capillary-type emitters in LMIS. So the LMIS made of CNTs can emit ions at a very lower voltage. A new mitigation device for space robot charging effects with very small weight and volume can be developed. The key steps for fabricating CNT emitters are presented.

Interface analysis and design in carbon nanotube array composite based on cohesive finite element approach

Mechanical properties of composites can be significantly improved by using well-aligned carbon nanotube array (CNTA) as reinforcements. However, damage and cracks at the interface between carbon nanotubes (CNTs) and matrix are still major factors hampering the desired reinforcement effect of the CNTA. In this paper, a micromechanics-based bilinear cohesive law was applied in cohesive finite element model to characterize CNT/matrix interface. The interfacial properties were described by varying the values of cohesive strength and fracture energy of the interface. Then numerical simulation for the interfacial fracture and macroscopic properties of the CNTA composites under transverse loadings was conducted based on the present cohesive finite element method. Remarkable influences of interfacial properties on the overall properties of the CNTA composites were verified. The brittle failure mode of the CNTA composites was found to be shifted to the ductile mode as the interface became more expandable. Moreover, it is proved that the CNTA composites have a potential improvement with increased CNTA volume fraction and optimized interfacial cohesive parameters.

Pretreatment Control of Carbon Nanotube Array Growth for Gas Separation: Alignment and Growth Studied Using Microscopy and Small-Angle X-ray Scattering

Aligned multiwalled carbon nanotube (CNT) arrays were prepared using chemical vapor deposition of C2H4 on Fe catalyst at 750 °C. CNT array height and alignment depends strongly on the duration of H2 pretreatment, with optimal height and alignment achieved using 10-15 min pretreatment. Small-angle X-ray scattering (SAXS) was used to quantify the alignment, distribution, and size of the CNTs in arrays produced from varying pretreatment times and the results correlated with microscopy measurements. SAXS analysis revealed that the higher section of the CNT arrays exhibited better alignment than the lower section. Combining these insights with transmission electron microscopy measurements of the CNT defects within each array enable a mechanism for the CNT growth to be proposed, where the loss of alignment arises from deformation of the CNTs during their growth. Gas permeation test across densified CNT arrays indicated that the alignment of the CNT array plays an important role in the gas transport, and that the gas diffusion across the well-aligned CNT arrays was enhanced by a factor of ~45, which is much more than that across the poorly aligned CNT arrays, with an enhancement factor of ~8.

High-Density Carbon Nanotube Buckypapers with Superior Transport and Mechanical Properties

High-density buckypapers were obtained by using well-aligned carbon nanotube arrays. The density of the buckypapers was as high as 1.39 g cm(-3), which is close to the ultimate density of ideal buckypapers. Then we measured the transport and mechanical properties of the buckypapers. Our results demonstrated that its electrical and thermal conductivities could be almost linearly improved by increasing its density. In particular, its superior thermal conductivity is nearly twice that of common metals, which enables it a lightweight and more efficient heat-transfer materials. The Young's modulus of the buckypapers could reach a magnitude over 2 GPa, which is greatly improved compared with previous reported results. In view of this, our work provided a simple and convenient method to prepare high-density buckypapers with excellent transport and mechanical properties.

Formation of free-standing carbon nanotube array on super-aligned carbon nanotube film and its field emission properties

Flexible and free-standing well-aligned carbon nanotube arrays have been synthesized on super-aligned carbon nanotube films. The combined structure of the carbon nanotube array and carbon nanotube film was formed during chemical vapor deposition on a quartz substrate which had previously been covered with a super-aligned carbon nanotube film. It was found that the growing carbon nanotube array could support up the super-aligned carbon nanotube film entirely, and the top of the array became densely entangled with the super-aligned carbon nanotube film. The carbon nanotube array with the super-aligned carbon nanotube film could be easily peeled off from the quartz substrate as a whole, giving a flexible and free-standing structure with good mechanical properties. The bottom of the array was also exposed after being peeled off and was used as a field emitter. The combined structure of the carbon nanotube array with the carbon nanotube film allowed adsorbent-free field emission by passing a heating current through it. Furthermore, due to the fast thermal response of the structure and the long time needed for re-adsorption of adsorbates in vacuum, it was found that pulsed heating with a 10% duty ratio was sufficient for adsorbent-free field emission. The heating power necessary to sustain the adsorbent-free state can be lowered in this way. Open image in new window

Macroscopic Synthesis of Vertically Aligned Carbon Nanotubes Using Floating Catalyst Chemical Vapor Deposition Method

In this paper, we report an efficient process to grow well-aligned carbon nanotube (CNT) arrays with a good area distribution density (about 5.6 ×107 CNT/mm2). Vertically aligned carbon nanotubes (VA-CNTs) have been produced by controlling flow rate, temperature and catalyst nanoparticles using a floating catalyst chemical vapor deposition (FC-CVD) technique. They were synthesized on quartz substrates at 800 °C from toluene as a carbon source. VA-CNT samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and their surface area and pore size were determined by nitrogen adsorption analysis. The synthesized CNTs have a length of 500 µm and diameters ranging from 120±40 nm. The CNT filaments form a strength structure and exhibit a good vertical alignment. The remarkable properties of CNTs make them attractive for separation applications, especially for water and wastewater treatment.

Investigation on Strain-Sensing Suspended Single-Walled Carbon Nanotube Arrays

An electromechanical system is constructed to explore the electrical properties of well-aligned horizontal suspended single-walled carbon nanotube (SWCNT) arrays under the influence of tensile stretching. The suspended SWCNT array sensing structure consists of a well-grown SWCNT array suspended between two separated metal electrodes on top of a silicon (Si) wafer with 500-nm-thick thermal oxide layer. Sensor properties are explored in linear region, including sensitivity (gauge factor ~248), linearity (better than 99%), and hysteresis. Results show that the suspended SWCNT array devices have potential application as strain gauges due to their high sensitivity.

Adhesive Enhancement Improved Field Emission Characteristics of Carbon Nanotube Arrays on Energetic Ion Pre-Bombarded Si Substrates

Field emission (FE) characteristics of well-aligned multiwall carbon nanotube arrays (CNTAs) grown on originally polished and energetic iron ion bombarded Si substrates were investigated. It was found that the FE characteristics have been improved remarkably by the pretreatment of iron ion bombardment, an evident promotion of the highest emission current density from 4.05 mA/cm2to 54.45 mA/cm2was as an expression of this enhancement, this enhancement in characteristics is attributed to the improved adhesion between CNTs and Si substrate for the existence of iron buffer layer. The relationship between adhesive force and emission current density has been introduced, and the calculation reveals that the adhesion has been enhanced by 14.4 times due to the energetic ion pre-bombardment on Si substrate.

A low-potential, H 2O 2-assisted electrodeposition of cobalt oxide/hydroxide nanostructures onto vertically-aligned multi-walled carbon nanotube arrays for glucose sensing

A novel nanocomposite was synthesized using a cathodic, low-potential, electrochemical reduction of H 2O 2 to homogeneously deposit cobalt oxide/hydroxide (denoted as CoOx·nH 2O) nanostructures onto vertically well-aligned multi-walled carbon nanotube arrays (MWCNTs), while the MWCNTs were prepared by catalytic chemical vapor deposition (CVD) on a tantalum (Ta) substrate. The CoOx· nH 2O–MWCNTs nanocomposite exhibits much higher electrocatalytic activity towards glucose (Glc) after modification with CoOx· nH 2O than before. This non-enzymatic Glc sensor has a high sensitivity (162.8 μA mM −1 cm −2), fast response time (<4 s) and low detection limit (2.0 μM at signal/noise ratio = 3), and a linear dynamic range up to 4.5 mM. The sensor output is stable over 30 days and unaffected by common interferents that co-exist with Glc in analytical samples; it is also resistant to chloride poisoning. These features make the CoOx·nH 2O–MWCNTs nanocomposite a promising electrode material for non-enzymatic Glc sensing in routine analysis.

Investigation on the Plasma-Induced Emission Properties of Large Area Carbon Nanotube Array Cathodes with Different Morphologies.

Large area well-aligned carbon nanotube (CNT) arrays with different morphologies were synthesized by using a chemical vapor deposition. The plasma-induced emission properties of CNT array cathodes with different morphologies were investigated. The ratio of CNT height to CNT-to-CNT distance has considerable effects on their plasma-induced emission properties. As the ratio increases, emission currents of CNT array cathodes decrease due to screening effects. Under the pulse electric field of about 6 V/μm, high-intensity electron beams of 170–180 A/cm2 were emitted from the surface plasma. The production mechanism of the high-intensity electron beams emitted from the CNT arrays was plasma-induced emission. Moreover, the distribution of the electron beams was in situ characterized by the light emission from the surface plasma.

Synthesis of Well-Aligned Multi-Walled Carbon Nanotubes by Floating Catalyst Chemical Vapor Deposition

Well-aligned multi-walled carbon nanotube (MWNT) arrays were grown by floating catalyst chemical vapor deposition (CVD) on quartz substrate. The MWNTs in arrays had a uniform diameter of 30-50nm and high degree of graphitization. We find that catalyst nanoparticles with different sizes can be separated and deposit at different position by carrier gas flow under gravity effect in floating catalyst CVD. It is one of the main reasons that lead to the growth of well-aligned MWNTs.

An amperometric non-enzymatic glucose sensor by electrodepositing copper nanocubes onto vertically well-aligned multi-walled carbon nanotube arrays

A non-enzymatic glucose (Glc) sensor was developed by potentiostatically electrodepositing metallic Cu nanocubes from a precursor solution onto vertically well-aligned multi-walled carbon nanotube arrays (MWCNTs). The electrochemical characteristics of the sensor were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The sensor shows significantly higher electrocatalytic activity to the oxidation of Glc in 0.1 M NaOH alkaline solution after modification of Cu nanocubes than before. The sensor response is rapid (<1 s) and highly sensitive (1096 μA mM −1 cm −2) with a wide linear range (up to 7.5 mM) and low detection limit (1.0 μM at signal/noise ratio (S/N) = 3); it also exhibits high stability and specificity to Glc and performs very well in detecting of Glc concentration in human blood serum.

Synthesis of patterned carbon nanotube arrays for field emission using a two layer Sn/Ni catalyst in an ethanol flame

Patterned carbon nanotube (CNT) arrays on Si substrate have been fabricated by using a two layer Sn/Ni catalyst in a diffusion ethanol flame. Vertically well-aligned CNT arrays were achieved on a Si substrate without any catalyst pretreatment. The Sn underlayer activated the substrates for CNT growth with Ni as catalyst, and provided a good contact between CNTs and the substrate, which is useful for field emission. Since the adhesion of Sn/Ni nanoparticles to the substrate is very strong, the growth of the CNTs follows a base-growth mode. The thickness of the Sn underlayer largely determines the diameter and diameter distribution of the as-grown CNTs. The morphologies and field electron emission properties of CNT arrays grown on Si substrates with different thicknesses of Sn and growth times have been investigated. The variation of emission current density was less than 5% during a 4 h test under a field of 1.77 V/µm.

Carbon Nanotubes as Active Components for Gas Sensors

The unique structure of carbon nanotubes endows them with fantastic physical and chemical characteristics. Carbon nanotubes have been widely studied due to their potential applications in many fields including conductive and high‐strength composites, energy storage and energy conversion devices, sensors, field emission displays and radiation sources, hydrogen storage media, and nanometer‐sized semiconductor devices, probes, and quantum wires. Some of these applications have been realized in products, while others show great potentials. The development of carbon nanotubes‐based sensors has attracted intensive interest in the last several years because of their excellent sensing properties such as high selectivity and prompt response. Carbon nanotube‐based gas sensors are summarized in this paper. Sensors based on single‐walled, multiwalled, and well‐aligned carbon nanotubes arrays are introduced. Modification of carbon nanotubes with functional groups, metals, oxides, polymers, or doping carbon nanotubes with other elements to enhance the response and selectivity of the sensors is also discussed.