Aligned Carbon Nanotube Arrays Research Articles

Remarkable bactericidal traits of a metal-ceramic composite coating elated by hierarchically structured surface.

SummaryA ceramic-based coating with a hierarchical surface structure was synthesized via solid-state reaction enabled by a double cathode glow discharge technique. This innovative coating comprises two distinct layers, specifically an outer layer with a well-aligned micro-pillar array and a dense inner layer. Both are composed of a face-centered cubic Cu(Co,Ni,Fe) solid solution phase together with a spinel-type Fe(Al,Cr)2O4 oxide. This coating exhibits superhydrophobicity and, yet, a very strong adhesion to water, i.e., the so-called “rose petal effect”. This coating also exhibits highly efficient antibacterial ability against both Staphylococcus aureus and Escherichia coli bacteria under both dark and visible light conditions. The excellent antibacterial property originates from the synergistic effects through the release of Cu ions coupled with photothermal activity upon light activation.

Tribological properties of vertically aligned carbon nanotube arrays and carbon nanotube sponge

Carbon nanotube (CNT) films showing excellent mechanical and frictional performances are one of the most competitive candidates for fabricating functional surfaces; in particular, the bulk form of the forest-like vertical aligned CNT (VACNT) film and CNT sponge are idea candidates for making a flexible solid lubricant surface due to the fact that their porous network has a high potential to experience large deformation. In this article, the frictional behavior of the VACNT and CNT sponge against a millimeter scale copper sphere has been studied under various conditions within a home-built system. Due to the intrinsic mechanical instability of VACNTs, a higher friction state than the CNT sponge has been observed, and beyond that, VACNTs typically show a run-in process as a function of sliding circle caused by the formation and rearrangement of quasi-periodic cracks; on the contrary, the friction of the CNT sponge is very stable. In addition, we have pinpointed the effects of sliding velocity, relative humidity, and temperature on friction. The sliding friction was observed to be independent of the velocity and temperature; however, due to the increase in capillary force, friction increases with the increase in relative humidity.

Electrical modeling of carbon nanotube‐based shielded through‐silicon vias for three‐dimensional integrated circuits

AbstractIn this article, two kinds of shielded carbon nanotube (CNT) through‐silicon vias (TSV) are proposed and investigated for high‐density three‐dimensional integrated circuits (3‐D ICs). First, vertical aligned CNT array is inserted into a single hole, and two isolated metal pads, that is, the central circular and outer annular pads, are deposited onto the surface to make distinct conduction paths. The shielded CNT TSV, which can also be named as coaxial TSV, is formed, with the semiconducting CNTs utilized to suppress lateral conductance. Based on a similar concept, the shielded differential CNT TSV is developed. By virtue of the proposed shielded CNT TSVs, the chip area can be saved significantly. The equivalent circuit models are established for the proposed shielded CNT TSVs. A passive equalizer is designed to improve the signal quality for shielded differential CNT TSV. Finally, the potential applications of the proposed TSVs in 3‐D IC power distribution network design are investigated.

The vertically aligned carbon nanotubes arrays as biointerface for the E. Coli strain M-17

The biological interaction materials study is necessary when creating biocompatible implantable devices, including biosensors. Important criteria for their creation are the bactericidal properties of such materials. In this paper, we study the bacteria with vertically aligned carbon nanotubes interaction. In this work we examined the bioaffinity of multi-walled carbon nanotubes samples with E. Coli strain M17 bacteria. We synthesized carbon nanotubes with various structural features on the surface of silicon wafers. Then westudied of the wettability of the obtained samples and tested bioactivity of E. Coli bacteria using spectrometry and photometry methods. It was found that E. Coli bacteria of strain M-17 demonstrated the best vital signs when interacting with the surfaces of hydrophobic samples of vertically oriented carbon nanotubes.

Effects of high temperature treatment of carbon nanotube arrays on graphite: increased crystallinity, anchoring and inter-tube bonding

Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 °C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young’s modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 °C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.

Homeotropic liquid crystal device employing vertically aligned carbon nanotube arrays as the alignment agent.

Vertically aligned carbon nanotube (VA-CNT) arrays were grown on several chromium (Cr)-coated glass substrates using a plasma-enhanced chemical vapor deposition system. The CNTs were 2μm long and had a site density of 2×10^{9}cm^{-2} on the substrates. Two VA-CNT slides on Cr glass substrates were put together to design a homeotropic electro-optic liquid crystal (LC) device. A negative dielectric anisotropic LC was used in the device. The π-π stacking interaction between the LC and the VA-CNTs allows the LC material to align homeotropically in the cell. When an external electric field was applied using the transparent conducting Cr layers, the LC achieves a planar orientation above a threshold field. These results successfully demonstrate the optical, electro-optical operations, and the field-induced dynamic response of a homeotropic LC device employing the VA-CNT arrays as the homeotropic-alignment agent. This study significantly advances the range and understanding of nanostructured surfaces that provide vertical alignment of LCs.

Influence of carbon dioxide plasma treatment on the dry adhesion of vertical aligned carbon nanotube arrays

Vertical aligned carbon nanotube (VACNT) arrays used as dry adhesive materials have broad prospects in the applied fields of space, medicine and electronics. The adhesion of VACNT arrays is believed to be related not only to the nano-array structure and a clean surface, but also to chemical composition. Here, radio-frequency (RF) carbon dioxide (CO2) plasma treatment is introduced as an effective method for purifying and functionalizing the surface to improve the dry adhesive performance of VACNT arrays. Scanning electron microscopy showed that the VACNT arrays retained the alignment architecture with minimal damage at low power. X-ray photoelectron spectroscopy and contact angle tests revealed that the content of non-polar components (C = C bonds) decreased after treatment, while the content of polar groups (C = O and O–C = O bonds) increased, which changed the surface polarity of the VACNT arrays. Raman analyses and transmission electron microscopy demonstrated that amorphous carbon can be selectively removed with increasing time (0–18 min), but was continuously generated with increasing power (30–90 W). The best adhesive strength of 18 N cm−2 (increased by 39%) was obtained after CO2 plasma treating for 10 min at 30 W power, which was attributed to the combined action of purification and polarization.

Investigation of the relationship between adhesion force and mechanical behavior of vertically aligned carbon nanotube arrays

The mechanical behavior of vertically aligned carbon nanotube (VACNT) arrays can largely impact their adhesion performance. In this paper, we fabricated various VACNT arrays to investigate the relationship between adhesion force and their mechanical behavior. High-volume fraction (3.4%) CNT arrays did not exhibit the applicable adhesion effect due to their intrinsic elastic property. Adhesion measurements on several low-density (less than 0.5%) VACNT arrays demonstrated that the adhesion performance is strongly related to the plastic deformation of the carbon nanotubes at the contact surface. Due to the nature of the growth of CNT arrays, the top region of the as-grown CNT arrays is denser and stiffer than the bottom region of the arrays. Therefore, compared with as-grown CNT arrays, the flipped CNT arrays reached higher adhesion efficiency (the ratio of adhesion force to preload) with lower preload due to the higher compliance at the top surface of the arrays. With cyclic loading under micro mechanical tests, stiffening of the surface and declining of adhesion force were also observed. These results illustrated that the mechanical compliance at the region near the contact interface is the dominant factor for the adhesion performance of VACNT arrays.

Asymmetric Modification of Carbon Nanotube Arrays with Thermoresponsive Hydrogel for Controlled Delivery.

In this work, bipolar electrochemistry is used to perform wireless indirect electrodeposition of two different polymer coatings on both sides of carbon nanotube arrays. Using a thermoresponsive hydrogel on one side and an inert insoluble polymer on the other side, it is possible to generate, in a single step, a nanoporous reservoir with Janus character closed on one side by a thermoresponsive membrane. The thermoresponsive polymer, poly(N-isopropylacrylamide) (pNIPAM), is generated by the local reduction of persulfate ions, which initiates radical polymerization of NIPAM. Electrophoretic paint (EP) is chosen as an inert polymer. It is deposited by precipitation because of a local decrease in pH during water oxidation. Both polymers can be deposited simultaneously on opposite sides of the bipolar electrode during the application of the electric field, yielding a double-modified Janus object. Moreover, the length and thickness of the polymer layers can be controlled by varying the electric field and the deposition time. This concept is applied to vertically aligned carbon nanotube arrays (VACNTs), trapped inside an anodic aluminum oxide membrane, which can further be used as a smart reservoir for chemical storage and release. A fluorescent dye is loaded in the VACNTs and its release is studied as a function of temperature. Low temperature, when the hydrogel layer is in the swollen state, allows diffusion of the molecule. Dye release occurs on the hydrogel-modified side of the VACNTs. At high temperatures, when the hydrogel layer is in the collapsed state, dye release is blocked because of the impermeability of the pNIPAM layer. This concept paves the way toward the design of advanced devices in the fields of drug storage and directed delivery.

Enhancement of mechanical properties of vertically aligned carbon nanotube arrays due to N+ ion irradiation

In this work we apply N+ ion irradiation on vertically aligned carbon nanotube (VACNT) arrays in order to increase the number of connections and joints in the CNT network. The ions energy was 50 keV and fluence 5 × 1017 ions cm−2. The film was 160 μm thick. SEM images revealed the ion irradiation altered the carbon bonding and created a sponge-like, brittle structure at the surface of the film, with the ion irradiation damage region extending ∼4 μm in depth. TEM images showed the brittle structure consists of amorphous carbon forming between nanotubes. The significant enhancement of mechanical properties of the irradiated sample studied by the cyclic nanoindentation with a flat punch indenter was observed. Irradiation on the VACNT film made the structure stiffer, resulted in a higher percentage recovery, and reduced the energy dissipation under compression. The results are encouraging for further studies which will lead to create a class of materials—ion-irradiated VACNT films—which after further research may find application in storage or harvesting energy at the micro/nanoscale.

Metallic Sandwiched-Aerogel Hybrids Enabling Flexible and Stretchable Intelligent Sensor.

Flexible strain sensors have been widely investigated with their rapid development in human-machine interfaces, soft robots, and medical care monitoring. Here, we report a new in situ catalytic strategy toward the fabrication of metallic aerogel hybrids, which are composed of vanadium nitride (VN) nanosheets decorated with well-defined vertically aligned carbon nanotube arrays (VN/CNTs) for the first time. In this architecture, the two-dimensional VN nanosheets as the main bone structure are favorable for the flexible devices due to their excellent structural compatibility during the repetitive deforming process. In addition, the sandwiched aerogel hybrids form highly conductive 3D network, affording outstanding sensitivity for the strain-responsive behaviors. Further, the VN/CNTs-based flexible strain sensors are successfully fabricated, showing a high gauge factor of 386 within a small strain of 10%, fast response, and extraordinary durability. The monitoring of physical signals and an actual real-time human-machine controlling system based on the sensors are also presented.

Bifunctional nickel ferrite-decorated carbon nanotube arrays as free-standing air electrode for rechargeable Zn–air batteries

A free-standing air electrode is constructed by direct growth of NiFeOxnanoparticles on vertically aligned carbon nanotube arrays for high-performance rechargeable Zn–air batteries.

Vertically aligned carbon nanotube arrays growth modeling at different temperatures and pressures in reactor

A model for the growth of carbon nanotubes was developed and the calculations for this model were compared with experiment. Experimental growth of carbon nanotubes arrays was carried out by the CVD method in a stream of acetylene, ammonia and argon at temperatures from 550 to 950 °C. A nickel film of 4 nm thickness on the surface of titanium nitride was used as a catalyst. The model takes into account the pyrolysis of hydrocarbons on the surface of the catalyst nanoparticles, the formation of a barrier layer on its surface, which slows down and stops the growth of the nanotube array, the interaction of the substance of the buffer layer with carbon in the catalyst nanoparticle. When developing the model, the mechanisms of individual processes were considered and the temperature dependences of the kinetic coefficients, which describe the growth of nanotubes, were obtained. It is these dependences that show a good agreement between the calculations and the experiment.

Atomic Layer Deposition of Inorganic Films for the Synthesis of Vertically Aligned Carbon Nanotube Arrays and Their Hybrids

Vertically aligned carbon nanotube arrays (VACNTs) have many excellent properties and show great potential for various applications. Recently, there has been a desire to grow VACNTs on nonplanar surfaces and synthesize core-sheath-structured VACNT–inorganic hybrids. To achieve this aim, atomic layer deposition (ALD) has been extensively applied, especially due to its atomic-scale thickness controllability and excellent conformality of films on three-dimensional (3D) structures with high aspect ratios. In this paper, the ALD of catalyst thin films for the growth of VACNTs, such as Co3O4, Al2O3, and Fe2O3, was first mentioned. After that, the ALD of thin films for the synthesis of VACNT–inorganic hybrids was also discussed. To highlight the importance of these hybrids, their potential applications in supercapacitors, solar cells, fuel cells, and sensors have also been reviewed.

MoSe2 nanoflakes-decorated vertically aligned carbon nanotube film on nickel foam as a binder-free supercapacitor electrode with high rate capability

A new type of composite electrode material, MoSe2 nanoflakes grown on the vertically aligned carbon nanotube array film (VACNTF) with binder-free nickel foam as current collector (VACNTF@MoSe2/NF), was fabricated by a simple spraying chemical vapor deposition method combined with the solvothermal technique. Owing to the introduction of the VACNTF with ordered channels and appropriate intertube spacing, which facilitate electrolyte ions quickly transferring and alleviate the volume changes in the electrochemical measurements, the VACNTF@MoSe2/NF sample presents superior electrochemical performance compared to pure MoSe2/NF sample. The VACNTF@MoSe2/NF sample exhibits high specific capacitance of 435 F·g−1 at 1 A·g−1, remarkable cycling stability (92% of the original capacitance maintaining over 5000 cycles) and especially excellent rate capability (84.1% capacitance retention with the current density changed from 1 to 15 A·g−1). Moreover, the VACNTF@MoSe2/NF based asymmetric supercapacitor exhibits a high energy density with 22 Wh·kg−1 for a power density of 330 W·kg−1. This paper offers a new strategy to prepare transition metal dichalcogenides based electrode materials with high rate performance.

Improving field emission properties of vertically aligned carbon nanotube arrays through a structure modification

Vertically aligned carbon nanotube (VACNT) emitters were synthesized directly on stainless steel substrate using DC plasma-enhanced chemical vapor deposition. Remarkable field emission (FE) properties, such as low turn-on electric field (ETO = 1.40 V/μm) and low threshold electric field (ETH = 2.31 V/μm), were observed from VACNT arrays with long length and moderate density. The FE performance was significantly enhanced by a uniquely bundled structure of VACNTs formed through a simple water treatment process. The FE properties of VACNTs were further improved by coating the exterior of CNTs with a uniform layer of crystalline SnO2 nanoparticles; the ETO and ETH were reduced to 1.18 and 2.01 V/μm, respectively. The enhancement of FE properties by SnO2 coating can be attributed to the morphological change of VACNTs caused by the solution phase coating process. The coated samples also exhibited an improved FE stability which is attributed to the enhancement of the mechanical strength and chemical stability of the VACNTs after the SnO2 coating. The VACNT emitters with characteristic features such as a conductive substrate, low contact resistance between the VACNTs and the substrate, uniform coating, and bundled morphology can be ideal candidates for FE devices.

Atomistic simulations on nanoimprinting of copper by aligned carbon nanotube arrays under a high-frequency mechanical vibration

Nanoimprinting behaviors of copper substrates and double-walled carbon nanotubes with interwall sp 3 bonds are investigated using molecular dynamics simulations. A high-frequency mechanical vibration with various amplitudes is applied on the carbon nanotube (CNT) mold and copper substrate in different directions. Results show that exciting mechanical resonances both on the CNT and substrate drastically decrease the maximum imprint force and interfacial friction up to 50% under certain amplitudes. Meanwhile, it is demonstrated that defects occur in the {111} plane in the copper substrate during nanoimprinting. For different CNT array densities, a higher grafting density needs more imprint force to transfer patterns. The maximum imprint force for a large range of CNT array densities can be reduced by vibrational perturbations, while reduction rates depend on the CNT grafting density. This work sheds deep insights into the nanoimprint process at the atomic level, suggesting that vibration perturbation is an effective approach for improving the nanoimprinting accuracy and preventing the fracture of nanopatterns.

Macroscopic Carbon Nanotube Structures for Lithium Batteries.

Carbon nanotubes (CNTs) are regarded as one of the most promising materials to manufacture high-performance lithium batteries. This prospect is closely related to the construction of macroscopic architectures of CNTs. The superaligned CNT (SACNT) array is a unique kind of vertically aligned CNT array. Its highly oriented feature and strong intertube force facilitate the fabrication of macroscopic SACNT structures with various forms, including unidirectional films, buckypapers, and aerogels, etc. The as-produced SACNT macroscopic architectures are successfully introduced into lithium batteries due to their outstanding electrical and mechanical properties. Herein, an overview of the functions of macroscopic SACNTs in lithium batteries is proposed, including their applications in composite electrodes, current collectors, interlayers, and flexible full cells.

Plasma‐functionalized Highly Aligned CNT‐based Biosensor for Point of Care Determination of Glucose in Human Blood Plasma

AbstractIn this study, a new method for modification of vertically aligned carbon nanotube arrays (VACNTs) for selective detection of glucose was developed. VACNTs were grown by chemical vapor deposition method on a silicon substrate deposited with alumina as a buffer layer and iron as a catalyst using radio frequency (RF) sputtering and electron beam evaporation, respectively. The surface of the electrode was modified with electrodeposition of polyaniline (PANI) followed by covalent attachment of glucose oxidase (GOx). The electrode was characterized using field emission scanning electron microscopy (FESEM), micro‐Raman spectroscopy, and attenuated total reflectance Fourier transform infrared spectrometer (ATR‐FTIR) techniques. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of the electrode. The fabricated electrode was successfully employed as a point‐of‐care (POC) biosensor for the detection of glucose in human blood plasma. The detection limit was 1.1 μM, and the sensitivity was 620 μA mM−1 cm−2 at the linear range of 2–426 μM.

CNT Electronics: Advances in High‐Performance Carbon‐Nanotube Thin‐Film Electronics (Adv. Electron. Mater. 8/2019)

The center of the image shows the device structure of a typical top-gate field-effect transistor based on aligned carbon nanotube (CNT) arrays, which, as discussed by Zhiyong Zhang, Lian-Mao Peng, and co-workers in article number 1900122, is a key component for future high-performance digital applications. The background shows examples of such an application–5-stage carbon nanotube ring oscillator circuits with an oscillation frequency of 5.54 GHz.