CNT Forest Research Articles

Three-dimensional carbon nanotubes/iron oxyhydroxide shell/core hybrid as a binder-free electrode for the flexible supercapacitor

Carbon nanotubes/iron oxyhydroxide (CNTs/FeOOH) three-dimensional hybrid with shell/core nanostructure is designed as a binder-free electrode for the flexible supercapacitor (SC) application. The coiled and dense CNT forest is preferentially fabricated on flexible carbon fiber cloth (CC) by chemical vapor deposition (CVD) and employed as a highly conductive carrier for electrodeposition growth of FeOOH. The average diameter and length of the single CNT are 30–60 nm and 2–3 μm. The shell/core structured CNTs/FeOOH three-dimensional hybrid maintains the consistent interconnecting network morphology, contributing to overcoming the problem of poor conductivity of FeOOH and the transmission of electron channels and the diffusion of electrolyte ions. The CNTs/FeOOH hybrid exhibits a high mass-specific capacitance of 824 F g−1 (or 0.59 F cm−2) in 1 M Na2SO4 electrolyte at 0.5 mA cm−2. By increasing the FeOOH deposition weight, the enhanced area-specific capacitance of 0.892 F cm−2 (or 564 F g−1) is obtained at 0.5 mA cm−2, and the enhanced capacitance retention can reach 96% after 3000 charge/discharge cycles. Besides, a flexible SC is fabricated using the CNTs/FeOOH hybrid electrode and carboxymethyl cellulose (CMC)/Na2SO4 gel electrolyte. The SC displays an energy density as high as 13.33 Wh kg−1 at a power density of 1000 W kg−1. The SC device shows large bending deformation, and these SC devices pack can drive a red diode to work. These results provide such a shell/core structured CNTs/FeOOH three-dimensional hybrid that can be used as potential and low-cost electrode material for flexible SC.

Fabrication of iron oxide-CNT based flexible asymmetric solid state supercapacitor device with high cyclic stability

Integration of high surface area nanostructures with conducting and deformable electrodes at large scale are of significant importance for flexible supercapacitors with high cyclic stability and low cost. Here, we report water assisted meter scale growth of aligned iron oxide and CNT 1D nanostructures on flexible stainless steel mesh for asymmetric supercapacitor device applications. Electron microscopic investigations revealed the uniform coverage of both iron oxide and CNT forest nanostructures over one meter length of SS mesh. Both iron oxide and CNT nanostructures were tested for supercapacitor electrode material in neutral electrolytes. Further, asymmetric solid state devices were fabricated and connected in serial fashion to demonstrate glowing of LEDs as well as rotation of 5 V micro fan. In addition, at bending angle of 90°, device showed 68% increase whereas, at 180° it showed 13% decrease in capacitance. The calculated specific capacitance for single device is found to be 14.4 mF cm−2. Corresponding energy density and power density are found to be 3 μW-hr cm−2 and 0.74 mW cm−2 respectively. The device showed remarkable capacitance retention of 87% over 25 000 charge discharge cycles. The flexible nature with remarkable cyclic stability of solid state iron oxide/CNT device is suitable for low cost flexible and wearable supercapacitor applications.

Directly Grown Aligned Carbon Nanotubes As a Novel Microporous Layer for Proton Exchange Membrane Fuel Cells

Proton Exchange Membrane Fuel Cells (PEMFC) convert electrochemical energy into electricity. Nevertheless, the system still needs to be improved in order to be economically relevant. In that purpose, it is needed to produce more current for a reduced use of materials. Working on developing new materials for PEMFCs, managing both high gas diffusion and adequate water transport, is necessary to achieve these goals. One of the most important materials used in the fuel cell is the gas diffusion layer (GDL). A microporous layer (MPL) is generally deposited on top of the gas diffusion layer to improve gas transport and water management, and thus enhance the cell performances and stability.Carbon nanotubes interest as a MPL or as catalyst support has already been demonstrated in several works [Kannan (2009); Tang (2011); Xie (2015)]. In the literature, most of works about CNTs as microporous layers are using bulk carbon nanotubes integrated in a carbon black MPL. A few works are displacing a different microporous layer structure where carbon nanotubes are obtained by direct growth and are forming a foam around the gas diffusion layer fibers. In this work, a layer made of vertically aligned CNTs was grown in-situ on the fibers of a gas diffusion layer by a hot filaments assisted chemical vapor deposition (HFCVD). It has been possible to successfully grow aligned CNTs on different commercial supports. Functional properties of the GDL with CNTs were characterized with SEM imaging, contact angle and electrical conductivity measurements. A variety of growth time, filaments temperature, chamber temperature and gas flows have been tested. These parameters influence the carbon nanotubes length, thickness, and the CNTs forest density. At last, electrochemical characterizations were conducted in a differential single cell. This cell allows a better homogeneity of flows on the surface. Several cell configurations were studied: gas diffusion layer with carbon nanotubes on the anode, on the cathode, and on both electrodes, either in dry conditions (no condensed water) or wet conditions (with condensed water). Polarization curves have been measured to study the electrochemical phenomena leading to the variation of performances of the various cell configurations. Impedance spectroscopy has been done to measure the overall cell resistance and its intrinsic composition such as the protonic resistance or the transport resistance.SEM imaging has shown that the CNTs layers are distributed all along the carbon fibers of the GDL, also inside the GDL pores. The overall structure strictly differs from conventional microporous layers as well as other CNT-made MPLs in the literature. 10-25 µm-long multiwall carbon nanotubes with a diameter ranging between 7-10nm were obtained. CNTs as a microporous layer gives better performances (10% in dry conditions, 25% in wet conditions) than commercial MPLs. Contact angle measurements indicates that the obtained gas diffusion media (GDL+MPL) is hydrophilic, which also differs from commercial hydrophobic GDLs. Although carbon nanotubes are individually expected to be hydrophobic, the CNT forest structure and its combination with the former GDL porosity have a different property. The measurement of electrical resistance of the global fuel cell with a commercial MPL or with CNT layers shows that carbon nanotubes don’t provide a better electrical transport.Electrochemical measurements gave access to the fuel cell performance in operating conditions. The results have been compared to the reference SGL 29BC and to the Department of Energy expectations for the fuel cell performances for the next years. In dry state, GDL with CNTs work as well as the reference gas diffusion media. In wet conditions, a dramatic improvement is obtained, especially at low current density. These results are all the more interesting as the gas diffusion layer with carbon nanotubes is hydrophilic, but can compete with the hydrophobic commercial GDLs. The arrangement of carbon nanotubes might also be important as it is aligned in the direction of gas flows and water flows in the fuel cell.In closing, the results of this work show the need to develop nanostructured materials for energy applications. Carbon nanotubes proved their interest as a material for fuel cells. Even with a hydrophilic and a strictly different structure of microporous layer, the fuel cell performances with carbon nanotubes compete with the best commercial reference results. This could lead to a better understanding of the flows phenomena in fuel cells on one side, and of the predominant factors inhibiting a dramatic improvement of the PEMFCs performances. Figure 1

A Potential High-Throughput Route to Collagen-Mimicked Carbon Nanotube Fiber via Domino Pushing and Ion Bombardment

Abstract Carbon nanotubes (CNTs) have been shown owning extraordinary mechanical properties for decades, but to date, their wide application as load-bearing structural materials has not been realized mainly due to the critical obstacles of weak interface, poor distribution and alignment, and lack of economic technology for mass production and processing. In order to overcome these obstacles, we proposed a potential route from as-grown CNT forest to collagen-mimicked CNT films with covalently crosslinked CNTs arranged in a staggered alignment. To consolidate the foundation of the route, its critical step of ion bombardment to construct the intertube crosslinks in CNT films was simulated using molecular dynamics simulations. Results show that the ion bombardment can efficiently construct the intertube crosslinks and greatly improve the elastic modulus and strength of CNT films by as much as 24% and 660%, respectively, with comparison to the nonbombarded ones. The influences of the number and the kinetic energy of the incident particles were systematically investigated and the corresponding contours were presented, suggesting the optimal energy and number of the incident particles for the elastic modulus and strength of collagen-mimicked CNT films. The work not only provides a novel route to mass fabrication of high-performance CNT fibers but also gives useful guidelines on the optimization of processing design.

Robust and High-Performance Electrodes via Crumpled Au-CNT Forests for Stretchable Supercapacitors

Summary Stretchable supercapacitors based on vertically aligned nanotubes or nanowires have attracted considerable attention because of their improved robustness and electrochemical performance under large and repeated deformations. Here, we demonstrate a robust and high-performance stretchable electrode based on crumpled Au-coated carbon nanotube forest (Au-CNT forest). Experimental measurements show that the resistance of the Au-CNT forest electrode is around one order magnitude lower than that of a pure CNT forest electrode. The biaxially crumpled Au-CNT forest electrode demonstrates nearly identical electrochemical performance at different measured charge/discharge rates under different strain conditions (i.e., from 0% to 800% area strain). The as-prepared symmetric supercapacitor demonstrates a maximum specific capacitance of ∼6 mF cm−2 at the current density of 40 mA cm−2 under large strains, exhibiting superior mechanical and electrochemical stability. This research presents a facile process to fabricate highly stretchable supercapacitors based on vertically aligned nanotubes or nanowires for achieving exceptional and robust electrochemical performance.

Infrared absorbance of vertically-aligned multi-walled CNT forest as a function of synthesis temperature and time

In this paper, the growth of optimized vertically aligned multi-walled carbon nanotube (VA-MWCNT) forests by LPCVD method for use in a large-area absorber in infrared detectors is presented. The effect of synthesis temperature (500−700 °C) and time (1−10 min) on the optical absorption coefficient in the infrared (2−20 μm) is investigated by FT-IR measurement at various incident angles (15-80°). The structural properties of VA-MWCNT are characterized by SEM, TEM and Raman spectroscopy. Spectral measurements show an increasing absorption with the height of the forest that results at increased synthesis time and temperature. However, the absorption coefficient decreases with increasing synthesize time and temperature, while it is also affected by other properties, such as diameter, density, alignment, and uniformity. Moreover, the reduction in absorption at oblique incident angles demonstrates the relevance of surface properties. Finally, a circular graphite waveguide system is used to model the absorption characteristics of an MWCNT forest.

Chemical vapor deposition of 3D graphene/carbon nanotubes networks for hybrid supercapacitors

We present the direct synthesis of graphene as well as carbon nanotube within the vertically-aligned carbon nanotube (VACNT) forests to form either the 3D CNT-graphene or 3D CNT-CNT network by means of chemical vapor deposition (CVD). The multi-dimensional material assembly process is achieved by the electroplating of a thin nickel layer around the individual CNTs followed by a second CVD process for the synthesis of graphene or CNTs branching out of the original VACNT, respectively. The combinations of large surface areas (graphene and CNT), high electrochemical reactions sites (graphene), and metal particles as pseudocapacitor materials improve the electrochemical capacitance. Compared with as-grown CNT forests, the capacitance of 3D CNT/graphene networks increases 16 times to ∼20 F/cm3 and 3D CNT/CNT networks increase 25 times to ∼30 F/cm3. A flexible supercapacitor based on the CNT/CNT forest electrode is demonstrated to achieve 90 % retention of its original capacitance after 10,000 charging-discharging cycles.

Robust and High-Performance Electrodes Via Crumpled Au-CNT Forests for Stretchable Supercapacitors

Stretchable supercapacitors based on vertically aligned nanotubes or nanowires have attracted considerable attention because of their improved robustness and electrochemical performance under large and repeated deformations. However, it is still challenging to maintain the low electric resistance of stretchable electrodes of such a stretchable supercapacitor under extremely large strains due to the variation of the contacts between individual nanotubes/wires. Here, we develop and demonstrate a robust and high-performance stretchable electrode based on crumpled Au coated CNT forest (Au-CNT-forest), which significantly increases the conductivity of the original CNT-forest electrode while maintaining its unique crumpled hierarchical structures. Experimental measurements show that the resistance of the Au-CNT- forest electrode is around one order magnitude lower than that of a pure CNT-forest electrode and is comparable to that of a conventional thin film electrode. The biaxially crumpled Au-CNT-forest electrode demonstrates nearly identical electrochemical performance at all the measured charge/discharge rates (i.e., from 0.5 to 80 mA cm-2) under different strain conditions (i.e., from 0% to 800%), which can not be achieved by a pure CNT-forest electrode. The as-prepared symmetric supercapacitor with crumpled Au-CNT forest electrodes demonstrates a maximum specific capacitance of ~ 6 mF cm-2 at the scan rate of 40 mA cm-2 under different strains, exhibiting superior mechanical and electrochemical stability. This research demonstrates a facile process to fabricate highly stretchable supercapacitors based on vertically aligned nanotubes or nanowires for achieving exceptional and robust electrochemical performance.

Scalable electric-field-assisted fabrication of vertically aligned carbon nanotube membranes with flow enhancement

We report a solution-based approach for fabricating vertically aligned carbon-nanotube (VACNT) membranes, which improves on the unaligned nature of CNT mixed-matrix membranes. This approach addresses important challenges regarding scalability and incorporation of different types and sizes of nanotube as pores in a membrane. In a new, solvent-deposition approach, CNTs are dispersed and then aligned and concentrated via electro-deposition from an organic solvent, using a composite AC + DC electric field to form aligned CNT arrays. This enables VACNT number densities that are two orders-of-magnitude higher than possible from direct suspension of CNTs in the liquid oligomer. The solvent is then replaced by a UV-curable oligomer, which is selectively cured to form macroscopic membranes of highly controlled thickness. After plasma etching to open pores, the VACNT membranes are shown to be permeable, and to have pore sizes consistent with flow through internal channels of the CNTs. In a first for field-aligned, solution-fabricated VACNT membranes, the pores show substantial, 100–300×, gas-flow enhancement compared to theory, similar to membranes fabricated via less scalable methods (i.e., by CVD growth of already aligned CNT forests). The solution-based, electric-field-assisted approach aligns nanotubes of different sizes and types grown by any means, and is scalable to the efficient fabrication of large-area VACNT membranes for a variety of important applications.

Multizone Rapid Thermal Processing to Overcome Challenges in Carbon Nanotube Manufacturing by Chemical Vapor Deposition

For the scalable production of commercial products based on vertically aligned carbon nanotubes (VACNTs), referred to as CNT forests, key manufacturing challenges must be overcome. In this work, we describe some of the main challenges currently facing CNT forest manufacturing, along with how we address these challenges with our custom-built rapid thermal processing chemical vapor deposition (CVD) reactor. First, the complexity of the multistep processes and reaction pathways involved in CNT growth by CVD limits the control on CNT population growth dynamics. Importantly, gas-phase decomposition of hydrocarbons, formation of catalyst nanoparticles, and catalytic growth of CNTs are typically coupled. Here, we demonstrated a decoupled recipe with independent control of each step. Second, significant run-to-run variations plague CNT growth by CVD. To improve growth consistency, we designed various measures to remove oxygen-containing molecules from the reactor, including air baking between runs, dynamic pumping down cycles, and low-pressure baking before growth. Third, real-time measurements during growth are needed for process monitoring. We implement in situ height kinetics via videography. The combination of approaches presented here has the potential to transform lab-scale CNT synthesis to robust manufacturing processes.

Ultrasensitive embedded sensor for composite joints based on a highly aligned carbon nanotube web

Herein, we present a novel approach for damage sensing in adhesively bonded joints using a carbon nanotube single layer web (CNT-SLW) which marks a significant departure from the approach of dispersing CNTs within epoxy resins. In this work, a very thin, highly aligned CNT-SLW (densified thickness ∼ 50 nm) with aerial density of 2.0 μg/cm2 was horizontally drawn from a vertically aligned CNT forest, positioned over an adhesive film, which was, in turn, placed between two non-conductive composite adherents. This was followed by the application of heat and pressure to cure the adhesive. These joints were subjected to quasi-static and cyclic loading to investigate the damage sensing performance of a CNT-SLW. The CNT-SLW sensor, placed parallel to the load direction, exhibits remarkably high cyclic stability as well as exceptionally high sensitivity to damage initiation and accumulation. The resistance increase (ΔR/Ro% ∼1633%) is significantly higher than that of adhesive sensors with dispersed CNTs/graphene reported in the literature. Morphological studies help to explain the sensing mechanism through interactions of the CNT-SLW with the evolution of micro-cracks. These results demonstrate the potential of macroscopic architectures of CNTs, with controlled orientation, for the development of high performance structural health monitoring (SHM) systems for damage detection.

Decoration of Vertically Aligned Carbon Nanotubes with Semiconductor Nanoparticles Using Atomic Layer Deposition.

Vertically aligned carbon nanotubes (VACNTs or “CNT forest”) were decorated with semiconductor particles (TiO2 and ZnO) by atomic layer deposition (ALD). Both the structure and morphology of the components were systematically studied using scanning (SEM) and high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray diffraction (XRD) methods. Characterization results revealed that the decoration was successful in the whole bulk of VACNTs. The effect of a follow-up heat treatment was also investigated and its effect on the structure was proved. It was attested that atomic layer deposition is a suitable technique for the fabrication of semiconductor/vertically aligned carbon nanotubes composites. Regarding their technological importance, we hope that semiconductor/CNT forest nanocomposites find potential application in the near future.

Synthesis of MWCNT Forests with Alumina-Supported Fe2O3 Catalyst by Using a Floating Catalyst Chemical Vapor Deposition Technique

In this study, multiwalled CNT bundles were synthesized with an alumina-supported Fe2O3 catalyst by using a floating catalyst chemical vapor deposition (FCCVD) technique. The metal catalyst was synthesized by dispersing Fe2O3 on alumina support. Ethylene molecules were decomposed over different amounts of metal nanoparticles in a FCCVD reactor. The CVD temperature was elevated from 600°C to 1000°C. The large active surface area of the metal nanobuds promoted the decomposition of a carbon precursor and the fast growth of CNT bundles. Least dense bundles of varying heights were observed at lower CVD temperatures of 600°C and 700°C. At 800°C, CVD process conditions were found suitable for the fast decomposition of hydrocarbon. The relatively better yield of well-structured CNTs was obtained with a catalyst weight of 0.3 g at 800°C. Above 800°C, CNT forests start losing alignment and height. The forest density was also decreased at temperatures above the optimum. The elemental composition of CNT bundles revealed the presence of carbon, aluminium, oxygen, and iron in percentages of 91%, 0.76%, 8.2%, and 0.04%, respectively. A very small ID to IG ratio of 0.22 was calculated for CNTs grown under optimized conditions.

Aligned CNT Forests on Stainless Steel Mesh for Flexible Supercapacitor Electrode with High Capacitance and Power Density

Carbon nanotube-based hybrid materials integrated with conducting stainless steel mesh is of great importance for developing electrochemically stable and mechanically flexible supercapacitors. We report sweet spot tunable CVD growth of vertically aligned carbon nanotube coated with TiO2 on stainless steel mesh with remarkable supercapacitor performance. Aligned CNT forest growth is observed at certain distance from the upstream inside the heating zone. We find that residence time of the carbon precursor has significant influence on controlling the density and height of vertically aligned carbon nanotube forest. When the residence time is increased by reducing the carrier gas flow rate from 590 to 300 sccm, vertically aligned carbon nanotube forest height is increased significantly from ∼9 to ∼31 μm on stainless steel mesh. The developed vertically aligned CNT forest on stainless steel mesh found to be suitable for supercapacitor electrode but its superhydrophobic nature limits its energy storage performan...

Tuning the Wettability of Vertically Aligned CNT–TiO2 Hybrid Electrodes for Enhanced Supercapacitor Performance

AbstractBoosting the energy density of carbon‐based materials is of great importance for developing supercapacitors with high cyclic stability. Chemical vapor deposition (CVD) growth of vertically aligned carbon nanotube (VACNT) forest is reported with millimeter height on Si/SiO2 substrate and engineer its microstructure and wettability for remarkable supercapacitor performance. A simple method to alter the microstructure of VACNT forest by adding small amount of ethanol in KOH electrolyte is demonstrated. The modified electrolyte facilitates the formation of pores and channels in CNT forest and leads to increased active surface area. Microstructure‐engineered CNT forest is further coated conformally with 3 nm of TiO2 using atomic layer deposition. The developed VACNT‐TiO2 hybrid shows 102‐fold increase in energy density, 20‐fold increase in specific capacitance, and 13‐fold increase in power density along with high capacitive retention as compared to bare VACNT in KOH. This improved performance is correlated to formation of micro channels that enable more accessible surface area for electrolytic ions. The demonstrated simple electrolyte engineering approach with increased energy density of aligned CNT‐TiO2 hybrid is relevant for portable energy storage applications.

Growth of CNT Forests on Titanium Based Layers, Detailed Study of Catalysts.

For better electrical contacts of potential devices, growth of vertically aligned carbon nanotubes (CNT forests) directly onto conductive substrates is an emerging challenge. Here, we report a systematic study on the CCVD synthesis of carbon nanotube forests on titanium based substrates. As a crucial issue, the effect of the presence of an insulating layer (alumina) on the growing forest was investigated. Other important parameters, such as the influence of water vapor or the Fe-Co catalyst ratio, were also studied during the synthesis. As-prepared CNT forests were characterized by various techniques: scanning and transmission electron microscopies, Raman spectroscopy, spectroscopic ellipsometry. CNT forests grown directly onto the conductive substrate were also tested as electrodes in hybrid halide perovskite photodetectors and found to be effective in detecting light of intensity as low as 3 nW.

Optical characterization of tip bended Vertically Aligned Carbon Nanotubes array

Vertically Aligned Carbon Nanotube arrays (also termed as VACNTs or CNT forest) have recently found to be transformable to a reflective mirror from a naturally black absorber. The feature of improved reflectance can be attained by the controllable tip bending process using the bottom surface of a rotated cylindrical tool (the process called micro-mechanical bending (M2B)). In this paper, the polarized light reflectance of bent and compacted region of the CNT forest using M2B method has been investigated. We observed that reflectance from the processed CNT zone was highly dependent on the angle of incidence and polarization state of the incident laser. For the first time, the refractive index of the tip bent CNT forests by M2B method was investigated and found to be in a range of ∼1.8.

Tungsten–Carbon Nanotube Composite Photonic Crystals as Thermally Stable Spectral‐Selective Absorbers and Emitters for Thermophotovoltaics

AbstractThermophotovoltaics (TPVs) is a promising energy conversion technology which can harvest wide‐spectrum thermal radiation. However, the manufacturing complexity and thermal instability of the nanophotonic absorber and emitter, which are key components of TPV devices, significantly limit their scalability and practical deployment. Here, tungsten–carbon nanotube (W‐CNT) composite photonic crystals (PhCs) exhibiting outstanding spectral and angular selectivity of photon absorbance and thermal emission are presented. The W‐CNT PhCs are fabricated by nanoscale holographic interferometry‐based patterning of a thin‐film catalyst, modulated chemical vapor deposition synthesis of high‐density CNT forest nanostructures, and infiltration of the CNT forests with tungsten via atomic layer deposition. Owing to their highly stable structure and composition, the W‐CNT PhCs exhibit negligible degradation of optical properties after annealing for 168 hours at 1273 K, which exceeds all previously reported high‐temperature PhCs. Using the measured spectral properties of the W‐CNT PhCs, the system efficiency of a GaSb‐based solar TPV (STPV) that surpasses the Shockley–Queisser efficiency limit at modest operating temperatures and input powers is numerically predicted. These findings encourage further practical development of STPVs, and this scalable fabrication method for composite nanostructures could find other applications in electromagnetic metamaterials.

Stable Wettability Control of Nanoporous Microstructures by iCVD Coating of Carbon Nanotubes.

Scalable manufacturing of structured materials with engineered nanoporosity is critical for applications in energy storage devices (i.e., batteries and supercapacitors) and in the wettability control of surfaces (i.e., superhydrophobic and superomniphobic surfaces). Patterns formed in arrays of vertically aligned carbon nanotubes (VA-CNTs) have been extensively studied for these applications. However, the as-deposited features are often undesirably altered upon liquid infiltration and evaporation because of capillarity-driven aggregation of low density CNT forests. Here, it is shown that an ultrathin, conformal, and low-surface-energy layer of poly perfluorodecyl acrylate, poly(1H,1H,2H,2H-perfluorodecyl acrylate) (pPFDA), makes the VA-CNTs robust against surface-tension-driven aggregation and densification. This single vapor-deposition step allows the fidelity of the as-deposited VA-CNT patterns to be retained during wet processing, such as inking, and subsequent drying. It is demonstrated how to establish omniphobicity or liquid infiltration by controlling the surface morphology. Retaining a crust of entangled CNTs and pPFDA aggregates on top of the patterned VA-CNTs produces micropillars with re-entrant features that prevent the infiltration of low-surface-tension liquids and thus gives rise to stable omniphobicity. Plasma treatments before and after polymer deposition remove the crust of entangled CNTs and pPFDA aggregates and attach hydroxyl groups to the CNT tips, enabling liquid infiltration yet preventing densification of the highly porous CNTs. The latter observation demonstrates the protective character of the pPFDA coating with the potential application of these surfaces for direct contact printing of microelectronic features.

Nickel Overlayers Modify Precursor Gases To Pattern Forests of Carbon Nanotubes

We analyzed the effect of nickel overlayers positioned in close proximity (bridges) or in contact (stencils) with the catalytic layer on the growth of vertically aligned carbon nanotubes (VACNTs) using thermal chemical vapor deposition (CVD). We studied the physical–chemical mechanisms, namely, the interaction of the overlayer with the gases and with the catalyst. We demonstrate that nickel inhibits CNT growth by adsorbing carbon to form graphene and by interacting with the gas precursors, leading to their modification into species that do not nucleate and grow CNTs. We demonstrate that the effect of the nickel bridge extends to the length of its boundary layer. We tested overlayer patterns and showed that the patterns were replicated during CNT growth. This facile method is a valid alternative to pattern CNT forests without the need for complex lithography and lift-off of the catalyst in applications where lithographic precision is not required.