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Interactions between carbon nanotubes (CNTs) and fluid flows are central to the operation of several emerging nanotechnologies. In this paper, we explore the fluid-structure interaction of CNT micropillars in wall-bounded shear flows, relevant to recently developed microscale wall shear stress sensors. We monitor the deformation of CNT micropillars in channel flow as the flow rate and wall shear stress are gradually varied. We quantify how the micropillars bend at low wall shear stress, and then will commonly tilt abruptly from their base above a threshold wall shear stress, which is attributed to the lower density of the micropillars in this region. Some micropillars are observed to flutter rapidly between a vertical and horizontal position around this threshold wall shear stress, before settling to a tilted position as wall shear stress increases further. Tilted micropillars are found to kink sharply near their base, similar to the observed buckling near the base of CNT micropillars in compression. Upon reducing the flow rate, micropillars are found to fully recover from a near horizontal position to a near vertical position, even with repeated on–off cycling. At sufficiently high wall shear stress, the micropillars were found to detach at the catalyst particle-substrate interface. The mechanical response of CNT micropillars in airflow revealed by this study provides a basis for future development efforts and the accurate simulation of CNT micropillar wall shear stress sensors. [ABSTRACT FROM AUTHOR]

Vertically aligned carbon nanotubes (VACNTs) exhibit outstanding mechanical strength, chemical stability, and electrical characteristics; however, their constrained mechanical elasticity and chemical responsiveness spurred research on atomic decoration techniques for enhancing their mechanochemical attributes. Nevertheless, achieving uniform atomic decoration on the VACNT surface is difficult because of the high density and large aspect ratio of VACNT. Herein, a strategy to design and apply nanopatterned VACNTs (nVACNTs) based on a nanotransfer printing process is proposed to improve atomic penetrability. Nanopatterns inherent to nVACNTs facilitate atomic penetration, allowing for the more consistent and higher quality deposition of functional materials such as zinc oxide and alumina by atomic layer deposition. Furthermore, physical vapor deposition provides an improved coating of metal catalysts such as gold. The uniform deposition of ceramic layers on the entire surface of nVACNTs strengthens its mechanical resilience, owing to the diminished van der Waals forces of CNTs. Surface‐decorated nVACNTs display an increased sensitivity to NO2 gas, which is attributed to the enhanced quality of the reactive catalyst deposition and augmented permeability. This strategy achieves a larger decorated area while increasing a catalytically active reaction area. The obtained results promise that the enhanced nVACNTs will expand the industrial applications of carbon nanotubes. [ABSTRACT FROM AUTHOR]

In this research work, vertically aligned carbon nanotubes (VACNTs) have been decorated with Sn-Ni alloy at three deposition times and were used as the anode for lithium-ion battery. The morphological and elemental analyses of the developed anodes were investigated. The results of the electrochemical analyses proved the Sn-Ni alloy possessed a relatively higher stable cycling performance when compared to previous works on Sn. Higher deposition times led to higher capacity loss, which was attributed to the possible clustering of Sn deposits as evidenced by morphological analysis. Higher thickness of the deposits also led to more intense irreversible capacity loss. For the selected optimal specimen, the fast capacity loss continued for the 13th cycle with the capacity of 400 mAh/g. This region was followed by a slower rate of capacity loss, and finally, the plateau capacity of 303.67 mAh/g was achieved after 100 cycles, which was stabilized at relatively low cycles. The ability of the specimen to reach the coulombic efficiency of 95% after five cycles also proved the efficiency of the electrode. [ABSTRACT FROM AUTHOR]

Both, aluminum doped zinc oxide (AZO) and vertically aligned carbon nanotubes (VACNT) have outstanding properties and promising applications in the future, however, there is little information in the scientific literature on whether this is feasible. In this study, we investigated the effects of catalyst layer deposition parameters and the synthesis parameters by using a simple and cost-effective dip coating method to form alumina support layer and iron and cobalt bimetal catalyst layer on the AZO surface thereafter performing synthesis via catalytic chemical vapor deposition technique at 650 °C. In order to gain useful information about the structure of the VACNTs, several parameters were varied during both catalyst layer preparation (e.g. catalyst ink concentration) and CCVD synthesis (e.g. water vapor gas feed, the presence of hydrogen gas). The resulting samples were investigated by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results indicated that the length and structure of CNTs were strongly affected by the catalyst ink concentration and water vapor. [ABSTRACT FROM AUTHOR]

This study aimed to assess the feasibility of utilizing surfaces coated with vertically aligned carbon nanotubes (VACNTs) to enhance the thermal capacity of micro heat pipes (MHPs) through numerical modeling. The developed model considered surface wettability, condensation rate, working fluid interaction, and heat transport within the MHP. Validation of the model against experimental references from the literature showed an average error of 5%. Using this validated model, conditions were extrapolated for two key parameters: (1) contact angles (CA) of 0 ∘ (superhydrophilicity) and 159 ∘ (superhydrophobicity), and (2) a condensation rate of 4.26 mL of water in 2 h, both characteristics obtained in previous experimental studies with VACNTs. This allowed for the evaluation of the benefits of employing VACNTs, resulting in a thermal resistance at least tenfold lower, with the ideal condensation rate lying between 334.50 and 836.25 μ W cm - 2 . The analysis also investigated the influence of different parameters on multiphysical systems, revealing that their interaction leads to a combined effect where the resulting magnitude exceeds the sum of the individual influences of each parameter. Through this study, a better understanding of heat pipes with wettability gradient system behavior was achieved, enabling separate studies of wettability and condensation rate parameters and facilitating more in-depth analyses. The use of VACNTs emerged as a promising option for enhancing heat pipes, offering potentially more efficient and significant results compared to conventional surface treatment methods. [ABSTRACT FROM AUTHOR]

Abstract An efficient and reproducible growth of vertically aligned carbon nanotubes by CCVD requires accurate and specific setting of the synthesis parameters and the properties of catalyst thin layers. In this work, the growth of vertically aligned carbon nanotubes onto AZO (= aluminum doped zinc oxide) glass substrate covered by Al2O3 and Fe-Co catalyst layer system is presented. Investigation of the effect of catalyst composition and synthesis temperature on CVD growth revealed the optimum condition of the synthesis. The analysis of as-prepared samples by SEM, TEM and Raman spectroscopy was carried out to prove the structure and quality of carbon deposit. Theoretical considerations have supported speculative ideas about the role of the support layer, the transformation of the catalyst layer in the presence of hydrogen gas and the growth mechanism of carbon nanotubes. The mechanism of CNT growth is modelled and the order of magnitude of experimentally observed vertical linear growth rate of CNT (several nm/s) is reproduced.

Background: Helmet systems most commonly experience oblique blunt impacts which cause simultaneous linear and rotational accelerations. The ability to attenuate both linear and rotational accelerations by absorbing the normal shock while accommodating large shear deformations with energy dissipation is critical to developing superior helmet liners that prevent traumatic brain injury (TBI). Objective: To investigate the quasistatic compression-shear response of vertically aligned carbon nanotube (VACNT) foams—which are known for their exceptional specific energy absorption in compression—and explore their potential of accommodating large shear strains at lower shear stress levels, under large compression-shear loadings. Methodology: We investigate the quasistatic compression shear response of freestanding vertically aligned carbon nanotube foams subjected to varied initial precompressions. We use in situ high speed microscopy to visualize the microscale deformations during shear. Results: Vertically aligned carbon nanotube foams exhibit a nonlinear hysteric shear stress–strain response that varies as a function of initial normal precompression. At a given precompression, initial linear response at very low shear strains leads to a behavior showing increasing compliance leading to a plateau like regime at moderate shear strains and then transitions into a stiffening behavior at high shear strains. The shear stress–strain response softens with the increase in initial precompression demonstrating the vertically aligned carbon nanotube foam's potential to accommodate large shear strains more effectively at severe compression-shear loads unlike other solids that typically jam. In situ high-speed microscopy reveals the unraveling of carbon nanotubes that collectively buckled during precompression, allowing them to accommodate large shear strains at low shear stress levels. Conclusion: We demonstrate the ability of vertically aligned carbon nanotube to accommodate large shear strains at lower shear stress levels under large compression-shear loadings. We propose a model to predict the compression-shear response at different precompressive strains and use this model to develop a deformation modality diagram that categorizes the dominant deformation mechanisms at different loads along different loading angles. [ABSTRACT FROM AUTHOR]

The fabrication of sponge-like vanadium pentoxide (V2O5) nanostructures using vertically aligned carbon nanotubes (VACNTs) as a template is presented. The VACNTs were grown on silicon substrates by chemical vapor deposition using the Fe/Al bilayer catalyst approach. The V2O5 nanostructures were obtained from the thermal oxidation of metallic vanadium deposited on the VACNTs. Different oxidation temperatures and vanadium thicknesses were used to study the influence of these parameters on the stability of the carbon template and the formation of the V2O5 nanostructures. The morphology of the samples was analyzed by scanning electron microscopy, and the structural characterization was performed by Raman, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. Due to the catalytic properties of V2O5 in the decomposition of carbonaceous materials, it was possible to obtain supported sponge-like structures based on V2O5/CNT composites, in which the CNTs exhibit an increase in their graphitization. The VACNTs can be removed or preserved by modulating the thermal oxidation process and the vanadium thickness. [ABSTRACT FROM AUTHOR]

Increasingly smaller fluid flow devices depend on increasingly smaller sensors to operate. In this work, we develop a miniature wall shear stress sensor consisting of a pair of carbon nanotube pillars that produce a measurable capacitance change when one is deflected by the flow. The sensor, including material producing the capacitance change, has a 50 μm × 60 μm footprint and <200 μm height. It provides 0.05–1 fF/Pa sensitivity with up to ±8 Pa range. Most sensors produced were found to have a wider operating range when the thinner pillar was positioned downstream because greater deflection could be achieved without contact between the pillars. Interestingly, a small number of sensors responded differently to flow due to twisting of the sensing element rather than bending or due to a dominant Bernoulli effect. These diverse sensing mechanisms could be exploited to tune sensitivity or operating range in future designs. [ABSTRACT FROM AUTHOR]

Nano-constituent incorporation into composites has been extensively studied in the literature due to its improvement in static and dynamic mechanical properties, as well as its prevention from interlaminar crack initiation and propagation. This work introduces a detailed manufacturing process of nano-engineered composite laminates, from impregnation to consolidation, without damaging the initial morphology of carbon nanotubes transferred on prepreg interfaces. Based on prepreg and vertically aligned carbon nanotubes (VACNTs) synthesized on an aluminium alloy (Al) substrate, the impregnation step allows for the transfer of VACNTs onto the prepreg surface through partial resin-rising capillarity. The Al alloy substrate is then removed from the VACNTs through a separation step, ensuring highly effective and repeatable transfer with more than 80% VACNTs transferred onto the prepreg surface. This paper provides insight into the impregnation and transfer processes and guides the choice of process parameters to ensure minimal VACNTs buckling during the consolidation of the hybrid composites at high pressure in an autoclave. [ABSTRACT FROM AUTHOR]

Delamination still remains one of the common concerns in continuous fibers reinforced polymer composites. In the literature, the incorporation of nanoconstituents into constitutive composites plies has been suggested with the aim of improving interface toughness. In this study, vertically aligned carbon nanotubes forests (VACNTs) are transferred at composites interfaces, and mode I (DCB tests) and mode II (ENF tests) fracture tests carried out on composite samples. Microscopic analysis of reference and nano‐engineered composites help to understand fracture behavior and toughness. While the crack path in ENF samples is observed at interlaminar VACNTs‐resin interfaces, the crack path in DCB samples is intralaminar, located within the unidirectional carbon fiber plies. These microscopic observations give explanation for unstable crack propagation in nano‐engineered ENF samples and the unchanged toughness from the nano‐engineered to the reference zone in DCB samples. [ABSTRACT FROM AUTHOR]

The fabrication of sponge-like vanadium pentoxide (V2O5) nanostructures using vertically aligned carbon nanotubes (VACNTs) as a template is presented. The VACNTs were grown on silicon substrates by chemical vapor deposition using the Fe/Al bilayer catalyst approach. The V2O5 nanostructures were obtained from the thermal oxidation of metallic vanadium deposited on the VACNTs. Different oxidation temperatures and vanadium thicknesses were used to study the influence of these parameters on the stability of the carbon template and the formation of the V2O5 nanostructures. The morphology of the samples was analyzed by scanning electron microscopy, and the structural characterization was performed by Raman, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. Due to the catalytic properties of V2O5 in the decomposition of carbonaceous materials, it was possible to obtain supported sponge-like structures based on V2O5/CNT composites, in which the CNTs exhibit an increase in their graphitization. The VACNTs can be removed or preserved by modulating the thermal oxidation process and the vanadium thickness.

Owing to their remarkable properties and ordered architecture, vertically aligned CNT forests (VACNT) hold promises for countless applications ranging from energy storage to multifunctional fiber production. Over the last three decades, studies of carbon nanotube (CNT) growth have provided invaluable insight into the CNT nucleation and growth mechanism and enabled critical advancements in nanotechnology. Nevertheless, the ability to fully harness the exceptional VACNT properties in commercial devices is bottlenecked by compatibility of current CNT synthesis processes with large-scale manufacturing. Metal foil substrates present an economic alternative to traditional insulating substrates, like silicon or quartz, and are compatible with both roll-to-roll and automated, large-scale, batch processes. Compared to CNT growth on Si substrates, metal foils present additional challenges, such as increased roughness and reactivity at high temperatures. Nonetheless, many successful VACNT growths on conducting metal foils have been reported, which demonstrate the feasibility of metal substrate use for large-volume production of high-quality CNTs. In this review, we discuss advancements in the field of VACNT growth on metal foil and specifically examine different choices for metal substrates, barrier and catalyst layers, deposition and growth methods, resulting CNT characteristics, and highlight a number of applications that benefit from CNT growth on metal substrates and transition to large-scale manufacturing. [Display omitted] • Exceptional VACNT properties are transformative for many technologies. • Challenges and successes of growing VACNTs on metal foils are described in detail. • Material choice, process conditions, and resulting CNT characteristics are reviewed. • Fundamental investigations and application driven developments are highlighted. • Products based on VACNTs grown on metal supports are at the market horizon. [ABSTRACT FROM AUTHOR]

Silicon is one of the most promising anode materials for lithium‐ion batteries. Silicon endures volume changes upon cycling, which leads to subsequent pulverization and capacity fading. These drawbacks lead to a poor lifespan and hamper the commercialization of silicon anodes. In this work, a hybrid nanostructured anode based on silicon nanoparticles (SiNPs) anchored on vertically aligned carbon nanotubes (VACNTs) with defined spacing to accommodate volumetric changes is synthesized on commercial macroscopic current collector. Achieving electrodes with good stability and excellent electrochemical properties remain a challenge. Therefore, we herein tune the active silicon areal loading either through the modulation of the SiNPs volume by changing the silicon deposition time at a fixed VACNTs carpet length or through the variation of the VACNT length at a fixed SiNPs volume. The low areal loading of SiNPs improves capacity stability during cycling but triggers large irreversible capacity losses due to the formation of the solid electrolyte interphase (SEI) layer. By contrast, higher areal loading electrode reduces the quantity of the SEI formed, but negatively impacts the capacity stability of the electrode during the subsequent cycles. A higher gravimetric capacity and higher areal loading mass of silicon is achieved via an increase of VACNTs carpet length without compromising cycling stability. This hybrid nanostructured electrode shows an excellent stability with reversible capacity of 1330 mAh g−1 after 2000 cycles. [ABSTRACT FROM AUTHOR]

We report a high growth rate (37 μm/min) synthesis of vertically aligned carbon nanotube (VACNT) forest, achieving remarkable height exceeding a millimetre with good crystallinity. VACNTs with few numbers of walls have been grown over Fe–Co/Al 2 O 3 /SiO 2 coated Si wafer using the water assisted atmospheric pressure chemical vapour deposition (WACVD) method. The key to this success lies in the synergistic combination of a bimetallic catalyst (Fe-Co) with buffer Al 2 O 3 layer and the WACVD method. Notably, the VACNT forest, synthesised at optimized conditions can be directly used without the need for additional post-growth purification processes, eliminating the risk of potential damage to the CNTs. Finally, the VACNT forest exhibits excellent areal capacitance of 133.33 mF/cm2 at a current density of 1 mA/cm2 with outstanding cyclic stability of 130 % @ 3000 cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

While electrochemical supercapacitors often show high power density and long operation lifetimes, they are plagued by limited energy density. Pseudocapacitive materials, in contrast, operate by fast surface redox reactions and are shown to enhance energy storage of supercapacitors. Furthermore, several reported systems exhibit high capacitance but restricted electrochemical voltage windows, usually no more than 1 V in aqueous electrolytes. Here, it is demonstrated that vertically aligned carbon nanotubes (VACNTs) with uniformly coated, pseudocapacitive titanium disulfide (TiS2 ) composite electrodes can extend the stable working range to over 3 V to achieve a high capacitance of 195 F g-1 in an Li-rich electrolyte. A symmetric cell demonstrates an energy density of 60.9 Wh kg-1 -the highest among symmetric pseudocapacitors using metal oxides, conducting polymers, 2D transition metal carbides (MXene), and other transition metal dichalcogenides. Nanostructures prepared by an atomic layer deposition/sulfurization process facilitate ion transportation and surface reactions to result in a high power density of 1250 W kg-1 with stable operation over 10 000 cycles. A flexible solid-state supercapacitor prepared by transferring the TiS2 -VACNT composite film onto Kapton tape is demonstrated to power a 2.2 V light emitting diode (LED) for 1 min.

Vertically aligned carbon nanotube (VACNT) materials is a promising candidate in different fields. The intrinsic performance of VACNTs, such as a large specific surface area, high conductivity, and especially its vertical conductive channel, stands out the VACNT-based device from conventional carbon material-based devices in the energy, environmental sustainability, and so on. In this review, a comprehensive and in-depth summary on the synthesis method and fundamental mechanisms, and design strategies for the novel VACNT materials, is presented. In addition, an overview of the latest development in high-efficiency utilization of VACNT materials in representative fields, including energy storage and conversion, catalysis, terahertz spectroscopy, biology and biomedicine, and environmental sustainability, is given. Finally, the challenges and promising perspectives of VACNT materials in future development are outlined.

Vertically aligned carbon nanotubes (VACNT) are manufactured nanomaterials with excellent properties and great potential for numerous applications. Recently, research has intensified toward achieving VACNT synthesis on different planar and non-planar substrates of various natures, mainly dependent on the user-defined application. Indeed, VACNT growth has to be adjusted and optimized according to the substrate nature and shape to reach the requirements for the application envisaged. To date, different substrates have been decorated with VACNT, involving the use of diffusion barrier layers (DBLs) that are often insulating, such as SiO2 or Al2O3. These commonly used DBLs limit the conducting and other vital physico-chemical properties of the final nanomaterial composite. One interesting route to improve the contact resistance of VACNT on a substrate surface and the deficient composite properties is the development of semi-/conducting interlayers. The present review summarizes different methods and techniques for the deposition of suitable conducting interfaces and controlled growth of VACNT on diverse flat and 3-D fibrous substrates. Apart from exhibiting a catalytic efficiency, the DBL can generate a conducting and adhesive interface involving performance enhancements in VACNT composites. The abilities of different conducting interlayers are compared for VACNT growth and subsequent composite properties. A conducting interface is also emphasized for the synthesis of VACNT on carbonaceous substrates in order to produce cost-effective and high-performance nano-engineered carbon composites. [ABSTRACT FROM AUTHOR]

Some of the least reflective materials are vertically aligned carbon nanotubes (VACNTs). However, VACNT films are extremely fragile, restricting the range of applications where they can be used. Here, we have formed VACNT/carbon composite films with greater than 500× stiffness and 50× strength compared to as-grown VACNTs while maintaining ultralow reflectance. This is achieved using an infiltration process that coats the individual nanotubes with a thin layer of nanocrystalline carbon, locking the nanotubes together, and then adding lateral subwavelength surface topography to the tops of the VACNTs with an oxygen plasma etch to reduce the reflectance. While still a delicate material, these composites are robust enough to be exposed to water and handled. We demonstrated that these composites can be transferred from the growth substrate to other surfaces resulting in a reflectance of less than 0.1%. [ABSTRACT FROM AUTHOR]

In this study, a growth mechanism of vertically aligned carbon nanotubes (VACNT) on a nanostructured porous silicon template (NPSiT) was proposed based on the experimental observations obtained. Camphor oil and ferrocene (Fe) were used as a carbon source and a catalyst, respectively. The NPSiT was optimised and used as a template to synthesise VACNT. The VACNT was synthesised on NPSiT by using a double thermal chemical vapour deposition (DTCVD) method. The synthesis was also performed via a floated method in a DTCVD reactor by using an in-situ catalyst in the absence of any catalysts pre-treatment. Each of the growth mechanisms was proposed based on the TEM images obtained at different synthesis conditions. From the results, a mixed top and bottom growth model was proposed for the growth mechanism of VACNT at the pores and pillars. On the contrary, the tip growth model was proposed for the growth inside the pores, while the valley growth model was proposed for the growth within the pillars of NPSiT. Furthermore, a mixed tip and valley growth model was proposed based on the location of Fe particles. [ABSTRACT FROM AUTHOR]

Capturing and analyzing cometary coma dust lead to elucidate the origin of water and organics within the Solar System. For future sample return missions of fragile organic microparticles from a cometary nucleus, rendezvous operations will become more favorable than flyby missions because the comet rendezvous can reduce impacting velocity of cometary dust particles slow enough to capture them intact, rather than hypervelocity flyby sampling like the Stardust mission to the Comet Wild 2. At JAXA/ISAS, we are developing a core technology for sample return of microparticles ejected at as a lower velocity as an order of 0.1 m/s to 100 m/s after rendezvous with a cometary nucleus. We have devised "Vertically Aligned Carbon Nanotube (VA-CNT)" carpets as an effective capture medium for such a purpose. The VA-CNT carpets can amplify van der Waals force with impacting particles due to the large contact area and can capture intact the microparticles of sub-mm in size or smaller in the vacuum space environment while preserving its adhesive strength. In this study, we modelled capturing mechanism of microparticles on the VA-CNT carpets by the impact analysis software "LS-DYNA" to further improve its particle capture performance. The stress–strain constitutive laws for the VA-CNT carpets were derived via indentation and inputted to our simulations that were consistent with impact experiment results. The simulations reveal that the mechanical property of the VA-CNT carpets is the key for the improvement of its particle capture performance suitable for sampling the cometary dust. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs. [ABSTRACT FROM AUTHOR]

Electrochemical energy storage is a key technology for a clean and sustainable energy supply. In this respect, supercapacitors (SC) have recently received considerable attention due to their excellent performance, including high‐power density and long‐cycle life. However, the poor binding strength between the active materials and substrate, the low active material loading, and small specific capacitance hinder the overall performance improvement of the device. In this study, an ultrahigh‐areal capacitance flexible SC based on the Al micro grid‐based hierarchical vertically aligned carbon nanotubes (VACNTs) is studied. Interestingly, the Al micro grid‐based VACNTs exhibit ultrahigh loading (13 mg cm−2), and the as‐fabricated VACNTs electrode display outstanding electrochemical performance, including an impressive areal capacitance of 1,300 mF cm−2 at the current density of 13 mA cm−2 and excellent stability with a retention ratio of 90% after 20,000 cycles at the current density of 130 mA cm−2. Furthermore, the hierarchical VACNT electrodes show excellent mechanical flexibility when assembled into quasi‐solid‐state SC using Na2SO4‐PVA gel as the electrolyte. The capacitance of this device is hardly changed bending different angles, even 180°. This study demonstrates the tremendous potential of Al micro grid‐based hierarchical VACNTs as electrodes for high‐performance flexible and wearable energy storage devices. [ABSTRACT FROM AUTHOR]

Smart thermal interface materials must exhibit self-healability and high thermal conductivity (k) and elastic deformation as they can experience repeated compression and undergo sudden damage. However, it remains challenging to ensure high phonon mobility/efficient phonon transfer, self-healing, and good elasticity by optimizing its molecular orientation or cross-links. Herein, a self-healing and elastic polyimide copolymer (EMPI) cross-linked by flexible and rigid segments is uniformly filled into the gaps of a forest of vertically aligned carbon nanotubes (VACNTs). The EMPI@VACNTs composite exhibits a high k value at 10.83 ± 0.22 W m−1 K−1, low interfacial thermal resistance at 6.83 ± 0.15 K mm2 W−1, high elastic compressive deformation (30% at 2.5 MPa), and strong surface adhesion (0.3 MPa). Further, it could recover 90.8% of its elastic modulus and 92% of its thermal resistance after self-healing at 80 °C for 80 h. An EMPI@VACNTs-Cu device exhibits efficient heat conduction not only by recovering after gradient compressive strains of up to 30% but also by self-healing its damage or reforming the interface with Cu. Thus, the thermally conductive, self-healing, and elastic EMPI@VACNTs composite opens new avenues for smart thermal management in various high-power/intelligent devices. Efficient heat conduction across the complex interface between two types of materials is essential for thermal management in advanced systems. The self-healable, elastic EMPI@VACNTs composite opens new avenues for smart thermal management, and it exhibits a high thermal conductivity, low interfacial thermal resistance, high elastic compressive deformation, and strong surface adhesion. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Vertically aligned carbon nanotubes (VACNTs) were synthesized on different oxide buffer layers using chemical vapor deposition (CVD). The growth of the VACNTs was mainly determined by three factors: the Ostwald ripening of catalyst nanoparticles, subsurface diffusion of Fe, and their activation energy for nucleation and initial growth. The surface roughness of buffer layers largely influenced the diameter and density of catalyst nanoparticles after annealing, which apparently affected the lifetime of the nanoparticles and the thickness of the prepared VACNTs. In addition, the growth of the VACNTs was also affected by the deposition temperature, and the lifetime of the catalyst nanoparticles apparently decreased when the deposition temperature was greater than 600 °C due to their serious Ostwald ripening. Furthermore, in addition to the number of catalyst nanoparticles, the density of the VACNTs was also largely dependent on their activation energy for nucleation and initial growth.

Vertically aligned carbon nanotubes (VACNT) are manufactured nanomaterials with excellent properties and great potential for numerous applications. Recently, research has intensified toward achieving VACNT synthesis on different planar and non-planar substrates of various natures, mainly dependent on the user-defined application. Indeed, VACNT growth has to be adjusted and optimized according to the substrate nature and shape to reach the requirements for the application envisaged. To date, different substrates have been decorated with VACNT, involving the use of diffusion barrier layers (DBLs) that are often insulating, such as SiO2 or Al2O3. These commonly used DBLs limit the conducting and other vital physico-chemical properties of the final nanomaterial composite. One interesting route to improve the contact resistance of VACNT on a substrate surface and the deficient composite properties is the development of semi-/conducting interlayers. The present review summarizes different methods and techniques for the deposition of suitable conducting interfaces and controlled growth of VACNT on diverse flat and 3-D fibrous substrates. Apart from exhibiting a catalytic efficiency, the DBL can generate a conducting and adhesive interface involving performance enhancements in VACNT composites. The abilities of different conducting interlayers are compared for VACNT growth and subsequent composite properties. A conducting interface is also emphasized for the synthesis of VACNT on carbonaceous substrates in order to produce cost-effective and high-performance nano-engineered carbon composites.

Nanomaterials have been commonly employed to enhance the performance of polymeric membrane materials that are used in several industrial applications. Carbon nanotubes (CNTs) have gained notable attention over the years for use in membrane technology due to their anti-biofouling properties, salt rejection capability, exceptional electrical conductivity, and mechanical properties. This paper aims to discuss some of the recent applications of CNTs in membrane technology and their effect on a larger scale. The paper reviews successful case studies of incorporation of CNTs in membranes and their impact on water purification, desalination, gas separations, and energy storage, in an effort to provide a better understanding of their capabilities. Regarding the future trends of this technology, this review emphasizes improving the large-scale production processes and addressing environmental and health-related hazards of CNTs during production and usage.

The one-step aerosol-assisted catalytic chemical vapor deposition (CCVD) process, when operated in a H 2 -based carrier gas, is shown to be effective at an extremely low ferrocene content (0.1 wt% in toluene), which enables to efficiently prepare forests of vertically aligned multiwalled carbon nanotubes (VACNTs) with high purity and good crystalline level. The resulting iron content in VACNT sample is only 0.5 wt% corresponding to a high catalytic yield of 200 while the steady growth rate (20 μm/min) is maintained at a significant value. The iron content in the sample is found proportional to the ferrocene concentration in the precursor, and when it decreases, a noticeable reduction in the iron encapsulation frequency in the nanotube channel is plainly observed. Lowering the ferrocene concentration generates a reduction in the VACNT number density while the growth rate increases and CNT diameters and crystalline structure remain similar. Such significant purity and crystalline levels involves a high oxidation resistance of the VACNT forest. These results, together with the in-situ continuous growth feature of the one-step aerosol assisted CCVD process, open up towards a new VACNT range made of pure and well-crystallized multi-walled carbon nanotubes, which is of interest for industrial production and commercial applications. Image 1 [ABSTRACT FROM AUTHOR]

Owing to their high stability against corrosive gases, carbon-based adsorbents are preferentially used for the adsorptive removal of SO2. In the present study, SO2 adsorption on different carbon nanomaterials namely carbon nanohorns (CNHs), multiwalled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) and vertically aligned carbon nanotubes (VACNTs) are investigated and compared against the adsorption characteristics of activated carbon and graphene oxide (GO). A comprehensive overview of the adsorption behavior of this family of carbon adsorbents is given for the first time. The relative influence of surface area and functional groups on the SO2 adsorption characteristics is discussed. The isosteric heat of adsorption values are calculated to quantify the nature of the interaction between the SO2 molecule and the adsorbent. Most importantly, while chemisorption is found to dominate the adsorption behavior in activated carbon, SO2 adsorption on carbon nanomaterials occurs by a physisorption mechanism.

An automated quantitative study of the alignment of vertically aligned carbon nanotubes (VA-CNTs) from scanning electron microscopy (SEM) images has been demonstrated. It is based on the fact that the image gradient (directional change in intensity or color) at every pixel in the image contains the information about the anisotropy at that particular pixel i.e., the local alignment is maintained in the orthogonal direction to the gradient. Structure tensor metrics are formulated demonstrating to be able to summarize the distribution of gradient directions within the neighborhood of any pixel within a two-dimensional domain (surface). An image analysis is presented that evaluates the alignment in desired regions of interest (ROIs) in SEM images of VA-CNTs. This method has been exploited to study the alignment of two different kinds of VA-CNTs: one grown via the thermal chemical vapor deposition (T-CVD) method and the second synthesized via the plasma enhanced chemical vapor deposition (PE-CVD) method. • Evaluating the alignment of nanostructures is important for tailoring material characteristics and designing functional materials with unique directional properties • Alignment of 1-D nanostructures can be defined by calculating the coherency from the SEM image. • PE-CVD method provides with improvement in the alignment of carbon nanotubes as compared to thermal CVD. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) offer unique properties that have the potential to address multiple issues in industry and material sciences. Although many synthesis methods have been developed, it remains difficult to control CNT characteristics. Here, with the goal of achieving such control, we report a bottom-up process for CNT synthesis in which monolayers of premade aluminum oxide (Al2O3) and iron oxide (Fe3O4) nanoparticles were anchored on a flat silicon oxide (SiO2) substrate. The nanoparticle dispersion and monolayer assembly of the oleic-acid-stabilized Al2O3 nanoparticles were achieved using 11-phosphonoundecanoic acid as a bifunctional linker, with the phosphonate group binding to the SiO2 substrate and the terminal carboxylate group binding to the nanoparticles. Subsequently, an Fe3O4 monolayer was formed over the Al2O3 layer using the same approach. The assembled Al2O3 and Fe3O4 nanoparticle monolayers acted as a catalyst support and catalyst, respectively, for the growth of vertically aligned CNTs. The CNTs were successfully synthesized using a conventional atmospheric pressure-chemical vapor deposition method with acetylene as the carbon precursor. Thus, these nanoparticle films provide a facile and inexpensive approach for producing homogenous CNTs.

The carbon nanoparticles film coating on top of vertically aligned carbon nanotubes on silicon substrate (CNPs/CNTs/silicon) has been prepared by the pyrolysis of FePC at 960 °C. The surface morphologies and structure of the prepared sample are characterized by Scanning Electron Microscope, X-ray energy dispersive spectroscopy and Raman Spectroscopy. The field electron emission (FEE) properties of the CNPs/CNTs are also measured. A low turn-on electric field of 1.3 V / μ m at a current density of 10 μ A / c m 2 , low threshold electric field of 1.8 V / μ m at a current density of 1 m A / c m 2 , a high emission density and good field emission stability are obtained. The above results make CNPs/CNTs/silicon an effective field emitter. • The CNPs/CNTs/silicon is prepared by the pyrolysis of FePC at 960 °C. • Low turn-on and threshold fields are observed. • High emission density and good field emission stability are obtained. [ABSTRACT FROM AUTHOR]

• We investigate the behavior of VA-CNTs under electrostatic tension. • Electrostatic tension reorganizes the CNTs and increases their alignment. • Stretched CNTs show an increased stiffness and a negative Poisson's ratio (NPR). • Highest NPR values were obtained in the top portion of the VA-CNTs. Due to their excellent physical properties and compatibility with micro-fabrication processes, vertically aligned carbon nanotubes (VA-CNTs) have been successfully integrated in various nano/micro-electromechanical system (NEMS/MEMS) devices, composites, and electronic circuits. Here, we investigate the behavior of VA-CNTs under electrostatic tension. Scanning electron microscopy revealed that electrostatic tension reorganizes the individual CNTs and increases their alignment, thereby increasing their stiffness, and resulting in a negative Poisson's ratio (NPR). High NPR values were obtained in the top portion of the VA-CNTs (the location of the greatest morphological change), while the other portions (a less significant morphological change) demonstrated smaller NPR values. Therefore, the electrostatic pressure induces an irreversible morphological change in the VA-CNTs, which, in turn, modifies their properties. This behavior makes VA-CNTs an attractive material for a wide range of micro- and nano-scale devices, wherein tunable mechanical properties and a versatile motion transformation are required. [ABSTRACT FROM AUTHOR]

Abstract As-grown VACNTs are subjected to mechanical densification by knock-down process to achieve higher volume fractions. In here, the preferential alignment of CNTs is preserved horizontally and an easy delamination of VACNTs are achieved to fabricate high volume fraction nanocomposites. Both physical and chemical properties of VACNTs such as alignment, quality, and purity etc. have been characterized by Raman spectroscopy, TGA, and SEM. The knocked-down VACNTs arrays are then used as 'reinforcing ply' with epoxy for PNCs fabrication. Since load transfer in between CNTs and epoxy is important to avoid interfacial slippage and reduction in loss factor, to increase interaction between CNTs and epoxy, ozone treatment was applied to CNTs. To observe the effect of ozone treatment on the viscoelastic response of polymer nanocomposites with non-ozone treated and ozone treated VACNT were tested by DMA under different frequencies. The ozone treatment time and CNT quality, investigated through Raman Spectroscopy, were correlated for viscoelastic properties. The results demonstrated that ozone treatment improved wettability and increased viscoelastic properties of PNCs under multi-frequency for short-term (<60 s) but resulted in a decrease in storage modulus when applied for in longer durations. [ABSTRACT FROM AUTHOR]

High-quality recordings of neural interfaces are crucial in advancing neuroscience research, but conventional electrodes with highly conductive materials have limitations due to their limited effective surface area. Here, we develop a neural probe integrated with an electrode implemented using vertically aligned carbon nanotubes (VACNTs) that remarkably improves recording capability. By directly synthesizing VACNT bundles on the electrode array of the neural probe, we successfully fabricate an electrode with the lowest area-specific impedance. Owing to the dramatically lowered impedance of the VACNT electrode, its signal-to-noise ratio increases by more than 3 times compared with that of a black Pt electrode with low impedance. Moreover, the number of spikes observed in the measured signals increases by more than 4 times. Notably, our VACNT electrode enables accurate mapping of the spatial distribution of neurons, demonstrating its potential to significantly advance neuroscience research through massive neural recordings with improved mapping capability. This powerful technology that maximizes electrode performance could pave the way for new discoveries and insights in the field of neuroscience. [Display omitted] • The first demonstration of an implantable neural probe with directly grown VACNTs. • The VACNTs-integrated electrodes drastically lowered the impedance. • The number of signal spikes increases by about 4 times compared to control group. • The position of neurons is estimated by measuring the neural activities. [ABSTRACT FROM AUTHOR]

Neural tissue-related illnesses have a high incidence and prevalence in society. Despite intensive research efforts to enhance the regeneration of neural cells into functional tissue, effective treatments are still unavailable. Here, a novel therapeutic approach based on vertically aligned carbon nanotube forests (VA-CNT forests) and periodic VA-CNT micropillars produced by thermal chemical vapor deposition is explored. In addition, honeycomb-like and flower-like morphologies are created. Initial viability testing reveals that NE-4C neural stem cells seeded on all morphologies survive and proliferate. In addition, free-standing VA-CNT forests and capillary-driven VA-CNT forests are created, with the latter demonstrating enhanced capacity to stimulate neuritogenesis and network formation under minimal differentiation medium conditions. This is attributed to the interaction between surface roughness and 3D-like morphology that mimics the native extracellular matrix, thus enhancing cellular attachment and communication. These findings provide a new avenue for the construction of electroresponsive scaffolds based on CNTs for neural tissue engineering., (© 2023 Wiley-VCH GmbH.)

Abstract: Wafer‐scale vertically aligned carbon nanotube/poly(vinyl alcohol) (VACNT/PVA) hydrogels are fabricated by infiltration of PVA among VACNTs and subsequent in situ hydrogelation. Owing to the homogeneous PVA infiltration, uniform distribution and orientation of the carbon nanotubes (CNTs) are well retained, which in turn provide large CNT‐PVA interfaces throughout the resulting hydrogels. Compared to bare PVA hydrogels, such composite hydrogels perform significantly enhanced longitudinal compressive responses upon both static and dynamic loadings, achieving improvements of up to 25.2‐ and 9.0‐fold in strength and loss modulus, respectively. The novel scalable fabrication of VACNT/PVA hydrogels and their attractive performances hold great potential for a wide range of applications. [ABSTRACT FROM AUTHOR]

Gas-phase reactions among carbon precursors could have a significant effect on the catalytic synthesis of vertically aligned (VA-) carbon nanotubes (CNTs). State-of-the-art adjustment of the gas-phase reaction conditions is done ad hoc with low reproducibility, ascribed partly to an incomplete understanding of the mechanism how the gas-phase reaction influences the growth kinetics of VA-CNTs. Here, we investigate this mechanism and propose that in the presence of prominent gas-phase reaction, the growth kinetics characterization shifts from a single rate-limiting reaction to a multi-route reaction with each pathway having its own rate-limiting step. The rate of the gas-phase reaction could be tailored by the partial pressure and thermal history of a carbon feedstock (e.g., acetylene). According to in-situ mass spectrometry and numerical simulation, a rich set of thermally rearranged secondary species (e.g., C 4 H 4 and C 6 H 6 ) are found above the catalyst surface. It appears that these secondary species, along with a chief precursor (C 2 H 2 ), can give variation to a yield of CNTs through various reaction pathways with altering the overall growth rate of VA-CNTs. Our findings would further the current understanding of the VA-CNT growth from thermally rearranged precursors, instrumental to applications such as diameter-controlled growth and CMOS-compatible low-temperature growth. [ABSTRACT FROM AUTHOR]

• Gold (Au) films were deposited onto vertically aligned carbon nanotubes (CNTs). • Au@CNTs have excellent cycling stability in 0.5 m H 2 SO 4 compared to Au electrode. • The results demonstrate the beneficial use of CNTs to fabricate a porous Au films. In this work, gold (Au) films were deposited onto vertically aligned carbon nanotubes (CNTs) by Dc magnetron sputtering method for use as super-capacitor electrodes. By so doing, we synthesize a porous Au deposit anchored on the CNTs with a high apparent surface area. The structure and microstructure studies revealed that the Au@CNTs have a porous nanostructure morphology. The porous Au/CNTs electrodes exhibit an a good areal capacitance compared to state of art Au based electrode (25.6 mF cm-2 at 5 mV.s-1) and excellent cycling stability (90% retention after 10.000 cycles) in 0.5 M H 2 SO 4 aqueous solution. These results demonstrate the beneficial use of CNTs to fabricate a porous Au deposit with improved electrochemical energy storage. In addition, these porous structures can also be used as templates for another type of materials for electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT) arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD). Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays.

Vertically aligned carbon nanotube (VACNT) forests are promising for supercapacitor electrodes, but their industrialisation requires a large-scale cost-effective synthesis process suitable to commercial aluminium (Al) foils, namely by operating at a low temperature (2 as a carrier gas, clean and dense forests of VACNTs of about 10 nm in diameter are obtained at 615 °C with a growth rate up to 5 µm/min. Such novel potentiality of this one-step CCVD process is at the state-of-the-art of the multi-step assisted CCVD processes. To produce thick samples, long synthesis durations are required, but growth saturation occurs that is not associated with a diffusion phenomenon of iron in aluminium substrate. Sequential syntheses show that the saturation trend fits a model of catalytic nanoparticle deactivation that can be limited by decreasing acetylene flow, thus obtaining sample thickness up to 200 µm. Cyclic voltammetry measurements on binder-free VACNT/Al electrodes show that the CNT surface is fully accessible to the ionic liquid electrolyte, even in these dense VACNT forests.

The present study focuses on a thermal damper that aims at smoothing the temperature peaks experienced by electronic components during transient solicitations. It consists of a silicon casing containing a densified or undensified carbon nanotube (CNT) array - linking directly both sides of the system - filled with phase change material (PCM). Theoretical consideration enables to define the concept of ideal thermal damper in order to study the foreseeable performance of this kind of system. Its thermal effectiveness can be predicted by means of two non-dimensional numbers, linked to the thermal capacity of the system and to the latent heat of the PCM. A numerical model shows that the behavior of a non-ideal thermal damper can differ from that of an ideal thermal damper: it is mostly affected by the thermal resistance at the interface between the silicon and the CNT and the temperature glide during the PCM phase change. To complete the study, prototypes of thermal dampers are experimentally characterized, in terms of heat storage and heat conduction performance. An estimation method of the total apparent thermal capacity of the tested sample is developed in order to quantify its latent heat storage capacity. The latent energy storage density is 1.6 J cm −2 for the best sample and is observed to be preserved after 850 thermal cycles. The total thermal resistance of the thermal damper is estimated by means of a laser flash test and a simple model of the sample. Sensitivity analyses show that the main thermal resistances are located at the interfaces between silicon and CNT. [ABSTRACT FROM AUTHOR]

Faradaic supercapacitors have been proposed as energy storage devices capable of providing both high energy and power densities. The exceptional attributes of high specific surface area and good electrical properties displayed by vertically aligned carbon nanotube (VACNT) arrays make them a promising candidate as faradaic capacitive electrode supports. However, some drawbacks to their use and performance exist including their resistance to wetting by an aqueous electrolyte solution, bad electrical continuity at the array/electrode base interface for binder-free applications, and potential collapse of the VACNT array because of capillary forces. This study explores possible solutions to these challenges by growing the arrays directly on conducting electrodes thus reducing the interfacial electrical resistance and removing the need for binders, using a combined plasma and forced vacuum wetting procedure to improve the wetting behavior, using a pulsed electrodeposition technique to obtain a uniform distribution of faradaic capacitive material (nickel cobaltite), and using freeze drying to prevent the collapse of the VACNT array’s native pore structure after electrodeposition. A specific capacitance of 970 Fg −1 at 2 Ag −1 is measured for the fabricated electrode with excellent performance ( > 80% retained capacity) over 3000 charge-discharge cycles. [ABSTRACT FROM AUTHOR]