Single-walled Carbon Nanotube Films Research Articles

Photolithographic Patterning of Organic Color-Centers.

Organic color-centers (OCCs) have emerged as promising single-photon emitters for solid-state quantum technologies, chemically specific sensing, and near-infrared bioimaging. However, these quantum light sources are currently synthesized in bulk solution, lacking the spatial control required for on-chip integration. The ability to pattern OCCs on solid substrates with high spatial precision and molecularly defined structure is essential to interface electronics and advance their quantum applications. Herein, a lithographic generation of OCCs on solid-state semiconducting single-walled carbon nanotube films at spatially defined locations is presented. By using light-driven diazoether chemistry, it is possible to directly pattern p-nitroaryl OCCs, which demonstrate chemically specific spectral signatures at programmed positions as confirmed by Raman mapping and hyperspectral photoluminescence imaging. This light-driven technique enables the fabrication of OCC arrays on solid films that fluoresce in the shortwave infrared and presents an important step toward the direct writing of quantum emitters and other functionalities at the molecular level.

Ultrathin films of functionalised single-walled carbon nanotubes: a potential bio-sensing platform

ABSTRACT The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.

Flexible terahertz imaging systems with single-walled carbon nanotube films

Sensing systems that can ensure product reliability in a broad range of environments are urgently required for broader application of the internet of things. Imaging technologies based on the terahertz (THz) frequency are considered a promising solution to the challenge of inspecting industrial products in a nondestructive manner. However, current THz imaging systems require bulky and complicated components that hamper their practical application. Therefore, we herein present flexible THz imaging systems based on single-walled carbon nanotube (CNT) films that leverage the material’s advantages of mechanical strength, broad THz absorption, high thermoelectric power, and flexibility. This work investigates and optimizes the physical parameters that govern the detection sensitivity of the proposed CNT THz detector, and then tests a flexible THz imaging system based on the optimization. These imaging systems can be used in a wide range of industrial sensing applications, including inline pharmaceutical quality screening, multi-view imaging, and portable THz imaging for nondestructive quality testing of industrial products, with no bulky measurement components.

Structure-dependent performance of single-walled carbon nanotube films in transparent and conductive applications

We investigate a complex relationship between structural parameters of single-walled carbon nanotubes (namely, mean length, diameter, and defectiveness) and optoelectrical properties (equivalent sheet resistance) of thin films composed of the nanotubes. We obtained a systematic dataset describing the influence of CO2 concentration and growth temperature. On the basis of the experimental results, we prove the high Raman peak ratio (IG/ID), length, and diameter of the nanotubes to decrease the equivalent sheet resistance of the nanotube-based film. The approach employed highlights the change in the nanotube growth mechanism at the temperature coinciding with the phase transition between α-Fe and γ-Fe catalyst phases. We believe this work to be of high interest for researchers working not only in the field of transparent and conductive films based on nanocarbons, but also for those who reveals the fundamentals of the nanotube growth mechanism.

Thin-film nanocomposite nanofiltration membrane with an ultrathin polyamide/UIO-66-NH2 active layer for high-performance desalination

In this work, ultrasmall metal-organic frameworks (MOFs) nanoparticles, UIO-66-NH2 nanoparticles were synthesized and embedded in an ultrathin polyamide (PA) active layer via the interfacial polymerization reaction on a polydopamine-wrapped single-walled carbon nanotube film. A thin-film nanocomposite nanofiltration (TFN NF) membrane with a PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was thus fabricated. The loading mass of the nanoparticles in the TFN NF membrane could be tuned by controlling the nanoparticles concentration in aqueous phase. Benefiting from the ultrathin thickness of active layer and the high loading mass of the MOFs nanoparticles, water permeability up to 46 L m−2 h−1 bar−1 along with a Na2SO4 rejection of 97.1% was achieved, which is 53% increase of the TFC NF membrane without the addition of UIO-66-NH2 nanoparticles. Our membrane owns the thinnest active layer in the category of TFN NF membranes reported so far and exhibits outstanding desalination performance.

Stable heating performance of carbon nanotube/silver nanowire transparent heaters

A flexible silver nanowire transparent heater (AgNW TH) was recently reported. However, the fabrication of AgNW THs that are durable over the long term is an important concern due to nanowire thermal instability. In this work, a thin AgNW film was coated with a dense single-walled carbon nanotube (SWCNT) film on glass and polyimide (PI) substrates. This simple hybrid heater was evaluated for heater performance and long-term working stability. The AgNW TH dried in air was unstable and failed more rapidly at elevated temperatures under Joule heating than that dried in vacuum. The AgNW TH had the same temperature limit irrespective of nanowire coating density due to the low melting point of AgNWs. The SWCNT/AgNW TH displayed a higher heating temperature and longer working stability than the AgNW TH. Based on thermoreflectance imaging and considering a power balance model, the improved thermal stability of the hybrid heater is attributed to thermal uniformity, in turn related to fast heat dissipation via heat transfer pathways of the dense SWCNT film, which delayed deformation and disconnection of the AgNWs. This simple hybrid structure could enhance the long-term working stability of AgNW-based THs in a wide range of practical applications.

Polymer additive-combusted thermoelectric buckypapers for three-dimensional stacked paper thermoelectric generator

The use of polymer additives is effective for the fabrication of homogeneous single-walled carbon nanotube (SWCNT) films. However, the polymer chains located on the surface of SWCNT bundles act as barriers for electrical transport between SWCNTs and the chemical doping of SWCNTs. In this study, the combustion process of freestanding SWCNT/polymer films for the effective removal of the polymer additive and thermoelectric applications were investigated. By introducing the combustion process, high-performance p-type and n-type thermoelectric buckypapers were fabricated. The combusted and FeCl3-doped buckypapers with excellent electrical conductivity can be used as electrode materials in thermoelectric generators. Furthermore, a paper-based thermoelectric generator three-dimensional stacked for efficient energy harvesting using the vertical temperature difference was demonstrated. The thermoelectric generator with a thermal contact area of 1.2cm2 exhibited a maximum output power of 2.48μW with a vertical temperature difference of 30K.

High concentration bolometric system with single-walled carbon nanotubes (SWCNT) absorber

We demonstrate that a planar single-walled carbon nanotube (SWCNT) film bolometer can exhibit enhanced thermal and optical properties. The SWCNT film were ink-printed on an oxidized silicon substrate between two pointed-tip Au electrodes across a gap of approximately 10 μm. We obtained a bolometer figure-of-merit temperature coefficient of resistance of greater than –3.0% at room temperature. An optical response of 1000 V W−1 was obtained from a 786 nm laser with an output power of 5 mW. The corresponding thermal time constant of 1.8 ms was estimated through the optical response by modulating the laser over a frequency range of 1 Hz–1 kHz. The optical noise equivalent power and optical detectivity of and respectively, were estimated from the responsivity, the spectral density, and area of the cell of the absorber, 4.9 × 10−4 cm2. We attribute the exceptional performance of the SWCNT microbolometer to the film nature of the absorber and to the high concentration of the incident electromagnetic radiation and localized heating between the tips of the electrode.

High-efficiency and stable silicon heterojunction solar cells with lightly fluorinated single-wall carbon nanotube films

High-quality single-wall carbon nanotube (SWCNT) films were lightly fluorinated by treatment with xenon difluoride at room temperature, which led to the formation of ionic C–F bonds on tube walls and controllable p-type doping of the nanotubes. The fluorinated SWCNT films showed improved electronic conductivity and a higher work function. In addition, the fluorination process increased the areal density of SWCNT films and decreased their surface roughness, leading to better interface contact between them and silicon. As a result, a heterojunction solar cell constructed using the lightly fluorinated SWCNT film has a high power conversion efficiency of 13.6% and excellent stability.

Open Circuit Voltage and Single Walled Carbon Nanotube (wt%) Dependency in Solid-State Complementary Metal Oxide Semiconductor-Compatible Glucose Fuel Cells

Solid-state complementary metal oxide semiconductor (CMOS)-compatible glucose fuel cells, with single-walled carbon nanotube (SWCNT) films and different amounts of carbon nanotube (wt%) were investigated. Those with a SWCNT content of 3 wt% were found to develop the highest open circuit voltage (OCV) of 400 mV, together with a high electrical conductivity, a power density of 0.53 μW/cm2 and current density of 1.31 μA/cm2. Measurements were performed by dipping the anode into a 30 mM glucose solution. The OCV and power density increased together with the fuel cell concentration. The developed fuel cell uses materials that are biocompatible with the human body (single-walled carbon nanotube-glucose). As a result, it was possible to attain an OCV of 400 mV with a single-walled carbon nanotube content of 3 wt% while improvements in the performance of the CMOS-compatible glucose fuel cell were obtained, and the parameters affecting the performance of the fuel cell were identified. This bio-fuel cell was fabricated using CMOS semiconductor processes on a silicon wafer. These findings are significant to realizing mobile or implantable devices that can be used for biomedical applications.

Adhesion of Single-Walled Carbon Nanotube Thin Films with Different Materials.

Single-walled carbon nanotubes (SWCNTs) possess extraordinary physical and chemical properties. Thin films of randomly oriented SWCNTs have great potential in many opto-electro-mechanical applications. However, good adhesion of SWCNT films with a substrate material is pivotal for their practical use. Here, for the first time, we systematically investigate the adhesion properties of SWCNT thin films with commonly used substrates such as glass (SiO2), indium tin oxide (ITO), crystalline silicon (C-Si), amorphous silicon (a-Si:H), zirconium oxide (ZrO2), platinum (Pt), polydimethylsiloxane (PDMS), and SWCNTs for self-adhesion using atomic force microscopy. By comparing the results obtained in air and inert Ar atmospheres, we observed that the surface state of the materials greatly contributes to their adhesion properties. We found that the SWCNT thin films have stronger adhesion in an inert atmosphere. The adhesion in the air can be greatly improved by a fluorination process. Experimental and theoretical analyses suggest that adhesion depends on the atmospheric conditions and surface functionalization.

Highly Sensitive Detection of NO2 by Au and TiO2 Nanoparticles Decorated SWCNTs Sensors.

The aim of this work is to investigate the gas sensing performance of single wall carbon nanotubes (SWCNTs)-based conductive sensors operating at low–medium temperatures (<250 °C). The investigated sensing films consists of an SWCNT network obtained by drop-casting a SWCNT suspension. Starting from this base preparation, different sensing devices were obtained by decorating the SWCNT network with materials suitable for enhancing the sensitivity toward the target gas. In particular, in this paper, nano-particles of gold and of TiO2 were used. In the paper, the performance of the different sensing devices, in terms of response time, sensitivity toward NO2 and cross-sensitivity to O2, CO and water vapor, were assessed and discussed. Sensors based on decorated SWCNT films showed high performance; in particular, the decoration with Au nano-particles allows for a large enhancement of sensitivity (reaching 10%/1 ppm at 240 °C) and a large reduction of response time. On the other hand, the addition of TiO2 nanoparticles leads to a satisfactory improvement of the sensitivity as well as a significant reduction of the response time at moderate temperatures (down to 200 °C). Finally, the suitability of using Au decorated SWCNTs-based sensors for room temperature sensing is demonstrated.

Polarized Raman imaging of large area aligned semiconducting single‐walled carbon nanotubes

AbstractThe current method of characterizing single‐walled carbon nanotube (SWCNT) alignment utilizes single‐point measurements of a few hundred square nanometers of polarized Raman spectroscopy to characterize an entire substrate of SWCNTs on the order of square centimeters. In this study, we demonstrate a new polarized Raman spectroscopy analyzation technique of orientation Raman imaging that images areas as large as 1 mm2. This provides a significantly more accurate representation of the spatial distribution in the alignment of any SWCNT film by increasing the measured area by 10 orders of magnitude over previous standard characterization techniques. Furthermore, this creates an “easy‐to‐see” visual representation of alignment based on optical anisotropy values. Improving the efficiency of characterizing alignment in SWCNT films via polarized Raman spectroscopy is an important step toward manufacturing scalable films of aligned SWCNTs.

High-performance transparent conducting films of long single-walled carbon nanotubes synthesized from toluene alone

Single-walled carbon nanotube (SWCNT) transparent conducting films (TCFs) are attracting increasing attention due to their exceptional optoelectronic properties. Toluene is a proposed carbon source for SWCNT synthesis, but the growth parameters of SWCNTs and their TCF optoelectronic performance (i.e., sheet resistance versus transmittance) have been insufficiently evaluated. Here, we have for the first time reported a systematic study of the fabrication of high-performance SWCNT TCFs using toluene alone as the carbon source. The mechanisms behind each observed phenomenon were elucidated using optical and microscopy techniques. By optimizing the growth parameters, high yields of SWCNT TCFs exhibiting a considerably low sheet resistance of 57 Ω/sq at 90% transmittance were obtained. This competitive optoelectronic performance is mainly attributable to long SWCNT bundles (mean length is 41.4 μm) in the film. Additionally, a chirality map determined by electron diffraction displays a bimodal distribution of chiral angles divided at 15°, which is close to both armchair and zigzag edges. Our study paved the way towards scaled-up production of SWCNTs for the fabrication of high-performance TCFs for industrial applications.

Preparing ripening-suppressed metallic nanoparticles using a laser-irradiated carbon nanotube sacrificial layer

Supported metallic nanoparticles on a substrate has wide applications in catalysis, sensors and biological detection, where small particle size and uniform distribution are desired. Among the various preparation methods, thermal-induced nanofilm dewetting is a cost-efficient approach to obtain such supported nanoparticles. However, the nanoparticle size always grows out of control in dewetting because of unavoidable ripening at an elevated temperature. Herein, a laser-irradiated single-wall carbon nanotubes (SWCNTs) film is skillfully introduced as a sacrificial layer in the process of Nickel (Ni) nanofilm dewetting, which can suppress particle ripening and is easy to be removed. Finally, uniform-distributed and small Ni nanoparticle array is achieved, showing a good catalytic effect in the chemical reaction of carbon nanotube etching. In principle, this sacrificial layer method also applies to preparing other ferromagnetic metallic nanoparticles such as Fe and Co, which will largely expand its application scope.

Temperature dependence of the Seebeck coefficient for mixed semiconducting and metallic single-wall carbon nanotube bundles

The temperature (T) dependence of the Seebeck coefficient (S) for single-wall carbon nanotube (SWCNT) bundles was systematically investigated as a function of the chemical potential (μ) through theoretical simulations employing non-equilibrium Green’s function theory. The bundles were modeled as laterally aligned parallel circuits of semiconducting and metallic SWCNTs. The T dependence of S varied substantially with μ and with metallic SWCNT content. The calculated results semi-quantitatively reproduced the typical behavior observed experimentally for SWCNT films with chemical doping reported previously.

One-directional thermal transport in densely aligned single-wall carbon nanotube films

Individual carbon nanotubes (CNTs) possess extremely high thermal conductivities. However, the thermal conductivities and their anisotropy of macroscopic assemblies of CNTs have so far remained small. Here, we report the results of directional thermal transport measurements on a nearly perfectly aligned CNT film fabricated via controlled vacuum filtration. We found the thermal conductivity to be 43 ± 2.2 W m−1 K−1 with a record-high thermal anisotropy of 500. From the temperature dependence of the thermal conductivity and its agreement with the atomistic phonon transport calculation, we conclude that the effect of intertube thermal resistance on heat conduction in the alignment direction is negligible because of the large contact area between CNTs. These observations thus represent ideal unidirectional thermal transport, i.e., the thermal conductivity of the film is determined solely by that of individual CNTs.

Machine Learning for Tailoring Optoelectronic Properties of Single-Walled Carbon Nanotube Films.

A machine learning technique, namely, support vector regression, is implemented to enhance single-walled carbon nanotube (SWCNT) thin-film performance for transparent and conducting applications. We collected a comprehensive data set describing the influence of synthesis parameters (temperature and CO2 concentration) on the equivalent sheet resistance (at 90% transmittance in the visible light range) for SWCNT films obtained by a semi-industrial aerosol (floating-catalyst) CVD with CO as a carbon source and ferrocene as a catalyst precursor. The predictive model trained on the data set shows principal applicability of the method for refining synthesis conditions toward the advanced optoelectronic performance of multiparameter processes such as nanotube growth. Further doping of the improved carbon nanotube films with HAuCl4 results in the equivalent sheet resistance of 39 Ω/□-one of the lowest values achieved so far for SWCNT films.

Broadening of van Hove Singularities Measured by Photoemission Spectroscopy of Single- and Mixed-Chirality Single-Walled Carbon Nanotubes

The occupied valence electronic states of single-walled carbon nanotubes (SWCNTs) are responsible for their optoelectronic properties and are unique for each SWCNT chirality. Photoemission spectroscopy (PES) is one of the few methods capable of directly measuring the electron density in the valence states of materials, but there are only a few reports which have observed the valence states of SWCNTs and no examples for single-chirality SWCNTs. Here, we prepare single- and mixed-chirality SWCNT films and characterize their valence states using PES. Chirality-pure SWCNTs were isolated using both gel permeation chromatography and single-stranded DNA-facilitated aqueous two-phase extraction from starting materials consisting of mixed-chirality species. Chirality separation and purity was confirmed with UV-vis-NIR absorption spectroscopy. SWCNT films were prepared for the single-chirality species (10,3), (7,6), (7,3), (6,5), (8,3), (9,1) along with SWCNT chirality mixture of metallic and semiconducting SWCNTs, and as-synthesized mixtures possessing a range of SWCNT diameter. PES using synchrotron radiation was completed for all samples with survey and C 1s core-level spectra obtained to confirm SWCNT coverage, defect level, and purity. Valence band PES was obtained to characterize the valence electronic states and showed significant broadening of the signal, in comparison to calculated density of states, which could not be accounted for by instrument resolution. An inverse diameter dependence of the broadening was observed with greater broadening for smaller-diameter SWCNTs. The broadening is hypothesized to be related to the photohole lifetime, which was found to be significantly longer for wide-diameter SWCNTs. The diameter dependence of the broadening and photohole lifetimes is discussed in terms of both Tomonaga-Luttinger and Landau theories of Fermi liquids.

Processing of Single-Walled Carbon Nanotubes with Femtosecond Laser Pulses

There are continued efforts to process and join single wall carbon nanotubes (SWCNTs) in order to exploit their exceptional functional properties for real-world applications. In this work, we report experimental observations of femtosecond laser irradiation on SWCNTs, in order to process and join them through an efficient and cost-effective technique. The nanotubes were deagglomerated in ethanol by an ultrasonicator and thin slurries of SWCNTs were spread evenly on glass substrates. A laser micromachining workstation for laboratory FemtoLAB (workshop of photonics) has been employed to irradiate the different SWCNTs film samples. The effect of laser parameters, such as pulse wavelength, laser power, etc., were systematically tuned to see the possibility of joining the SWCNTs ropes. Several experiments have been performed to optimize the parameters on different samples of SWCNTs. In general, the nanotubes were mostly damaged by the infrared (1st harmonics femtosecond laser) irradiation on the focal plane. However, the less damaging effect was observed for second harmonics (green wavelength) irradiation. The results suggest some joining of nanotubes along the sides of the focus plane, as well as on the center at the brink of nanotubes. The joining is considered to be established within the region of the high field intensity of the exposed femtosecond laser beam.