Carbon Nanotube Thin Films Research Articles

Electrochemical reservoir computing based on surface-functionalized carbon nanotubes

Reservoir computing, a type of neural network computing, is an energy-efficient and fast machine learning method, expected to realize low-power edge processing in sensor devices. This study constructs an electrochemical reservoir using carbon nanotube (CNT) thin-film electrodes on flexible plastic and proves the capability of the electrochemical functionalization of CNT thin films to improve the reservoir's performance. The performance of the time-series data prediction task, called the nonlinear autoregressive moving average (NARMA) task, can be improved using multiple CNT electrodes functionalized under different conditions. Based on the correlation coefficient analysis of the reservoir output, we illustrate that the reservoir dimensionality is enhanced by combining CNT electrodes with different functionalization conditions. Furthermore, the dimensionality and memory capacity of the reservoir can be improved using the displacement current of the electric double layer and the redox current in the electrochemical electrode. We demonstrate the time-series data prediction of blood glucose levels in patients with type 1 diabetes using a physical reservoir for the first time. The use of functionalized CNTs enables flexible and high-performance reservoir computing, leading to the low-power in-sensor edge processing of wearable sensors.

Controlled Formation of Honey Carbon Nanotube Thin Films by Tailoring the Ratio of Admixture Concentration and Annealing Time.

Controlled Formation of Honey Carbon Nanotube Thin Films by Tailoring the Ratio of Admixture Concentration and Annealing Time.

Single-Walled Carbon Nanotube (SWCNT) thin films via automatic spray coating and nitric acid vapor treatment

In the realm of optoelectronics to produce thin film, SWCNT (Single-Walled Carbon Nanotube) is a promising alternative to Indium Tin Oxide (ITO). However, it is still challenging to manufacture SWCNT thin film that is low-cost, homogenous and has minimal sheet resistance. In this work, SWCNT thin films were deposited by using the automated spray coating method. To enhance the film quality and optoelectronic characteristics, post-deposition treatment through nitric acid vapor was carried out. The optimized SWCNT thin films exhibited optical transparency in the range of 60.4% at 800 nm and sheet resistance of 6.6 Ω/square. The sheet resistance of our fabricated SWCNT thin films was lower than the value of ITO films (10 Ω/square), putting forth evidence which suggests the potential of SWCNTs as an alternative to ITO.

A simple, fast, portable and selective system using carbon nanotubes films and a 3D-printed device for monitoring hydroxychloroquine in environmental samples

In this work, an electrochemical method was developed for rapid and sensitive detection of hydroxychloroquine (HCQ), an ineffective candidate drug for COVID-19 treatment however widely consumed during the pandemic, in aqueous samples using a multi-walled carbon nanotubes (MWCNT) film produced through the interfacial method on the indium tin oxide electrode (ITO). According to Raman spectroscopy, X-ray diffraction, UV–vis spectroscopy, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy, the interfacial method produces homogeneous thin films of carbon nanotubes on the substrate surface, which keep connected to the surface forming a three-dimensional microporous structure. The electrochemical behavior and oxidation kinetics of HCQ were also investigated in the MWCNT film. The sensor showed a 7 times higher oxidation current for (69.88 μA) for HCQ than the ITO electrode (9.33 μA) due to the electrocatalytic properties MWCNTs. The ITO-modified electrode was assembled on a portable 3D-printed batch-injection cell for the amperometric detection of HCQ. The oxidation peak current of HCQ is linearly proportional to the concentrations of HCQ ranging from 1.0 to 100.0 μmol L−1, with a limit of detection of 0.27 μmol L−1. Water samples (river and tap water) were spiked with HCQ, without the need for dispendious pretreatment (except filtration), and analyzed by the portable system, revealing the detection of HCQ with the recovery of 92.0%–99.8%, which suggested the great potential for real environmental monitoring application.

P‐153: Late‐News Poster: Temporal Photo‐Response Analysis of Inkjet‐Printed Transparent Single‐Walled Carbon Nanotube Thin‐Film Transistors

We demonstrated the temporal photo‐response of transparent and flexible carbon nanotube thin‐film transistors. Fabricated carbon nanotube thin film transistors showed exponential degradation with light illumination and linear recovery after light off. The result indicates that the principal mechanism of photo‐response in carbon nanotube transistors is photo‐desorption of oxygen molecules.

Mixed Ionic‐Electronic Conduction Enables Halide‐Perovskite Electroluminescent Photodetector

AbstractLight emission and detection are the two fundamental features of optoelectronic communication systems. Until now, both functions have been realized with a p–n diode, which is used in a wide range of applications. However, due to the competing dynamics of carrier injection and photocarrier collection, in such devices, electroluminescence and photodetection are realized separately by switching the direction of the applied electrical bias. Here, mobile ions in halide perovskites are benefited from to demonstrate electroluminescence and photodetection simultaneously, without switching the direction of the applied electrical bias. The electroluminescent photodetector consists of a CsPbBr3 microwire integrated with electrodes made of a single‐walled carbon nanotube thin film, providing Schottky barriers at the interfaces. The dual functionality stems from the modulation of these barriers by mobile ions in cooperation with photogenerated charge carriers. Furthermore, such complex charge dynamics additionally result in a novel effect: light‐enhanced electroluminescence. The new optoelectronic phenomena demonstrated in the simple lateral device design will expand the applications of mixed ionic‐electronic conductors toward cheap and efficient multifunctional optoelectronic devices able to simultaneously generate and receive optical data.

Near‐Intrinsic Photo‐ and Electroluminescence from Single‐Walled Carbon Nanotube Thin Films on BCB‐Passivated Surfaces

AbstractTheir outstanding electrical and optical properties make semiconducting single‐walled carbon nanotubes (SWCNTs) highly suitable for charge transport and emissive layers in near‐infrared optoelectronic devices. However, the luminescence spectra of SWCNT thin films on commonly used glass and Si/SiO2 substrates are often compromised by broadening of the main excitonic emission and unwanted low‐energy sidebands. Surface passivation with a commercially available, low dielectric constant, cross‐linked bis‐benzocyclobutene‐based polymer (BCB) enhances the emission properties of SWCNTs to the same level as hexagonal boron nitride (h‐BN) flakes do. The presence of BCB suppresses sideband emission, especially from the Y1 band, which is attributed to defects introduced by the interaction of the nanotube lattice with oxygen‐containing terminal groups of the substrate surface. The facile and reproducible deposition of homogeneous BCB films over large areas combined with their resistance against common solvents and chemicals employed during photolithography make them compatible with standard semiconductor device fabrication. Utilizing this approach, light‐emitting (6,5) SWCNT network field‐effect transistors are fabricated on BCB‐treated glass substrates with excellent electrical characteristics and near‐intrinsic electroluminescence. Hence, passivation with BCB is proposed as a standard treatment for substrates used for spectroscopic investigations of and optoelectronic devices with SWCNTs and other low‐dimensional emitters.

Acid-modified CNT/Zinc Oxide nanowires based high performance broadband photodetector

In this study, the authors have reported the impact of post-treatment via exposure to acid on single walled carbon nanotubes (SWNTs) thin film (TF) based SWNT/ZnO Nanowire (NW) broad band photodetector. The ZnO NWs were deposited on SWNT (with and without acid-treated) using a simple catalytic free process called glancing angle deposition (GLAD) technique. Acid-treated SWNT samples warranted the growth of high quality ZnO NWs over them. On fabricating photodetectors with the acid-treated ZnO NW/SWNT TF heterostructure (HS) gave better device performance as compared to the as-deposited ZnO NW/SWNT TF HS (without acid-treatment) sample. The acid-treated device showed a large responsivity (85.45 A/W), specific detectivity (0.859 × 1012 Jones) and with a low noise equivalent power of 3.9101 pW values. Moreover, the oxygen adsorption–desorption mechanism in SWNTs impacted the electrical resistance of the nanotubes which affected nanotube conductivity. The acid-treatment favoured relatively faster charge separation at the ZnO NW/SWNT heterojunction thus providing a fast device response (trise = 0.11 s, tfall = 0.39 s at + 5 V). The fabricated acid-treated device showed good broad band detection (250 nm-750 nm) which was explained with respect to the optical absorption profile of the sample.

Fully solution-processed carbon nanotubes thin film transistors and PMOS inverters on glass substrate

We report fully solution-processed thin film transistors and PMOS inverters fabricated on glass substrates using single-walled carbon nanotubes (SWCNTs) as active semiconducting material. All the electrodes (gate, source, and drain) were inkjet-printed using silver (Ag) as conductive ink. Spin coated poly-4-vinylphenol dielectric was optimized in terms of thickness and heating conditions for solution-processed SWCNTs thin film transistors to achieve a mobility equal to 0.81 cm2 V−1s−1. We will show that, hole traps at the dielectric-semiconductor interface are responsible for the hysteresis in the transfer curve, and controlled by the different sweep rate of the gate field. Drain-current transients under different bias conditions were studied and the increase in current occurs due to slow polarizations of residual dipolar groups in the dielectric. The adopted technology has been exploited to fabricate a PMOS inverter and studied for high gain and noise margin values at the supply voltage, V DD = −40 V.

Study of gate induced sensitivity amplification in carbon nanotube thin film transistor based ammonia sensor

Gas sensors based on carbon nanotube thin film transistors (CNT TFT) have been widely investigated in the past. However, studies on the active sensing properties i.e. effects of gate induced variations in sensing of such devices are deficient. In this work the effects of gate voltage on the ammonia sensing properties of a single wall CNT TFT are investigated. It is observed that under the influence of a gate field, the device sensitivity and detection limit (LOD) can be improved by more than 11 and 6 times respectively. The amplification of sensor response is found to occur for both the gate polarities and this is attributed to a combination of two phenomena. Firstly, ab-initio Molecular dynamics (MD) based adsorption studies of ammonia molecules to a CNT device indicate that the introduction of a gate field leads to an increase in the adsorption energy of ammonia to the device especially for a positive gate which is directly relatable to the observed amplification in sensing. Additionally, in the negative gate regime, a reversible increase of the contact resistance induced by ammonia exposure is thought to be the primary contributing factor in increasing the responsivity of the sensor. This is also thought to contribute to improving the sensor selectivity at negative gate.

Single-walled carbon nanotube (SWCNT) thin film for optoelectronics device prepared by spray coating technique.

CNT is a novel material with exceptional properties. SWCNT thin films have been used in many different applications. To fabricate the SWCNT film, various methodologies have been introduced, however, the problem of fabricating uniform SWCNT thin film remains unsolved. Spray coating technique (SCT) is the most effective method for producing a uniform SWCNT thin film. The CNT thin films were deposited on glass substrates via SCT with different nozzle distances (from 2.5 cm to 12.5 cm). The morphological, topological, electrical and optical properties of CNT thin films were characterized using appropriate techniques. The electrical analysis depicted that the sheet resistance of thin films reduced from 40220 Ω/sq. to 1330 Ω/sq. as the spray nozzle distance was increased from 2.5 cm to 10 cm sheet resistance reached 2133 Ω/sq. for 12.5 cm which confirmed the concentration of CNT was highest at 10 cm nozzle distance. The optical analysis of the CNT thin films gave transmittance values in percentage of 64%, 60%, 52%, 43%, and 46%, respectively for the nozzle distance of 2.5 cm, 5 cm, 7.5 cm, 10 cm, and 12.5 cm. Transmittance percentage decreased from 2.5 cm to 10 cm nozzle distance, indicative of an uniform film coverage of CNT layer. The findings of this study could be a platform for producing an optimized CNT thin film using a SCT for optoelectronic devices.

Tunable THz flat zone plate based on stretchable single-walled carbon nanotube thin film

Tunable optoelectronics have attracted a lot of attention in recent years because of their variety of applications in next-generation devices. Among the potential uses for tuning optical elements, those allowing consistent parameter control stand out. We present an approach for the creation of mechanically tunable zone plate lenses in the THz range. Our devices comprise single-walled carbon nanotube (SWCNT) thin films of predetermined design integrated with stretchable polymer films. These offer high-performance and in situ tunability of focal length up to 50%. We studied the focusing properties of our lenses using the backward-wave oscillator THz imaging technique, supported by numerical simulations based on the finite element frequency domain method. Our approach may further enable the integration of SWCNT films into photonic and optoelectronic applications and could be of use for the creation of a variety of flexible and stretchable THz optical elements.

Ultrafast Optomechanical Terahertz Modulators Based on Stretchable Carbon Nanotube Thin Films

For terahertz wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump–terahertz probe spectroscopy, single-walled carbon nanotube (SWCNT) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNT thin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain and enabled the development of a new type of an optomechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of approximately 2 times of magnitude under the strain because of the structural modification in the SWCNT network. Stretching was used to control the terahertz signal with a modulation depth of around 100% without strain and 65% at a high strain operation of 40%. The sensitivity of modulators to beam polarization is also shown, which might also come in handy for the design of a stretchable polarizer. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.

An interfacial toughening strategy for high stability 2D/3D perovskite X-ray detectors with a carbon nanotube thin film electrode.

Single-crystalline metal halide perovskite materials hold great promise for developing next-generation low-dose X-ray detection. To bring this new technology into reality, it is important to improve the durability of perovksite detectors by suppressing the well-known corrosion and ion diffusion problems at the perovskite/electrode interface. For imaging application, it is also imperative to develop new assembling approaches to realise non-planar interconnection between thick perovskite crystals and thin-film transistor (TFT) backplanes. Herein, a flexible and mechanically robust carbon nanotube (CNT) film was proposed to replace noble metal electrodes. The proposed CNT film, whose binder contains a carboxyl group, can form solid contact with a phenethylamine-based two-dimensional (2D) perovskite via amide coupling, thus toughening the perovskite-electrode interface. The resulting CNT/2D-3D perovskite detector shows an applaudable low dark current, high sensitivity, a low dose detection limit and excellent stability, retaining 98% of its initial sensitivity after storage for three months. Moreover, the flexible CNT films are also beneficial for making non-planar interconnection between thick perovskite crystals and TFT backplanes. The proposed flexible CNT thin film electrode thus provides a facile route towards realising a low-dose, high-resolution and highly stable perovskite X-ray detector.

Large area roll-to-roll printed semiconducting carbon nanotube thin films for flexible carbon-based electronics.

A universal roll-to-roll (R2R) printing approach was developed to construct large area (8 cm × 14 cm) semiconducting single-walled carbon nanotube (sc-SWCNT) thin films on flexible substrates (such as polyethylene terephthalate (PET), paper, and Al foils) at a printing speed of 8 m min-1 using highly concentrated sc-SWCNT inks and crosslinked poly-4-vinylphenol (c-PVP) as the adhesion layer. Bottom-gated and top-gated flexible printed p-type TFTs based on R2R printed sc-SWCNT thin films exhibited good electrical properties with a carrier mobility of ∼11.9 cm2 V-1 s-1, Ion/Ioff ratios of ∼106, small hysteresis, and a subthreshold swing (SS) of 70-80 mV dec-1 at low gate operating voltages (±1 V), and excellent mechanical flexibility. Furthermore, the flexible printed complementary metal oxide semiconductor (CMOS) inverters demonstrated rail-to-rail voltage output characteristics under an operating voltage as low as VDD = -0.2 V, a voltage gain of 10.8 at VDD = -0.8 V, and power consumption as low as 0.056 nW at VDD = -0.2 V. To the best of our knowledge, the electrical properties of the printed SWCNT TFTs (such as Ion/Ioff ratio, mobility, operating voltage, and mechanical flexibility) and printed CMOS inverters based on the R2R printed sc-SWCNT active layer in this work are excellent compared to those of R2R printed SWCNT TFTs reported in the literature. Consequently, the universal R2R printing method reported in this work could promote the development of fully printed low-cost, large-area, high-output, and flexible carbon-based electronics.

Areal Density Control of Liquid-Supported Carbon Nanotube Thin Films.

Carbon nanotube (CNT) films have extensive applications due to their excellent electrical, mechanical, and thermal properties. A grand challenge is controlling areal density of CNT films to accommodate various applications. Here, a method based on the Marangoni effect is used to fabricate liquid-supported CNT films with tunable areal density, scalable area, and transferability to arbitrary substrates. By adjusting the viscosity and surface tension of the base liquid media, the Marangoni flow area of surfactant-assisted single-walled CNT (SWCNT) dispersion on the surface of base media was controllable and sparse or dense SWCNT films can be easily obtained. The thickness of the films is controlled by changing the concentration of the SWCNT dispersion. These SWCNT-based transparent-conductive films have widely controllable transmittance and conductivity and exhibit great photoelectric properties (T ∼ 82.4%, Rs ∼ 407 Ω/sq).

High performance carbon nanotubes thin film transistors by selective ferric chloride doping

Single wall carbon nanotubes (SWNT) have been a significant research topic as active layers for thin film transistors (TFTs) due to their high charge carrier mobility beyond that of crystalline silicon. In this study, we report an effective approach to achieve a very high field-effect mobility and on/off ratio for solution processed semiconducting SWNT TFTs, by selective doping through contact with a thin ferric chloride (FeCl3) dopant layer. The semiconducting layer is formed by a double spin coating of the highly purified (>99%) high pressure carbon mono oxide (HiPCO) SWNT sorted by wrapping of poly (3-dodecylthiophene-2,5-diyl) (P3DDT). In order to achieve effective hole injection from the top Au source electrode without increasing the off-state drain current, less purified (98-99%) SWNTs produced by the plasma discharge process sorted by wrapping of poly (9,9-di-n-dodecylfluorene) (PFDD) are formed on the top of HiPCO film. Significantly improved TFT performance is achieved by the insertion of a few nanometers of a FeCl3 dopant layer at the semiconductor-contact interface. A significant high hole field-effect of 48.35 ± 3.11 cm2V−1s−1 (bare: 6.18 ± 0.87 cm2V−1s−1) with a reasonable on/off current ratio of 105, and low off current of ∼80 pA, are obtained by controlling the concentration of FeCl3 dopant (thickness = 1.5 nm) at the contact. Mobility is improved further at 2.5 nm thickness of the FeCl3 dopant layer resulting in a hole mobility of 177 ± 13.2 cm2 V−1s−1, an on/off ratio of 7.4 × 103, and off state current of 1.2 × 10−9 A.

Progress on research of construction of carbon nanotubes/carbon fiber cross-scale interface enhancement systems

<p indent="0mm">Carbon fiber reinforced composites (CFRP) have a broad application prospect in aerospace, military equipment and other fields because of their many excellent properties such as high strength and stability. However, the inert surface structure of carbon fiber (CF) seriously affects the load transfer efficiency with the matrix, which hinders the full play of the excellent performance of the composites. Therefore, the optimization and design of the interfacial structure between the two phases has become a hot research topic. Carbon nanotubes (CNTs) with excellent mechanical properties were deposited on the surface of CF to form a three-dimensional network hybrid structure with multiple orders of magnitude, thereby improving the interfacial bonding ability between the CF and the matrix. This paper introduces four process routes for the construction of cross-scale enhancement systems, including chemical vapor deposition (CVD), electrophoretic deposition (EPD), chemical grafting and dip-coating spraying process. The advantages, limitations and key process parameters of each method are summarized. The study of CVD method focuses on the influence of process parameters such as catalysts (type, morphology, concentration), growth time, treatment temperature, carbon source and carrier gas (type, mixing ratio, inlet speed) on the growth morphology (length, density, thickness) of CNTs. This method achieves the direct directional growth of CNTs on the CF surface, but the CF is affected by the pre-activation treatment, metal catalyst etching, and high-temperature environment, which leads to a significant decrease in its own strength. In the EPD method, the adjustment of key process parameters (applied voltage, energization time, electrode distance, and electrode shape) becomes the key to successful application of the EPD method. Although the EPD method is capable of producing textured CNT coatings or thin films on the CF, the weak van der Waals force bonding form and the “disorder” of deposition are the main pain points of this method. In the chemical grafting process, the reaction between multiple reactive functional groups and the use of macromolecular coupling agents provide a more diversified preparation scheme, and the bonding strength between CNTs and CF is greatly enhanced by chemical bonding. The construction of CNTs/CF interfacially enhanced structures, using two different processes, surface dip coating and spraying, is considered to be simple and effective, and the degree of dispersion of CNTs in sizing agents or different solvents becomes an important consideration for good deposition on the CF surface. Although the combination between CNTs and CF is not strong, the simple operation process and reasonable economic cost show a high suitability for industrialization. In this paper, three different attachment types of CNTs, namely radial embedding, random topology and surface attachment, are proposed in summary to investigate the stress transfer paths between the composite matrix and the form of interfacial enhancement. The three different attachment types contribute to the enhancement of the interface properties in different ways and to different degrees, with radially embedded structures contributing the most to the enhancement of the interface properties, vertically oriented CNTs significantly weakening the radial stresses between the CF and the matrix, and surface-applied CNTs suppressing the shear stresses more significantly than the radial stresses. Finally, the application of the CNTs/CF cross-scale interfacial reinforcement system in composites is explored, resulting in CFRP exhibiting superior properties in a number of ways, but only in terms of the mechanical properties of the system, which are exploited. Therefore, the development and application of multi-functional materials such as heat and electricity, as well as the preparation of high efficiency, high quality and low cost CNTs/CF/matrix three-phase composites will be the main development direction in the field of nano-reinforced CF composites in the future.

Highly accurate heart failure classification using carbon nanotube thin film biosensors and machine learning assisted data analysis

While carbon nanotube (CNT)-based biosensors have been demonstrated to achieve high sensitivity and fast response, their intrinsic variation has been a challenge for the robustness of CNT-based diagnostic systems and greatly hindered their real-world clinical applications. The solution through conventional analytical methods demands advanced electronics and computing systems, which limits the feasibility of CNT-based biosensors in near-patient settings considering the device size, cost, and usability. Here, we present a machine learning (ML) assisted solution by analyzing electrochemical impedance spectroscopy (EIS) data generated by CNT thin film (CNT-TF) biosensors in response to B-type natriuretic peptide (BNP) for the diagnosis and management of heart failure (HF). We trained a deep neural network to predict the BNP level, where a K-fold cross-validation was used to optimize the network structure. This algorithm circumvents the error-prone analytical methods that require calibration curves, and significantly enhanced the reliability of diagnostic results without the need for advanced hardware or major design change. We first demonstrated the feasibility of our method using EIS data acquired in phosphate-buffered saline (PBS) and then applied the algorithm to venous blood samples collected from HF patients. Overall, an out-of-sample prediction accuracy of 80.0% (and an in-sample accuracy of 97.2%) was achieved for the PBS data and 80.0% (95.6%) for the clinical data, which shows that ML-assisted algorithms greatly improve the performance and applicability of CNT-TF biosensors in point-of-care testing. In general, this work demonstrates the great potential of ML in navigating challenges in sensor data analysis, especially in situations involving noisy data and complex data structures.

Poly(ionic liquid) dielectric for high performing P- and N-type single walled carbon nanotube transistors

There is an increasing demand for low-cost and high-performance electronics which has stimulated a need for new high-performance dielectric materials. We have developed a facile synthesis of poly(2-(methacryloyloxy)ethyl trimethylammonium bis(trifluoromethylsulfonyl)azanide-ran-methyl methacrylate) (P(METATFSI-MMA)), a polymeric ionic liquid that can be used as a high-performance dielectric for semiconducting single walled carbon nanotube (SWCNTs) thin film transistors (TFTs). The P(METATFSI-MMA) polymer was synthesized at both 35 and 62 mol% of 2-(methacryloyloxy)ethyl trimethylammonium bis(trifluoromethylsulfonyl)azanide and produced p- and n-type devices that functioned under ambient conditions. These TFTs were then used to study the impact of electrochemical doping on the performance of SWCNT TFTs when switching from n-type, where an electrical double layer is formed, to p-type, where the TFSI− anions are free to interact with the SWCNTs. The TFTs operating in p-type had higher current on/off ratios and a larger transconductance than those operating in n-type, which is characteristic of electrochemically doped transistors. Furthermore, we tested the impact of operating frequency on device performance and discovered that decreasing the operating frequency of the TFTs resulted in a decreased hysteresis. The decrease in hysteresis was also observed to be more significant for the 35 mol% polymer.