CNT Doping Research Articles

Flexible piezoelectric pressure sensor based on BaTiO3-CNT/RTV composite film with filter paper microstructures for monitoring hand motions

Flexible piezoelectric sensors are widely used in various applications such as physiological signal monitoring and human-computer interaction. The present study introduces a BaTiO3-CNT/RTV piezoelectric sensor fabricated using a filter paper template. It incorporates micro-scale fiber stacking and a 1% CNT doping in the microstructure, resulting in a notable enhancement of sensor sensitivity, increasing it from 0.07 V N−1 to 0.69 V N−1, representing an almost tenfold improvement. Furthermore, the study investigates the influence of affecting factors like the flexible substrate of the sensing film, thickness, and mass fractions of various materials on the output voltage. The sensor exhibits superior characteristics such as good repeatability under 5000 cyclic loads, high elongation at break, fast response (80 ms) and recovery times (90 ms), and good linearity. It also demonstrates outstanding sensitivity (12 mV/10°) when monitoring different finger bending states, enabling real-time, sensitive, and reliable hand motion tracking. This sensor holds promising prospects for future developments in the fields of intelligent grasping and sign language translation.

A Novel Resistive Sensor Network Utilizing an SAP-Enhanced Ionic Layer and CNT Doping for Multipoint Pressure Measurement.

Amidst the rapid advancements in flexible electronics, flexible pressure sensors have achieved widespread applications in fields such as wearable devices and motion monitoring. Nevertheless, it is still a challenge to design a sensor with high sensitivity, cost-effectiveness, and a simplified manufacturing process. This paper introduces a piezoresistive sensor built upon a composite conductive filler. The sensor incorporates a super absorbent polymer (SAP) to absorb a phosphoric acid solution and doped carbon nanotubes as the composite conductive filler. In contrast to conventional rigid conductive fillers, the elastic polymer SAP enhances the sensor's stability significantly by exhibiting superior compatibility with the polydimethylsiloxane matrix, all the while reducing its Young's modulus. This work aims to theoretically elucidate the underlying principles that enable the sensor to achieve high sensitivity. It focuses on the induction of charge carriers due to pressure, which leads to the formation of a conductive pathway and subsequent changes in resistance, thus facilitating precise pressure detection. The paper also discusses the effects of piezoresistive layers with varying thicknesses and conductive fillers on the sensor's output performance. The results highlight the sensor's high sensitivity (0.094 kPa-1), rapid response time (105 ms), and exceptional cyclic load/unload stability (>5000 cycles). Furthermore, this paper establishes a versatile sensing network by integrating a portable inductance, capacitance, and resistance instrument with a programmable logic controller module. Compared to individual sensors, this system enables multipoint measurements, offering high spatial resolution and real-time monitoring capabilities, significantly expanding its overall practicality.

Inkjet printing of highly dispersed, shortened, and defect-rich MWCNTs to construct flexible electrochemical sensors for the detection of bisphenol A in milk samples

An inkjet-printed electrochemical bisphenol A (BPA) sensor was developed by exploiting the high dispersibility of shortened and defect-rich nitrogen-doped multi-walled carbon nanotubes (MWCNTs). To enhance the dispersibility of MWCNTs in water-based dispersant, the defect concentration was increased by both creating shortened CNT and heteroatom doping, and modification of their surfaces with sulfonate (SO3H) groups. CNT-based inks were prepared by dispersing modified CNT structures in deionized water and the stability and physical properties of the inks were determined. The results suggested that the shortening of MWCNT and SO3H functionalization strategies improved the stability of CNT-based aqueous inks significantly, which enabled the preparation of highly concentrated inks up to 20 mg/ml with high stability. The CNT-based inks were printed on flexible polyethylene tetraflate (PET) and used as an electrochemical BPA sensor. The electrochemical analytical performance of the printed sensors was evaluated using chronoamperometry and differential pulse voltammetry methods. The sensors showed a wide linear range of 5–100 (CA) and 60–700 (DPV) with a LOD of 0.7 μM. The real sample analysis was conducted in milk and high recoveries were obtained, suggesting the applicability of the sensors in real media.

Fabrication and mechanical properties of multi-walled carbon nanotubes doped AlN ceramics prepared by spark plasma sintering

In this study, multi-walled carbon nanotubes (MWCNTs) are uniformly dispersed in aluminium nitride (AlN) powders, and the MWCNTs-doped AlN ceramics are sintered at 1500 °C with a holding time of 5 min by spark plasma sintering using Y 2 O 3 as the sintering additive. The effects of the MWCNTs content on the microstructure and mechanical properties of the as-obtained ceramic composites are investigated. The results reveal that many submicron pores are generated when protecting the structure of the CNTs, thereby reducing the density of the AlN ceramic. However, the gradual filling of the grain gap may compensate for the strengthening after CNT doping. The relative density and hardness reach the maximum values of 89.6% of the theoretical density and 7.0 ± 0.3 GPa, respectively, at the doping amount of 2.5 wt%.

Multifunctional Catalytic Properties of Pd/CNT Catalysts for 4‐Nitrophenol Reduction

AbstractCarbon nanotubes are arousing real interest in catalysis, either as catalyst support or as catalyst itself. In this work, the influence of CNT doping (O, N, S) on the catalytic performance of CNT and Pd/CNT catalysts have been investigated in the reduction of 4‐nitrophenol both under H2 or using NaBH4 as a hydride source. The morphology, composition, particle size and crystallinity of the materials were investigated by various techniques including HRTEM, STEM, XPS, Raman spectroscopy and XRD. Among the CNT carbocatalysts, only N‐CNT is active for 4‐nitrophenol reduction at room temperature, and only in the presence of NaBH4. As far as supported Pd catalysts are concerned, the nature of the support influences the Pd nanoparticle location (confinement), the Pd nanoparticles/Pd single atoms ratio and the extent of H‐spillover, three catalyst features that directly affect the catalytic activity. The best combination of Pd nanoparticles/Pd single atoms ratio, H‐spillover and confinement for 4‐nitrophenol reduction using NaBH4, is found in Pd/O‐CNT catalysts, while for reactions performed under H2, Pd/N‐CNT presents the best combination.

Trace Hydrogen Sulfide Sensing Inspired by Polyoxometalate-Mediated Aerobic Oxidation.

A high-performance chemiresistive gas sensor is described for the detection of hydrogen sulfide (H2S), an acutely toxic and corrosive gas. The chemiresistor operates at room temperature with low power requirements potentially suitable for wearable sensors or for rapid in-field detection of H2S in settings such as pipelines and wastewater treatment plants. Specifically, we report chemiresistors based on single-walled carbon nanotubes (SWCNTs) containing highly oxidizing platinum-polyoxometalate (Pt-POM) selectors. We show that by tuning the vanadium content and thereby the oxidation reactivity of the constituent POMs, an efficient chemiresistive sensor is obtained that is proposed to operate by modulating CNT doping during aerobic H2S oxidation. The sensor shows exceptional sensitivity to trace H2S in air with a ppb-level detection limit, multimonth stability under ambient conditions, and high selectivity for H2S over a wide range of interferants, including thiols, thioethers, and thiophene. Finally, we demonstrate that the robust sensing material can be used to fabricate flexible devices by covalently immobilizing the SWCNT-P4VP network onto a polyimide substrate, further extending the potentially broad utility of the chemiresistors. The strategy presented herein highlights the applicability of concepts in molecular aerobic oxidation catalysis to the development of low-cost analyte detection technologies.

A Novel Highly Durable Carbon/Silver/Silver Chloride Composite Electrode for High-Definition Transcranial Direct Current Stimulation.

High-definition transcranial direct current stimulation (HD-tDCS) is a promising non-invasive neuromodulation technique, which has been widely used in the clinical intervention and treatment of neurological or psychiatric disorders. Sintered Ag/AgCl electrode has become a preferred candidate for HD-tDCS, but its service life is very short, especially for long-term anodal stimulation. To address this issue, a novel highly durable conductive carbon/silver/silver chloride composite (C/Ag/AgCl) electrode was fabricated by a facile cold rolling method. The important parameters were systematically optimized, including the conductive enhancer, the particle size of Ag powder, the C:Ag:PTFE ratio, the saline concentration, and the active substance loading. The CNT/Ag/AgCl-721 electrode demonstrated excellent specific capacity and cycling performance. Both constant current anodal polarization and simulated tDCS measurement demonstrated that the service life of the CNT/Ag/AgCl-721 electrodes was 15-16 times of that of sintered Ag/AgCl electrodes. The much longer service life can be attributed to the formation of the three-dimensional interpenetrating conductive network with CNT doping, which can maintain a good conductivity and cycling performance even if excessive non-conductive AgCl is accumulated on the surface during long-term anodal stimulation. Considering their low cost, long service life, and good skin tolerance, the proposed CNT/Ag/AgCl electrodes have shown promising application prospects in HD-tDCS, especially for daily life scenarios.

Effect of electrospun nanofibres and MWCNTs on the low velocity impact response of carbon fibre laminates

The effects of electrospun veil position, areal density and concurrent presence of MWCNTs on the low velocity impact behaviour and damage tolerance of thin cross-ply carbon/epoxy laminates were investigated. Three different interleaved configurations were tested along with baseline laminates and the optimal configuration was then used to assess the effect of veil density (1.5 gsm and 4.5 gsm) and CNT doping on the damage tolerance. The presence of nanofibrous interlayers resulted in a decrease higher than 40% in the delaminated area for impacts up to 7.5 J without weight penalty and degradation of the in-plane flexural properties. SEM micrographs of fractured surfaces allowed to identify the synergistic contribution of MWCNTs and nanofibres to the effective toughening of traditional laminates. Energy absorption mechanisms were found similar to those described in fracture toughness studies, which resulted in a better damage tolerance of modified laminates in terms of residual flexural strength and stiffness.

Fabrication of carbon nanotube functionalized MIL-101(Fe) for enhanced visible-light photocatalysis of ciprofloxacin in aqueous solution

Improving the performance of metal–organic frameworks (MOFs) through modifications is an important issue to expand their potential applications. In the current study, multi-walled carbon nanotube functionalized MIL-101(Fe) (CNT@MIL-101(Fe)) was synthesized and used to construct a visible-light photocatalysis system for elimination of ciprofloxacin. CNT@MIL-101(Fe) has a lower band gap energy (2.19 eV) than MIL-101(Fe) (2.46 eV), rendering it the visible light absorption from 400 nm to 565 nm. In the CNT@MIL-101(Fe)-photocatalysis system, some optimized reaction conditions were: CNT doping ratio = 5%, pH = 3.0, [H2O2] vs. [CNT@MIL-101(Fe)] mass ratio = 11.3. Under 2.0 mW cm−2 visible light irradiation, degradation of ciprofloxacin followed an apparent pseudo-first-order kinetic reaction rate at 6.85 × 10−4 s−1. Using CNT@MIL-101(Fe), faster activation and electron transfer were achieved due to the high conductibility of CNT, resulting in a higher removal efficiency of ciprofloxacin (3.02 μM, ~90% at 45 min) than using MIL-101(Fe) (~65%). Furthermore, the iron ions leakage of CNT@MIL-101(Fe) was only half the one of MIL-101(Fe), suggesting a better stability in water. The reactive mechanism was confirmed to be OH oxidation, in which visible photocatalysis was the dominant reaction. Generally, CNT@MIL-101(Fe) has enhanced performance and stability, which can act as potential catalyst of organic contaminants.

Modification of ZIF-8 using direct mixing method at a room temperature

ZIF-8 modified with CNT doping have been successfully synthesized using direct mixing methods at room temperature. The characteristics of ZIF-8 and ZIF-8 with CNT were studied using XRD and SEM. The structural integrity and phase purity of both materials were obtained through X-ray diffraction patterns and was found comparable to that of sodalite-type ZIF-8. The peaks were found at 2θ = 7.4°, 16.5°, 22.1°, 25.7°, 26.7°, and 32.53°. When ZIF-8 was doped with CNT, the peaks of ZIF-8 decreased. Scanning electron microscopy of pure ZIF-8 showed hexagonal nanocrystals, and the particle sizes were distributed at approximately 50-140 nm. CNT-doped ZIF-8 showed that ZIF-8 attached to CNT was uniformly with diameters of approximately 80-120 nm. It was concluded that ZIF-8 modified using CNT had been succesfully synthesized.

Visible light photocatalytic activity of Cu doped TiO2-CNT nanocomposite powder prepared by sol–gel method

In this paper, TiO2-10 wt.% CNT nanocomposite powder doped with 1 at.% Cu was synthesized by sol–gel method and its application for the degradation of organic pollutant in aqueous solution was examined in the visible light region. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, differential thermal analysis, surface area analysis, diffuse reflectance spectroscopy, photoluminescence spectroscopy and ultraviolet-visible spectrophotometer. The effect of CNT and doped Cu on the phase transformation during the calcination of as-synthesized amorphous TiO2 was studied in detail. A coating of anatase phase TiO2 with the thickness of 80 nm on the well dispersed CNTs was observed in the microstructure of calcined nanopowder at 440 °C. Also, addition of CNTs to the TiO2 led to a decrease in band gap energy from 3.2 to 3.05 eV and more decrease to 2.85 eV by both addition of CNT and Cu doping to TiO2. The effect of main parameters of photocatalytic dosage, irradiation time and MB concentration were investigated on methylene blue degradation efficiency and optimal conditions were proposed. The Cu doped TiO2-CNT catalyst exhibited better photocatalytic activity for methylene blue degradation (81.5%) than the TiO2-CNT catalyst (62%) and pure TiO2 sample (5%) after 60 min visible light irradiation. The detailed mechanism to explain the enhancement of the photocatalytic properties was proposed, as well.

Tunable n-Type Doping of Carbon Nanotubes through Engineered Atomic Layer Deposition HfOX Films.

Although digital systems fabricated from carbon-nanotube-based field-effect transistors (CNFETs) promise significant energy efficiency benefits, realizing these benefits requires a complementary CNFET technology, i.e., CNFET CMOS, comprising both PMOS and NMOS CNFETs. Furthermore, this CNFET CMOS process must be robust ( e.g., air-stable), tunable ( e.g., ability to control CNFET threshold voltages), and siliconCMOScompatible (to integrate within existing manufacturing facilities and process flows). Despite many efforts, such a siliconCMOScompatible CNT doping strategy for forming NMOS CNFETs does not exist. Techniques today are either not air-stable (using reactive low work function metals), not solid-state or siliconCMOScompatible (employing soluble molecular dopants in ionic solutions), or have not demonstrated precise control over the amount of doping (for setting threshold voltage, VT). Here, we demonstrate an electrostatic doping technique that meets all of these requirements. The key to our technique is leveraging atomic layer deposition (ALD) to encapsulate CNTs with nonstoichiometric oxides. We show that ALD allows for precise control of oxide stoichiometry, which translates to direct control of the amount of CNT doping. We experimentally demonstrate the ability to modulate the strength of the p-type conduction branch by >2500× (measured as the change in current at fixed bias), realize NMOS CNFETs with n-type conduction ∼500× stronger than p-type conduction (also measured by the relative current at fixed biases), and tune VT over a ∼1.5 V range. Moreover, our technique is compatible with other doping schemes; as an illustration, we combine electrostatic doping and low work function contact engineering to achieve CNFET CMOS with symmetric NMOS and PMOS ( i.e., CNFET ON-current for NMOS and PMOS is within 6% of each other). Thus, this work realizes a solid-state, air-table, very large scale integration and siliconCMOScompatible doping strategy, enabling integration of CNFET CMOS within standard fabrication processes today.

Synergistic effect of non-covalent interaction in colloidal nematic liquid crystal doped with magnetic functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs), CNT@Fe3O4, and Fe3O4 nanocomposites were doped to eutectic uniaxial nematic liquid crystal (NLC's) (E5CN7) to improve physiochemical properties such as phase transition temperature, activation energy (Ea), dielectric anisotropy, and electro-optical properties. The thermal study of nematic phase shows a decrease in the nematic to isotropic phase transition temperature as CNT is doped. However, higher doping concentration of CNTs leads to the further increase in transition temperature. The anchoring effect or π-π interaction plays a key role in N-I phase transition. The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the magnetic susceptibility is increased. The functionalized CNT doping to NLC's decrease significantly the phase transition temperature compared to doping of non-functionalized CNTs. Attractive interaction between guest and host molecules by magnetic and geometry effect increased the enthalpy and entropy of phase transition in the SWCNT@Fe3O4 sample compared to non-functionalized CNT doped system. Also, the Ea values are decreased as SWCNT@Fe3O4 is doped to pure E5CN7. The difference of N-I phase transition temperature was observed in Fe3O4 and CNT@Fe3O4 compared to SWCNT doped systems. Finally, dielectric anisotropy was increased in the doped system compared to pure NLC.

Improved Electro-Optical Response of Induced Chiral Nematic Liquid Crystal Doped with Multi-Walled Carbon Nanotubes

ABSTRACTMultiwalled carbon nanotubes functionalized with COOH were dispersed into induced chiral nematic liquid crystals confined in a planar aligned cell. Dopant concentration was varied to investigate electro-optical behaviour and morphology of the doped samples in the presence of surface anchoring forces. An increase in the conductivity, refractive index, and dielectric constant of the material was observed. Polarized fluorescence spectroscopy confirmed the anisotropic changes brought in by CNT doping. A significant change in the onset voltage of Freedericksz transition and an emergence of electro optic memory due to stabilization of the sample by nanotubes ensure the practical use of the material.

Temperature-dependent electro-optical and elastic properties of carbon nanotube doped polar smectogen octylcyanobiphenyl

We present a detailed study of electro-optical and elastic properties of smectogen octylcyanobiphenyl (8CB) liquid crystal doped with well-dispersed multi-walled carbon nanotubes (MWCNTs). We report new experimental data for the temperature dependence of threshold voltage, dielectric anisotropy, splay elastic constant, and rotational viscosity of MWCNT doped 8CB samples. We have observed that the dielectric permittivity along the long molecular axis and the splay elastic constant decrease with increasing CNT content while the threshold voltage remains the same. Throughout nematic and smectic A phases, the incorporation of CNTs into 8CB has been observed to decrease the dielectric anisotropy, resulting in decreased orientational order. Through optical on and off response time measurements, we have documented that doping 8CB with CNTs results in slower optical relaxation and increased viscosity. Our experimental results directly evidence that CNT doping disturbs the orientational order in 8CB-CNT composites, as previously advocated based on calorimetric data.

Variability and reliability analysis of CNFET technology: Impact of manufacturing imperfections

Carbon nanotube field-effect transistors (CNFETs) are promising candidates to substitute silicon transistors. Boasting extraordinary electronic properties, CNFETs exhibit characteristics rivaling those of state-of-the-art Si-based metal–oxide–semiconductor field-effect transistors (MOSFETs). However, as any technology that is in development, CNFET fabrication process still have some imperfections that results in carbon nanotube variations, which can have a severe impact on the devices’ performance and jeopardize their reliability (in this work the term reliability means time-zero failure due to manufacturing variations). This paper presents a study of the effects on transistors of the main CNFET manufacturing imperfections, including the presence of metallic carbon nanotubes (m-CNTs), imperfect m-CNT removal processes, chirality drift, CNT doping variations in the source/drain extension regions, and density fluctuations due to non-uniform inter-CNT spacing.

Electrical Properties of Composites of Polystyrene and Multi-Walled Carbon Nanotubes

The dependencies of electrical conductivity on the electrical field and temperature of high-resistivity polystyrene/carbon nanotube (CNT) composites were investigated. The electrical conductivity of the samples and their thermal activation energy were systematically dependent on the CNT doping level. Several unusual phenomena were observed which could be explained by the inhomogeneous distribution of CNTs in the polystyrene matrix. At higher levels of CNT doping, an interconnected conducting network is formed. If the amount of CNT is equal to or less than 0.6%, “islands” of CNT become separated by the layers of polystyrene, which limit charge transport. At low voltages, there is a sharper decrease in conductance as the voltage decreases.

A carbon nanotube/cement composite with piezoresistive properties

This paper studies the piezoresistive property of the CNT/cement composite to explore itsfeasibility as an embedded stress sensor for civil structures such as roadways, levees andbridges. The experimental results show that the electrical resistance of the CNT/cementcomposite changes with the compressive stress level, indicating the potential of using theCNT/cement composite as a stress sensor for civil structures. The piezoresistive responsesof the composite with different fabrication methods and CNT doping levels were alsostudied. It is found that dispersion-assistant surfactants could block the contacts amongcarbon nanotubes, thus impairing the piezoresistive response of the composite, while ahigher CNT doping level could improve the sensitivity of the composite stress response.

Electrical conductivity of carbon nanotubes and polystyrene composites

AbstractWe report investigation of electrical conductivity of high resistivity polystyrene/carbon nanotube composites. The films consisted of a thiol‐bonded network of wrapped MWNTs within a polystyrene matrix with mass ratios ranging from 0% to 1%. The electrical conductivity and its thermal activation energy were systematically depending on the CNT doping level. A number of phenomena could be explained by the presence of CNT ‘islands’ in the polystyrene matrix at doping levels below the percolation threshold. At higher levels of CNTs an interconnected conducting network is formed. The results appear consistent with fluctuation‐assisted tunnelling through barriers between conducting carbon nanotubes for medium and large voltages. However, at low voltages there is a sharper decrease in conductance as voltage decreases that could arise from Coulomb blockade effects or other small barriers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Carbon Substitution on the Superconducting Properties of ${\rm MgB}_{2}$ Doped With Multi-Walled Carbon Nanotubes and Nano Carbon

We have fabricated the multiwalled carbon nanotube (MWCNT) and nano-C doped MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk and wire to investigate the effect of carbon substitution in the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Carbon substitution into boron site was confirmed by the shrinkage of the lattice parameter a with the increasing of the doping level. It was found that the lattice distortion and optimum doping level are different in the CNT and nano-C samples. This can be explained by carbon substitution, which is a more direct substitution process with the nano-C precursor. With CNT doping, carbon substitution only occurred after break out of carbon atoms from CNT. Both dopants showed significant enhancement in both magnetic critical current density, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (H), and transport critical current at high sintering temperature like 900degC . Transport I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of magnitude 14 A and 30 A was observed at 4.2 K and 12 T for CNT and nano-C doping, respectively.