Single-walled Carbon Nanotube Channel Research Articles

C60 Functionalized Single‐Walled Carbon Nanotube‐based Phototransistor for Efficient Detection of Visible Light Under Appropriate Gate Electrostatics

AbstractThe current study concerns highly reliable visible light sensing by C60 fullerene functionalized single‐walled carbon nanotube (SWCNT) based phototransistor. The absorbance of visible light (532 nm) increases significantly due to the formation of an interlink between the SWCNT network and C60 clusters. Photogenerated excess electrons in SWCNT are trapped by the C60 clusters and increase the effective hole concentrations in the SWCNT channel, which eventually improves the photoconductive gain. C60‐SWCNT channel is further integrated into the back gated field effect transistor (FET) structure in which 90 nm SiO2 dielectric thickness is used. The responsivity toward visible light is further enlarged with appropriate negative gate electrostatic. In order to ensure the morphological and structural behavior of C60‐SWCNT, various microscopic and spectroscopic characterizations are performed. The C60‐SWCNT phototransistor exhibits responsivity of 1.219 A W−1 at Vgs = – 21 V. The detectivity and rise/fall time of C60‐SWCNT came around to be 2.34 × 1010 Jones, 86.42 ms/3.35 ms at the same Vgs. The maximum external quantum efficiency (EQE) of the C60‐SWCNT phototransistor is very high, ≈274%. In the overall study, a comprehensive discussion is introduced on the effect of variable gate potential on the performance of the C60‐SWCNT phototransistor.

Photogating interfacial effects in carbon nanotube-based transistors on a Si/SiO2 substrate toward highly sensitive photodetection.

Single-walled carbon nanotubes (SWCNTs) are considered to be promising material platforms for various photodetectors (including phototransistors) due to their unique optoelectrical properties (e.g., high mobility and a wide variety of bandgap values). Herein, we present highly sensitive phototransistors which utilised sparse networks of SWCNTs on a silicon/silica substrate and operated by means of the photogating effect. The response of SWCNTs to photo-induced electrostatic charges (photogating effect) was highly dependent on the conductivity type of the channel, which was "metallic" or "semiconducting", depending on the SWCNT density. We determined the performance of these transistors depending on the characteristics of the substrate and conductivity type of the SWCNT channel. The optimized configuration of phototransistors with a channel comprising a sparse network of SWCNTs permitted improvement in the specific detectivity and relative response compared with previously reported photodetectors based on graphene and carbon nanotubes. We demonstrated an absolute responsivity of ∼60 A W-1 at an incident light power of ∼2 nW, specific detectivity of 7.8 × 1011 cm·Hz1/2 W-1, and response time of 300 μs. These data revealed the high potential of photogating-based SWCNTs detectors for extremely weak signals with a high signal-to-noise ratio.

Subthreshold Schottky-contacted carbon nanotube network film field-effect transistors for ultralow-power electronic applications

Ultralow-power electronics is critical to wearable, portable, and implantable applications where the systems could only have access to very limited electrical power supply or even be self-powered. Here, we report on a type of Schottky barrier (SB) contacted single-walled carbon nanotube (SWCNT) network film field-effect-transistors (FETs) that are operated in the subthreshold region to achieve ultralow-power applications. The thin high-k gate dielectric and the overlap between the gate and the source electrodes offer highly efficient gate electrostatic control over the SWCNT channel and the SB at the source contact, resulting in steep subthreshold switching characteristics with a small subthreshold swing (∼67 mV dec−1), a large current on/off ratio (∼106), and a low off-state current (∼0.5 pA). A p-channel metal-oxide-semiconductor inverter built with the subthreshold SB-SWCNT-FETs exhibits a well-defined logic functionality and small-signal amplification capability under a low supply voltage (∼0.5 V) and an ultralow power (∼0.05 pW μm−1). The low-voltage and deep subthreshold operations reported here could lay an essential foundation for high-performance and ultralow-power SWCNTs-based electronics.

Cucurbit[6]uril as a co-catalyst for hydrogen production from formic acid

Cucurbiturils are organic macrocycles, which are only rarely used for catalytic reactions. We studied a composite comprising of single-walled carbon nanotubes (SWCNTs), cucurbit[6]uril (CB6) and Au species and demonstrated that CB6 is a co-catalyst for hydrogen production from formic acid. Thus, insertion of CB6 into SWCNTs with open tips provides a decrease of the reaction temperatures by 60 K as compared to those over pure SWCNTs. This indicates that CB6 is a metal-free catalyst for this reaction. The use of CB6 during the synthesis of Au catalysts supported on SWCNTs leads to even a stronger decrease of the reaction temperature by 110 K as compared to the Au/SWCNTs catalyst. Density functional theory (DFT) calculations show that these effects could be explained by abstraction of the hydrogen atom from the hydroxyl group of the formic acid molecule on the basic carbonyl portal of the CB6 molecule with the formation of the formate containing adduct. Unusual sandwich-like structures of Au were formed inside the SWCNTs channels due to the interaction of Au with CB6. The results create a base for the development of catalysts containing cucurbiturils for the energy related reactions taking place through the hydrogen abstraction from reactant molecules.

4f-metal chlorides effect on electronic properties of carbon nanotubes

In the present work, the channels of single-walled carbon nanotubes were filled with melts of ZnCl2, CdCl2, and TbCl3 by a capillary method with subsequent slow cooling. The detailed study of electronic structure of filled nanotubes was performed using Raman, optical absorption, and X-ray photoelectron spectroscopy. The obtained data are in mutual agreement and it proves that the filling of carbon nanotube channels with all these salts leads to the charge transfer from nanotube walls to the incorporated compounds, thus acceptor doping of nanotubes takes place. It was found out that encapsulated terbium chloride has the largest influence on the electronic properties of carbon nanotubes.

A Multimodal Electronic Nose Based on High-Density Flexible Sensor Array of Carbon Nanotubes and Photoactive Macromolecules Hybrid Nanostructures

We report a multimodal electronic nose system based on photoactive carbonaceous hybrid nanomaterials for the detection and quantification of gaseous odors. The e-nose system comprises a high-density flexible sensor array, colorimetric and electrical measurement electronics, data acquisition software, and data analysis algorithms. The e-nose system combines the unique advantages of electrical, chemical, and physical properties of single-walled carbon nanotubes (SWNTs) with optical and chemical properties of various classes of organic macrocyclic compounds, such as pyrenes, porphyrins, and phthalocyanines, for multimodal gas sensing. Photoactive macromolecules such as metalloporphyrins and metallophthalocyanines have been previously developed into colorimetric sensors to various gas analytes. Their intrinsically low electrical conductivity prevents direct application of porphyrins and phthalocyanines in chemiresistive sensors. However, when used as a secondary sensing material via functionalization onto SWNTs, which intrinsically lacks chemical selectivity, these macromolecules confer their chemical selectivity and optical properties to the intrinsically semiconducting SWNT channel. This hybrid nanostructure allows both chemiresistive sensing and colorimetric sensing modalities. Another beneficial property of this hybrid nanostructure is the optoelectronic tunability of the nanomaterial to allow for direct modulation of chemical and electrical behaviors leading to tunable gas sensing capability.Using the high-density array containing 118 individually addressable sensors, over 60 different secondary sensing materials (functionalized onto SWNTs) were investigated, which include chemical derivatives of pyrenes, porphyrins, and phthalocyanines, which have a large variety of side-groups, and metal centers. Additionally, by integrating a large variety of secondary sensing materials into each sensing element of the 118-sensor array, we take advantage of the different chemical and electrical characteristics of each macromolecules which allow for different affinities to specific VOC species to enhance overall selectivity of the e-nose system. The functionality of the multimodal e-nose system was demonstrated to distinguish and quantify various volatile organic compounds (VOCs).

A Multimodal Electronic Nose Based on High-Density Flexible Sensor Array of Carbon Nanotubes and Photoactive Macromolecules Hybrid Nanostructures

We report a multimodal electronic nose system based on photoactive carbonaceous hybrid nanomaterials for the detection and quantification of gaseous odors. The e-nose system comprises a high-density flexible sensor array, colorimetric and electrical measurement electronics, data acquisition software, and data analysis algorithms. The e-nose system combines the unique advantages of electrical, chemical, and physical properties of single-walled carbon nanotubes (SWNTs) with optical and chemical properties of various classes of organic macrocyclic compounds, such as pyrenes, porphyrins, and phthalocyanines, for multimodal gas sensing. Photoactive macromolecules such as metalloporphyrins and metallophthalocyanines have been previously developed into colorimetric sensors to various gas analytes. Their intrinsically low electrical conductivity prevents direct application of porphyrins and phthalocyanines in chemiresistive sensors. However, when used as a secondary sensing material via functionalization onto SWNTs, which intrinsically lacks chemical selectivity, these macromolecules confer their chemical selectivity and optical properties to the intrinsically semiconducting SWNT channel. This hybrid nanostructure allows both chemiresistive sensing and colorimetric sensing modalities. Another beneficial property of this hybrid nanostructure is the optoelectronic tunability of the nanomaterial to allow for direct modulation of chemical and electrical behaviors leading to tunable gas sensing capability.Using the high-density array containing 118 individually addressable sensors, over 60 different secondary sensing materials (functionalized onto SWNTs) were investigated, which include chemical derivatives of pyrenes, porphyrins, and phthalocyanines, which have a large variety of side-groups, and metal centers. Additionally, by integrating a large variety of secondary sensing materials into each sensing element of the 118-sensor array, we take advantage of the different chemical and electrical characteristics of each macromolecules which allow for different affinities to specific VOC species to enhance overall selectivity of the e-nose system. The functionality of the multimodal e-nose system was demonstrated to distinguish and quantify various volatile organic compounds (VOCs).

Enhancing the Charge Transportation Ability of Yolk-Shell Structure for High-Rate Sodium and Potassium Storage.

The microstructure of large-capacity anodes is of great importance in determining the performance of sodium- and potassium-ion batteries. Yolk-shell nanostructures promise excellent structural stability but suffer from insufficient charge transfer rate during cycles. Herein, we tackle this challenge by constructing a single-walled carbon nanotube (SWNT) internally bridged yolk-shell structure, inside which SWNTs cover the surface of the yolk and connect the yolk and shell, for better electron/ion transportation. Combining the merits of both yolk-shell structure and conductive SWNT channels, the as-prepared Fe1-xS/SWNT@C composite manifests high reversible capacity and ultralong cycling stability up to 8700 cycles. Moreover, it displays the best rate capability (317 mA h g-1 at 20 A g-1 for Na+ and 236 mA h g-1 at 10 A g-1 for K+) among the reported yolk-shell structures and iron-sulfide-based anodes thus far. The kinetic analysis and density functional theory calculations further reveal that the Fe1-xS/SWNT heterointerface can effectively enhance the reversibility of K+ storage and decrease the K+ diffusion energy barrier, leading to excellent pseudocapacitive behavior and fast ion transportation for outstanding rate capability.

Carbon nanotube ferroelectric random access memory cell based on omega-shaped ferroelectric gate

This paper presents a flexible ferroelectric random access memory (FeRAM) cell with a one-transistor-one-transistor structure. The FeRAM cell was composed of a control transistor (CT) and an omega-shaped ferroelectric memory transistor (MT). An inkjet-printed single-walled carbon nanotube (SWCNT) were utilized as a semiconducting channel layers of both transistors. An omega-shaped ferroelectric gate was formed through inkjet-printing of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) onto the SWCNT channel of the MT. The gate electrode of the CT was electrically connected to the drain electrode of the MT, while the gate electrode of the MT was connected to the source electrode of the CT. The 1T1T architecture enabled the separation of the writing and reading operations, which afforded nondestructive readout capability. The desired multi-level conductance states could be deterministically controlled by tuning the dipole polarization in the ferroelectric P(VDF-TrFE) layer of the MT. The resulting FeRAM cell showed excellent device performances such as five-level data storage, a high programming/erasing current ratio (>105), a retention time (>104 s), and operational stability (>1000 cycles). The 1T1T FeRAM cell fabricated by inkjet printing technique opens up new opportunities for realizing future large-area flexible memory cells.

Gate-Tunable Synaptic Dynamics of Ferroelectric-Coupled Carbon-Nanotube Transistors.

Artificial neural networks (ANNs) based on synaptic devices, which can simultaneously perform processing and storage of data, have superior computing performance compared to conventional von Neumann architectures. Here, we present a ferroelectric coupled artificial synaptic device with reliable weight update and storage properties for ANNs. The artificial synaptic device, which is based on a ferroelectric polymer capacitively coupled with an oxide dielectric via an electric-field-permeable, semiconducting single-walled carbon-nanotube channel, is successfully fabricated by inkjet printing. By controlling the ferroelectric polarization, synaptic dynamics, such as excitatory and inhibitory postsynaptic currents and long-term potentiation/depression characteristics, is successfully implemented in the artificial synaptic device. Furthermore, the constructed ANN, which is designed in consideration of the device-to-device variation within the synaptic array, efficiently executes the tasks of learning and recognition of the Modified National Institute of Standards and Technology numerical patterns.

Global Photocurrent Generation in Phototransistors Based on Single‐Walled Carbon Nanotubes toward Highly Sensitive Infrared Detection

AbstractBecause of their cost‐effective synthesis and appropriate bandgap opening by various mechanisms, single‐walled carbon nanotubes (SWCNTs) exhibit significant promise for highly efficient near‐infrared photodetection. In this work, the first investigation of manipulating the electrode contact and exciton effect is performed on photocurrent generation of SWCNT transistors by separately depositing Cr or Pd as symmetric source/drain electrodes. Two different photoconducting behaviors of the devices, namely localized and global photocurrent generations, are then observed, where these effects are attributed to thermally assisted tunneling at the 1D‐SWCNTs/3D‐metal contact. A phototransistor with global photocurrent generation is demonstrated having a typical photoconductive effect with a responsivity of 2 A W−1 at λ = 785 nm and a fast rise (decay) time of ≈7.35 µs (11.8 µs). However, the corresponding optical response at 2000 nm is still weak due to low incident photon energy and large exciton binding energy. By further spin coating PbS quantum dots onto the SWCNTs channel, the optical response can be greatly enhanced for 2000 nm irradiation. All these results can not only illustrate the photoresponse of SWCNTs but also indicate that photogating plays a crucial role in these devices, providing valuable insights for the performance enhancement.

Nanocomposite: Antimony Sulfide in Channels of Single-Walled Carbon Nanotubes

A nanocomposite of antimony sulfide Sb2S3 embedded into the channels of single-walled carbon nanotubes (SWCNTs) has been prepared for the first time by the capillary wetting method and has been characterized by X-ray powder diffraction, transmission electron microscopy (TEM), transmission scanning electron microscopy (TSEM), and X-ray energy dispersive (EDX) spectroscopy. Antimony sulfide fills the channels of almost all SWCNTs. Channel filling is continuous along the entire length of the tube up to 1 μm. The diameters of filled SWCNTs fall in the range 0.6–3.5 nm. The periodicity of Sb2S3 crystal clusters observed on electron microscopic images is 2.0–2.2 nm along the nanotube axis and 2.5–3.5 nm in the transverse direction. A structural model of a Sb2S3 cluster is suggested.

Affinity sensor for haemoglobin A1c based on single-walled carbon nanotube field-effect transistor and fructosyl amino acid binding protein

Haemoglobin A1c (HbA1c) is a significant glycaemic marker for diabetes mellitus. The level of HbA1c reflects the mean blood glucose level over the prior 2–3 months and it is useful for the assessment of therapeutic effectiveness and for diagnosis. In this study, we report the label-free affinity sensor for HbA1c based on the chemiresistor-type field-effect transistor, which has a simple sensor configuration. Single-walled carbon nanotubes (SWNTs) were used as the transducing element. The fructosyl amino acid binding protein from Rhizobium radiobacter (SocA), which binds to α-fructosyl amino acid specifically, was used as the biorecognition element for fructosyl valine (FV), the product of the proteolytic hydrolysis of HbA1c. The developed sensor shows the ability to measure as low as 1.2 nM FV, which is 14-fold more sensitive compared to the previously reported fluorescence-based sensor using SocA. This sensor also exhibits high specificity where no significant response is observed from either fructosyl lysine (FK) or glucose, which are potential interferents. FK is the ε-fructosyl amino acid from glycated albumin, another glycated protein, whereas glucose is naturally present at very high concentration in the blood. We propose that the modulation of the surface charges on the SWNTs caused by the conformational change in SocA upon ligand binding leads to the proportionate changes in the number of carriers in the SWNT channel.

Structure of One-Dimensional Rubidium and Silver Iodide Crystals in the Channels of Single-Walled Carbon Nanotubes

The structures of one-dimensional (1D) RbI, AgI, and RbAg4I5 crystals inside single-walled carbon nanotube (SWCNT) channels of 1D crystal@SWCNT nanocomposites formed by the capillary technique have been studied by high-resolution (scanning) transmission electron microscopy and computer modeling. 1D RbI crystals form a cubic lattice in a limited space, while 1D AgI crystals form a hexagonal lattice, as in their ternary compounds. The 1D RbAg4I5 structure differs from known bulk analogs and can be described by a distorted cubic lattice formed in two different directions.

Phototransistors with Negative or Ambipolar Photoresponse Based on As‐Grown Heterostructures of Single‐Walled Carbon Nanotube and MoS2

AbstractA facile synthesis method for the heterostructures of single‐walled carbon nanotubes (SWCNTs) and few‐layer MoS2 is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS2 on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS2 conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS2 to SWCNT is observed while positive photoresponse is observed in MoS2 conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS2 channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100–1000 AW−1) at low bias voltages (0.1 V) in the visible spectrum (500–700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS2).

Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10–21 m2/s, which corresponds to an activation-barrier height of ~1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

High-sensitivity pH sensor using separative extended-gate field-effect transistors with single-walled carbon-nanotube networks

We fabricate high-sensitivity pH sensors using single-walled carbon-nanotube (SWCNT) network thin-film transistors (TFTs). The sensing and transducer parts of the pH sensor are composed of separative extended-sensing gates (ESGs) with SnO2 ion-sensitive membranes and double-gate structure TFTs with thin SWCNT network channels of ∼1 nm and AlOx top-gate insulators formed by the solution-deposition method. To prevent thermal process-induced damages on the SWCNT channel layer due to the post-deposition annealing process and improve the electrical characteristics of the SWCNT-TFTs, microwave irradiation is applied at low temperatures. As a result, a pH sensitivity of 7.6 V/pH, far beyond the Nernst limit, is obtained owing to the capacitive coupling effect between the top- and bottom-gate insulators of the SWCNT-TFTs. Therefore, double-gate structure SWCNT-TFTs with separated ESGs are expected to be highly beneficial for high-sensitivity disposable biosensor applications.

Translocation of Bioactive Molecules through Carbon Nanotubes Embedded in the Lipid Membrane.

One of the major challenges of nanomedicine and gene therapy is the effective translocation of drugs and genes across cell membranes. In this study, we describe a systematic procedure that could be useful for efficient drug and gene delivery into the cell. Using fully atomistic molecular dynamics (MD) simulations, we show that molecules of various shapes, sizes, and chemistries can be spontaneously encapsulated in a single-walled carbon nanotube (SWCNT) embedded in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer, as we have exemplified with dendrimers, asiRNA, ssDNA, and ubiquitin protein. We compute the free energy gain by the molecules upon their entry inside the SWCNT channel to quantify the stability of these molecules inside the channel as well as to understand the spontaneity of the process. The free energy profiles suggest that all molecules can enter the channel without facing any energy barrier but experience a strong energy barrier (≫kBT) to translocate across the channel. We propose a theoretical model for the estimation of encapsulation and translocation times of the molecules. Whereas the model predicts the encapsulation time to be of the order of few nanoseconds, which match reasonably well with those obtained from the simulations, it predicts the translocation time to be astronomically large for each molecule considered in this study. This eliminates the possibility of passive diffusion of the molecules through the CNT-nanopore spanning across the membrane. To counter this, we put forward a mechanical method of ejecting the encapsulated molecules by pushing them with other free-floating SWCNTs of diameter smaller than the pore diameter. The feasibility of the proposed method is also demonstrated by performing MD simulations. The generic strategy described here should work for other molecules as well and hence could be potentially useful for drug- and gene-delivery applications.

Controlling conducting channels of single-walled carbon nanotube array with atomic force microscopy

In this paper, we report a technique of controlling the number of single-walled carbon nanotubes (SWNTs) between two electrodes. The SWNT devices consist of an array of SWNTs between two silver/palladium electrodes, which are fabricated with electron beam lithography and silver. Using the tip-sample interaction in contact mode of atomic force microscopy (AFM), the number of individual SWNTs can be controllably decreased. The current–voltage measurements indicate that the resistance increases when the conducting channels of SWNTs are reduced. This simple and controllable approach could be useful for the assembly of high performance devices with a desired number of channels for future electronic investigations.

Thread-Like CMOS Logic Circuits Enabled by Reel-Processed Single-Walled Carbon Nanotube Transistors via Selective Doping.

The realization of large-area electronics with full integration of 1D thread-like devices may open up a new era for ultraflexible and human adaptable electronic systems because of their potential advantages in demonstrating scalable complex circuitry by a simply integrated weaving technology. More importantly, the thread-like fiber electronic devices can be achieved using a simple reel-to-reel process, which is strongly required for low-cost and scalable manufacturing technology. Here, high-performance reel-processed complementary metal-oxide-semiconductor (CMOS) integrated circuits are reported on 1D fiber substrates by using selectively chemical-doped single-walled carbon nanotube (SWCNT) transistors. With the introduction of selective n-type doping and a nonrelief photochemical patterning process, p- and n-type SWCNT transistors are successfully implemented on cylindrical fiber substrates under air ambient, enabling high-performance and reliable thread-like CMOS inverter circuits. In addition, it is noteworthy that the optimized reel-coating process can facilitate improvement in the arrangement of SWCNTs, building uniformly well-aligned SWCNT channels, and enhancement of the electrical performance of the devices. The p- and n-type SWCNT transistors exhibit field-effect mobility of 4.03 and 2.15 cm2 V-1 s-1 , respectively, with relatively narrow distribution. Moreover, the SWCNT CMOS inverter circuits demonstrate a gain of 6.76 and relatively good dynamic operation at a supply voltage of 5.0 V.