Suspended Carbon Nanotubes Research Articles

Nanoparticle dispersionizer by ultrasonic cavitation and streaming

An ultrasonic dispersion method using ultrasonic cavitation and streaming effects is suggested for the effective dispersion of nanoparticle suspensions. To generate ultrasonic cavitation efficiently, a high-intensity ultrasonic field is formed with arrayed piezoelectric transducers in the inner surface of a cylinder. To use the eddy current effect caused by ultrasonic streaming in the suspension, the arrayed piezoelectric transducers are tilted by a regular degree from the inner surface of the cylinder. Titanium dioxide (TiO2) and carbon nanotube (CNT) suspensions that were dispersed by the suggested dispersion method showed excellent dispersion characteristics compared with those dispersed by the conventional method.

A new smart nanoforce sensor based on suspended gate SOIMOSFET using carbon nanotube

This paper presents a new nanoforce sensor based on a suspended carbon nanotube gate field-effect transistor. To do so, a numerical investigation of Suspended Gate Silicon-on-Insulator MOSFET (SG-SOIMOSFET) is carried out using ATLAS 2D simulator. Based on the relationship between the nanotube’s deflection and the applied force, a comprehensive study of the proposed nanoforce sensor behavior is performed. Moreover, we describe the evolution of the drain current characteristics as a function of the applied force while examining the influence of capacity variation of the insulating gate on the drain current in the saturation region. It is found that the sensor has a good sensitivity of 230.68 ln(A)/pN. Our second contribution in this paper is to develop a model based on artificial neural networks (ANNs). We successfully integrate our neural model of nanoforce sensor as a new component in the ORCAD-PSPICE electric simulator library; this component must accurately express the behavior of the sensor. A second model based on neural networks, which deals with correction and linearization of the sensor output signal, is designed and implemented into the same simulator. The proposed device can be considered as a potential alternative for CMOS-based nanoforce sensing.

(Invited) Avalanche Photoemission in Suspended Carbon Nanotubes: Light without Heat

We report bright electroluminescence from suspended carbon nanotube (CNT) field effect transistors (FETs) under extremely low applied electrical powers (∼nW). Here, light emission occurs under positive applied gate voltages, with the FET in its “off” state. This enables us to apply high bias voltages (4 V) without heating the CNT. Under theseconditions, we observe light emission at currents as small as 1 nA and corresponding electrical powers of 4nW, which is 3 orders of magnitude lower than previous studies. Thermal emission is ruled out by monitoring the G band Raman frequency, which shows no evidence of heating under these small electrical currents. The mechanism of light emission isunderstood on the basis of steep band bending that occurs in the conduction and valence band profiles at the contacts, which produces a peak electric field of 500 kV/cm, enabling the acceleration of carriers beyond the threshold of exciton emission. The exciton-generated electrons and holes are then accelerated in this field and emit excitons in an avalanche process. This is evidenced by an extremely sharp increase in the current with bias voltage (45 mV/dec). We also observe light emission at negative applied gate voltages when the FET is in its “on” state at comparable electrical powers to those reported previously (∼5 μW). However, substantial Joule heating (T > 1000 K) is also observed under these conditions, and it is difficult to separate the mechanisms of thermal emission from hot carrier photoemission in this regime. Bo Wang, Fatemeh Rezaeifar, Jihan Chen, Sisi Yang, Rehan Kapadia and Stephen B. Cronin, ACS Photonics , DOI:10.1021/acsphotonics.7b00455 (2017)

Printed Carbon Nanotube Biosensor for Cardiac Health Monitoring

Precise and accurate diagnosis of human-related diseases (i.e., genetic disorders, pathogen infection, etc.) is of paramount importance for health care. Early disease detection ensures the appropriate treatment response, leading to a better prognosis. Portable analytical devices hold great potential in minimizing the time between diagnosis and appropriate treatment whether in the doctor’s office or the field. Electrochemical biosensor devices are prime candidates for the development of cheap, disposable and sensitive diagnostic tests considering that they have low power requirements, linear output, can operate at room temperature and can be manufactured using high-throughput technologies (1). Inkjet printing is one of the promising manufacturing procedures for the development of reliable, low-cost, disposable electrochemical biosensor devices and allows mass production on inexpensive, flexible substrates such as paper and polymers (2). Here we present the first steps of the development of a print-on-demand carbon nanotube (CNT) electrochemical biosensor device for the detection of cardiac troponin T (cTnT). cTnT is one of the preferred biomarkers of cardiac infarction monitoring, being elevated up until 14 days after cardiac injury (3) and the infarct size can be estimated from the cTnT levels at 72 hours (4). Our cTnT device is comprised of a fully printed 3 electrode sensor. The first crucial step is to manufacture a suspended CNT ink by the generation of CNT defect sites and increased carboxylic acid functional groups. These functional groups aid in the dispersion of the CNT in water and improve the jetability of the CNTs. Inks are printed using a Dimatix piezo drop-on-demand printer. Upon CNT electrode printing, silver leads are printed, from a commercial silver nanoparticle ink, and insulated using dielectric material, such as SU-8. The surface of the CNTs were modified with antibody probes, anti-cTnT, using an EDC/NHS coupling reaction, to promote the specific detection of cTnT. The surface modification and the interaction between the antibody and cTnT were confirmed by an increase of the charge transfer resistance, measured via electrochemical impedance spectroscopy (EIS) (5) and by a decrease in the differential pulse voltammetry signal (DPV) (6). The immobilized antibodies mediate the specific capture of the target protein leading to the formation of a CNT-antibody-cTnT complex further increasing the charge transfer resistance (3,5) and decreasing the DPV signal. Initial results in device fabrication and cTnT will be presented. Yamanaka,K., Vestergaard,M.C. and Tamiya,E. (2016) Printable electrochemical biosensors: A focus on screen-printed electrodes and their application. Sensors (Switzerland), 16, 1–16.Li,J., Rossignol,F. and Macdonald,J. (2015) Inkjet printing for biosensor fabrication: combining chemistry and technology for advanced manufacturing. Lab Chip, 15, 2538–2558.Kurz,K., Schild,C., Isfort,P., Katus,H.A. and Giannitsis,E. (2009) Serial and single time-point measurements of cardiac troponin T for prediction of clinical outcomes in patients with acute ST-segment elevation myocardial infarction. Clin. Res. Cardiol., 98, 94–100.Licka,M., Zimmermann,R., Zehelein,J., Dengler,T.J., Katus,H. a and Kübler,W. (2002) Troponin T concentrations 72 hours after myocardial infarction as a serological estimate of infarct size. Heart, 87, 520–524.Yun,Y.H., Bange,A., Heineman,W.R., Halsall,H.B., Shanov,V.N., Dong,Z., Pixley,S., Behbehani,M., Jazieh,A., Tu,Y., et al. (2007) A nanotube array immunosensor for direct electrochemical detection of antigen-antibody binding. Sensors Actuators, B Chem., 123, 177–182.Shen,G., Zhang,X., Shen,Y. and Zhang,C. (2015) Immobilization of antibodies on aldehyde-functionalized polymer/graphene films for the fabrication of a label-free electrochemical immunosensor. J. Electroanal. Chem., 759, 67–71.Periyakaruppan,A., Gandhiraman,R.P., Meyyappan,M. and Koehne,J.E. (2013) Label-Free Detection of Cardiac Troponin-I Using Carbon Nano fi ber Based Nanoelectrode Arrays. Anal. Chem., 85, 3858–3863.

Probing Phonon Dynamics in Individual Single-Walled Carbon Nanotubes.

Interactions between elementary excitations, such as carriers, phonons, and plasmons, are critical for understanding the optical and electronic properties of materials. The significance of these interactions is more prominent in low-dimensional materials and can dominate their physical properties due to the enhanced interactions between these excitations. One-dimensional single-walled carbon nanotubes provide an ideal system for studying such interactions due to their perfect physical structures and rich electronic properties. Here we investigated G-mode phonon dynamics in individual suspended chirality-resolved single-walled carbon nanotubes by time-resolved anti-Stokes Raman spectroscopy. The improved technique allowed us to probe the intrinsic phonon information on a single-tube level and exclude the influences of tube-tube and tube-substrate interactions. We found that the G-mode phonon lifetime ranges from 0.75-2.25 ps and critically depends on whether the tube is metallic or semiconducting. In comparison with the phonon lifetimes in graphene and graphite, we revealed structure-dependent carrier-phonon and phonon-phonon interactions in nanotubes. Our results provide new information for optimizing the design of nanotube electronic/optoelectronic devices by better understanding and utilizing their phonon decay channels.

Ultraclean individual suspended single-walled carbon nanotube field effect transistor

In this work, we report an effective technique of fabricating ultraclean individual suspended single-walled carbon nanotube (SWNT) transistors. The surface tension of molten silver is utilized to suspend an individual SWNT between a pair of Pd electrodes during annealing treatment. This approach avoids the usage and the residues of organic resist attached to SWNTs, resulting ultraclean SWNT devices. And the resistance per micrometer of suspended SWNTs is found to be smaller than that of non-suspended SWNTs, indicating the effect of the substrate on the electrical properties of SWNTs. The ON-state resistance (∼50 kΩ), mobility of 8600 cm2 V–1 s–1 and large on/off ratio (∼105) of semiconducting suspended SWNT devices indicate its advantages and potential applications.

Impact of surfactant and clay platelets on electrokinetic potential and size distribution in carbon nanotubes aqueous suspensions

Stabilization of aqueous suspensions of carbon nanotubes (CNTs) is an acute task for a number of technological processes. The effects of cationic surfactant (cetyltrimethyl-ammonium bromide, CTAB) and clay platelets (Laponite RD® (Lap)) on the electrokinetic potential and aggregation stability/size distribution of CNTs have been studied. The studies were performed at constant pH (4.5 ± 0.1), and at different values of the added amount of the reagent, mass ratio between Lap/CNTs, aging time as well as duration of the suspension ultrasonic treatment. In a CTAB concentration interval of Cs = 3.64.10−5 − 1.82.10-2 wt.% a narrow monomodal size distribution was found. The median size of aggregates was 21–24 μm that is two times larger than the length of individual CNTs (5–10 μm). At higher CTAB concentrations (above critical micelle concentrations (CMC)), formation of aggregates with median size of 140–150 μm takes place, with preserving the monomodal size distribution. Aggregation of CNTs in this case probably occurs by deposition of individual CNT on the surface of primary aggregates. Addition of Lap platelets in the range from X = 0 to 0.4 (where X is the mass ratio of Lap/CNTs) causes a monotonic decrease of the ζ-potential of the CNTs from −40 mV to −30 mV with reaching its plateau value at X = 0.4–1.0. This evidences the high surface coverage of CNTs by Lap platelets at which the CNT + Lap complex acquires the ζ-potential value of Lap. In mixed CNT + Lap suspensions (X = 1.0), a bimodal particle size distribution was registered, with appearance of big aggregates (≈150–300 μm), both in dilute (Cs = 3.64.10−5 – 3.64.10-3 wt.%) and concentrated (Cs > CsCMC) solutions. These big hybrid CNT + Lap aggregates were loose, rather unstable, and they could be easily destroyed by ultrasonic treatment.

Magnetic anisotropy of functionalized multi-walled carbon nanotube suspensions

We report on the magnetic properties of stable suspensions from oxidized Multiwalled Carbon Nanotubes (MWCNT) functionalized with aminopyrene (AP). MWCNT form π−π stacking adducts with AP (AP-MWCNT), originating homogenous, stable, suspensions in N,N-dimethylformamide (DMF) or melted agarose. First, we investigated the magneto-optical properties of these adducts. When applying series of pulsed magnetic fields to nanotube suspensions in DMF, the pattern of light dispersed increased during the magnetic pulse and decreased in the intervals, a behavior consistent with magnetic field induced orientation of the adducts. When adducts were suspended in a melted agarose gel under an external magnetic field, the extinction coefficient of polarized light through the gel, was larger when the polarization plane was parallel to the magnetic field direction. Based on the magneto-optical responses observed, we further investigated the magnetic properties of AP-MWCNT implementing measurements with Superconducting Quantum Interference Device, Zero Field Cooling and Field Cooling, Thermogravimetric and Differential Scanning Calorimetry. Pre-oriented AP-MWCNT suspensions depicted a clear superparamagnetic character with hysteresis loops revealing larger magnetic susceptibility values along their longitudinal axis. In summary, magneto-optical and SQUID measurements revealed that nanotube adducts in suspension, behave as nanoscale compass needles aligning their long axis parallel to externally applied magnetic fields.

Universal interaction-driven gap in metallic carbon nanotubes

Clean experimental testing grounds for strongly interacting electrons confined to one dimension are hard to find. Thus, suspended carbon nanotubes (CNTs) are a unique model system. Previous work showed that electron transport in suspended metallic CNTs can be frozen by strong electron-electron interactions. However, a detailed understanding of this exotic insulating phase has remained elusive. Here, the authors characterize the energy gap associated with the insulating phase in nominally metallic CNTs, and compare the gap to precise measurements of CNT diameter and chirality.

A mean-density model of ionic surfactants for the dispersion of carbon nanotubes in aqueous solutions

We propose a new analytical model of ionic surfactants used for the dispersion of carbon nanotubes (CNTs) in aqueous solutions. Although ionic surfactants are commonly used to facilitate the dispersion of CNTs in aqueous solutions, understanding the dispersion process is challenging and time-consuming owing to its complexity and nonlinearity. In this work, we develop a mean-density model of ionic surfactants to simplify the calculation of interaction forces between CNTs stabilized by ionic surfactants. Using this model, we can evaluate various interaction forces between the CNTs and ionic surfactants under different conditions. The dispersion mechanism is investigated by estimating the potential of mean force (PMF) as a function of van der Waals forces, electrostatic forces, interfacial tension, and osmotic pressure. To verify the proposed model, we compare the PMFs derived using our method with those derived from molecular dynamics simulations using comparable CNTs and ionic surfactants. Notably, for stable dispersions, the osmotic pressure and interfacial energy are important for long-range and short-range interactions, respectively, in comparison with the effect of electrostatic forces. Our model effectively prescribes specific surfactants and their concentrations to achieve stable aqueous suspensions of CNTs.

Thermal Conductivity of CNT - Wated Nanofluids: a Review

Abstract In heat transportation applications, water is most commonly used fluid. The efficiency of equipment used in these applications depends on thermal characteristics of water used. The thermal characteristics of water could be upgraded by suspending high thermal conducting solid nanoparticles. In this paper an attempt has been made to know how the use of surfactants and functionalization of carbon nanotube walls can affect the thermal characteristics and stability of nanofluid. A thorough analysis of collected literature revealed that carbon nanotubes have much higher thermal conductivity than any other nanoparticles and hence improve the thermal properties of water when suspended in them. Further it is concluded that suspension of carbon nanotubes in water requires use of surfactant or functionalization of carbon nanotube walls with proper group. By setting optimum pH and better dispersion, better thermal conductivity is possible. Experimental studies in the literature survey reveal that chemical stabilization techniques and physical stabilization techniques together decide the stability of the nanofluid.

Model and mechanism of carbon nanotube stabilization with plasticizer

Mechanism of stabilization of carbon nanotube (CNT) water suspension with plasticizer based on sulfated naphthalene formaldehyde resins is proposed in this article. CNT stabilization is achieved at the expense of fixing plasticizer group on the nanoparticle surface. Nonpolar part of plasticizer provides the formation of high-viscosity streak between CNTs particles and dispersion medium, and polar part provides the formation of double electrical layer, that supports formation of CNT micelle. Model of carbon nanotube micelle is described. It is determined that the conducting of ultrasonic dispersion of CNTs water suspensions with plasticizer based on sulfated naphthalene formaldehyde resins provides stability of CNTs suspensions for 7 and more days. Optimal options of ultrasonic effect are identified. It is shown that CNT suspension stabilized with sulfated naphthalene formaldehyde evenly apportion in volume of cement system in conclusion of the adding them to composition of cement paste. This distribution helps with obtaining cement stone with high exploitative properties.

Magnetic field induced orientational transitions in liquid crystals doped with carbon nanotubes.

We propose a continuum theory of orientational phase transitions induced by an external magnetic field in a suspension of carbon nanotubes in a nematic liquid crystal. It is shown that in a magnetic field a non-uniform and two different uniform phases are possible in the suspension. The uniform phases of the suspension differ by the type of orientational coupling of nanotubes with the liquid crystal matrix (the planar type when the nanotubes are oriented along the matrix director, and the homeotropic type when the nanotubes are perpendicular to the director). The possibility of a redistribution of the nanotube concentration (segregation effect) is shown. The fields of orientational transitions between uniform and non-uniform phases of the suspension are found analytically. It is shown that, when the nanotubes are weakly coupled to the matrix, the magnetic field induces reentrant transitions (uniform planar phase–non-uniform phase–uniform homeotropic phase–non-uniform phase). These transitions can be of first or of second order depending on the carbon nanotubes segregation intensity.

Nanosecond nonlinear optical and optical limiting properties of hollow gold nanocages

Gold nanocages (NCs) were prepared using the galvanic replacement reaction. Transmission electron microscopy images confirmed the porous morphology and completely hollow interior of the gold NCs. The nanosecond nonlinear optical and optical limiting (OL) properties of the NCs were characterized using the open-aperture Z-scan technique with 8-ns laser pulses at 532 nm. The gold NCs exhibited intensity-dependent transformation from saturable absorption to reverse-saturable absorption. The nonlinear absorption coefficient and saturable energy of the NCs were 5 × 10− 12 m/W and 2.5 × 1010 W/m2, respectively. Meanwhile, the gold NCs were found to display strong OL properties towards nanosecond laser pulses. The OL threshold of the gold NCs was lower than that of solid gold nanoparticles and comparable with that of a carbon nanotube suspension. Input fluence and angle-dependent scattering measurements indicated that nonlinear scattering plays an important role in the OL behavior of the gold nanostructures at high laser excitation. The improved OL response in gold NCs was discussed from the viewpoint of structural characteristic. The ultrathin and highly porous walls of the gold NCs can effectively transfer the photon-induced heat to the surrounding solvent, resulting in enhanced OL properties compared with those of solid gold nanoparticles. The intensity-dependent transformation from saturable absorption to reverse-saturable absorption and excellent OL response indicate that the smart gold NCs with ultrathin and highly porous walls can be considered as potential candidate in pulse shaping, passive mode locking, and eye protection against powerful lasers.

Single-Carbon-Nanotube Manipulations and Devices Based on Macroscale Anthracene Flakes.

Because of the outstanding mechanical and electrical properties of carbon nanotubes (CNTs), a CNT-based torsion pendulum is demonstrated to show great potential in nano-electromechanical systems. It is also expected to achieve various manipulations for further characterization and increase device sensitivity using ultrlong CNTs and macroscale moving parts. However, the reported top-down method limits the CNT performance and device size by introducing inevitable contamination and destruction, which greatly hinders the development of single-molecule devices. Here, a bottom-up method is introduced to fabricate heterostructures of anthracene flakes (AFs) and suspended CNTs, providing a nondamaging CNT mechanical measurement before further applications, especially for the twisting behavior, and providing a controllable and clean transfer method to fabricate CNT-based electrical devices under ambient conditions. Based on the unique geometry ofCNT/AF heterostructures, various complex manipulations of single-CNT devices are conducted to investigate CNT mechanical properties and prompt novel applications of similar structures in nanotechnology. The AF-decorated CNTs show high Young's modulus (≈1 TPa) and tensile strength (≈100 GPa), and can be considered as the finest and strongest torsional springs. CNT-based torsion balance enables to measure fN-level forces and the torsional spring constant is two orders of magnitude lower than previously reported values.

Large-Scale Fabrication of Suspended, Aligned, and Strained Single-Walled Carbon Nanotube Networks

Large-scale fabrication of suspended single-walled carbon nanotubes remains a challenge, especially at specific locations and in specific directions. In this work, we demonstrate an effective, fast and large-scale technique to fabricate suspended, strained, and aligned SWNT networks, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between each two prefabricated palladium patterns in high temperature. The SWNTs are aligned in eight directions: up, down, left, right, upper right, lower right, upper left, and lower left. The simulated calculations show that the driving force leading the silver liquid motion on the substrate is around 0.66 μN. The Raman spectra of the SWNTs network were measured, and the downshift of the G+ band indicates that, for the suspended SWNTs, the uniaxial strain is around 0.13%. This technique could be extended to two-dimensional material systems and open the pathway toward better optoelectronic and nanoelectromechanical systems.

Effect of surfactants on MWNT filled elastomer composites by latex mixing

The recent interest in advanced elastomer composites has led to an intensive study of nanomaterials, which exhibit a range of excellent chemical and physical properties. The advent of carbon nanotubes (CNTs) has created attractive opportunities for developing novel high performance nanomaterials. However, due to their strong van der Waals binding energies, CNTs have a tendency to aggregate, and so disaggregation and homogeneous dispersion remain critical challenges to the synthesis of successful elastomer composites. Here, we prepared a non‐covalently functionalized CNT suspension using a surfactant, without degrading the physical and chemical properties of the CNTs. Furthermore, the suspension was mixed with styrene butadiene rubber (SBR) latex to enhance the dispersion of the CNTs in the elastomer matrix. The eco‐friendly, cost‐effective, and scalable preparation method shows great potential for the production of elastomer nanocomposites. The successful homogenous dispersion of the MWNT in the SBR matrix resulted in composites with outstanding mechanical, thermal, and electrical properties at low loadings. Furthermore, to confirm their potential use in green (uncured) tyre applications, we employed them directly as fillers in the tread compounds of a pneumatic tyre, which exhibited enhanced abrasion, wet grip, and rolling resistance performance. This research opens new opportunities for preparing high performance elastomer composites for future industrial applications. POLYM. ENG. SCI., 58:1843–1848, 2018. © 2017 Society of Plastics Engineers

Observation of Van Hove Singularities and Temperature Dependence of Electrical Characteristics in Suspended Carbon Nanotube Schottky Barrier Transistors

A Van Hove singularity (VHS) is a singularity in the phonon or electronic density of states of a crystalline solid. When the Fermi energy is close to the VHS, instabilities will occur, which can give rise to new phases of matter with desirable properties. However, the position of the VHS in the band structure cannot be changed in most materials. In this work, we demonstrate that the carrier densities required to approach the VHS are reached by gating in a suspended carbon nanotube Schottky barrier transistor. Critical saddle points were observed in regions of both positive and negative gate voltage, and the conductance flattened out when the gate voltage exceeded the critical value. These novel physical phenomena were evident when the temperature is below 100 K. Further, the temperature dependence of the electrical characteristics was also investigated in this type of Schottky barrier transistor.

Magneto-hydrodynamic Blasius flow and heat transfer from a flat plate in the presence of suspended carbon nanofluids

In this article, we have discussed the effect of external magnetic field and other governing parameters on the flow and heat transfer in the presence of suspended carbon nanotubes over a flat plate. The governing equations of flow and heat transfer are derived from the Navier–Stokes and Prandtl boundary layer concept. The derived governing equations of flow and energy are non-linear partial differential equation, and these equations are converted into non-linear ordinary differential equations with corresponding boundary conditions using some suitable similarity transformations and are solved numerically using fourth-order Runge–Kutta method with efficient shooting technique. Effects of governing parameters on flow and heat transfer are shown through various graphs and explained with physical interpretation in detail. This study has applications in glass-fiber production and technology. On observing the results of this study, we can conclude that external magnetic field shows opposite behaviors on velocity and temperature and it enhances the rate of heat transfer.

Cattaneo-Christov Heat Flux on Blasius and Sakiadis Flow in a Suspension of Carbon Nanotubes with Thermal Radiation

Cattaneo-Christov Heat Flux on Blasius and Sakiadis Flow in a Suspension of Carbon Nanotubes with Thermal Radiation