Nanotube Contacts Research Articles

Mastering thermal transport across carbon nanotube contacts through morphological control

Thermally conductive nanomaterials hold great promise for applications in thermal management. However, the interfaces between nanomaterials can significantly impede heat flow, and a comprehensive understanding of thermal transport across nanoscale contacts is highly desired. Here, by integrating a movable nano-manipulator within an electron microscope with a nanofabricated thermal sensor, we adjusted the contact positions, overlapping length, and crossing angles between two carbon nanotubes (CNTs) as desired, while concurrently measuring the thermal contact resistance (TCR) at the van der Waals junction. The TCR far surpassed that of the studied 6 μm-long CNTs, particularly in contacts affected by inevitable nanoscale surface contamination. The TCR per unit area exhibited significant variations across different contact morphologies, spanning two orders of magnitude even for identical pairs of samples, attributable to structural non-uniformity within the CNTs. This in-situ approach and the notable morphology effects can guide the control of heat at the nanoscale.

Percolation in Carbon Nanotube-Reinforced Polymers for Strain-Sensing Applications: Computational Investigation on Carbon Nanotube Distribution, Curvature, and Aggregation.

The present article investigates the possibility of simulating the electrical conductivity of carbon nanotube-reinforced polymer composites by numerical methods. Periodic representative volume elements are generated by randomly distributing perfectly conductive reinforcements in an insulating matrix and are used to assemble an electrical network representative of the nanocomposite, where the nanotube-nanotube contacts are considered equivalent resistors modeled by means of Simmons' equation. A comparison of the results with experimental data from the literature supports the conclusion that a random distribution of reinforcements is not suitable for simulating this class of materials since percolation thresholds and conductivity trends are different, with experimental percolation taking place before the expectations. Including nanotube curvature does not solve the issue, since it hinders percolation even further. In agreement with experimental observations, the investigation suggests that a suitable approach requires the inclusion of aggregation during the volume element generation to reduce the volume fraction required to reach percolation. Some solutions available in the literature to generate properly representative volume elements are thus listed. Concerning strain sensing, the results suggest that representative volume elements generated with random distributions overestimate the strain sensitivity of the actual composites.

Theoretical Estimation of the Shearing Strength of Polymer/Carbon Nanotube Contact: A Fractal Model

Theoretical Estimation of the Shearing Strength of Polymer/Carbon Nanotube Contact: A Fractal Model

Novel Potentiometric Screen-printed Carbon Electrodes for Bisphenol S Detection in Commercial Plastic Samples.

Novel miniaturized poly(vinyl chloride) matrix membrane sensors based on screen-printed carbon electrodes and responsive to bisphenol S (BPS) were formulated. Polymeric membranes are based on an ion-pair complex of BPS anion with an Aliquat 336S counter cation. A solid conductive contact of multi-walled carbon nanotubes (MWCNTs) was used on screen-printed carbon platforms. After drop-casting and drying of the MWCNTs on a carbonaceous substrate, it was coated with a layer of polymeric poly(vinyl chloride) PVC sensing membrane containing the recognition complex. Prepared electrodes revealed a near-Nernstian response towards BPS with a -28.2 ± 0.8 mV/decade anionic slope, 0.02 μg/mL detection limit and 2.5 × 10-7 - 1.0 × 10-3 M concentration range (r2 = -0.9994). Signals were recorded in a 30 mM HCO3-/CO32- buffer, pH 10, with fast response times <10 s. A suggested sensing system was effectively applied in the quantitative determination of diminished BPS levels released from plastic bottle samples, and obtained results were statistically assessed against a chromatographic HPLC independent reference method.

The temperature dependence of electron transport in a composite film of graphene oxide with single-wall carbon nanotubes: an analysis and comparison with a nanotube film

The work describes the results of low-temperature studies (5–291 K) of electron transport in composite films of graphene oxide with single-wall nanotubes (GO-SWNTs) obtained by vacuum filtration of their aqueous suspension. The emergence of conductivity in such films is shown to be related to nanotubes, since the GO film, unlike the nanotube film, has no conductivity. For a comparative analysis, the electrical conductivity of the SWNT film was also considered. The GO-SWNT and SWNT films exhibit a semiconductor behavior with a negative temperature coefficient of electrical conductivity. The temperature dependences of film resistance have been analyzed using the 3D Mott model that describes the motion of electrons (due to thermally activated tunneling through barriers) with variable-range hopping (the VRH model) in an interval of 5–240 K. The analysis of the dependences yielded estimates for the parameters of electron transport in the composite GO-SWNT film and SWNT nanotube film: the average hopping range and energy of the electron; their temperature dependences have been plotted. A comparison of these parameters for different films showed that nanotube contact with the GO surface hinders electron transport in the composite film. To describe the temperature dependence of film resistance at Т &amp;gt; 240 K, the Arrhenius model is used from which the potential barrier value has been obtained.

Amelioration of the pool boiling heat transfer performance via self-assembling of 3D porous graphene/carbon nanotube hybrid film over the heating surface

This study investigates the boiling heat transfer enhancement of 3D porous graphene/carbon nanotube hybrid surface formed via self-assembling. Experimentally, colloidal suspensions of functionalized carbon nanotubes and graphene oxide (at 1:10 wt ratio) and only graphene oxide in water are prepared via sonication using three weight concentrations; 0.00005%, 0.0005%, and 0.005%. Boiling tests are conducted for each prepared fluid using a custom-made boiling apparatus. After boiling tests, Scanning Electron Microscopy analysis is carried out over the heating surfaces in order to observe the deposition behavior of the suspended nanoparticles. For wettability analysis, the contact angle of sessile water droplets on the heating surfaces are measured using the goniometry method. The boiling performance of the heating surface formed by self-assembling of graphene oxide/functionalized carbon nanotube outperforms the self-assembled graphene oxide-only surface with greater critical heat flux and heat transfer coefficient values at all the tested concentrations. A decent interfacial contact of graphene sheets and carbon nanotubes improves surface capillarity and thermal activity. The highly porous surface improves the nucleation site density, bubble departure diameter, and frequency of departure. All these factors contribute enhancement of heat transfer coefficient and critical heat flux.

Ultrahigh Sensitive MoS2/rGo Photodetector Based on Aligned CNT Contacts

Molybdenum disulfide (MoS2)/reduced Graphene Oxide (rGo)-based photodetector was fabricated based on a convenient method using a novel aligned carbon nanotube (CNT) contact configuration. With this device, one can successfully meet the challenges in device fabrication based on nano-sized 2-D materials. For this purpose, patterned CNTs were grown on a 285-nm SiO2/Si substrate using plasma-enhanced chemical vapor deposition. Then, thermally reduced few-layered go was drop casted on CNTs electrode followed by deposition of MoS2 nanosheets through dispersion. The photo response of the device was investigated under laser illumination with different wavelengths (375, 405, 455, and 532) and various power intensities. Despite adding small portion of MoS2 nanosheets, the results demonstrate an ultra-high photo responsivity of 115 mA/W at ${V}_{\textit {ds}}=\textsf {1}$ V under 405-nm laser illumination, which is quite comparable with other reports.

Conjugated system in metal-free 1D polyaniline nanotubes/carbon nitride hollow composites with strong adsorption and enhanced visible-light photocatalytic activities

Metal-free 1D polyaniline nanotubes/carbon nitride (PNCN) hollow composites are fabricated by self-assembly chemisorption and solvent evaporation method for the first time. The results show that carbon nitride (g-C3N4) is successfully covered onto polyaniline (PANI) nanotubes. Due to similar electronic structures of nitrogen-rich materials of PANI and g-C3N4, the combination of two π-conjugated system not only benefits the separation of photogenerated charge carriers but also increases the light absorption range of g-C3N4. The compact contact of the PANI nanotubes and g-C3N4 nanosheets as well as their matched energy level is the determinant factor for interfacial heterojunction. Specially, the hollow 1D “Janus” heterojunction impels photogenerated charge pairs to separate and transfer to opposite directions in a short diffusion path, with the additional benefits of exposure of more active sites and transmission of reactants for catalytic surface reactions. As expected, PNCN composites are photoactive and exhibit enhanced photocatalytic performance under visible-light irradiation over pure g-C3N4 and PANI nanotubes. In addition, PNCN composites possess strong adsorption capacity. This versatile 1D PNCN hollow composites prepared from a cost-effective and green process have potential applications in catalysis, drug delivery system, sensors, and energy storage and conversion.

Towards More Stable and Flexible Perovskite Solar Cells by Graphene and Nanotube Contacts

Towards More Stable and Flexible Perovskite Solar Cells by Graphene and Nanotube Contacts

Rhodium clustering process on defective (8,0) SWCNT: Analysis of chemical and physical properties using density functional theory

The Spin-polarized density functional theory is used to study the effect of a single vacancy in a (8,0) single-walled carbon nanotube (SWCNT) on the Rh clustering process. The vacancy is considered oxygenated and non-oxygenated and, in each case, different Rhn cluster sizes (n=1–4) are taken into account. For the analysis of these systems some physical and chemical properties are calculated, such as binding energy (Eb), work function (WF), magnetic moment, charge transfer, bond length, band gap (Eg), and density of state (DOS). From this analysis it can be concluded that: a single Rh atom and Rh2 dimer are adsorbed on vacancy without oxygen, whereas Rh3 and Rh4 clusters prefer to be adsorbed on oxygenated vacancy. In all cases, Rh adsorption induces a magnetic moment. When the Rh atom and Rh2 dimer are bonded to the defective SWCNT, it has been found that they show a semiconductor behavior that could be interesting to use in the spintronic area. In the case of Rh3 and Rh4 clusters our results show a metallic behavior suggesting that these systems are good candidates for nanotube contact.

Strain sensing behaviors of epoxy nanocomposites with carbon nanotubes under cyclic deformation

The strain sensing behavior of multi-walled carbon nanotubes (MWCNT)/epoxy (EP) conductive composites subjected to tensile strain was studied in detail. With increasing the load to rupture, the responsivity (ΔR/R0, R0 is the original resistance, ΔR is instantaneous change in resistance) increased in a linear fashion and then began to decrease at a critical strain (εc), which was remarkably different from the thermoplastic conductive composites only with a monotonic increase of the responsivity. It was attributed to the decrease of the nanotube contact points, the increase in the gaps before εc, and the reorientation and violent alignment of nanotubes in the zones of high local deformation (after εc). In addition, when the extension-retraction cycles were applied, the values of max ΔR/R0 showed a distinct tendency with different strains around the εc. These behaviors were attributed to the competition of network destruction and reconstruction during the cyclic deformation. The mechanism of this unique sensing behavior was proposed as well.

Understanding thermal conductance across multi-wall carbon nanotube contacts: Role of nanotube curvature

Thermal energy transfer at the interconnects in carbon based nanoelectronic devices plays a crucial role towards their performance as well as their reliability. In this study, we investigate such thermal energy transfer across physically interacting multi-wall carbon nanotubes (MWCNTs) as a function of their diameter, length, number of walls, inter-layer chirality differences, and different angular orientation of the cross-contact. Using non-equilibrium molecular dynamics simulations for phonon energy transfer, we predict that MWCNTs' curvature and their number of walls emerge as two critical factors, with each of them determining the limiting value of the thermal conductance across MWCNT contacts in different diameter regimes. For thinner MWCNTs, the curvature determines the limiting value of the conductance and leads to an interesting non-monotonic character, while the number of walls dominates the contact conductance for large diameter MWCNTs. We discuss their respective origins and distinguish their governing regimes using several arguments –focusing of phonons, and confinement of the phonon focusing cone, large mean free path of graphite– and how they modulate radial thermal transport, leading to observed trends of thermal conductance across MWCNT contacts.

Low-temperature easy-processed carbon nanotube contact for high-performance metal- and hole-transporting layer-free perovskite solar cells

Abstract Expensive and energy-consuming vacuum process of metal deposition with ambient-unstable hole transporters are incompatible with large-scale and low-cost production of perovskite solar cells (PSCs) and thus hampers their commercialization. For the first time, we demonstrate cost-effective novel carbon nanotube (CNT) paste that was applied to FTO substrate by the facile doctor blade method and processed at low temperature (100 °C). Herein we report a new method of cost-efficient perovskite solar cells with the use of conventional hole transporters by directly clamping a selective hole extraction electrode made of CNT and a TiO 2 /perovskite photoanode. Most importantly, under optimized conditions in the absence of an organic hole-transporting material and metal contact, CH 3 NH 3 PbI 3 and CNTs formed a solar cell with an efficiency of up to 7.83%. The PSC devices are fabricated in air without high-vacuum deposition which simplifies the processing and lowers the threshold of both scientific research and industrial production of PSCs. Electrochemical impedance spectroscopy demonstrates good charge transport characteristics of CEs on the photovoltaic performance of devices. The PSCs exhibited good stability over 50 h. The abundance, low cost, and excellent properties of the CNT material offer wide prospects for further applications in PSCs.

Terahertz Spectroscopy of Individual Single-Walled Carbon Nanotubes as a Probe of Luttinger Liquid Physics.

Luttinger liquid theory predicts that collective electron excitations due to strong electron-electron interactions in a one-dimensional (1D) system will result in a modification of the collective charge-propagation velocity. By utilizing a circuit model for an individual metallic single-walled carbon nanotube as a nanotransmission line, it has been shown that the frequency-dependent terahertz impedance of a carbon nanotube can probe this expected 1D Luttinger liquid behavior. We excite terahertz standing-wave resonances on individual antenna-coupled metallic single-walled carbon nanotubes. The terahertz signal is rectified using the nanotube contact nonlinearity, allowing for a low-frequency readout of the coupled terahertz current. The charge velocity on the nanotube is determined from the terahertz spectral response. Our measurements show that a carbon nanotube can behave as a Luttinger liquid system with charge-propagation velocities that are faster than the Fermi velocity. Understanding what determines the charge velocity in low-dimensional conductors is important for the development of next generation nanodevices.

Thermal conductance of carbon nanotube contacts: Molecular dynamics simulations and general description of the contact conductance

The contact conductance of carbon nanotube (CNT) junctions is the key factor that controls the collective heat transfer through CNT networks or CNT-based materials. An improved understanding of the dependence of the intertube conductance on the contact structure and local environment is needed for predictive computational modeling or theoretical description of the effective thermal conductivity of CNT materials. To investigate the effect of local structure on the thermal conductance across CNT-CNT contact regions, nonequilibrium molecular dynamics (MD) simulations are performed for different intertube contact configurations (parallel fully or partially overlapping CNTs and CNTs crossing each other at different angles) and local structural environments characteristic of CNT network materials. The results of MD simulations predict a stronger CNT length dependence present over a broader range of lengths than has been previously reported and suggest that the effect of neighboring junctions on the conductance of CNT-CNT junctions is weak and only present when the CNTs that make up the junctions are within the range of direct van der Waals interaction with each other. A detailed analysis of the results obtained for a diverse range of intertube contact configurations reveals a nonlinear dependence of the conductance on the contact area (or number of interatomic intertube interactions) and suggests larger contributions to the conductance from areas of the contact where the density of interatomic intertube interactions is smaller. An empirical relation accounting for these observations and expressing the conductance of an arbitrary contact configuration through the total number of interatomic intertube interactions and the average number of interatomic intertube interactions per atom in the contact region is proposed. The empirical relation is found to provide a good quantitative description of the contact conductance for various CNT configurations investigated in the MD simulations and is suitable for incorporation into mesoscopic models capable of predicting the effective thermal transport properties of CNT materials.

Competitive Impact of Nanotube Assembly and Contact Electrodes on the Performance of CNT-based FETs

We report the fabrication and characterization of highly dense field-effect-transistor (FET) arrays based on single-walled carbon nanotubes (SWCNTs). The nanotubes were sorted according to the electronic type by using density gradient ultracentrifugation (DGU). By employing dielectrophoresis (DEP), SWCNTs with enriched semiconducting (sc) content were systematically integrated as active elements into FETs. The performance of air-operating FETs was addressed via an extended statistic study involving both electrical and structural analyses. The competitive impact of nanotube purity and assembly as well as the metal electrode composition and a thermal treatment on the final device performance was shown. Regardless of the used sc-content, the device-to-device consistency was improved via employing annealing up to 250 °C for 1 h in a vacuum. The observed clockwise hysteresis, known so far only in connection with CNT–FETs built on ferroelectric substrates as well as electrolyte gated CNT–FETs, was found to reve...

An analytical method for modeling and analysis gas-water relative permeability in nanoscale pores with interfacial effects

This paper provides an analytical method for modeling and analyzing gas-water relative permeability in nanoscale pores with interfacial effects in terms of Hagen Poiseuille formula and capillary pressure curve. The flow models considering the interfacial effects in nanoporous shows good agreements with experimental data comparing with other models. The changing characteristics of gas-water relative permeability were analyzed under different conditions such as nanotube radius, film thickness, surface diffusion and contact angle. The results show that the larger the nanotube radius, the greater the relative permeability values because of decreasing both interfacial microstructure effect and the resistance of fluid flow. With the increasing of film thickness, surface diffusion which is positive for flow decreases in nanoscale pores. When the contact angle >90° solid interface repel water and the hydrophobic of surfaces reduce the resistance to fluid flow, and the gas-water relative permeability increases with increasing contact angle. On the contrary when contact angle <90°, the solid interface shows hydrophilic properties which play a negative effect to the fluid flow. This study has provided a new insight and theoretical basis for development of shale gas reservoirs with nanoscale pores.

Charge Transfer Dynamics between Carbon Nanotubes and Hybrid Organic Metal Halide Perovskite Films.

In spite of the rapid rise of metal organic halide perovskites for next-generation solar cells, little quantitative information on the electronic structure of interfaces of these materials is available. The present study characterizes the electronic structure of interfaces between semiconducting single walled carbon nanotube (SWCNT) contacts and a prototypical methylammonium lead iodide (MAPbI3) absorber layer. Using photoemission spectroscopy we provide quantitative values for the energy levels at the interface and observe the formation of an interfacial dipole between SWCNTs and perovskite. This process can be ascribed to electron donation from the MAPbI3 to the adjacent SWCNT making the nanotube film n-type at the interface and inducing band bending throughout the SWCNT layer. We then use transient absorbance spectroscopy to correlate this electronic alignment with rapid and efficient photoexcited charge transfer. The results indicate that SWCNT transport and contact layers facilitate rapid charge extraction and suggest avenues for enhancing device performance.

Investigating the benefits of a compliant gold coated multi-walled carbon nanotube contact surface in micro-electro mechanical systems switching

The application of a metal-carbon nanotube composite consisting of Au sputtered coated multi-walled carbon nanotubes as an electrical contact has been shown to greatly improve the lifetime and switching characteristics. A benefit of this contact surface is shown here to be the compliance of the composite, which allows the contact to conform the shape of its opposite counterpart and increase apparent contact area. The improvement of the lifetime is shown to be affected by the contact force applied, with a limit at 4.5 mN where the composite begins to fail under “hot switching” conditions (0.4 W) at only 1.5 × 106, an order of magnitude lower than at 4 mN.

New Evidence for a Quasi-Simultaneous Proton-Coupled Two-Electron Transfer and Direct Wiring for Glucose Oxidase Captured by the Carbon Nanotube–Polymer Matrix

Systematic cyclic voltammetry (CV) studies of glucose oxidase (GOx) and its cofactor, flavine adenine dinucleotide (FAD), almost similarly captured by the matrix of single-walled carbon nanotube and polymer complex, in turn, deposited on GC electrodes have been performed. The comparative analysis of kinetic data obtained for the FAD and GOx specimens treated through the same Marcus theory-based algorithmic procedure strongly suggests that the GOx species, notwithstanding the deeply buried position of FAD, mechanistically behave virtually in the same manner as isolated FADs (the operationally capable, nearly intact structure of GOx was confirmed by the catalytic activity vs glucose), strongly suggesting that FADs inside GOx are directly wired to the GC electrode, presumably, via almost direct contact of nanotubes with both FADs residing inside each GOx biomolecule (as basically suggested by Guiseppi-Elie, A.; et al. Nanotechnology 2002, 13, 559–564, and shortly supported by a number of valued researchers). Furthermore, the nonadiabatic, quasi-simultaneous two-proton-coupled two-electron transfer/exchange mechanism was concluded from further cross-analysis based on a generalized Marcus theory for the proton-coupled electron transfer (PCET), extra furnished by the first-time temperature-dependent CV studies and a subsequent Arrhenius treatment.