Multi-walled Carbon Nanotube Bundles Research Articles

The mitigation of signal integrity issues in coupled MWCNT bundles and a comparison with Cu interconnects

In the nanoscale regime, carbon nanotubes (CNTs) are being considered as a future alternative interconnect material for traditional copper (Cu) wires in integrated circuit technology. The advances in device scaling and the continuous increase of clock frequencies in very large-scale integration technology have resulted in signal integrity (SI) issues. The reduction of such SI issues in coupled multiwalled CNT bundle interconnects is evaluated herein. The worst-case crosstalk delay and peak noise voltage are simulated for three-line coupled interconnects at the 22-nm technology node. To minimize the crosstalk effects, a passive shielding technique is proposed, resulting in reductions of 15.3% and 40.8% in the dynamic in-phase and out-phase crosstalk condition, respectively. The SI of single- and two-line coupled MWCNT bundle interconnects is also investigated based on eye diagrams in a channel simulator and compared with that of Cu interconnects. The eye-opening height is significantly enhanced in the MWCNT bundle and Cu interconnects when using the proposed technique. Moreover, the MWCNT bundle has a higher eye-opening compared with its Cu counterpart.

Dry sonication process for preparation of hybrid structures based on graphene and carbon nanotubes usable for chemical sensors

The combination of graphene (G) and multi-walled carbon nanotubes (MWCNTs) creates three-dimensional hybrid structures particularly suitable as next-generation electrical interface materials. Nevertheless, efficient mixing of the nanopowders is challenging, unless previous disaggregation and eventual surface modification of both is reached. To avoid use of solvents and multistep purification process for synthesis of stable G/MWCNTs hybrids, herein, a novel dry method based on an air sonication process was used. Taking advantage from the vigorous turbulent currents generated by powerful ultrasonication in air that induces strong thermal convection or radiation to and from the particles, it simultaneously ensures disentanglement of the large MWCNT bundles and G exfoliation and their only mild surface modifications. By changing the ratio between MWCNTs and G, a range of hybrids was obtained, different in surface morphology and chemistry. These hybrids have shown great potential as sensing material for designing mass-based sensors for toxic gases and chemiresistor for vapors detection.

Multifunctional flower-like WS2 hybrids with carbon nanotube veins and WS2 petals: Its sodium ion storage and hydrogen evolution properties

Abstract A hierarchical flower-like hybrid with tungsten disulfide (WS2) nano-sheet petals and multi-walled carbon nanotube (MWCNT) veins is prepared via a facile solvothermal method. High concentration functional groups and defects on the acid-treated MWCNTs bundles initiated the growth of WS2 nano-flowers with an average diameter of 500 nm, inducing strong interface interaction between WS2 and MWCNTs. Furthermore, the MWCNTs are adopted as viens to improve the electron transportation and as interconnected 3D network to alleviate the structural change and restacking of WS2 petals. Meanwhile, the WS2 nano-flowers with abundant edge tungsten atoms are beneficial for sodium ion storage and hydrogen evolution reaction. As a result, the hybrid exhibits excellent electrochemical performances: a specific capacity of 250 mAh g−1 at 0.5 A g−1 after 45 cycles is retained as anode for sodium ion battery; an 80 mV dec−1 Tafel slope and an overpotential of −0.25 V (vs. RHE) are delivered with excellent stability in acidic condition.

Novel Circuit Model of Multi-walled CNT Bundle Interconnects Using Multi-valued Ternary Logic

This research paper presents a novel circuit modeling and analysis of ternary logic for MWCNT bundle interconnects with active shielding under the influence of temperature variations. The far end crosstalk-induced noise and propagation delay of MWCNT bundle interconnects has been analyzed with and without the effect of shielding. A standard ternary inverter (STI) driver model is used to obtain the ternary logic at output. The temperature-dependent analysis is also carried out at different temperatures such as 300, 400 and 500 K. The temperature-dependent comparative analysis for MWCNT bundle, SWCNT bundle and copper interconnects with and without shielding is also performed. It has been observed that MWCNT bundle with active shielding outperforms the SWCNT and Cu by 75.7% and 84.4%, respectively. Similarly, the power dissipation is substantially reduced in the case of MWCNT bundle with respect to the Cu and SWCNT interconnects. It is also reported that the noise margin is marginally stable in ternary interconnects under the influence of temperature variation.

Recovery of lanthanum cations by functionalized magnetic multi-walled carbon nanotube bundles.

Rare-earth elements (REE), including La, are critical raw materials in many technological advancements. Collection of physically adsorbed REEs on clay minerals can be realized first by ion-exchange leaching, followed by adsorption enrichment. Ever increasing demand and limited resources of REEs have fueled the development of nanostructured adsorbents. In this paper, multi-walled carbon nanotubes (MWCNTs) were purified using concentrated H2SO4 and HNO3, then coupled with magnetic Fe3O4 nanoparticles to make low concentration La ion extraction from water possible. The MWCNT@Fe3O4 composites were further crosslinked with 0.1 wt% epichlorohydrin and functionalized with 0.5 wt% carbon disulfide to achieve a La3+ adsorption capacity of 23.23 mg g−1. We fully probed the morphology, crystallinity, chemical composition, and magnetic properties of the as-prepared adsorbent by scanning/transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, vibrating-sample magnetometry, and thermal gravimetry. These results indicated that the MWCNT@Fe3O4 nanohybrid may be a promising candidate for recovering La ions from aqueous solutions.

Ionotronics Based on Horizontally Aligned Carbon Nanotubes

AbstractControlled ion transport through ion channels of cell membranes regulates signal transduction processes in biological systems and has also inspired the thriving development of ionic electronics (ionotronics or iontronics) and biocomputing. However, for constructing highly integrated ionic electronic circuits, the integration of natural membrane‐spanning ion channel proteins or artificial nanomembrane‐based ionic diodes into planar chips is still challenging due to the vertically arranged architecture of conventional nanomembrane‐based artificial ionic diodes. Here, a new design of ionic diode is reported, which allows chip‐scale integration of ionotronics, based on horizontally aligned nanochannels made from multiwalled carbon nanotubes (MWCNTs). The rectification of ion transport through the MWCNT nanochannels is enabled by decoration of oppositely charged polyelectrolytes on the channel entrances. Advanced ionic electronic circuits including ionic logic gates, ionic current rectifiers, and ionic bipolar junction transistors (IBJT) are demonstrated on planar nanofluidic chips by stacking a series of ionic diodes fabricated from the same bundles of MWCNTs. The horizontal arrangement and facile chip‐scale fabrication of the MWCNT ionic diodes may enable new designs of complex but monolithic ionotronic systems. The MWCNT ionic diode may also prove to be an excellent platform for investigation of electrokinetic ion transport in 1D carbon materials.

Micellar extraction with vesicle coated multi-walled carbon nanotubes to assist the dispersive micro-solid-phase extraction of natural phenols in Dendrobium

Here, catanionic surfactant vesicles were prepared by varying the types and compositions of anions and cations and the number of alkyl tails of the surfactants. The formed vesicles were employed to disaggregate and stabilize multiwalled carbon nanotubes bundles in aqueous solutions. Furthermore, the vesicle coated carbon nanotubes were used as the adsorbent in the dispersive micro-solid phase extraction. Additionally, micellar extraction was employed for the sample pre-extraction to avoid the use of toxic organic extraction solvents. The relative parameters that affect the extraction efficiency of targets were optimized using response surface methodology. Under the optimal microextraction conditions, the analytical performance of the established method was evaluated. The limits of detection (2.3−13 ng/mL) and quantification (7.6−42 ng/mL), inter- and intra- day precision (1.2–4.0 %, 2.0–5.0 %), and spiked recovery values (80–91 %) were obtained. The proposed method showed high sensitivity, precision and trueness. It was successfully applied to analyze phenols in Dendrobium genus samples.

Novel Nanohybrids Based on Supramolecular Assemblies of Meso-tetrakis-(4-sulfonatophenyl) Porphyrin J-aggregates and Amine-Functionalized Carbon Nanotubes.

The ability of multiwalled carbon nanotubes (MWCNTs) covalently functionalized with polyamine chains of different length (ethylenediamine, EDA and tetraethylenepentamine, EPA) to induce the J-aggregation of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) was investigated in different experimental conditions. Under mild acidic conditions, protonated amino groups allow for the assembly by electrostatic interaction with the diacid form of TPPS, leading to hybrid nanomaterials. The presence of only one pendant amino group for a chain in EDA does not lead to any aggregation, whereas EPA (with four amine groups for chain) is effective in inducing J-aggregation using different mixing protocols. These nanohybrids have been characterized through UV/Vis extinction, fluorescence emission, resonance light scattering and circular dichroism spectroscopy. Their morphology and chemical composition have been elucidated through transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM and STEM analysis evidence single or bundles of MWCNTs in contact with TPPS J-aggregates nanotubes. The nanohybrids are quite stable for days, even in aqueous solutions mimicking physiological medium (NaCl 0.15 M). This property, together with their peculiar optical features in the therapeutic window of visible spectrum, make them potentially useful for biomedical applications.

The Influence of N,N-Dimethylformamide on Dispersion of Multi-Walled Carbon Nanotubes

Preparation of highly homogeneous disperse ions multi-walled carbon nanotubes (MWCNTs) has vital effect on their applications. In this research, the ultrasonication and heat treatment were used to prepare suspensions of MWCNTs using N,N-dimethylformamide (DMF) as dispersant innovatively. The suspensions were characterized by UV–Vis absorbance spectroscopy, adsorption isotherm, transmission electron microscopy, atomic force microscope and fourier transform infrared. The experimental results showed that the optimum concentration of DMF was 0.9 g/L, the best sonication time was 30 min and the optimum temperature was 50°C; The TEM and AFM images showed that the agglomeration of bundles was broken up, and the thickness of MWCNTs decreased because of the incorporation of DMF. In addition, the dispersing mechanism is that molecules of DMF get into the space of MWCNTs bundles to break up the aggregation, and amide groups of DMF easily form intermolecular hydrogen bonds to decrease surface tension. Using DMF to disperse MWCNTs had a remarkable effect, dispersed MWCNTs may be added into cement-based materials or other composite materials to improve their performance.

Design of MWCNT based Through Silicon Vias with Polymer Liners to Reduce the Crosstalk Effects

This paper presents a unique method to reduce the crosstalk noise, power consumption, power delay product (PDP) and energy delay product (EDP) in coupled multi-walled carbon nanotube (MWCNT) based through silicon vias (TSVs) with polymer liners. A novel structure of TSVs is proposed, where the MWCNT bundles are placed as conducting material and polymer liners are placed as dielectric material. The electrical equivalent model of the proposed TSVs is used and simulated in HSPICE to evaluate the performance. The performance analysis determines that there is a significant improvement in crosstalk noise, power consumption, PDP and EDP for polymer liners such as polyimide, polypropylene carbonate (PPC) and benzocyclobutene (BCB) over the conventional silicon dioxide (SiO2) liner. Moreover, the performance is also analyzed by varying the pitch between the TSVs from 100 μm to 3000 μm. It is noted that the induced crosstalk noise issues are reduced as the TSV pitch is increased. Similarly, the power consumption, PDP and EDP of the proposed TSVs are also reduced for the high pitch value. From the simulation results, it is observed that the proposed MWCNT TSVs with BCB liner show improvements up to 18.01%, 35.37% and 49.06%, respectively in terms of power consumption, PDP and EDP over the TSVs with SiO2 liner.

Difference in the interaction of nano-diameter rod and tubular particles with a disclination line in a nematic liquid crystal.

In the presence of a disclination line, inclusions within an aligned nematic liquid crystal (LC) are first attracted and ultimately trapped in it. The kind of orientational distortion created by the inclusions is fundamental in determining the trapping. In the present work, we observe differences in the trapping behaviour, onto a ½ defect line in a nematic LC, of two types of particles both elongated but different in their actual geometry. Even if both types have cylindrical shape, aggregates of Mo6S2I8 nanowires (rod-like shape) and multiwall carbon nanotubes (tubular shape, i.e. hollow) trap differently although still due to deformations induced in the LC director field. Attractive forces are stronger on elongated bundles of nanowires than on similarly sized bundles of multi-wall carbon nanotubes. The reason is the difference in the attraction forces originating from different types of distortions of the LCs. The hollow and the full cylinders are not homotopically equivalent and this inequivalence holds also for the liquid crystal around them. The nanowires induce defects in the LC close-by their surfaces as shown for microrods, topologically equivalent to spheres. In contrast, multi-wall carbon nanotubes, being hollow, do not form defects close to their ends. However, the tubes are strongly bent and the strong planar anchoring of LC at the surface induces deformation in the LC enabling attraction forces with the defect line. HiPco single wall carbon nanotubes could not be trapped because their bundles looked much straighter and smaller than the ones of MWCNTs and thus neither defects nor standard strong deformations are expected. In conclusion, even if the shape of both types of particles is cylindrical, the topological difference between rods and tubes has profound consequences on the physical behaviour and on the presence and type of defect-mediated nematic attraction forces.

Mathematical Framework of Tetramorphic MWCNT Configuration for VLSI Interconnect

Having a 1D material like Multiwall Carbon Nanotube (MWCNT) as a potential candidate for high speed Very Large Scale Integration (VLSI) interconnect creates a good scope to reduce the delay by estimating the parasitic elements i.e. Resistance ( $R$ ), Inductance ( $L$ ) and Capacitance ( $C$ ) properly. We have contrived an innovative configuration namely Tetramorphic (TM) for the bundle of MWCNTs with four different diameters. We have focused on 45 nm, 22 nm, 11 nm and 7 nm technology nodes to justify the novelty of our proposed configuration over the existing MWCNT bundle configurations. Having the parasitic $RLC$ elements for a specific technology node, the diameter optimization took place in this work. Subsequently, we obtain the propagation delay results for local, semi-global and global level interconnect. Finally, we compare the results with the other existing configuration to show the supremacy of our introduced configuration for MWCNT bundle to explore high speed VLSI interconnect and represent crosstalk delay and power dissipation. Moreover, this configuration is highly dense which will offer the size shrinkage feature in a substantial manner.

Hierarchical Nanorods Constructed by Vertical WS2 Nanosheets on Carbon Nanotube Cores with Enhanced Lithium Storage Properties

AbstractA nanorod hybrid constructed by vertical WS2 nanosheets on multi‐walled carbon nanotubes (MWCNTs) core is synthesized by a facile solvothermal method. The WS2 nanorod is difficult to form compared to its MoS2 counterpart because of the relatively sluggish dynamics of W4+. Herein, multi‐site nucleation of WS2 are initiated by the acid‐ and heat‐treated MWCNT bundles with high concentration of defects and functional groups, forming nanorods with high aspect ratio, and inducing strong interface interaction between MWCNTs and WS2. WS2 nanosheets are vertically assembled on the surfaces of MWCNT bundles without agglomeration, exposing abundant active sites for Li+ storage. A three‐dimensional electron conductive network is formed by the nanorods to improve the charge transport efficiency and alleviate the structure change/restacking of WS2 during lithium‐ion batteries cycling. A specific capacity of 963 mAh g−1 at 0.5 A g−1 after 500 cycles is retained by the nanorod hybrid anode, showing excellent electrochemical performances.

Efficient Passive Shielding of MWCNT Interconnects to Reduce Crosstalk Effects in Multiple-Valued Logic Circuits

In this paper, the effectiveness of passive shielding of multiwalled carbon nanotube (MWCNT) bundle interconnects in reducing the crosstalk effects in carbon nanotube FET based ternary circuits is comprehensively investigated. In addition, based on the tighter sublithographic pitch of MWCNTs compared to Cu, we decrease the space between the carbon nanotube (CNT) interconnects to reduce the area overhead, while still having significantly higher effectiveness compared with Cu. The worst-case crosstalk delay and noise for passively shielded MWCNT and Cu wires at 14 nm technology are evaluated using comprehensive HSPICE simulations. The results indicate that the crosstalk delay and noise area in the efficient passively shielded MWCNT bundle interconnects are much smaller than the shielded Cu wires for ternary logic. Furthermore, the impacts of process variation on the crosstalk effects in these interconnects in ternary logic are investigated using Monte Carlo simulations. The results demonstrate the robustness of the passively shielded MWCNT bundles in ternary logic.

Influence of concentration, length and orientation of multiwall carbon nanotubes on the electromechanical response of polymer nanocomposites

Multiwall carbon nanotube (MWCNT)/polymethyl methacrylate (PMMA) composites were fabricated by solution casting with a range of MWCNT concentrations, two groups of MWCNT lengths and with or without the application of electric field. As-received (CNTs) and fragmented (FCNTs) MWCNTs were used to fabricate composites with MWCNT concentrations between 0.05 wt% and 0.7 wt%. A well-controlled procedure to systematically fragment the MWCNTs based on the application of high-density ultrasonic energy was implemented, and MWCNT length distributions were obtained by a formal statistical analysis. The relationship between the sparseness of the MWCNT network (macroscale morphology), electrical conductivity and piezoresistive sensitivity was evaluated. In order to evaluate the effect of the MWCNT alignment on the composite properties, specific MWCNT concentrations were selected for composites with CNTs and FCNTs under the application of an electric field. Composites with FCNTs exhibited a sparser network, higher transparency, lower electrical conductivity, higher percolation threshold and higher piezoresistive sensitivity than their counterparts with CNTs. On the other hand, composites with electric field-aligned MWCNT bundles presented higher electrical conductivity and piezoresistive sensitivity than their non-aligned counterparts, for both fragmented and non-fragmented cases. The evaluation of the combined effect of carbon nanotube length and alignment on the electromechanical properties of the composites represents an important step on the understanding of the structure-property relation of polymer nanocomposites.

Carbon Nanotubes Readily Disperse in Linear Silicones and Improve the Thermal Stability of Dimethylsilicone Elastomers.

Stable silicone fluid-carbon nanotube dispersions were prepared in minutes by simple mixing processes, without the addition of solvents or surfactants and without the chemical modification of the nanotubes. With linear silicones of sufficient viscosity, a dual asymmetric centrifuge (SpeedMixer) was sufficient for dispersion; lower viscosity silicones required a brief ultrasound treatment. Optical microscopy indicates a homogeneous dispersion of multiwalled carbon nanotube (MWCNT) bundles in linear poly(dimethylsiloxane) (PDMS) oils. The facile dispersion of carbon nanotubes in PDMS has been reported in several previous publications and this appears to be general for silicones. MWCNTs also disperse readily, and to a greater extent, as assessed by optical microscopy, in poly(methylphenylsiloxane) and, in particular, poly(diethylsiloxane). Linear PDMS/MWCNT dispersions are stable against agglomeration for months. Platinum-catalyzed hydrosilylation of MWCNT-containing vinyl-/hydride-functionalized PDMS liquids yielded filled elastomers that unexpectedly exhibit significantly increased thermal stability. This enhancement occurs with only fractions of a weight percent of MWCNTs. Thermal gravimetric analysis shows a 54 °C increase in peak weight loss temperature (446-500 °C), an increased decomposition activation energy (158-233 kJ/mol), a second higher temperature decomposition process, and doubled char formation (20-40%) with only 0.5 wt %-added MWCNT. Pyrolysis combustion flow calorimetry confirmed the enhancement in thermal stability. Improvements in electrical conductivity were observed at loadings as low as 0.025 wt %. Spontaneous adsorption of dialkylsiloxane chains to MWCNT surfaces (wetting) and the resulting changes in the composite structure are implicated as the basis for dispersion and thermal behavior changes.

Reactive Polymer-Functionalized Aligned Multiwalled Carbon Nanotube Bundles-Induced Porous Poly(ethylene terephthalate) Fibers

Porous poly(ethylene terephthalate) (PET) fibers were fabricated by the melt-spinning method. Here, reactive polymer-functionalized aligned multiwalled carbon nanotube bundles (RP@ACNTB) were intro...

Active Shielding of MWCNT Bundle Interconnects: An Efficient Approach to Cancellation of Crosstalk-Induced Functional Failures in Ternary Logic

This study presents an efficient geometry for active shielding of multiwalled carbon nanotube (MWCNT) bundle interconnects which cancels the crosstalk-induced functional failures in ternary logic. In this geometry, MWCNT bundles are used innovatively as shields on both sides of the signal transmission line to reduce the crosstalk effects while maintaining the minimum interconnect pitch. Simulations are performed using HSPICE for intermediate and global interconnects in ternary logic at 14-nm node. The results indicate that the crosstalk-induced functional failure in ternary logic is omitted by using the proposed structure. Moreover, according to the results, our proposed geometry reduces the crosstalk noise peak as compared to the widened MWCNT bundles, distanced MWCNT bundles and Cu interconnects on average by 41%, 44%, and 61% for the intermediate interconnects and 61%, 46%, and 74% for the global interconnects, respectively, without any considerable power consumption penalties.

Comparative Analysis of Mixed CNTs and MWCNTs as VLSI Interconnects for Deep Sub-micron Technology Nodes

This research paper presents a performance analysis of the mixed carbon nanotube (CNT) as an interconnect for very large-scale integration (VLSI) circuits at deep sub-micron (DSM) technology nodes. The mixed CNT interconnect is a combination of multiwall CNTs (MWCNTs) and single-walled CNTs (SWCNTs). Using hierarchical modeling, a multiconductor circuit model is proposed for the mixed CNT bundle at global-level interconnect lengths. Due to the insertion of SWCNTs in a MWCNT interconnect, the overall density of the conducting tubes in the proposed mixed CNT interconnect structure increases, thereby decreasing the overall resistance and inductance of the mixed CNTs. The performance of the proposed mixed CNT interconnect is estimated in terms of delay and power delay product (PDP) for different technology nodes (32 nm, 22 nm, and 16 nm) at different interconnect lengths. For comparative analysis, a similar analysis is performed using MWCNT bundle interconnects. The comparative results show that there is reduction in the overall propagation delay and PDP for the proposed mixed CNTs compared to MWCNTs as the interconnect material for DSM technology nodes at global-level interconnect lengths.

Comparative Analysis of Simultaneous Switching Noise Effects in MWCNT Bundle and Cu Power Interconnects in CNTFET-Based Ternary Circuits

In this paper, the impacts of the simultaneous switching noise (SSN) in carbon nanotube field effect transistor-based ternary circuits are investigated. These effects, including the peak noise on the $V_{\mathrm {DD}}$ and ground rails and the SSN-induced delay and output noise are compared between traditional Cu and multiwall carbon nanotube bundle power interconnects in ternary circuits. Simulations are performed using HSPICE for global power interconnects at 14- and 7-nm technology nodes. The results indicate that for interconnects with 200- $\mu \text{m}$ length, the peak SSN voltage on the $V_{\mathrm {DD}}$ and ground rails for a power distribution network, including ten ternary buffers, using multi-walled carbon nanotube (MWCNT) bundle power interconnects is 53% and 40% lower, respectively, compared to Cu power interconnects in the last stage at the 14-nm node. Also, with scaling down the technology to 7 nm, these improvements increase to 60% and 59%, respectively. Moreover, MWCNT bundle power interconnects reduce the SSN-induced delay at the output of the tenth stage for interconnects with 200- $\mu \text{m}$ length on average by 82% as compared to the Cu interconnects at the 14-nm node. This improvement is 73% for the 7-nm technology node.