Multi-walled Carbon Nanotube Bundles Research Articles

Analysis of Crosstalk Effects for Multiwalled Carbon Nanotube Bundle Interconnects in Ternary Logic and Comparison with Cu interconnects

In this study, the crosstalk-induced effects are investigated in ternary logic by using the three-line bus architecture. The worst case crosstalk delays for both repeated and unrepeated interconnect and the peak crosstalk noise voltage on the victim net are investigated. Analyses have been done for global level multiwalled carbon nanotube (MWCNT) bundle and copper interconnects with carbon nanotube FET-based drivers and receivers at 22 nm node. According to the HSPICE simulations, the crosstalk delay and noise area in the MWCNT bundle interconnects are much smaller than the Cu wires for the ternary logic. In addition, the MWCNT bundle interconnects require a lower number of repeaters as compared to the Cu wires, which results in lower complexity and power consumption. The results indicate that utilizing the MWCNT interconnects instead of Cu wires in ternary systems leads to 63% shorter crosstalk delay without repeater insertion and 65% lower crosstalk noise area and 75% lower power consumption with repeater insertion. It is concluded from the results that the MWCNT bundle global wires are more suitable for ternary very large scale integration systems as compared to the Cu wires.

Quantum dot decorated aligned carbon nanotube bundles for a performance enhanced photoswitch.

Photoactive materials that are triggered by the irradiation of light to generate an electrical response provide an ecofriendly platform to afford efficient power sources and switches. A chemical assembly of well-known elements with aligned carbon nanotube bundles is reported here, which was employed to form an efficient photo-induced charge transfer device. The primary elements of this device are ultra-long multi-walled carbon nanotube (MWCNT) bundles, polyaniline (PANI) thin film coating, and CdSe quantum dots (QDs). Highly ordered and horizontally aligned MWCNT bundles were coated with PANI to enhance charge transfer properties of active QDs in this platform. The obtained device (CdSe-MWCNT@PANI) constructed on a silicon base exhibits highly efficient power conversion capabilities owing to the aligned MWCNT bundle assisted enhanced charge transport pathways generated within the device. The device also shows a short circuit current density (Jsc) of 9.81 mA cm(-2) and an open circuit voltage (Voc) of 0.46 V. The power conversion efficiency (PCE) of the device is 5.41%, and the current response is quite stable, highly responsive, and reproducible.

Supramolecular Approach to Decorate Multi-Walled Carbon Nanotubes with Negatively Charged Iron(II) Complexes

Poly(4-vinylpyridine) (P4VP) and P4VP/pentacyanoferrate(II) metallopolymer were used to suspend up to 1 mg mL-1 of multi-walled carbon nanotubes (MWCNT) in ethanol/water mixtures, providing noncolavent decoration of MWCNT with electroactive iron complex. The major interaction between polymer side chains and nanotubes is via π-π stacking, rather than charge-transfer interaction reported for many nitrogenated interacting molecules. Preservation of structural integrity of the nanotubes after functionalization was attested by Raman, which was reflected in the semiconducting character of the dried nanocomposites. Proximity of pentacyanoferrate(II) to MWCNT walls was suggested by its solvatochromic shift of metal-to-ligand charge transfer band attributed to [Fe(CN)5]3− bound to P4VP pyridyl moieties. Electronic microscopy revealed smooth films and good adhesion between MWCNT bundles and the matrix. The procedure described herein can be used to combine unique properties of transition metal compounds able to coordinate to pyridyl groups, with the film-forming ability of P4VP and conductivity provided by MWCNT.

Multi-walled carbon nanotube-filled polyvinyl chloride composites: Influence of processing method on dispersion quality, electrical conductivity and mechanical properties

The influences of dispersion quality and processing conditions on the electrical and mechanical properties of multi-walled carbon nanotube-filled polyvinyl chloride (MWCNT/PVC) composites are examined for potential use in sensor-enabled geosynthetics and other applications involving electrically-conductive polymer composites. Electrical conductivity and mechanical properties of the composite samples made using four different dispersion methods (i.e. probe sonication, bath sonication, mechanical stirring and batch mixing) are measured. Subsurface dispersion in the samples is quantified using laser scanning confocal microscopy and scanning electron microscopy, indicating that MWCNT bundle volumes resulting from all dispersion methods had a log-normal distribution. Dispersion qualities using different mixing methods are compared using the Kolmogorov–Smirnov D-statistic. Findings indicate that samples with higher dispersion quality exhibit greater ultimate strength and failure strain, whereas poorly-dispersed specimens have greater elastic modulus values, which are found to be in good agreement with those predicted by the Halpin–Tsai model.

Dispersion Properties of Aligned Multi-Walled Carbon Nanotubes

Aligned carbon nanotubes (CNTs) composites can be prepared by post-growth alignment or through the use of CNT bundles. Post-growth alignment requires stringent processing conditions (high-voltage electric field/high-strength magnetic field). In this study, we focused on well-aligned multi-walled CNT bundles (AMWNTs). Achieving a balance between dispersion and required orientation was the main aim of this study. Ultrasonic dispersion will inevitably produce heat, which will adversely affect dispersion. Hence, we developed and attached a temperature-control system to a water bath ultrasonic dispersion device. Further, we studied effects of additional factors such as the type and amount of surfactant on dispersion.

Temperature-Dependent Modeling and Performance Evaluation of Multi-Walled CNT and Single-Walled CNT as Global Interconnects

The influence of temperature on multi-walled carbon nanotube (MWCNT) interconnects have been studied. A temperature-dependent equivalent circuit model is presented for the impedance parameters of MWCNT bundle interconnects that captures various electron–phonon scattering mechanisms as a function of temperature. To estimate the performance of MWCNT bundle interconnects, the signal delay, power dissipation and power delay product (PDP) were simulated based on a temperature-dependent model that results in improvement in the delay, power and PDP estimation accuracy compared to the temperature-independent model. The results revealed that the power delay product of MWCNT bundle interconnects increases with increasing temperature from 200 K to 450 K for three different technology nodes, i.e., 32 nm, 22 nm and 16 nm, based upon a 1000-μm interconnect length. A similar analysis was performed for single-walled carbon nanotube (SWCNT) bundle interconnects and the results are compared with MWCNT bundle interconnects, indicating that the delay, power and power delay product (PDP) also increased with increasing temperature from 200 K to 450 K. The interconnects of the MWCNT bundle interconnects gave a better performance in terms of delay, power and PDP as compared to the SWCNT bundle interconnects.

A Shish-kebab superstructure in low-crystallinity elastomer nanocomposites: Morphology regulation and load-transfer

In this paper, a regulated morphology of multi-walled carbon nanotube bundles (CNTBs) in olefin block copolymer (OBC) is achieved via a facile method of short-time strong sonication and solution blending. Inside the CNTBs which consist of several to dozens of nanotubes, the nanotubes exhibit a well aligned structure. With the incorporation of CNTBs, a hybrid shish-kebab superstructure is formed that nanotubes in CNTBs form the central stems and OBC crystals form kebabs on the surface of nanotubes. Superior reinforcement is achieved, e.g., the tensile strength and Young’s modulus can be both tripled with 2 wt% CNTB incorporation. A downshift of G'band of CNTBs in nanocomposites in in situ Raman Spectra can be strikingly 10.09 cm−1, presenting remarkably effective load-transfer and leading to significant reinforcement. Additionally, unique morphology of CNTBs and the low compliance of rigid shish-kebab superstructure with large stereo hindrance could also contribute to the reinforcement of OBC/CNTB nanocomposites. In rheological tests, the nanocomposites exhibit quite low rheological percolation threshold of 0.34 wt% and gel point of 0.634 wt% as well as notable difference in terminal behavior in low frequency zone compared to that of neat OBC, revealing that the rigid bundle structure of CNTBs has remarkable effect on the viscoelastic behavior of OBC. Open image in new window

Influence of temperature on MWCNT bundle, SWCNT bundle and copper interconnects for nanoscaled technology nodes

This paper presents the comparative analysis of temperature dependent performance of Multi-walled carbon nanotubes (MWCNT), Single-walled carbon nanotube (SWCNT) and copper interconnects for nanoscaled technology nodes. The temperature dependent impedance circuit model is proposed for MWCNT bundle interconnects. The proposed model for MWCNT bundle shows the various electron–phonon scattering mechanisms dependency as a function of temperature. The performance in terms of propagation delay, power dissipation and power delay product for MWCNT bundle interconnects is simulated on the basis of temperature dependent electrical parameters for global interconnects at three different technology nodes viz. 32, 22 and 16 nm for temperature range 200 to 450 K. A similar analysis is performed for SWCNT bundle and copper interconnects and results are compared with the MWCNT bundle interconnects. The comparative results revealed that the performance of MWCNT bundle interconnects is better than the performance of SWCNT bundle and copper interconnects at different temperature ranging from 200 to 450 K for 32, 22 and 16 nm technology nodes at global interconnects.

Synthesis of Carbon Nanoparticles via Co-Pyrolysis of Waste Slop Oil and Ferrocene

Co-pyrolysis of slop oil with ferrocene was carried out to convert waste of petroleum into carbon nanoparticles (CNPs). Since slop oil is a mixture of hydrocarbons (HCs) with broad molecular weight distribution, it could be simply fractionated into some certain fractions by batch distillation. Distillate containing hydrocarbons with small molecules was mainly focused as an alternative carbon source for synthesis of CNPs. A two-stage furnace was employed for evaporating a mixture of distillated slop oil and ferrocene at 200 °C in the 1st stage of the furnace and then formation of CNPs at 900 °C could be observed in the 2nd stage. Laboratory-grade ferrocene was mixed with slop oil with a designated weight-ratio of 1:2. Microscopic analyses based on SEM and TEM micrographs reveals that CNPs obtained from distillated slop oil mostly consist of bundles of multi-walled carbon nanotubes (MWCNTs) with nominal diameters of 20-50 nm. Raman spectroscopic analyses of the synthesized CNPs exhibit the notably high value of IG/ID, suggesting that the synthesized CNPs preferably consist of graphitic nanostructure. Moreover, TGA analysis shows that 39.8 and 32.9 wt% of Fe contents exist in the CNP samples synthesized from original slop oil and distillated slop oil, respectively.

Mechanisms and modeling of halogenated aliphatic contaminant adsorption by carbon nanotubes

This paper examines the adsorption of environmentally relevant halogenated aliphatic compounds using single-walled (SWCNT) and multi-walled carbon nanotubes (MWCNT), and the development of linear solvation-energy relationships (LSER) to examine those adsorption mechanisms. The poly-parameter LSER model was also compared to those previously generated for the adsorption of aromatic compounds by CNTs. The adsorption affinity of aliphatic compounds was greater on the SWCNT than MWCNT with similar oxygen contents. This was attributed to the pore-filling mechanism that was enhanced by higher micropore volume of the SWCNT bundles over the MWCNT bundles. LSER models showed that, at higher concentrations, B (the hydrogen bond accepting ability) was the most influential descriptor for both SWCNT and MWCNT. Other important descriptors were V followed by P, both of which exhibited a positive correlation with adsorption, indicating that their size and polarizability favors adsorption. The contribution of these descriptors to overall adsorption was 2–3 times less than the B. In comparison, V was the most important descriptor in the aromatic compound LSER models. This difference indicates that adsorbate hydrophobicity greatly affects the adsorption of aromatic compounds by CNTs, whereas, aliphatic compounds are affected by both the hydrophobic driving force and other interactions.

Raman-Based Steady-State Thermal Characterization of Multiwall Carbon Nanotube Bundle and Buckypaper.

Electrical methods for thermal characterization, like 3ω method, micro-bridge method and TET method have been widely used in the thermal property measurement, while always been limited by the electrical conductance of samples or other temperature dependent thermal resistors. As an optical method, Raman thermometry has been developed and broadly applied in thermal characterization in recent years. In this work, we present a steady-state method based on Raman spectroscopy for the localized thermal characterization of micro/nanowires and thin film materials, respectively. The physical models are developed and two kinds of materials: a MWCNT bundle and a piece of buckypaper are measured to validate this method. The thermal conductivities are measured as 4.92 W/m K and 0.83 W/m K for CNT bundle and buckypaper respectively. Compared with other optical methods, this steady-state Raman method features easy and fast way for thermal characterization, being capable of measuring samples from millimeters down to nanometers.

Catalyst free low temperature synthesis and antioxidant activity of multiwalled carbon nanotubes accessed from ghee, clarified butter of cow׳s milk

Multiwalled carbon nanotubes (MWCNTs) have been synthesized at low temperature on silicon substrates in a thermal chemical vapor reactor from ghee, clarified butter from cow׳s milk as the carbon source without using any catalyst. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses revealed bundles of micrometer long MWCNTs with an interlayer separation of 0.33nm consisting of 25 concentric graphene sheets with outer and inner diameters of 27.45 and 13.68nm, respectively. The powder X-ray diffraction (XRD) pattern showed a hexagonal structure of graphitic carbon with average crystallite size of 4.6nm. The MWCNTs exhibited pronounced antioxidant activity.

Glucose-functionalized multi-walled carbon nanotubes dispersing and hosting nanotubes for poly(amide–imide) bionanocomposites containing N,N’-(pyromellitoyl)-bis-S-valine

Hybrid bionanocomposites (BNCs) were produced via incorporating multi-walled carbon nanotubes (MWCNTs) into a biodegradable poly(amide-imide) (PAI) matrix. MWCNTs were functionalized with glucose as a biologically active molecule in a green pathway to achieve a fine dispersion of MWCNT bundles in the polymer matrix. The optically active and biodegradable PAI was formed from the polycondensation reaction of N,N’-(pyromellitoyl)-bis-S-valine as an optically active diacid with 4,4′-methylene-bis(3-chloro-2,6-diethylaniline) as an aromatic diamine in a green condition. The polymer obtained and glucose-functionalized MWCNTs (f-MWCNTs) were used to prepare PAI/f-MWCNT BNCs through ultrasonic irradiation. BNCs containing 5, 10, and 15 wt.% of f-MWCNTs exhibited a relatively good dispersion at the macroscopic scale. Field emission scanning and transmission electron microscopy micrographs of the composites showed that f-MWCNTs made a good interaction with polymer chains, and nanotubes wholly separated and uniformly dispersed in the polymer matrix. Adding f-MWCNTs into the polymer matrix significantly increased the thermal stability of the BNCs due to the increased interfacial interaction between the PAI matrix and the modified f-MWCNTs and their improved dispersion.

Modeling and Analysis of Crosstalk Induced Effects in Multiwalled Carbon Nanotube Bundle Interconnects: An ABCD Parameter-Based Approach

In this paper, the crosstalk effects in both small and large diameter multiwalled carbon nanotube bundle interconnects (MWCNTs) for the future nanoscale integrated circuits are studied with the help of ABCD parameter matrix approach for global levels of interconnects at 22- and 14-nm technology nodes. Here, isolated MWCNTs are modeled using an equivalent single conductor transmission line. The simulation results show that the results are at par with the result of SPICE model. It is observed that performance wise, the large diameter MWCNT bundles are better than both small diameter MWCNT bundles and copper wire for both repeated and unrepeated interconnects. The same trend is observed with the number of inserted repeaters. For repeated wires, the optimized placement of repeaters offsets the delay advantage numbers of MWCNT bundles over copper wire. Technology scaling adversely impacts the delay advantage numbers of small diameter MWCNT bundles. As far as the worst-case crosstalk noise peak voltage is concerned, the large diameter MWCNT bundles also outperform both small diameter MWCNT bundles and copper wire for longer interconnects. However, for shorter interconnects, copper wire and small diameter bundles outclass the large diameter bundles due to their relatively larger time constant. We have compared our crosstalk analysis results with the earlier work to justify the validity of our proposed model and observed that the results with our model are in well conformity with the existing work. It is seen that even the tall Cu vias are not going to significantly affect the performance of MWCNT bundle interconnects. Twice the minimum width global level interconnects are the optimal choice to achieve the maximum delay advantage using MWCNT bundle interconnects in comparison with Cu-based interconnects. Finally, our analysis shows that from the performance and signal integrity perspective, the large diameter MWCNT bundles are a suitable alternative to both small diameter MWCNT bundles and copper interconnects for future integrated circuit technology generations.

Performance and analysis of temperature dependent multi-walled carbon nanotubes as global interconnects at different technology nodes

A temperature dependent performance in terms of power delay product (PDP) of multi-walled carbon nanotube (MWCNT) bundle interconnect has been analyzed for temperature range from 200 to 450 K at three different technology nodes viz. 32, 22 and 16nm. A similar analysis is performed for copper interconnect and results are compared with MWCNT bundle interconnect. Comparative results revealed that delay and PDP is increased with rise in temperature ranging from 200 to 450 K. It has also been observed that the temperature dependent MWCNT bundle interconnect gives better performance in terms of delay, power and PDP as compared to copper interconnect for three technology nodes at global interconnect length.

Impact of the atomic layer deposition precursors diffusion on solid-state carbon nanotube based supercapacitors performances

A study on the impact of atomic layer deposition (ALD) precursors diffusion on the performance of solid-state miniaturized nanostructure capacitor array is presented. Three-dimensional nanostructured capacitor array based on double conformal coating of multiwalled carbon nanotubes (MWCNTs) bundles is realized using ALD to deposit Al2O3 as dielectric layer and TiN as high aspect-ratio conformal counter-electrode on 2 μm long MWCNT bundles. The devices have a small footprint (from 100 μm2 to 2500 μm2) and are realized using an IC wafer-scale manufacturing process with high reproducibility (≤0.3E-12F deviation). To evaluate the enhancement of the electrode surface, the measured capacitance values are compared to a lumped circuital model. The observed discrepancies are explained with a partial coating of the CNT, that determine a limited use of the available electrode surface area. To analyze the CNT coating effectiveness, the ALD precursors diffusions inside the CNT bundle is studied using a Knudsen diffusion mechanism.

Photosynthetic reaction centre/carbon nanotube bundle composites

Since their discovery, carbon nanotubes (CNTs) have attracted intense attention to broad range of potential applications. In contrast to the 1D isolated single‐walled carbon nanotubes (SWCNT), 2D films or bundles made of thousands of tubes have been introduced as more advantageous building blocks for new types of applications in mechanically flexible and stretchable, optically transparent electronic systems. In our experiments, we combined photosynthetic reaction centre proteins, the light energy converter units in living cells, purified from purple bacteria, with multiwalled carbon nanotube (MWCNT) bundles. The change in the conductivity of the bare MWCNT bundles and the RC/MWCNT composite after light excitation was measured and compared. We found that the electrical conductivity under light excitation depends on the intrinsic conductivity of individual tubes within the bundles and on structural characteristics, like geometry (diameter, length, spatial arrangement, interconnects, etc.) and the electronic coupling with the RCs.

High Production of Carbon Nanotube Bundles with Fe<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> Catalyst

In this study, Fe2O3/Al2O3 catalyst was prepared by using co-precipitation method. This catalyst weight was varied from 0.1 to 0.5 g and multiwalled carbon nanotubes (MWCNTs) bundles were synthesized with ethylene as a carbon precursor at reaction temperature of 800°C by using floating catalytic chemical vapor deposition reactor. The grown MWCNTs bundles were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The obtained data revealed that as prepared CNTs actually existed in bundles and these should be attributed to the Fe2O3/Al2O3 catalyst, as transition metal Mo was not used in the catalyst. It was noted that an increase in weight of the catalyst significantly affects the quality, quantity, crystallinity, diameter and the growth of nanotubes bundles. Nanotubes yield increased with an increase in Fe2O3/Al2O3 weight. The carbon yield obtained with different weights of Fe2O3/Al2O3 was ranging from 68-93%. However, the surface defects in the grown tubes were also increased with an increase in the catalyst weight. High purity and high yield with the low surface defects was found for 0.3 g catalyst. It was found that less value of ID/IG ratio (0.78) was obtained in case of 0.3 g catalyst which indicated the structural perfection and low defect levels. The average outer diameter of the grown CNTs bundles were ranged from 240 to 550 nm. The formation of CNTs bundles were found defective with few black spots and impure above and below the use of 0.3 g catalyst.

Modeling a copper/carbon nanotube composite for applications in electronic packaging

A model is developed to determine the current density for a copper/carbon nanotube matrix configured as through silicon vias, an appropriate structure for interconnect applications. The electrical behavior of aligned carbon nanotube bundles mixed with copper at varying ratios is studied. The impact of the carbon nanotube dimensions and joule heating on electrical properties are analyzed. The results are compared for copper combined with single-walled carbon nanotube bundles and copper combined with multi-walled carbon nanotube bundles. The results suggest that through silicon vias filled with a copper/carbon nanotube matrix exhibit a more homogeneous current distribution with reduced skin effect compared to vias filled with only copper.

Imaging of soft material with carbon nanotube tip using near-field scanning microwave microscopy.

In this manuscript, a near-field scanning microwave microscope (NSMM) of our own design is introduced while using a multi-walled carbon nanotube (MWCNT) bundle as the tip (referred to as 'CNT tip'). Clear images of gold-patterned numbers, photoresist stripes and corneal endothelial cells (cell line B4G12) were obtained by mapping the resonant frequency fr and S11 amplitude of a given area while the NSMM is operating in tapping mode. The CNT tip helps to improve image quality and reveals more information about the sample as compared to a traditional metallic tip. The CNT tip is flexible and does not scratch the surface of the sample during the scan, which is useful for imaging soft material in biological science. In the imaging of the B4G12 endothelial cells, the nuclei and cytoplasm can be clearly distinguished from the rest of the cell and its surrounding medium.