Nanotube Bundles Research Articles

Thermally aware performance analysis of single-walled carbon nanotube bundle as VLSI interconnects

A comparative performance analysis in terms of delay, power dissipation, power delay product (PDP), and crosstalk noise between SWCNT bundle interconnects with resistance estimated using conventionally (temperature independent model), and thermally aware model is investigated. The results are also compared with those of currently used copper interconnects at 22 nm technology node. It is observed that, with rise in temperature from 300 to 500 K, SWCNT bundles have a lower delay than that of copper interconnect at different lengths from 100 to $$1000\,\upmu \hbox {m}$$1000μm whereas reverse is true for power dissipation. The SPICE simulation results further reveal that for temperature variations ranging from 300 to 500 K, compared to conventional metal (copper) conductors, crosstalk noise voltage levels (positive peaks) in capacitively coupled SWCNT bundle, at the far end of victim line, are significantly low. Moreover, a relative average improvement in delay, power, and PDP using a thermally aware model in comparison with a temperature independent model is about 22.44, 7.59 and 31.96 %, respectively, with length variations from 100 to $$1000\,\upmu \hbox {m}$$1000μm, whereas for varied tube diameter is about 16.6, 5.6 and 19.72 %, respectively. The average relative improvement in the time duration reduction of victim output, for varied tube diameters, is about 21.7 % by using a thermally-aware model instead of a temperature-independent model of an SWCNT bundle resistance.

Heat capacity of one-dimensional chains of methane molecules in the outer grooves of carbon nanotube bundles

The heat capacity at constant pressure CP of 1D-chains of methane molecules adsorbed in the grooves on the outer surface of the bundles of closed single-walled nanotubes was measured in the temperature range from 2 to 60 K for the first time. The behavior of the temperature dependence of CP below 12 K indicates the presence of a Schottky-type anomaly originated from the tunneling between the lowest energy levels of the rotational spectra of the A, T, and E nuclear-spin species of methane molecules. The feature observed in the vicinity of 14 K is presumably caused by an orientational phase transition, in which the nature of the rotational motion of the molecules changes from libration to hindered rotation. It was found that the rotational heat capacity in the temperature range of 30–40 K is close to that of freely rotating methane molecules. An increase in the derivative dCP(T)/dT above 40 K and the feature in the CP(T) near 52 K are due to the decay of 1D chains of CH4.

Innovative Nanostructured Wicks for Heat Pipes

A good wicking structure is necessary for the design of a highly efficient heat pipe. Several unique aluminum oxide nanostructures were developed as wicks for heat pipes. The wicks were manufactured via an anodization process at various anodization voltages and etching times. This allows for the manufacture of spatially variable wicking structures that can be tuned for specific applications. The resulting nanostructures were characterized with a scanning electron microscope. Six distinct wicking structures are shown in Fig. 1. The honeycomb nanostructure is a self-ordered, hexagonal columnar array. The clumped nanotube structure is composed of bundles of nanotubes separated by deep grooves. The teepee nanostructure has a honeycomb bottom covered with a conical structure top. The horizontal nanofiber structure consists of nanofibers laying parallel to the substrate surface. The ridge network nanostructure is a multiscaled structure with nanoporous ridges. The clumped nanofiber structure is formed from long tangled fibers that meet in a thin ridge. Each of these structures has features useful for nucleation, evaporation, and condensation. These wicks will have many applications in the fields of heat pipes and two-phase heat transfer.

Molecular simulation of adsorption and separation of pure noble gases and noble gas mixtures on single wall carbon nanotubes

Grand Canonical Monte Carlo simulations were performed to systematically study the adsorption and separation of noble gases on single wall carbon nanotube (SWCNT) bundles. Pure noble gases, as well as binary and ternary mixtures, were simulated in carbon nanotube systems under various conditions. Adsorption data was collected at 100K and 300K over a wide range of pressures. Carbon nanotube bundles present distinct adsorption capacities towards different noble gases. In particular, larger and heavier noble gases are easier to be adsorbed at low pressure, while lighter atoms with smaller sizes can be better stored at high pressure. For noble gas mixtures with equal molar loadings, selective adsorption was observed and the selectivity inverted at different pressure ranges according to the choice of mixtures. Furthermore, the influence of loading proportion of the components on the adsorption behavior was investigated by varying the loading partial pressure in binary mixtures from 1% to 99%. The results suggest gas–CNT interactions dominate the adsorption selectivity at low loading conditions, whereas the entropic effect plays a more important role at high loadings.

Robust carboxylated polymer pores from a cyclic peptide template

Functionalized pores that are stable to chemical degradation are attractive for use in a variety of applications ranging from sensing to catalysis. Herein, robust polymer nanotube bundles decorated with carboxylate groups inside the pores have been developed in two steps from a cyclic peptide template containing polymerizable norbornene units. The cyclic peptide forms nanotube bundles of ca. 35 nm in diameter. Polymerization of the exposed norbornene units gives peptide–polymer hybrid nanotube bundles of ca. 100 nm diameter that have improved thermal and chemical stability compared to cyclic peptide nanotubes. Hydrolysis of the ester linkage connecting norbornene to the peptide scaffold and removal of the peptide provide robust polymer pores of ca. 100 nm that are not only chemically stable, but also have carboxylate groups in the pores. Such nanotube bundles with carboxylate groups can be potentially used for encapsulation of cations or biomimetic ion transport.

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.

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.

Propene adsorption on gold–palladium nanoalloys supported on bundle nanotubes

Propene adsorption on (Pd–Au)N nanoalloys supported on carbon nanotube (CNT) bundles has been investigated using molecular dynamics (MD) simulations at 300 K.

Tuning cation-binding selectivity and capacity via side chain-dependent molecular packing in the solid state.

Cavity-containing cation-binding pentameric macrocycles readily assemble, via side chain-dependent molecular packing, into either 1D nanotube bundles with the smallest being 10 nm in diameter or nanoplates of different sizes. The resultant nanostructures are able to selectively remove metal salts from aqueous solutions with varying selectivities and capacities.

Theoretical and experimental investigations of the Li storage capacity in single-walled carbon nanotube bundles

Lithium stored in interstitial sites reflects the actual low capacity observed from the 2nd cycle and beyond.

High-rate capability of bamboo-like single crystalline LiFePO4 nanotubes with an easy access to b-axis 1D channels of olivine structure

Bamboo-like vertically standing LFP nanotube bundles enable a better accessibility for Li-ion movement along 1D-channels in b-axis of olivine structure.

The influence of geometric heterogeneity of closed carbon nanotube bundles on benzene adsorption from the gaseous phase-Monte Carlo simulations

Benzene adsorption from the gaseous phase at 298 K and the thermodynamics of this process using Monte Carlo methods is studied. A series of closed single-walled carbon nanotube (SWCNT) bundles (triangular packing arrangement) with various distance between nanotubes is investigated. Isolated closed nanotube is treated as the reference system. Benzene is considered as a model compound to represent aromatics. Simulation results show the significant effect of the geometric heterogeneity on benzene adsorption as well as the enthalpy and entropy at low surface coverages. For insignificantly separated nanotubes and at low benzene uptakes, the entropy of the adsorbed phase is close to the entropy of solid benzene. Therefore, C6H6 molecules strongly interacting with walls are ordered in quasi-solid structures. At higher surface coverages, the ordering and packing of benzene molecules is liquid-like. The geometry of bundles (mutual position of SWCNTs) significantly influences the position and orientation of adsorbed molecules against the wall.

Defect-Free Carbon Nanotube Coils.

Carbon nanotubes are promising building blocks for various nanoelectronic components. A highly desirable geometry for such applications is a coil. However, coiled nanotube structures reported so far were inherently defective or had no free ends accessible for contacting. Here we demonstrate the spontaneous self-coiling of single-wall carbon nanotubes into defect-free coils of up to more than 70 turns with identical diameter and chirality, and free ends. We characterize the structure, formation mechanism, and electrical properties of these coils by different microscopies, molecular dynamics simulations, Raman spectroscopy, and electrical and magnetic measurements. The coils are highly conductive, as expected for defect-free carbon nanotubes, but adjacent nanotube segments in the coil are more highly coupled than in regular bundles of single-wall carbon nanotubes, owing to their perfect crystal momentum matching, which enables tunneling between the turns. Although this behavior does not yet enable the performance of these nanotube coils as inductive devices, it does point a clear path for their realization. Hence, this study represents a major step toward the production of many different nanotube coil devices, including inductors, electromagnets, transformers, and dynamos.

Review on carbon nanotubes and carbon nanotube bundles for gas/ion separation and water purification studied by molecular dynamics simulation

Water and air pollutants have huge impacts on the entire living system. In addition, the newly emerging nanopollutants, increasing global warming, and consequent climate changes are posing major threats to the freshwater or fresh air availability. This has made it urgent to invent an appropriate water/air treatment technology that removes nanopollutants and also desalinates water to a significant extent. Carbon-based nanomaterials have generated marvelous interest in a wide range of research activities due to their high adsorption capacities. Carbon nanotubes, carbon nanotube bundles, and related materials have potential applications in gas/ion separation and water purification. Recently, gas/ion separation and water purification through carbon-based nanomaterials have received increasing attention. This review summarizes the properties of carbon nanotubes and carbon nanotube bundles related to gas separation, ion separation, and water purification using molecular dynamics simulations. Membranes-based carbon nanomaterials show promise of water purification and gas separation. These attractive properties of carbon nanotubes-based and carbon nanotube bundles-based nanomaterials make them proper candidates for gas separation, gas molecular-sieving processes, and desalination purposes in nanoscale dimensions.

Exploration of the environmentally benign and highly effective approach for improving carbon nanotube homogeneity in aqueous system

The present research highlighted the use of different plant-based phytochemical extracts on the dissolution of carbon nanotubes (CNTs) bundles in aqueous solution. Three new plant extracts (i.e., Cinnamon, Barley grass and Androganis Pinnaculata) were introduced in this research on top of the previously studied green tea and tannic acid as dispersants. FT-IR results strongly suggest the evidence of phenolic-rich component containing within each plant. Further, significantly low quantity of plant extract was required to isolate CNTs based on spectroscopy data. The results also suggest the existence of an optimum CNTs/plant extract proportion to promote higher rate of CNTs dissolution. The high level of CNTs affinity toward water was vindicated via contact angle measurement, indicating the successful encapsulation of phenolic compound on CNTs sidewall. Thermal conductivity measurement data showed as high as 18 % enhancement at very low CNTs concentration relative to base fluid which was attributed to the well-dispersed CNTs complexes. The rheological measurements exhibit Newtonian behavior identical to water and produce negligible increase in viscosity (i.e., less than 3 %), by which when combine with the much higher increase in thermal conductivity, paves a favorable condition toward achieving highly efficient thermal transport medium.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology.

We demonstrate a method for the low temperature growth (350 °C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-κ dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

Molecular dynamics simulation of doxorubicin adsorption on a bundle of functionalized CNT

In this study, molecular dynamics simulation is used to investigate the adsorption of an anticancer drug, doxorubicin, on bundles of functionalized single-walled carbon nanotubes (SWNTs) in an aqueous solution. Carboxylic group has been selected as the functional group. Molecular dynamics (MD) simulations are performed for both separated systems containing a SWNT bundle and a functionalized carbon nanotube bundle, and results are compared with existing experimental data. MD results show that doxorubicin can be adsorbed on CNTs using different methods such as entrapment within CNT bundle, attachment to the side wall of the CNT, and adsorption on the CNT inner cavity. For functionalized CNT, the adsorption of drugs on the functional groups is essential for predicting the enhancement of drug loading on the functionalized nanotubes. Furthermore, the adsorption behavior of doxorubicin on CNTs is fitted with Langmuir and Freundlich isotherm models. The results show that Langmuir model can predict the adsorption behavior of doxorubicin on CNTs more accurately than Freundlich model does. As predicted by this isotherm model, the adsorption process of doxorubicin on CNTs is relatively difficult, but it can be improved by increasing the functional groups on the CNTs surface.

Improvements in the mechanical properties of carbon nanotube fibers through graphene oxide interlocking

Carbon nanotubes (CNTs) have attracted remarkable attention due to their high mechanical performance and low density which are desirable for application as lightweight materials in automotive and aerospace industries to improve fuel efficiency. However, CNT fibers generally exhibit far lower mechanical properties (strength, toughness, etc.) than individual CNTs due to the weak interfacial shear strength between adjacent shells, nanotubes, and nanotube bundles, causing insufficient load transfer. In this study, to improve the interfacial shear strength of the fibers, graphene oxide (GO) was infiltrated into the CNT fibers to interlock CNT bundles. GO was selected due to its high mechanical properties and similar carbon-based structure as the CNT fibers. In addition, GO interfaces are known to exhibit higher frictional forces for sliding contacts than those found for pristine graphene sheets, which makes it more desirable for enhancing the shear interactions. GO particles with a width of ∼40 nm, which match closely to the void size within fibers, were optimal for enhancing the mechanical properties of the CNT fibers. Tensile testing demonstrated optimized GO infiltrated CNT fibers exhibited improvement in: stiffness ∼100%, yield strength ∼110%, ultimate tensile strength ∼56%, and energy to failure ∼30% of pristine CNT fibers.

Multiple spectroscopic studies on the interaction of BSA with pristine CNTs and their toxicity against Donax faba

Enhanced biomedical applications of carbon nanotubes (CNTs) have necessitated the need for the fundamental understanding behind their interaction with biomolecules. Carbon nanotube bundles were dispersed with tween 20 to attain individual nanotubes that are active in UV–vis region. Plasmon resonance of dispersions was obtained at 252nm of 4.88eV. FT-Raman bands of dispersions of SWCNTs and MWCNTs at 1346 and 1573cm−1 corresponds to the existence of Disordered and Graphitic band of CNTs after dispersion. XRD revealed crystalline feature of graphitic structures of CNTs. SEM-EDAX showed tubular structures of CNTs along with the existence of lower percentage contents of metal impurities. Hyperchromic effect of BSA–CNT complex suggested the existence of ground state complex between them. Quenching nature of CNTs against the intrinsic fluorescence potential of BSA followed static mechanism. 3D fluorescence spectra of BSA confirmed the possibilities of their binding with CNTs via tryptophan and tyrosine residues, followed by the disturbances to their aromatic environment. Alterations were observed in the amide band position of FTIR spectra of BSA–CNT conjugates. Loss of alpha-helical structures and alteration in the tryptophan position were evidenced with respect to CD spectra. The toxicity profile of pristine and BSA–CNT conjugates were evaluated against Donax faba. On comparison with pristine CNTs, BSA–CNTs conjugates showed higher LC50 dose values. In addition, the histopathology of the tissues, treated with CNT–BSA conjugates has shown decreased effect on the cellular integrity rather than the pristine ones. Hence, the adsorption of biomolecules such as the proteins over CNTs surface could have possible effect on reducing their toxicity profile in nature.