Cu-carbon Nanotube Research Articles

Effect of W concentration on the thermal stability of Cu-carbon nanotube hybrids

Carbon nanotube (CNT)-metal hybrids have been increasingly focused as a promising candidate for flexible circuit, but the metal agglomeration is their main failure mode under elevated temperature. In this study, we found the thermal stability of Cu-CNT hybrids can be significantly enhanced by W alloying. For CNT-Cu hybrids, the nano-grains suffered from serious agglomeration and growth after annealing at 473 K. And this phenomenon could be more significant by increasing annealing temperature. By adding W atoms with 4 at% into Cu matrix, the grain growth is weakened during annealing and the agglomeration is suppressed even at the temperature of 673 K. As the W content increases, the agglomeration is further suppressed at the higher temperature (873 K). The mechanism for the improved thermal stability was related to the stabilized grain boundaries by W atoms that were dissolved into Cu during deposition and further precipitated at higher W content or/and higher annealing temperatures.

A novel Cu-carbon nanotube sheet composite manufactured via the ARB process: A microstructural and mechanical study

A Cu matrix composite was designed and produced successfully by adding carbon nanotubes (CNTs) as reinforcement particles. The accumulative roll bonding (ARB) process was used to introduce the material in the shape of the sheet. The process was repeated up to five ARB cycles to obtain a uniform composite with good mechanical properties. Different amounts of CNTs were added to the matrix of Cu in order to evaluate the behavior of the CNTs in the matrix of the Cu. Microstructural evaluations confirmed that by increasing the ARB cycles, a uniform distribution of the CNTs was achieved. However, for Cu-1%CNT considerable numbers of unbonded areas led to weak bonding. Also, the material responded differently to the applied tensile test during loading. For low amounts of CNT-contained composites, the ultimate tensile strength (UTS) was increased in each ARB pass, but, for Cu-1%CNT composite, the UTS was the lowest. Also, microscopy observations were used to study the distribution/configuration of CNTs. The weak bonding of the Cu layers in some spots was attributed to the agglomeration of CNTs between the layers. Fractography of the samples after the tensile test, also, showed remarkable separation between the unbonded layers.

Deciphering the interaction mechanism between copper and polysulfides for enhanced performance and cost-efficiency in quasi-sodium-sulfur batteries

Room-temperature Na-S batteries with Al current collectors face the long-standing challenges of poor cycling performance and rate capability due to the serious sodium polysulfides (NaPSs) shuttling and sluggish reaction kinetics. Here, we demonstrate that a high-performance and low-cost quasi-Na-S battery can be realized by using the Cu@carbon nanotube (CNT) cathode host and unconventional Cu current collector (Cu-CC) in an ether electrolyte. Detailed ex-situ characterizations reveal that the Cu@CNT/S was transformed to NaPSs anchoring on Cu7S4 nanocrystals (~11 nm) during the cycling, forming the NaPS@Cu7S4/CNT cathode with robust sulfur immobilization and enhanced Na+ reaction kinetics. Moreover, the chemical interaction between NaPSs and Cu-CC in situ creates a robust Cu-CC/electrode interface with ultra-small resistance (< 4 Ω), greatly improving the electrode stability and charge transfer kinetics. The synergy of efficient NaPSs trapping and favorable Cu/electrode interface endows the quasi-Na-S battery with a moderate discharge plateau (around 1.2~1.75 V), excellent rate capability (396.9 mAh g-1 at 10 A g-1), and ultra-stable cycling performance (nearly no capacity decay over 1190 cycles). These features make it quite suitable for stable and cost-sensitive grid-scale applications.

Modeling and analyzing coupling noise effect of Cu-carbon nanotube composite through-silicon vias interconnects using NILT based

In the modern field of microelectronics, the performance of interconnects tends to decrease as the technology node advances. Therefore, Cu-CNT composite TSV interconnects are utilized due to their favorable performance. In this article, Cu-CNT composite TSV interconnects have been studied. The objective of this work was to propose an accurate method for calculating time domain coupling noise in 3D structures based on Cu-CNT composite TSVs. The equivalent lumped element circuit, the NILT method, and the T-matrix were exploited. Throughout the study, the influence of geometric parameters, temperature, and CNT filling ratio were examined. The proposed method has been validated using PSpice results. The obtained results have shown good performance and accuracy. The average percentage error observed is less than 1 %.

Potential of Copper-doped nanotubes as catalysts for SO2 oxidation

The SO2 oxidation by using of the Cu-carbon nanotube and Cu-borne nitride nanotube is investigated by LH and ER mechanisms. The Eformation values of CNT (7, 0), BNNT (7, 0), Cu-CNT (7, 0) and Cu-BNNT (7, 0) are negative and so the CNT (7, 0), BNNT (7, 0), Cu-CNT (7, 0) and Cu-BNNT (7, 0) are stable structures, from thermodynamic viewpoint. Based on abilities of Cu-CNT and Cu-BNNT, SO2 is joined to Cu-surface-O2* to produce intermediate. The cis-Cu-surface-O-SO2-O* in ER is more stable than corresponding complex in LH. Results indicated that the most stable complexes of O2, SO2 and SO3 species have lower EHLG values than other corresponding complexes, significantly. The ER pathway can be considered to oxidize of SO2 molecule via Cu-CNT and Cu-BNNT surfaces. The ER pathway is recommended pathway to creation of primary SO3 molecule as main step in SO2 oxidation (SO2 + Cu-surface-O2* → SO3 + Cu-surface-O*). Finally, the Cu-CNT and Cu-BNNT can catalyze oxidation of SO2, efficiently.

Modeling and Analysis of Cu-Carbon Nanotube Composites for Sub-Threshold Interconnects

The sub-threshold regime is suited for applications requiring ultra-low power consumption with low to medium frequency (tens to hundreds of MHz) of operation. Therefore, this paper presents electrical modeling and comprehensive analysis of copper-carbon nanotube (Cu-CNT) composite interconnects for sub-threshold circuit design. At lower operating frequencies, the effective complex conductivity of Cu-CNT composites in the nanoscale is formulated by developing an analytical model. Based on the proposed equivalent single conductor model, the frequency-dependent resistance and inductance of composite interconnects are computed. Finally, the sub-threshold crosstalk effect, transfer gain, and Nyquist stability of coupled Cu-CNT composite interconnect are analyzed using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ABCD</i> matrix approach.

An improvement of current driving and electrical conductivity properties incovetics

Compared to pure Cu, Cu lattice retaining carbon atoms, called a covetic material, can have better electrical conductivity. Furthermore, the incorporation of carbon nanostructures into Cu-alloys could improve the mechanical properties of Cu-alloys. In the simulation study, we investigated Joule heating due to applied DC current on molten Cu metal concerning how to improve current density of covetic materials. In addition, we will discuss interfacial effects on covetic-metal electrodes to meet better current driving performance. The covetic composite excited at one electrode (width = 10 nm) has a higher current drive capability as a value of 3.54 $10^{7}$ $A /m^{2}$, for 1000 A current at a temperature of 1073.2 K, this value is a constant while temperature is changing up to 1573.2 K. We measured the conductivity of the proposed covetic materials at various carbon nanotube densities at room temperature. Experimental results show the lowest resistivity value accomplished after mixing and temperature annealing as a value of 1.78 $10^{-8}$ $\Omega.m$, where the covetic sample has 1.27$\%$ carbon nanotube density, and that the electrical conductivity is superior to that of Cu-carbon nanotube composites previously reported.

Enhancement of electrical conductivity of carbon nanotube sheets through copper addition using reduction expansion synthesis

The ability to translate the high electrical conductivity of individual carbon nanotubes to bulk carbon nanotube materials has proven challenging. In this work, we present the use of reduction expansion synthesis to attach copper nanoparticles to the surface of tubes within carbon nanotube sheets. Those metallic particulates serve as a link between the tube strands in the carbon nanotube network and promote an increase in electrical conductivity. The reduction expansion synthesis process included the introduction of copper salts into the carbon nanotube structure and thermal treatment of the sheets in the presence of urea, under inert atmospheres. As a result, through the reduction process promoted by the urea decomposition byproducts, copper nanoparticles directly nucleate on the nanotube surface. The enhanced conductive nature of the Cu-carbon nanotube sheets observed establishes reduction expansion synthesis as an inexpensive, rapid and scalable alternative to increase the electrical conductivity of bulk carbon nanotube materials.

Interfacing Copper and Carbon Nanotubes with Titanium for Enhanced Electrical Performance

Hybrid Cu-carbon nanotube (CNT) conductors provide high electrical conductivities, while benefiting from the low temperature coefficient of resistance for CNTs. However, the poor interaction between Cu and CNTs requires a method of interfacing the components to improve the connectivity of the Cu-CNT conductor while preserving the electrical properties. Herein, Ti and Ni were evaluated as interfacial metals by thermally evaporating 10 nm layers onto a CNT conductor to assess the nanoscale morphology and impact on temperature dependent electrical properties. SEM analysis shows Ni deposits onto the CNT surface as a continuous layer in the form of discrete nanoscale crystallites. In contrast, Ti deposits a uniform layer along the surface of the CNT network. The Ni crystallites coalesce from the initially continuous layer upon exposure to temperatures up to 400 °C, while Ti is shown to remain as a stable uniform coating on the CNTs over such temperatures. Subsequent deposition of a 100 nm Cu layer onto CNT, Ti-CNT, and Ni-CNT conductors was performed to measure electrical stability with increasing annealing temperature. The 100 nm Cu layer forms gaps as it delaminates from the CNTs after exposure to 400 °C in a H2/Ar anneal when no adhesion metal is present, and the resistance per length (R/L) increases by 40%. The gaps formed in the Cu layer by the 400 °C anneal expose underlying CNTs, indicating poor surface interaction. The Cu-Ni-CNT conductor maintains Cu layer integrity from the adhesion metal, but exhibits a 125% increase in R/L for similar annealing conditions. In comparison, Ti sustains favorable interaction for the metal layers on CNTs, and achieves a 12% reduction in R/L after exposure to 400 °C. Temperature dependent electrical measurements performed under vacuum confirm the permanent change in electrical properties at elevated temperature for the hybrid conductors with an adhesion metal, demonstrating the increase in R/L for the Cu-Ni-CNTs and a decrease in R/L for Cu-Ti-CNT conductors. Thus, Ti emerges as an effective adhesion metal for use in metal-CNT conductor operation at elevated temperatures, demonstrating sustained adhesion up to 400 °C, and improvement in electrical properties for Cu-Ti-CNT conductors. Transitioning to scalable systems for integrated CNT conductors, a chemical vapor deposition (CVD) technique will be investigated as a delivery route for improved penetration of Ti into the CNT network.

Thermal expansion of Cu/carbon nanotube composite wires and the effect of Cu-spatial distribution

We report for the first time the coefficient of thermal expansion (CTE) of Cu/carbon nanotube (Cu/CNT) macroscopic wire composites and its strong dependence on CNT-Cu mixing. Homogeneous composite wires with 40 vol% nanotubes uniformly mixed in continuous Cu matrix showed CTE ∼4.42 × 10−6 °C-1 (∼26% Cu-CTE and similar to Si-CTE). The value matches with Turner’s model predictions implying that when nanotube-Cu shared contact is high, both low thermal expansion and high bulk modulus of CNTs contribute to offsetting Cu thermal expansion. In contrast, absence of or non-uniform CNT-Cu mixing i.e., reduced shared interface led to higher wire-composite CTEs (∼53−92% Cu-CTE) even with higher CNT vol%.

Understanding Electromigration in Cu-CNT Composite Interconnects: A Multiscale Electrothermal Simulation Study

In this paper, we report a hierarchical simulation study of the electromigration (EM) problem in Cu-carbon nanotube (CNT) composite interconnects. This paper is based on the investigation of the activation energy and self-heating temperature using a multiscale electrothermal simulation framework. We first investigate the electrical and thermal properties of Cu-CNT composites, including contact resistances, using the density functional theory and reactive force field approaches, respectively. The corresponding results are employed in macroscopic electrothermal simulations taking into account the self-heating phenomenon. Our simulations show that although Cu atoms have similar activation energies in both bulk Cu and Cu-CNT composites, Cu-CNT composite interconnects are more resistant to EM thanks to the large Lorenz number of the CNTs. Moreover, we found that a large and homogenous conductivity along the transport direction in interconnects is one of the most important design rules to minimize the EM.

Electrical Modeling and Analysis of Cu-CNT Heterogeneous Coaxial Through-Silicon Vias

An equivalent-circuit model of Cu-carbon nanotube heterogeneous coaxial through-silicon vias (HCTSVs) in 3-D integrated circuits (3-D ICs) is proposed in this paper. Based on the complex effective conductivity method, the resistances and inductances of Cu-single walled carbon nanotube (SWCNT) HCTSVs and Cu-multi walled carbon nanotube (MWCNT) HCTSVs are compared with that of Cu coaxial through-silicon vias (CTSVs). Furthermore, using the proposed model, the magnitudes of their insertion losses are compared. It is shown that the transmission performance of Cu-SWCNT HCTSVs with higher metallic fraction and Cu-MWCNT HCTSVs is better than that of Cu CTSVs, and the improvement of Cu-MWCNT HCTSVs is more obvious at high frequencies. Finally, the transmission characteristics of Cu-MWCNT HCTSVs are analyzed deeply to provide helpful design guidelines for them in future high-speed 3-D ICs.

High-Frequency Analysis of Cu-Carbon Nanotube Composite Through-Silicon Vias

A high-frequency analysis of Cu-carbon nanotube (CNT) composite through-silicon vias (TSVs) is conducted. The electrical modeling of the Cu-CNT composite TSVs is performed, with the effective complex conductivity formulated for accurate characterization of kinetic inductance. It is shown that, after codepositing CNT with Cu, the electrical conductivity of the TSVs can be improved and the influence of kinetic inductance variation can be suppressed in comparison with the CNT TSVs. On the other hand, the Cu-CNT composite TSVs can exhibit little compromise in performance yet much enhanced reliability by comparison to the Cu counterpart. That is, the Cu-CNT composite TSVs can provide a better tradeoff between reliability and performance than the Cu and CNT counterparts.

Analysis of Load Transfer Mechanism in Cu Reinforced with Carbon Nanotubes Fabricated by Powder Metallurgy Route

In this research, ductile and high-strength Cu-carbon nanotube (Cu-CNT) composites with different volume fractions of CNTs were fabricated using powder metallurgy route including mechanical milling and hot pressing and microstructure and tensile properties of the resulting materials were studied. Microstructural characterization through scanning electron microscope and quantifying the CNT agglomeration revealed that uniform dispersion of CNTs in Cu matrix decreases with increasing CNT volume fraction. In case of the higher volume fraction of CNTs (i.e., 8 vol.%), ~ 40% of CNTs were observed as agglomerates in the microstructure. Compared to unreinforced Cu, the yield and ultimate tensile strengths increased considerably (about 33% and 12%, respectively) with incorporation of CNTs up to 4 vol.%, but remained constant afterward. Meanwhile, the elongation decreased from 15.6% for Cu to 6.9% for Cu with 8 vol.% CNT. The relationship between the change in yield strength of the composite and the microstructure was investigated using analytical models. The results showed good consistency between calculated and measured data when the negative effect of CNT agglomerates in the models were taken into account.

Microstructural Characterization and Consolidation of Severely Deformed Copper Powder Reinforced with Multiwalled Carbon Nanotubes

In this paper, the mechanical milling process for various durations was used to generate a homogeneous distribution of 1 wt.% carbon nanotube within Cu powder. E ects of milling time on morphology, microstructure, and microhardness of the powder were studied. The results showed that work hardened Cu-carbon nanotube nanocomposite powder with nanosized grains can be fabricated by the mechanical milling of the elemental materials. The addition of carbon nanotubes accelerated the morphological and microstructural evolution during the mechanical milling and in uenced the compressibility of the powder. The compressibility behavior of the powder was analyzed using analytical models and used to estimate the strength of the powder. The nanocomposite compacts were sintered in vacuum and showed the maximum relative density of ≈91% at optimum condition.

Study of Mechanical Properties of an LM24 Composite Alloy Reinforced with Cu-CNT Nanofillers, Processed Using Ultrasonic Cavitation

This study investigates the effect of Cu-Carbon Nanotube (Cu-CNT´s) composite powders on the mechanical properties of an Al-Si9.5-Cu4-Fe1.3 wt.% (LM24) aluminium matrix composite (AMC). Carbon nanotubes (CNT’s) can exhibit exceptional mechanical properties, e.g. stiffness up to 1000 GPa and strength in the order of 100 GPa. In recent years there has been significant scientific interest in improving properties in conventional alloys, via fabricating CNT metal matrix composites in order to attempt to harness their extraordinary attributes. In this study mechanically alloyed Cu-CNTS powders were added to molten LM24. The melt was processed using ultrasonic cavitation and subsequently high pressure die casting to form as-cast tensile specimens. SEM results indicate that CNT’s can be successfully introduced into the melt using this method. Compared to the unreinforced alloy, the CNT additions resulted in an increment (~20±10 MPa) to both ultimate tensile strength and yield strength, with a corresponding decline (~1±0.5l %) in elongation. This observed increase in strengthening may be attributed to the CNT’s pinning and hindering both grain boundary and dislocation migration during applied loading. Interestingly, no significant difference in properties were found with an increase in the CNT content (from 0.05 to 0.1 wt.%) potentially indicating a saturation limit.

Strong and ductile nanostructured Cu-carbon nanotube composite

Nanocrystalline carbon nanotube (CNT)—reinforced Cu composite (grain size &amp;lt;25 nm) with high strength and good ductility was developed. Pillar testing reveals that its strength and plastic strain could be as large as 1700 MPa and 29%, respectively. Compared with its counterpart made under the same condition, an addition of 1 wt % CNTs leads to a dramatic increase in strength, stiffness and toughness without a sacrifice in ductility. Microstructural analysis discloses that in the Cu matrix, CNTs could be distributed either at grain boundaries or inside grains and could inhibit dislocation nucleation and motion, resulting in an increase in the strength.

Processing and characterization of nanostructured Cu-carbon nanotube composites

Carbon nanotube (CNT) reinforced nanostructured Cu matrix composite with a grain size less than 25 nm has been successfully fabricated via a combination of ball milling and high-pressure torsion. CNTs were found to be homogeneously dispersed into the metal matrix, leading to grain refinement with a narrow grain size distribution and significant increase in hardness.

Electromigration Studies of Cu/Carbon Nanotube Composite Interconnects Using Blech Structure

The electromigration (EM) properties of pure Cu and Cu/carbon nanotube (CNT) composites were studied using the Blech test structure. Pure Cu and Cu/CNT composite segments were subjected to a current density of 1.2 times 106 A/cm2. The average void growth rate of Cu/CNT composite sample was measured to be around four times lower than that of the pure copper sample. The average critical current-density-length threshold products of the pure Cu and Cu/CNT composites were estimated to be 1800 and 5400 A/cm, respectively. The slower EM rate of the Cu/CNT composite stripes is attributed to the presence of CNT, which acts as trapping centers and causes a decrease in the diffusion of EM-induced migrating atoms.