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Through-silicon-via (TSV) interposers using silicon and copper represent a critical element in microelectronic packaging, as they bridge between fine-pitch inputs/outputs at the integrated circuit ...

Preserving the quality of carbon nanotubes (CNTs) is essential to fully utilize the characteristics in dispersions and other forms. To fabricate CNT dispersions retaining the quality, we propose to...

Suspended thin film carbon nanotubes with suitable mechanical strength are in high demand for applications such as sensors, particle filters, or thermoacoustic speakers. However, researchers working on the production and development of applications for thin films have found difficulty in evaluating their mechanical strength. This research shows the nano-indentation behavior of thin (

In this work, we demonstrate controlled introduction of O-functional groups on commercial carbon nanotube fibers (CNTFs) with different nanotube morphologies obtained by dry- and wet-spinning by treatment with gaseous ozone (O3(g)). Our test samples were (1) wet-spun fibers of smalldiameter (1–2 nm) singlewall (SW)-CNTs and (2) dry-spun fibers containing large-diameter (20 nm) multiwall (MW)-CNTs. Our results indicate that SW-CNTFs undergo oxygenation to a higher extent than MW-CNTFs due to the higher reactivity of SW-CNTs with a larger curvature strain. Oxygenation resulting from O3 exposure was evidenced as increase in surface O atomic% (at% by X-ray photoelectron spectroscopy, XPS) and as reductions in G/D (by Raman spectroscopy) as well as electrical conductivities due to changes in nanotube graphitic structure. By XPS, we identified the emergence of various types of O-functionalities on the fiber surfaces. After long duration O3 exposure (>300 s for SW-CNTFs and >600 s for MW-CNTFs), both sp2 C═O (carbonyl) and sp3 C–O moieties (ether/hydroxy) were observed on fiber surfaces. Whereas, only sp3 C–O (ether/hydroxy) components were observed after shorter exposure times. O3 treatment led to only changes in surface chemistry, while the fiber morphology, microstructure and dimensions remained unaltered. We believe the surface chemistry controllability demonstrated here on commercial fibers spun by different methods containing nanotubes of different structures is of significance in aiding the practical application development of CNTFs.

Carbon nanotubes (CNTs) have garnered tremendous attention as building blocks for self-supporting membranes owing to remarkable developments in the manufacturing technology of high-quality CNT films. CNT films are expected to be applied in a wide range of applications, such as ultrafiltration membranes and as switching or sensing elements in microelectromechanical systems. However, the main challenge has been in fabricating CNT films by versatile and scalable processes suitable for industrial production while retaining lab-scale high performance. In this work, we succeed in fabricating macroscale (10 cm2) free-standing CNT films with thicknesses as low as 200 nm showing tensile strengths of ∼166 MPa by simple, versatile, and scalable blade-coating of CNT suspensions. Our study demonstrates that it is possible to control CNT film bundle size distribution and pore structure by controlling the CNT dispersibility and entanglement in the suspensions. We find that controlling bundle size distribution, pore structure uniformity, and packing can lead to five-fold, four-fold, and three-fold higher tensile strengths, fracture strain, and Young’s modulus, respectively, compared to films with poorer uniformity and packing.

We propose vacuum annealing to purify carbon nanotube wires (CNTWs) manufactured from surfactant dispersions by removing residual carbonaceous impurities (surfactant and solvent) included during wire-spinning. We analysed the CNTW purity post-annealing vs. treatment temperature and time by scanning electron microscopy, Raman spectroscopy, and thermogravimetry. Our results suggest that maximal purification is achieved after annealing at 800 °C (for ≥3 h) or at 1000 °C (for ≥1 h). The optimally purified wires show higher CNT content and G/D (∼93 wt% and >30, respectively) than the untreated wires (∼71 wt% and 25, respectively).

We report the importance of carbon nanotube (CNT) wire Cu electrodeposition parameters to fabricate structurally uniform CNT-Cu wire composites as potential lightweight Cu wire substitutes. We find promoting Cu deposition within CNT wires (CNTWs) and controlling surface deposition as key to obtaining composite wires containing a continuous Cu matrix and nanotubes distributed homogeneously (defined as structurally uniform CNT-Cu wires). We applied an optimized 2-step Cu electrodeposition to obtain the structurally uniform CNT-Cu wires. The 2-step electrodeposition included (i) initial Cu-seeding within hydrophobic CNTWs from an organic electrolyte (Cu(CH 3 COO) 2 in CH 3 CN), followed by (ii) seed growth by routinely used aqueous acidified CuSO 4 deposition. We find both steps crucial to realize internal Cu deposition and composite wires with even CNT/Cu mixing. We tested the effect of various electrodeposition parameters at both stages, such as current density, electrolyte concentration, and time on CNT-Cu wire surface and bulk Cu distribution. Our results show that only parameters allowing for slow (∼ 4 μg/h per cm of wire) and moderate (∼ 145 μg/h per cm of wire) Cu deposition rates during the seeding and seed growth stages, respectively lead to high internal Cu filling and controlled surface deposition and hence, structurally uniform CNT-Cu wires. These structurally uniform CNT-Cu wires obtained under optimal conditions are 2/3rd as light as Cu (density: ∼5.2 g/cm 3 ) with 40–45 vol% CNTs and 98 wt% Cu.

We report ultralong conducting lightweight multiwall carbon nanotube (MWCNT)-Cu composite wires with MWCNTs uniformly distributed in a continuous Cu matrix throughout. With a high MWCNT vol% (40–45%), the MWCNT-Cu wire density was 2/3rd that of Cu. Our composite wires show manufacturing potential because we used industrially compatible Cu electrodeposition protocols on commercial CNT wires. Further, we systematically varied Cu spatial distribution on the composite wire surface and bulk and measured the associated electrical performance, including resistivity (ρ), temperature dependence of resistance, and stability to current (measured as current carrying capacity, CCC in vacuum). We find that a continuous Cu matrix with homogeneous MWCNT distribution, i.e., maximum internal Cu filling within MWCNT wires, is critical to high overall electrical performances. Wires with maximum internal Cu filling exhibit (i) low room temperature ρ, 1/100th of the starting MWCNT wires, (ii) suppressed resistance-rise with temperature-increase and temperature coefficient of resistance (TCR) ½ that of Cu, and (iii) vacuum-CCC 28% higher than Cu. Further, the wires showed real-world applicability and were easily soldered into practical circuits. Hence, our MWCNT-Cu wires are promising lightweight alternatives to Cu wiring for weight-reducing applications. The low TCR is specifically advantageous for stable high-temperature operation, e.g., in motor windings.

In order to establish design rules for micro-supercapacitors (micro-SCs), the influence of electrode shape, specifically aspect ratio, was investigated on the operational speed of micro-SCs. The operational speed, as characterized by the relaxation time constant, was found to nonlinearly decrease (85 to ∼0.5 ms) as the electrode aspect ratio increased (0.2 to 7). This was achieved by simplifying the electrode design to a basic parallel electrode geometry. In so doing, all factors, such as electrode height, volume, electrolyte volume, inter-electrode separation, etc. could be maintained while adjusting the electrode aspect ratio (AR). In addition, the results showed that the relaxation time constant showed only moderate improvement for aspect ratios above 1, illustrating the limitation on this single shape parameter. Investigation into the underlying reasons for this behavior showed that the observed dependence of the relaxation time constant with the electrode AR originated from differences in the electrolyte resistance within the electrode for each electrode shape as determined by electrochemical impedance spectroscopy. Although these results demonstrate that the operational speed of a micro-SC can be improved by increasing the electrode AR, our results also show that this factor alone is insufficient to improve the speed into the microsecond regime within our experimental scope.

We demonstrate anisotropic, vertical deep etching of graphite and densely packed carbon nanotube (CNT) thick layer beyond the micrometer scale, which representing the first step toward nanocarbon bulk micromachining. This micromachining process is compatible with standard lithography and therefore allows the fabrication of graphite and CNT architectures with 1 μm lateral resolution and up to 10 μm scale depth.

New lithographically processable materials with high ampacity are in demand to meet the increasing requirement for high operational current density at high temperatures existing in current pathways within electronic devices. To meet this demand, we report an approach to fabricate a high ampacity (similar to 100 times higher than Cu) carbon nanotube-copper (CNT-Cu) composite into a variety of complex nano-scale, planar and multi-tiered current pathways. The approach involved the use of a two-stage electrodeposition of copper into a pre-patterned template of porous, thin CNT sheets acting as the electrode. The versatility of this approach enabled the realization of completely suspended multi-tier, dielectric-less 'air-gap' CNT-Cu circuits that could be electrically isolated from each other and are challenging to fabricate with pure Cu or any metal. Importantly, all such complex structures, ranging from 500 nm to 20 mu m in width, exhibited similar to 100-times higher ampacity than any known metal, with comparable electrical conductivity as Cu. In addition, CNT-Cu structures also exhibited a superior temperature stability compared to the similar to 10-times wider Cu counterparts. We believe that the combination of our approach and the properties demonstrated here are vital achievements for the future development of efficient and powerful electrical devices.

A method for the selective semiconducting single-walled carbon nanotube (SWCNT) growth over a continuous range from 67% to 98%, within the diameter range of 0.8-1.2 nm, by the use of a "catalyst conditioning process" prior to growth is reported. Continuous control revealed an inverse relationship between the selectivity and the yield as evidenced by a 1000-times difference in yield between the highest selectivity and non-selectivity. Further, these results show that the selectivity is highly sensitive to the presence of a precise concentration of oxidative and reductive gases (i.e. water and hydrogen), and the highest selectivity occurred along the border between the conditions suitable for high yield and no-growth. Through these results, a phenomenological model has been constructed to explain the inverse relationship between yield and selectivity based on catalyst deactivation. We believe our model to be general, as the fundamental mechanisms limiting selective semiconducting SWCNT growth are common to the previous reports of limited yield.

Clothes represent a unique textile, as they simultaneously provide robustness against our daily activities and comfort (i.e., softness). For electronic devices to be fully integrated into clothes, the devices themselves must be as robust and soft as the clothes themselves. However, to date, no electronic device has ever possessed these properties, because all contain components fabricated from brittle materials, such as metals. Here, we demonstrate robust and soft elastomeric devices where every component possesses elastomeric characteristics with two types of single-walled carbon nanotubes added to provide the necessary electronic properties. Our elastomeric field effect transistors could tolerate every punishment our clothes experience, such as being stretched (elasticity: ∼ 110%), bent, compressed (4.0 MPa, by a car and heels), impacted (6.26 kg m/s, by a hammer), and laundered. Our electronic device provides a novel design principle for electronics and wide range applications even in research fields where devices cannot be used.

We have developed the coating and microfabrication technique of the single walled carbon nanotubes and its composite with rubbers in the way compatible to the conventional device technology in order to incorporate the unique properties of SWCNTs, such as diversity of electrical properties depending on the charity, mechanical flexibility and stretchability arising from the formation of network structure, with device applications. Utilizing the process technologies, we have recently succeeded in assembling the field effect transistor of all rubbery materials on the rubber substrate, demonstrating that it exhibits the transistor performance comparable to the conventional CNT-transistors and significant tolerance to the mechanical loadings. The stretchability and robustness of our FET is promising for the wearable electronics, especially which is used for human body.

A rational torsion sensing material was fabricated by wrapping aligned single-walled carbon nanotube (SWCNT) thin films onto the surface of a rod with a predetermined and fixed wrapping angle without destroying the internal network of the SWCNTs within the film. When applied as a torsion sensor, torsion could be measured up to 400 rad/meter, that is, more than 4 times higher than conventional optical fiber torsion sensors, by monitoring increases in resistance due to fracturing of the aligned SWCNT thin films.

We report a general approach to overcome the enormous obstacle of the integration of CNTs into devices by bonding single-walled carbon nanotubes (SWNTs) films to arbitrary substrates and transferring them into densified and lithographically processable "CNT wafers". Our approach allows hierarchical layer-by-layer assembly of SWNTs into organized three-dimensional structures, for example, bidirectional islands, crossbar arrays with and without contacts on Si, and flexible substrates. These organized SWNT structures can be integrated with low-power resistive random-access memory.

We present research progress made in developing copper/carbon nanotube composites (Cu/CNT) to fulfil a growing demand for lighter copper substitutes with superior electrical, thermal and mechanical performances. Lighter alternatives to heavy copper electrical and data wiring are needed in automobiles and aircrafts to enhance fuel efficiencies. In electronics, better interconnects and thermal management components than copper with higher current- and heat-stabilities are required to enable device miniaturization with increased functionality. Our literature survey encouragingly indicates that Cu/CNT performances (electrical, thermal and mechanical) reported so far rival that of Cu, proving the material's viability as a Cu alternative. We identify two grand challenges to be solved for Cu/CNT to replace copper in real-life applications. The first grand challenge is to fabricate Cu/CNT with overall performances exceeding that of copper. To address this challenge, we propose research directions to fabricate Cu/CNT closer to ideal composites theoretically predicted to surpass Cu performances (i.e. those containing uniformly distributed Cu and individually aligned CNTs with beneficial CNT–Cu interactions ). The second grand challenge is to industrialize and transfer Cu/CNT from lab bench to real-life use. Toward this, we identify and propose strategies to address market-dependent issues for niche/mainstream applications. The current best Cu/CNT performances already qualify for application in niche electronic device markets as high-end interconnects. However, mainstream Cu/CNT application as copper replacements in conventional electronics and in electrical/data wires are long-term goals, needing inexpensive mass-production by methods aligned with existing industrial practices. Mainstream electronics require cheap CNT template-making and electrodeposition procedures, while data/electrical cables require manufacture protocols based on co-electrodeposition or melt-processing. We note (with examples) that initiatives devoted to Cu/CNT manufacturing for both types of mainstream applications are underway. With sustained research on Cu/CNT and accelerating its real-life application, we expect the successful evolution of highly functional, efficient, and sustainable next-generation electrical and electronics systems.

We present the influence of density, structural regularity, and purity of carbon nanotube wires (CNTWs) used as Cu electrodeposition templates on fabricating homogeneous high-electrical performance CNT–Cu wires lighter than Cu. We show that low-density CNTWs ( 90 wt %) are essential for making homogeneous CNT–Cu wires. These homogeneous CNT–Cu wires show a continuous Cu matrix with evenly mixed nanotubes of high volume fractions (~45 vol %) throughout the wire-length. Consequently, the composite wires show densities ~5.1 g/cm3 (33% lower than Cu) and electrical conductivities ~6.1 × 104 S/cm (>100 × CNTW conductivity). However, composite wires from templates with higher densities or structural inconsistencies are non-uniform with discontinuous Cu matrices and poor CNT/Cu mixing. These non-uniform CNT–Cu wires show conductivities 2–6 times lower than the homogeneous composite wires.

Increased portability, versatility and ubiquity of electronics devices are a result of their progressive miniaturization, requiring current flow through narrow channels. Present-day devices operate close to the maximum current-carrying-capacity (that is, ampacity) of conductors (such as copper and gold), leading to decreased lifetime and performance, creating demand for new conductors with higher ampacity. Ampacity represents the maximum current-carrying capacity of the object that depends both on the structure and material. Here we report a carbon nanotube–copper composite exhibiting similar conductivity (2.3–4.7 × 105 S cm−1) as copper (5.8 × 105 S cm−1), but with a 100-times higher ampacity (6 × 108 A cm−2). Vacuum experiments demonstrate that carbon nanotubes suppress the primary failure pathways in copper as observed by the increased copper diffusion activation energy (∼2.0 eV) in carbon nanotube–copper composite, explaining its higher ampacity. This is the only material with both high conductivity and high ampacity, making it uniquely suited for applications in microscale electronics and inverters., High electrical conductivity and ampacity are usually mutually exclusive properties. Here, in a carbon nanotube–copper composite, Subramaniam et al. achieve a similar conductivity to copper, but with a hundred fold increase in current carrying capacity.

We report the investigation on the reproducibility of micro-scale electric double layer capacitors (micro-EDLCs). The micro-EDLC components were fabricated parallel using photolithography, wet and dry processing. Electrodes of the micro-EDLCs are highly dense packed Single Wall Carbon Nanotubes (SWCNTs) that form a mesh structure. The micro- EDLCs are connected 1-10 in series and in parallel being unified electrical circuits to tune the capacitance and the operational voltage. To confirm the reproducibility of the cells as well as the yield we performed electrochemical measurements in order to define the performance uniformity between cells strings and individual cells connected in a string. For 1-10 cells in series and in parallel the trends for the capacitance and operational voltage satisfied electrophysics rules governing cells addition. However, the measurements of the individual cells in a string revealed the significant performance discrepancy that might result in a shorten life cycling of a circuit.