Crystalline and Electrical Property Improvement of Filtrated, Exfoliated Graphite Sheets by an In-Plane Current and Heating Treatment.

We report an approach to fabricate high conductivity graphite sheets based on a heat-and-current treatment of filtrated, exfoliated graphite flakes. This treatment combines heating (~ 900 °C) and in-plane electrical current flow (550 A·cm) to improve electrical conductivity through the reduction of crystalline defects. This process was shown to require only a 1-min treatment time, which resulted in a 2.

A sweet spot for highly efficient growth of vertically aligned single-walled carbon nanotube forests enabling their unique structures and properties.

We investigated the correlation between growth efficiency and structural parameters of single-walled carbon nanotube (SWCNT) forests and report the existence of a SWCNT "sweet spot" in the CNT diameter and spacing domain for highly efficient synthesis. Only within this region could SWCNTs be grown efficiently. Through the investigation of the growth rates for ∼340 CNT forests spanning diameters from 1.

The Application of Gas Dwell Time Control for Rapid Single Wall Carbon Nanotube Forest Synthesis to Acetylene Feedstock.

One aspect of carbon nanotube (CNT) synthesis that remains an obstacle to realize industrial mass production is the growth efficiency. Many approaches have been reported to improve the efficiency, either by lengthening the catalyst lifetime or by increasing the growth rate. We investigated the applicability of dwell time and carbon flux control to optimize yield, growth rate, and catalyst lifetime of water-assisted chemical vapor deposition of single-walled carbon nanotube (SWCNT) forests using acetylene as a carbon feedstock.

Scalability of the Heat and Current Treatment on SWCNTs to Improve their Crystallinity and Thermal and Electrical Conductivities.

We have investigated the scalability of our post-synthesis graphitization process for single-walled carbon nanotubes (SWCNTs), which applies heat and current to SWCNTs to improve the thermal and electrical conductivities. This investigation was performed by examining the relationship between the processing conditions and the amount of treated SWCNTs. Characterization of all cases of treated SWCNTs showed the same level of improvement of ~3 times to both the thermal and electrical conductivities and that the SWCNTs remained SWCNTs, i.

The relationship between the growth rate and the lifetime in carbon nanotube synthesis.

We report an inverse relationship between the carbon nanotube (CNT) growth rate and the catalyst lifetime by investigating the dependence of growth kinetics for ∼330 CNT forests on the carbon feedstock, carbon concentration, and growth temperature. We found that the increased growth temperature led to increased CNT growth rate and shortened catalyst lifetime for all carbon feedstocks, following an inverse relationship of a fairly constant maximum height. For the increased carbon concentration, the carbon feedstocks fell into two groups where ethylene/butane showed an increased/decreased growth rate and a decreased/increased lifetime indicating different rate-limiting growth processes.

Current treatment of bulk single walled carbon nanotubes to heal defects without structural change for increased electrical and thermal conductivities.

By applying electrical current with heat, we succeeded in improving the graphitization of single walled carbon nanotubes (SWCNTs) without increasing the diameter and wall number. At 800 °C, 150 A cm(-2) (1150 W cm(-2)) for 1 min, we achieved a 3.2-times increase in the Raman G- to D-band ratio, a 3.

Quantitative assessment of the effect of purity on the properties of single wall carbon nanotubes.

We quantitatively demonstrate the importance of high purity for the application of single wall carbon nanotubes (SWCNTs), materials solely composed of one surface, by examining the effects of carbon impurities on the electrical, thermal, and mechanical properties of both as-grown SWCNT forests and processed buckypaper. While decreases in properties were expected, our results showed the extreme sensitivity of SWCNT properties to carbonaceous impurities either through scattering in the individual SWCNTs or an inhibition of the ability to form inter-SWCNT junctions. Each property showed a nonlinear decrease (as high as 40%) with the addition of low levels of carbon impurities (∼15 wt%), which demonstrates that purity is as important as the crystalline structure.

Elastomeric thermal interface materials with high through-plane thermal conductivity from carbon fiber fillers vertically aligned by electrostatic flocking.

Electrostatic flocking is applied to create an array of aligned carbon fibers from which an elastomeric thermal interface material (TIM) can be fabricated with a high through-plane thermal conductivity of 23.3 W/mK. A high thermal conductivity can be achieved with a significantly low filler level (13.

Diameter control of single-walled carbon nanotube forests from 1.3-3.0 nm by arc plasma deposition.

We present a method to both precisely and continuously control the average diameter of single-walled carbon nanotubes in a forest ranging from 1.3 to 3.0 nm with ~1 Å resolution.

Influence of lengths of millimeter-scale single-walled carbon nanotube on electrical and mechanical properties of buckypaper.

The electrical conductivity and mechanical strength of carbon nanotube (CNT) buckypaper comprised of millimeter-scale long single-walled CNT (SWCNT) was markedly improved by the use of longer SWCNTs. A series of buckypapers, fabricated from SWCNT forests of varying heights (350, 700, 1,500 μm), showed that both the electrical conductivity (19 to 45 S/cm) and tensile strength (27 to 52 MPa) doubled. These improvements were due to improved transfer of electron and load through a reduced number of junctions for longer SWCNTs.

The infinite possible growth ambients that support single-wall carbon nanotube forest growth.

We report the virtually infinite possible carbon feedstocks which support the highly efficient growth of single-wall carbon nanotubes (SWCNTs) using on the water-assisted chemical vapor deposition method. Our results demonstrate that diverse varieties of carbon feedstocks, in the form of hydrocarbons, spanning saturated rings (e.g.

Absence of an ideal single-walled carbon nanotube forest structure for thermal and electrical conductivities.

We report the fundamental dependence of thermal diffusivity and electrical conductance on the diameter and defect level for vertically aligned single-walled carbon nanotube (SWCNT) forests. By synthesizing a series of SWCNT forests with continuous control of the diameter and defect level over a wide range while holding all other structures fixed, we found an inverse and mutually exclusive relationship between the thermal diffusivity and the electrical conductance. This relationship was explained by the differences in the fundamental mechanisms governing each property and the optimum required structures.

One hundred fold increase in current carrying capacity in a carbon nanotube-copper composite.

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.

A Fundamental Limitation of Small Diameter Single-Walled Carbon Nanotube Synthesis-A Scaling Rule of the Carbon Nanotube Yield with Catalyst Volume.

Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT forests continuously spanning a wide range of diameters (1.9-3.

Direct wall number control of carbon nanotube forests from engineered iron catalysts.

We present the direct wall number control of carbon nanotube (CNT) forests grown on engineered iron (Fe) catalysts in a catalytic chemical vapor deposition (CVD). Engineered Fe catalysts were fabricated by annealing thickness-tuned (0.8-3 nm) Fe films with small thickness variations prepared by a low-deposition-rate sputter deposition.

Diameter and density control of single-walled carbon nanotube forests by modulating Ostwald ripening through decoupling the catalyst formation and growth processes.

A continuous and wide range control of the diameter (1.9-3.2 nm) and density (0.

Unexpectedly high yield carbon nanotube synthesis from low-activity carbon feedstocks at high concentrations.

We report a new direction for highly efficient carbon nanotube (CNT) synthesis where, in place of conventional highly reactive carbon feedstocks at low concentrations, highly stable carbon feedstocks at high concentrations were shown to produce superior yields. We found that a saturated hydrocarbon that is considered to possess a low reactivity, delivered at high concentrations, could achieve an extremely high growth yield (2.5 times that when using ethylene).

Electron Density Modification of Single Wall Carbon Nanotubes (SWCNT) by Liquid-Phase Molecular Adsorption of Hexaiodobenzene.

Electron density of single wall carbon nanotubes (SWCNT) is effectively modified by hexaiodobenzene (HIB) molecules using liquid-phase adsorption. UV-Vis-NIR absorption spectra of the HIB-adsorbed SWCNT, especially in the NIR region, showed a disappearance of S transitions between the V1 valance band and the C1 conduction band of van Hove singularities which can be attributed to the effective charge transfer between HIB and the SWCNT. The adsorption of HIB also caused significant peak-shifts (lower frequency shift around 170 cm and higher shift around 186 cm) and an intensity change (around 100-150 cm and 270-290 cm) in the radial breathing mode of Raman spectra.

Alignment control of carbon nanotube forest from random to nearly perfectly aligned by utilizing the crowding effect.

Alignment represents an important structural parameter of carbon nanotubes (CNTs) owing to their exceptionally high aspect ratio, one-dimensional property. In this paper, we demonstrate a general approach to control the alignment of few-walled CNT forests from nearly random to nearly ideally aligned by tailoring the density of active catalysts at the catalyst formation stage, which can be experimentally achieved by controlling the CNT forest mass density. Experimentally, we found that the catalyst density and the degree of alignment were inseparably linked because of a crowding effect from neighboring CNTs, that is, the increasing confinement of CNTs with increased density.

Mutual exclusivity in the synthesis of high crystallinity and high yield single-walled carbon nanotubes.

We report the mutually exclusive relationship between carbon nanotube (CNT) yield and crystallinity. Growth conditions were optimized for CNT growth yield and crystallinity through sequential tuning of three input variables: growth enhancer level, growth temperature, and carbon feedstock level. This optimization revealed that, regardless of the variety of carbon feedstock and growth enhancer, the optimum conditions for yield and crystallinity differed significantly with yield/crystallinity, preferring lower/higher growth temperatures and higher/lower carbon feedstock levels.

Mechanically durable and highly conductive elastomeric composites from long single-walled carbon nanotubes mimicking the chain structure of polymers.

By using long single-walled carbon nanotubes (SWNTs) as a filler possessing the highest aspect ratio and small diameter, we mimicked the chain structure of polymers in the matrix and realized a highly conductive elastomeric composite (30 S/cm) with an excellent mechanical durability (4500 strain cycles until failure), far superior to any other reported conductive elastomers. This exceptional mechanical durability was explained by the ability of long and traversing SWNTs to deform in concert with the elastomer with minimum stress concentration at their interfaces. The conductivity was sufficient to operate many active electronics components, and thus this material would be useful for practical stretchable electronic devices.

Role of subsurface diffusion and Ostwald ripening in catalyst formation for single-walled carbon nanotube forest growth.

Here we show that essentially any Fe compounds spanning Fe salts, nanoparticles, and buckyferrocene could serve as catalysts for single-walled carbon nanotube (SWNT) forest growth when supported on AlO(x) and annealed in hydrogen. This observation was explained by subsurface diffusion of Fe atoms into the AlO(x) support induced by hydrogen annealing where most of the deposited Fe left the surface and the remaining Fe atoms reconfigured into small nanoparticles suitable for SWNT growth. Interestingly, the average diameters of the SWNTs grown from all iron compounds studied were nearly identical (2.

Gas dwell time control for rapid and long lifetime growth of single-walled carbon nanotube forests.

The heat history (i.e., "dwell time") of the carbon source gas was demonstrated as a vital parameter for very rapid single-walled carbon nanotube (SWNT) forest growth with long lifetime.

Tailoring temperature invariant viscoelasticity of carbon nanotube material.

Using carbon nanotubes (CNTs) as building blocks, we fabricated a viscoelastic material. In contrast to existing conventional materials where the stiffness (storage modulus) increases when the viscosity (damping ratio) decreases, both of these two aspects could be simultaneously improved for the viscoelastic CNT material. This allows fabricating both strong and highly viscous materials.