We demonstrate the efficient chemical vapor deposition synthesis of singlewalled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis.

Among all known materials, we found that a forest of vertically aligned single-walled carbon nanotubes behaves most similarly to a black body, a theoretical material that absorbs all incident light. A requirement for an object to behave as a black body is to perfectly absorb light of all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition. We found a material that can absorb light almost perfectly across a very wide spectral range (0.2-200 m). We attribute this black body behavior to stem from the sparseness and imperfect alignment of the vertical single-walled carbon nanotubes.absorbance ͉ emissivity ͉ reflectance A black body is a theoretical object that absorbs all light that falls on it, because no light is transmitted or reflected (1). As a result, it appears perfectly black at room temperature and is the most efficient thermal absorber and emitter because any object at thermal equilibrium will emit the same amount of light as it absorbs at every wavelength. The radiation spectrum of a black body is determined solely by the temperature and not by the material, properties, and structure. These features, as an ideal source to emit or absorb radiation, make the black body valuable for many applications. For example, because the black body efficiently converts light to heat, it has great importance to solar energy collectors (2-5) and infrared thermal detectors, such as pyroelectric sensors (6-8). As a perfect emitter of radiation, a hot material with black body behavior would create an efficient infrared heater and would be valuable for heat liberation (9), particularly in space or in a vacuum where convective cooling is negligible.A requirement for an object to behave as a black body is that it perfectly absorbs light of all wavelengths; yet, in reality, black bodies do not exist. Emissivity is a measure of how similar an object is to a black body and is defined as the ratio of the energy radiated by that object and by a black body. Therefore, a black body would possess emissivity of unity for all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition, and thus, the emissivity of any real object is less than unity and is wavelength dependent.A good approximation of a black body is a cavity; however, this structure limits its utility. A material exhibiting black body behavior would solve this structural limitation and increase its practical usefulness. Hence, various processes and materials have been developed to blacken the surface by chemical treatment (10, 11), plating (4-6), and painting (8). Despite these efforts, emissivities for black coatings (Astro Black), chemically treated black surfaces (Hino Black), and microscale needle-like structure of nickel-phosphorus alloy (Anritsu Black) can be as high as 0.96 at 5-9 m but decreases notably at Ͼ9 m (Fig...

Here we investigate the kinetics of water-assisted CVD (henceforth denoted as supergrowth CVD) by a quantitative time-evolution analysis based on a simple growth model. We found that the supergrowth can be well described by a model where the dynamics of the catalyst activity is treated similar to radioactive decay. An in-depth analysis based on this growth model revealed the kinetics of the supergrowth CVD, showing a scale relationship between the carbon source and water, and elucidated the role of water as a catalyst activity enhancer and preserver.

We have succeeded in synthesizing vertically aligned doubled-walled carbon nanotube (DWNT) forests with heights of up to 2.2 mm by water-assisted chemical vapour deposition (CVD). We achieved 85% selectivity of DWNTs through a semi-empirical analysis of the relationships between the tube type and mean diameter and between the mean diameter and the film thickness of sputtered Fe, which was used here as a catalyst. Accordingly, catalysts were engineered for optimum DWNT selectivity by precisely controlling the Fe film thickness. The high efficiency of water-assisted CVD enabled the synthesis of nearly catalyst-free DWNT forests with a carbon purity of 99.95%, which could be templated into organized structures from lithographically patterned catalyst islands.

In order to be useful as microelectromechanical devices, carbon nanotubes with well-controlled properties and orientations should be made at high density and be placed at predefined locations. We address this challenge by hierarchically assembling carbon nanotubes into closely packed and highly aligned three-dimensional wafer films from which a wide range of complex and three-dimensional nanotube structures were lithographically fabricated. These include carbon nanotube islands on substrates, suspended sheets and beams, and three-dimensional cantilevers, all of which exist as single cohesive units with useful mechanical and electrical properties. Every fabrication step is both parallel and scalable, which makes it easy to further integrate these structures into functional three-dimensional nanodevice systems. Our approach opens up new ways to make economical and scalable devices with unprecedented structural complexity and functionality.