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...

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Variations in molecular electronic structures related to conformational change are exceedingly attractive because of their key role in the understanding and development of functional processes in molecular electronics and biology. We observed, for the first time, the novel phase switching of a photoactive isomeric molecule, N-(2-mercaptoethyl)-4-phenylazobenzamide (Azo molecule) at a single-molecule level, which exhibits a distinctive change in the conductive characteristic under scanning tunneling microscope (STM) measurement. In comparison with the results obtained by the measurement of photoactive isomerization of the isolated Azo molecule, which was performed also for the first time, the observed characteristics are attributed to the results of the trans and cis phase transformation of the Azo molecule, under the condition of an external electric field and current flow. A specific point is that the potential landscape of the system is controllable by the electric field and provides a conformational stability with asymmetric bias dependence resulting in rectification.

A highly active iron-nitrogen-doped carbon nanotube catalyst for the oxygen reduction reaction (ORR) is produced by employing vertically aligned carbon nanotubes (VA-CNT) with a high specifi c surface area and iron(II) phthalocyanine (FePc) molecules. Pyrolyzing the composite easily transforms the adsorbed FePc molecules into a large number of iron coordinated nitrogen functionalized nanographene (Fe-N-C) structures, which serve as ORR active sites on the individual VA-CNT surfaces. The catalyst exhibits a high ORR activity, with onset and halfwave potentials of 0.97 and 0.79 V, respectively, versus reversible hydrogen electrode, a high selectivity of above 3.92 electron transfer number, and a high electrochemical durability, with a 17 mV negative shift of E 1/2 after 10 000 cycles in an oxygen-saturated 0.5 M H 2 SO 4 solution. The catalyst demonstrates one of the highest ORR performances in previously reported any-nanotube-based catalysts in acid media. The excellent ORR performance can be attributed to the formation of a greater number of catalytically active Fe-N-C centers and their dense immobilization on individual tubes, in addition to more effi cient mass transport due to the mesoporous nature of the VA-CNTs.

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By means of scanning tunneling microscopy (STM), we succeeded for the first time in the quantitative analysis of the intramolecular conformation of a supramolecule, cyclodextrin (CyD) necklace, driven by hydrogen bonding. Contrary to the current model, based on macroscopic analyses, which indicates that all CyDs are arranged in head-to-head or tail-to-tail (secondary-secondary or primary-primary hydrogen bonding) conformation, about 20% head-to-tail (primary-secondary hydrogen bonding) conformation was found to exist in the molecule. In addition, comparing the STM results with the theoretical model of the necklace formation, the formation ratio of the tail-to-tail and head-to-tail conformations due to the strength difference between primary-primary and primary-secondary hydrogen bonds of CyDs was directly obtained, for the first time, to be 2:1.

We explored advantages of diverse carbon nanotube forests with tailored structures synthesized by water-assisted chemical vapor deposition (CVD) growth (supergrowth) from engineered catalysts. By controlling the catalyst film thickness, we synthesized carbon nanotube (CNT) forests composed from nanotubes with different size and wall number. With extensive characterizations, many interesting dependencies among CNT forest structures and their properties, which were unknown previously, were found. For example, multiwalled carbon nanotubes (MWNTs) showed superior electronic conductivity while single-walled carbon nanotubes (SWNTs) showed superior thermal diffusivity, and sparse MWNTs achieved lower threshold voltage for field emission than dense SWNTs. These interesting trends highlight the complexity in designing and choosing the optimum CNT forest for use in applications.

A gas shower system was introduced to improve the growth of single-walled carbon nanotube (SWNT) forests by controlling the gas flow direction. Delivery of gases from the top of the forest enabled direct and precise supply of ethylene and water vapor to the Fe catalysts. As such, this approach solved one of the limiting factors of water-assisted chemical vapor deposition method (CVD), that is, delivery of the very small optimum water level to the catalysts. Consequently, this approach improved SWNT forests growth stability, uniformity, reproducibility, carbon efficiency (32%), and catalyst lifetime. With this improved growth, we could synthesize a 1 cm tall forest with 1 x 1 cm size. Also we employed this approach to grow an A4 size SWNT forest to highlight the scalability of water-assisted CVD.