Ryo Kitaura

Highly controlled acetylene accommodation in a metal-organic microporous material.

Metal–organic microporous materials (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage, separation and heterogeneous catalysis. One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls. This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

A layered ionic crystal of polar Li@C 60 superatoms

If the physical properties of C(60) fullerene molecules can be controlled in C(60) products already in use in various applications, the potential for industrial development will be significant. Encapsulation of a metal atom in the C(60) fullerene molecule is a promising way to control its physical properties. However, the isolation of C(60)-based metallofullerenes has been difficult due to their insolubility. Here, we report the complete isolation and determination of the molecular and crystal structure of polar cationic Li@C(60) metallofullerene. The physical and chemical properties of Li@C(60) cation are compared with those of pristine C(60). It is found that the lithium cation is located at off-centre positions in the C(60)-I(h) cage interior and that the [Li(+)@C(60)] salt has a unique two-dimensional structure. The present method of purification and crystallization of C(60)-based metallofullerenes provides a new C(60) fullerene material that contains a metal atom.

Fabrication of Metal Nanowires in Carbon Nanotubes via Versatile Nano-Template Reaction

A nano-template reaction has been developed to fabricate metal nanowires using metallofullerene nanopeapods (i.e., carbon nanotubes (CNTs) encapsulating endohedral metallofullerenes) as starting materials. In this nanometer-scale reaction, the structure of resulting products should possess specific low-dimensional structures, because of their uniform starting orientation of metallofullerene molecules and the rigid restriction of reaction space by the presence of walls of CNTs. Using the nano-template reaction, we have fabricated various Gd nanowires, including a single Gd atomic chain, a one-dimensional alignment of Gd squares, and Gd nanowires that correspond to a one-dimensional segment of the bulk close-packed structure. The same reaction, in principle, can be applied to fabricate more than 20 different types of metal nanowires in the CNTs, which simply are dependent on the use of the corresponding different types of metallofullerenes as encapsulates in the CNTs. The present novel reaction will provide a wide variety of unusual low-dimensional nanowires and nanomaterials in the CNTs, which have not been synthesized via the fabrication techniques that have been reported so far.

Direct chemical vapor deposition growth of WS2 atomic layers on hexagonal boron nitride.

Atomically thin transition metal dichalcogenides (TMDCs) have attracted considerable interest owing to the spin-valley coupled electronic structure and possibility in next-generation devices. Substrates are one of the most important factors to limit physical properties of atomic-layer materials, and among various substrates so far investigated, hexagonal boron nitride (hBN) is the best substrate to explore the intrinsic properties of atomic layers. Here we report direct chemical vapor deposition (CVD) growth of WS2 onto high-quality hBN using a 3-furnace CVD setup. Triangular-shaped WS2 grown on hBN have shown limited crystallographic orientation that is related to that of the underlying hBN. Photoluminescence spectra of the WS2 show an intense emission peak at 2.01 eV with a quite small fwhm of 26 meV. The sharp emission peak indicates the high quality of the present WS2 atomic layers with high crystallinity and clean interface.

Size-selective complexation and extraction of endohedral metallofullerenes with cycloparaphenylene.

A new strategy for the non-chromatographic extraction of metallofullerenes from solutions of arc-processed raw soot is based on the size-selective complexation with cycloparaphenylene (CPP). [11]CPP has a high affinity for Mx @C82 (x=1, 2); for example, Gd@C82 can be selectively extracted from a fullerene mixture by the addition of [11]CPP. This approach should open new opportunities in metallofullerene chemistry, including for the bulk extraction of metallofullerenes.

A simple alcohol-chemical vapor deposition synthesis of single-layer graphenes using flash cooling

We report the synthesis of single-layer graphenes from ethanol using, what we call, “flash cooling” just after chemical vapor deposition. The single-layer graphenes synthesized are high-quality and several micrometers in grain size as revealed by Raman spectroscopy. Detailed comparison of the cooling processes suggests that the single-layer graphene growth does not occur during the carbon precipitation but rather stems from surface diffusions of carbon on a nickel substrate. Because of the present simple and easiness for the large-scale synthesis under an inert gas atmosphere and at atmospheric pressure, the present method can easily be applied for the future large-scale and low-cost graphene production.

Rock‐Salt‐Type Crystal of Thermally Contracted C60 with Encapsulated Lithium Cation

Rock solid: fullerene-encapsulated Li(+) (Li(+)@C(60)) is an alkaline cation owing to the spherical shape and positive charge. Li(+)@C(60) crystallizes as a rock-salt-type crystal in the presence of PF(6)(-). The orientations of C(60) and PF(6)(-) (orange) are perfectly ordered below 370 K, and Li(+) (purple) hops within the cage. At temperatures below 100 K two Li(+) units are localized at two polar positions within each C(60) .

Growth of carbon nanotubes via twisted graphene nanoribbons.

Carbon nanotubes have long been described as rolled-up graphene sheets. It is only fairly recently observed that longitudinal cleavage of carbon nanotubes, using chemical, catalytical and electrical approaches, unzips them into thin graphene strips of various widths, the so-called graphene nanoribbons. In contrast, rolling up these flimsy ribbons into tubes in a real experiment has not been possible. Theoretical studies conducted by Kit et al. recently demonstrated the tube formation through twisting of graphene nanoribbon, an idea very different from the rolling-up postulation. Here we report the first experimental evidence of a thermally induced self-intertwining of graphene nanoribbons for the preferential synthesis of (7, 2) and (8, 1) tubes within parent-tube templates. Through the tailoring of ribbon’s width and edge, the present finding adds a radically new aspect to the understanding of carbon nanotube formation, shedding much light on not only the future chirality tuning, but also contemporary nanomaterials engineering.

Enhanced 1520 nm Photoluminescence from Er3+ Ions in Di-erbium-carbide Metallofullerenes (Er2C2)@C82 (Isomers I, II, and III)

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.

High-Performance Thin-Film Transistors with DNA-Assisted Solution Processing of Isolated Single-Walled Carbon Nanotubes

2010 WILEY-VCH Verlag Gmb Two-dimensional networks of single-walled carbon nanotubes (SWNTs) have attracted much attention because of their excellent transport properties and expected scalable integration into devices such as thin-film transistors (TFTs) and chemical/ biological sensors. To realize these promising applications in such electronics, it is essential to develop sophisticated fabrication processes of the networks. Until now the networks of SWNTs have been fabricated by mainly using two different processes: dry and wet processes. The former includes direct synthesis and deposition of SWNTs on substrates using the chemical vapor deposition (CVD) method,, and the latter includes drop casting, spin coating, inkjet printing, and dip coating by using a solution of dispersed SWNTs. Even though the TFTs fabricated by the CVD process oftentimes show high device performance, the solution processes, in particular, receive increasing interests in recent years because of their low manufacturing cost and of high scalability. However, virtually all of the present solution processes have shown fatal drawbacks of aggregation of individual nanotubes during the network making. The aggregation basically causes i) a wide variation in bundle size and network morphology and ii) a bundling of metallic and semiconducting SWNTs. These obviously will degrade the device performance such as an on/ off current ratio, sensitivity and reproducibility. So far, most of the solution processes have incorporated the dispersion of bundled SWNTs. Since SWNT bundles may contain metallic SWNTs serving as a conductive wire, the network of bundled SWNTs tends to have conducting paths. Even though the enrichment of high-purity semiconducting SWNTs has been achieved, the TFT characteristics can still be degraded by a small number of metallic SWNTs which oftentimes creeps into bundled SWNT networks. To avoid the use of the bundles, several research groups have utilized aqueous solution of surfactant-wrapped individual SWNTs. However, the transistor characteristics of these individual SWNTs have never exceeded those of the bundled SWNTs for non-separated SWNTs. This is presumably because of the fact that such solution normally contains a large amount of free surfactants (usually hundreds times larger than SWNTs in weight) resulting in an inability to achieve effective inter-nanotube contacts. The development of a new and effective solution process of isolated SWNTs is, therefore, highly required to realize high performance TFT devices. One of the most promising candidates for realizing highperformance TFTdevices is to incorporate DNA-wrapped SWNTs as TFTchannels. It has been reported that individual SWNTs can easily be dispersed in water using DNA in the form of DNAwrapped SWNT hybrids (DNA-SWNTs). Importantly, they are completely stable without unbound and free DNA molecules unlike the surfactant-wrapped SWNTs case. Furthermore, the DNA-SWNTs can be sorted by chirality and length of nanotubes, which provides major advantages in the device applications. Here, we show that the DNA-SWNTs can provide an effective way to fabricate the uniform networks of highly isolated and structure-sorted nanotubes for TFTs of high performance. We have prepared a high purity aqueous solution of DNA-SWNTs using sonication, ultracentrifugation, and size-exclusion liquid chromatography (SEC). The SWNTs were wrapped by DNA molecules during the sonication in water. After removing unwrapped SWNTs through ultracentrifugation, the supernatant was collected. This supernatant contains the DNA-SWNTs and excessive amount of free DNA molecules (approximately 100 times the total weight of DNA-SWNTs), which disturb the inter-nanotube contacts. To remove the free DNA, the DNA-SWNTs were purified using SEC incorporating a newly developed HPLC column. Figure 1a shows typical SEC chromatograms of the supernatant, where the detecting UV wavelengths at 260 and 350 nm are used to trace DNA and SWNTs fraction, respectively. The DNA-SWNTs were completely separated from the free DNA because of their difference in size. The broad absorption band of DNA-SWNTs derives from a wide variety of their lengths. In SEC separations, the chromatographic retention time increases as the size of the molecule decreases. The DNA-SWNT hybrids, therefore, can be separated by their length. Figure 1b shows a histogram on the length distribution for a fraction of the retention time corresponding from 20 to 21min (hereafter refer to as fraction 20), which