The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Vijay Kumar - One of the best experts on this subject based on the ideXlab platform.
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Design of a very thin direct-band-gap semiconductor nanotube of germanium with Metal Encapsulation
Physical Review B, 2005Co-Authors: Abhishek K Singh, Vijay Kumar, Y. KawazoeAbstract:Using ab initio total energy calculations we design a very thin semiconducting nanotube of germanium with a direct band gap by Encapsulation of $\mathrm{Mo}$ or $\mathrm{W}$. This finding is an outcome of studies of assemblies of ${\mathrm{Ge}}_{18}{\mathrm{Nb}}_{2}$ clusters into nanotubes. The infinite $\mathrm{Nb}$-doped nanotube is Metallic. However, the electronic structure has a significant gap above the Fermi level. When $\mathrm{Nb}$ is replaced by a $Z+1$ element such as $\mathrm{Mo}$ or $\mathrm{W}$, it leads to the formation of a semiconducting nanotube. The atomic structure of these nanotubes is based on a novel alternate prism and antiprism stacking of hexagonal rings of germanium. Such an arrangement is optimal for ${\mathrm{Ge}}_{18}{M}_{2}$ ($M=\mathrm{Nb}$, $\mathrm{Mo}$, and $\mathrm{W}$) clusters that serve as the building blocks of nanotubes. These results demonstrate that by just changing the $M$ atom in the growth process, we can form Metallic, semiconducting, and $n$ or $p$ types of nanotubes, opening new possibilities for nanoscale devices.
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Predictions of novel nanostructures of silicon by Metal Encapsulation
Computational Materials Science, 2004Co-Authors: Vijay KumarAbstract:Abstract Recent studies using ab initio total energy calculations have shown exciting possibilities of developing novel Metal encapsulated caged clusters of silicon with fullerene-like, Frank–Kasper and other polyhedral structures. In contrast to carbon for which empty cage fullerene structures are stable with 20 or more atoms, 10–16 atom silicon cage structures are stabilized by a guest Metal atom. These nanoclusters are predicted to exhibit luminescence in the visible range and could find applications in biological systems, optoelectronics, and as tagging material. The Raman and infrared spectra have been calculated and they could help in the experimental identification of the structures. Interaction of these clusters with Metal as well as oxygen or hydrogen atoms show that the fullerene structure is stable. Also the interaction between clusters themselves is weak and the ionization potentials, large. These properties make them attractive for cluster assembled materials such as nanowires, nanotubes, and other 2 and 3D structures. Studies on hydrogen interaction have led to the predictions of empty center hydrogenated silicon fullerenes Si n H n with large HOMO–LUMO gaps. These could further be doped endohedrally or exohedrally to produce novel silicon fullerenes with a variety of properties opening new ways of using silicon for diverse applications.
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cluster assembled Metal encapsulated thin nanotubes of silicon
Nano Letters, 2002Co-Authors: Abhishek K Singh, Vijay Kumar, Tina Marie Briere, Y. KawazoeAbstract:Using ab initio total energy calculations we demonstrate that the recently found Metal encapsulated silicon clusters Si12Be can be assembled to form hexagonal nanotubes of silicon. This is in contrast to undoped silicon structures that are distorted and have a tendency to agglomerate. The finite nanotubes have varying HOMO−LUMO gaps depending upon the length and amount of doping. However, infinite nanotubes are Metallic, symmetric, and stable, making Metal Encapsulation a useful route to generate Metallic silicon nanowires for miniature devices.
Mitsuo Sawamoto - One of the best experts on this subject based on the ideXlab platform.
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amphiphilic thermosensitive ruthenium ii bearing star polymer catalysts one pot synthesis of peg armed star polymers with ruthenium ii enclosed microgel cores via Metal catalyzed living radical polymerization
Macromolecules, 2007Co-Authors: Takaya Terashima, Makoto Ouchi, Tsuyoshi Ando, Masami Kamigaito, Mitsuo SawamotoAbstract:Amphiphilic and thermosensitive star polymers with Ru(II) complex−encapsulating microgel cores were directly synthesized in high yield via RuCl2(PPh3)3-catalyzed living radical polymerization. For the solvo- and thermal responsiveness, the arms stem from a block copolymer of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with a small amount of methyl methacrylate. For the Metal Encapsulation into the core, a phosphine-ligand monomer [CH2CH(C6H4)PPh2] was “copolymerized” with a divinyl compound (linking agent); upon block polymer formation, in situ addition of these two components induced the linking reaction of the arm chains and, subsequently, the formation of Ru(II)-bearing microgels (cores) via ligand exchange between the triphenylphoshines in the original catalyst and the pendent phosphines in the core network. Thus, the hydrophobic catalyst [RuCl2(PPh3)3] for polymerization was in situ transformed into an amphiphilic core-bound catalyst. The star polymers with different Ru(II) contents were ...
Y. Kawazoe - One of the best experts on this subject based on the ideXlab platform.
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Metal encapsulated nanotubes of germanium with Metal dependent electronic properties
The European Physical Journal D - Atomic Molecular Optical and Plasma Physics, 2005Co-Authors: A. Kumar Singh, V. Kumar, Y. KawazoeAbstract:Using ab initio total energy calculations we demonstrate that the nanotubes of germanium with atomic structure based on an alternate prism and antiprism stacking of hexagonal rings, can be stabilized by Metal Encapsulation. The V or Nb doped infinite nanotube is Metallic. However, Mo doping leads to the formation of a Metal encapsulated direct band gap semiconducting nanotube of germanium. These nanotubes with Metal dependent electronic properties could prove to be vital for the development of future nanotechnologies.
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Design of a very thin direct-band-gap semiconductor nanotube of germanium with Metal Encapsulation
Physical Review B, 2005Co-Authors: Abhishek K Singh, Vijay Kumar, Y. KawazoeAbstract:Using ab initio total energy calculations we design a very thin semiconducting nanotube of germanium with a direct band gap by Encapsulation of $\mathrm{Mo}$ or $\mathrm{W}$. This finding is an outcome of studies of assemblies of ${\mathrm{Ge}}_{18}{\mathrm{Nb}}_{2}$ clusters into nanotubes. The infinite $\mathrm{Nb}$-doped nanotube is Metallic. However, the electronic structure has a significant gap above the Fermi level. When $\mathrm{Nb}$ is replaced by a $Z+1$ element such as $\mathrm{Mo}$ or $\mathrm{W}$, it leads to the formation of a semiconducting nanotube. The atomic structure of these nanotubes is based on a novel alternate prism and antiprism stacking of hexagonal rings of germanium. Such an arrangement is optimal for ${\mathrm{Ge}}_{18}{M}_{2}$ ($M=\mathrm{Nb}$, $\mathrm{Mo}$, and $\mathrm{W}$) clusters that serve as the building blocks of nanotubes. These results demonstrate that by just changing the $M$ atom in the growth process, we can form Metallic, semiconducting, and $n$ or $p$ types of nanotubes, opening new possibilities for nanoscale devices.
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cluster assembled Metal encapsulated thin nanotubes of silicon
Nano Letters, 2002Co-Authors: Abhishek K Singh, Vijay Kumar, Tina Marie Briere, Y. KawazoeAbstract:Using ab initio total energy calculations we demonstrate that the recently found Metal encapsulated silicon clusters Si12Be can be assembled to form hexagonal nanotubes of silicon. This is in contrast to undoped silicon structures that are distorted and have a tendency to agglomerate. The finite nanotubes have varying HOMO−LUMO gaps depending upon the length and amount of doping. However, infinite nanotubes are Metallic, symmetric, and stable, making Metal Encapsulation a useful route to generate Metallic silicon nanowires for miniature devices.
Atsushi Nakajima - One of the best experts on this subject based on the ideXlab platform.
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nitric oxide oxidation of a ta encapsulating si cage nanocluster superatom ta si16 deposited on an organic substrate a si cage collapse indicator
Physical Chemistry Chemical Physics, 2018Co-Authors: Masahiro Shibuta, Toshiki Niikura, Toshiaki Kamoshida, Hironori Tsunoyama, Atsushi NakajimaAbstract:The chemical reaction kinetics of an alkali-like superatom comprising a tantalum encapsulating Si16 cage nanocluster (Ta@Si16) deposited on an n-type organic substrate composed of overlayered C60 fullerene upon exposure to nitric oxide (NO) as a reactive gas are investigated. Core level X-ray photoelectron spectroscopy reveals that Ta@Si16 oxidation with NO proceeds stepwise from the outer Si16 cage to the central Ta atom; during the initial stage, NO is dissociatively chemisorbed by the cage surface of Ta@Si16 without penetrating the cage, while under extreme reaction conditions, the collapse of the Si16 cage leads to NO oxidation of the central Ta atom. In particular, molecular NO adsorption is associated with Ta oxidation only after the collapse of the Si16 cage of Ta@Si16. The reaction kinetics of M@Si16 with NO in the earlier stages of oxidation are discussed in conjunction with density functional theory calculations. Due to the superatomic nature of the shell closure with valence electrons coupled with Metal Encapsulation, surface oxidation of the caged Si in Ta@Si16 takes place gently compared to that of a naked Si surface, with molecularly physisorbed NO functioning as an indicator of Si cage collapse.
Joost N. H. Reek - One of the best experts on this subject based on the ideXlab platform.
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Transition-Metal Encapsulation within Supramolecular Diphosphine Capsules
Current Organic Chemistry, 2013Co-Authors: Tatiana Besset, Rafael Gramage-doria, Joost N. H. ReekAbstract:This review provides a detailed overview on the research carried out in self-assembled supramolecular capsules enabling en-capsulation of transition Metals within their inner space. The supramolecular assemblies discussed are based on cationic/anionic interactions between cone-shaped building blocks, derived from quaternary ammonium and sulfonated salts, which upon assembly give rise to closed cavitands. Furthermore, one or both of the ionic building blocks contain diphosphine groups located at the cavity core. Thus, upon chelation of a transition-Metal ion to the phosphorus(III) donor atoms, the Metal fragment lies positioned in the molecular container. In addition, Metal coordination does not affect the overall structure of the supramolecular capsule.
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Diphosphine capsules for transition-Metal Encapsulation
Chemistry an Asian journal, 2011Co-Authors: Tehila S. Koblenz, Henk L. Dekker, Chris G. De Koster, Piet W. N. M. Van Leeuwen, Joost N. H. ReekAbstract:Self-assembly and characterization of novel heterodimeric diphosphine capsules formed by multiple ionic interactions and composed of one tetracationic diphosphine ligand and one complementary tetraanionic calix[4]arene are described. Encapsulation of a palladium atom within a diphosphine capsule is achieved successfully by using the Metal complex of the tetracationic diphosphine ligand for the assembly process. In this templated approach to Metal Encapsulation, the transition-Metal complex is an integrated part of the capsule with the transition Metal located inside the capsule and is not involved in the assembly process. We present two approaches for capsule assembly by mixing solutions of the precharged building blocks in methanol and mixing solutions of the neutral building blocks in methanol. The scope of the diphosphine capsules and the Metallodiphosphine capsules is easily extended by applying tetracationic diphosphine ligands with different backbones (ethylene, diphenyl ether, and xanthene) and cationic binding motifs (p-C6H4-CH2-ammonium, m-C6H4-ammonium, and m-C6H4-guanidinium). These tetracationic building blocks with different flexibilities and shapes readily associate into capsules with the proper capsular structure, as is indicated by 1H NMR spectroscopy, 1D NOESY, ESI-MS, and modeling studies