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Cage Structure (cage + structure)
Selected AbstractsDual Relationship Between Large Gold Clusters (Antifullerenes) and Carbon Fullerenes: A New Lowest-Energy Cage Structure for Au50.CHEMINFORM, Issue 18 2007Dongxu Tian Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Molecular dynamics in the formation process of single-walled carbon nanotubesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2003Yasushi Shibuta Abstract The mechanism of the nucleation and formation of single-walled carbon nanotubes (SWNTs) was investigated using molecular dynamics simulations. When the initial state was chosen so that carbon and nickel atoms were randomly distributed in a simulation domain, the formation of a random cage structure made up of carbon atoms, which had a few nickel atoms inside it, was observed by 6 ns. The nickel atoms, which move inside or on the surface of the cage, were seen to be preventing the complete closure of the cage and its anneal into the fullerene structure. Further, in order to observe a longer time-scale growth process, the simulation cell was artificially shrunk by the progress of simulation so that collisions between precursor clusters were promoted to comply with the limitation in the calculation time. Collisions of the imperfect random-cage clusters led to an elongated tubular cage structure, which could be regarded as an initiation of SWNTs. The simulation results were compared with FT-ICR mass spectra of the positive clusters generated by a laser-vaporization supersonic-expansion cluster beam source. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 690,699, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10123 [source] Isomers of C20: An energy profile IIJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2003Kyle A. Beran Abstract Semi-empirical calculations, at the PM3 level provided within the Winmopac v2.0 software package, are used to geometrically optimize and determine the absolute energies (heats of formation) of a variety of C20 isomers that are predicted to exist in and around the bowl and cage isomers. Using the optimized Cartesian coordinates for the bowl and the cage isomers, a saddle-point calculation was performed. The output file generated, containing energy, distance, and geometry information, is then organized into a graphical format. The resulting graph, which plots the energy of the 20-atom system as a function of the distance from the geometric midpoint, is a two-dimensional energy profile. This profile illustrates an estimation of the contours on the potential energy surface, showing energy minima and maxima that are encountered as the bowl evolves into the cage structure, or vice-versa. To expand the surface into three dimensions, geometry optimizations were performed on the sets of Cartesian coordinates that correspond to energy minima in the bowl-cage profile. Based on these optimizations, eight additional isomers of C20 have been identified and are predicted to be energetically stable. These additional isomers were subsequently subjected to saddle-point calculations in order to identify those isomers that lie adjacent to one another on the three-dimensional surface. Two isomers that are adjacent to each other will exhibit an energy profile that progresses smoothly from the potential well of each isomer up to the saddle point separating them. Consequently, these adjacent pairs of isomers establish a step-wise transformation between the bowl and the cage. This process, which extends out over the three-dimensional surface, is predicted to require less energy than that of the direct, two-dimensional transformation predicted in the bowl-cage profile. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1287,1290, 2003 [source] Structure Characterization of HSQ Films for Low Dielectrics Uses D4 as Sacrificial Porous MaterialsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Guiqin Yin Hydrogensilsesquioxane (HSQ) (low- k) films were prepared by spin-on deposition using D4 (octamethyl cyclotetrasiloxane) as a sacrificial porous material. The dielectric constant of silica films significantly changed from 3.0 to 2.2. Fourier transform infrared spectroscopy was used to identify the network structure and cage structure of the Si,O,Si bond and other bonds that may appear. We studied the structural and electrical properties of the spin-coated films prepared by mixing HSQ and D4 films after oxygen plasma exposure for 5 min, and studied the structural recovery of the damage by annealing at 350°C for 1.5 h in a nitrogen (N2) ambient. This structure results in significant lowering of the dielectric constant (k) on annealing at 350°C for 1.5 h in an N2 ambient and improvement in the leakage current density. [source] A new intumescent flame-retardant: preparation, surface modification, and its application in polypropylenePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2008Xingyi Wang Abstract Melamine salt of tripentaerythriol phosphate (MTP), as a new intumescent flame-retardant, was prepared from tripentaerythritol (TPE), polyphosphoric acid, phosphoric pentoxide, and melamine, and then incorporated into polypropylene (PP) to obtain flame-retarded PP-MTP. FT-IR analysis showed that MTP was in the form of cage structure. The flammability, combustion behavior, and thermal degradation and stability of flame-retarded PP were characterized by using LOI, UL-94 test, cone calorimetry, and TGA, respectively. By SEM, the char structure of PP-MTP was analyzed. XRD diffraction tests showed that PP-matrix of PP-MTP presented better crystallized phases, when MTP was modified by methyl hydrogen siloxane. The relations of the dispersion of MTP in PP matrix to the compatibility between PP and MTP, and to the flame retardancy were discussed. Copyright © 2008 John Wiley & Sons, Ltd. [source] K3(Sc0.875Nb0.125)Nb2O9H1.75: a new scandium niobate with a unique cage structureACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Matthew Mann Potassium scandium niobate hydroxide, K3(Sc0.875Nb0.125)Nb2O9H1.75, is a new scandium niobate with a unique cage structure. The structure contains two non-equivalent K+ sites (3m and m2 site symmetry), one disordered Sc3+/Nb5+ site (m site symmetry), one Nb5+ site (3m site symmetry), two O2, sites (m and mm2 site symmetry) and one H+ site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube-like cage built of seven octahedra, while the other K atom is encapsulated by an eight-membered trigonal face-bicapped prism. The cages form sheets that extend along the ab plane. [source] Tetra-,-acetato- O:O,-bis[(7-azaindole- N)copper(II)]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000Yoshiyuki Kani The title complex, [Cu2(C2H3O2)4(C7H6N2)2], shows a binuclear cage structure having an inversion centre. There are intramolecular N,H,O hydrogen bonds between the 7-azaindole ligands and the bridging acetate O atoms. [source] Ultralow Dielectric Constant Tetravinyltetramethylcyclotetrasiloxane Films Deposited by Initiated Chemical Vapor Deposition (iCVD)ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Nathan J. Trujillo Abstract Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140,cm,1) and Raman (1117,cm,1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma-enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as-deposited films. The high degree of structural retention in the as-deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ,Q' groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as-deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade-off between improved mechanical properties and higher dielectric constants. Films annealed at 410,°C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4,GPa, respectively. The solvent-less and low-energy nature of iCVD make it attractive from an environmental safety and health perspective. [source] Nanoparticles of CdCl2 with closed cage structuresISRAEL JOURNAL OF CHEMISTRY, Issue 1 2001Reshef Tenne Nanoparticles of various layered compounds having a closed cage or nanotubular structure, designated also inorganic fullerene-like (IF) materials, have been reported in the past. In this work IF -CdCl2 nanoparticles were synthesized by two methods. In one technique, a high temperature evaporation and subsequent condensation of dried cadmium chloride powder was used. In the other method, electron beam irradiation of the source powder led to its recrystallization into closed nanoparticles with a nonhollow core. The two methods are shown to produce nanoparticles of different topologies. While mostly spherical nested structures are obtained from the high temperature process, polyhedra with hexagonal or elongated rectangular characters are obtained by the electron beam induced process. The analysis also shows that, while the source (dried) powder is orthorhombic cadmium chloride monohydrate, the crystallized IF cage consists of the anhydrous 3R polytype which is not stable as bulk material in ambient atmosphere. Consistent with previous observations, this study shows that the seamless structure of the IF materials can stabilize phases, which are otherwise unstable in ambient conditions. [source] Dimeric copper(II) 3,3-dimethylbutyrate adducts with ethanol, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine and 3,3-dimethylbutyric acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2000Masato Goto In the crystals of the five title compounds, tetrakis-(,-3,3-dimethylbutyrato- O:O,)bis(ethanol- O)dicopper(II),ethanol (1/2), [Cu2(C6H11O2)4(C2H6O)2]·2C2H6O, (I), tetrakis(,-3,3-dimethylbutyrato- O:O,)bis(2-methylpyridine- N)dicopper(II), [Cu2(C6H11O2)4(C6H7N)2], (II), tetrakis-(,-3,3-dimethylbutyrato- O:O,)bis(3-methylpyridine- N)di-copper(II), [Cu2(C6H11O2)4(C6H7N)2], (III), tetrakis-(,-3,3-dimethylbutyrato- O:O,)bis(4-methylpyridine- N)di-copper(II), [Cu2(C6H11O2)4(C6H7N)2], (IV), and tetrakis-(,-3,3-dimethylbutyrato- O:O,)bis(3,3-dimethylbutyric acid- O)dicopper(II), [Cu2(C6H11O2)4(C6H12O2)2], (V), the dinuclear CuII complexes all have centrosymmetric cage structures and (IV) has two independent molecules. The Cu,Cu separations are: (I) 2.602,(3),Å, (II) 2.666,(3),Å, (III) 2.640,(2),Å, (IV) 2.638,(4),Å and (V) 2.599,(1),Å. [source] | |||||||||||||