Infinite Sheet Research Articles

Dirac point resonances due to atoms and molecules adsorbed on graphene and transport gaps and conductance quantization in graphene nanoribbons with covalently bonded adsorbates

We present a tight binding theory of the Dirac point resonances due to adsorbed atoms and molecules on an infinite 2D graphene sheet based on the standard tight binding model of the graphene p-band electronic structure and the extended Huckel model of the adsorbate and nearby graphene carbon atoms. The relaxed atomic geometries of the adsorbates and graphene are calculated using density functional theory. Our model includes the effects of the local rehybridization of the graphene from the sp^2 to sp^3 electronic structure that occurs when adsorbed atoms or molecules bond covalently to the graphene. Unlike in previous tight-binding models of Dirac point resonances, adsorbed species with multiple extended molecular orbitals and bonding to more than one graphene carbon atom are treated. More accurate and more general analytic expressions for the Green's function matrix elements that enter the T-matrix theory of Dirac point resonances than have been available previously are obtained. We study H, F, OH and O adsorbates on graphene and for each we find a strong scattering resonance (two resonances for O) near the Dirac point of graphene, by far the strongest and closest to the Dirac point being the resonance for H. We extract a minimal set of tight binding parameters that can be used to model resonant electron scattering and electron transport in graphene and graphene nanostructures with adsorbed H, F, OH and O accurately and efficiently. We also compare our results for the properties of Dirac point resonances due to adsorbates on graphene with those obtained by others using density functional theory-based electronic structure calculations, and discuss their relative merits. We then present calculations of electronic quantum transport in graphene nanoribbons with these adsorbed species...

Neodymium diffusion in orthopyroxene: Experimental studies and applications to geological and planetary problems

We have determined the Nd 3+ diffusion kinetics in natural enstatite crystals as a function of temperature, f(O 2) and crystallographic direction at 1 bar pressure and applied these data to several terrestrial and planetary problems. The diffusion is found to be anisotropic with the diffusion parallel to the c-axial direction being significantly greater than that parallel to a- and b-axis. Also, D(// a) is likely to be somewhat greater than D(// b). Diffusion experiments parallel to the b-axial direction as a function of f(O 2) do not show a significant dependence of D(Nd 3+) on f(O 2) within the range defined by the IW buffer and 1.5 log unit above the WM buffer. The observed diffusion anisotropy and weak f(O 2) effect on D(Nd 3+) may be understood by considering the crystal structure of enstatite and the likely diffusion pathways. Using the experimental data for D(Nd 3+), we calculated the closure temperature of the Sm–Nd geochronological system in enstatite during cooling as a function of cooling rate, grain size and geometry, initial (peak) temperature and diffusion direction. We have also evaluated the approximate domain of validity of closure temperatures calculated on the basis of an infinite plane sheet model for finite plane sheets showing anisotropic diffusion. These results provide a quantitative framework for the interpretation of Sm–Nd mineral ages of orthopyroxene in planetary samples. We discuss the implications of our experimental data to the problems of melting and subsolidus cooling of mantle rocks, and the resetting of Sm–Nd mineral ages in mesosiderites. It is found that a cooling model proposed earlier [Ganguly J., Yang H., Ghose S., 1994. Thermal history of mesosiderites: Quantitative constraints from compositional zoning and Fe–Mg ordering in orthopyroxene. Geochim. Cosmochim. Acta 58, 2711–2723] could lead to the observed ∼90 Ma difference between the U–Pb age and Sm–Nd mineral age for mesosiderites, thus obviating the need for a model of resetting of the Sm–Nd mineral age by an “impulsive disturbance” [Prinzhoffer A, Papanastassiou D.A, Wasserburg G.J., 1992. Samarium–neodymium evolution of meteorites. Geochim. Cosmochim. Acta 56, 797–815].

Weight functions and strip yield solution for two equal-length collinear cracks in an infinite sheet

The problem of two equal-length collinear cracks in an infinite sheet is treated using the weight function method. Exact weight functions for the inner and outer crack tips are derived based on the crack opening displacement solution for a reference load case. These weight functions are used to calculate stress intensity factors for different load cases, plastic zone sizes and crack tip opening displacements of the strip yield model. The approach is validated by the perfect agreement between the present strip yield model solutions and Collins and Cartwright’s analytical results based on the direct complex stress function formulation.

Synthesis and characterization of four cubical molybdenum(V) tetramers and their catalytic properties for the epoxidation of cis-cyclooctene using H 2O 2

Molybdenum tetramers: Mo 4(μ 3-O) 4[μ-O 2P(CH 2Cl) 2] 4O 4 ( 1), Mo 4(μ 3-O) 4(μ-O 2P(CH 2OH) 2) 4O 4 ( 2), Mo 4(μ 3-O) 4[μ-O 2P(PhOMe) 2] 4O 4 ( 3), and Mo 4(μ 3-O) 4[μ-O 2P(o-C 6H 4(CH 2) 2)] 4O 4 ( 4) have been synthesized and characterized by IR, UV–Vis, and 31P NMR spectroscopy. Molybdenum tetramers 1 and 4 along with the ligands L2A and L4 were structurally characterized by single crystal X-ray crystallography. An infinite 2D polymeric sheet was formed via inter and intra hydrogen bonds in the crystals of L2A. The crystals of L4 consist of infinite polymeric chains formed through hydrogen bonding. All molybdenum tetramers were tested as catalysts for the epoxidation of cis-cyclooctene in the presence of H 2O 2. Compounds 1 and 2 resulted in more than 80% epoxide after 24 hours at 70 °C, and displayed superior catalytic activities over compounds 3 and 4 under identical conditions. The superior catalytic activities of compounds 1 and 2 may be attributed to their better solubility in the ethanol/H 2O 2 system.

Synthesis, structure and DFT calculation of a hexanuclear mixed-valence copper cluster supported by 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate)

A homoleptic hexanuclear Cu cluster, [(Cu(DSB)(CBT)) 2(Cu 2Br) 2][PPh 4] 2 ( 1-PPh 4 ) [DSB = 2,3-disulfidobenzoate; CBT = 3-carboxybenzene-1,2-bis(thiolate)] was synthesized as dark green crystals by the reaction of CuCl 2 with 2,3-dimercaptobenzoic acid in acetate buffer solution. The X-ray crystal study of 1-PPh 4 revealed its unique structural features: (1) one of two types of crystallographically distinct Cu centers adopted a square planer geometry and the other center had a tetrahedral geometry, and (2) intermolecular H-bonding interactions connected between carboxylic acid group of CBT and the carboxylate group of DSB led to the construction of an unprecedented topologic architecture of a zigzag patterned infinite sheet. In addition, taking into account the total charge of the molecule, which contained 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate), and the diamagnetic nature of 1-PPh 4 , 1-PPh 4 led to it is assignment as a mixed-valence Cu(I)/Cu(III) cluster. Such mixed valence states of Cu atoms were also examined by density functional theory calculation.

Space Technology 5 multipoint observations of transpolar arc-related field-aligned currents

[1] We present two transpolar arc events where for the first time we are able to analyze changes in field-aligned currents associated with high-latitude transpolar auroral arcs on time scales of a few minutes. This is accomplished through the use of highly accurate multipoint magnetic field measurements provided by the Space Technology 5 mission, which consists of three microsatellites in low-Earth orbit. In the first event we examine measurements of an arc that is part of a highly dynamic auroral pattern, that of a hook-shaped arc. In the second event, a more stable dusk oval-aligned arc is analyzed. These events illustrate the dynamic nature of arc formation and show the usefulness of high-resolution multipoint measurements. Minimum variance analysis is used to determine the appropriateness of the infinite current sheet approximation and to calculate arc alignment angles which are then compared with those estimated from UV images or precipitating particle data.

(6-Oxido-2-oxo-1,2-dihydropyrimidine-5-carboxylato-κ2O5,O6)bis[2-(2-pyridyl)-1H-benzimidazole-κ2N2,N3]manganese(II) monohydrate

In the title compound, [Mn(C(5)H(2)N(2)O(4))(C(12)H(9)N(3))(2)]·H(2)O, the Mn(II) centre is surrounded by three bidentate chelating ligands, namely, one 6-oxido-2-oxo-1,2-dihydropyrimidine-5-carboxylate (or uracil-5-carboxylate, Huca(2-)) ligand [Mn-O = 2.136 (2) and 2.156 (3) Å] and two 2-(2-pyridyl)-1H-benzimidazole (Hpybim) ligands [Mn-N = 2.213 (3)-2.331 (3) Å], and it displays a severely distorted octahedral geometry, with cis angles ranging from 73.05 (10) to 105.77 (10)°. Intermolecular N-H···O hydrogen bonds both between the Hpybim and the Huca(2-) ligands and between the Huca(2-) ligands link the molecules into infinite chains. The lattice water molecule acts as a hydrogen-bond donor to form double O···H-O-H···O hydrogen bonds with the Huca(2-) O atoms, crosslinking the chains to afford an infinite two-dimensional sheet; a third hydrogen bond (N-H···O) formed by the water molecule as a hydrogen-bond acceptor and a Hpybim N atom further links these sheets to yield a three-dimensional supramolecular framework. Possible partial π-π stacking interactions involving the Hpybim rings are also observed in the crystal structure.

Динамика плоской солитонной волны сжатия в наноленте графена

It is demonstrated that planar solitary waves of the <br /> longitudinal compression can propagate in a graphene <br /> sheet with supersonic velocities from a narrow range. In <br /> an infinite sheet, such a solitary wave does not change its <br /> shape, and interaction between two solitary waves is elastic <br /> with no energy loss for radiation. However, in a graphene <br /> nanoribbon the solitary waves are affected by the nanoribbon <br /> edges which stipulate the phonon emission. As a result, the <br /> soliton lifetime becomes finite, and it is roughly equal to the <br /> double width of the nanoribbon.

Synthesis and characterization of an infinite sheet of metal–alkyl bonds: unfolding the elusive structure of an unsolvated alkali-metal trisalkylmagnesiate

The study of co-complexation reactions between NaCH(2)SiMe(3) and Mg(CH(2)SiMe(3))(2) has allowed the isolation and structural elucidation of the first solvent-free alkali-metal alkylmagnesiate [{NaMg(CH(2)SiMe(3))(3)}(∞)] (1) as well as the related solvent-free sodium alkyl [{(NaCH(2)SiMe(3))(4)}(∞)] (3).

Aspects of the theory of graphene

Following a brief review of the device-friendly features of graphene, recent work on its Green's functions with and without a normal magnetic field are discussed, for an infinite graphene sheet and also for a quantum dot, with analyses of the Landau-quantized energy spectra of the sheet and dot. The random phase approximation dielectric response of graphene is reviewed and discussed in connection with the van der Waals interactions of a graphene sheet with atoms/molecules and with a second graphene sheet in a double layer. Energy-loss spectroscopy for a graphene sheet subject to both parallel and perpendicular particle probes of its dynamic, non-local response properties are also treated. Furthermore, we discuss recent work on the coupling of a graphene plasmon and a surface plasmon, yielding a collective plasma mode that is linear in wavenumber. Finally, we discuss the unusual aspects of graphene conduction and recent work on diffusive charge transport in graphene, in both the DC and AC regimes.

Lattice density-functional theory on graphene

A density-functional approach on the hexagonal graphene lattice is developed using an exact numerical solution to the Hubbard model as the reference system. Both nearest-neighbour and up to third nearest-neighbour hoppings are considered and exchange-correlation potentials within the local density approximation are parameterized for both variants. The method is used to calculate the ground-state energy and density of graphene flakes and infinite graphene sheet. The results are found to agree with exact diagonalization for small systems, also if local impurities are present. In addition, correct ground-state spin is found in the case of large triangular and bowtie flakes out of the scope of exact diagonalization methods.

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

Four new zinc(II) complexes [Zn(dien)( μ-nic)] 2(BPh 4) 2·2CH 3OH ( 1), {[Zn(dien)(isonic)]BPh 4} n ( 2), [Zn(tren)(nic)]BPh 4 ( 3) and [Zn(tren)(isonic)]BPh 4 ( 4) (dien/tren = diethylenetriamine/triethylenetriamine, nic/isonic = nicotinate/isonicotinate anion) were synthesized and structurally characterized by IR, 1H NMR and single crystal X-ray diffraction. In the zinc(II) complexes of dien, both nicotinate and isonicotinate connect the zinc(II) ions via N,O-bis-monodentate mode. Complex 1 contains a centrosymmetric dinuclear unit bridged by two nicotinate anions in anti-parallel way. Complex 2 is characterized by an infinite one-dimensional zigzag chain bridged by isonicotinate anion in an end-to-end mode. The Zn···Zn distance is 6.782 for 1 and 8.805 Å for 2. While in the complexes of tren, both 3 and 4 are mononuclear complexes with nicotinate and isonicotinate coordinated to zinc(II) ion through only one oxygen atom of their carboxylate groups. The zinc(II) ions in all of the four complexes are in a distorted trigonal bipyramidal geometry. Complex 3 forms a dinuclear unit and complex 4 forms an infinite 2D sheet structure through intermolecular H-bonds. In all of the crystal lattices, the BPh 4 - counterions act to balance the electronic charge at the same time to construct different 3D structures through noncovalent interactions such as C–H···π, N–H···π and van der Waals interactions.

A partly and fully cracked triangular XFEM element for modeling cohesive fracture

This paper discusses the build-up of a partly cracked cohesive crack tip element. The crack tip element is based on the principles of the eXtended Finite Element Method (XFEM) and is of Linear Strain Triangle (LST) type. The composition of the enrichment has been in focus to achieve as complete a description as possible on both sides of the crack. The stress accuracy within the crack tip element has been improved to a level, so that the crack tip stresses can be evaluated locally without introducing nonlocal averaging in the surroundings of the crack tip. The partly cracked element can also be applied as a fully cracked element with a few restrictions in the displacement field. The performance of the developed element has been tested in three examples. One example is an infinite sheet with an initial flaw in pure tension, where a semianalytical solution exists. The two other examples are the two benchmark tests: Three-point Bending Test (TPBT) and the Four-point Shear Beam (FPSB). The partly cracked element performs well, and captures the overall structural response even for coarse meshes in all the three examples. Copyright © 2010 John Wiley & Sons, Ltd.

N′-[(E)-(1-Methyl-1H-pyrrol-2-yl)methylidene]pyridine-4-carbohydrazide

In the title compound, C12H12N4O, the pyridine and pyrrole rings are inclined at an angle of 29.22 (8)° and an intra­molecular C—H⋯N inter­action geneates an S(6) ring. In the crystal, mol­ecules are linked by N—H⋯N hydrogen bonds, forming (010) C(7) chains. The chains are cross-linked by weak C—H⋯O inter­actions, which generate R 2 2(18) ring motifs within an infinite sheet. Finally, two C—H⋯π inter­actions are present, where the C—H groups are from the pyridine ring and π is the pyrrole ring.

1-(3,4-Dihydroxyphenyl)hexan-1-one

In the title compound, C12H16O3, a fully extened hexyl carbon chain is attached to a benzene ring; the mean planes formed by the atoms in the benzene ring and the hexa­none are inclined at an angle 8.5 (2)° with respect to each other. In the crystal, inter­molecular O—H⋯O hydrogen bonds join the mol­ecules into an infinite sheet.

(en)Mn2(V2O7): A 3D manganese vanadate built by Mn–O layers and two types of pillars of V2O7 and en bridges

Abstract An unexpected 3D manganese vanadate (en)Mn2(V2O7) (1) (en = ethylenediamine) has been hydrothermally obtained by H2E2Ge2O3 (E = − CH2CH2COO−) ligands and well-prepared mixture of V–Mn-amine and characterized by IR spectroscopy, elemental analysis, thermal stability and powder X-ray diffraction. Single-crystal X-ray diffraction analysis reveals that the structure is a novel pillared-layer, in which MnO5N octahedra are corner-linked to form an infinite sheet with 4-membered rings (MRs) and further condensed to the 3D framework. The most prominent feature of 1 is the connection between the sheets via double bridges, namely, inorganic V2O7 dimeric units and organic en molecules. It is noteworthy that inorganic and organic double bridges between sheets have not been seen in manganese vanadates.

Migration of gold atoms in graphene ribbons: Role of the edges

The migration of gold atoms attached to single vacancies near the edges of graphene ribbons is studied using density-functional theory calculations. The stable position for a single gold atom is found to be on top of a vacancy, as in an infinite graphene sheet. An energy of 5 eV is needed for the Au atom to move through the vacancy to the other side of the sheet, but the Au atom can migrate in lateral direction together with the vacancy, with a migration barrier of about 2.2 eV. The sites near the edges of the graphene layer are energetically more favorable for gold-atom-vacancy pairs than sites in the middle of extended graphene layers. The migration barriers for different pathways show that it is easier for the gold atom to move toward the edge where it can be captured. When the gold atom reaches the edge, it can migrate along the edge with an energy barrier of only 1.4 eV. Our results explain recent experimental observations [Y. Gan et al., Small 4, 587 (2008)] and provide information on the dynamics of metal atoms on substitutional sites in graphene as well as on their agglomeration at defects and at edges of graphene ribbons.

Two-dimensional flagellar synchronization in viscoelastic fluids

Experimental studies have demonstrated that spermatozoa synchronize their flagella when swimming in close proximity. In a Newtonian fluid, it was shown theoretically that such synchronization arises passively due to hydrodynamic forces between the two swimmers if their waveforms exhibit a front–back geometrical asymmetry. Motivated by the fact that most biological fluids possess a polymeric microstructure, here we address synchronization in a viscoelastic fluid analytically. Using a two-dimensional infinite sheet model, we show that the presence of polymeric stresses removes the geometrical asymmetry constraint and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers are seen to be driven into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid.

Computationally Designed Families of Flat, Tubular, and Cage Molecules Assembled with “Starbenzene” Building Blocks through Hydrogen‐Bridge Bonds

Using density functional calculations, we demonstrate that the planarity of the nonclassical planar tetracoordinate carbon (ptC) arrangement can be utilized to construct new families of flat, tubular, and cage molecules which are geometrically akin to graphenes, carbon nanotubes, and fullerenes but have fundamentally different chemical bonds. These molecules are assembled with a single type of hexagonal blocks called starbenzene (D(6h) C(6)Be(6)H(6)) through hydrogen-bridge bonds that have an average bonding energy of 25.4-33.1 kcal mol(-1). Starbenzene is an aromatic molecule with six pi electrons, but its carbon atoms prefer ptC arrangements rather than the planar trigonal sp(2) arrangements like those in benzene. Various stability assessments indicate their excellent stabilities for experimental realization. For example, one starbenzene unit in an infinite two-dimensional molecular sheet lies on average 154.1 kcal mol(-1) below three isolated linear C(2)Be(2)H(2) (global minimum) monomers. This value is close to the energy lowering of 157.4 kcal mol(-1) of benzene relative to three acetylene molecules. The ptC bonding in starbenzene can be extended to give new series of starlike monocyclic aromatic molecules (D(4h) C(4)Be(4)H(4)(2-), D(5h) C(5)Be(5)H(5)(-), D(6h) C(6)Be(6)H(6), D(7h) C(7)Be(7)H(7)(+), D(8h) C(8)Be(8)H(8)(2-), and D(9h) C(9)Be(9)H(9)(-)), known as starenes. The starene isomers with classical trigonal carbon sp(2) bonding are all less stable than the corresponding starlike starenes. Similarly, lithiated C(5)Be(5)H(5) can be assembled into a C(60)-like molecule. The chemical bonding involved in the title molecules includes aromaticity, ptC arrangements, hydrogen-bridge bonds, ionic bonds, and covalent bonds, which, along with their unique geometric features, may result in new applications.

Hydrothermal synthesis, crystal structure and magnetic characterization of two 4f–3d heterometallic coordination polymers

Two new 4f–3d heterometallic coordination polymers [Gd 2Co(L 1) 3(ox)(H 2O) 4]·2.5H 2O ( 1, L 1 = pyridine-2,5-dicarboxylate anion, ox = oxalate dianion) and [GdNi(L 2) 2(ox) 0.5(H 2O) 3]·3H 2O ( 2, L 2 = pyridine-2,3-dicarboxylate anion) were successfully synthesized under hydrothermal conditions. In compound 1, one dimensional heterometallic and lanthanide infinite sheets were constructed with sole L 1 spacers and L 1–ox mixed bridges, respectively. While similar one dimensional heterometallic infinite sheet and normal lanthanide infinite zigzag chain were formed based on sole L 2 and L 2–ox mixed bridges, respectively in compound 2. Both of the two compounds exhibited new and interesting three dimensional topologies. In addition, the magnetic properties of the two compounds were analyzed via solid-state dc magnetic susceptibility measurements.