6,332 publications from this institution
Higher AHEI-2010 score may be associated with lower overall mortality, moderate alcohol consumption and lower consumption of sugar sweetened beverages and juices combined appeared to account for most of the observed associations.
This paper describes the use of microcontact printing (μCP) to generate patterned self‐assembled monolayers (SAMs) of alkanethiolates on the surfaces of evaporated films of silver. Using patterned SAMs of alkanethiolates as nanometer‐thick resists, patterned microfeatures of silver with sizes down to ∼200 nm were fabricated on by selective etching in aqueous solutions containing , and . Complete etching of silver can be achieved more rapidly than that of gold: ∼20 s vs. ∼20 min for 50 nm thick metal films when similar ferricyanide etchants were used. Microstructures of silver produced by the present method have higher edge resolution (typically, ∼20 nm vs. ∼100 nm) and far fewer defects (∼10 pits/mm2 vs. ∼103 pits/mm2) than those of gold fabricated by a similar procedure. Silver lines (0.2 μm in thickness, ∼50 μm in width, and ∼5 mm in length) had the expected metallic conductivity (≈5.56 × 105 S/cm); parallel lines of silver (0.2 μm in thickness, ∼10 μm in width, ∼1 mm in length, and separated by ∼10 μm) were electrically isolated from each other. Aqueous solutions containing other coordinating ligands and oxidants, , and , were also selective etchants for use with patterned SAMs of alkanethiolates on silver. Patterned structures of silver (50 nm thick) on could be used as secondary masks for etching of in aqueous solutions of , and of Si(100) in aqueous solutions of KOH and i‐propanol. Patterned films of silver (0.2 μm thick) on silicon wafers could be used as masters to cast elastomeric stamps with surface relief to be used for μCP. By choosing appropriate etching conditions, microparticles of MX (M = Ag; X = Cl, Br, I, OH, and SCN) could be formed in situ on the underivatized regions of the SAM‐patterned surface during etching of silver.
This chapter discusses the physical properties of metal-doped fullerene superconductors. The key component of the fullerene superconductors is the molecular cluster C60, or Buckminsterfullerene. The chapter provides an overview of the experimental status of the fullerene superconductors emphasizing on (1) the normal state and superconducting state phenomenology and (2) experimental probes of the microscopic mechanism of superconductivity in two new molecular superconductors (K3C60 and Rb3C60). The chapter also presents a few models to explain fullerene superconductivity. Theoretical models put forth to explain superconductivity in the fullerenes range from the conventional electron-phonon-mediated pairing model of Bardeen, Copper, and Schreiffer (BCS) to models in which pairing is mediated by electron correlation effects. Finally, within the context of these models, the chapter provides an overview of (1) the dependence of critical transition temperatures on lattice constant of C60, (2) the energy gap, (3) phonons, and (4) the isotope effect.
Challenges facing the scaling of microelectronics to sub-50 nm dimensions and the demanding material and structural requirements of integrated photonic and microelectromechanical systems suggest that alternative fabrication technologies are needed to produce nano-scale devices. Inspired by complex, functional, self-assembled structures and systems found in Nature we suggest that self-assembly can be employed as an effective tool for nanofabrication. We define a self-assembling system as one in which the elements of the system interact in pre-defined ways to spontaneously generate a higher order structure. Self-assembly is a parallel fabrication process that, at the molecular level, can generate three-dimensional structures with sub-nanometer precision. Guiding the process of self-assembly by external forces and geometrical constraints can reconfigure a system dynamically on demand. We survey some of the recent applications of self-assembly for nanofabrication of electronic and photonic devices. Five self-assembling systems are discussed: 1) self-assembled molecular monolayers; 2) self-assembly in supramolecular chemistry; 3) self-assembly of nanocrystals and nanowires; 4) self-assembly of phase-separated block copolymers; 5) colloidal self-assembly. These techniques can generate features ranging in size from a few angstroms to a few microns. We conclude with a discussion of the limitations and challenges facing self-assembly and some potential directions along which the development of self-assembly as a nanofabrication technology may proceed.
The General weight function expressions given in Gao (J. Mech. Phys. Solids 37, 133, 1989), referred to here as part I, for combined-mode crack-dislocation interaction problems in the three-dimensional regime are applied to solve for the stress field and energy of a shear dislocation loop emerging from the tip of a half-plane crack. The results are compared to the previously proposed approximate estimates for shear loops by Anderson and Rice (J. Mech. Phys. Solids 35, 743, 1987), who solved exactly for prismatic opening dislocation loops that are co-planar with the crack and also for the analogous 2-D cases of general crack tip-parallel line dislocations. The energy results are presented in terms of a correction factor m, following Anderson and Rice, to the usual estimate of energy for an emergent crack tip loop as half the energy of a full loop (identified as the emergent loop and its image relative to the crack front) in an uncracked solid. For a full circular shear loop the energy is U = [(2 − ν)μb 2 r/4(1-ν)] In (8r/e2 r 0), where r 0 denotes the core cut-off parameter and μ, ν are the shear modulus and Poisson ratio. Thus for a semicircular loop emerging from the crack tip, the energy is expressed as U = [(2 − ν)μb 2 r/8(1-ν] In (8mr/e2r0 ), where the constant m depends on the orientation angle Ψ of the Burgers vector relative to a line normal to the crack tip and the inclination angle φ of the dislocated plane relative to the crack plane. The m factors are calculated at selected angles φ for rectangular and semicircular loops. This involves multiple numerical integrations based on the weight functions of part I, first to obtain the stress field and then to integrate it over the dislocated area to get the energy, and requires a large amount of computing CPU time. An approximate formula for m is proposed for general inclined dislocation loops, based on known 2-D results for m factors for arbitrary angles φ calculated by Anderson and Rice (1987) and the 3-D m(φ = 0) results given here for shear dislocation loops in the crack plane. It compares well to the exact results.
