8,766 research outputs found
Enhanced microhardness of nanocrystalline carbon nanotube-reinforced Cu composite using planar shock-wave compaction
No full textPlanar shock-wave compaction (SWC), at a peak pressure of similar to 15 GPa, was used to fabricate 90% dense carbon nanotube-reinforced-Cu composite (SWC-CNT/Cu). Transmission electron microscopy analysis of SWC-CNT/Cu revealed retention of nanoscale size Cu grains, and the presence of shear bands and homogeneous dispersion of CNTs in the Cu matrix. These findings explain the significantly enhanced hardness observed. A Vickers hardness and nanoindentation test for SWC-CNT/Cu indicated enhanced microhardness of 1190 and 1794 MPa, respectively, proving the efficiency of the SWC technique. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.This work was financially supported by Defense Acquisition
Program Administration and Agency for Defense
Development under the contract UD060006AD
and the Korea Research Foundation Grant funded by
the Korean Government (MOEHRD) (KRF-2005-005-
J09701)
Optical Second Harmonic Generation Study by Molecular Orientation Dependence on the Chain Length
No full textAdsorption structure and doping effect of azidotrimethyltin on graphene
No full textThe adsorption structure and the electronic property of azidotrimethyltin (ATMT) on monolayer graphene were investigated using scanning tunneling microscopy and core-level photoemission spectroscopy. We also confirmed the n-type doping effect by scanning tunneling spectroscopy and work function measurements. We will systematically demonstrate the variation of characteristic of graphene induced by the chemical functionalized molecule as we confirmed the results using scanning tunneling microscopy in conjunction with core- level photoemission spectroscopy. (C) 2011 Elsevier B.V. All rights reserved
AN ELECTROCHEMICAL STUDY ON ZN-SN-ALLOY-COATED STEEL SHEETS DEPOSITED BY VACUUM EVAPORATION .1.
No full textZn-Sn-alloy-coated steel sheets were prepared by a vacuum evaporation method to overcome the shortcomings of the conventional hot-dip-galvanizing and electrogalvanizing processes. The electrochemical behaviours of these alloy-coated steel sheets were evaluated in a neutral 3.5% NaCl solution. Zn-Sn alloy coatings with an Sn content lower than the eutectic composition consist of a simple mixture of Zn and Sn because of the poor solid solubility between them. During the coating process by vacuum evaporation, Sn tends to become enriched at the interface between the coating and the steel substrate by forming an FeSn2 phase. During polarization in a neutral 3.5% NaCl solution, one passive region due to oxidation of Sn is always observed and a second passive region due to formation of zinc hydroxide may be observed at lower potentials if local alkalization by reduction of dissolved oxygen occurs preferentially on the Sn surface. The order of dissolution of the three elements from the Zn-Sn-alloy-coated steel sheet is Zn, Sn and Fe. The electrochemical test data suggest that the optimum composition is close to Zn-69.8wt.%Sn.X114sciescopu
Pd-Sn Alloy Electrocatalysts for Interconversion Between Carbon Dioxide and Formate/Formic Acid
No full textPd-Sn alloy catalysts, fabricated using a coelectrodeposition method, were used for the interconversion of carbon dioxide and formate/formic acid. The morphologies and compositions of the Pd-Sn alloy catalysts were controlled by changing the Sn precursor concentration in the deposition bath. The as-prepared catalysts exhibited bifunctional catalytic activities in both formic acid oxidation and carbon dioxide reduction. By increasing Sn content in the Pd-Sn alloy catalyst, its catalytic activity was enhanced in carbon dioxide reduction, but diminished in formic acid oxidation. The stability of the catalyst was poor because of the highly positive potential range in which formic acid oxidation occurs. After the annealing process, both bifunctional activity and stability in formic acid oxidation were improved. Among the alloys, H-2-annealed Pd45Sn55 alloy was the most suitable catalyst for unitized regenerative fuel cells based on carbon dioxide and formate/formic acid, because of its bifunctional activity, stability, and tolerance of carbon monoxide poisoning.11Nscopu
A-Site Effect on the Oxidation Process of Sn-Halide Perovskite: First-Principles Calculations
No full textTin-halide perovskite solar cells (Sn-PSCs) are promising candidates as an alternative to toxic lead-halide PSCs. However, Sn2+ is easily oxidized to Sn4+, so Sn-PSCs are unstable in air. Here, we use first-principles density functional theory calculations to elucidate the oxidation process of Sn2+ at the surface of ASnBr(3) [A = Cs or CH3NH3 (MA)]. Regardless of the A-site cation, adsorption of O2 leads to the formation of SnO2, which creates a Sn vacancy at the surface. The A-site cation determines whether the created vacancies are stabilized in the bulk or at the surface. For CsSnBr3, the Sn vacancy is stabilized at the surface, so further oxidation is limited. For MASnBr(3), the Sn vacancy moves into bulk region, so additional Sn is supplied to the surface; as a result, a continuous oxidation process can occur. The stabilization of Sn vacancy is closely related to the polarization that the A-site cation causes in the system.11Nsciescopu
Ordering of organic molecules on templated surfaces
No full textThis thesis describes the controlled growth of molecular nanostructures using modified metallic and semiconductor surfaces. The Ag/Si(lll)-(root3 x root3),the Sn/Cu(100) surface alloy system and the Bi/Si(100) nanolines and (2xn) surfaces were all investigated as suitable substrates for the controlled growth of pentacene, (C22H14) or trimesic acid, (C6H3(COOH)3) organic molecules. The following techniques were used in this study; Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED), Normal Incident X-Ray Standing Waves (NIXSW) and Temperature Programmed Desorption (TPD).
The room temperature growth and ordering of trimesic acid on the AgfSi(ll1)-(root3 x root3) surface was investigated. An oblique unit cell was determined and a model proposed for the highly ordered close-packed domains.
The discovery of a new submonolayer phase on Sn/Cu(100) and the re-examined known phase are discussed. New models for these reconstructions are proposed. Adsorption of trimesic acid at room temperature on the clean substrate the lowest Sn coverage phase were studied. Two new Sn coverage dependent structures were discovered and bonding schemes in upright and flat orientations are discussed.
BifSi(100)-(2xn) surface was exploited as a template for the ordered growth of pentacene, which exhibited orientation specific adsorption. The Bi/Si(100)-(2xn) single domain surface created on vicinal silicon was used to test the suitable of Daresbury 4.2 beamline for NIXSW Imaging experiments and the quality of the results are discussed
Second nearest-neighbor modified embedded atom method interatomic potentials for Na-M-Sn (M=Cu, Mn, Ni) ternary systems
No full textInteratomic potentials for Mn-Sn, Ni-Sn, Na-Cu, Na-Mn, and Na-Ni binary systems and Na-Cu-Sn, Na-Mn-Sn, and Na-Ni-Sn ternary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental materials properties such as structural, elastic, thermodynamic, and thermal properties in reasonable agreement with experiments and DFT calculations. It is demonstrated that the potentials can be used for atomistic simulations to understand material phenomena and to search for optimal tin-based alloy anode materials for sodium ion batteries.11Nsciescopu
Static and dynamic indentation damage in SiC and Si(3)N(4)
No full textHertzian and explosive indentations were used to determine the damage behavior of SiC and Si(3)N(4) ceramics. Specimens were selected with different microstructures. In order to observe the subsurface damaged zone, the bonded interface technique was adopted. It was found that the damage response depends strongly on the microstructure of ceramics. Examination of subsurface damage reveals a competition between brittle and quasiplastic damage mode: brittle fracture mode is dominant in fine grain microstructure; quasiplastic deformation occurs in coarse grain. Dynamic indentation induces subsurface yield zone which contains extensive micro-cracks. The role of microstructure on static and dynamic damage behavior are discussed in terms of the weakness of grain boundary and grain size
Half-metallic ferromagnetism and metal–insulator transition in Sn-doped SrRuO3 perovskite oxides
No full textWe investigate the electronic and magnetic properties of SrRu1-xSnxO3 by carrying out density-functional-theory calculations to show that a half-metallic ferromagnetic ground state emerges for the Sn doping of x≳0.5. To examine the effect of on-site Coulomb interactions for the Ru d orbitals, which was suggested to enhance the half-metallicity in SrRuO3, we employed both the local spin-density approximation (LSDA) as well as the LSDA + U method. For all the possible configurations of Sn doping for x=1/8,1/4,1/2,5/8,3/4, and 7/8 within the 2×2×2 unit cell, we monitor the Ru t2g bandwidth as well as the valence band maximum in the majority-spin channel and demonstrate that the Ru d electron hopping is blocked by the Sn-substituted sites so that the Ru t2g bandwidth becomes reduced as the doping x increases. For x0.7, the Ru t2g bandwidth gets so narrow that even a small on-site Coulomb interaction, e.g., Ueff=1.0 eV induces a band-gap, which indeed corresponds to a gap of the Ru impurity bands in the SrSnO3 oxide semiconductor. © 2018 Elsevier B.
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