Papers by Keyword: Au

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Authors: Wei Wei Ju, Tong Wei Li
Abstract: The adsorption of Au on clean Si(001) surface is investigated by the local density approximation using first-principles pseudopotentials. We found that the adsorption energy of Au on ideal Si(001)-(1×1) surface is lower than that on reconstructed Si(001)-(2×1) surface, suggesting that adsorbed Au atoms chemically react with the surface Si atoms and break Si-Si dimer bonds of the substrate. Furthermore, the intermixing of Au and Si is also considered and the calculation suggests that intermixing will not take place at low temperature. But due to the small energy barrier for Au atoms to diffuse into Si substrate, we can conclude that the Au-Si alloy is easily formed at relatively high temperature. This result should be one of the reasons of the lack of consensus on the issue of intermixing of Au and Si.
Authors: Avi Shalav, Sherman Wong, Simon Ruffell, Robert G. Elliman
Abstract: This study demonstrates a novel technique for the fabrication of ordered arrays of Au rich nanoparticles on a Si substrate. Si substrates, with their native oxides intact, are pre-patterned using nanoindentation to create regions on the surface that readily alloy at higher temperatures with a thin thermally evaporated Au layer. Larger Au rich particles are observed to form at the indentation sites after high temperature annealing in an inert atmosphere. After mechanical wiping, the Au rich particles lying within the indentation sites remain while almost all the particles on the native oxide surface are readily removed. Using PECVD techniques, multi-prong Si nanowires are shown to grow from the remaining arrays of Au rich particles.
Authors: K.L. Merkle, D. Wolf
Authors: Nicolás Di Lalla, Rodolfo A. Pérez, Fanny Dyment
Authors: Y. X. Wang, Z. Y. Pan, B. E. Zhu, Y. Xiao, S. H. Guo
Abstract: Classical molecular dynamics simulation was used to investigate the structure, melting and mechanical properties of Au nanowires encapsulated in single-walled carbon nanotubes (SWCNT). A possibility of synthesizing controlled Au nanowires was firstly studied by encapsulating small clusters into CNTs with suitable diameters. The nanowires with multi-shell structure of cylindrical symmetry are predicted as a consequence of spontaneous and confined coalescence of gold clusters. The investigation of melting temperature and behavior of a gold nanowire with multi-shells in a carbon nanotube (CNT) showed that the melting temperature of the enclosed Au nanowire is lower than its bulk counterpart and higher than that observed for free-standing ones. Different from the melting behavior of freestanding Au nanowires, the melting of Au nanowires enclosed in CNTs with tube diameters (D) in the range of 1.08 nm < D < 2.09 nm investigated here was found to initiate from the center layers. Finally, the deformation behavior of the gold-filled single-walled carbon nanotube was simulated under axial compression. The results show that the buckling strength of the Au-filled carbon nanotube is increased compared with that of a hollow tube, and is similar to the case of filling with gases or fullerenes. The interactions between filling elements and the carbon wall help restrain the collapse of the tube. With Au-filling, the filled tube experiences an elastic-inelastic transition, somewhat like the behavior of metals, which is different from the cases when it is filled with gases or fullerenes, particularly for low filling density.
Authors: Luis Escobar-Alarcón, Emmanuel Velarde Granados, Diana Villa Sanchez, Oscar Olea-Mejia, Emmanuel Haro-Poniatowski, Alma Arrieta Castañeda, Dora Alicia Solis-Casados
Abstract: The aim of this work is to report on the preparation of bismuth and gold nanoparticles ablating the corresponding target immersed in different liquid solutions: water and ethanol. The effect of the liquid environment and laser fluence used for ablation on the size and size distribution of the nanoparticles synthesized was investigated. The nanoparticle size was measured by transmission electron microscopy (TEM). In general terms, for both metals, the results obtained reveal smaller sizes as low as approximately 2 nm. The bismuth nanoparticles, as deposited, are highly crystalline in nature and, depending on the conditions of preparation, either Bi or Bi2O3 nanoparticles are obtained in both liquids. UV-Vis measurements show the typical band absorption characteristic of spherical particles of nanometric size. It is worth mentioning that the gold colloids obtained using water are very stable.
Authors: Yoichi Okamoto, Masami Aono, Hisashi Miyazaki, Yudai Ogata, Makoto Tokuda, Tamotsu Mashimo
Abstract: There were still unclear questions in the new method that fabricate the high quality poly crystalline Si thin film from amorphous Si thin film with lower annealing temperature than conventional Si recrystallization temperature. In that recrystallization process, the recrystallization mechanism was generally explained by the MIC (Metal Induced Crystallization) of Au. In this paper, we have discussed the effects of film structure and strong gravity on recrystallization, by using conventional furnace and high-temperature ultracentrifuge furnace system. The five kinds of samples (two bilayered Si/Au thin films, two multilayered Si/Au thin films and trilayered Si/Au/Si thin film) and found the effects of structure and strong gravity. The best for crystallization was Au/Si multilayered thin film, which is almost finished to crystallize even at 673 K annealing. The strong gravity advanced and retreated the crystallization, depending to thin film structure.
Authors: S.W.H. Eijt, A. van Veen, P.E. Mijnarends, C.V. Falub, H. Schut, M.A. van Huis
Authors: T.D Dzhafarov, S. Aydin, D. Oren
Abstract: Porous silicon (PS) layers with porosity of 60% on n-type (111) Si substrates were prepared by anodic etching under the white illumination. Metal (Cu, Ag or Au)/PS/Si and metal (Cu, Ag or Au)/Si structures have been fabricated by evaporation of thin metal film onto the PS or Si surface, respectively. The diffusion annealing of structures was carried out in air at 100-250oC. Examination of Cu, Ag and Au concentration distribution in PS layer and monocrystalline Si substrate was performed by successive removal of thin layers from sample and measuring the energy dispersive X-ray fluorescence (EDXRF) intensity of CuKα1, AgKα1 and AuLβ1 peak. The effective diffusion coefficients for investigated metals along PS surfaces decrease in series Cu, Ag and Au and temperature dependences are described as D(Cu)=7.8 exp(-0.62eV/kT), D(Ag)=4.2x10 exp(-0.72eV/kT) and D(Au)=1.2x102 exp(-0.81eV/kT). Diffusion coefficients of Cu, Ag and Au along PS surfaces are larger (by a factor of 104-105) than those into monocrystalline Si. The diffusion mechanism of Cu, Ag and Au along PS surfaces is discussed and data on influence of diffusion of these metals on humidity-sensitive characteristics of metal(Cu, Ag or Au)/PS Schottky type gas sensors is also presented. Diffusion of metals of I group in PS is accompanied by increase of humidity-sensitivity of metal/PS structures by a factor of 1.2-1.4.
Authors: Chung Seog Oh, Sung Hoon Choa, Chang Seung Lee, Hak Joo Lee
Abstract: The accurate characterization of linear coefficient of thermal expansion (CTE) of thin films is vital for predicting the thermal stress, which often results in warpage and failure of a MEMS structure. In this paper, special emphasis is placed on the development of novel test method to extend an ISDG (Interferometric Strain/Displacement Gage) technique to the direct and accurate CTE measurement of MEMS materials, AlN and Au. The freestanding AlN and Au films are 1 μm thick and 5 mm wide. Strain is directly measured by a brand-new digital type ISDG with two Cr lines deposited on the specimen while heating a specimen in a furnace. The whole test system is verified first by measuring the CTE for the NIST’s SRM (Standard Reference Material) 736 (Cu) block. The measured CTE is 17.3 με/oC up to 167 oC, which agrees well with the NIST’s certified value. The CTE of Au is 25.4 ± 1.15 με/oC and that of AlN film is 3.77 ± 0.12 με/oC. The in-plane displacement resolution is about 5 nm at the best circumstances.
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