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Crystals, Volume 3, Issue 3 (September 2013), Pages 391-516

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Research

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Open AccessArticle Corrosion Study and Intermetallics Formation in Gold and Copper Wire Bonding in Microelectronics Packaging
Crystals 2013, 3(3), 391-404; doi:10.3390/cryst3030391
Received: 8 May 2013 / Revised: 31 May 2013 / Accepted: 2 July 2013 / Published: 17 July 2013
Cited by 12 | PDF Full-text (751 KB) | HTML Full-text | XML Full-text
Abstract
A comparison study on the reliability of gold (Au) and copper (Cu) wire bonding is conducted to determine their corrosion and oxidation behavior in different environmental conditions. The corrosion and oxidation behaviors of Au and Cu wire bonding are determined through soaking in
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A comparison study on the reliability of gold (Au) and copper (Cu) wire bonding is conducted to determine their corrosion and oxidation behavior in different environmental conditions. The corrosion and oxidation behaviors of Au and Cu wire bonding are determined through soaking in sodium chloride (NaCl) solution and high temperature storage (HTS) at 175 °C, 200 °C and 225 °C. Galvanic corrosion is more intense in Cu wire bonding as compared to Au wire bonding in NaCl solution due to the minimal formation of intermetallics in the former. At all three HTS annealing temperatures, the rate of Cu-Al intermetallic formation is found to be three to five times slower than Au-Al intermetallics. The faster intermetallic growth rate and lower activation energy found in this work for both Au/Al and Cu/Al as compared to literature could be due to the thicker Al pad metallization which removed the rate-determining step in previous studies due to deficit in Al material. Full article
(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)
Open AccessArticle Electroless Nickel-Based Catalyst for Diffusion Limited Hydrogen Generation through Hydrolysis of Borohydride
Crystals 2013, 3(3), 405-418; doi:10.3390/cryst3030405
Received: 31 May 2013 / Revised: 5 July 2013 / Accepted: 15 July 2013 / Published: 19 July 2013
Cited by 1 | PDF Full-text (558 KB) | HTML Full-text | XML Full-text
Abstract
Catalysts based on electroless nickel and bi-metallic nickel-molybdenum nanoparticles were synthesized for the hydrolysis of sodium borohydride for hydrogen generation. The catalysts were synthesized by polymer-stabilized Pd nanoparticle-catalyzation and activation of Al2O3 substrate and electroless Ni or Ni-Mo plating of
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Catalysts based on electroless nickel and bi-metallic nickel-molybdenum nanoparticles were synthesized for the hydrolysis of sodium borohydride for hydrogen generation. The catalysts were synthesized by polymer-stabilized Pd nanoparticle-catalyzation and activation of Al2O3 substrate and electroless Ni or Ni-Mo plating of the substrate for selected time lengths. Catalytic activity of the synthesized catalysts was tested for the hydrolyzation of alkaline-stabilized NaBH4 solution for hydrogen generation. The effects of electroless plating time lengths, temperature and NaBH4 concentration on hydrogen generation rates were analyzed and discussed. Compositional analysis and surface morphology were carried out for nano-metallized Al2O3 using Scanning Electron Micrographs (SEM) and Energy Dispersive X-Ray Microanalysis (EDAX). The as-plated polymer-stabilized electroless nickel catalyst plated for 10 min and unstirred in the hydrolysis reaction exhibited appreciable catalytic activity for hydrolysis of NaBH4. For a zero-order reaction assumption, activation energy of hydrogen generation using the catalyst was estimated at 104.6 kJ/mol. Suggestions are provided for further work needed prior to using the catalyst for portable hydrogen generation from aqueous alkaline-stabilized NaBH4 solution for fuel cells. Full article
Figures

Open AccessArticle Electronic Origin of the Orthorhombic Cmca Structure in Compressed Elements and Binary Alloys
Crystals 2013, 3(3), 419-430; doi:10.3390/cryst3030419
Received: 24 May 2013 / Revised: 21 June 2013 / Accepted: 15 July 2013 / Published: 19 July 2013
Cited by 5 | PDF Full-text (364 KB) | HTML Full-text | XML Full-text
Abstract
Formation of the complex structure with 16 atoms in the orthorhombic cell, space group Cmca (Pearson symbol oC16), was experimentally found under high pressure in the alkali elements (K, Rb, Cs) and polyvalent elements of groups IV (Si, Ge) and V (Bi).
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Formation of the complex structure with 16 atoms in the orthorhombic cell, space group Cmca (Pearson symbol oC16), was experimentally found under high pressure in the alkali elements (K, Rb, Cs) and polyvalent elements of groups IV (Si, Ge) and V (Bi). Intermetallic phases with this structure form under pressure in binary Bi-based alloys (Bi-Sn, Bi-In, Bi-Pb). Stability of the Cmca-oC16 structure is analyzed within the nearly free-electron model in the frame of Fermi sphere-Brillouin zone interaction. A Brillouin-Jones zone formed by a group of strong diffraction reflections close to the Fermi sphere is the reason for the reduction of crystal energy and stabilization of the structure. This zone corresponds well to the four valence electrons in Si and Ge, and leads to assume an spd-hybridization for Bi. To explain the stabilization of this structure within the same model in alkali metals, that are monovalents at ambient conditions, a possibility of an overlap of the core, and valence band electrons at strong compression, is considered. The assumption of the increase in the number of valence electrons helps to understand sequences of complex structures in compressed alkali elements and unusual changes in their physical properties, such as electrical resistance and superconductivity. Full article
(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)
Open AccessArticle Zintl Salts Ba2P7X (X = Cl, Br, and I): Synthesis, Crystal, and Electronic Structures
Crystals 2013, 3(3), 431-442; doi:10.3390/cryst3030431
Received: 1 June 2013 / Revised: 16 July 2013 / Accepted: 6 August 2013 / Published: 26 August 2013
Cited by 7 | PDF Full-text (981 KB) | HTML Full-text | XML Full-text
Abstract
Two barium phosphide halides, Ba2P7Br and Ba2P7I, were synthesized and structurally characterized by single crystal X-ray diffraction. Both compounds crystallize in the monoclinic space group P21/m (No. 11) and are isostructural
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Two barium phosphide halides, Ba2P7Br and Ba2P7I, were synthesized and structurally characterized by single crystal X-ray diffraction. Both compounds crystallize in the monoclinic space group P21/m (No. 11) and are isostructural to Ba2P7Cl. The crystal structures of Ba2P7X (X = Cl, Br, I) feature the presence of heptaphosphanortricyclane P73− clusters along with halogen anions and barium cations. According to the Zintl concept, Ba2P7X compounds are electron-balanced semiconductors. Quantum-chemical calculations together with UV-Visible spectroscopy confirm the title compounds are wide bandgap semiconductors. The bonding in the P73− clusters was analyzed by means of electron localization function. The elemental compositions were confirmed using energy dispersive X-ray spectroscopy. Full article
(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)
Figures

Open AccessArticle Bonding Schemes for Polar Intermetallics through Molecular Orbital Models: Ca-Supported Pt–Pt Bonds in Ca10Pt7Si3
Crystals 2013, 3(3), 504-516; doi:10.3390/cryst3030504
Received: 15 July 2013 / Revised: 16 August 2013 / Accepted: 20 August 2013 / Published: 3 September 2013
Cited by 7 | PDF Full-text (791 KB) | HTML Full-text | XML Full-text
Abstract
Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca10Pt
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Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca10Pt7Si3, whose large Ca content offers the potential for negative formal oxidation states on the Pt. The structure can be divided into a sublattice of Ca cations and a Pt–Si polyanionic network built from Pt7Si3 trefoil units linked through Pt–Pt contacts of 3.14 Å. DFT-calibrated Hückel models reveal that the compound adheres well to a Zintl-like electron counting scheme, in which the Pt–Si and Pt–Pt contacts are equated with two-center two-electron bonds. The experimental electron count is in excess of that predicted by 2%, a discrepancy which is attributed to the electron transfer from the Ca to the Pt–Si network being incomplete. For the Pt–Pt contacts, the occupancy of the bonding orbitals is dependent on the participation of the surrounding Ca atoms in bridging interactions. This use of multi-center interactions isolobal to classical two-center two-electron bonds may illustrate one path by which the bonds delocalize as one moves from the Zintl phases toward the Hume-Rothery domain. Full article
(This article belongs to the Special Issue New Trends in Intermetallics Development and Application)

Review

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Open AccessReview High Birefringence Liquid Crystals
Crystals 2013, 3(3), 443-482; doi:10.3390/cryst3030443
Received: 28 June 2013 / Revised: 27 July 2013 / Accepted: 31 July 2013 / Published: 3 September 2013
Cited by 46 | PDF Full-text (1757 KB) | HTML Full-text | XML Full-text
Abstract
Liquid crystals, compounds and mixtures with positive dielectric anisotropies are reviewed. The mesogenic properties and physical chemical properties (viscosity, birefringence, refractive indices, dielectric anisotropy and elastic constants) of compounds being cyano, fluoro, isothiocyanato derivatives of biphenyl, terphenyl, quaterphenyl, tolane, phenyl tolane, phenyl ethynyl
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Liquid crystals, compounds and mixtures with positive dielectric anisotropies are reviewed. The mesogenic properties and physical chemical properties (viscosity, birefringence, refractive indices, dielectric anisotropy and elastic constants) of compounds being cyano, fluoro, isothiocyanato derivatives of biphenyl, terphenyl, quaterphenyl, tolane, phenyl tolane, phenyl ethynyl tolane, and biphenyl tolane are compared. The question of how to obtain liquid crystal with a broad range of nematic phases is discussed in detail. Influence of lateral substituent of different kinds of mesogenic and physicochemical properties is presented (demonstrated). Examples of mixtures with birefringence ∆n in the range of 0.2–0.5 are given. Full article
(This article belongs to the Special Issue Advances in Liquid Crystals)
Open AccessReview High Performance Negative Dielectric Anisotropy Liquid Crystals for Display Applications
Crystals 2013, 3(3), 483-503; doi:10.3390/cryst3030483
Received: 8 July 2013 / Revised: 21 August 2013 / Accepted: 26 August 2013 / Published: 3 September 2013
Cited by 20 | PDF Full-text (1241 KB) | HTML Full-text | XML Full-text
Abstract
We review recent progress in the development of high birefringence (Δn ≥ 0.12) negative dielectric anisotropy (Δε < 0) liquid crystals (LCs) for direct-view and projection displays. For mobile displays, our UCF-N2 (low viscosity, negative Δε, high Δn
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We review recent progress in the development of high birefringence (Δn ≥ 0.12) negative dielectric anisotropy (Δε < 0) liquid crystals (LCs) for direct-view and projection displays. For mobile displays, our UCF-N2 (low viscosity, negative Δε, high Δn) based homogeneous alignment fringe-field switching (called n-FFS) mode exhibits superior performance to p-FFS in transmittance, single gamma curve, cell gap insensitivity, and negligible flexoelectric effect. For projection displays using a vertical alignment liquid-crystal-on-silicon (VA LCOS), our high birefringence UCF-N3 mixture enables a submillisecond gray-to-gray response time, which is essential for color sequential displays without noticeable color breakup. Our low viscosity UCF-N2 also enables multi-domain VA displays to use a thinner cell gap for achieving faster response time. Full article
(This article belongs to the Special Issue Advances in Liquid Crystals)

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