Two-Phase Metallic Thermal Interface Materials Processed Through Liquid Phase Sintering Followed by Accumulative Roll Bonding

Thermal interface materials (TIMs) form a mechanical and thermal link between a heat source and a heat sink. Thus, they should have high thermal conductivity and high compliance to efficiently transfer heat and accommodate any differential strain between the heat source and the sink, respectively. This paper reports on the processing and the characterization of potential metallic TIM composite solders comprising of Cu, a high conductivity phase, uniformly embedded in In matrix, a highly compliant phase. We propose the fabrication of such a material by a two-step fabrication technique comprising of liquid phase sintering (LPS) followed by accumulative roll bonding (ARB). To demonstrate the efficacy of the employed two-step processing technique, an In-40 vol. % Cu composite solder was produced first using LPS with short sintering periods (30 or 60 s at 160 degrees C) followed by ARB up to five passes, each pass imposing a strain of 50%. Mechanical response and electrical and thermal conductivities of the fabricated samples were evaluated. It was observed that processing through ARB homogenizes the distribution of Cu in an In matrix, disintegrates the agglomerates of Cu powders, and also significantly increases thermal and electrical conductivities, almost attaining theoretically predicted values, without significantly increasing the flow stress. Furthermore, the processing technique also allows the insertion of desired foreign species, such as reduced graphene oxide, in In-Cu for further enhancing a target property, such as electrical conductivity.

Designer porous antibacterial membranes derived from thermally induced phase separation of PS/PVME blends decorated with an electrospun nanofiber scaffold

We report the development of porous membranes by thermally induced phase separation of a PS/PVME (polystyrene/polyvinylmethyl ether]) blend, which is a typical LCST mixture. The morphology of the membrane after etching out the PVME phase was characterized by scanning electron microscopy. To give the membrane an antibacterial surface, polystyrene (PS) and polyvinyl(methyl ether)]-alt-maleic anhydride (PVME-MAH) with silver nanoparticles (nAg) were electrospun on the membrane surface. Pure water flux was evaluated by using a cross-flow membrane setup. The microgrooved fibers changed the flux across the membrane depending on the surface properties. The antibacterial properties of the membrane were confirmed by the reduction in the colony count of E. coli. The SEM images show the disruption of the bacterial cell membrane and the antibacterial mechanism was discussed.

Liquid phase epitaxy growth of AlxGayIn1-x-yPzAs1-zGaAs with direct band gap up to 2.0 eV

III-V pentenary semiconductor AlGaInPAs with a direct band gap of up to 2.0 eV has been grown successfully on GaAs substrates by liquid phase epitaxy;(LPE). With the introduction of the energy bowing parameters of quaternaries, the theoretical calculations agree well with the measured PL peak energy data from pentenary samples.

Structural, Electrical, And Optical Properties Of Inasxsb1-X Epitaxial Films Grown By Liquid-Phase Epitaxy

The InAsxSb1-x films were grown on (100) GaSb substrates by liquid-phase epitaxy, and their structural, electrical, and optical properties were investigated. The high-resolution x-ray diffraction results reveal that the single crystalline InAsxSb1-x films with a midrange composition are epitaxially grown on the GaSb substrates. Temperature dependence of the Hall mobility was theoretically modeled by considering several predominant scattering mechanisms. The results indicate that ionized impurity and dislocation scatterings dominate at low temperatures, while polar optical phonon scattering is important at room temperature (RT). Furthermore, the InAsxSb1-x films with the higher As composition exhibit the better crystalline quality and the higher mobility. The InAs0.35Sb0.65 film exhibits a Hall mobility of 4.62x10(4) cm(2) V-1 s(-1). The cutoff wavelength of photoresponse is extended to about 12 mu m with a maximum responsivity of 0.21 V/W at RT, showing great potential for RT long-wavelength infrared detection. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989116]

Ga1-xMnxSb grown on GaSb substrate by liquid phase epitaxy

The Gal(1-x)Mn(x)Sb epilayer was prepared on the n-type GaSb substrate by liquid phase epitaxy. The structure of the Gal(1-x)Mn(x)Sb epilayer was analyzed by double-crystal X-ray diffraction. From the difference of the lattice constant between the GaSb substrate and the Ga1-xMnxSb epilayer, the Mn content in the Ga1-xMnxSb epilayer were calculated as x = 0.016. The elemental composition of Ga1-xMnxSb epilayer was analyzed by energy dispersive spectrometer. The carrier concentration was obtained by Hall measurement. The hole concentration in the Ga1-xMnxSb epilayer is 4.06 x 10(19)cm(-3). It indicates that most of the Mn atoms in Ga1-xMnxSb take the site of Ga, and play a role of acceptors. The current-voltage curve of the Ga1-xMnxSb/GaSb heterostructure was measured, and the rectifying effect is obvious. (C) 2003 Elsevier B.V. All rights reserved.

InAs0.3Sb0.7 films grown on (100) GaSb substrates with a buffer layer by liquid-phase epitaxy

The growth of InAsxSb1-x films on (100) GaSb substrates by liquid-phase epitaxy (LPE) has been investigated and epitaxial InAs0.3Sb0.7 films with InAs0.9Sb0.09 buffer layers have been successfully obtained. The low X-ray rocking curve FHWM values of InAs0.3Sb0.7 layer shows the high quality of crystal-orientation structure. Hall measurements show that the highest electron mobility in the samples obtained is 2.9 x 10(4) cm(2) V-1 s(-1) and the carrier density is 2.78 x 10(16)cm(-3) at room temperature (RT). The In As0.3Sb0.7 films grown on (10 0) GaSb substrates exhibit excellent optical performance with a cut-off wavelength of 12 mu m. (c) 2007 Elsevier B.V. All rights reserved.

Sputtering of the gallium-indium eutectic alloy in the liquid phase

We have measured sputtering yields and angular distributions of sputtered atoms from both the solid and liquid phases of gallium, indium, and the gallium-indium eutectic alloy. This was done by Rutherford backscattering analysis of graphite collector foils. The solid eutectic target shows a predominance of indium crystallites on its surface which have to be sputtered away before the composition of the sputtered atoms equals the bulk target composition. The size of the crystallites depends upon the conditions under which the alloy is frozen. The sputtering of the liquid eutectic alloy by 15 keV Ar⁺ results in a ratio of indium to gallium sputtering yields which is 28 times greater than would be expected from the target stoichiometry. Furthermore, the angular distribution of gallium is much more sharply peaked about the normal to the target surface than the indium distribution. When the incident Ar⁺ energy is increased to 25 keV, the gallium distribution broadens to the same shape as the indium distribution. With the exception of the sharp gallium distribution taken from the liquid eutectic at 15 keV, all angular distributions from liquid targets fit a cos² θ function. An ion-scattering-spectroscopy analysis of the liquid eutectic alloy reveals a surface layer of almost pure indium. A thermodynamic explanation for this highly segregated layer is discussed. The liquid eutectic alloy provides us with a unique target system which allows us to estimate the fraction of sputtered material which comes from the first monolayer of the surface.

Preparation of crystalline beta barium borate thin films on Sr2+-doped alpha barium borate substrates by liquid phase epitaxy

Thin films of beta barium borate have been prepared by liquid phase epitaxy on Si2+-doped alpha-BaB2O4 (alpha-BBO, the high temperature phase of barium berate) (001) and (110) substrates. The results of X-ray diffraction indicate that the films show highly (001) preferred orientation on (001)-oriented substrates while the films grown on (110) substrates are textured with (140) orientation. The crystallinity of these films was found to depend on growth temperature, rotation rate, dip time and orientation of substrate. Growth conditions were optimized to grow films with (001) orientation on (001) substrates reproducibly. The films show second harmonic generation of 400 nm light upon irradiation with 800 nm Ti: Sapphire femtosecond laser light. (c) 2005 Elsevier B.V. All rights reserved.

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (000 1) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 gm were gown in the temperature range 700-720 degrees C. The growth rate of ZnO films was estimated to be 0.3 mu m h(-1). Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films. (c) 2006 Elsevier B.V. All rights reserved.

Phase separation induced by Au catalysts in ternary InGaAs nanowires.

We report a novel phase separation phenomenon observed in the growth of ternary In(x)Ga(1-x)As nanowires by metalorganic chemical vapor deposition. A spontaneous formation of core-shell nanowires is investigated by cross-sectional transmission electron microscopy, revealing the compositional complexity within the ternary nanowires. It has been found that for In(x)Ga(1-x)As nanowires high precursor flow rates generate ternary In(x)Ga(1-x)As cores with In-rich shells, while low precursor flow rates produce binary GaAs cores with ternary In(x)Ga(1-x)As shells. First-principle calculations combined with thermodynamic considerations suggest that this phenomenon is due to competitive alloying of different group-III elements with Au catalysts, and variations in elemental concentrations of group-III materials in the catalyst under different precursor flow rates. This study shows that precursor flow rates are critical factors for manipulating Au catalysts to produce nanowires of desired composition.

Single sublattice endotaxial phase separation driven by charge frustration in a complex oxide.

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation.