In flip-chip packages, the effect of Ni metallization on the substrate side on interfacial reactions between solders and an Al/Ni(V)/Cu under-bump metallization (UBM) on the chip side was investigated during the reflow process. The Ni substrate metallization greatly accelerated interfacial reactions on the chip side and quickly degraded the thermal stability of the UBM due to a fast consumption of the Ni(V) layer. This phenomenon can be explained in terms of rapid Ni or Sn diffusion in the ternary (Cu,Ni)6Sn5 phase, which was formed in the solder adjacent to the Ni(V) layer and the enhanced dissolution of (Cu,Ni)6Sn5 into the molten solder. Without the Ni metallization on the substrate side, the Al/Ni(V)/Cu UBM remained very stable with both eutectic SnPb and Pb-free solders.

Boron nitride nanotubes (BNNTs) filled with zirconium oxide (ZrO2) nanorods were synthesized by the improved solid-gas multiphase reaction method. The structure of ZrO2 nanorods was monoclinic single crystal or multi-twin crystal. The diameters of ZrO2 nanorods varied from 20 to 40 nm. The inner diameters of BNNTs were similar to those of corresponding ZrO2 nanorods. The BNNTs exhibited open end, closed end, or an end connected with a short tube grown from the tip of the ZrO2 nanorod. No preferred orientation was observed for the growth of ZrO2 nanorods.

This communication presents the effects of nitrogen pressure on the crystallization behavior of Si3.0B1.1C5.3N3.0 ceramics annealed at 1800 °C for 3 h. Transmission electron microscopy observation reveals that increasing nitrogen pressure results in the retardation of the crystallization process. Besides SiC and Si3N4 nanocrystals, individual large crystallites were also detected. These crystals were composed only of Si and N, and they possessed hexagonal structure with lattice parameters a = 0.737 nm and c = 0.536 nm. Crystallites of this novel phase were more frequently found with increased nitrogen pressure.

Y-branching multiwalled carbon nanotubes with a bamboolike structure were grown by chemical vapor deposition from a C–H–N gas system when B2O3 and Ti was supplied. Transmission electron microscopy images reveal that these novel junctions contain a tube branched into two tubes with nearly the same diameter. In addition, the tube walls show perpendicularly stacked graphite planes, which take on a bamboolike structure. The influence of preparation conditions on the structure of these carbon nanotubes is discussed. This novel structure may offer promising application for nanotube-based composites.

Europium-doped yttrium oxide (Y2O3:Eu3+) luminescent coatings were produced in a single step directly from a solution precursor using a radio frequency induction plasma spray technique. Crystalline and luminescent coatings were grown on Si(100) and steel substrates by this process. X-ray diffraction analyses on these coatings confirmed that polycrystalline cubic Y2O3 phase formed in situ with no impurity phases. The observed photoluminescence from these coatings is in all probability due to the highly crystalline nature of the coating combined with submicron spherical morphology of the grains.

Near-ternary eutectic Sn–Ag–Cu alloys are leading candidates for Pb-free solders. These alloys have three solid phases: β–Sn, Ag3Sn, and Cu6Sn5. Starting from the fully liquid state in solidifying near-eutectic Sn–Ag–Cu alloys, the equilibrium eutectic transformation is kinetically inhibited. The Ag3Sn phase nucleates with minimal undercooling, but the β–Sn phase requires a typical undercooling of 15 to 30 °C for nucleation. Because of this disparity in the required undercooling for nucleation, large, platelike Ag3Sn structures can grow rapidly within the liquid phase, before the final solidification of the solder joints. At lower cooling rates, the large Ag3Sn plates can subtend the entire cross section of solder joints and can significantly influence the mechanical deformation behavior of the solder joints under thermomechanical fatigue conditions. In this paper, it is demonstrated that the Ag3Sn plate formation can be inhibited, an important factor in assuring the reliability of solder joints composed of these alloys.

TiC nanoparticles (average diameter 10–150 nm) were prepared by reacting bulk Ti powders (average diameter 20 μm) with gaseous 1-chlorobutane at a relatively low temperature (1073–1273 K). 1-Chlorobutane provided the carbon atom in the TiC and the chlorine atom that assisted the shrinking of the size of the original Ti powders. The apparently simple procedure is a complex heterogeneous process combining etching, deposition, and carburization reactions.

Cellular solids were processed from machined scraps of a medium carbon steel by sintering. Mechanical properties of the cellular solids were investigated by compressive tests from the viewpoint of effects of high dislocation density in the machined scraps on the solid-state bonding. The flow stress in the plateau region for the cellular solid made of the as-machined scraps was higher than that of the one made of the annealed scraps. Clearly, the bonding strength between scraps was increased by the high dislocation density in the as-machined scraps.

In this work, (Ba1−xCex)Ti1−x/4(VTi)x/4O3 ceramics with x = 0.02, 0.04, 0.06, and 0.08 (VTi denotes titanium vacancies) were synthesized by the mixed-oxide method. The results of x-ray diffraction analysis and scanning electron microscopy show that all the samples are monophasic. The crystalline structure can be indexed as tetragonal for the samples with x ≤ 0.06, but as cubic for x = 0.08. Three phase transitions were observed in the temperature dependence of the dielectric permittivity, similar to those observed in pure BaTiO3, and the three phase transition temperatures (Tc, T1, and T2) shifted to lower temperatures with the rates of −18, −12, and −7 K per molar percentage of Ce3+, respectively. This is quite different from that observed in BaTiO3 with Ce substitution at the Ti-site, in which Tc shifted to a lower temperature, and T1 and T2 to higher temperatures. The permittivity maximum increased with increasing Ce content, which is mainly attributed to an increase in the grain size.

Cold isostatic pressing (CIP) is often used in the compaction of nano-sized powders. For technological reasons, however, uniaxial pressing prior to CIP takes place. This paper reveals the first quantitative measurements of density gradients within and the asymmetric sintering response of nanoscale zirconia compacts formed by (i) simple uniaxial compaction and (ii) specific ratios of uniaxial and CIP pressure. We find that CIP forms an exterior “skin” of higher but variable surface density and decreases the width of the density distribution. It does not eliminate density gradients; nonuniform shrinkage still occurs during sintering. The high- and low-density zones (the moving and fixed ram ends, respectively) that form during uniaxial compaction are reversed during CIP. Considering both density distribution width and spring-back cracking, the “best” uniaxial-CIP pressure combination is 1–20 ksi for this particular powder and an L/D of 1.0. The greater final compaction of the low-density zone during CIP causes relatively large variations in final dimensions (nearly 400 microns) in spite of the smaller density distribution width. The usually neglected uniaxial pressing step has definite technological impacts on the production of nanostructured components via compaction.

A simple approach has been developed for the synthesis of Au@CdS core-shell nanoparticles by a direct self-assembling process. Stable Au@CdS composite colloids were prepared by thiourea, as a double-functional reagent that acted as the linkage agent between Cd2+ ions and gold nanoparticles. The CdS-capped gold composite nanoparticles were successfully integrated into BaTiO3 films. A significant enhancement of third-order nonlinear optical susceptibility in the Au@CdS nanoparticles with core-shell structure is reported. To compare the effect of enhanced nonlinear response, single gold or CdS nanoparticles embedded in BaTiO3 films were also prepared.

A transmission electron microscopy investigation on the microstructure evolution of the sintered compact of zirconium diboride was carried out. Grain boundary phases, structure, and morphology of the grains and defect structures were studied to understand the sintering behavior of these borides. The impurities, such as Fe, were found to stay at the triple junction point as (Fe, Zr)2B. Different types of defect structures, such as dislocations, twins, and faceted growth, were observed. No diffusion of Fe into ZrB2 could be observed, but the Zr diffusion into Fe was established.

Nanoparticles were produced on the surface of silicon upon pulsed-laser irradiation in the presence of an inert gas atmosphere at fluences close to the melting threshold. It was observed that nanoparticle formation required redeposition of ablated material. Redeposition took place in the form of a thin film intermixed with extremely small nanoparticles possibly formed in the gas phase. Through the use of nonpolarized laser light, it was shown that nanoparticles, fairly uniform in size, became grouped into curvilinear strings distributed with a short-range ordering. Microstructuring of part of the surface prior to the laser treatment had the remarkable effect of producing nanoparticles lying along straight and fairly long (approximately 1 mm) lines, whose spacing equaled the laser wavelength for normal beam incidence. In this work, it is shown that the use of polarized light eliminated the need of an aiding agent: nanoparticle alignment ensued under similar laser treatment conditions. The phenomenon of nanoparticle alignment bears a striking similarity with the phenomenon of laser-induced periodic surface structures (LIPSS), obeying the same dependence of line spacing upon light wavelength and beam angle of incidence as the grating spacing in LIPSS. The new results strongly support the proposition that the two phenomena, LIPSS and laser-induced nanoparticle alignment, evolve as a result of the same light interference mechanism.

Single as well as graded compositions were fabricated in the Ti–B system using a microwave-activated combustion synthesis (MACS) process. When synergistically combined with microwave processing, combustion synthesis offers great potential for the fabrication of ceramic structures and composites. Combustion waves were triggered using a SiC susceptor to initially absorb microwaves. The effects of processing variables, such as thermal insulation, and atmosphere on the process were investigated. Examination of reacted samples by means of x-ray diffraction indicated the presence of titanium monoboride and diboride along with unreacted titanium. Compared with conventional combustion synthesized products, MACS resulted in smaller pores. However, the total amount of porosity remained almost the same. The microstructure of the graded layers and interfaces were examined using optical and scanning electron microscopy. Over the entire cross section, the interfaces were continuous and crack free.

The absence of a low dielectric constant layer at the barium strontium titanate (BST)/Pt interface and a decreased roughness are critical issues in the production of (Ba0.5Sr0.5)TiO3 thin films with high tunabilities and low losses. An improvement in dielectric properties was achieved by the insertion of seed layers at the BST/Pt interface by pulsed laser deposition. The higher tunability can be attributed to (100) texturing of the BST films, which is independent of grain size and grain morphologies, thus leading to a variation in seed layer thicknesses. The tunability and dielectric constant of 1600-Å-thick BST films showed a maximum of 53% and 720, respectively, at a seed layer thickness of 100 Å. Dielectric loss is dependent on the roughness of BST films and reached a minimum of 0.8% at a root mean square roughness of 28 Å. The maximum figures of merit, defined as the ratio of tunability to dielectric loss, of approximately 58 at 100 kHz and 198 kV/cm were obtained at a seed layer thickness of 70 Å. The optimized seed layer thickness for BST deposition onto Pt/Ti/SiO2/Si substrates plays an important role in maintaining the high tunabilities and low loss, which are suitable for microwave device applications.

Microwave energy was used to sinter high thermal conductivity AlN ceramics (160–225 W/mK). The effects of sintering time, temperature, and amount of additive on phase composition, phase distribution, densification behavior, grain growth, and thermal conductivity were studied. The thermal conductivity of AlN was greatly improved by the addition of Y2O3, extended sintering time, and higher sintering temperatures. Thermal conductivity development in Y2O3-doped AlN showed two distinctive time regimes: (i) densification, where full densification, secondary phase formation, concentration and segregation, and rapid purification of AlN grains occur, accompanied by a large increase in thermal conductivity; (ii) postdensification, where grain growth and secondary phase sublimation/evaporation occur, yielding a further increase in thermal conductivity. Our results indicate that microwave sintering is a promising approach for synthesis of high thermal conductivity AlN ceramics.

The influence of synthesis conditions on the formation of yttrium aluminum garnet (YAG) powders starting from the same solution precursors was investigated by employing a citrate–nitrate gel combustion process and a precursor plasma spraying technique. YAG powders were formed at ≥500 °C, through the citrate–nitrate gel combustion process, without any intermediate phase formation. Time-resolved x-ray experiments were performed for the first time on these citrate–nitrate precursor materials to understand their mode of decomposition. The in situ data confirmed a single-step conversion to YAG from the precursor powder without any intermediate phase formation. Ex situ experiments also produced similar results. However, the use of the same citrate–nitrate precursor solution as a liquid feedstock material in the precursor plasma spraying technique revealed an entirely different transformation mechanism to YAG through intermediate phases like H–YalO3 and O–YalO3.

Heteroepitaxial KTaO3 thin films were synthesized by the hydrothermal method below 175 °C in highly alkaline aqueous KOH solutions. KTaO3 films synthesized in 7 M KOH solutions contained a defect pyrochlore phase that had (400) and (111) out-of-plane orientations. The (400) oriented pyrochlore islands were epitaxially related to the (100) SrTiO3 substrate while the (111) oriented pyrochlore islands had four in-plane variants. Pyrochlore-free KTaO3 films could be synthesized in a 15 M KOH solution. Pyrochlore-free films were also grown at 7 M KOH by delaying the introduction of the (100) SrTiO3 substrate into the synthesis solution until the conditions favoring the formation of the pyrochlore phase had dissipated.

The combustion process of a titanium–carbon system with sodium chloride as an inert diluent was investigated. The combustion laws and microstructure of final products according to diluent content were obtained. It was shown that sodium chloride not only decreases combustion temperature but also makes effective protective shells around primary carbide crystals and keeps this ultrafine structure up to the end of combustion. As a result, nano-sized titanium carbide powders were successfully obtained.

Iron crystals were deposited by thermally activated chemical vapor deposition with imposition of magnetic field. In this study, the deposition was conducted by imposing a magnetic field up to 3.5 T in a temperature range between 0.48 and 0.51 of TmFe (melting point of iron), which is below the Curie point of iron (0.58 TmFe). The microstructures and crystal orientations of the deposits were investigated. In the deposition process, island-shaped crystals were formed on a scale of several microns; then a film was grown by their coalescence. As the magnetic field magnitude increased, population of the island-shaped crystals having a cubic shape increased. Simultaneously, their ω-scanned (200) profile became sharper. Their degree of (100) preferred orientation was dependent on the magnetic field up to 3.5 T, which is usually high enough for the saturated magnetization of iron crystals. However, when the substrate was placed parallel to the magnetic field, (100) preferred orientation was not observed for the island-shaped crystals. A large and bimodal ω-scanned (110) profile having sharp peaks was obtained when the substrate was inclined 45° to the field. Preferred (100) orientation was not obtained from the iron films, for which two reasons were pointed out. The first is the secondary grown crystals on the island-shaped crystals having different orientations, and the second is the observed zone III grain structure of the films, where grain boundary migration occurred.