Void Trapping Research Articles

Construction of anchoring traps-reinforced ultrafine ruthenium nanoparticles as efficient catalysts for boosting H2 production from ammonia-borane hydrolysis

Hydrogen release through ammonia-borane hydrolysis (ABH) is vital for mitigating the energy crises and environmental problems from fossil fuels. However, improving the catalytic performance for ABH via concomitantly regulating the atom utilization efficiency and electronic metal-support interaction of supported catalysts remains challenging. Herein, anchoring traps-reinforced nano-ruthenium integrated hollow N-doped carbon spheres (Ru@HNCS) are synthesized and utilized for ABH toward hydrogen production. The synergy of void trapping and N-anchoring effects enables the fabrication and uniform distribution of ultrafine Ru (1.47 nm in diameter) nanoparticles (NPs) onto the HNCS matrix. Compared with the Ru@C analogue, the achieved Ru@HNCS exhibits much higher catalytic activity (turnover frequency: 1051 min−1), lower activation energy (26.9 kJ mol−1) and higher reusability toward hydrogen production from ABH. The high atomic utilization efficiency of metal species and electronic metal-support interaction can effectively accelerate the oxidative cleavage of the H–O bonds in the attacked H2O, thus kinetically boosting catalytic performance for ABH. The present study represents a useful strategy to fabricate efficient supported nanocatalysts for catalytic applications.

Copper Electroless Bonding of Dome-Shaped Pillars for Chip-to-Package Interconnect

Electroless plating was used to achieve compliant bonding between two components with electroplated copper pillars for chip-to-package interconnects. The geometry of the pillars was modified from flat-topped to round, dome-shaped structures by addition of a leveler to the electroplating bath used to form the pillars. The effect of the dome-shaped structure on the electroless joining process was studied using different electroless plating baths. The baths contained a surfactant and used forced convection during electroplating. Void trapping was observed in the electroless region between the domed, electroplated pillars, however, the size of the voids is smaller than previously reported with flat-topped pillars. The surfactant, Triton X-100 was found to decrease void formation at the electroless joint.

Fabrication and electrical characterization of through-Si-via interconnect for 3-D packaging

Fabrication process of through-Si-via (TSV) interconnects and their electrical characterization method were investigated for 3-D stacked packaging. A prototype, three-layer module with a flip-chip bonding process with anisotropic conductive film (ACF) was fabricated with the process. To measure a single interconnect resistance, a Kelvin structure was designed and applied on the chip and substrate. A theoretical model to calculate the connection resistance of the 3-D TSV interconnects was also derived and used to verify the experimentally measured resistance by applying the Kelvin structure designed. Optimum conditions for the formation of through-holes with the deep reactive ion-etching process were a coil power of 200 W, cycle time of 6.5/5 s, and SF6:C4F8 gas flow rate of 260:100 sccm. Pulse-reverse current provided the finest grain growth during the Cu electroplating and thus prevented the trapping of voids. The experimentally measured resistance was successfully verified by the theoretical model, and the model shows that the resistance value was mainly contributed by the ACF interconnect, not by TSVs.

Simulation of capacitor discharge stud welding process and void formation

Dynamic behaviour and void formation of the capacitor discharge (CD) stud welding process are investigated through simulation and experiments. Mechanical and electrical models are coupled to predict the current and voltage waveform of the stud welding, and the calculated results show good agreement with the experiment results. The mechanism of void formation and the void trapping condition are explained using the void flow model. While the results of the void flow model show that removal of the void is almost impossible, partial improvement in void reduction is achieved by adjusting the short circuit current between 1200 and 1700 A.

Three-dimensional simulation of void migration at the interface between thin metallic film and dielectric under electromigration

A kinetic Monte Carlo simulation of the electromigration-induced void migration behavior of three-dimensional nanovoids at the interface between a metal conductor and its dielectric overlayer is presented. Major stages of the recently observed failure mode of surface void migration and accumulation at the cathode via of Cu damascene interconnects were simulated, including the trapping at and detachment from grain boundaries (GBs) and GB triple junctions. The migration and shape evolution of voids along the interface and along the grain boundaries intersecting this interface have also been investigated in detail. The main results of the simulation correlate well with in situ observations as well as with simple analytical models of void trapping and detachment from GBs and their junctions.

Control of chaos in laser-induced vapor capillaries

Vapor capillaries associated with deep penetration laser welding (keyholes) are inherently unstable and it is well known that the bounded evolution of unstable modes of nonlinear dynamic systems can lead to complex fluctuations of state and/or output variables. In the case of keyholes, the magnitude of self-induced fluctuations is sometimes large enough to cause occasional closure (“collapse”) and trapping of voids in the solidifying weld metal. Since voids are serious and frequent defects in partial penetration laser welds, methods to improve the stability of the keyhole, and thereby reduce or eliminate their incidence are of considerable practical interest. One technique that is known to simplify the complicated behavior of chaotic systems involves the application of periodic perturbations to accessible system inputs or boundaries. Consequently, this work investigated the effect of power modulation on porosity formation in laser welds. Frozen glycerin was used as the medium for welding since its transparency allowed visualization of the keyhole, facilitating control parameter development. Statistical and spectral analysis of penetration depth signals for the uncontrolled system was performed to characterize the nonlinear keyhole dynamics. In the control studies, it was found that the optimum frequency of power modulation at 400 Hz was very effective for reducing porosity. A 15° leading beam incidence angle was found to provide further improvements. Three-dimensional phase portraits of the keyhole depth for uncontrolled and controlled signals showed that the control did not convert depth fluctuations to a completely predictable limit cycle but that the remaining fluctuations were more predictable than those of the uncontrolled system.

Morphological instabilities in the low pressure synthesis of diamond

Morphological instabilities attending the high growth rate of diamond films are examined. Pertinent literature on morphological instabilities and microstructure evolution in vapor deposited films is reviewed and theoretical treatments related to the case of diamond growth are discussed. Diamond films of various thicknesses have been synthesized utilizing the combustion flame synthesis technique involving diamond growth rates of ∼1 μm/min. Films of thicknesses under 20 μm are found to be dense and the surface smoothness of such films is governed by facets on the individual crystallites that make up the film. Increasing film thicknesses, at high growth rates, results in extremely rough surfaces, the trapping of voids and discontinuities, and the incorporation of non-diamond phases in the growing film. These characteristics are typical of morphological instabilities when surface diffusion and re-evaporation processes are absent and instability is promoted by the high rate arrival of the appropriate species from the flame ambient to the surface. Factors contributing to morphological instabilities include competitive shadowing and nutrient starvation and growth anisotropy of the different crystallographic faces on individual diamond crystals. It is shown that surface temperature and the presence of oxidizing species in the flame ambient contribute to anisotropic growth of diamond crystals and hence to morphological instabilities in diamond films. An approach to avoiding these instabilities is briefly discussed.