Zhong Chen

Bio: Zhong Chen is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Medicine & Chemistry. The author has an hindex of 80, co-authored 1000 publications receiving 28171 citations. Previous affiliations of Zhong Chen include Institute of High Performance Computing Singapore & National Institute of Education.

Effect of TiO2 nanoparticle addition on electroless Ni–P under bump metallization for lead-free solder interconnection

Abstract: One primary purpose of this study is to introduce an electroless Ni–P–TiO 2 (17.5 at% of P) composite coating as a pad finish for advanced electronic packaging. In this study, TiO 2 nanoparticles were incorporated into the Ni–P layer by electroless deposition and its function as novel under bump metallization (UBM) was intensively investigated. The majority of the added TiO 2 nanoparticles were proved to be uniformly distributed in UBM by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The interfacial reaction between electrolessly deposited Ni–P–TiO 2 layer and Sn–3.5Ag solder alloy was systematically analyzed. The prime Ni–P UBM was used for comparison to evaluate the effect of TiO 2 nanoparticle on the interfacial microstructure and mechanical property. Both solder/Ni–P and solder/Ni–P–TiO 2 joints were aged at temperature from 150 °C to 190 °C for different aging periods in order to study the intermetallic compounds (IMCs) growth and calculate the activation energy. It was found the growth of Ni 3 Sn 4 IMC layer and the void formation at the reaction interface were successfully suppressed with the help of the TiO 2 nanoparticle. The activation energies for the growth of Ni 3 Sn 4 on Ni–P and Ni–P–TiO 2 layers were calculated to be 50.9 kJ/mol and 55.7 kJ/mol, respectively. The extensive growth of Ni 3 P and Ni–Sn–P phases as well as the consumption rate of the amorphous UBM was controlled in joints with TiO 2 nanoparticles. Thus Ni–P–TiO 2 UBM blocked the Cu diffusion from substrate to interface. A detailed reaction induced diffusion mechanism was proposed. The solder/Ni–P–TiO 2 solder joint consistently demonstrated higher shear strength than solder/Ni–P joint as a function of aging time. TiO 2 nanoparticle contributed to slow down the declining rate of shear strength from 0.021 Mpa/h to 0.013 Mpa/h with the aging time. Moreover, after the shear strength test, fracture mainly occurred at solder matrix of the solder/Ni–P–TiO 2 joint; the morphology showed a ductile fracture pattern with a large distribution of dimples on the rough surface.

Creep behavior of Sn–Bi solder alloys at elevated temperatures studied by nanoindentation

Abstract: The creep mechanisms of eutectic Sn–Bi alloy were evaluated with indentation constant strain rate (CSR) method at elevated temperatures. The activation energy (Q) and creep stress exponent (n) of eutectic Sn–Bi alloy and other alloy compositions were measured in the temperature range from 25 to 100 °C. Prior to this, the indentation CSR testing protocol for evaluation of Q and n was validated through evaluating the pure Sn (grain size >100 µm) at various temperatures. The creep mechanism of large grain-sized Sn was found to be dislocation climb controlled by core diffusion in bulk. Dislocation climb though core diffusion and power-law breakdown were suggested to be the deformation mechanism for pure Bi and Sn–3%Bi alloy, respectively. For the two-phased eutectic Sn–Bi alloy, the creep mechanism was found to be strain rate and temperature dependent. Individual constituent phases were found to take turns to dominate the creep rate at different strain rates.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Principles of Neural Science

Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...