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 …

I and i

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.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Recent advances in mechanics and materials provide routes to integrated circuits that can offer the electrical properties of conventional, rigid wafer-based technologies but with the ability to be stretched, compressed, twisted, bent, and deformed into arbitrary shapes. Inorganic and organic electronic materials in microstructured and nanostructured forms, intimately integrated with elastomeric substrates, offer particularly attractive characteristics, with realistic pathways to sophisticated embodiments. Here, we review these strategies and describe applications of them in systems ranging from electronic eyeball cameras to deformable light-emitting displays. We conclude with some perspectives on routes to commercialization, new device opportunities, and remaining challenges for research.

http://science.sciencemag.org/content/sci/327/5973/1603.full.pdf

Materials and mechanics for stretchable electronics

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Conventional electronic (e‐) skins are a class of thin‐film electronics mainly fabricated in laboratories or factories, which is incapable of rapid and simple customization for personalized healthcare. Here a new class of e‐tattoos is introduced that can be directly implemented on the skin by facile one‐step coating with various designs at multi‐scale depending on the purpose of the user without a substrate. An e‐tattoo is realized by attaching Pt‐decorated carbon nanotubes on gallium‐based liquid‐metal particles (CMP) to impose intrinsic electrical conductivity and mechanical durability. Tuning the CMP suspension to have low‐zeta potential, excellent wettability, and high‐vapor pressure enables conformal and intimate assembly of particles directly on the skin in 10 s. Low‐cost, ease of preparation, on‐skin compatibility, and multifunctionality of CMP make it highly suitable for e‐tattoos. Demonstrations of electrical muscle stimulators, photothermal patches, motion artifact‐free electrophysiological sensors, and electrochemical biosensors validate the simplicity, versatility, and reliability of the e‐tattoo‐based approach in biomedical engineering.

A Personalized Electronic Tattoo for Healthcare Realized by On‐the‐Spot Assembly of an Intrinsically Conductive and Durable Liquid‐Metal Composite

c SK Hynix, 2091 Gyeongchung-daero, Bubal-eub, Icheon-si, Gyeonggi-do, 467-701, Republic of Korea Abstract. Characterization of silicon stress near copper (Cu)-filled through-silicon via(s) (TSVs) was demon- strated using high-resolution micro-Raman spectroscopy. For depth profiling of Si stress distribution near TSVs, a polychromator-based, multiwavelength excitation Raman measurement with different probing depths was used. The design concept of the polychromator-based, multiwavelength micro-Raman spectroscopy system, including the importance of the high-spectral resolution and multiwavelength excitation capability in three-dimen- sional (3-D) Si stress characterization, was described. Silicon stress near Cu-filled TSVs, with various sizes and layouts, was measured and analyzed before and after Cu annealing steps. Main factors impacting Si stress near Cu-filled TSVs are analyzed based on Raman characterization results on various types of TSV structures, lay- outs, and Cu annealing conditions. Large variations in Si stress in TSV arrays were measured in wafers with poor Cu fill characteristics and in wafers annealed in nonoptimized conditions. The Cu annealing sequence and annealing conditions are found to be significantly important for managing Si stress and the reliability of Cu-filled TSVs. Substantially lower Si stress was measured near Cu-filled TSVs with voids. Multiwavelength micro- Raman spectroscopy can be used as a very effective noncontact, nondestructive, inline TSV process and Si stress monitoring technique. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1 .JMM.13.1.011205)

/pdf/multiwavelength-raman-characterization-of-silicon-stress-1os1983b34.pdf

Multiwavelength Raman characterization of silicon stress near through-silicon vias and its inline monitoring applications

Lithium (Li) metal is an ideal anode material for next-generation batteries. However, the commercialization of Li metal-based batteries is impeded by uncontrollable Li dendrite formation and the accumulation of a solid-electrolyte interphase (SEI). Recently, various polymers have been investigated to form a stable SEI layer on Li metal and extend its cycle life. In this study, a polymer film composed of sodium alginate (Na-Alg), which is a natural biopolymer obtained from brown algae, and poly(ethylene oxide) (PEO), was used as a separator. Na-Alg sustained the film structure and PEO facilitated Li-ion diffusion by absorbing the liquid electrolyte. Without using any additives in the commercial carbonate electrolyte, this method extended the cycle life of a Li metal symmetric cell to 1000 h with an overpotential <10 mV, and the cycle life of a full-cell (LiNi0.6Co0.2Mn0.2O2 cathode) to 200 cycles. This study suggests that the use of a biopolymer may enable the practical use of Li metal in next-generation batteries.

A biopolymer-based functional separator for stable Li metal batteries with an additive-free commercial electrolyte

Self-healing features that mimic the biological mechanisms for self-repair have recently been applied to high-capacity but extreme volume expansion electrode materials such as silicon anodes to overcome the short cycle-life caused by electrical contact loss and active material pulverization. In this study, we adopt a freestanding composite design for effective relaxation of lithiation induced stresses and enhancement of electrochemical reliability. Silicon microparticles are homogenously dispersed and embedded within a self-healing polymer matrix that enables free volume expansion and contraction during lithiation and delithiation. The freestanding electrode, which does not require a separate current collector, demonstrated 91.8% capacity retention after 100 cycles at C/10 rate with an average specific capacity and gravimetric capacity, including current collector mass, of ∼2100 mA h g−1 and ∼1050 mA h g−1 respectively, which is a significant improvement compared to the conventional design of simple self-healing polymer coatings on silicon particle embedded current collectors. The fabricated freestanding silicon microparticle and self-healing polymer composite electrode demonstrated stable electrochemical performance after being completely cut, reattached, and cycled and retained at most 95% of its initial capacity. Overall, the proposed freestanding silicon microparticle and self-healing polymer composite design demonstrated excellent gravimetric capacity, cycle life, and self-healing capability without employing expensive and complex nanostructures.

Freestanding silicon microparticle and self-healing polymer composite design for effective lithiation stress relaxation

Spalling of a brittle semiconductor substrate is an attractive method for fabricating sub-50 μm thick single crystal semiconductor wafers in large area. Here, a spalling process to fabricate single crystal Si foils with controlled thicknesses ranging from sub-5 to 38 μm is demonstrated using electroplated Ni stressor layers on Si substrates. In this study, the thickness profile of the Ni stressor layer was varied by changing the Ni electroplating current density, and the effect of thickness variation on the crack initiation and propagation in the underlying Si substrate was evaluated. The critical Ni thickness for crack initiation in our Ni/Si bilayer system was determined and we also show that the crack propagation depth, i.e., spalled Si thickness, is proportional to the thickness of the Ni layer at the central area of the Si wafer. Ni layer plated using 40 mA/cm2 resulted in sub-5 μm thick Si foil. In addition, the spalling mechanics of a Ni/Si bilayer system was analytically explored to give insight i...

Seung Min Han

Papers

A Personalized Electronic Tattoo for Healthcare Realized by On‐the‐Spot Assembly of an Intrinsically Conductive and Durable Liquid‐Metal Composite

Multiwavelength Raman characterization of silicon stress near through-silicon vias and its inline monitoring applications

A biopolymer-based functional separator for stable Li metal batteries with an additive-free commercial electrolyte

Freestanding silicon microparticle and self-healing polymer composite design for effective lithiation stress relaxation

Sub-5 μm-thick spalled single crystal Si foils by decoupling crack initiation and propagation