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

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

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High-κ gate dielectrics: Current status and materials properties considerations

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

인공고관절의 세라믹 볼 헤드의 기계적 안정성 평가를 위한 3 차원 유한요소 해석

Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.

/pdf/studies-on-the-scale-up-of-the-microwave-assisted-387fpg23bq.pdf

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Ferroelectric wurtzites have the potential to revolutionize modern microelectronics because they are easily integrated with multiple mainstream semiconductor platforms. However, the electric fields required to reverse their polarization direction and unlock electronic and optical functions need substantial reduction for operational compatibility with complementary metal-oxide semiconductor (CMOS) electronics. To understand this process, we observed and quantified real-time polarization switching of a representative ferroelectric wurtzite (Al0.94B0.06N) at the atomic scale with scanning transmission electron microscopy. The analysis revealed a polarization reversal model in which puckered aluminum/boron nitride rings in the wurtzite basal planes gradually flatten and adopt a transient nonpolar geometry. Independent first-principles simulations reveal the details and energetics of the reversal process through an antipolar phase. This model and local mechanistic understanding are a critical initial step for property engineering efforts in this emerging material class. Description Editor’s summary Nitride-based ferroelectric wurtzites are an emerging family of crystals that are highly attractive as switching materials for modern microelectronics. The chemistry of these materials is a good match for current semiconductor platforms. Calderon et al. used an array of characterization tools to determine exactly how a representative wurtzite composed of aluminum, boron, and nitrogen undergoes polarization switching. A more detailed understanding of this process is vital for lowering the electric field under which these materials switch, because this is a limiting factor in moving them into applications. —Brent Grocholski Real-time switching studies in wurtzite ferroelectrics reveal that an antipolar metastable state mediates polarization inversion.

Atomic-scale polarization switching in wurtzite ferroelectrics

/pdf/magnetic-coupling-in-epitaxial-bifeo-3-la-0-7-sr-0-3-mno-3-kmsgb6vtq0.pdf

Magnetic coupling in Epitaxial BiFeO$_{3}$-La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Heterostructures Integrated on Si(100)

Photovoltaic cells including silicon solar cells are provided. A silicon substrate having an n-type silicon layer is provided with a silicon nitride layer, a reactive metal in contact with said silicon nitride layer, and a non-reactive metal in contact with the reactive metal. This assembly is fired to form a low Shottky barrier height contact comprised of metal nitride, and optionally metal silicide, on the silicon substrate, and a conductive metal electrode in contact with said low Shottky barrier height contact. The reactive metal may be titanium, zirconium, hafnium, vanadium, niobium, and tantalum, and combinations thereof, and the non-reactive metal may be silver, tin, bismuth, lead, antimony, arsenic, indium, zinc, germanium, nickel, phosphorus, gold, cadmium, berrylium, and combinations thereof.

Photovoltaic device electrical contacts

We determine the infrared absorption spectra of a gas due to evanescent plasmonic electromagnetic fields in a system where surface interactions (physisorption and chemisorption) are demonstrably negligible. The plasmonic host material, the degenerate semiconductor CdO:Dy, has high mobility (366-450 cm2/(V s)) and carrier density ((0.6-3.5) × 1020 cm-3), and therefore supports low-loss surface plasmon resonances in the mid-IR. This high-mobility layer gives the highest resolution observed in a plasmonic conducting material in the infrared, higher than that of gold and rivaling that of silver. The high resolution permits a new understanding of the nature of the interaction of emerging fields with molecular transitions. Using different carrier concentrations, the resonance condition of the surface plasmon polariton (SPP) frequency (ωSPP) and N2O vibrational absorption spectral frequency (ωN2O) can be controlled, thereby allowing a critical test of field-molecule interactions. Experiment and theory both indicate a dispersive N2O line shape for ωSPP < ωN2O, an absorptive line shape for ωSPP < ωN2O, and an abrupt change between the two when the resonance condition ωSPP < ωN2O is reached. A first-order expansion of the Airy equation describes this behavior analytically. The SPP surface enhancement is 6.8 ± 0.5 on-resonance, lower than enhancements observed in other systems, but in agreement with recent quantitative reports of surface enhanced infrared reflection absorption spectroscopy (SEIRA). Our results show that interactions of infrared SPPs with molecular vibrations are in the weak coupling limit, and that enhancements comparable those reported for noble metals can be achieved.

Jon Paul Maria

Papers

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Atomic-scale polarization switching in wurtzite ferroelectrics

Magnetic coupling in Epitaxial BiFeO$_{3}$-La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Heterostructures Integrated on Si(100)

Photovoltaic device electrical contacts

Critical Test of the Interaction of Surface Plasmon Resonances with Molecular Vibrational Transitions.