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

The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.

/pdf/roll-to-roll-production-of-30-inch-graphene-films-for-3syrg1ob8a.pdf

Roll-to-roll production of 30-inch graphene films for transparent electrodes

Graphene nanoribbons, narrow straight-edged strips of the single-atom-thick sheet form of carbon, are predicted to exhibit remarkable properties, making them suitable for future electronic applications. Before this potential can be realized, more chemically precise methods of production will be required. Cai et al. report a step towards that goal with the development of a bottom-up fabrication method that produces atomically precise graphene nanoribbons of different topologies and widths. The process involves the deposition of precursor monomers with structures that 'encode' the topology and width of the desired ribbon end-product onto a metal surface. Surface-assisted coupling of the precursors into linear polyphenylenes is then followed by cyclodehydrogenation. Given the method's versatility and precision, it could even provide a route to more unusual graphene nanoribbon structures with tuned chemical and electronic properties. Graphene nanoribbons (GNRs) have structure-dependent electronic properties that make them attractive for the fabrication of nanoscale electronic devices, but exploiting this potential has been hindered by the lack of precise production methods. Here the authors demonstrate how to reliably produce different GNRs, using precursor monomers that encode the structure of the targeted nanoribbon and are converted into GNRs by means of surface-assisted coupling. Graphene nanoribbons—narrow and straight-edged stripes of graphene, or single-layer graphite—are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices1,2,3. In particular, although the two-dimensional parent material graphene4,5 exhibits semimetallic behaviour, quantum confinement and edge effects2,6 should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical7,8,9, sonochemical10 and lithographic11,12 methods as well as through the unzipping of carbon nanotubes13,14,15,16, the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling17,18 of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation19,20. The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots21, superlattice structures22 and magnetic devices based on specific graphene nanoribbon edge states3.

Atomically precise bottom-up fabrication of graphene nanoribbons

Graphene nanoribbons—narrow and straight-edged stripes of graphene, or single-layer graphite—are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices. In particular, although the two-dimensional parent material graphene exhibits semimetallic behaviour, quantum confinement and edge effects should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical, sonochemical and lithographic methods as well as through the unzipping of carbon nanotubes, the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation. The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots, superlattice structures and magnetic devices based on specific graphene nanoribbon edge states.

/pdf/atomically-precise-bottom-up-fabrication-of-graphene-4p6ixf0dyo.pdf

Atomically Precise Bottom-up Fabrication of Graphene Nanoribbons JINMING CAI, Empa, Swiss Federal Laboratories for Materials Science and Technology

Dry Etching of High Aspect Ratio 4H-SiC Microstructures

We have employed aerosol deposition (AD) to deposit 39 µm thick polycrystalline films of yttrium iron garnet at room temperature onto sapphire at a rate of 1‐3 µm/min as an initial investigation of utilizing AD for fabricating ferrite-integrated on-chip inductors. We characterize the structural and magnetic properties of the as-received starting powder, as-deposited film, and a pressed puck formed from the starting powder. Results show that the films are comprised of randomly oriented polycrystalline grains with structural and magnetic properties that closely resemble that of the starting powder. Results from coating a gold single-turn inductor show an increase in inductance of 79% up to ∼300 MHz without affecting the Q-factor. These results demonstrate AD as a promising technique for depositing thick ferrite films at high deposition rates for low-temperature fabrication of ferrite-integrated on-chip inductors.

Aerosol Deposition of Yttrium Iron Garnet for Fabrication of Ferrite-Integrated On-Chip Inductors

III-Nitride high electron mobility transistors (HEMTs) have been of critical importance for commercial and military applications which require the high frequency, high power density enabled by the favorable properties of Gallium Nitride. However, the long-term reliable operation of GaN at high power has continued to face unique challenges originating from the simultaneously high electric field and high temperature within a small volume of a HEMT [1]. Mitigating self-heating using a CVD diamond cap have resulted in about 20% lower device temperature at the expense of additional process complexity in order to integrate the heat spreading close to the 2DEG channel [2]. Similarly, GaN -on-diamond technology has produced excellent electrothermal performance by integrating GaN -on-Si with CVD diamond growth on the N-polar back side [3]. Such advances in thermal management have demonstrated that GaN HEMTs have the potential to operate reliably at very high power density $(> 10\mathrm{W}/\mathrm{mm})$ . In this work, we have quantified the electrothermal performance of state-of-the-art AIGaN/GaN HEMTs on Si and diamond substrates and demonstrate very high DC output power operation at a reliably low temperature.

Thermal Performance Improvement of GaN-on-Diamond High Electron Mobility Transistors

The incorporation of In2O3 into Ga2O3 allows for tailoring of the bandgap over a wide range in (InxGa1−x)2O3, and this material is emerging as a candidate in transparent electrodes on optoelectronic devices, heterostructure transistors, photodetectors, and gas sensors. We have measured the band alignments for atomic layer deposited SiO2 and Al2O3 over the composition range x = 0.25–0.74 for (InxGa1−x)2O3 grown by pulsed laser deposition. The valence band offsets from 1.95 to 2.30 eV for SiO2 and 0.88 to 1.23 eV for Al2O3 over this composition range. The bandgaps of (InxGa1−x)2O3 spanned from 4.55 to 4.05 for x = 0.74–0.25. This led to nested band alignments for SiO2 and Al2O3 for the entire composition range of (InxGa1−x)2O3 investigated.

Marko J. Tadjer

Papers

Dry Etching of High Aspect Ratio 4H-SiC Microstructures

Aerosol Deposition of Yttrium Iron Garnet for Fabrication of Ferrite-Integrated On-Chip Inductors

Thermal Performance Improvement of GaN-on-Diamond High Electron Mobility Transistors

Valence band offsets for ALD SiO2 and Al2O3 on (InxGa1−x)2O3 for x = 0.25–0.74

Band Alignment of Atomic Layer Deposited SiO2 and Al2O3 on (AlxGa1-x)2O3 for x = 0.2-0.65