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

A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors

M-plane GaN terahertz quantum cascade laser structure design and doping effect for resonant-phonon and phonon-scattering-injection schemes

Observation of compensation in GaN films grown by metalorganic chemical vapor deposition

GaN-based Micro-LED has become a research hotspot as a novel display technology due to its numerous unique advantages. Especially in augmented reality and smart glasses applications, Micro-LED display chip with high transparency possesses unparalleled opportunities. In this work, GaN-based transparent single-color Micro-LED display chip based on double-side polished sapphire substrate was designed with a single pixel size of $20\,\,\mu \text{m}\times 20\,\,\mu \text{m}$ , and a resolution of 254 pixel per inch (PPI). The transparency reaches 80% among the whole display area ~ 0.18 inch, and the luminance of display chip can reach up to 25000 nits. It demonstrates a broad application prospects in augmented reality, smart glasses, and etc., providing promising vista for the development of “Metaverse” in the future.

Gallium Nitride Blue/Green Micro-LEDs for High Brightness and Transparency Display

In this work, a low leakage current and high responsivity GaN p-i-n ultraviolet (UV) photodetector (PD) is fabricated for a photocurrent instability study. When the illumination condition shifts from dark to constant UV illumination, the PD’s photocurrent is found first to increase sharply and then go through a slow rising process until reaching its saturation value in tens of seconds. The degree of photocurrent instability lessens as UV illumination intensity increases. Meanwhile, when the PD is illuminated by periodic square-wave UV light, its transient response time is measured to be ∼1–2  μs. The observed photocurrent instability behavior is likely due to photocarrier trapping by yellow luminescence band related defects in GaN, which is supported by multiwavelength light illumination and photocurrent decay measurements.

Yellow luminescence band defect related photocurrent instability of GaN p-i-n ultraviolet photodetectors

Fe films have been grown on different oriented Si substrates by MOCVD, and then samples were put in the air without any protection for nearly fifteen years We have used methods such as XRD and XPS to identify the composition and structure of the epitaxial films on different oriented substrates It is obvious that different orientation of the substrates results in different epitaxial film with different characteristics Using methods such as VSM and FMR, we also investigate the magnetic properties of the epitaxial layers on different oriented substrates The magnetic properties depend on the composition and structure of the epitaxial layers Different substrate orientation results in different easy magnetization direction, anisotropy and coercive force The FMR analysis results match the VSM ones quite well

http://ieeexplore.ieee.org/iel5/10100/32360/01511419.pdf

Youdou Zheng

Papers

M-plane GaN terahertz quantum cascade laser structure design and doping effect for resonant-phonon and phonon-scattering-injection schemes

Observation of compensation in GaN films grown by metalorganic chemical vapor deposition

Gallium Nitride Blue/Green Micro-LEDs for High Brightness and Transparency Display

Yellow luminescence band defect related photocurrent instability of GaN p-i-n ultraviolet photodetectors

Studies on the oxidation of iron films on differently oriented Si substrates