Jong Hyun Ahn

Bio: Jong Hyun Ahn is an academic researcher from Yonsei University. The author has contributed to research in topics: Graphene & Graphene nanoribbons. The author has an hindex of 74, co-authored 287 publications receiving 39786 citations. Previous affiliations of Jong Hyun Ahn include National University of Singapore & University of Illinois at Urbana–Champaign.

Synthesis of wafer-scale uniform molybdenum disulfide films with control over the layer number using a gas phase sulfur precursor

Abstract: We describe a method for synthesizing large-area and uniform molybdenum disulfide films, with control over the layer number, on insulating substrates using a gas phase sulfuric precursor (H2S) and a molybdenum metal source. The metal layer thickness was varied to effectively control the number of layers (2 to 12) present in the synthesized film. The films were grown on wafer-scale Si/SiO2 or quartz substrates and displayed excellent uniformity and a high crystallinity over the entire area. Thin film transistors were prepared using these materials, and the performances of the devices were tested. The devices displayed an on/off current ratio of 105, a mobility of 0.12 cm2 V−1 s−1 (mean mobility value of 0.07 cm2 V−1 s−1), and reliable operation.

Graphene-based bimorph microactuators.

Abstract: A novel graphene-on-organic film fabrication method that is compatible with a batch microfabrication process was developed and used for electromechanically driven microactuators. A very thin layer of graphene sheets was monolithically integrated and the unique material characteristics of graphene including negative thermal expansion and high electrical conductivity were exploited to produce a bimorph actuation. A large displacement with rapid response was observed while maintaining the low power consumption. This enabled the successful demonstration of transparent graphene-based organic microactuators.

Kinetically controlled, adhesiveless transfer printing using microstructured stamps

Abstract: This letter describes the physics and application of an approach to transfer printing that uses stamps with microstructures of relief embossed into their surfaces. Experimental measurement of velocity-dependent adhesive strength as a function of relief geometry reveals key scaling properties and provides a means for comparison to theoretical expectation. Formation of transistor devices that use nanoribbons of silicon transfer printed directly onto glass substrates without adhesive layers demonstrates the use of this type of approach for a high-performance (mobilities >325 cm2/V s and on/off ratios >105) single crystal silicon on glass technology.

A high performance PZT ribbon-based nanogenerator using graphene transparent electrodes

Abstract: We report a simple and effective approach for high performance PbZr0.52Ti0.48O3 (PZT) based flexible and semi-transparent NGs that exploit the electrical, mechanical and transparent properties of graphene. PZT NGs are successfully demonstrated for continuous driving of a liquid crystal display screen and a light emitting diode. A good quality PZT film was deposited on Pt/Ti/SiO2/Si wafer by the sol–gel method, exhibiting a typical hysteresis loop in the low voltage region. A graphene film was used in the interdigitated electrode form to improve the PZT/graphene interface under mechanical stress. Further improvement in NGs performance was realized by p-type doping in graphene, resulting in an increase in current density. NGs showed a high output voltage ∼2 V, current density ∼2.2 μA cm−2 and power density ∼88 mW cm−3 at an applying force of 0.9 kgf. This can efficiently run commercially available electronic components in a self-powered mode, without any external electrical supply.

Graphene for displays that bend

Abstract: Jong-Hyun Ahn and Byung Hee Hong discuss how graphene can be used in the development of flexible electronics.

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.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.