Ji Feng

Bio: Ji Feng is an academic researcher from Peking University. The author has contributed to research in topics: Physics & Graphene. The author has an hindex of 38, co-authored 115 publications receiving 8734 citations. Previous affiliations of Ji Feng include Cornell University & University of Pennsylvania.

Valley-selective circular dichroism of monolayer molybdenum disulphide

Abstract: The monolayer transition-metal dichalcogenide molybdenum disulphide has recently attracted attention owing to its distinctive electronic properties. Cao and co-workers present numerical evidence suggesting that circularly polarized light can preferentially excite a single valley in the band structure of this system.

Strain-engineered artificial atom as a broad-spectrum solar energy funnel

Abstract: A highly strained ultrathin membrane of MoS2 could lead to the creation of a solar funnel, a new form of solar cell which absorbs a much broader range of the solar spectrum that a usual single junction device.

Self-Supported Formation of Needlelike Co3O4 Nanotubes and Their Application as Lithium-Ion Battery Electrodes†

Abstract: Lithium ion batteries (LIBs) are currently the dominant power source for portable electronic devices. The ever-growing need for high capacity and/or high power, especially for emerging large-scale applications (e.g., electric cars), has prompted numerous research efforts towards developing new high-performance electrode materials for next-generation LIBs. As a new class of negative electrode materials for LIBs discovered in 2000, transition metal oxides (Co3O4 in particular) can in principle deliver as high as three times the capacity of currently used graphite (< 372 mAh g). However, they usually suffer from poor capacity retention upon cycling and/or poor rate capability, which remain major challenges for use in practical cells. These problems have long been partly attributed to the large volume changes during repeated lithium uptake and removal reactions, which cause local stress and eventually lead to electrode failure, and the formation of a polymer/gel-like layer and solid electrolyte interface (SEI) by catalyzed degradation of electrolyte. One generally accepted strategy to alleviate these problems is to prepare nanometer-sized materials with designed structures. Indeed, there is increasing evidence showing that tailored nanostructured materials can significantly improve electrochemical properties compared to their bulk counterpart. 19] For example, electrochemically prepared nano-architectured Fe3O4-Cu and Ni-Sn electrodes are shown to exhibit high rate capabilities, and virus-templated Co3O4 nanowires have recently been demonstrated as LIB electrodes with improved properties. Although nanotubes of a wide range of materials in various types have been prepared by different strategies, it remains a challenge to synthesize nanotubes of metal oxides with isotropic crystal structure. Recently, Yang and others have prepared single-crystalline nanotubes of semiconductors (e.g., GaN and Si) and metal oxides (e.g., Fe3O4) by using a novel “epitaxial casting” against single-crystalline nanowires. More recently, single-crystalline spinel ZnAl2O4 nanotubes have been fabricated based on the Kirkendall effect, normally applied for preparation of hollow nanoparticles, in which amorphous Al2O3 was coated on ZnO nanowires by atomic layer deposition followed by annealing at high temperature. Herein, we report a one-step self-supported topotactic transformation approach for synthesis of needlelike nanotubes made of electrochemically active Co3O4. As-prepared Co3O4 nanotubes are shown to manifest ultrahigh capacity with improved cycle life and high rate capability. Figure 1 schematically illustrates the self-supported topotactic transformation process for synthesis of needlelike Co3O4 nanotubes. At the early stage of the synthesis, needlelike b-Co(OH)2 nanorods with growth direction along [001] are formed due to the highly anisotropic hexagonal crystal structure (Fig. 1a). With the constant mediation of air, C O M M U N IC A TI O N

Epitaxial monolayer MoS2 on mica with novel photoluminescence.

Abstract: Molybdenum disulfide (MoS2) is back in the spotlight because of the indirect-to-direct bandgap tunability and valley related physics emerging in the monolayer regime. However, rigorous control of the monolayer thickness is still a huge challenge for commonly utilized physical exfoliation and chemical synthesis methods. Herein, we have successfully grown predominantly monolayer MoS2 on an inert and nearly lattice-matching mica substrate by using a low-pressure chemical vapor deposition method. The growth is proposed to be mediated by an epitaxial mechanism, and the epitaxial monolayer MoS2 is intrinsically strained on mica due to a small adlayer-substrate lattice mismatch (∼2.7%). Photoluminescence (PL) measurements indicate strong single-exciton emission in as-grown MoS2 and room-temperature PL helicity (circular polarization ∼0.35) on transferred samples, providing straightforward proof of the high quality of the prepared monolayer crystals. The homogeneously strained high-quality monolayer MoS2 prepared...

The chemical imagination at work in very tight places.

Abstract: Diamond-anvil-cell and shock-wave technologies now permit the study of matter under multimegabar pressure (that is, of several hundred GPa). The properties of matter in this pressure regime differ drastically from those known at 1 atm (about 105 Pa). Just how different chemistry is at high pressure and what role chemical intuition for bonding and structure can have in understanding matter at high pressure will be explored in this account. We will discuss in detail an overlapping hierarchy of responses to increased density: a) squeezing out van der Waals space (for molecular crystals); b) increasing coordination; c) decreasing the length of covalent bonds and the size of anions; and d) in an extreme regime, moving electrons off atoms and generating new modes of correlation. Examples of the startling chemistry and physics that emerge under such extreme conditions will alternate in this account with qualitative chemical ideas about the bonding involved.

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.