There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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。

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

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

/pdf/electronics-and-optoelectronics-of-two-dimensional-2jbqr1unvw.pdf

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

Fabrication techniques developed for graphene research allow the disassembly of many layered crystals (so-called van der Waals materials) into individual atomic planes and their reassembly into designer heterostructures, which reveal new properties and phenomena. Andre Geim and Irina Grigorieva offer a forward-looking review of the potential of layering two-dimensional materials into novel heterostructures held together by weak van der Waals interactions. Dozens of these one-atom- or one-molecule-thick crystals are known. Graphene has already been well studied but others, such as monolayers of hexagonal boron nitride, MoS2, WSe2, graphane, fluorographene, mica and silicene are attracting increasing interest. There are many other monolayers yet to be examined of course, and the possibility of combining graphene with other crystals adds even further options, offering exciting new opportunities for scientific exploration and technological innovation. Research on graphene and other two-dimensional atomic crystals is intense and is likely to remain one of the leading topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. The first, already remarkably complex, such heterostructures (often referred to as ‘van der Waals’) have recently been fabricated and investigated, revealing unusual properties and new phenomena. Here we review this emerging research area and identify possible future directions. With steady improvement in fabrication techniques and using graphene’s springboard, van der Waals heterostructures should develop into a large field of their own.

/pdf/van-der-waals-heterostructures-3nf3oeh0jk.pdf

Van der Waals heterostructures

Most optoelectronic devices operate at high photocarrier densities, where all semiconductors suffer from enhanced nonradiative recombination. Nonradiative processes proportionately reduce photoluminescence (PL) quantum yield (QY), a performance metric that directly dictates the maximum device efficiency. Although transition metal dichalcogenide (TMDC) monolayers exhibit near-unity PL QY at low exciton densities, nonradiative exciton-exciton annihilation (EEA) enhanced by van-Hove singularity (VHS) rapidly degrades their PL QY at high exciton densities and limits their utility in practical applications. Here, by applying small mechanical strain (less than 1%), we circumvented VHS resonance and markedly suppressed EEA in monolayer TMDCs, resulting in near-unity PL QY at all exciton densities despite the presence of a high native defect density. Our findings can enable light-emitting devices that retain high efficiency at all brightness levels.

Inhibited nonradiative decay at all exciton densities in monolayer semiconductors.

In this work, we report lateral heterojunction formation in as-exfoliated MoS2 flakes by thickness modulation. Kelvin probe force microscopy is used to map the surface potential at the monolayermultilayer heterojunction, and consequently the conduction band offset is extracted. Scanning photocurrent microscopy is performed to investigate the spatial photocurrent response along the length of the device including the source and the drain contacts as well as the monolayermultilayer junction. The peak photocurrent is measured at the monolayer-multilayer interface, which is attributed to the formation of a type-I heterojunction. The work presents experimental and theoretical understanding of the band alignment and photoresponse of thickness modulated MoS2 junctions with important implications for exploring novel optoelectronic devices. Semiconducting transition metal dichalcogenides (TMDCs) with a layered crystal structure exhibit unique electrical 1,2 and optical properties 3–5 . TMDCs provide opportunities in exploring new device concepts given their atomic level flatness, and ability to form van der Waals (vdW) heterostructures with strong interlayer coupling 6–8 . For instance, vdW heterobilayers of MoS2/WSe2 have been recently reported to exhibit spatially direct light absorption but spatially indirect light emission, representing a highly intriguing material property 9,10 . Here, we explore the optoelectronic properties of lateral “hetero”-junctions formed on a single crystal of MoS2 of varying thickness (i.e., number of layers). As a result of the quantum confinement effect 11 , when the thickness of a MoS2 crystal is scaled down to a monolayer the optical band gap increases from 1.29 eV (indirect) to 1.85 eV (direct) 12,13 . The change in the band structure and the electron affinity of MoS 2 with layer number opens up the path to the formation of atomically sharp heterostructures, not by changing composition but rather by changing layer thickness 14 . We experimentally examine the surface potential of this thickness modulated heterojunction by using Kelvin probe force microscopy (KPFM). We further use scanning photocurrent microscopy (SPCM) to probe the photoresponse of the junction. A large photocurrent response is observed at the monolayer/ multilayer junction interface which confirms the presence of a strong built-in electric field at the inter face. Device modeling is used in parallel to experiments to understand the underlying mechanism of the observed photocurrents and the band-alignments at the junction interface, suggesting the formation of a type-I heterojunction. SPCM has been previously used to study the photoresponse of metal contacted MoS2 transistors, where the channel thickness for MoS2 was uniform throughout the device 15,16 . The results have shown that the photoresponse is primarily driven by the metal/MoS2 Schottky contacts and photothermoelectric effect 16 . In distinct contrast to previous studies, we observe that the peak photoresponse is spatially located at the MoS2 monolayer/multilayer junction for our lateral heterojunctions and not at the metal contacts.

/pdf/mos-2-heterojunctions-by-thickness-2wmewen8jt.pdf

MoS 2 Heterojunctions by Thickness

We report on the use of nano-emitters, for example carbon nano-tubes(CNTs), to ionize deuterium atoms and the creation of neutrons in a deuterium-deuterium reaction in a pre-loaded target. Acceleration voltages in the range of 50–80kV are used and the creation of positive and negative deuterium ions is investigated. We discuss optimization of emitters and show preliminary data of first neutron production.

/pdf/7-3-development-of-a-compact-neutron-source-based-on-field-2xz8lt3ye2.pdf

7.3: Development of a compact neutron source based on field ionization processes

Nanostructures are implemented in a manner that facilitates controlled, nano-scale dimensional manufacture and implementation. According to an example embodiment of the present invention, a nanostructure is formed from a layer of deposited metallic material, sized using a mask and, in some applications, metal deposition angle. The deposited metallic material is heated to form a metallic nanocluster having a cross-section (e.g., diameter-type or width-type dimensional characteristics) that is less than a width of the layer of deposited metal material. In one application, the metallic material is deposited on a substrate and in wells defined by a mask formed on the substrate. The metallic material is annealed to form metallic nanoclusters having a diameter that is on an order of magnitude less than a width and/or diameter of the wells.

Nanoparticles with controlled growth

Here we consider two hypotheses to explain the open-circuit voltage (Voc) degradation observed in thin-film vapor-liquid-solid (TF-VLS) grown p-type InP photovoltaic cells: bandgap narrowing and local shunting. First, a bandgap (Eg) narrowing effect is hypothesized, based on the surface inhomogeneity of VLS InP captured by the photoluminescence (PL) image. The PL data was used to estimate a spatially-resolved active Voc across surface of the InP sample. Combining this data with the effective Jsc allowed an assessment of the I-V characteristics of individual unit cells. Next, an H-SPICE diode compact model was utilized to reproduce the I-V characteristics of the whole sample. We find a good fit to the I-V performance of TF-VLS grown InP solar cell. Second, a local shunting effect was also considered as an alternative explanation of the Voc degradation effect. Again, PL image data was used, and small local shunt resistance was added in arbitrary elementary unit cells to represent certain dark spots seen in the PL image and dictate the Voc degradation occurred in the sample.

Ali Javey

Papers

Inhibited nonradiative decay at all exciton densities in monolayer semiconductors.

MoS 2 Heterojunctions by Thickness

7.3: Development of a compact neutron source based on field ionization processes

Nanoparticles with controlled growth

Voc degradation in TF-VLS grown InP solar cells