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.

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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.

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Van der Waals heterostructures

Recent years have seen the development of a broad range of novel contacting strategies for crystalline silicon (c-Si) solar cells. This study is focused on the use of a sparse layer of platinum nanoparticles to enhance the hole contact characteristics of a c-Si/transparent conductive oxide hole contact. It is shown that the addition of the Pt nanoparticle layer results in a 2 order of magnitude reduction in contact resistivity on both lightly and heavily doped p-type surfaces with values of ~3 and $\sim 0.2 m\Omega cm^{2}$ , respectively. A high transparency can be maintained for such contacts from strict control of the nanoparticle deposition process with a predicted Jsc loss of just 0.15 mA/cm2as a result of the Pt nanoparticle layer. Finally, the thermal and damp heat stability of the Pt nanoparticle contact is investigated, revealing promising initial results.

Metal Nanoparticle Hole Contacts for Silicon Solar Cells

1. Photovoltaics and Thin Film Electronics Laboratory, Ecole Polytechnique Fédérale de Lausanne, Neuchâtel, Switzerland 2. PV center, Swiss Center for Electronics and Microtechnology, Neuchâtel, Switzerland 3. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, USA 4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA. 5. Research School of Engineering, The Australian National University, Canberra, Australia

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/3FB62C4B2E589CF1C9F830AEDC97E31D/S1431927616008965a.pdf/div-class-title-advanced-tem-characterization-of-new-electrical-contacts-for-high-efficiency-c-si-solar-cells-div.pdf

Advanced TEM characterization of new electrical contacts for high efficiency c-Si solar cells

Efficient carrier selective contacts and excellent surface passivation are essential for solar cells to reach high power conversion efficiencies. Exploring MoO, as a dopant-free, hole-selective contact in combination with an intrinsic hydrogenated amorphous silicon passivation layer between the oxide and the crystalline silicon absorber, we demonstrate a silicon hetero-junction solar cell with a high open-circuit voltage of 711 mV and a power conversion efficiency of 18.8%. Compared to the traditional p-type hydrogenated amorphous silicon emitter of a traditional silicon heterojunction solar cell, we observe a substantial gain in photocurrent of 1.9 mA/cm2 for MoO, due to its wide band gap of 3.3 eV. Our results on MoO, have important implications for other combinations of transition metal oxides and photovoltaic absorber materials. solar cells, high workfunction, molybdenum trioxide, passivation, photovoltaics, silicon, selective contact, x-ray photoelectron spectroscopy

/pdf/contact-for-silicon-heterojunction-solar-cells-2xbtlcrq3u.pdf

Contact for Silicon Heterojunction Solar Cells

Author(s): Takei, Kuniharu; Fang, Hui; Kumar, Bala; Kapadia, Rehan; Gao, Qun; Madsen, Morten; Kim, Ha Sul; Liu, Chin-Hung; Plis, Elena; Krishna, Sanjay; Bechtel, Hans A; Guo, Jing; Javey, Ali | Abstract: Nanoscale size-effects drastically alter the fundamental properties of semiconductors. Here, we investigate the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nanomembranes with varied thicknesses of 5-50 nm. First, optical absorption studies are performed by transferring InAs "quantum membranes" (QMs) onto transparent substrates, from which the quantized sub-bands are directly visualized. These sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Finally, the effective electron mobility of InAs QMs is shown to exhibit anomalous field- and thickness-dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The results provide an important advance towards establishing the fundamental device physics of 2-D semiconductors.

/pdf/highly-quantum-confined-inas-nanoscale-membranes-4r0msawxmc.pdf

Highly Quantum-Confined InAs Nanoscale Membranes

The goal of this paper is to provide an overview of an in situ transmission electron microscopy (TEM) technique used to study the thermal stability of various transition metal oxide-based contacts used as carrier-selective contacts in silicon solar cells. In the present work, MoO x /Al and WO x /Al were investigated as hole-selective rear contacts using a combination of in situ TEM and transmission line measurements (TLM).

/pdf/in-situ-transmission-electron-microscopy-a-powerful-tool-for-482e453oam.pdf

Ali Javey

Papers

Metal Nanoparticle Hole Contacts for Silicon Solar Cells

Advanced TEM characterization of new electrical contacts for high efficiency c-Si solar cells

Contact for Silicon Heterojunction Solar Cells

Highly Quantum-Confined InAs Nanoscale Membranes

In Situ Transmission Electron Microscopy: A Powerful Tool for the Characterization of Carrier-Selective Contacts