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.

Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.

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Graphene: Status and Prospects

Topological insulators are new states of quantum matter which cannot be adiabatically connected to conventional insulators and semiconductors. They are characterized by a full insulating gap in the bulk and gapless edge or surface states which are protected by time-reversal symmetry. These topological materials have been theoretically predicted and experimentally observed in a variety of systems, including HgTe quantum wells, BiSb alloys, and Bi2Te3 and Bi2Se3 crystals. Theoretical models, materials properties, and experimental results on two-dimensional and three-dimensional topological insulators are reviewed, and both the topological band theory and the topological field theory are discussed. Topological superconductors have a full pairing gap in the bulk and gapless surface states consisting of Majorana fermions. The theory of topological superconductors is reviewed, in close analogy to the theory of topological insulators.

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Topological insulators and superconductors

There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

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Graphene and Graphene Oxide: Synthesis, Properties, and Applications

The unique properties of graphene have recently attracted major attention leading to proposals in electronic, optoelectronic, and detector applications. Micro-Raman spectroscopy has been utilized as a convenient tool for identifying graphene layers. Most Raman studies were limited to layers on silicon substrates with an oxide layer thickness of 300 nm, rendering graphene visible under an optical microscope. The development of graphene technology requires its integration with different materials and strict control of the number of layers and defects. Thus it is important to extend the nanometrology capabilities of Raman spectroscopy to arbitrary substrates and temperatures. Here we report that the deconvolution of the 2D band allows one to count graphene layers even when placed on “inconvenient” substrates such as glass or sapphire. We also show that even small excitation laser power typically used for Raman spectroscopy may lead to strong heating in graphene. The determined temperature coefficients for graphene allowed us to evaluate the temperature rise and decouple the temperature effects from those due to variations in the graphene edges or substrates.

Raman nanometrology of graphene on arbitrary substrates and at variable temperature

Bismuth telluride (Bi2Te3) and its alloys are the best bulk thermoelectric materials known today. Bi2Te3 has the rhombohedral crystal structure (D3d5 – R(-3)m) with five atoms in one unit cell. It has large lattice parameter cH = 3.045 nm. It was theoretically predicted that quantum wells made of bismuth telluride should have strongly enhanced thermoelectric figure of merit ZT either due to quantum confinement of carriers [1] or confinement of acoustic phonons [2]. To achieve the strong confinement regime required for a drastic increase of ZT one needs ultra-thin crystalline films with the thickness of just few atomic planes (~ 1 nm or less). Conventional film growth techniques (CVD, MBE, electro-deposition, etc.) do not provide such quality crystalline thermoelectric films. The bismuth telluride family of materials was also demonstrated to be topological insulators with a large energy gap and gapless surface states consisting of a single Dirac cone [3]. In this talk, I will demonstrate that separate BiTe atomic layers can be mechanically exfoliated from bulk Bi2Te3 in a “graphene-like” fashion [4-5]. The presence of the van der Waals gap allowed us to disassemble Bi2Te3 crystal into its building blocks – five mono-atomic sheets of –[Te(1)-Bi-Te(2)-Bi-Te(1)]-, which have the thickness of ~1 nm. Our microscopy data (AFM, SEM and TEM) proves that the atomic bonds inside the atomic five-folds can be broken further leading to quasi-2-D crystals of Bi-Te (Fig. 1). The atomicallythin films were suspended across trenches in Si/SiO2 wafers to reduce coupling to the substrate and investigate the physical properties of this materials consisting entirely of surfaces and interfaces. We developed micro-Raman based nanometrology technique to identify few-quintuples layers of bismuth telluride and related materials [6]. By altering the thickness and sequence of atomic planes one can create “designer” non-stoichiometric crystalline films, change the composition, doping and other properties (Fig. 2). The obtained results may pave the way for producing crystalline bismuth telluride quantum wells with the strong quantum confinement of charge carriers, which were predicted to have an order-of-magnitude higher thermoelectric figure of merit. It may also become a reliable method for fabrication of topological insulator thin films.

"Graphene-Like" Exfoliation of Atomically-Thin Films of Bi2Te3 and Related Materials: Applications in Thermoelectrics and Topological Insulators

Bismuth telluride (Bi2Te3) and its alloys are the best bulk thermoelectric materials known today. The stacked quasi-two-dimensional (2D) layers of Bi2Te3 were also identified as topological insulators. In this paper we describe a method for graphene-inspired exfoliation of crystalline bismuth telluride films with a thickness of a few atoms. The atomically thin films were suspended across trenches in Si/SiO2 substrates, and subjected to detail characterization. The presence of the van der Waals gaps allowed us to disassemble Bi2Te3 crystal into its quintuple building blocks - five mono-atomic sheets consisting of Te(1)-Bi-Te(2)-Bi-Te(1). By altering the thickness and sequence of atomic planes we were able to create designer non-stoichiometric quasi-2D crystalline films, change their composition and doping, as well as other properties. The exfoliated quintuples and ultra-thin films have low thermal conductivity, high electrical conductivity and enhanced thermoelectric properties. The obtained results pave the way for producing stacks of crystalline bismuth telluride quantum wells with the strong spatial confinement of charge carriers and acoustic phonons for thermoelectric devices. The developed technology for producing free-standing quasi-2D layers of Te(1)-Bi-Te(2)-Bi-Te(1) creates an impetus for investigation of the topological insulators and their possible practical applications.

From Graphene to Bismuth Telluride: Mechanical Exfoliation of Quasi-2D Crystals for Applications in Thermoelectrics and Topological Insulators

Graphene, a monolayer of carbon atoms, is a high-interest material in the research community and semiconductor industry due to its extraordinary electronic, thermal, and mechanical properties. Graphene layer identification is very important since its intrinsic properties change drastically between each 0.34-nm thick layer. Current methods of identification rely on restrictive small-area microscopy techniques, the most robust being micro-Raman spectroscopy. Here we present a new method for a large-area graphene layer identification characterized by low cost, high accuracy, high throughput, complete automation, and scalability. Our metrology tool is based on a fast image processing algorithm, which analyzes optical contrasts between single-layer, bi-layer, and few-layer graphene used for exfoliated, transferred, or grown graphene flakes on large wafers verified by micro-Raman spectroscopy.

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Desalegne Teweldebrhan

Papers

Raman nanometrology of graphene on arbitrary substrates and at variable temperature

"Graphene-Like" Exfoliation of Atomically-Thin Films of Bi2Te3 and Related Materials: Applications in Thermoelectrics and Topological Insulators

From Graphene to Bismuth Telluride: Mechanical Exfoliation of Quasi-2D Crystals for Applications in Thermoelectrics and Topological Insulators

Large-Scale Automated Identification and Quality Control of Exfoliated and CVD Graphene via Image Processing Technique

Properties of Quasi-Two-Dimensional Crystals of Titanium Ditelluride