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

BACKGROUND Materials by design is an appealing idea that is very hard to realize in practice. Combining the best of different ingredients in one ultimate material is a task for which we currently have no general solution. However, we do have some successful examples to draw upon: Composite materials and III-V heterostructures have revolutionized many aspects of our lives. Still, we need a general strategy to solve the problem of mixing and matching crystals with different properties, creating combinations with predetermined attributes and functionalities. ADVANCES Two-dimensional (2D) materials offer a platform that allows creation of heterostructures with a variety of properties. One-atom-thick crystals now comprise a large family of these materials, collectively covering a very broad range of properties. The first material to be included was graphene, a zero-overlap semimetal. The family of 2D crystals has grown to includes metals (e.g., NbSe 2 ), semiconductors (e.g., MoS 2 ), and insulators [e.g., hexagonal boron nitride (hBN)]. Many of these materials are stable at ambient conditions, and we have come up with strategies for handling those that are not. Surprisingly, the properties of such 2D materials are often very different from those of their 3D counterparts. Furthermore, even the study of familiar phenomena (like superconductivity or ferromagnetism) in the 2D case, where there is no long-range order, raises many thought-provoking questions. A plethora of opportunities appear when we start to combine several 2D crystals in one vertical stack. Held together by van der Waals forces (the same forces that hold layered materials together), such heterostructures allow a far greater number of combinations than any traditional growth method. As the family of 2D crystals is expanding day by day, so too is the complexity of the heterostructures that could be created with atomic precision. When stacking different crystals together, the synergetic effects become very important. In the first-order approximation, charge redistribution might occur between the neighboring (and even more distant) crystals in the stack. Neighboring crystals can also induce structural changes in each other. Furthermore, such changes can be controlled by adjusting the relative orientation between the individual elements. Such heterostructures have already led to the observation of numerous exciting physical phenomena. Thus, spectrum reconstruction in graphene interacting with hBN allowed several groups to study the Hofstadter butterfly effect and topological currents in such a system. The possibility of positioning crystals in very close (but controlled) proximity to one another allows for the study of tunneling and drag effects. The use of semiconducting monolayers leads to the creation of optically active heterostructures. The extended range of functionalities of such heterostructures yields a range of possible applications. Now the highest-mobility graphene transistors are achieved by encapsulating graphene with hBN. Photovoltaic and light-emitting devices have been demonstrated by combining optically active semiconducting layers and graphene as transparent electrodes. OUTLOOK Currently, most 2D heterostructures are composed by direct stacking of individual monolayer flakes of different materials. Although this method allows ultimate flexibility, it is slow and cumbersome. Thus, techniques involving transfer of large-area crystals grown by chemical vapor deposition (CVD), direct growth of heterostructures by CVD or physical epitaxy, or one-step growth in solution are being developed. Currently, we are at the same level as we were with graphene 10 years ago: plenty of interesting science and unclear prospects for mass production. Given the fast progress of graphene technology over the past few years, we can expect similar advances in the production of the heterostructures, making the science and applications more achievable.

2D materials and van der Waals heterostructures

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of atomic-scale thickness, direct bandgap, strong spin–orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examined and their properties are discussed, with particular attention to their charge density wave, superconductive and topological phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties. Two-dimensional transition metal dichalcogenides (TMDCs) exhibit attractive electronic and mechanical properties. In this Review, the charge density wave, superconductive and topological phases of TMCDs are discussed, along with their synthesis and applications in devices with enhanced mobility and with the use of strain engineering to improve their properties.

2D transition metal dichalcogenides

In the applications of low-power device design and large-scale integrated circuit, MOSFETs play an important role but suffer from the doping complexity and short channel effect when the technology node is further shrinking. Thus, it is of great interest to develop new transistor architecture with atomically thin channel materials to meet the demand for high-density integration and low-power consumption electronics. Here, we develop a dual-junctions field-effect transistor (DJFET) consisting of van der Waals MoS2/Te/MoS2 heterojunctions where the MoS2 on top and bottom serves as dual-gate and the tellurium (Te) in middle is the carrier transport channel. The novel transistor exhibits superior transfer and output characteristics with p-type behavior, high mobility of 270.3 cm<inline-formula> <tex-math notation="LaTeX">$^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ </tex-math></inline-formula> and large transconductance of <inline-formula> <tex-math notation="LaTeX">$16.4~\mu \text{S}$ </tex-math></inline-formula>, competing with widely-reported MOSFETs based on 2-D semiconductors. Additionally, the devices can be operated as a self-driven photodetector with a high responsivity of 879.2 mAW<inline-formula> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> and a specific detectivity of <inline-formula> <tex-math notation="LaTeX">$3.47\times 10^{{11}}$ </tex-math></inline-formula> Jones. This work proposes a new dual-junctions transistor as a highly desirable candidate for next-generation electronic applications.

Dual-Junctions Field Effect Transistor Based on MoS2/Te/MoS2

Herein, we report a graphite (Gr)/WTe2/Ge mixed-dimensional van der Waals (vdWs) heterojunction-based Schottky photodetector (PD) for self-powered near-infrared detection. Notably, the fabricated device can respond to the wide spectrum of 400–2200 nm with the optimal wavelength around 1550 nm. In particular, it exhibited remarkable photovoltaic characteristics with a maximum responsivity of 2.3 A/W, a specific detectivity of <inline-formula> <tex-math notation="LaTeX">$3.4\times 10^{{10}}$ </tex-math></inline-formula> Jones, and a light <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio of over <inline-formula> <tex-math notation="LaTeX">$10^{{3}}$ </tex-math></inline-formula> with a fast response speed of 4.4/<inline-formula> <tex-math notation="LaTeX">$8.6 \mu \text{s}$ </tex-math></inline-formula> under 1550 nm. Moreover, a clear single-point image of “SCNU” in the self-driven mode can be obtained under 1550 nm illumination. The above results suggest that the constructed Gr/WTe2/Ge PD shows great potential in the field of ultrafast near-infrared detection and high-resolution imaging.

Room-Temperature Near-Infrared and Self-Powered Photodetectors Based on Graphite/WTe2/Ge Mixed van der Waals Heterostructure

A Comparative Study Uncovering the Different Effect of Nb, Mo and W Dopants on Phase Transition of Vanadium Dioxide

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi2O2Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi2O2Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi2O2Se/MoSe2 photodiode designed with type-II band alignment demonstrates a high rectification ratio of 103. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 μs (zero bias) and 17.17 A/W and 100/110 μs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi2O2Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi2O2Se nanowires. Furthermore, 1D Bi2O2Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel.

With the rapid development of two‐dimensional semiconductor technology, the inevitable chemical disorder at a typical metal–semiconductor interface has become an increasingly serious problem that degrades the performance of 2D semiconductor optoelectronic devices. Herein, defect‐free van der Waals contacts have been achieved by utilizing topological Bi2Se3 as the electrodes. Such clean and atomically sharp contacts avoid the consumption of photogenerated carriers at the interface, enabling a markedly boosted sensitivity as compared to counterpart devices with directly deposited metal electrodes. Typically, the device with 2D WSe2 channel realizes a high responsivity of 20.5 A W−1, an excellent detectivity of 2.18 × 1012 Jones, and a fast rise/decay time of 41.66/38.81 ms. Furthermore, high‐resolution visible‐light imaging capability of the WSe2 device is demonstrated, indicating its promising application prospect in future optoelectronic systems. More inspiringly, the topological electrodes are universally applicable to other 2D semiconductor channels, including WS2 and InSe, suggesting its broad applicability. These results open fascinating opportunities for the development of high‐performance electronics and optoelectronics.

Jingbo Li

Papers

Dual-Junctions Field Effect Transistor Based on MoS2/Te/MoS2

Room-Temperature Near-Infrared and Self-Powered Photodetectors Based on Graphite/WTe2/Ge Mixed van der Waals Heterostructure

A Comparative Study Uncovering the Different Effect of Nb, Mo and W Dopants on Phase Transition of Vanadium Dioxide

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel.

Integration of Self‐Passivated Topological Electrodes for Advanced 2D Optoelectronic Devices