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编译 | 李言

Science, 22 OCT 2021, VOL 374, ISSUE 6566

《科学》2021年10月22日，第374卷，6566期

材料科学Materials Science

Broadband electro-optic polarization conversion with atomically thin black phosphorus

原子薄黑磷的宽带电光偏振转换

▲ 作者：SOUVIK BISWAS, MEIR Y. GRAJOWER, KENJI WATANABE et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj7053

▲ 摘要

有源偏振控制在光子系统中是非常理想的，但主要局限于大体积介质中的离散结构和基于液晶的可变延迟器。

在次，我们报道利用集成在法布里－珀罗腔中的三层黑磷（TLBP）在范德华层状材料中通过通信波长（1410到1575纳米）的电可重构极化转换。TLBP中双折射的大电可调谐性使得光谱宽带偏振控制成为可能。

我们发现，通过光谱调谐，可以在庞加莱球体的很大一部分产生极化状态，而电调谐使极化转换的状态跨越了庞加莱球体的近一半。我们观察了线性到圆形和交叉极化电压转换，证明了高动态范围的通用性。

▲ Abstract

Active polarization control is highly desirable in photonic systems but has been limited mostly to discrete structures in bulky dielectric media and liquid crystal–based variable retarders. Here, we report electrically reconfigurable polarization conversion across telecommunication wavelengths (1410 to 1575 nanometers) in van der Waals layered materials using tri-layer black phosphorus (TLBP) integrated in a Fabry-Pérot cavity. The large electrical tunability of birefringence in TLBP enables spectrally broadband polarization control. We found that polarization states could be generated over a large fraction of the Poincaré sphere through spectral tuning, and that electrical tuning enables the state of polarization conversion to span nearly half the Poincaré sphere. We observed both linear to circular and cross-polarization conversion with voltage, demonstrating versatility with a high dynamic range.

Lightweight, strong, moldable wood via cell wall engineering as a sustainable structural material

通过细胞壁工程将轻而坚固的可模压木材作为可持续的结构材料

▲ 作者：SHAOLIANG XIAO, XCHAOJI CHEN, XQINQIN XIA et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abg9556

▲ 摘要

木材是一种可持续的结构材料，但它不能在保持机械性能的同时容易塑形。我们报告了一种处理策略，利用细胞壁工程将硬木平面板塑造成通用的三维结构。

在分解木材的木质素成分并通过蒸发水关闭导管和纤维后，我们在快速水冲击过程中部分地重新膨胀木材，选择性地打开导管。

这形成了独特的皱纹细胞壁结构，允许材料折叠并成型为所需的形状。由此产生的3D成型木材比起始木材强六倍，可与广泛使用的轻质材料（如铝合金）相媲美。这种方法增加了木材作为结构材料的潜力，降低了对建筑和交通应用的环境影响。

▲ Abstract

Wood is a sustainable structural material, but it cannot be easily shaped while maintaining its mechanical properties. We report a processing strategy that uses cell wall engineering to shape flat sheets of hardwood into versatile three-dimensional (3D) structures. After breaking down wood’s lignin component and closing the vessels and fibers by evaporating water, we partially re-swell the wood in a rapid water-shock process that selectively opens the vessels. This forms a distinct wrinkled cell wall structure that allows the material to be folded and molded into desired shapes. The resulting 3D-molded wood is six times stronger than the starting wood and comparable to widely used lightweight materials such as aluminum alloys. This approach widens wood’s potential as a structural material, with lower environmental impact for buildings and transportation applications.

In situ design of advanced titanium alloy with concentration modulations by additive manufacturing

利用增材制造设计成分调制钛合金

▲ 作者：TIANLONG ZHANG, ZHENGHUA HUANG, TAO YANG et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj3770

▲ 摘要

增材制造是一项革命性的技术，为材料加工和设计提供了不同的途径。然而，如果没有协同的组合，新材料或新加工技术的创新很少能成功。我们展示了一种原位设计方法，利用激光粉末床聚变调制合金浓度空间。

我们发现，两种不同合金熔体——Ti-6Al-4V和少量316L不锈钢的部分均匀化，使我们能够对Ti-6Al-4V基体中316L中所含的元素进行微米级浓度调节。相稳定性以及微观组织形成了α’马氏体和亚稳定β母相在三维空间中的周期性分布及独特微观组织。

亚稳定β相发生明显的相变诱导塑性，从而极大地改善了增材制造钛合金的均匀变形和加工硬化能力。这种方法为结构和功能应用的浓度调制异质合金设计开辟了一条途径。

▲ Abstract

Additive manufacturing is a revolutionary technology that offers a different pathway for material processing and design. However, innovations in either new materials or new processing technologies can seldom be successful without a synergistic combination. We demonstrate an in situ design approach to make alloys spatially modulated in concentration by using laser-powder bed fusion. We show that the partial homogenization of two dissimilar alloy melts—Ti-6Al-4V and a small amount of 316L stainless steel—allows us to produce micrometer-scale concentration modulations of the elements that are contained in 316L in the Ti-6Al-4V matrix. The corresponding phase stability modulation creates a fine scale–modulated β + α′ dual-phase microstructure that exhibits a progressive transformation-induced plasticity effect, which leads to a high tensile strength of ~1.3 gigapascals with a uniform elongation of ~9% and an excellent work-hardening capacity of >300 megapascals. This approach creates a pathway for concentration-modulated heterogeneous alloy design for structural and functional applications.

物理学Physics

Evolution of water structures in metal-organic frameworks for improved atmospheric water harvesting

改善大气水收集的金属-有机框架中水结构的演变

▲ 作者：NIKITA HANIKEL, XIAOKUN PEI, SAUMIL CHHEDAHAO LYU et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj0890

▲ 摘要

虽然水在多孔晶体中的位置可以确定，但确定它们的填充顺序仍然具有挑战性。通过进行一系列单晶x射线衍射测量和密度泛函理论计算，我们破译了最先进的金属有机框架MOF-303的充水机制。

第一个水分子与极性有机连接物紧密结合; 接着是额外的水分子形成孤立的簇，然后是簇链，最后形成一个水网络。

这种水结构的进化促使我们通过多元方法改变孔隙，从而精确地调节第一个水分子的结合强度，并调节吸水行为。这导致了更高的水生产率，以及再生温度和焓的可调性，而不影响容量和稳定性.

▲ Abstract

Although the positions of water guests in porous crystals can be identified, determination of their filling sequence remains challenging. We decIPhered the water-filling mechanism for the state-of-the-art water-harvesting metal-organic framework MOF-303 by performing an extensive series of single-crystal x-ray diffraction measurements and density functional theory calculations. The first water molecules strongly bind to the polar organic linkers; they are followed by additional water molecules forming isolated clusters, then chains of clusters, and finally a water network. This evolution of water structures led us to modify the pores by the multivariate approach, thereby precisely modulating the binding strength of the first water molecules and deliberately shaping the water uptake behavior. This resulted in higher water productivity, as well as tunability of regeneration temperature and enthalpy, without compromising capacity and stability.

化学Chemistry

Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells

硫锚定合成用于制造燃料电池的铂金属间化合物纳米颗粒催化剂

▲ 作者：CHENG-LONG YANG, LI-NA WANG, PENG YIN et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj9980

▲ 摘要

原子有序金属间化合物纳米颗粒在催化应用方面前景广阔，但由于原子有序所需的高温退火不可避免地会加速金属烧结，从而导致更大的晶体，因此很难生产。

我们在多孔硫掺杂碳载体上制备了平均粒径小于5纳米的铂金属间化合物。在多孔硫掺杂碳载体上，铂与硫之间的强相互作用抑制了金属烧结至1000℃。

我们合成了由46种铂与16种其他金属元素组合而成的金属间化合物库，并用它们研究了电催化氧还原反应活性对合金成分和铂表皮应变的依赖关系。金属间化合物库在质子交换膜燃料电池中具有很高的质量效率，在0.9伏特电压下可以达到1.3到1.8安培每毫克铂的高活性。

▲ Abstract

Atomically ordered intermetallic nanoparticles are promising for catalytic applications but are difficult to produce because the high-temperature annealing required for atom ordering inevitably accelerates metal sintering that leads to larger crystallites. We prepared platinum intermetallics with an average particle size of <5 nanometers on porous sulfur-doped carbon supports, on which the strong interaction between platinum and sulfur suppresses metal sintering up to 1000°C. We synthesized intermetallic libraries of small nanoparticles consisting of 46 combinations of platinum with 16 other metal elements and used them to study the dependence of electrocatalytic oxygen-reduction reaction activity on alloy composition and platinum skin strain. The intermetallic libraries are highly mass efficient in proton-exchange-membrane fuel cells and could achieve high activities of 1.3 to 1.8 amperes per milligram of platinum at 0.9 volts.

General method for iron-catalyzed multicomponent radical cascades–cross-couplings

铁催化多组分自由基级联交叉偶联的通用方法

▲ 作者：LEI LIU, MARIA CAMILA AGUILERA, WES LEE et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj6005

▲ 摘要

过渡金属催化交叉偶联反应是化学合成中应用最广泛的方法之一。然而，尽管铁作为一种潜在的更便宜、更丰富、毒性更小的过渡金属催化剂具有显著的优势，但它在多组分交叉偶联中的实际应用在很大程度上仍然不成功。我们展示了1,2-双(二环己基膦基)乙烷催化的α-硼基自由基(由硼酸乙烯基选择性自由基加成生成)与格氏试剂的偶联反应。

然后，我们扩展了这些自由基级联的范围，开发了一个通用和广泛适用的铁催化多组分环化交叉耦合协议，该协议涉及广泛的π-体系，允许实际合成环氟化合物。机理研究与双芳基化的Fe(II)物种负责生成烷基自由基引发催化一致，而单芳基化的Fe(II)中心和瞬态烷基自由基之间进行碳-碳键形成。

▲ Abstract

Transition metal–catalyzed cross-coupling reactions are some of the most widely used methods in chemical synthesis. However, despite notable advantages of iron (Fe) as a potentially cheaper, more abundant, and less toxic transition metal catalyst, its practical application in multicomponent cross-couplings remains largely unsuccessful. We demonstrate 1,2-bis(dicyclohexylphosphino)ethane Fe–catalyzed coupling of α-boryl radicals (generated from selective radical addition to vinyl boronates) with Grignard reagents. Then, we extended the scope of these radical cascades by developing a general and broadly applicable Fe-catalyzed multicomponent annulation–cross-coupling protocol that engages a wide range of π-systems and permits the practical synthesis of cyclic fluorous compounds. Mechanistic studies are consistent with a bisarylated Fe(II) species being responsible for alkyl radical generation to initiate catalysis, while carbon-carbon bond formation proceeds between a monoarylated Fe(II) center and a transient alkyl radical.

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