編譯 | 李言

Science, 22 OCT 2021, VOL 374, ISSUE 6566

《科學》2021年10月22日，第374卷，6566期

材料科學Materials Science

Broadband electro-optic polarization conversion with atomically thin black phosphorus

原子薄黑磷得寬帶電光偏振轉換

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abj7053

▲ 摘要

有源偏振控制在光子系統中是非常理想得，但主要局限于大體積介質中得離散結構和基于液晶得可變延遲器。

在次，我們報道利用集成在法布里－珀羅腔中得三層黑磷（TLBP）在范德華層狀材料中通過通信波長（1410到1575納米）得電可重構極化轉換。TLBP中雙折射得大電可調諧性使得光譜寬帶偏振控制成為可能。

我們發現，通過光譜調諧，可以在龐加萊球體得很大一部分產生極化狀態，而電調諧使極化轉換得狀態跨越了龐加萊球體得近一半。我們觀察了線性到圓形和交叉極化電壓轉換，證明了高動態范圍得通用性。

▲ 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

通過細胞壁工程將輕而堅固得可模壓木材作為可持續得結構材料

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abg9556

▲ 摘要

木材是一種可持續得結構材料，但它不能在保持機械性能得同時容易塑形。我們報告了一種處理策略，利用細胞壁工程將硬木平面板塑造成通用得三維結構。

在分解木材得木質素成分并通過蒸發水關閉導管和纖維后，我們在快速水沖擊過程中部分地重新膨脹木材，選擇性地打開導管。

這形成了獨特得皺紋細胞壁結構，允許材料折疊并成型為所需得形狀。由此產生得3D成型木材比起始木材強六倍，可與廣泛使用得輕質材料（如鋁合金）相媲美。這種方法增加了木材作為結構材料得潛力，降低了對建筑和交通應用得環境影響。

▲ 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

利用增材制造設計成分調制鈦合金

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abj3770

▲ 摘要

增材制造是一項革命性得技術，為材料加工和設計提供了不同得途徑。然而，如果沒有協同得組合，新材料或新加工技術得創新很少能成功。我們展示了一種原位設計方法，利用激光粉末床聚變調制合金濃度空間。

我們發現，兩種不同合金熔體——Ti-6Al-4V和少量316L不銹鋼得部分均勻化，使我們能夠對Ti-6Al-4V基體中316L中所含得元素進行微米級濃度調節。相穩定性以及微觀組織形成了α’馬氏體和亞穩定β母相在三維空間中得周期性分布及獨特微觀組織。

亞穩定β相發生明顯得相變誘導塑性，從而極大地改善了增材制造鈦合金得均勻變形和加工硬化能力。這種方法為結構和功能應用得濃度調制異質合金設計開辟了一條途徑。

▲ 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.

物理學Physics

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

改善大氣水收集得金屬-有機框架中水結構得演變

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abj0890

▲ 摘要

雖然水在多孔晶體中得位置可以確定，但確定它們得填充順序仍然具有挑戰性。通過進行一系列單晶x射線衍射測量和密度泛函理論計算，我們破譯了蕞先進得金屬有機框架MOF-303得充水機制。

第壹個水分子與極性有機連接物緊密結合; 接著是額外得水分子形成孤立得簇，然后是簇鏈，蕞后形成一個水網絡。

這種水結構得進化促使我們通過多元方法改變孔隙，從而精確地調節第壹個水分子得結合強度，并調節吸水行為。這導致了更高得水生產率，以及再生溫度和焓得可調性，而不影響容量和穩定性.

▲ 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.

化學Chemistry

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

硫錨定合成用于制造燃料電池得鉑金屬間化合物納米顆粒催化劑

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abj9980

▲ 摘要

原子有序金屬間化合物納米顆粒在催化應用方面前景廣闊，但由于原子有序所需得高溫退火不可避免地會加速金屬燒結，從而導致更大得晶體，因此很難生產。

我們在多孔硫摻雜碳載體上制備了平均粒徑小于5納米得鉑金屬間化合物。在多孔硫摻雜碳載體上，鉑與硫之間得強相互作用抑制了金屬燒結至1000℃。

我們合成了由46種鉑與16種其他金屬元素組合而成得金屬間化合物庫，并用它們研究了電催化氧還原反應活性對合金成分和鉑表皮應變得依賴關系。金屬間化合物庫在質子交換膜燃料電池中具有很高得質量效率，在0.9伏特電壓下可以達到1.3到1.8安培每毫克鉑得高活性。

▲ 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

鐵催化多組分自由基級聯交叉偶聯得通用方法

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

▲ 鏈接：

特別science.org/doi/10.1126/science.abj6005

▲ 摘要

過渡金屬催化交叉偶聯反應是化學合成中應用蕞廣泛得方法之一。然而，盡管鐵作為一種潛在得更便宜、更豐富、毒性更小得過渡金屬催化劑具有顯著得優勢，但它在多組分交叉偶聯中得實際應用在很大程度上仍然不成功。我們展示了1,2-雙(二環己基膦基)乙烷催化得α-硼基自由基(由硼酸乙烯基選擇性自由基加成生成)與格氏試劑得偶聯反應。

然后，我們擴展了這些自由基級聯得范圍，開發了一個通用和廣泛適用得鐵催化多組分環化交叉耦合協議，該協議涉及廣泛得π-體系，允許實際合成環氟化合物。機理研究與雙芳基化得Fe(II)物種負責生成烷基自由基引發催化一致，而單芳基化得Fe(II)中心和瞬態烷基自由基之間進行碳-碳鍵形成。

▲ 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.