《自然》（20230817出版）一周論文導讀

原文地址：http://news.sciencenet.cn/htmlnews/2023/8/506828.shtm

Nature, 17 August 2023, VOL 620, ISSUE 7974

《自然》2023年8月17日，第620卷，7974期

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物理學Physics

Microstructure and crystal order during freezing of supercooled water drops

過冷水滴凍結過程中的微觀結構和結晶有序

▲ 作者：Armin Kalita, Maximillian Mrozek-McCourt, Thomas F. Kaldawi, Philip R. Willmott, N. Duane Loh, Sebastian Marte, et al.

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▲ 摘要：

過冷水滴被廣泛用于研究過冷水、冰成核和液滴凍結。過冷水滴在大氣中的凍結影響云的動力學和氣候反饋，并通過二次冰的產生加速云的凍結。液滴凍結發生在幾個時間尺度和長度尺度上，并且具有足夠的隨機性，使兩個凍結的液滴不可能完全相同。

研究組使用光學顯微鏡和X射線激光衍射研究了真空中數萬個水微滴在約234~235K均質冰成核后的凍結過程。在水滴圖像的基礎上建立了一個七階段凍結模型，并用該模型對衍射數據計時。

冰晶衍射結果表明，長程晶序在凍結后不到1ms的時間內形成，而剩余液體的衍射結果則與預融冰上的準液體層相似。冰剛凍結時具有應變的六方晶體結構，這是一種早期亞穩態，可能先于具有堆疊缺陷的冰形成。

該技術可助力確定其他條件下的凍結動力學，比如云中的水滴凍結，或助力理解其他材料的快速凝固。

▲ Abstract：

Supercooled water droplets are widely used to study supercooled water, ice nucleation and droplet freezing. Their freezing in the atmosphere affects the dynamics and climate feedback of clouds and can accelerate cloud freezing through secondary ice production. Droplet freezing occurs at several timescales and length scales and is sufficiently stochastic to make it unlikely that two frozen drops are identical. Here we use optical microscopy and X-ray laser diffraction to investigate the freezing of tens of thousands of water microdrops in vacuum after homogeneous ice nucleation around 234–235?K. On the basis of drop images, we developed a seven-stage model of freezing and used it to time the diffraction data. Diffraction from ice crystals showed that long-range crystalline order formed in less than 1?ms after freezing, whereas diffraction from the remaining liquid became similar to that from quasi-liquid layers on premelted ice. The ice had a strained hexagonal crystal structure just after freezing, which is an early metastable state that probably precedes the formation of ice with stacking defects. The techniques reported here could help determine the dynamics of freezing in other conditions, such as drop freezing in clouds, or help understand rapid solidification in other materials.

材料科學Materials Science

Reversible spin-optical interface in luminescent organic radicals

發光有機自由基的可逆自旋光界面

▲ 作者：Sebastian Gorgon, Kuo Lv, Jeannine Grüne, Bluebell H. Drummond, William K. Myers, Giacomo Londi, et al.

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▲ 摘要：

分子為量子信息科學提供了一個通用平臺，是傳感和計算應用的候選者。穩健的自旋光學界面是利用材料量子資源的關鍵。迄今為止，碳基候選材料均不發光，這限制了通過發射進行光學讀出。

研究組報道了自旋多重性S>1時，具有高效發光且激發態近單位產率的有機分子。基于設計發射雙重態和三重態能級之間的能量共振，實現了三（2,4,6-三氯苯基）甲基咔唑自由基和蒽的共價偶聯。

研究組觀察到，雙光子激發在幾皮秒內離域到連接并苯上，并隨后演化為1.8 eV附近混合自由基-三重態特征的純高自旋態（單自由基為四重態，雙自由基為五重態）。即使在295K下，這些高自旋態也可用于微波相干尋址，通過反向系間竄越到發射態來實現光學讀出。

此外，對于雙自由基，在返回基態時，先前不相關的自由基自旋在蒽的兩側均顯示出很強的自旋相關性。該方法在室溫下同時支持高效初始化、自旋調控和基于光的讀出。發光和高自旋態集成為新興量子技術創造了一個有機材料平臺。

▲ Abstract：

Molecules present a versatile platform for quantum information science and are candidates for sensing and computation applications. Robust spin-optical interfaces are key to harnessing the quantum resources of materials. To date, carbon-based candidates have been non-luminescent, which prevents optical readout via emission. Here we report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with spin multiplicity S > 1. This was achieved by designing an energy resonance between emissive doublet and triplet levels, here on covalently coupled tris(2,4,6-trichlorophenyl) methyl-carbazole radicals and anthracene. We observed that the doublet photoexcitation delocalized onto the linked acene within a few picoseconds and subsequently evolved to a pure high-spin state (quartet for monoradical, quintet for biradical) of mixed radical–triplet character near 1.8?eV. These high-spin states are coherently addressable with microwaves even at 295?K, with optical readout enabled by reverse intersystem crossing to emissive states. Furthermore, for the biradical, on return to the ground state the previously uncorrelated radical spins either side of the anthracene shows strong spin correlation. Our approach simultaneously supports a high efficiency of initialization, spin manipulations and light-based readout at room temperature. The integration of luminescence and high-spin states creates an organic materials platform for emerging quantum technologies.

Autonomous healing of fatigue cracks via cold welding

疲勞裂紋的冷焊自動修復

▲ 作者：Christopher M. Barr, Ta Duong, Daniel C. Bufford, Zachary Milne, Abhilash Molkeri, Nathan M. Heckman, et al.

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▲ 摘要：

金屬疲勞是指在重復機械載荷作用下，通過裂紋的增量擴展而逐漸失效。在結構應用中，疲勞占在役失效的90%。疲勞的預防依賴于大安全系數和低效過度設計的實施。在傳統的抗疲勞冶金設計中，人們開發微觀結構來阻止或減緩裂紋的發展。

裂紋生長被假定為不可逆的。相比之下，在其他材料類別中，存在一種基于潛在修復機制和傷害逆轉的令人信服的替代方案。

研究組報道了純金屬的疲勞裂紋也可以進行內在自修復。他們直接觀察到納米級疲勞裂紋的早期發展，不出所料，裂紋在局部微觀結構障礙處前進、偏轉和停止。然而，出乎意料的是，裂紋也被觀察到通過局部應力狀態和晶界遷移共同引發的裂紋側面冷焊過程而自我修復。

疲勞裂紋可通過與微觀結構特征的局部相互作用而在金屬中自動修復，這一假設對工程師如何設計和評估結構材料疲勞壽命的最基本理論提出了挑戰。研究組討論了在各種服務環境中疲勞會有何影響。

▲ Abstract：

Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.

能源科學Energy Science

Inverted perovskite solar cells using dimethylacridine-based dopants

使用二甲基吖啶摻雜劑的倒置鈣鈦礦太陽能電池

▲ 作者：Qin Tan, Zhaoning Li, Guangfu Luo, Xusheng Zhang, Bo Che, Guocong Chen, et al.

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▲ 摘要：

鈣鈦礦半導體摻雜及其晶界鈍化仍頗具挑戰性，但對于推進高效鈣鈦礦太陽能電池至關重要。尤其是在不預先沉積一層空穴傳輸材料的情況下，構建基于鈣鈦礦/氧化銦錫（ITO）肖特基接觸的倒置器件至關重要。

研究組報道了一種基于二甲基吖啶的分子摻雜工藝，用于構建匹配良好的p-鈣鈦礦/ITO接觸以及晶界的全面鈍化，并實現了25.39%的認證功率轉換效率（PCE）。在氯苯淬火結晶過程中，分子從前驅體溶液擠壓到晶界和薄膜表面底部，被稱之為分子擠壓過程。

分子的去質子化磷酸基團與鈣鈦礦聚碘化鉛之間的核配位配合物既負責機械吸收又負責電子電荷轉移，導致了鈣鈦礦膜的p型摻雜。研究組創造了一種PCE為25.86%（反向掃描）的高效設備，在光照1000小時后仍保持96.6%的初始PCE。

▲ Abstract：

Doping of perovskite semiconductors and passivation of their grain boundaries remain challenging but essential for advancing high-efficiency perovskite solar cells. Particularly, it is crucial to build perovskite/indium tin oxide (ITO) Schottky contact based inverted devices without predepositing a layer of hole-transport material. Here we report a dimethylacridine-based molecular doping process used to construct a well-matched p-perovskite/ITO contact, along with all-round passivation of grain boundaries, achieving a certified power conversion efficiency (PCE) of 25.39%. The molecules are shown to be extruded from the precursor solution to the grain boundaries and the bottom of the film surface in the chlorobenzene-quenched crystallization process, which we call a molecule-extrusion process. The core coordination complex between the deprotonated phosphonic acid group of the molecule and lead polyiodide of perovskite is responsible for both mechanical absorption and electronic charge transfer, and leads to p-type doping of the perovskite film. We created an efficient device with a PCE of 25.86% (reverse scan) and that maintained 96.6% of initial PCE after 1,000?h of light soaking.

地球科學Earth Science

Future emergence of new ecosystems caused by glacial retreat

冰川退縮導致未來新生態系統的出現

▲ 作者：J. B. Bosson, M. Huss, S. Cauvy-Fraunié, J. C. Clément, G. Costes, M. Fischer, et al.

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▲ 摘要：

與人為氣候變化相關的冰川萎縮和冰后期生態系統的發展是某種持續時間最快的生態系統變化，具有顯著的生態和社會連鎖后果。然而，據人們所知，目前還沒有完整的空間分析來量化或預測這種重要轉變。

研究組表明，到2100年，南極和格陵蘭冰蓋以外所有冰川的減少可能會產生新的陸地、海洋和淡水生態系統，面積范圍從尼泊爾（149,000±55,000平方千米）到芬蘭（33.9,000±99,000平方千米）不等。該分析表明，冰川面積的損失將在22±8%至51±15%之間，具體取決于氣候情景。

在冰川消融地區，新興生態系統將以極端到溫和的生態條件為特征，為適應寒冷的物種提供庇護，或有利于初級生產力和廣幅種。面對氣候變化、生物多樣性喪失和淡水稀缺，探索冰川地區的未來凸顯了冰川和新興冰后期生態系統的重要性。

而目前只有不到一半的冰川區位于保護區。研究組贊同聯合國最近宣布2025年為國際冰川保護年的決議和《全球生物多樣性框架》，強調迫切需要同時加強減緩氣候變化和對這些生態系統的就地保護，以確保其存在、功能和價值。

▲ Abstract：

Glacier shrinkage and the development of post-glacial ecosystems related to anthropogenic climate change are some of the fastest ongoing ecosystem shifts, with marked ecological and societal cascading consequences. Yet, no complete spatial analysis exists, to our knowledge, to quantify or anticipate this important changeover. Here we show that by 2100, the decline of all glaciers outside the Antarctic and Greenland ice sheets may produce new terrestrial, marine and freshwater ecosystems over an area ranging from the size of Nepal (149,000 ± 55,000?km2) to that of Finland (339,000??±??99,000??km2). Our analysis shows that the loss of glacier area will range from 22?±?8% to 51?±?15%, depending on the climate scenario. In deglaciated areas, the emerging ecosystems will be characterized by extreme to mild ecological conditions, offering refuge for cold-adapted species or favouring primary productivity and generalist species. Exploring the future of glacierized areas highlights the importance of glaciers and emerging post-glacial ecosystems in the face of climate change, biodiversity loss and freshwater scarcity. We find that less than half of glacial areas are located in protected areas. Echoing the recent United Nations resolution declaring 2025 as the International Year of Glaciers’ Preservation and the Global Biodiversity Framework, we emphasize the need to urgently and simultaneously enhance climate-change mitigation and the in situ protection of these ecosystems to secure their existence, functioning and values.

Enhanced inner core fine-scale heterogeneity towards Earth’s centre

向地球中心增強的內核精細尺度非均質性

▲ 作者：Guanning Pang, Keith D. Koper, Sin-Mei Wu, Wei Wang, Marine Lasbleis & Garrett Euler

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▲ 摘要：

地球內核在流體外核內凝固時獲得了“紋理”。組成紋理的大部分鐵粒的大小、形狀和方向記錄了內核的生長，并可能隨地質時間的推移而演變，以響應地球動力和扭矩。地震產生的地震波可用來成像地核的紋理或織構，從而深入了解地核的歷史和演變。

研究組觀察和模擬了在更大規模上構成內核織構的精細尺度（小于10km）非均質性反向散射的地震能量。使用一個由全球小孔徑地震陣列（用于探測地下核爆炸的微小信號）創建的新數據集，以建立內核精細尺度非均質性的三維模型。

該模型顯示，內核散射普遍存在，存在于所有采樣的經緯度上，并且在內核邊界以下500~800km處強度顯著增加。在較深內核中增強的散射與延遲成核后的快速增長時代相兼容。

▲Abstract：