《自然》（20240523出版）一周论文导读

 

编译 | 未玖

Nature, 23 May 2024, VOL 629, ISSUE 8013

《自然》2024年5月23日，第629卷，8013期

天文学Astronomy

The solar dynamo begins near the surface

太阳发电机效应始于太阳表面附近

▲ 作者：Geoffrey M. Vasil, Daniel Lecoanet, Kyle Augustson, Keaton J. Burns, Jeffrey S. Oishi, Benjamin P. Brown, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07315-1

▲ 摘要：

太阳磁发电机效应周期具有独特模式：太阳黑子出现的传播区域位于纬度30°附近，每11年在赤道附近消失。此外，被称为扭转振荡的纵向流动与太阳黑子迁移密切相关，毫无疑问具有共同原因。

与暗示这些现象深层起源的理论相反，日震学将低纬度扭转振荡精确定位于太阳外层的5~10%，即近太阳表面剪切层。在该区域内，向内增加的差动旋转与极向磁场耦合，强烈暗示了磁旋转不稳定性，这在吸积盘理论中很突出，在实验室中亦可观测。总之，这两个事实引出了一个普遍的问题：太阳发电机效应是否源于近太阳表面的不稳定性。

研究组报告了强有力的肯定证据，与关注更深差旋层的传统模型形成鲜明对比。简单的分析估计表明，近太阳表面磁旋转不稳定性更好地解释了扭转振荡的时空尺度和推断的太阳内部磁场振幅。

最先进的数值模拟证实了这些估计，并重现了半球磁流螺旋度定律。发电机效应产生于一个被充分理解的近太阳表面现象，这有助于对影响地球电磁基础设施的全磁周期和空间天气进行准确预测。

▲ Abstract：

The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating region of sunspot emergence appears around 30° latitude and vanishes near the equator every 11?years. Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause. Contrary to theories suggesting deep origins of these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface shear layer. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability, prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: whether the solar dynamo is possibly a near-surface instability. Here we report strong affirmative evidence in stark contrast to traditional models focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, affecting the electromagnetic infrastructure of Earth.

物理学Physics

Lithium tantalate photonic integrated circuits for volume manufacturing

可量产的钽酸锂光子集成电路

▲ 作者：Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07369-1

▲ 摘要：

基于铌酸锂（LiNbO3）的电-光光子集成电路（PICs）已被证明具有高Pockels系数材料的巨大能力。这实现了互补金属-氧化物-半导体电压水平下工作的线性和高速调制器可用于数据中心通信、高性能计算和AI光子加速器等应用。

然而，这种技术的工业应用受到单片晶圆高成本和有限晶圆尺寸的阻碍。高成本是由于在微电子领域的巨大投资推动了绝缘体上硅（SOI）光子学的采用，而在其他领域缺乏现有的高容量应用。

研究组报道了由钽酸锂（LiTaO3）制成的低损耗PIC，LiTaO3已在商业上用于5G射频滤波器，因此可以低成本进行可扩展的制造，并且LiTaO3具有与LiNbO3相似甚至在某些情况下更优的性能。结果表明，使用基于深紫外（DUV）步进的制造工艺，LiTaO3可被蚀刻以创建低损耗（5.6 dB m-1）PIC。

他们演示了一种LiTaO3马赫-曾德尔调制器（MZM），其半波电压-长度积为1.9 V cm，电光带宽高达40 GHz。与LiNbO3相比，LiTaO3具有极低的双折射率，可实现所有电信频段上的高密度电路和宽带操作。此外，该平台还支持生成孤子微梳。该工作为低成本和大批量的下一代光电PIC的可扩展制造铺平了道路。

▲ Abstract：

Electro-optical photonic integrated circuits (PICs) based on lithium niobate (LiNbO3) have demonstrated the vast capabilities of materials with a high Pockels coefficient. They enable linear and high-speed modulators operating at complementary metal–oxide–semiconductor voltage levels to be used in applications including data-centre communications, high-performance computing and photonic accelerators for AI. However, industrial use of this technology is hindered by the high cost per wafer and the limited wafer size. The high cost results from the lack of existing high-volume applications in other domains of the sort that accelerated the adoption of silicon-on-insulator (SOI) photonics, which was driven by vast investment in microelectronics. Here we report low-loss PICs made of lithium tantalate (LiTaO3), a material that has already been adopted commercially for 5G radiofrequency filters and therefore enables scalable manufacturing at low cost, and it has equal, and in some cases superior, properties to LiNbO3. We show that LiTaO3 can be etched to create low-loss (5.6 dB m-1) PICs using a deep ultraviolet (DUV) stepper-based manufacturing process. We demonstrate a LiTaO3 Mach–Zehnder modulator (MZM) with a half-wave voltage–length product of 1.9 V cm and an electro-optic bandwidth of up to 40 GHz. In comparison with LiNbO3, LiTaO3 exhibits a much lower birefringence, enabling high-density circuits and broadband operation over all telecommunication bands. Moreover, the platform supports the generation of soliton microcombs. Our work paves the way for the scalable manufacture of low-cost and large-volume next-generation electro-optical PICs.

材料科学Materials Science

Selenium-alloyed tellurium oxide for amorphous p-channel transistors

硒合金氧化碲助力非晶p沟道晶体管

▲ 作者：Ao Liu, Yong-Sung Kim, Min Gyu Kim, Youjin Reo, Taoyu Zou, Taesu Choi, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07360-w

▲ 摘要：

与多晶半导体相比，非晶半导体提供了固有成本效益，易于加工和统一制造。传统的非晶氢化硅在电性能方面存在不足，亟需开发新材料。

高迁移率非晶n型金属氧化物（如a-InGaZnO）的产生及其与薄膜晶体管（TFTs）的集成，推动了现代大面积电子器件和新一代显示器的进步。然而，寻找类似的p型对应物颇具挑战，阻碍了互补金属-氧化物-半导体技术和集成电路的进展。

研究组介绍了一种非晶p型半导体的开创性设计策略，将高迁移率碲引入至非晶亚氧化碲基体，并展示了其在高性能、稳定的p沟道TFTs和互补电路中的应用。理论分析揭示了具有浅受主态的碲5p带的离域价带，可实现过量的空穴掺杂和输运。

硒合金化抑制了空穴浓度，促进了p轨道的连接，实现了高性能的p沟道TFTs，其平均场效应空穴迁移率约为15 cm2 V-1 s-1，开/关电流比为106~107，且在偏置应力和环境老化下具有晶圆级均匀性和长期稳定性。这项研究代表了以低成本和工业兼容的方式建立商业上可行的非晶p沟道TFT技术和互补电子设备的关键一步。

▲ Abstract：

Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simple and uniform manufacturing. Traditional amorphous hydrogenated Si falls short in electrical properties, necessitating the exploration of new materials. The creation of high-mobility amorphous n-type metal oxides, such as a-InGaZnO, and their integration into thin-film transistors (TFTs) have propelled advancements in modern large-area electronics and new-generation displays. However, finding comparable p-type counterparts poses notable challenges, impeding the progress of complementary metal–oxide–semiconductor technology and integrated circuits. Here we introduce a pioneering design strategy for amorphous p-type semiconductors, incorporating high-mobility tellurium within an amorphous tellurium suboxide matrix, and demonstrate its use in high-performance, stable p-channel TFTs and complementary circuits. Theoretical analysis unveils a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p-orbital connectivity, realizing high-performance p-channel TFTs with an average field-effect hole mobility of around 15?ccm2 V-1 s-1 and on/off current ratios of 106~107, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient ageing. This study represents a crucial stride towards establishing commercially viable amorphous p-channel TFT technology and complementary electronics in a low-cost and industry-compatible manner.

电子工程Electronic Engineering

Full-colour 3D holographic augmented-reality displays with metasurface waveguides

具有超表面波导的全彩3D全息增强现实显示器

▲ 作者：Manu Gopakumar, Gun-Yeal Lee, Suyeon Choi, Brian Chao, Yifan Peng, Jonghyun Kim, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07386-0

▲ 摘要：

新兴空间计算系统将数字信息无缝叠加在用户观察到的物理环境上，从而实现了娱乐、教育、通信和培训等各个领域的变革性体验。然而，由于增强现实（AR）显示器的光引擎投影光学元件体积庞大，且无法准确描绘虚拟内容的三维（3D）深度信号等因素，其广泛采用受到限制。

研究组介绍了一种全息AR系统，使用反向设计的全彩超表面光栅、紧凑的色散补偿波导几何结构和人工智能驱动的全息算法的独特组合来克服这些挑战。这些元件是协同设计的，消除了空间光调制器和波导之间对庞大准直光学器件的需求，并以紧凑设备规格来呈现生动的全彩3D AR内容。

为了通过该原型提供前所未有的视觉质量，研究组开发了一种融合物理精确的波导模型与相机反馈自动校准的学习组件的创新图像形成模型。这种独特的纳米光子超表面波导和人工智能驱动全息算法的联合设计代表了在紧凑可穿戴设备中创建视觉上引人注目的3D AR体验的重大进步。

▲ Abstract：

Emerging spatial computing systems seamlessly superimpose digital information on the physical environment observed by a user, enabling transformative experiences across various domains, such as entertainment, education, communication and training. However, the widespread adoption of augmented-reality (AR) displays has been limited due to the bulky projection optics of their light engines and their inability to accurately portray three-dimensional (3D) depth cues for virtual content, among other factors. Here we introduce a holographic AR system that overcomes these challenges using a unique combination of inverse-designed full-colour metasurface gratings, a compact dispersion-compensating waveguide geometry and artificial-intelligence-driven holography algorithms. These elements are co-designed to eliminate the need for bulky collimation optics between the spatial light modulator and the waveguide and to present vibrant, full-colour, 3D AR content in a compact device form factor. To deliver unprecedented visual quality with our prototype, we develop an innovative image formation model that combines a physically accurate waveguide model with learned components that are automatically calibrated using camera feedback. Our unique co-design of a nanophotonic metasurface waveguide and artificial-intelligence-driven holographic algorithms represents a significant advancement in creating visually compelling 3D AR experiences in a compact wearable device.

化学Chemistry

Observation of a promethium complex in solution

溶液中钷配合物的观测

▲ 作者：Darren M. Driscoll, Frankie D. White, Subhamay Pramanik, Jeffrey D. Einkauf, Bruce Ravel, Dmytro Bykov, et al.

▲ 链接：

https://www.nature.com/articles/s41586-024-07267-6

▲ 摘要：

镧系稀土金属在现代技术中普遍存在，但人们对第61号元素钷（Pm）的化学性质知之甚少，Pm是一种高度放射性且难以接近的镧系元素。尽管Pm很重要，但其在镧系元素的实验研究中罕有涉及，阻碍了人们对所谓镧系元素收缩现象的全面理解：这是通用化学教科书中引用元素周期表的一个基本方面。

研究组证明了通过新合成的有机二甘醇酰胺配体在水溶液中可与147Pm放射性核素（半衰期为2.62年）稳定螯合。利用同步X射线吸收光谱和量子化学计算，研究了所得到的均配型PmIII配合物，确定了钷的配位结构和键距。这些基本见解使人们能够对一整套同构镧系元素配合物进行完整的结构研究，最终仅在实验观察的基础上捕获溶液中的镧系收缩。

研究结果表明，在镧系元素系列开始时键缩短加速，这与二甘醇酰胺显示的分离趋势有关。在水环境中对放射性PmIII配合物的表征加深了人们对镧系元素内部行为以及f区元素化学和分离的理解。

▲ Abstract：

Lanthanide rare-earth metals are ubiquitous in modern technologies, but we know little about chemistry of the 61st element, promethium (Pm), a lanthanide that is highly radioactive and inaccessible. Despite its importance, Pm has been conspicuously absent from the experimental studies of lanthanides, impeding our full comprehension of the so-called lanthanide contraction phenomenon: a fundamental aspect of the periodic table that is quoted in general chemistry textbooks. Here we demonstrate a stable chelation of the 147Pm radionuclide (half-life of 2.62 years) in aqueous solution by the newly synthesized organic diglycolamide ligand. The resulting homoleptic PmIII complex is studied using synchrotron X-ray absorption spectroscopy and quantum chemical calculations to establish the coordination structure and a bond distance of promethium. These fundamental insights allow a complete structural investigation of a full set of isostructural lanthanide complexes, ultimately capturing the lanthanide contraction in solution solely on the basis of experimental observations. Our results show accelerated shortening of bonds at the beginning of the lanthanide series, which can be correlated to the separation trends shown by diglycolamides. The characterization of the radioactive PmIII complex in an aqueous environment deepens our understanding of intra-lanthanide behaviour and the chemistry and separation of the f-block elements.

Boron catalysis in a designer enzyme

人工酶中的硼催化作用

▲ 作者：Lars Longwitz, Reuben B. Leveson-Gower, Henri?tte J. Rozeboom, Andy-Mark W. H. Thunnissen & Gerard Roelfes

▲ 链接：

https://www.nature.com/articles/s41586-024-07391-3

▲ 摘要：

酶在提高化工生产的友好性和效率方面发挥着越来越重要的作用，但由于酶的反应机理范围相对狭窄，其应用的多样性严重落后于化学催化剂。含有非生物功能酶的创造促进了自然界经典之外的反应机制，并为完全可编程的生物催化铺平了道路。

研究组提出了一种完全遗传编码的含硼酸的人工酶，其有机催化活性是天然或工程生物催化剂无法实现的。这种硼酶通过肟形成催化羟基酮的动力学拆分，其中与蛋白质支架的关键相互作用有助于催化。定向进化运动导致了对几种不同底物具有天然酶样对映体选择性的变体。

利用X射线晶体学、高分辨率质谱（HRMS）和11B NMR波谱证实了硼酶的独特活化模式。研究结果表明，遗传密码扩展可用于创建可进化的对映选择性酶，这些酶依赖于外源性催化部分，如硼酸和通过天然或人工酶的催化混杂性无法达到的通路反应机制。

▲ Abstract：

Enzymes play an increasingly important role in improving the benignity and efficiency of chemical production, yet the diversity of their applications lags heavily behind chemical catalysts as a result of the relatively narrow range of reaction mechanisms of enzymes. The creation of enzymes containing non-biological functionalities facilitates reaction mechanisms outside nature’s canon and paves the way towards fully programmable biocatalysis. Here we present a completely genetically encoded boronic-acid-containing designer enzyme with organocatalytic reactivity not achievable with natural or engineered biocatalysts. This boron enzyme catalyses the kinetic resolution of hydroxyketones by oxime formation, in which crucial interactions with the protein scaffold assist in the catalysis. A directed evolution campaign led to a variant with natural-enzyme-like enantioselectivities for several different substrates. The unique activation mode of the boron enzyme was confirmed using X-ray crystallography, high-resolution mass spectrometry (HRMS) and 11B NMR spectroscopy. Our study demonstrates that genetic-code expansion can be used to create evolvable enantioselective enzymes that rely on xenobiotic catalytic moieties such as boronic acids and access reaction mechanisms not reachable through catalytic promiscuity of natural or engineered enzymes.