编译 | 冯维维

Nature, Volume 629 Issue 8014, 30 May 2024

《自然》第629卷，8014期，2024年5月30日

物理学Physics

Suppressed thermal transport in silicon nanoribbons by inhomogeneous strain

非均匀应变抑制硅纳米带中的热输运

▲ 作者：Lin Yang, Shengying Yue, Yi Tao, Shuo Qiao, Hang Li, Zhaohe Dai, Bai Song, Yunfei Chen, Jinlong Du, Deyu Li & Peng Gao

▲ 链接：

https://www.nature.com/articles/s41586-024-07390-4

▲ 摘要：

纳米级结构可以产生极端应变，从而实现前所未有的材料特性，例如定制电子带隙，提高超导温度和增强的电催化活性。虽然已知均匀应变对热流的影响有限，但由于界面和缺陷的共存，非均匀应变的影响仍然难以捉摸。

研究者通过在定制的微器件上弯曲单个硅纳米带引入非均匀应变，并测量其对热输运的影响，同时以亚纳米分辨率表征应变相关的振动谱，从而解决了这一空白。

研究结果表明，每纳米0.112%的应变梯度可以导致热导率急剧下降34±5%，与均匀应变下测量的几乎恒定值形成鲜明对比。研究者进一步利用电子能量损失谱绘制了局部晶格振动谱，这揭示了声子沿应变梯度的峰值位移为数百万电子伏特。

第一性原理计算证明，这种独特的声子谱展宽效应增强了声子散射，极大地阻碍了热输运。研究揭示了长期存在的非均匀应变下晶格动力学难题的一个关键部分，这在均匀应变下是不存在的，并且超出了传统的理解。

▲ Abstract：

Nanoscale structures can produce extreme strain that enables unprecedented material properties, such as tailored electronic bandgap, elevated superconducting temperature and enhanced electrocatalytic activity. While uniform strains are known to elicit limited effects on heat flow, the impact of inhomogeneous strains has remained elusive owing to the coexistence of interfaces and defects. Here we address this gap by introducing inhomogeneous strain through bending individual silicon nanoribbons on a custom-fabricated microdevice and measuring its effect on thermal transport while characterizing the strain-dependent vibrational spectra with sub-nanometre resolution. Our results show that a strain gradient of 0.112% per nanometre could lead to a drastic thermal conductivity reduction of 34?±?5%, in clear contrast to the nearly constant values measured under uniform strains. We further map the local lattice vibrational spectra using electron energy-loss spectroscopy, which reveals phonon peak shifts of several millielectron-volts along the strain gradient. This unique phonon spectra broadening effect intensifies phonon scattering and substantially impedes thermal transport, as evidenced by first-principles calculations. Our work uncovers a crucial piece of the long-standing puzzle of lattice dynamics under inhomogeneous strain, which is absent under uniform strain and eludes conventional understanding.

Self-oscillating polymeric refrigerator with high energy efficiency

高能效自振荡聚合物制冷机

▲ 作者：Donglin Han, Yingjing Zhang, Cenling Huang, Shanyu Zheng, Dongyuan Wu, Qiang Li, Feihong Du, Hongxiao Duan, Weilin Chen, Junye Shi, Jiangping Chen, Gang Liu, Xin Chen & Xiaoshi Qian

▲ 链接：

https://www.nature.com/articles/s41586-024-07375-3

▲ 摘要：

介电材料中同时存在着电热和电致伸缩效应。结合这两种效果可以实现轻量化，紧凑的局部热管理，这是由电热制冷所承诺的。尽管有一些数值模型和示意图，目前的电热冰箱仍然依赖于外部附件来驱动工作体，因此导致设备级冷却功率密度和性能系数（COP）较低。

研究者报告了一种利用聚合铁电体提供的电热机械协同作用的电热薄膜装置。在一次交流电刺激下，该装置由工作体自身进行热循环和机械循环，形成无外部驱动、自循环的软冰箱。

该原型提供了直接测量的冷却功率密度为6.5 W g-1，在零温度范围下的峰值COP超过58。该器件仅为30微米厚的聚合物薄膜，在开放环境中，在4K的温度范围内实现了接近24的COP（32%的热力学效率）。

与被动冷却相比，薄膜冰箱可以立即对电子芯片产生17.5 K的额外温度下降。柔软的聚合物冰箱可以感知、驱动和泵送热量，以提供自动的局部热管理。

▲ Abstract：

Electrocaloric and electrostrictive effects concurrently exist in dielectric materials. Combining these two effects could achieve the lightweight, compact localized thermal management that is promised by electrocaloric refrigeration. Despite a handful of numerical models and schematic presentations current electrocaloric refrigerators still rely on external accessories to drive the working bodies and hence result in a low device-level cooling power density and coefficient of performance (COP). Here we report an electrocaloric thin-film device that uses the electro-thermomechanical synergy provided by polymeric ferroelectrics. Under one-time a.c. electric stimulation, the device is thermally and mechanically cycled by the working body itself, resulting in an external-driver-free, self-cycling, soft refrigerator. The prototype offers a directly measured cooling power density of 6.5 W g-1 and a peak COP exceeding 58 under a zero temperature span. Being merely a 30-μm-thick polymer film, the device achieved a COP close to 24 under a 4 K temperature span in an open ambient environment (32% thermodynamic efficiency). Compared with passive cooling, the thin-film refrigerator could immediately induce an additional 17.5?K temperature drop against an electronic chip. The soft, polymeric refrigerator can sense, actuate and pump heat to provide automatic localized thermal management.

Strain-invariant stretchable radio-frequency electronics

应变不变可拉伸射频电子学

▲ 作者：Sun Hong Kim, Abdul Basir, Raudel Avila, Jaeman Lim, Seong Woo Hong, Geonoh Choe, Joo Hwan Shin, Jin Hee Hwang, Sun Young Park, Jiho Joo, Chanmi Lee, Jaehoon Choi, Byunghun Lee, Kwang-Seong Choi, Sungmook Jung, Tae-il Kim, Hyoungsuk Yoo & Yei Hwan Jung

▲ 链接：

https://www.nature.com/articles/s41586-024-07383-3

▲ 摘要：

无线模块通过射频（RF）电子器件提供通信和能量收集功能，是皮肤界面可拉伸电子器件的重要组成部分。然而，最近对可拉伸射频元件的研究表明，即使在相对较低的弹性应变下，电性能也会发生实质性变化，例如天线谐振频率的移位。

这种变化直接导致可拉伸系统中的无线信号强度或功率传输效率大大降低，特别是在诸如皮肤表面的物理动态环境中。研究者提出了应变不变的可拉伸射频电子元件，能够在各种弹性应变下完全保持原始射频特性，使用“介电弹性”材料作为衬底。

介电弹性材料具有物理可调谐的介电特性，可有效地避免射频电子接口中产生的频移。与传统的可拉伸基板材料相比，这种材料具有优越的电气、机械和热性能，适用于高性能可拉伸射频电子设备。

研究者描述了材料、制造和设计策略，这些策略是基于实验和计算研究实现关键射频元件应变不变行为的基础。最后，作者提出了一套基于应变不变可拉伸射频电子器件的皮肤接口无线医疗监视器，其在应变下的无线操作距离可达30米。

▲ Abstract：

Wireless modules that provide telecommunications and power-harvesting capabilities enabled by radio-frequency (RF) electronics are vital components of skin-interfaced stretchable electronics. However, recent studies on stretchable RF components have demonstrated that substantial changes in electrical properties, such as a shift in the antenna resonance frequency, occur even under relatively low elastic strains. Such changes lead directly to greatly reduced wireless signal strength or power-transfer efficiency in stretchable systems, particularly in physically dynamic environments such as the surface of the skin. Here we present strain-invariant stretchable RF electronics capable of completely maintaining the original RF properties under various elastic strains using a ‘dielectro-elastic’ material as the substrate. Dielectro-elastic materials have physically tunable dielectric properties that effectively avert frequency shifts arising in interfacing RF electronics. Compared with conventional stretchable substrate materials, our material has superior electrical, mechanical and thermal properties that are suitable for high-performance stretchable RF electronics. In this paper, we describe the materials, fabrication and design strategies that serve as the foundation for enabling the strain-invariant behaviour of key RF components based on experimental and computational studies. Finally, we present a set of skin-interfaced wireless healthcare monitors based on strain-invariant stretchable RF electronics with a wireless operational distance of up to 30?m under strain.

电子信息学Electronic informatics

A vision chip with complementary pathways for open-world sensing

具有开放世界传感互补路径的视觉芯片

▲ 作者：Zheyu Yang, Taoyi Wang, Yihan Lin, Yuguo Chen, Hui Zeng, Jing Pei, Jiazheng Wang, Xue Liu, Yichun Zhou, Jianqiang Zhang, Xin Wang, Xinhao Lv, Rong Zhao & Luping Shi

▲ 链接：

https://www.nature.com/articles/s41586-024-07358-4

▲ 摘要：

在开放世界应用中，图像传感器在处理动态、多样化和不可预测的场景时面临着巨大的挑战。然而，图像传感器向高速、高分辨率、大动态范围和高精度方向发展受到功率和带宽的限制。

研究者提出了一种受人类视觉系统启发的互补感知范式，该范式涉及将视觉信息解析为基于原语的表示，并将这些原语组合成两条互补的视觉路径：用于准确认知的以认知为导向的路径和用于快速反应的以行动为导向的路径。

为实现这一范式，研究者开发了一种名为“天眸芯”的视觉芯片，该芯片结合了混合像素阵列和并行异构读出架构。利用互补视觉路径的特性，天眼实现了高达10,000 fps的高速传感，130 dB的动态范围，在空间分辨率，速度和动态范围方面都是先进的数字。

此外，它自适应地减少了90%的带宽。他们展示了将天眸芯集成到自动驾驶系统中的能力，即使在开放道路上具有挑战性的角落情况下，也能实现准确、快速和强大的感知。基于原始的互补传感范式有助于克服开发用于各种开放世界应用的视觉系统的基本限制。

▲ Abstract：

Image sensors face substantial challenges when dealing with dynamic, diverse and unpredictable scenes in open-world applications. However, the development of image sensors towards high speed, high resolution, large dynamic range and high precision is limited by power and bandwidth. Here we present a complementary sensing paradigm inspired by the human visual system that involves parsing visual information into primitive-based representations and assembling these primitives to form two complementary vision pathways: a cognition-oriented pathway for accurate cognition and an action-oriented pathway for rapid response. To realize this paradigm, a vision chip called Tianmouc is developed, incorporating a hybrid pixel array and a parallel-and-heterogeneous readout architecture. Leveraging the characteristics of the complementary vision pathway, Tianmouc achieves high-speed sensing of up to 10,000?fps, a dynamic range of 130?dB and an advanced figure of merit in terms of spatial resolution, speed and dynamic range. Furthermore, it adaptively reduces bandwidth by 90%. We demonstrate the integration of a Tianmouc chip into an autonomous driving system, showcasing its abilities to enable accurate, fast and robust perception, even in challenging corner cases on open roads. The primitive-based complementary sensing paradigm helps in overcoming fundamental limitations in developing vision systems for diverse open-world applications.

Low-latency automotive vision with event cameras

带有事件摄像头的低延迟汽车视觉

▲ 作者：Daniel Gehrig & Davide Scaramuzza

▲ 链接：

https://www.nature.com/articles/s41586-024-07409-w

▲ 摘要：

目前，高级驾驶辅助系统中使用的计算机视觉算法依赖于基于图像的RGB摄像头，为了提供安全的驾驶体验，带宽延迟是一个关键的权衡。为了解决这个问题，事件摄像机已经成为另一种视觉传感器。

事件相机异步测量强度的变化，提供高时间分辨率和稀疏性，显著降低带宽和延迟要求。尽管有这些优点，基于事件相机的算法要么效率很高，但在准确性方面落后于基于图像的算法，要么牺牲事件的稀疏性和效率来获得类似的结果。

为了克服这个问题，研究者提出了一种基于事件和帧的混合对象检测器，它保留了每种模式的优点，因此不会受到这种权衡的影响。该方法利用事件的高时间分辨率和稀疏性以及标准图像中丰富但低时间分辨率的信息来生成高效，高速率的目标检测，减少感知和计算延迟。

研究表明，使用每秒20帧的RGB相机加上事件相机可以实现与每秒45帧相机带宽的5000帧相机相同的延迟，而不会影响精度。该方法通过揭示事件相机的潜力，为在边缘情况下实现高效和稳健的感知铺平了道路。

▲ Abstract：

The computer vision algorithms used currently in advanced driver assistance systems rely on image-based RGB cameras, leading to a critical bandwidth–latency trade-off for delivering safe driving experiences. To address this, event cameras have emerged as alternative vision sensors. Event cameras measure the changes in intensity asynchronously, offering high temporal resolution and sparsity, markedly reducing bandwidth and latency requirements1. Despite these advantages, event-camera-based algorithms are either highly efficient but lag behind image-based ones in terms of accuracy or sacrifice the sparsity and efficiency of events to achieve comparable results. To overcome this, here we propose a hybrid event- and frame-based object detector that preserves the advantages of each modality and thus does not suffer from this trade-off. Our method exploits the high temporal resolution and sparsity of events and the rich but low temporal resolution information in standard images to generate efficient, high-rate object detections, reducing perceptual and computational latency. We show that the use of a 20 frames per second (fps) RGB camera plus an event camera can achieve the same latency as a 5,000-fps camera with the bandwidth of a 45-fps camera without compromising accuracy. Our approach paves the way for efficient and robust perception in edge-case scenarios by uncovering the potential of event cameras.

能源Energy

Electric recycling of Portland cement at scale

大规模水泥电回收

▲ 作者：Cyrille F. Dunant, Shiju Joseph, Rohit Prajapati & Julian M. Allwood

▲ 链接：

https://www.nature.com/articles/s41586-024-07338-8

▲ 摘要：

水泥生产造成了全球7.5%的人为二氧化碳排放，这是由石灰石脱碳和化石燃料燃烧引起的。目前的脱碳策略包括用补充材料取代波特兰熟料，但这些主要出现在排放过程中，开发替代粘合剂但尚未达到规模，或者采用仍然释放一些排放的碳捕获和储存。

然而，用过的水泥是一种潜在的丰富的脱碳原料。作者研究表明，回收的水泥浆可以再熟化，如果作为部分替代石灰白云石助熔剂用于目前的钢铁回收。所得矿渣满足现有硅酸盐熟料的要求，可与煅烧粘土和石灰石有效混合。

该工艺对回收的水泥膏体的二氧化硅含量以及可能来自废料的二氧化硅和氧化铝含量很敏感，但这可以很容易地调整。研究表明，拟议的工艺可能具有经济竞争力，如果由无排放的电力供电，可以实现零排放水泥，同时还可以通过减少石灰助熔剂需求来减少钢铁回收的排放。

到2050年，全球用于回收的废钢供应量可能会增加两倍，而且每单位回收的钢铁很可能会产生更多的炉渣。随着建筑材料效率的提高，这条路线可以满足未来全球对水泥的需求。

▲ Abstract：

Cement production causes 7.5% of global anthropogenic CO2 emissions, arising from limestone decarbonation and fossil-fuel combustion. Current decarbonation strategies include substituting Portland clinker with supplementary materials, but these mainly arise in emitting processes, developing alternative binders but none yet promises scale, or adopting carbon capture and storage that still releases some emissions. However, used cement is potentially an abundant, decarbonated feedstock. Here we show that recovered cement paste can be reclinkered if used as a partial substitute for the lime–dolomite flux used in steel recycling nowadays. The resulting slag can meet existing specifications for Portland clinker and can be blended effectively with calcined clay and limestone. The process is sensitive to the silica content of the recovered cement paste, and silica and alumina that may come from the scrap, but this can be adjusted easily. We show that the proposed process may be economically competitive, and if powered by emissions-free electricity, can lead to zero emissions cement while also reducing the emissions of steel recycling by reducing lime flux requirements. The global supply of scrap steel for recycling may treble by 2050, and it is likely that more slag can be made per unit of steel recycled. With material efficiency in construction future global cement requirements could be met by this route.