《自然》(20240822出版）一周论文导读
编译｜冯维维
Nature, Volume 632 Issue 8026, 22 August 2024《自然》，第632卷，8026期，2024年8月22日
Attosecond delays in X-ray molecular ionization
X射线分子电离的阿秒延迟
▲ 作者：Taran Driver, Miles Mountney, Jun Wang, Lisa Ortmann, Andre Al-Haddad, Nora Berrah, Christoph Bostedt, Elio G. Champenois, Louis F. DiMauro, Joseph Duris, Douglas Garratt, James M. Glownia, Zhaoheng Guo, Daniel Haxton, Erik Isele, Igor Ivanov, Jiabao Ji, Andrei Kamalov, Siqi Li, Ming-Fu Lin, Jon P. Marangos, Razib Obaid, Jordan T. O’Neal, Philipp Rosenberger, James P. Cryan Show authors
▲ 链接：https://www.nature.com/articles/s41586-024-07771-9
▲ 摘要：光电效应并非真正瞬时的，而是表现出阿秒的延迟，可以揭示复杂的分子动力学。亚飞秒持续时间的光脉冲为解决光电离动力学提供了必要的工具。过去十年，人们对单光子吸收极紫外光子后的光电离延迟进行了大量的研究。然而，测量时间分辨核能级的光离仍然遥不可及。所需的X射线光子能量所需的核心级光电离是不可用阿秒桌面源。
研究者报告了对核心能级电子的X射线光发射延迟的测量，其延迟出乎意料地大，在氧K壳层阈值附近的NO中高达700阿秒（1阿秒=10-18秒）。这些测量利用来自自由电子激光器的阿秒软X射线脉冲扫描K壳层阈值附近的整个区域。
研究者还发现延迟谱是丰富调制的，这表明有几个贡献，包括由于形状共振引起的光电子的瞬态捕获，在分子的快速非辐射弛豫中发射的与奥格-迈特纳电子的碰撞以及多电子散射效应。结果表明，在综合理论模型的支持下，X射线阿秒实验可以揭示核能级光电离复杂的相关动力学。
▲ Abstract：The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700?as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger–Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.
A hot-emitter transistor based on stimulated emission of heated carriers
基于受热载流子受激发射的热发射极晶体管
▲ 作者：Chi Liu, Xin-Zhe Wang, Cong Shen, Lai-Peng Ma, Xu-Qi Yang, Yue Kong, Wei Ma, Yan Liang, Shun Feng, Xiao-Yue Wang, Yu-Ning Wei, Xi Zhu, Bo Li, Chang-Ze Li, Shi-Chao Dong, Li-Ning Zhang, Wen-Cai Ren, Dong-Ming Sun & Hui-Ming Cheng▲ 链接：https://www.nature.com/articles/s41586-024-07785-3
▲摘要：热载流子晶体管是一类利用载流子的多余动能的器件。与依赖稳态载流子传输的常规晶体管不同，热载流子晶体管将载流子调制到高能状态，从而提高了器件的速度和功能。这些特性对于需要快速切换和高频操作的应用至关重要，例如先进的电信和尖端的计算技术。
然而，传统的热载流子产生机制要么是载流子注入，要么是加速，这在功耗和负差分电阻方面限制了器件性能。混合维器件结合了大块材料和低维材料，可以通过利用由能带组合形成的各种势垒，为热载流子产生提供不同的机制。
研究者报告了一种基于双混合维石墨烯/锗肖特基结的热发射极晶体管，该晶体管利用受热载流子的受激发射，实现了超过玻尔兹曼极限的每十年低于1毫伏的亚阈值摆幅，以及在室温下峰谷电流比大于100的负差分电阻。进一步演示了具有高逆变增益和可重构逻辑状态的多值逻辑。
这项工作报告了一种多功能热发射极晶体管，具有低功耗和负差分电阻应用的巨大潜力，标志着后摩尔时代的一个有希望的进步。
