近日，新加坡南洋理工大学的Liang Jie Wong及其研究团队取得一项新进展。经过不懈努力，他们成功获得自由电子驱动范德华结构水窗X射线的基本定标律。相关研究成果已于2024年10月28日在国际知名学术期刊《自然—光子学》上发表。
该研究团队通过展示自由电子驱动的范德华材料产生桌面级水窗X射线来解决这一挑战，实现了在整个水窗范围内光子能量的连续调谐。此外，研究人员提出一个真正具有预测性的理论框架，将第一性原理电磁学与蒙特卡洛模拟相结合，以绝对数量准确预测光子通量和亮度。
研究人员获得了可调光子通量的基本定标律，与实验结果相符，并为设计基于自由电子驱动量子材料的高效能发射器提供了方法。研究表明，有潜力实现成像和光谱应用所需的光子通量（样品上的光子通量超过103个每秒的光子通量和使用约50纳安电流的验证）。
重要的是，这一理论强调了范德华结构特有的大平均自由程和层间原子间距所起的关键作用，展示了范德华结构在产生水窗X射线方面相对于其他材料的优势。
据悉，水窗X射线在医学和生物学应用中至关重要，它无需外部染色即可实现生物细胞的自然对比度成像。然而，除了大型同步加速器设施外，要获得具有特定光子能量（高对比度成像所需）的水窗X射线源仍然面临挑战。
附：英文原文
Title: Fundamental scaling laws of water-window X-rays from free-electron-driven van der Waals structures
Author: Pramanik, Nikhil, Huang, Sunchao, Duan, Ruihuan, Zhai, Qingwei, Go, Michael, Boothroyd, Chris, Liu, Zheng, Wong, Liang Jie
Issue&Volume: 2024-10-28
Abstract: Water-window X-rays are crucial in medical and biological applications, enabling the natural-contrast imaging of biological cells without external staining. However, water-window X-ray sources with bespoke photon energies—needed in high-contrast imaging—remain challenging to obtain, except at large synchrotron facilities. Here we address this challenge by demonstrating tabletop, water-window X-ray generation from free-electron-driven van der Waals materials, enabling the continuous tuning of photon energies across the entire water-window regime. Additionally, we present a truly predictive theoretical framework combining first-principles electromagnetism with Monte Carlo simulations to accurately predict the photon flux and brightness in absolute quantities. We obtain fundamental scaling laws for the tunable photon flux, matching the experimental results and providing a way to design powerful emitters based on free-electron-driven quantum materials. We show that we can potentially achieve photon fluxes needed for imaging and spectroscopy applications (over 108photonss–1 on the sample—verified by our framework based on our experimentally achieved fluxes of about 103photonss–1 using ~50nA current). Importantly, our theory highlights the critical role played by the large mean free paths and interlayer atomic spacings unique to van der Waals structures, showing the latter’s advantages over other materials in generating water-window X-rays.
DOI: 10.1038/s41566-024-01547-3
Source: https://www.nature.com/articles/s41566-024-01547-3