Zhu Jingtao, Zhang Jiayi, Li Haochuan, Tu Yuchun, Chen Jinwen, Wang Hongchang, Dhesi Sarnjeet S, Cui Mingqi, Zhu Jie, Jonnard Philippe
MOE Key Laboratory of Advanced Micro-structured Materials, Institute of Precision Optical Engineering, School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China.
Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom.
J Synchrotron Radiat. 2020 Nov 1;27(Pt 6):1614-1617. doi: 10.1107/S1600577520011741. Epub 2020 Oct 9.
The `water window', covering 2.4-4.4 nm, is an important wavelength range particularly essential to biology research. Cr/Ti multilayers are one of the promising reflecting elements in this region because the near-normal-incidence reflectivity is theoretically as high as 64% at 2.73 nm. However, due to multilayer imperfections, the reported reflectivity is lower than 3% for near-normal incidence. Here, B and C were intentionally incorporated into ultra-thin Cr/Ti soft X-ray multilayers by co-deposition of BC at the interfaces. The effect on the multilayer structure and composition has been investigated using X-ray reflectometry, X-ray photoelectron spectroscopy, and cross-section electron microscopy. It is shown that B and C are mainly bonded to Ti sites, forming a nonstoichiometric TiBC composition, which hinders the interface diffusion, supresses the crystallization of the Cr/Ti multilayer and dramatically improves the interface quality of Cr/TiBC multilayers. As a result, the near-normal-incidence reflectivity of soft X-rays increases from 4.48% to 15.75% at a wavelength of 2.73 nm.
覆盖2.4 - 4.4纳米的“水窗”是一个重要的波长范围，对生物学研究尤为关键。铬/钛多层膜是该区域有前景的反射元件之一，因为在2.73纳米处，近正入射反射率理论上高达64%。然而，由于多层膜存在缺陷，报道的近正入射反射率低于3%。在此，通过在界面处共沉积硼碳将硼和碳有意引入超薄铬/钛软X射线多层膜中。利用X射线反射测量法、X射线光电子能谱和截面电子显微镜研究了其对多层膜结构和成分的影响。结果表明，硼和碳主要与钛位点结合，形成非化学计量比的TiBC成分，这阻碍了界面扩散，抑制了铬/钛多层膜的结晶，并显著提高了铬/钛硼碳多层膜的界面质量。结果，在2.73纳米波长处，软X射线的近正入射反射率从4.48%提高到了15.75%。
