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 B₄C 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 TiB_xC_y composition, which hinders the interface diffusion, supresses the crystallization of the Cr/Ti multilayer and dramatically improves the interface quality of Cr/TiB_xC_y 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.

中文翻译：

---

通过共沉积B4C改善Cr / Ti多层膜的软X射线反射率

覆盖2.4-4.4 nm的“水窗”是重要的波长范围，对生物学研究特别重要。Cr / Ti多层膜是该区域中很有希望的反射元素之一，因为理论上在2.73 nm处，接近法线入射的反射率高达64％。但是，由于存在多层缺陷，报告的反射率在接近法线入射时低于3％。在这里，通过在界面处共同沉积B ₄ C，将B和C故意掺入超薄Cr / Ti软X射线多层膜中。使用X射线反射仪，X射线光电子能谱和截面电子显微镜研究了对多层结构和成分的影响。结果表明，B和C主要与Ti位键合，形成非化学计量的TiB _x阻碍界面扩散的C _y成分抑制了Cr / Ti多层膜的结晶，并显着提高了Cr / TiB _x C _y多层膜的界面质量。结果，在2.73 nm波长处，软X射线的近法线入射反射率从4.48％增加到15.75％。