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Structure, stress and optical properties of Cr/C multilayers for the tender X-ray range

DOI: 10.1107/S1600577519001668 DOI Help

Authors: Jiangtao Feng (Tongji University) , Qiushi Huang (Tongji University) , Hongchang Wang (Diamond Light Source) , Xiaowei Yang (Shanghai Tec University) , Angelo Giglia (CNR) , Chun Xie (Tongji University) , Zhanshan Wang (Tongji University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Synchrotron Radiation , VOL 26

State: Published (Approved)
Published: May 2019

Abstract: Cr/C multilayer optics are a suitable choice for the tender X-ray range (1–4 keV) that covers the K absorption edges of P, S, Cl and 3d transition metals as well as the L absorption edges of 4d transition metals. In particular, these optics are studied in order to optimize the optical properties of collimated plane-grating monochromators. In this paper, the structure, stress and optical properties of Cr/C multilayers (fabricated using direct-current magnetron sputtering) with bi-layer number of 20 and the same period (about 11.64 nm) but different Cr thickness ratio (0.20–0.80) are investigated. Firstly, the grazing-incidence X-ray reflectivity at 8.04 keV was measured. These measurements were fitted assuming a multilayer structure with a four-layer and non-periodic model. Results and fitting show that interface widths increase with the Cr thickness ratio. The results obtained from X-ray diffraction at 8.04 keV were consistent with high-resolution transmission electron microscopy which showed an increase in grain size of the Cr layers. In addition, the stresses of the Cr/C multilayers have been measured and the results show that the stress value approaches zero when the Cr thickness ratio is about 0.45. The reflectivity of a Cr/C multilayer with Cr thickness ratio of 0.37 was measured and reaches 26.6% at 1.04 keV. The measured reflectivity matches very well with the predicted value using the four-layer and non-periodic model, which confirmed the viability of the prediction. Thus, the reflectivity at 1.04 keV of a Cr/C multilayer with different Cr thickness ratio was predicted and was found to drastically decrease when the Cr thickness ratio is larger than 0.37. It has been determined that a Cr thickness ratio value of 0.37 is the best choice for a Cr/C multilayer in view of high reflectivity and low stress.

Keywords: X-ray optics; Cr/C multilayer; structure; stress; high reflectivity

Subject Areas: Technique Development, Physics


Technical Areas: Optics