Open AccessStructure and stress studies of low temperature annealed W/Si multilayers for the X-ray telescope
Author(s) -
Qiushi Huang,
Zhang Jin-Shuai,
Runze Qi,
Yang Yang,
Fengli Wang,
Jie Zhu,
Zhong Zhang,
Zhanshan Wang
Publication year - 2016
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.24.015620
Subject(s) - materials science , annealing (glass) , stress relaxation , amorphous solid , microstructure , optics , transmission electron microscopy , stress (linguistics) , scattering , composite material , crystallography , nanotechnology , creep , linguistics , chemistry , physics , philosophy
Low stress W/Si multilayer mirrors are demanded in the hard X-ray telescopes to achieve the high angular resolution. To reduce the stress of the as-deposited multilayer and maintain a high reflectivity, two groups of low-temperature annealing experiments were performed on the periodic multilayers with a d-spacing of ~3.8 nm. The temperature-dependent experiments show that the 150 °C annealing can slightly increase the reflectivity while the stress reduced only by 24%. Higher temperature annealing induced a larger reduction of the stress and the multilayer reached an almost zero stress state at 250 °C. The stress relaxation was accompanied by a small drop of reflectivity of ≤5% and a period compaction of <0.02 nm. The time-dependent experiments indicate that most of the stress changes occurred within the first 10 minutes while a prolonged annealing is not useful. The X-ray scattering and transmission electron microscopy were further used to study the microstructure changes of the multilayers. It is found that the W/Si multilayer exhibits an amorphous structure before and after annealing, while an enhanced diffusion and intermixing is the main reason for the stress relaxation and structure changes.