Growth of nano-dots on the grazing-incidence mirror surface under FEL irradiation

A new phenomenon on X‐ray optics surfaces has been observed: the growth of nano‐dots (40–55 nm diameter, 8–13 nm height, 9.4 dots µm−2 surface density) on the grazing‐incidence mirror surface under irradiation by the free‐electron laser (FEL) FLASH (5–45 nm wavelength, 3° grazing‐incidence angle). W...

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Bibliographic Details
Published in:Journal of synchrotron radiation 2016-01, Vol.23 (1), p.78-90
Main Authors: Kozhevnikov, I. V., Buzmakov, A. V., Siewert, F., Tiedtke, K., Störmer, M., Samoylova, L., Sinn, H.
Format: Article
Language:English
Subjects:
Beams (radiation)
Density
FEL mirrors
Free electron lasers
interaction of FEL radiation with matter
Irradiation
Mathematical models
nano-dots
Nanostructure
Reflection
Synchrotron radiation
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Summary:A new phenomenon on X‐ray optics surfaces has been observed: the growth of nano‐dots (40–55 nm diameter, 8–13 nm height, 9.4 dots µm−2 surface density) on the grazing‐incidence mirror surface under irradiation by the free‐electron laser (FEL) FLASH (5–45 nm wavelength, 3° grazing‐incidence angle). With a model calculation it is shown that these nano‐dots may occur during the growth of a contamination layer due to polymerization of incoming hydrocarbon molecules. The crucial factors responsible for the growth of nano‐dots in the model are the incident peak intensity and the reflection angle of the beam. A reduction of the peak intensity (e.g. replacement of the FEL beam by synchrotron radiation) as well as a decrease of the incident angle by just 1° (from 3° to 2°) may result in the total disappearance of the nano‐dots. The model calculations are compared with surface analysis of two FLASH mirrors.
ISSN:1600-5775
0909-0495
1600-5775
DOI:10.1107/S160057751502202X