title: Growth of nano-dots on the grazing-incidence mirror surface under FEL irradiation.
abstract: 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.
authors.affiliation: Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskiy Prospect 59, Moscow 119333, Russian Federation.
authors.forename: I V
authors.initials: IV
authors.lastname: Kozhevnikov
authors.affiliation: Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskiy Prospect 59, Moscow 119333, Russian Federation.
authors.forename: A V
authors.initials: AV
authors.lastname: Buzmakov
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert Einstein Strasse 15, 12489 Berlin, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Siewert
authors.affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Tiedtke
authors.affiliation: Helmholtz-Zentrum Geesthacht, Institute of Materials Research, Max-Planck-Strasse 1, 21502 Geesthacht, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Störmer
authors.affiliation: European XFEL GmbH, Albert Einstein Ring 19, 22761 Hamburg, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Samoylova
authors.affiliation: European XFEL GmbH, Albert Einstein Ring 19, 22761 Hamburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Sinn
keywords: FEL mirrors; free-electron lasers; interaction of FEL radiation with matter; nano-dots