Ex-situ characterization of synchrotron radiation induced carbon contamination on LiF window

Synchrotron radiation induced carbon contaminations on optical elements is a major concern for a beamline designer. Growth mechanism of carbon deposition is not well understood. Structural characterization of radiation (3.5-11.8 eV) induced contamination layer on LiF window is carried out by soft x-ray reflectivity (SXR) and grazing incidence x-ray diffraction (GIXRD) techniques. Diffraction peaks at 2θ = 28.3° (002) shows a graphitic structures and peak at 75.3° (220) show a mixed phase (carbonado) of carbon. Out-of-plane cluster/grain sizes ∼6.05 nm and ∼2.45 nm are measured respectively for crystalline graphite and carbonado phase of carbon by Debye Scherrer equation. For elemental analysis x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques are used. In Raman spectroscopy measurements the crystalline graphite G band (1556 cm−1) and disordered graphite D bands (1350 cm−1) are observed. In-plane cluster size∼ 9.62 nm was calculated by empirical relation using ID and IG ratio of Raman peaks. XPS peak at 291 eV indicates that most of the carbon is in the form of carbonate (ROCOOR') that is polymerizing in form of rings/chains and converted into polymer like (PLCH) and graphitic like hydrogenated (GLCH) carbon due to continuous exposure by radiation. Contamination layer properties also compared with commercial graphitic structure.