Characterization, optimization and surface physics aspects ofin situplasma mirror cleaning

Abstract

Although the graphitic carbon contamination of synchrotron beamline optics has been an obvious problem for several decades, the basic mechanisms underlying the contamination process as well as the cleaning/remediation strategies are not understood and the corresponding cleaning procedures are still under development. In this study an analysis of remediation strategies all based on in situ low-pressure RF plasma cleaning approaches is reported, including a quantitative determination of the optimum process parameters and their influence on the chemistry as well as the morphology of optical test surfaces. It appears that optimum results are obtained for a specific pressure range as well as for specific combinations of the plasma feedstock gases, the latter depending on the chemical aspects of the optical surfaces to be cleaned.

Towards chemically neutral carbon cleaning processes: plasma cleaning of Ni, Rh and Al reflective optical coatings and thin Al filters for free-electron lasers and synchrotron beamline applications

“…In the same vein and following previous studies (Gonzá lez Cuxart et al, 2016;Pellegrin et al, 2014;Moreno Ferná ndez et al, 2018), the ICP-type ibss model GV10x low-pressure plasma source together with N 2 /O 2 /H 2 and N 2 /H 2 feedstock gases have been used to clean Ni, Rh and Al foil materials and ultrathin Al filters for EUV applications.…”

“…A set of Ni, Rh and Al metal foils with micrometric thickness were contaminated with 50 nm of amorphous carbon (a-C) using electron beam deposition inside a commercial deposition setup together with high-purity polycrystalline graphitic carbon targets (Pellegrin et al, 2014) for simulating a photon-beam induced carbon contamination ( Fig. 1).…”

“…However, reflective optics, as well as transmission filters, are subject to carbon contamination buildup, representing an increasingly serious problem for the operation of highperformance FEL beamlines. Previous publications have shown that it is possible to clean this carbon contamination (Gonzá lez Cuxart et al, 2016;Pellegrin et al, 2014;Moreno Ferná ndez et al, 2018;Graham et al, 2002;Thedsakhulwong & Thowladda, 2008;Strein et al, 2008;Eggenstein et al, 2001;Hopf et al, 2002;Pellegrin et al, 2013) by using a different kind of plasma such as, for example, capacitively coupled plasma (CCP), inductively coupled plasma (ICP) and microwave plasma obtaining different results depending on the gas mixture, RF input power, frequencies and surfaces to be cleaned. Other alternative approaches include the use of oxygen gas bleeding in conjunction with the photon beam inside the UHV optics chambers (Warburton & Pianetta, 1992) or the in situ use of ozone generated via UV lamps (Yao-Leclerc et al, 2011).…”

Refurbishment of an Au-coated toroidal mirror by capacitively coupled RF plasma discharge

“…They also measured the cleaning rates of carbon allotropes by varying the RF power and the distance between source and object. Pellegrin et al (2014) used a capacitively coupled RF plasma system for the study of carbon cleaning rates from a quartz crystal microbalance. They observed that the carbon cleaning rate increases with increasing RF power and oxygen gas flow rate, but they did not measure the surface properties of the crystal after plasma cleaning.…”

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

“…In order to refurbish the contaminated optics to pristine efficiency, different groups have suggested and applied several online and offline cleaning techniques (UV/O 3 cleaning, RF plasma cleaning, in-situ cleaning in beam lines by Oxygen activated by synchrotron radiations, etc.) [10,[12][13][14][15][16].…”