Characterization of Carbon-Contaminated B4C-Coated Optics after Chemically Selective Cleaning with Low-Pressure RF Plasma

摘要

Boron carbide (B4C) is one of the few materials that is expected to be mostlyresilient with respect to the extremely high brilliance of the photon beamgenerated by free electron lasers (FELs) and is thus of considerable interestfor optical applications in this field. However, as in the case of many otheroptics operated at modern light source facilities, B4C-coated optics aresubject to ubiquitous carbon contaminations. These contaminations represent aserious issue for the operation of high performance FEL beamlines due to severereduction of photon flux, beam coherence, creation of destructive interference,and scattering losses. A variety of B4C cleaning technologies were developed atdifferent laboratories with varying success. We present a study regarding thelow-pressure RF plasma cleaning of carbon contaminated B4C test samples viainductively coupled O2/Ar, H2/Ar, and pure O2 RF plasma produced followingprevious studies using the same IBSS GV10x downstream plasma source. Resultsregarding the chemistry, morphology as well as other aspects of the B4C opticalcoating before and after the plasma cleaning are reported. We conclude fromthese comparative plasma processes that pure O2 feedstock plasma only exhibitsthe required chemical selectivity for maintaining the integrity of the B4Coptical coating.