Structural variation in a synchrotron‐induced contamination layer (a‐C:H) deposited on a toroidal Au mirror surface

• Published in: Journal of synchrotron radiation 2017-07, Vol.24 (4), p.757-764
• Main Authors: Yadav, P. K., Gupta, R. K., Swami, M. K., Modi, M. H
• Format: Article
• Language: English
• Subjects: Bulk density; Carbon; Contamination; Electric power distribution; Gaussian beams (optics); Gold; Grazing incidence; Hydrocarbons; hydrogenerated carbon; Incidence; Normal distribution; Optical components; Parameter estimation; Photoelectrons; Photons; Raman spectra; Raman spectroscopy; Reflectance; reflectivity; Scattering; X-ray diffraction; X-rays
• ISSN: 1600-5775; 0909-0495; 1600-5775
• DOI: 10.1107/S1600577517007123

A carbon layer deposited on an optical component is the result of complex interactions between the optical surface, adsorbed hydrocarbons, photons and secondary electrons (photoelectrons generated on the surface of optical elements). In the present study a synchrotron‐induced contamination layer on a 340 mm × 60 mm Au‐coated toroidal mirror has been characterized. The contamination layer showed a strong variation in structural properties from the centre of the mirror to the edge region (along the long dimension of the mirror) due to the Gaussian distribution of the incident photon beam intensity/power on the mirror surface. Raman scattering measurements were carried out at 12 equidistant (25 mm) locations along the length of the mirror. The surface contamination layer that formed on the Au surface was observed to be hydrogenated amorphous carbon film in nature. The effects of the synchrotron beam intensity/power distribution on the structural properties of the contamination layer are discussed. The I(D)/I(G) ratio, cluster size and disordering were found to increase whereas the sp2:sp3 ratio, G peak position and H content decreased with photon dose. The structural parameters of the contamination layer in the central region were estimated (thickness ≃ 400 Å, roughness ≃ 60 Å, density ≃ 72% of bulk graphitic carbon density) by soft X‐ray reflectivity measurements. The amorphous nature of the layer in the central region was observed by grazing‐incidence X‐ray diffraction. A synchrotron radiation induced contamination layer (a‐C:H) on a mirror surface showed a strong variation in structural properties with photon dose. The D‐ to G‐peak intensity ratio [I(D)/I(G)], cluster size and disordering were found to increase with photon dose whereas the sp2:sp3 ratio, G‐peak position and hydrogen content were found to decrease with photon dose. In the central region on the mirror surface structural parameters were obtained by soft X‐ray reflectivity.