Optical constants determination of samarium, holmium, and erbium in the 15-850 eV spectral range using a transmittance method

Abstract

The optical constants β and δ of the complex refractive index ñ=1-δ+iβ of Sm, Ho, and Er were obtained in the 1.5-850eV energy range using a transmittance method. Thin films of Sm, Ho, and Er were deposited by magnetron sputtering, and transmittance was measured using synchrotron radiation under a high vacuum condition. All films were directly coated on Si photodiodes, which were used as coating substrates, as well as photon detectors. Si was used as capping layer while a thin W layer was used as barrier against interface diffusion between Si and the highly reactive rare earth elements. The constants β were extracted from transmittance results, and the constants δ were calculated based on measured β values using the Kramers-Kronig formalism. Small deficiencies determined from the present data using the partial sum rules were partly attributed to the sputtered film densities that could be slightly lower than the bulk values.