Optical constants of very thin gold films in the soft x-ray region

Optical constants of gold in the soft-x-ray region from reflection and transmission measurements

The optical constants of gold deposited on 300-nm-thick freestanding polyimide films have been measured in the energy range of 40-1350 eV. The optical constants of the polyimide films were known from a previous investigation. By performing both transmission measurements with Kramers-Kronig analysis and multiangle reflection measurements with analysis by fitting to a Fresnel multilayer model including roughness, one could carry out a detailed error analysis. In the energy range above 500 eV systematic deviations between the results obtained by both methods were found. For gold films the discrepancies can be attributed to deviations from Beckmann-type behavior at small grazing-incidence angles.

Simultaneous determination of the optical constants and thickness of very thin films by using soft-x-ray reflectance measurements

A nonlinear, least-squares curve-fitting method is described that simultaneously determines the optical constants and the thickness of a very thin (≲ 100-Å) film from reflectance versus angle of incidence (R - θ) data measured in the soft-x-ray region. The method is applied to R - θ data obtained for very thin, sputtered films of carbon (65 Å thick) and gold (94 Å thick) at photon energies of 60-900 eV. The results show that the present method is capable of accurately determining the thickness of very thin films even for transparent materials, and that the obtained optical constants are in good agreement with values reported for films with a thickness of 1000 Å.