Reflectance measurements on clean surfaces for the determination of optical constants of silicon in the extreme ultraviolet–soft-x-ray region

Regina Soufli, Eric M. Gullikson
1997 Applied Optics  
The refractive index n ϭ 1 Ϫ ␦ ϩ i␤ of Si in the energy range 50 -180 eV is investigated with angledependent reflectance measurements. The optical constants ␦ and ␤ are both determined by fitting to the Fresnel equations. The results of this method are compared with the values in the atomic tables derived from experimental data for ␤ and implementation of the Kramers-Kronig relations for ␦. The samples were prepared by UV irradiation and HF:ethanol dipping to H passivate the surface. It is
more » ... surface. It is found that the values of ␦ in the atomic tables are 8 -15% too high in the region 50 -90 eV. This is attributed to missing oscillator strength in the tabulated absorption coefficient for Si. The measured values of ␤ for crystalline Si exhibit structure below the L 2,3 edge ͑99.8 eV͒, as was previously observed in transmission measurements of Si͑111͒. It is also found that the method of least-squares fitting reflectance data to obtain optical constants is most effective for energies well below the edge, where ␦ Ͼ ␤, while for a range of energies around and above the edge, where ␦ Ͻ ␤, the optical constants are determined with large uncertainties. This behavior is not unique to the Si L 2,3 edge.
doi:10.1364/ao.36.005499 pmid:18259372 fatcat:t2fvhbp6craqjcj7dtasfgu2kq