The refractive index n = 1 - δ + iβ of Si in the energy range 50–180 eV is investigated with angle-dependent reflectance measurements. The optical constants δ and β 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 β and implementation of the Kramers–Kronig relations for δ. The samples were prepared by UV irradiation and HF:ethanol dipping to H passivate the surface. It is found that the values of δ 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 β for crystalline Si exhibit structure below the L2,3 edge (99.8 eV), as was previously observed in transmission measurements of Si(111). 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 δ > β, while for a range of energies around and above the edge, where δ < β, the optical constants are determined with large uncertainties. This behavior is not unique to the Si L2,3 edge.
© 1997 Optical Society of AmericaPDF Article