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The refractive index of a y-cut SiO2 crystal surface is reconstructed from orientation-dependent soft X-ray reflectometry measurements in the energy range from 45 to 620 eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed.

Soft X-ray reflectometry measurements were conducted at the X-ray radiometry beamline, operated by the Physikalisch-Technische Bundesanstalt (PTB), at the electron storage ring BESSY II in Berlin (Scholze et al., 2001). The beamline covers the photon energy range from 45 to 1800 eV and is designed to produce a beam with low divergence (<1 mrad) with minimal halo. The sample was mounted on a six-axis goniometer in the ellipso-scatterometer under ultrahigh vacuum conditions. The angle of incidence was aligned with respect to the beam with an uncertainty of 0.01°. The angle of incidence was varied between 0° and 88.7° in the s-polarization direction from the sample normal. The measured range of incident angles was adapted to the different photon energies in order to effectively cover the relevant angle range. The analyzed quartz (type II) surface (y cut) was polished (roughness average Ra < 1 nm) and aligned perpendicular to the plane of incidence. In addition, to resolve the anisotropy of the crystal structure of quartz, the reflection measurements in the near-edge region of Si L2,3 and O K were performed with a energy increment slightly lower than the energy resolution of the beamline.

A. Andrle et al. J. Appl. Cryst. (2021). 54, 402-408

Quartz Data


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