Abstract
We report optical constants of e-beam evaporated yttrium oxide Y2O3 thin films as determined from angle-dependent reflectance measurements at wavelengths from 5 to 50 nm. Samples were measured using synchrotron radiation at the Advanced Light Source. The experimental reflectance data were fit to obtain values for the index of refraction and thin film roughness. We compare our computed constants with those of previous researchers and those computed using the independent atom approximation from the CXRO website. We found that the index of refraction near 36 nm is much lower than previous data from Tomiki as reported by Palik. The real part of the optical constants is about 10% to 15% below CXRO values for wavelengths between 17 nm and 30 nm. Films were also characterized chemically, structurally, and optically by ellipsometry and atomic force microscopy.
Highlights
In 2000 the IMAGE mission carried into space an extreme ultraviolet (EUV) instrument designed to produce pictures of the earth’s magnetosphere over time [1]
It would have been superior to designs using a SiC/Si multilayer mirror similar to the design produced by Soufli, et al [5] or a SiC/Mg multilayer mirror similar to the design produced by Fernández-Peria, et al [6] which had reflectances of a few percent at both of these wavelengths
The indices of refraction (δ and β) of two yttria samples were experimentally determined for wavelengths of 5–49 nm
Summary
In 2000 the IMAGE mission carried into space an EUV instrument designed to produce pictures of the earth’s magnetosphere over time [1]. An effort was made to design a dual-function multilayer mirror coating that strongly reduced the reflectance of this line in a way that did not interfere with the mirrors’ intended reflectance at 30.4 nm [2] As part of this effort, Lunt, et al used a genetic algorithm program to investigate what materials and thicknesses would produce high 30.4 nm reflectance and low 58.4 nm reflectance [3, 4]. The program picked, instead, as one of the layers in the bilayer multilayer a compound: yttrium oxide (Y2O3) [3] While this material, termed yttria, is used in thin-film optics in the near IR, optical, and UV range, its utility in the extreme ultraviolet was unknown [7,8,9]. Our purpose was to investigate the nature of these discrepancies and to extend the range for which the indices of refraction for yttria, in thin film form, are known
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