Crystallographic orientation of orthorhombic aragonite using reflection generalized ellipsometry

G. E. Jellison, D. N. Leonard, L. M. Anovitz, M. C. Cheshire, E. D. Specht, T. M. Rosseel

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Abstract

The 2-modulator generalized ellipsometry microscope (2-MGEM) has been used to study a natural crystal of aragonite. Like its polymorph calcite, aragonite has a large refractive index difference between light polarized parallel to the c-axis and light polarized perpendicular to the c-axis. Unlike calcite, aragonite is orthorhombic, so there is also a very small difference between the refractive indices polarized along the a- and b-directions. As a result, it is not possible to use the 2-MGEM to obtain a definitive map of the optic axis directions of a sample as was possible with calcite, but it is possible to determine approximately the orientation of the c-axis with respect to the surface normal. If the c-axis is in the sample surface plane, it is possible to measure very small deviations of the c-axis direction with an accuracy of ∼0.2°. If the c-axis is oriented normal to the sample surface, 2-MGEM data can be used to identify different crystallites due to rotations about the c-axis. For comparison, the orientations of some of the crystallites have also been measured using X-ray Laue and electron beam backscatter diffraction. In addition, spectroscopic generalized ellipsometry measurements have been used to determine the refractive indices of aragonite.

Original languageEnglish
Article number043102
JournalJournal of Applied Physics
Volume126
Issue number4
DOIs
StatePublished - Jul 28 2019

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© 2019 Author(s).

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