Resonant Soft X-Ray Scattering – Combining Structural with Spectroscopic Refinement

Friday, September 28, 2012 - 10:00am

SSRL Presents Kevin Stone

X-ray absorption spectroscopy has become an important tool in understanding the electronic structure of materials.  Resonant absorption edges in the soft x-ray regime are especially interesting as they allow the study of the lighter elements, such as in organic or organo-metallic substances, as well as important L-edges of the 3d transition metals important in magnetic and oxide systems.  Measurements of soft x-ray absorption spectra are inherently surface sensitive, and are plagued by issues such as extinction (in electron yield measurements) or self absorption (in fluorescence yield measurements), which make accurate determination of the optical constants difficult.  Accurate modeling of energy resolved scattering measurements made across the resonant absorption edges can provide accurate optical constants for a material.

We have developed a novel technique for analyzing both angle and energy resolved reflectivity to extract optical constants alongside structural information in a free-form, depth resolved manner.  A natural means of resolving depth dependent information is through scattering and, more specifically, reflectivity.  In common practice, the optical properties of the constituent components of a material must be known prior to modeling of the scattered intensity.  As resonant scattering becomes more refined, we increasingly encounter cases where the spatial variation of resonant optical properties themselves is of interest.  We present a means of refining electronic structure, in the form of optical properties, simultaneously with physical structure, in a Kramers-Kronig consistent manner.  Our approach is fully capable of modeling arbitrary spectral shapes, with impressive sensitivity to variations in the physical structure of a sample, and can be generalized to consider more complex scattering processes, including magnetic scattering.  Several examples will be discussed, from both hard and soft condensed matter systems.

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