Abstract
A method to separate the non-resonant inelastic X-ray scattering signal of a micro-metric sample contained inside a diamond anvil cell (DAC) from the signal originating from the high-pressure sample environment is described. Especially for high-pressure experiments, the parasitic signal originating from the diamond anvils, the gasket and/or the pressure medium can easily obscure the sample signal or even render the experiment impossible. Another severe complication for high-pressure non-resonant inelastic X-ray measurements, such as X-ray Raman scattering spectroscopy, can be the proximity of the desired sample edge energy to an absorption edge energy of elements constituting the DAC. It is shown that recording the scattered signal in a spatially resolved manner allows these problems to be overcome by separating the sample signal from the spurious scattering of the DAC without constraints on the solid angle of detection. Furthermore, simple machine learning algorithms facilitate finding the corresponding detector pixels that record the sample signal. The outlined experimental technique and data analysis approach are demonstrated by presenting spectra of the Si L2,3-edge and O K-edge of compressed α-quartz. The spectra are of unprecedented quality and both the O K-edge and the Si L2,3-edge clearly show the existence of a pressure-induced phase transition between 10 and 24 GPa.
Highlights
Non-resonant inelastic X-ray scattering from core electrons, or X-ray Raman scattering (XRS) spectroscopy, has proven a valuable tool for the study of shallow electronic absorption edges under extreme pressure and temperature conditions (Mao et al, 2001; Rueff & Shukla, 2010; Sternemann & Wilke, 2016)
XRS is the sibling of soft X-ray absorption spectroscopy (Henderson et al, 2014) and electron energy-loss spectroscopy, suited to investigate samples contained inside diamond anvil cells
We presented a scheme to conduct XRS spectroscopy experiments from diamond anvil cells using the direct tomography imaging technique
Summary
Non-resonant inelastic X-ray scattering from core electrons, or X-ray Raman scattering (XRS) spectroscopy, has proven a valuable tool for the study of shallow electronic absorption edges under extreme pressure and temperature conditions (Mao et al, 2001; Rueff & Shukla, 2010; Sternemann & Wilke, 2016). XRS possesses the unique strength to probe shallow electronic absorption edges of light elements such as oxygen and silicon, using hard X-rays that penetrate several millimeters of diamond (Sternemann et al, 2013). In this respect, XRS is the sibling of soft X-ray absorption spectroscopy (Henderson et al, 2014) and electron energy-loss spectroscopy, suited to investigate samples contained inside diamond anvil cells. In order to cope with these difficulties, it is important to utilize brilliant X-ray sources, an efficient detection scheme (large solid angle of detection) and an efficient procedure for the separation of the desired signal from the spurious scattering originating from the high-pressure sample environment. Data from the O K- and Si L2,3-edge of SiO2 quartz at high pressure obtained with this setup are presented in section x4, and, x5 gives a summary and outlook for our new procedure
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