Air-sensitivity of a sample material (change of properties in direct contact with oxygen or/and water) is an important issue for many research fields. Besides other materials, a large number of pharmaceuticals, catalysts, materials for gas storage applications, battery research, etc. requires an oxygen-/water-free atmosphere for their characterization.
Adequate protection of a sample material from air during an X-ray experiment is an important factor for a successful analysis. Here we present a comparative study of different sample holders for air-sensitive materials (based on air-tightness, contribution to background and transparency to X-rays).
In this application note it is shown that Anton Paar domed sample holder with a PEEK dome is the most air-tight option, which comes at a cost of the strongest contribution to the XRD background. However, PEEK dome background contribution can be reduced by placing the detector anti-scatter slit closer to the sample.
In the figure below we compare the XRD background of two air-sensitive sample holder types, measured using two instrument configurations for X-ray diffraction in reflection:
1. Instrument configuration with the detector anti-scatter slit at the standard position
2. Instrument configuration with the anti-scatter slit for transmission geometry placed in front of the 1D detector.
For the standard setup with programmable slits background contribution of the Anton Paar domed sample holder with a PEEK dome (green line) is quite significant, much stronger than that of the PANalytical sample holder with a Kapton foil (red line). Similar result is observed for the standard instrument configuration with the fixed slits (not shown here).
For the non-standard configuration, with the detector anti-scatter slit for transmission, the PEEK dome background contribution (blue line) is significantly reduced whilst background of the PANalytical sample holder (brown line) is virtually the same.
The non-standard instrument configuration with the detector anti-scatter slit for transmission geometry is undoubtedly beneficial when using Anton Paar domed sample holder. However, considering the narrow opening of the detector anti-scatter slit, incident beam divergence should be optimized to ensure correct peak intensity over the entire measured 2Theta range. We advice to use fixed divergence slit mode with rather narrow slit opening.
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