tfPDF: Thin film PDF

Our recent work on tfPDF has been highlighted on the BNL website!

Functional thin films are deposited onto a substrate, often silicon, silicon dioxide, or aluminum oxide. This makes it difficult to study the thin film structure because of the small amount of film material and large amount of substrate. To minimize the scattering of x-rays off the substrate, thin film x-ray scattering studies are usually done using grazing incidence (GI) X-ray experiments. However, GI studies are challenging, and are yet to be successfully applied for PDF analysis. Nanostructure analysis of thin films have therefore not been possible – until now.

Taking advantage of the high X-ray flux at the XPD beamline at NSLS-II, we spent our first beamtime at the new beamline studying thin films. Instead of using the complicated GI setup, we used simple normal incidence measurements, letting the X-rays pass through the thick substrate before hitting the film. 99% of the collected total scattering signal therefore originates from the substrate, but with careful background subtraction using xPDFsuite, we were able to isolate the signal from the film and obtain high quality PDFs for nanostructure analysis of the films.

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We demonstrated this studying Iron Antimony films, described in a recent paper:

Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films. K. M. Ø. Jensen, A. B. Blichfeld, S. R. Bauers, S. R. Wood, E. Dooryhée, D. C. Johnson, B. B. Iversen & S. J. L. Billinge (2015). IUCrJ 2, doi:10.1107/S2052252515012221.

This work was a collaboration with the Bo Iversen group at Aarhus University and Dave Johnson’s group at University of Oregon. The same collaboration resulted in another paper, diving deeper into the FeSbx structures:

Structural Evolution of Iron Antimonides from Amorphous Precursors to Crystalline Products Studied by Total Scattering Techniques. Sage R. Bauers, Suzannah R. Wood, Kirsten M. Ø. Jensen, Anders B. Blichfeld, Bo B. Iversen, Simon J. L. Billinge, and David C. Johnson. J. Amer. Chem. Soc, 2015, doi: 10.1021/jacs.5b04838