Demonstration of thin film pair distribution functionanalysis (tfPDF) for the study of local structure in amorphous and crystalline thin films.

Kirsten M Ø Jensen,Simon J L Billinge,Sage R Bauers,Anders B Blichfeld,David C Johnson,Eric Dooryhée,Suzannah R Wood,Bo B Iversen

doi:10.1107/s2052252515012221

Kirsten M Ø Jensen, Simon J L Billinge + Show 6 more

Open Access

https://doi.org/10.1107/s2052252515012221

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Abstract

By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The 'tfPDF' method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.

Highlights

Thin films are fundamental in applications from electronics to catalysis to tribology in structural materials (Nomura et al, 2004; Tang et al, 1989; O’Regan & Gratzel, 1991; Ginley & Bright, 2000)
We show that by using high-flux, high-energy X-rays from third-eneration synchrotron sources, normal-incidence total scattering measurements can be used to extract reliable pair distribution functions (PDF) from thin films on amorphous substrates
We firstly illustrate that reliable PDFs can be obtained from thin films on amorphous substrates, using the data obtained for sample 1A and sample 1C as an example

Summary

Introduction

Thin films are fundamental in applications from electronics to catalysis to tribology in structural materials (Nomura et al, 2004; Tang et al, 1989; O’Regan & Gratzel, 1991; Ginley & Bright, 2000). When preparing thin films (10–1000 nm), the precursor compounds are typically deposited on a much thicker substrate of, for example, Si, SiO2 or Al2O3 This sample geometry challenges the conventional methods for structural analysis using X-ray diffraction, as data collected using standard scattering configurations (i.e. Debye–Scherrer or Bragg– Brentano setups) are dominated by scattering from the substrate. For example, Rietveld analysis can be performed after careful corrections and provides valuable structural insight (Quaas et al, 1998; Simeone et al, 2011), most of the X-ray analysis done for thin films is qualitative and used mainly for identification of crystalline phases by considering the Bragg peak position This approach is not adequate to characterize, for example, the complex nanostructures present in modern materials, which may not possess long-range order (Billinge & Kanatzidis, 2004). Our studies give new insight into the crystallization of the metastable FeSb3 phase and open for a range of new investigations of film materials

Preparation of FeSbx

Data analysis

Obtaining the tfPDF: amorphous and crystalline FeSb3 films

Structures in the FeSbx system: sample 1

Conclusion

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