Abstract
Atomic pair distribution function (PDF) analysis is the most powerful technique to study the structure of condensed matter on the length scale from short- to long-range order. Today, the PDF approach is an integral part of research on amorphous, nanocrystalline and disordered materials from bulk to nanoparticle size. Thin films, however, demand specific experimental strategies for enhanced surface sensitivity and sophisticated data treatment to obtain high-quality PDF data. The approach described here is based on the surface high-energy X-ray diffraction technique applying photon energies above 60 keV at grazing incidence. In this way, reliable PDFs were extracted from films of thicknesses down to a few nanometres. Compared with recently published reports on thin-film PDF analysis from both transmission and grazing-incidence geometries, this work brought the minimum detectable film thickness down by about a factor of ten. Depending on the scattering power of the sample, the data acquisition on such ultrathin films can be completed within fractions of a second. Hence, the rapid-acquisition grazing-incidence PDF method is a major advancement in thin-film technology that opens unprecedented possibilities for in situ and operando PDF studies in complex sample environments. By uncovering how the structure of a layered material on a substrate evolves and transforms in terms of local and average ordering, this technique offers new opportunities for understanding processes such as nucleation, growth, morphology evolution, crystallization and the related kinetics on the atomic level and in real time.
Highlights
Over the past two decades, materials scientists have gradually embraced the emerging potential of the atomic pair distribution function (PDF), in particular to describe the short-range order of amorphous and nanocrystalline phases, as well as local deviations from the average structure in periodic systems (Billinge & Kanatzidis, 2004; Billinge & Levin, 2007; Young & Goodwin, 2011; Playford et al, 2014; Mancini & Malavasi, 2015; Keen & Goodwin, 2015)
We present how we extracted and analyzed grazing-incidence pair distribution functions (GIPDFs) from films as thin as 3 nm at a time resolution down to 0.5 s, with the data collected by surface high-energy X-ray diffraction on a large area detector
As the increase of the penetration depth for incidence above the critical angle is very steep and scales with the photon energy, even minor deviations from the ideal total reflection geometry give rise to scattering from the substrate. This effect is observable in high-energy GIPDF experiments since the relevant angles lie in the range of a few tens of millidegrees
Summary
Over the past two decades, materials scientists have gradually embraced the emerging potential of the atomic pair distribution function (PDF), in particular to describe the short-range order of amorphous and nanocrystalline phases, as well as local deviations from the average structure in periodic systems (Billinge & Kanatzidis, 2004; Billinge & Levin, 2007; Young & Goodwin, 2011; Playford et al, 2014; Mancini & Malavasi, 2015; Keen & Goodwin, 2015). We introduce rapid acquisition PDF analysis based on high-energy SXRD measurements, which represents a significant expansion of methods with respect to sensitivity and high-speed detection to determine the local structure of thin films That this technique is available, it provides a new resource for insight into the structure of amorphous, disordered and polycrystalline thin films under real conditions in real time during their growth and operation with a potentially large impact for technologies including energy harvesting and storage, health, and smart electronic devices and appliances. We present how we extracted and analyzed grazing-incidence pair distribution functions (GIPDFs) from films as thin as 3 nm at a time resolution down to 0.5 s, with the data collected by surface high-energy X-ray diffraction on a large area detector. A pre-annealed ZrO2 sample was heated on a silicon nitride hot plate (Bach Resistor Ceramics GmbH, Werneuchen, Germany) at 10C minÀ1 in air to the final temperature of 900C
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