Pair distribution functions of amorphous organic thin films from synchrotron X-ray scattering in transmission mode

Abstract

Using high-brilliance high-energy synchrotron X-ray radiation, for the first time the total scattering of a thin organic glass film deposited on a strongly scattering inorganic substrate has been measured in transmission mode. The organic thin film was composed of the weakly scattering pharmaceutical substance indomethacin in the amorphous state. The film was 130 mm thick atop a borosilicate glass substrate of equal thickness. The atomic pair distribution function derived from the thin-film measurement is in excellent agreement with that from bulk measurements. This ability to measure the total scattering of amorphous organic thin films in transmission will enable accurate in situ structural studies for a wide range of materials.

Local atomic structure of thin and ultrathin films via rapid high-energy X-ray total scattering at grazing incidence

“…Aside from the low absolute amount of sample in a thin film, two major aspects have impeded PDF analysis of thin films: (i) the strong scattering from the substrate the film is deposited on, whose thickness exceeds the film thickness usually by at least three orders of magnitude, causing an unfavorable signal-tobackground ratio, and (ii) texture, owing to different growth behavior parallel and perpendicular to the surface and/or in different crystallographic directions. Different approaches have been taken to circumvent these problems, including exfoliating the film off the substrate and grinding it Kurzman et al, 2015) as well as measuring the film on the substrate in transmission and carefully subtracting the dominant background signal of the amorphous substrate (Jensen et al, 2015;Nakamura et al, 2017;Shi et al, 2017;Wood et al, 2017). Both these methods have drawbacks: in the first case, structural changes may occur during the mechanical treatment and, in addition, any texture information is lost completely, whereas in the latter case, the signal-to-background ratio effectively sets a detection limit on the film thickness.…”

xINTERPDF: a graphical user interface for analyzing intermolecular pair distribution functions of organic compounds from X-ray total scattering data

“…) which are the building blocks of organic compounds. The atomic pair distribution function (PDF) calculated from X-ray (and/or neutron, electron) total scattering has been demonstrated to be a valuable tool for investigating structures of disordered and amorphous organic compounds (Shi et al, 2017;Prill et al, 2015Prill et al, , 2016Benmore & Weber, 2011;Rademacher et al, 2012;Chen et al, 2014;Gorelik et al, 2015). Although existing tools such as DiffPy-CMI (Juhá s et al, 2015) and XISF (Mou et al, 2015) can be used for this problem, a new software program that provides a user-friendly graphical user interface (GUI, as opposed to script-based programming in DiffPy-CMI) and analyzes the data in real space (as opposed to in reciprocal space in XISF) is still of great value.…”

Comparison and evaluation of pair distribution functions, using a similarity measure based on cross-correlation functions

“…The analysis of the atomic pair distribution function (PDF) is the method of choice to investigate amorphous or nanocrystalline samples, as frequently found in nature (Poulain et al, 2019) and in novel, complex, engineered materials (Cliffe et al, 2010;Young & Goodwin, 2011;Zobel et al, 2015;Roeser et al, 2017;Usher et al, 2018;Billinge, 2019), e.g. metal-organic frameworks (Bennett & Cheetham, 2014;Mazaj et al, 2016;Castillo-Blas et al, 2020), glasses and pharmaceuticals (Moore et al, 2009;Nollenberger et al, 2009;Thakral et al, 2016;Shi et al, 2017).…”