Unwarping GISAXS data

Structural evolution and nanodomain formation in blend films of a block copolymer and homopolymer

This study explores the concurrent formation of surface perforations, parallel cylinders, and double gyroids in symmetric PS-b-PMMA/hPS blend films during isothermal annealing at 205 and 240 °C. By controlling the weight fraction ratio of PS-b-PMMA to hPS at 75/25, we systematically examined the impact of film thickness and annealing temperature on nanodomain development. Using in situ GISAXS and ex situ SEM, we observed that thin films rapidly formed surface perforations and underlying parallel cylinders at both annealing temperatures. For thicker films, annealing at 205 °C resulted in the coexistence of surface perforations and parallel cylinders, while annealing at 240 °C yielded the additional formation of double gyroids besides surface perforations and parallel cylinders. Furthermore, the double gyroids, which grew independently with {121}DG planes parallel to the substrate, did not exhibit in-plane epitaxial relationships with the other structures. These findings highlight the critical role of annealing temperature and film thickness in directing nanodomain morphology, offering new insights for the design of nanostructured materials with tailored properties.

Molecular-weight effects of a homopolymer on the AB- and ABC-stacks of perforations in block copolymer/homopolymer films

We have demonstrated the molecular-weight effects of adding homopolystyrene (hPS) on the evolution of perforated layers and double gyroids in polystyrene-block-poly(methyl methacrylate)-based films during isothermal annealing. Two homopolystyrenes of 2.8 and 17 kg mol-1 were used. To prepare blend films, PS-b-PMMA and hPSx (x: 2.8 or 17) were mixed at a weight-fraction ratio of 75/25 in toluene and then spin-coated at SiOx/Si. Spin coating inevitably produced films with thick edges at the periphery of the substrate. The structural evolution of the spun films was in situ characterized by grazing incidence small-angle X-ray scattering (GISAXS). The annealed films were then characterized using a scanning electron microscope (SEM). We found that thin middle regions behaved differently from thick beads for the films. The middle of the blend films mainly formed perforated layers with different spatial orders and orientations, depending on the molecular weight of added hPS chains. Hexagonally perforated layers quickly formed at 205 °C for PS-b-PMMA/hPS2.8 films. However, when hPS17 was used instead of hPS2.8, perforated layers formed with defects in PS-b-PMMA/hPS17 films annealed at 205 °C. Annealing at 240 °C improved the spatial order and orientation of perforated layers for a PS-b-PMMA/hPS17 film. Nevertheless, annealing at 240 °C inversely depressed the in-plane spatial order of perforated layers for a PS-b-PMMA/hPS2.8 film. The depression in the in-plane spatial order is ascribed to a dilution effect of added short chains. Compared to the middle regions, the thick beads went through several metastable phases, such as perpendicularly oriented perforated layers and double gyroids.

Strategy to simulate and fit 2D grazing-incidence small-angle X-ray scattering patterns of nanostructured thin films

Grazing-incidence small-angle X-ray scattering (GISAXS) is a widely used method for the characterization of the nanostructure of supported thin films and enables time-resolved in situ measurements. The 2D scattering patterns contain detailed information about the nanostructures within the film and at its surface. However, this information is distorted not only by the reflection of the X-ray beam at the substrate-film interface and its refraction at the film surface but also by scattering of the substrate, the sample holder and other types of parasitic background scattering. In this work, a new, efficient strategy to simulate and fit 2D GISAXS patterns that explicitly includes these effects is introduced and demonstrated for (i) a model case nanostructured thin film on a substrate and (ii) experimental data from a microphase-separated block copolymer thin film. To make the protocol efficient, characteristic linecuts through the 2D GISAXS patterns, where the different contributions dominate, are analysed. The contributions of the substrate and the parasitic background scattering - which ideally are measured separately - are determined first and are used in the analysis of the 2D GISAXS patterns of the nanostructured, supported film. The nanostructures at the film surface and within the film are added step by step to the real-space model of the simulation, and their structural parameters are determined by minimizing the difference between simulated and experimental scattering patterns in the selected linecuts. Although in the present work the strategy is adapted for and tested with BornAgain, it can be easily used with other types of simulation software. The strategy is also applicable to grazing-incidence small-angle neutron scattering.

Past, present and future-sample environments for materials research studies in scattering and spectroscopy; a UK perspective

Small angle x-ray scattering and x-ray absorption fine structure are two techniques that have been employed at synchrotron sources ever since their inception. Over the course of the development of the techniques, the introduction of sample environments for added value experiments has grown dramatically. This article reviews past successes, current developments and an exploration of future possibilities for these two x-ray techniques with an emphasis on the developments in the United Kingdom between 1980-2020.

A refraction correction for buried interfaces applied to in situ grazing-incidence X-ray diffraction studies on Pd electrodes

In situ characterization of electrochemical systems can provide deep insights into the structure of electrodes under applied potential. Grazing-incidence X-ray diffraction (GIXRD) is a particularly valuable tool owing to its ability to characterize the near-surface structure of electrodes through a layer of electrolyte, which is of paramount importance in surface-mediated processes such as catalysis and adsorption. Corrections for the refraction that occurs as an X-ray passes through an interface have been derived for a vacuum-material interface. In this work, a more general form of the refraction correction was developed which can be applied to buried interfaces, including liquid-solid interfaces. The correction is largest at incidence angles near the critical angle for the interface and decreases at angles larger and smaller than the critical angle. Effective optical constants are also introduced which can be used to calculate the critical angle for total external reflection at the interface. This correction is applied to GIXRD measurements of an aqueous electrolyte-Pd interface, demonstrating that the correction allows for the comparison of GIXRD measurements at multiple incidence angles. This work improves quantitative analysis of d-spacing values from GIXRD measurements of liquid-solid systems, facilitating the connection between electrochemical behavior and structure under in situ conditions.

Future trends in synchrotron science at NSLS-II

In this paper, we summarize briefly some of the future trends in synchrotron science as seen at the National Synchrotron Light Source II, a new, low emittance source recently commissioned at Brookhaven National Laboratory. We touch upon imaging techniques, the study of dynamics, the increasing use of multimodal approaches, the vital importance of data science, and other enabling technologies. Each are presently undergoing a time of rapid change, driving the field of synchrotron science forward at an ever increasing pace. It is truly an exciting time and one in which Roger Cowley, to whom this journal issue is dedicated, would surely be both invigorated by, and at the heart of.

GIWAXS-SIIRkit: scattering intensity, indexing and refraction calculation toolkit for grazing-incidence wide-angle X-ray scattering of organic materials

Grazing-incidence wide-angle X-ray scattering (GIWAXS) has become an increasingly popular technique for quantitative structural characterization and comparison of thin films. For this purpose, accurate intensity normalization and peak position determination are crucial. At present, few tools exist to estimate the uncertainties of these measurements. Here, a simulation package is introduced called GIWAXS-SIIRkit, where SIIR stands for scattering intensity, indexing and refraction. The package contains several tools that are freely available for download and can be executed in MATLAB. The package includes three functionalities: estimation of the relative scattering intensity and the corresponding uncertainty based on experimental setup and sample dimensions; extraction and indexing of peak positions to approximate the crystal structure of organic materials starting from calibrated GIWAXS patterns; and analysis of the effects of refraction on peak positions. Each tool is based on a graphical user interface and designed to have a short learning curve. A user guide is provided with detailed usage instruction, tips for adding functionality and customization, and exemplary files.

BornAgain: software for simulating and fitting grazing-incidence small-angle scattering

BornAgain is a free and open-source multi-platform software framework for simulating and fitting X-ray and neutron reflectometry, off-specular scattering, and grazing-incidence small-angle scattering (GISAS). This paper concentrates on GISAS. Support for reflectometry and off-specular scattering has been added more recently, is still under intense development and will be described in a later publication. BornAgain supports neutron polarization and magnetic scattering. Users can define sample and instrument models through Python scripting. A large subset of the functionality is also available through a graphical user interface. This paper describes the software in terms of the realized non-functional and functional requirements. The web site https://www.bornagainproject.org/ provides further documentation.

A corrective prescription for GISAXS

A new 'unwarping' algorithm presented by Liu and Yager in this issue constructs SAXS data consistent with experimental GISAXS data, eliminating many of the complications arising in GISAXS that are commonly modeled within the framework of the distorted-wave Born approximation. The method promises to open new pathways for processing, modeling and analyzing GISAXS data using techniques developed for SAXS.