Grazing-Incident Wide-Angle X-Ray Scattering (GIWAXS)
Grazing-Incident Wide-Angle X-Ray Scattering (GIWAXS) is an advanced analytical technique used to investigate the structure and properties of thin films and surfaces at the nanoscale. By directing a highly focused X-ray beam at a shallow angle onto the sample, GIWAXS captures scattering patterns that provide valuable information about the arrangement of atoms and molecules within the material. This method offers high-resolution insights into the crystalline structure, morphology, and orientation of thin films, making it a powerful tool in materials science, surface chemistry, and nanotechnology research.
GIWAXS is particularly useful for studying organic and inorganic thin films, polymers, nanocomposites, and self-assembled monolayers. Its ability to probe the surface and near-surface regions of materials while preserving their integrity makes it a preferred technique for understanding thin film growth mechanisms, molecular ordering, and interfacial interactions. As GIWAXS continues to evolve and be refined, it promises to advance our understanding of nanomaterials and contribute to the development of novel materials with tailored properties for various technological applications.
Photovoltaics
To explore the crystal orientation within perovskite films, conventional (ex-situ) Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) experiments were carried out, and the findings are depicted in Figure 1a–d. In the absence of additives, distinct Debye–Scherrer rings corresponding to the (111) plane are evident, indicating the presence of numerous randomly oriented crystals in the film. Upon introducing methylammonium thiocyanate (MASCN), the diffraction rings of the (111) plane gradually transform into well-defined Bragg spots with heightened intensity, suggesting an enhanced vertical crystal orientation with potential benefits for efficient charge transport and extraction. To quantitatively analyze the orientation distribution, an azimuth figure was plotted along the (111) ring (q = 9.5 to 10.5 nm−1) for perovskite films with varying amounts of MASCN, where the azimuth represents the angle of the projection of the diffraction vector in relation to the qxy axis. In instances where the quasi-2D perovskite exhibits a vertical orientation, it grows along the normal of the ( 202) plane, with the (111) plane displaying a preferred azimuth at 90° (Figure 1e). The normalized intensity-azimuth curves depicted in Figure 1f reveal that films with MASCN display low baselines between 10° and 80°, indicating a reduced content of randomly oriented crystals.
Reference:
D. Liang, C. Dong, L. Cai, Z. Su, J. Zang, C. Wang, X. Wang, Y. Zou, Y. Li, L. Chen, L. Zhang, Z. Hong, A. El-Shaer, Z. Wang, X. Gao, B. Sun. Unveiling Crystal Orientation in Quasi‐2D Perovskite Films by In Situ GIWAXS for High‐Performance Photovoltaics. Small 2021, 2100972.
https://onlinelibrary.wiley.com/ doi/epdf/10.1002/smll.202100972
Thermoelectric Application
In this study, the crystallinity of pristine P3HT and doped films, treated with a dopant solution for 30 minutes, was analyzed using Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) (Figure 2). Out-of-plane patterns for both pristine and doped S-P3HT films exhibited multiple-order lamellar stacking peaks, indicating the coexistence of edge-on and face-on orientations. In contrast, dominated edge-on orientations were observed in all L-P3HT films. Doping led to an increase in lamellar distance and a decrease in π−π stacking distance for all films, suggesting dopants preferentially intercalate into side chains. Fe(OTf)3 -doped P3HT showed the shortest π−π stacking distance and longest lamellar distance, indicating efficient intercalation. The trends in lamellar and π−π stacking distances correlated with doping levels, affecting charge transport. Despite the desired short π−π stacking distance, FeCl3 -doped P3HT exhibited higher mobility compared to Fe(OTf)3 -doped P3HT, suggesting discrete high -doped regions in the latter film. Analysis of the crystalline grain size, determined by full-width at half-maximum (FWHM), revealed that Fe(OTf)3 improved polymer packing and film crystallinity, while Fe(Tos)3 showed reduced crystalline size, indicating low doping efficiency.
Reference:
Lili Wu, Hui Li, Haoyu Chai, Qing Xu, Yanling Chen, and Lidong Chen. Anion-Dependent Molecular Doping and Charge Transport in Ferric Salt-Doped P3HT for Thermoelectric Application. ACS Appl. Electron. Mater. 2021, 3, 1252− 1259. https://pubs.acs.org/doi/abs/10.1021/acsaelm.0c01067
Polymer Solar Cells
This study focuses on utilizing thermal annealing to enhance the solid-state organization of thin films of a pure polymer deposited on glass substrates, with the aim of improving power conversion efficiency (PCE). Grazing Incidence Wide Angle X-ray scattering was employed to analyze the thin films (Figure 3). The observed peak at low angles, corresponding to the interplanar distance ruled by the alkyl chain length, exhibited significant modifications during thermal treatment. The intensity and area of the diffraction peak increased with temperature, reaching a plateau around 200°C. Gaussian deconvolutions were applied to quantify the peak variations, revealing a negligible change in interplanar distance beyond 140°C. The peak area showed a substantial 51.6% increase, reaching optimal crystalline organization after 10 minutes of thermal annealing at 200 °C. The study suggests the potential for improving the efficiency of devices based on this polymer and potentially others through controlled thermal treatment.
Reference:
Jose Jonathan Rubio Arias, Isabela Custódio Mota, Maria De Fátima Vieira Marques. Synthesis of thiophene-benzodithiophene wide bandgap polymer and GIWAXS evaluation of thermal annealing with potential for application in ternary polymer solar cells. Polym Adv Technol. 2020,1–11.
https ://onlinelibrary.wiley.com/doi/abs/10.1002/pat.5187
Bioscience
The study utilized Driselase and chloroform treatments on onion cell walls to investigate GIWAXS reflections. Driselase, an enzyme removing polysaccharides, preserved in-plane reflections but eliminated out-of-plane arcs (Fig. 4a). The absence of these arcs suggests complete cellulose crystal digestion, with an isotropic band indicating amorphous residues. In-plane features corresponding to crystalline epicuticular wax were observed, affirming the contribution of cuticular waxes to GIWAXS peaks (Fig. 4c). Scattering profiles were created by integrating 2D images azimuthally, capturing both out-of-plane (-17° to 17°) and in-plane (78° to 88°) directions (Fig. 4d). For primary cell wall samples, GIWAXS data revealed out-of-plane peaks at q = 1.15 Å−1 and q = 1.55 Å−1, slightly varying for moss leaves (q = 1.13 Å−1 and q = 1.57 Å−1). After treating with chloroform, in-plane features in GIWAXS vanish, while out-of-plane features remain (Figs. 4b and 4e). Fig. 4f shows no clear peaks in the in-plane scattering profile, but a faint shoulder near q = 1.5 Å−1. This suggests that chloroform treatment removes crystalline wax from the cell wall. The GIWAXS image (Fig. 4c) of the reconstituted wax exhibits similar in-plane features as the unextracted and Driselase-digested (Fig. 4a) onion epidermal cell walls. However, in Fig. 4f, the in-plane scattering profiles of the reconstituted wax show slight differences in peak locations and shapes compared to the native wax in unextracted and Driselase-digested epidermis, likely due to the re-crystallization process in an organic solvent and sensitivity to the local environment.
Reference:
Ye, D., Rongpipi, S., Kiemle, SN et al. Preferred crystallographic orientation of cellulose in plant primary cell walls. Nat Commun 11, 4720 (2020).
https://doi.org/10.1038/s41467-020- 18449-x