Fig. 3
From: Defect-enriched iron fluoride-oxide nanoporous thin films bifunctional catalyst for water splitting
Atomic-resolution structure analyses of IFONFs samples. a–e HRTEM images and corresponding FFT patterns of IFONFs with various Tfluorinated for a 15 min, b 30 min, and c–e 45 min. The IFONFs-45 heterostructures in c–e consist of numerous dislocations and distortions marked with “T”, and maintain the original two phases arrangement with nanodomain structure. f STEM images for IFONFs-45, revealing continuous lattice fringes (top right for (101) of FeF2 and bottom right for (400) of Fe2O3). Moiré patterns are observed in FeF2 and Fe2O3 nanograins, with slight rotation in the phase junction architecture48, which suggests a defect-rich heterogeneous structure. g STEM image and i, j the corresponding FFT patterns of iron fluoride-oxide nanodomains at selected regions. h, k The zoom-in image of yellow-boxed region in g depicts the detailed structure of stacking faults and vacancy-type defects, respectively. The O vacancies in Fe2O3 lattice in k are highlighted by darkcyan circles. l, m Crack and distortions in iron fluoride-oxide nanodomains. Apart from microstructural imperfections (yellow rectangle) and dislocations (yellow circles) in m, IFONFs-45 also has lattice imperfections (yellow “T”) along with few overlapped planes, illustrating the defective heterostructure consists of amorphous and crystalline planes. n Atomic structural models of FeF2–F2O3 hybrid, top and bottom parts are from side and top view, respectively. FeF2 (101) surface has fluorine or iron termination, and Fe2O3 (400) surface has oxygen or iron termination; Fe2O3 (400) surface with oxygen termination is more reactive than iron termination to iron termination of FeF2 (101) surface, and thus the FeF2–F2O3 heterostructure can be constructed. Accordingly, the O atoms in the Fe2O3 matrix could bond with Fe atoms in the FeF2 matrix, leaving the about four O atoms unsaturated per Fe2O3 unit cell, namely, the bonding number of O atoms in bulk Fe2O3 subtracts the bonding number of O atoms in Fe2O3 (400) and FeF2 (101) surfaces, because of the relatively less ratio of Fe atoms to other atoms in FeF2 than Fe2O3. Turquoise = F, purple = Fe, magenta = O. Scale bar, 1 nm in a–g and l–m, 0.3 nm in h, k
