Combined EDS mapping and ADF-STEM tomography for interface characterisation in glass composites

Session

Poster Session Two

Authors

Miss Jessica Snelson (2, 3), Ashleigh Chester (1), Dr Thomas Bennett (1), Dr Sean Collins (2, 3)

Affiliations

1. Department of Materials Science and Metallurgy, University of Cambridge
2. School of Chemical and Process Engineering, University of Leeds
3. School of Chemistry, University of Leeds

Keywords

EDS, ADF, STEM, tomography, interface characterisation, MOF glass, composites, structure, beam sensitive, 3D, 2D, imaging

Abstract text

Metal organic frameworks (MOFs) are a highly diverse class of material with applications from chemical separations and gas storage to membranes and coatings in batteries or optoelectronics devices. The range of applications derives from the tunability achieved through control of atomic structure as well as chemical functionalisation through coordination chemistry of metals and organic linker molecules. Liquid and glassy MOFs have appeared more recently, creating opportunities to blend these MOFs with secondary phases or to encapsulate other particles when melted, with the resulting composites retaining the MOF coordination network structure and modulating the composite chemical and physical properties (1,2). MOF glass blends incorporating an inorganic glass as the second component suggests the resulting multi-component glasses are more scratch resistant and mechanically stronger (3,4). To confirm the presence of these blended particles, X-ray energy dispersive spectroscopy (EDS) can be utilised to acquire information on elemental distribution within the particles and annual dark field (ADF) tilt-series can be taken to obtain 3D tomographic reconstructions. Issues arise when collecting electron microscope data for these blends, as the glassy ZIF-62 MOF and especially the inorganic glass composite (30Na2O-70P2O5) are both beam sensitive. These inorganic glasses are particularly known to undergo significant mass loss under electron beam exposures required for EDS mapping. Here, to circumvent this challenge, we combine EDS mapping with chemically sensitive annular dark field (ADF) STEM tomography for combined 2D+3D analysis of the interface structures in MOF/inorganic glass blends. 

With reduced electron exposures in ADF-STEM, we first acquired tilt-series with 2o tilt increments across approximately ±70o. EDS maps were subsequently acquired to corroborate the ADF-STEM contrast. We used compressed sensing electron tomography to achieve high fidelity reconstructions with improved contrast recovered in 3D imaging relative to weighted back-projection and simultaneous iterative reconstruction technique approaches (5,6). An edge spread function was applied to the reconstructed 3D volumes (7,8), which identified the intensity thresholds between the two glasses as well as the background. The thresholds were adjusted and applied to the 3D volumes, and once separated, revealed a core/shell inorganic glass/MOF structure. These separate volumes were then compared to the single 2D EDS maps to confirm the accuracy of the reconstruction and separation. Together, these findings identify extended interface formation between the MOF and inorganic glass components with single particles. This tandem ADF-STEM tomography and EDS mapping approach outlines a route for wider application of 3D chemically sensitive imaging for beam-sensitive materials, particularly where interfaces are obscured in 2D projection images. 

References

1. Orellana-Tavra, C., et al. Chem Commun. 2015, 73, 13878-13881.
2. Gaillac, R., et.al. Nat. Mater. 2017, 16, 1149, 1154.
3. Tuffnell, J.M., et al. Chem. Commun. 2019, 55, 8705-8715.
4. Hou, J., et al. Nat. Commun. 2019, 10, 2580.
5. Li, L., et al. BMC Bioinformatics. 2020, 21, 202.
6. Leary, R., et al. Ultramicroscopy. 2013, 131, 70-91.
7. Zanaga, D., et al. Part. Part. Syst. Charact. 2016, 33, 396-403.
8. Collins, S.M., MacArthur, K.E., et al. APL Mater. 2019, 7, 091111.

References

1. Orellana-Tavra, C., et al. Chem Commun. 2015, 73, 13878-13881.
2. Gaillac, R., et.al. Nat. Mater. 2017, 16, 1149, 1154.
3. Tuffnell, J.M., et al. Chem. Commun. 2019, 55, 8705-8715.
4. Hou, J., et al. Nat. Commun. 2019, 10, 2580.
5. Li, L., et al. BMC Bioinformatics. 2020, 21, 202.
6. Leary, R., et al. Ultramicroscopy. 2013, 131, 70-91.
7. Zanaga, D., et al. Part. Part. Syst. Charact. 2016, 33, 396-403.
8. Collins, S.M., MacArthur, K.E., et al. APL Mater. 2019, 7, 091111.