Nanostructured oxides are coated with self-assembled monolayers of functional organic molecules for various applications, reaching from solar energy conversion to catalysis or medical applications. One example are recently developed "solar capsules", encapsulated dye sensitized solar cells based on titanium dioxide nanotubes.¹ A second example are zirconia nanotubes designed for local, triggered drug release from implant surfaces.² These hybrid materials consist of a porous, inorganic oxide matrix that is modified or filled with organic compounds. Even though these hybrid organic-inorganic nanostructures show good performance, we still lack control and understanding about the depth distribution of the organic molecules within the nanostructures. The analysis of the distribution of the organic compounds within the inorganic porous material is challenging, as a range of artefacts may occur during the sample preparation for analysis, or the analysis itself. To overcome these issues in depth-resolved characterization of hybrid organic-inorganic nanostructures, this study compares the possibilities given by the use of ToF-SIMS depth profiling and ToF-SIMS in combination with cross-section-polishing (CSP) and focused-ion-beam (FIB) cuts.

References

(1) P. Hartwich, S. Naidu Vakamulla Raghu, C. Pritzel, M.S. Killian, “Preparation and characterization of encapsulated dye sensitized solar cells”, submitted.

(2) S. Naidu Vakamulla Raghu, G. Onyenso, S. Mohajernia, M.S. Killian “Functionalization strategies to facilitate multi-depth, multi-molecule modifications of nanostructured oxides for triggered release applications”, Surf. Sci. 2022, 719, 122024, doi: 10.1016/j.susc.2022.122024.

Chemical imaging, e.g. by secondary ion mass spectrometry (SIMS), usually does not need dedicated sample preparation. However, for biological materials vacuum-stability must be achieved, while a close to native fixation is crucial to avoid redistribution or washout of water-soluble ions. Therefore, dedicated cryo approaches have been used in the past and undergo constant further development.

Here, we introduce a novel tool for high resolution imaging and chemical analysis of frozen-hydrated specimen using a cryo-FIB (focused ion beam) platform based on an ultra-high brightness Gas Field Ion Source (GFIS; primary ion species He⁺ and Ne⁺, < 35 keV landing energy range) [1]. Sub-nanometer spatially resolved secondary electron (SE) images with a high depth of field and topographic contrast are predominantly obtained with the finely focused He⁺ ion beam. Sub-surface or volume information at nanometre scale can be retrieved from thin (about 100 nm thickness) samples using the recently developed scanning transmission ion microscopy (STIM) detection system located below the sample [2]. Compositional information, e.g. for identification and subcellular localisation of individual metal nanoparticles embedded in biological matrices can be obtained with the Ne⁺ beam and using the incorporated compact magnetic sector SIMS system with a lateral resolution below 15 nm [3]. Its micro channel plate delay line based continuous focal plane detector features parallel mass detection for each scanned sample pixel over the selected mass range, offering hyperspectral SIMS imaging. Key for cryo-FIB investigations is the integration of a piezo-driven 5-axis cryo-stage along with cryo-capabilities for sample transfers. In combination with dedicated cryo-sample preparation equipment, e.g. a specialised low humidity nitrogen atmosphere glovebox, the cryo-FIB platform is an ideal tool for in-situ correlative studies.

Exemplary data will be presented not only for biological but also other beam sensitive materials like Si-Au core-shell structures and nanoparticles [4].

[1] O. De Castro et al., Anal. Chem. 2021, 93 (43), 14417–14424.

[2] E. Serralta et al., Beilstein J. Nanotechnology 11 (2020), p. 1854.

[3] J.-N. Audinot et al., Rep. Prog. Phys. 84 (2021) 105901

[4] This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 720964 and was supported by the Luxembourg National Research Fund via the projects INTER/DFG/19/13992454 and FNR CORE C21/BM/15754743.

The high demand for portable energy storage has boosted Li-ion battery research in recent years. Special focus has been given to the improvement of specific capacity, safety and the use of environmentally friendly components. There is a continuous effort to correlate electrode structure, morphology and chemical composition with behaviour, performance and failure mechanisms; however, many fundamental aspects have not yet been fully described [1,2]. Among the analytical techniques, Secondary Ion Mass Spectrometry (SIMS) is particularly suitable for analysing the electrodes due to the excellent sensitivity and capability to detect all elements and their isotopes. Its surface-sensitivity makes it appropriate for investigating electrodes and their interfaces (e.g. Solid Electrolyte Interphase)[3].
In recent years, a FIB-SEM-SIMS system has been developed to combine the advantages of high-resolution imaging by SEM and analytics of a magnetic sector SIMS in a single instrument [4]. With a SIMS spatial resolution down to 15 nm, this microscope is a powerful tool for correlative microscopy. The great added value of this platform includes the Ga+ FIB in-situ sample preparation avoiding sample transfer to another system and thus minimising the risk of contamination of air-sensitive electrode components.
In this work we survey graphite electrodes before and after cycling, developing analytical protocols to study surface and internal structure. A combination of in-situ sample preparation with depth profiling and SIMS imaging was developed to probe both interfaces of the electrode and provide in 3D the elemental and isotopic distribution on surface and in volume. Our results demonstrate the capability of a single instrument to investigate the morphology and composition of battery components with nanoscale spatial resolution and high sensitivity, addressing environmental contamination issues of electrode components.
This work was co-funded by the Luxembourg National Research Fund (FNR) through the grant INTER/ANR/21/NANOLIT.
References:
[1] Gauthier, M., Carney, T. J., Grimaud, A., Giordano, L., Pour, N., Chang, H. H., ... & Shao-Horn, Y. (2015). The journal of physical chemistry letters, 6(22), 4653-4672.
[2] Asenbauer, J., Eisenmann, T., Kuenzel, M., Kazzazi, A., Chen, Z., & Bresser, D. (2020). Sustainable Energy & Fuels, 4(11), 5387-5416.
[3] Waldmann, T., Iturrondobeitia, A., Kasper, M., Ghanbari, N., Aguesse, F., Bekaert, E., ... & Wohlfahrt-Mehrens, M. (2016). Journal of The Electrochemical Society, 163(10), A2149.
[4] O. De Castro, J.-N. Audinot, H. Q. Hoang, C. Coulbary, O. Bouton, R. Barrahma, A. Ost, C. Stoffels, C. Jiao, M. Dutka, M. Geryk, T. Wirtz, Analytical Chemistry, 94(30), 10754-10763 (2022).