AVS 71 Session CA-ThP: Chemical Analysis and Imaging at Interfaces Poster Session

Many Secondary Ion Mass Spectrometry ( SIMS) instumentscan perform at cryogenic temperatures, however, complex sample handling requirements and high cryogen consumption have meant that such experiments have hitherto been expensive and complicated. Utilising Ionoptika’s J Series III cluster SIMS instrument with Cryo stage, we show that long-term Cryogenic studies may be carried out on both soft and hard materials, with demonstrable improvements in results compared to RT analysis. We demonstrate 3D depth profiling of perovskite solar cells and show that the precision of the depth profile is increased at Cryo temperatures when compared with RT analysis. The current common approach to analyse such samples is to peel off the hardest capping layer and then analyse the perovskite layers using Ar GCIB to sputter and Bi to analyse. Alternatively, a Cs beam may be used to sputter to just above the interface, and then low energy an Ar GCIB and Bi beam used for sputtering and analysis. However these approaches are flawed; the peeling process can cause migration of elements to the free surface, and Cs and monoatomic Ar sputtering can cause intermixing of consecutive layers.The J Series III Cluster SIMS system employs GCIB as the primary ion beam which can sputter and analyse simultaneously, meaning no sputter-only cycles. For thin layers, this is crucial, asit precludes loss of information about the layers and/or interface. In addition, the GCIB used has a high (70 kV) beam energy and provides a range of cluster sizes from monoatomic to large cluster sizes such as 30k. We have previously demonstrated use ofsmaller cluster beams to sputter though 1.5 um thickness of perovskite solar cell samples from the capping layer to the glass substrate with less preferential sputtering and intermixing effects. Therefore, J Series III analysis using a small cluster GCIB promises to show more ‘genuine’ information than the current dual beam method for hard and mixed materials including metals and organics.In this work, pristine and aged samples of perovskite tandem solar cells are analysed with an Ar350 Cluster at 70 keV beam in the J Series III at RT and cryo temperatures to demonstrate the suitability, less intermixing effect and lack of preferential sputtering especially at cryo temperatures that show higher depth resolution and sputter rate with less damage.We conclude that analysis of hybrid semiconductor samples results in superior data when conducted with small clusters at Cryogenic temperatures.

Catalysts can be described by three important aspects activity, selectivity, and stability. Activity is the ability of a catalyst to convert reactants into products. Selectivity is the ratio of the desired product to the total amount of converted molecules. Stability is the ability of a catalyst to maintain activity with respect to time on stream (TOS, time since initial contact of reactant gas to the catalyst bed) in continuous reactors. MXene, a class of two-dimensional metal carbides, can be used as a support material to create a coke-resistant nanolayer catalyst with excellent activity, selectivity, and stability. MXene has empirical formula of M_n+1X_nT_x, where M is an early transition metal, X is a carbon or nitrogen, and T is a surface functional group (such as F^- or OH^-). In our prior studies,^[1,2] platinum (Pt) was loaded onto Mo₂TiC₂ MXene using incipient wetness impregnation to synthesize a 0.5% (wt.) Pt/Mo₂TiC₂ Pt nanolayer MXene catalyst. The Pt nanolayer catalyst exhibited excellent activity with turnover frequencies (TOFs, converted molecules per surface Pt atom) of 0.4~1.2 s^-1 for converting methane^[1] and ethane^[2]. 0.5% Pt/Mo₂TiC₂ displayed high selectivity, with over 98% to C₂ products for non-oxidative coupling of methane (NOCM) and over 95% selectivity for catalytic dehydrogenation of ethane to ethylene. Robust catalyst stability is obtained with no loss in catalytic activity for 72 hr. and 24 hr. for NOCM and ethane dehydrogenation, respectively, owing to its strong coke-resistance. However, the active site and surface activity are not easy to study. In this presentation, we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate MXene catalytic effects. ToF-SIMS is a highly sensitive surface analysis technique, capable of molecular, atomic, and isotopic analysis. Depth profiling and mass spectral mapping allow for analysis of subsequent monolayers of the catalyst’s surface. Measurements, including surface spectra, two-dimensional imaging, secondary electron imaging, and depth profiling (three-dimensional imaging), were used to probe the surface and reveal structures of both unloaded Mo₂TiC₂ MXene support and 0.5% Pt/Mo₂TiC₂ nanolayer MXene catalysts. The large dispersion of Pt⁺ ions throughout the bulk of Pt/Mo₂TiC₂ nanolayer MXene supports the hypothesis that the MXene channel prohibits access to the terrace site, a critical site for the structure-sensitive coking reaction.

[1] Li Z. et al., Nano Research, 17 (2024) 1251–1258.

[2] Li Z. et al., Nature Catalysis, 10 (2021) 882–891.

Modern near-ambient pressure X-ray photoelectron spectroscopy (NAP or AP-XPS) instruments now cover the pressure range typical of standard plasma applications, expanding the capabilities of XPS to plasma environments. We recently demonstrated that XPS spectra can be successfully collected in these conditions, extending the application of XPS to plasma interactions [1]. In previous work [2], we highlighted the influence of plasma chamber wall reactions on sample surface chemistry and showed that plasma-XPS can capture plasma chemistry in the gas phase.

In this study, we apply plasma-XPS to poorly conducting samples, where we observed anomalous XPS binding energy shifts due to sample charging during plasma exposure. We propose mechanisms that explain these shifts. Additionally, we noted plasma-induced binding energy shifts and peak splitting when measuring XPS from the plasma gas phase.

Plasma-induced charging and damage of wafers is a well-known challenge in semiconductor fabrication [3], and plasma-XPS offers significant potential for advancing diagnostics and mitigation strategies for these issues.

References

[1] J.T. Diulus, A.E. Naclerio, J.A. Boscoboinik, A.R. Head, E. Strelcov, P.R. Kidambi, A. Kolmakov, The Journal of Physical Chemistry C, 128 (2024) 7591-7600.

[2] J.T. Diulus, A.R. Head, J.A. Boscoboinik, A. Kolmakov, arXiv preprint arXiv:.19303, (2025).

[3] K.P. Cheung, Plasma charging damage, Springer-Verlag, London, 2000.

We use X-Ray Photoelectron Spectroscopy under bias to track surface population and electrical potentials on multilayered graphene electrodes with two ionic liquid mixtures, one containing the same cation (DEME+) and two different anions (TFSI- and BF4-) and the other one with two different cations (DEME+ and Rb+) and same anion (TFSI-). As bias increases, peak intensities change and binding energies shift, revealing both ion concentrations and also the local electrical potentials simultaneously. In addition the capacitance of the device increases significantly, providing crucial insights for developing new energy storage devices.

Advanced manufacturing of cermets, heat-resistant materials made of ceramic and sintered metal, is necessary for radio isotope production to decrease waste and increase efficiency. The High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory currently uses Al as the filler material for irradiation targets. While Al has offered the ease of use and high thermal conductivity, it is limited by the post processing procedures creating a high charge density of the Al cation, creating instable aluminum nitrates, and forming oxidation decreasing the overall performance of the irradiation target. Transitioning from Al to a graphite matrix could reduce the issues aluminum poses. Graphite has similar thermal stability, thermal conductivity, and chemical properties. The manufacturing process using carbon can reduce waste by lowering solution volumes and overall complexity. ²²³Ra is a radio isotope used for cancer treatments and is produced via a series of beta decays starting with ²²⁶Ra. To test method development, Ba, is used as a surrogate to radium. This work examines the barium encapsulation by graphite using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Specifically, high resolution spectroscopy and 2D/3D imaging modes were used to study the BaCO₃ pellets prepared in different manner.Current manufacturing process uses a mixture of graphite and barium carbonate either vacuum hot pressed or cold pressed and sintered. The mass spectrometry results verify that BaC as this is the preferred extraction radio isotope and not the oxide or carbonate. Also, depth profiling results show the BaCO₃, BaC₂, and BaO distributions across the surface and into the bulk of the pellet, indicative of the usefulness of different pellet processing steps.

Key words:

Barium, Radium, Graphite, Advanced Manufacturing, Nuclear Engineering, Radioisotopes, ToF-SIMS