SIMS-23 2022 Session BS-TuP: Beyond SIMS Poster Session

Development of low temperature operating catalysts has been one of the challenges in exhaust gas catalysis since the most commonly used Pt-group catalysts are generally active above 150 ^oC causing ‘cold-start emission’. Fe-oxide nanoparticle catalysts have been studied extensively due to their high low-temperature activity and thermal stability, and many experimental/theoretical studies have been conducted to unveil the relationship between the structure and activity of the Fe-oxide nanocatalysts. In the present work, ToF-SIMS technique, which has not been used widely on iron oxide nanocatalysts, was utilized to elucidate the structure-activity relations on Fe-oxide/Al₂O₃ for the low temperature (~50 ^oC) CO oxidation. The combined results of various surface analyzing tools including ToF-SIMS showed a scaling relationship of ternary interfacial sites of Fe-C-Al with the CO oxidation activity below 50 ^oC, indicating that the Fe-C-Al species facilitate low temperature CO oxidation. This work shows that ToF-SIMS can provide valuable information on the structure-activity relations in heterogenous catalysts.

Metal-oxide (MO) surfaces have successfully been modified to elicit surface functionality different than the parent material via facile application of self-assembled monolayers (SAM). Previously reported MO surfaces demonstrate superhydrophobicitywhen functionalized with phosphonic acid carbohydrate molecules.^[1] In this work, we shed light on the role of SAM facilitated hydrophobic-effect as a result of application technique, i.e., immersion in bulk solution (BI) and micro-contact printing (μCP).These modifiedZrNTs were evaluated along their tube length in the depth-profiling mode using time-of-flight secondary ions mass spectrometry (ToF-SIMS). Using the depth profile mode, we were successfully able to ascertain the presence of targeted molecules at various depths inside the nanotubes. These results were used to provide in proof the possibility to develop multi-depth and multi-functional modifications within nanotubes as shown in Fig. 1a. Herein, the nanotube walls could effectively be functionalized at different depths via wet-chemistry and soft-lithography techniques devoid of clean-room fabrication.^[2]In combination, with the developed synthesis and characterization strategies of ZrNT, we are able to demonstrate an enhanced functionality in addition to tailor-made storage capabilities of such nanotubular surfaces. The nanotube reservoirs were evaluated for volumetric storage via simulated dye-release behaviour as seen in Fig. 1b. Such nanotubular reservoirs developed on the implant surface would be capable of facilitating developmental strategies towards controlled multi-drug release models that can even elicit sequential release of drugs to limit clotting, inhibit infection and ultimately promote healing.

REFERENCES

[1]S.N. Vakamulla Raghu, M.S. Killian, Wetting behavior of zirconia nanotubes, RSC Adv. 11 (2021) 29585–29589. https://doi.org/10.1039/D1RA04751E.

[2]S.N.V. 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. 719 (2022) 122024. https://doi.org/10.1016/j.susc.2022.122024.

Process of surface modification of steel (s235 and ss304), molybdenum and tungsten samples was carried out with the two techniques - by a high-energy electron beam line scanning in vacuum in a device used for electron beam welding, and by a technique of electric discharge machining (EDM) in which samples are submerged in dielectric fluid.

In the case of electron beam technique we use a beam of 18 keV energy and approx. 500 µm diameter, which is linearly scanned over the surface of the samples at a speed of 0.5 m/s. The used beam currents of 0.5, 1, 2, 5 and 10 mA correspond to the transmitted energy ranging from 10 to 200 J per 10 mm long line scan lasting 0.02 s.

In case of EDM [1] we use electrical energy to generate the spark between the tool made of copper and a workpiece so that material removal is taking place from the sample surface by local melting or vaporization. EDM pulse generator is set for discharge voltage from 80 V to 30 V with calculated charging time = 4.7∗10e-5 s and discharge time = 9.8∗10e-9 s. We use processing time from 100 to 2200 s to erode 10 mm long and 1 mm wide grooves. Deposited energy for such grooves ranges from 10 to 220 J.

For mapping of the modified samples we use two quadrupole-type mass analyser systems: SIMS and glow discharge mass spectrometry (GDMS). Using the two techniques of imaging one can acquire a quantifiable image of the elemental distribution from a sample’s surface.

SIMS maps are registered due to scanning of a 100 nA, 5 keV O₂⁺ beam over area of 3x3 mm, in the Hiden SIMS Workstation apparatus [2], while GDMS maps are obtained with SMWJ-01 system [3], in which the glow discharge of 0.8 mA current at a voltage of 1.2 kV DC is used. GDMS measurements are carried out by moving the sample line by line in the range of 7x7 mm above the stationary cell of the glow discharge.

This work is supported by the National Center for Research and Development, Poland and Ministry of Science and Technology, Taiwan (Task ID: PL-TW/VII/4/2020).

[1] Sheu, D. Y. (2004) Journal of Micromechanics and Microengineering, 15(1), 185.
[2] Hiden Analytical, 420 Europa Boulevard, Gemini Business Park, Warrington, WA5 7UN, UK
[3] Konarski, P., Miśnik, M., & Zawada, A. (2016) Journal of Analytical Atomic Spectrometry, 31(11), 2192-2197.

Transition metal dichalcogenides are promising candidates for alternative matrix-assisted laser desorption and ionization (MALDI) matrices owing to their excellent physicochemical properties.[1,2] Characteristics of tungsten disulfide (WS₂) such as strong UV absorbance, direct bandgap, low thermal conductivity and high electron mobility are conducive to serve as an effective inorganic matrix; however, its application in mass spectrometry (MS) is rarely reported.[3,4] Here, we present a sensitive time-of-flight (TOF) MS platform by utilizing WS₂ nanosheet-assisted laser desorption ionization (LDI) for quantitative analysis of immunosuppressive drugs in the blood of organ transplant patients. By adopting a micro-liquid dispensing inkjet microarray system, high-throughput analysis of the patient samples with enhanced sensitivity and reproducibility was achieved. To evaluate the performance of our LDI-MS platform, up to 80 cases of patient samples were analyzed and the results were compared with those of liquid chromatography tandem mass spectrometry (LC-MS/MS). The results obtained by inkjet-printed WS₂-assisted LDI-MS were in good agreement with those of LC-MS/MS while being rapid and cost-effective. Our advanced material and method will facilitate therapeutic monitoring of blood samples from a large number of patients for accurate immunosuppressive drug prescriptions.

[1] Kim, Y. K.; Wang, L. S.; Landis, R.; Kim, C. S.; Vachet, R. W.; Rotello, V. M. Nanoscale2017, 9 (30), 10854–10860.

[2] Zhao, Y.; Deng, G.; Liu, X.; Sun, L.; Li, H.; Cheng, Q.; Xi, K.; Xu, D. Anal. Chim. Acta2016, 937, 87–95.

[3] Choi, W.; Choudhary, N.; Han, G. H.; Park, J.; Akinwande, D.; Lee, Y. H. Mater. Today2017, 20 (3), 116–130.

[4] Joh, S.; Na, H. K.; Son, J. G.; Lee, A. Y.; Ahn, C. H.; Ji, D. J.; Wi, J. S.; Jeong, M. S.; Lee, S. G.; Lee, T. G. ACS Nano2021, 15 (6), 10141–10152.

Keywords: Tungsten Disulfide, Laser desorption ionization, Therapeutic drug monitoring, Nanosheets

As the United States strives to develop a hydrogen-based energy infrastructure, there is a heavy industrial focus on the optimization and scale up of reliable hydrogen production. A promising system for large-scale hydrogen production is the proton exchange membrane water electrolyzer (PEMWE). Unfortunatly, there are still major advances that need to be made with both cost efficiency and durability before PEMWE’s can be used on a commercial scale. In PEMWE’s, the porous transport layer (PTL) contributes to a large percentage of overall cell cost. Due to the harsh operating conditions of the anode, protective coatings are applied to the PTLs, but the use of noble metals leads to cost concerns. Additionally, the degradation of coated PTLs at various operating conditions is not well understood. As the hydrogen production industry continues to try to improve the PTL, and ensure reliable operation of the device over long-term, advanced physicochemical characterization at various stages of fabrication and testing is vital to improve durability and meet cost targets.

Currently, the state-of-the-art characterization technique to analyze PTL’s and their respective protective coatings is Focused Ion Beam Scanning Electron Microscope, Scanning Transition Electron MicroscopeEnergy Dispersive X-ray Spectroscopy(FIB-SEM STEM-EDS). This technique is labor and time intensive and only targets a small area of the PTL, thus is an impractical technique to rely on for industrial testing. This talk will introduce ToF SIMS as a promising technique for the characterization of PTLs with focus on protective coatings and interface between coating and PTL. This presentation will highlight the benefits of this technique in comparison to current techniques, as well as discuss challenges with optimization of ToF SIMS for these morphologically challenging samples.