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Time-of-Flight Secondary Ion Mass Spectrometry

ToF
ToF
ToF

Time-of-flight (ToF) secondary ion mass spectrometry (SIMS) is a powerful surface analysis tool available at the Environmental Molecular Sciences Laboratory (EMSL) to investigate scientific questions in biological, environmental, and energy research. Among the most sensitive of surface analysis tools, it uses a high-vacuum technique with parts-per-million- to parts-per-billion-level detection limits. The sample surface is bombarded with energetic (normally 10–30 keV) primary ions and the secondary ions generated by this process are separated and detected with a ToF analyzer. The mass spectra provide critical information about elemental, isotopic, and molecular components of the sample surface.

The EMSL ToF-SIMS instrument is equipped with an Argon cluster ion (Arn+) gun, a liquid metal ion gun with Bin+ sources, and a Cs+/O2+ sputter ion gun. The capabilities include surface spectroscopy with high sensitivity and mass resolution, surface imaging with high lateral resolution, depth profiling with high-depth resolution, and three-dimensional (3-D) imaging. The ability to provide cluster primary ions, such as Bin+, enables EMSL users to obtain substantial improvements in detection of molecular ions, especially in organic and biological samples. The Arn+ ion gun can provide ultimate high mass sensitivity, superior imaging, and a powerful organic sputter depth profiling capability. Low primary ion energy and low ion dose density settings allow surface analysis without significant surface alteration. The system is equipped with an antechamber and a glove box for sample transfer under a controlled environment.

Recently, EMSL staff developed a new, in situ liquid SIMS capability to provide unique elemental, isotopic, and molecular information at solid-liquid interfaces with a few-nm resolution depth. The in situ liquid SIMS can also be used to examine the molecular structure of various liquid samples and is more versatile than traditional electrospray ionization mass spectrometry analysis. This instrument significantly improves investigation in areas such as microbial forensics, organic analysis, energy storage, electrocatalysis, and biological imaging.

Research applications

  • ToF-SIMS supports research in the Biogeochemical Transformations Integrated Research Platform and the Terrestrial-Atmospheric Processes Integrated Research Platform by providing information in the following areas:
    • Biogeochemistry – ToF-SIMS can be used for two-dimensional (2-D) molecular mapping of the rhizosphere to elucidate root-mineral-organic matter-microbe interactions. Combining ToF-SIMS spectra analysis and principal component analysis can reveal active adsorption sites of various organic matters on mineral surfaces.
    • Environmental microbiology – ToF-SIMS can provide 3-D tracing of interesting elements and small functional organic molecules that affect pollutant cleanup or generate biofuels in microorganisms such as microbial colonies.
    • Atmospheric Sciences – Aerosol particles can be 3-D imaged with high spatial resolution using ToF-SIMs to elucidate their mixing states.
    • Materials sciences – ToF-SIMS offers molecular surface analysis with excellent sensitivity, elemental and isotopic depth profiling with parts-per-million sensitivity and 1- to 2-nm depth resolution, and 2-D and 3-D elemental and isotopic mapping.
    • Solid-liquid interfaces – In situ liquid SIMS can study biofilm attachment, solid-electrolyte interphase in Li-ion barrerites, electrocatalysis reactions, and more.
    • Weak interactions in various liquids – In situ liquid SIMS capability allows molecular investigation of ion solvation, ion pair formation, initial nucleation of nanoparticle formation, electrolyte degradation, and more.

Tips for success

  • We strongly recommend contacting your EMSL science point of contact before preparing samples for ToF-SIMs.
  • Though ToF-SIMS sample preparation is similar to scanning electron microscope sample preparation, its analysis is more sensitive to surface contamination, sample size, and sample degassing. We prefer to prepare ToF-SIMS samples separately or, at least, perform ToF-SIMS analysis first.

Related publications

Li, Y.; Zhou, Y.; Guo, W.; Zhang, X.; Huang, Y.; He, E.; Li, R.; Yan, B.; Wang, H.; Mei, F.*; Liu, M.*; Zhu, Z.* “Molecular Imaging Reveals Two Distinct Mixing States of PM2.5 Particles Sampled in a Typical Beijing Winter Pollution Case” Environ. Sci. Technol. 2023, 57, 6273−6283. DOI: 10.1021/acs.est.2c0869

Niedek, C. R.; Mei, F.; Zawadowicz, M. A.; Zhu, Z.; Schmid, B.; Zhang, Q.* “Quantitative chemical assay of nanogram-level particulate matter using aerosol mass spectrometry: characterization of particles collected from uncrewed atmospheric measurement platforms”, Atmos. Meas. Tech.; 2023, 16, 955–968. DOI: 10.5194/amt-16-955-2023.  

Bhattacharjee, A.; Qafoku, O.; Richardson, J. A.; Anderson, L. N.; Schwarz, K.; Bramer, L. M.; Lomas, G. X.; Orton, D. J.; Zhu, Z.; Engelhard, M. H.; Bowden, M. E.; Nelson, W. C,; Jumpponen, A.; Jansson, J. K.; Hofmockel, K. S.; Anderton, C. R.* “A Mineral-Doped Micromodel Platform Demonstrates Fungal Bridging of Carbon Hot Spots and Hyphal Transport of Mineral-Derived Nutrients”, mSystems  2022, 7(6), e0091322. (doi: 10.1128/msystems.00913-22)

Liu, W.; Huang, L.; Komorek, R.; Handakumbura, P. P.; Zhou, Y.; Hu, D.; Engelhard, M. H.; Jiang, H.; Yu, X.-Y.; Jansson, C. Zhu, Z.* “Correlative surface imaging reveals chemical signatures for bacterial hotspots on plant roots”, Analyst, 2020, 145, 393-401. (Journal Cover) https://doi.org/10.1039/C9AN01954E

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