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ToF-SIMS (time-of-flight secondary ion mass spectrometry) is a surface-analysis technique: a pulsed primary ion beam strikes a solid, the secondary ions it releases are separated by their flight time to the detector, and the result is a mass spectrum or a chemical image of the outermost 1-2 nm of the sample. In search queries “sims tof”, “tof sims” and “tof-sims” all mean this method. It is not the “SIMS” of games or school information systems, and it is not MALDI-TOF, which ionises a sample with a laser and matrix.
Short answer
ToF-SIMS identifies elements and molecular fragments on the top 1-2 monolayers of a solid, maps where they sit across the surface, and can be run in a destructive mode that profiles composition with depth. Facility descriptions and vendor notes agree that it is mainly a qualitative technique; quantification needs standards or known reference conditions. Sources below quote different resolution and detection-limit figures, so this page attributes each number to the document that states it.
Definition and scope
Secondary ion mass spectrometry (SIMS) probes a solid surface with a primary ion beam. In the time-of-flight version, secondary ions leave the surface and travel through a field-free analyzer at velocities that depend on their mass-to-charge ratio; heavier ions arrive later. Because every primary-ion pulse yields a complete mass spectrum from arrival times, the instrument can record a spectrum at every pixel as the beam is rastered (Physical Electronics technical bulletin, “Time-of-Flight Secondary Ion Mass Spectrometry”, 2012; read 2026-11-08).
The NC State Analytical Instrumentation Facility describes a pulsed Bi+ beam that gives organic and inorganic information from a solid surface or vacuum-compatible material, with output as a mass spectrum and mass spectral images (facility description of ToF-SIMS; read 2026-11-08).
How ToF-SIMS is used in practice
Desorption and the static limit
Desorption of surface species happens by a “collision cascade” triggered by the primary ion. The PHI bulletin describes a pulsed primary source with pulses shorter than 1 ns. In “static” conditions the primary ion dose stays below 1012 ions/cm2; below that limit roughly fewer than 1 in 1,000 surface atoms or molecules is struck, so the analysis reflects an essentially undisturbed surface.
Three analysis modes
| Mode | What it returns | Figures stated by the source | Source |
|---|---|---|---|
| Spectroscopy | High mass resolution spectrum of the surface; “static SIMS” | Mass resolution 8000 (m/Δm); separates Si+ (m/z 27.9764) from C2H4+ (m/z 28.0308) | NC State AIF |
| Imaging | Chemical image; a mass spectrum at each pixel (256 × 256 in the PHI description) | Spatial resolution 300 nm at the NC State facility; below 120 nm quoted for the PHI instrument, set by primary beam diameter | NC State AIF; PHI |
| Depth profiling | Composition versus depth; destructive, because a sputter ion gun removes material | Depth resolution of a few nm (NC State); PHI describes shallow depth profiling with all species monitored simultaneously | NC State AIF; PHI |
Spectroscopy and imaging analyse only the outermost 1-2 monolayers (PHI), which NC State states as an information depth of the top 1-2 nm. Depth profiling is the mode that consumes the sample.
Where it matters for labs and facilities
What the sources say about sample suitability
The PHI bulletin lists solids, including conductors, semiconductors and insulators, with a typical sample under 2 cm in diameter and under 10 mm thick, and a typical analysis area under 600 × 600 µm. NC State describes the method as applicable to vacuum-compatible materials such as metals, semiconductors, polymers, paints, coatings, glass, paper, ceramics and pharmaceuticals. Listed applications include surface contamination, delamination, surface modification, trace impurities, thin-film depth profiling and adhesion failure analysis.
Checklist before approaching a facility
Built only from the sample limits above, ask or confirm:
- Is the sample a solid and vacuum-compatible?
- Does it fit the stated typical size (under 2 cm across, under 10 mm thick) for that instrument?
- Do you need the outer 1-2 nm only (spectroscopy or imaging) or composition with depth (destructive)?
- Do you need to map lateral distribution, and at what resolution does that facility’s instrument operate? Resolutions differ by instrument.
- Do you need numbers or identification? Intensities are not directly concentrations (see below).
Standards and interlaboratory evidence
Two ISO documents exist for the method: ISO 23830:2008, “Surface chemical analysis – Secondary-ion mass spectrometry – Repeatability and constancy of the relative-intensity scale in static SIMS”, and ISO 13084:2018, “Surface chemical analysis – Calibration of the mass scale for a time-of-flight secondary ion mass spectrometer”. An interlaboratory study of 19 ToF-SIMS instruments in 12 countries (Green, Gilmore, Lee, Spencer and Seah, Surface and Interface Analysis 42(3):129-138, 2010; abstract read 2026-11-08) used reference materials (PTFE, thin polycarbonate on silicon, patterned Irganox 1010) and reported intensity constancy of about 5% and relative quantification precision of about 5% for 16 instruments. Four laboratories improved mass accuracy by factors of roughly 1.8, 2.2, 2.3 and 8.6 using the mass calibration procedure then in draft; the authors noted the need for more robust reference materials.
Related techniques
ToF-SIMS differs from laser-based time-of-flight methods in what it ionises and how deep it looks. For the laser-and-matrix technique see MALDI-TOF; for imaging across tissue see the mass spectrometry imaging workflow and spatial proteomics methods. General background is in what is a mass spectrometer, and the terms used in the table are explained in resolving power and mass accuracy and mass calibration.
Common misunderstandings
- “It is the same as MALDI-TOF.” Both use a time-of-flight analyser, but ToF-SIMS uses a primary ion beam on a solid surface and reports from the top 1-2 nm.
- “Imaging is non-destructive and so is everything else.” Static spectroscopy and imaging stay under 1012 ions/cm2; depth profiling is destructive.
- “Peak height equals amount.” Secondary ion yields vary by orders of magnitude, and NC State states the analysis is usually qualitative rather than quantitative; with known implants it describes quantification below 5% atomic concentration.
- “Detection limits are a single number.” PHI quotes ppm to ppb for its instrument; NC State quotes about 0.1%-0.01% atomic concentration. Both are attributed statements about different instruments and species.
FAQ
What does ToF-SIMS stand for?
Time-of-flight secondary ion mass spectrometry. “Sims tof” and “tof sims” are reversed word orders of the same name.
What is the difference between SIMS and ToF-SIMS?
SIMS is the family of techniques that analyse secondary ions sputtered from a surface by a primary beam. ToF-SIMS is the version that measures ion flight time, giving a full mass spectrum per primary-ion pulse.
How deep does ToF-SIMS analyse?
Spectroscopy and imaging probe the outermost 1-2 monolayers (about 1-2 nm per NC State). Depth profiling goes deeper by sputtering, with depth resolution of a few nm at that facility.
Is ToF-SIMS quantitative?
Mostly qualitative. Quantification is possible in specific cases with known reference conditions, and standards such as ISO 23830 and ISO 13084 address intensity repeatability and mass-scale calibration.
Sources
- Physical Electronics, Technical Bulletin, “Time-of-Flight Secondary Ion Mass Spectrometry” (2012), phi.com. Read 2026-11-08.
- NC State Analytical Instrumentation Facility, “ToF SIMS” general description, aif.ncsu.edu. Read 2026-11-08.
- Green F.M., Gilmore I.S., Lee J.L.S., Spencer S.J., Seah M.P., Surf. Interface Anal. 42(3):129-138 (2010), National Physical Laboratory record eprintspublications.npl.co.uk/4612. Read 2026-11-08.
- ISO 23830:2008 and ISO 13084:2018, titles as published by ISO.
