TOF-SIMS

tof-sims

The Facility houses the technique of time-of-flight secondary-ion mass spectrometry, with the ION-TOF TOF-SIMS IV system (upgraded with a bismuth source). Support was derived from the NSF (DMR-9724307). TOF-SIMS is a surface sensitive technique used to probe a material’s long-range chemical structure through the mass spectral analysis of desorbed molecules and molecular fragment ions. An incident primary ion produces molecular fragments from the sample surface; positive or negative secondary ions are collected from these fragments and their mass is determined by flight time to a detector.

Several operational modes are now available in the facility:

  • static SIMS mode – very low incident ion doses are used to probe the molecular structure and long-range chemistry of surfaces; the low ion dose ensures that intrinsic surface chemistry, and not ion-induced chemistry, is being probed; static SIMS is highly complementary to XPS for monolayer and polymer surface analysis of organic materials, providing long-range chemical information.
  • dynamic SIMS mode – high incident ion doses are used to sputter off surface layers and probe elemental composition as a function of depth into a sample; most molecular information is scrambled; quantitation and sensitivity can be as high as parts per billion in some cases; dynamic SIMS is useful for layered samples, inorganic materials and impurity analysis.
  • imaging SIMS mode – a focused ion beam can be rastered over a surface to collect static SIMS spectra as a function of lateral position; resolution better than 100 nm can be achieved with very high mass resolution (m/Dm > 10,000). An example of such an image of a patterned surface is shown below, in which the protein fibronectin is present in the squares (CN- ion image), and a polyethylene oxide brush polymer is present between the squares (O- and CH3O+ ion images).
  • SEM mode – a focused ion beam (sub-50 nm) can be rastered over a surface while secondary electrons are collected, as in a conventional SEM.  This mode can be used to locate features of interest.

 

O- CN- Image184
154 × 154 µm2 154 × 154 µm2 154 × 154 µm2

O ion image

CN ion image

CH3O+ ion image