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University of Washington Engineered Biomaterials
Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is a surface analysis technique which analyzes mass fragments of the top 10-20 Å of a solid surface. An ion beam is used to bombard a sample in order to remove small numbers of atoms from the surface. When the primary ions strike the surface, atoms and molecular fragments and ions (called secondary ions) are produced. These are ejected, and the ejected ions alone are extracted into a time-of-flight mass spectrometer, where they are separated depending on their velocities (smaller ions move more rapidly than larger ions). The velocity of the ions is also proportional to their mass/charge ratio, m/z. The structure and composition of these fragments are directly related to the molecular structure of the surface they were emitted from.
Usually only ions with mass/charge ratios below 2,000 Daltons are observed. However, with careful sample preparation, m/z ratios of up to 10,000 Daltons can be observed. The TOF analyzer is one of the more sensitive analyzers, with detection limits in the parts per billion range. This high sensitivity makes it a very valuable tool for surface sensitive applications, such as self-assembled monolayers andsurfaces treated by plasma deposition. TOF-SIMS can also be used as an imaging tool, to chemically map out the outermost surface layer of a sample.
For more information about TOF-SIMS: