Cluster ion mass spectrometry

Article By:

Winograd, Nicholas Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania.

Last reviewed:2010

DOI:https://doi.org/10.1036/1097-8542.YB100243

The chemical analysis of multicomponent molecular solids poses a particularly challenging problem in materials science, biology, and nanotechnology. Recent developments in cluster ion mass spectrometry research are opening new directions for this field. With this tool, an energetic primary ion beam is created using various types of molecular ions to create a projectile consisting of many different atomic components. Next, this beam is accelerated to 10–20 keV of kinetic energy, tightly focused to a submicrometer probe size and directed to the surface of the sample. As this energetic cluster projectile interacts with the target, positive and negative secondary ions are emitted from near the impact point as a result of a complex series of energy transfer events. These secondary ions are extracted into a mass spectrometer to reveal the chemical composition of the desorbed species. Determination of this mass distribution is referred to as secondary ion mass spectrometry or SIMS. The chemical nature of these ions is strongly dependent on the type and energy of the projectile. For purely atomic ion projectiles, the secondary ion intensity is low, and the chemical composition is often different from that on the surface itself, limiting the analytical utility. As the number of atoms in the cluster projectile is increased, however, the number of secondary ions and the amount of reliable chemical information associated with the mass spectrometry increases greatly. With a microfocused cluster ion beam probe, imaging of the two- and three-dimensional (2D and 3D) chemical composition is possible for a wide variety of materials, ranging from inorganic and organic multilayer structures to biomaterials, sensors, and single biological cells.

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