Secondary ion MS (SIMS) provides trace analysis in solid samples, with detection levels in the parts per billion range. The technique can be utilized to provide imaging of a sample’s surface, or even a three-dimensional picture of the sample. The measurement process begins with an ion beam being directed at the surface. When the ions interact with the surface, atoms or molecules making up the sample are ejected from the surface. These secondary ions are then directed to the mass analyzer.

There are several different configurations of the technique. One of the simplest variations is in the ion gun, since many possibilities exist for the ionic species produced by the it. Common examples include cesium, gallium, argon and oxygen. Recently, cluster ion sources have become a popular alternative. Instead of producing individual ionized atoms, cluster sources emit higher mass polyatomic ions. Although the mass of the ion impacting the surface is larger, the energy per atom is much lower, producing a gentler impact. Where smaller ions generally break apart molecular bonds in the surface, making the technique more suited for elemental analysis, the larger clusters can liberate intact molecules for analysis, allowing SIMS to carry out molecular composition analysis. This has enabled new applications, particularly in life science.

Another choice of configuration is in the mass analyzer. Quadrupole, magnetic sector and TOF analyzers are all commercial possibilities. Magnetic sector instruments provide the best sensitivity and resolving power, while TOF instruments are efficient in measuring the complete mass spectrum in a simultaneous fashion. Regardless of the configuration, the ion beam can be rastered across the surface to build up an image of the surface, with compositional information at each point.

SIMS instruments can be operated in two analysis modes. In static SIMS, only the surface layer is examined. In dynamic SIMS, the ion gun is used to completely remove the uppermost layer of the sample, allowing depth profiling analysis. This provides a method for examining any differences in composition as one moves from the surface layer deeper into the sample.

Because SIMS directly probe the uppermost layers of a sample and can also perform depth profiling, the technique is commonly used to measure thin films and in chemical studies of corrosion and oxidation of surfaces. Semiconductor materials are another common sample type. The technique’s sensitivity allows the quantification of contaminants or doping elements that affect the electronic properties of the semiconductor material. Many other areas of materials science also make use of SIMS.

The leaders in the SIMS market, Cameca and Physical Electronics (Ulvac-PHI), are focused on related technologies for surface analysis. Other competitors include Henniker Scientific, Hiden Analytical, Kore Technology, Millbrook Scientific, SPECS and Tescan. In 2011, the market for SIMS was nearly $100 million.

SIMS at a Glance:

Leading Suppliers

• Cameca (AMETEK)

• Ulvac-PHI

• ION-TOF

Largest Markets

• Semiconductors

• Thin Films

• Academia

Instrument Cost

• $200,000–$2 million