Secondary ion

Secondary-ion mass spectrometry

Old magnetic sector SIMS, model IMS 3f, succeeded by the models 4f, 5f, 6f, 7f and most recently, 7f-Auto, launched in 2013 by the manufacturer CAMECA.

Secondary-ion mass spectrometry (SIMS) is a technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. The mass/charge ratios of these secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface to a depth of 1 to 2 nm. Due to the large variation in ionization probabilities among different materials, SIMS is generally considered to be a qualitative technique, although quantitation is possible with the use of standards. SIMS is the most sensitive surface analysis technique, with elemental detection limits ranging from parts per million to parts per billion.

In 1910 British physicist J. J. Thomson observed a release of positive ions and neutral atoms from a solid surface induced by ion bombardment. Improved vacuum pump technology in the 1940s enabled the first prototype experiments on SIMS by Herzog and Viehböck in 1949, at the University of Vienna, Austria. In the mid-1950s Honig constructed a SIMS instrument at RCA Laboratories in Princeton, New Jersey. Then in the early 1960s two SIMS instruments were developed independently. One was an American project, led by Liebel and Herzog, which was sponsored by NASA at GCA Corp, Massachusetts, for analyzing moon rocks, the other at the University of Paris-Sud in Orsay by R. Castaing for the PhD thesis of G. Slodzian. These first instruments were based on a magnetic double focusing sector field mass spectrometer and used argon for the primary beam ions. In the 1970s, K. Wittmaack and C. Magee developed SIMS instruments equipped with quadrupole mass analyzers. Around the same time, A. Benninghoven introduced the method of static SIMS, where the primary ion current density is so small that only a negligible fraction (typically 1%) of the first surface layer is necessary for surface analysis. The Castaing and Slodzian design was developed in the 1960s by the French company CAMECA S.A.S and used in materials science and surface science. Instruments of this type use pulsed primary ion sources and time-of-flight mass spectrometers and were developed by Benninghoven, Niehuis and Steffens at the University of Münster, Germany and also by Charles Evans & Associates. Recent developments are focusing on novel primary ion species like C₆₀⁺, ionized clusters of gold and bismuth, or large gas cluster ion beams (e.g., Ar₇₀₀⁺). The sensitive high resolution ion microprobe (SHRIMP) is a large-diameter, double-focusing SIMS sector instrument based on the Liebl and Herzog design, and produced by Australian Scientific Instruments in Canberra, Australia.