Chapter 1: Focused ion beam (FIB): site-specific sample preparation, nano-analysis, nano-characterization and nano-machining
Richard Wirth
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Focused gallium ion beam devices were developed simultaneously at the University of Chicago and at the Oregon Graduate Institute in the mid-1970s. Micron-sized structures were milled from integrated circuits applying a high-current-density focused ion beam from a liquid metal ion source (LMIS) (Puretz et al., 1984). Previously, focused ion beam (FIB) was used preferentially in the semiconductor industry. Typical applications are quality control, wafer repair and microelectronic failure analysis. In the late 1980s and the early 1990s transmission electron microscope (TEM) foil preparation with FIB was introduced. The great success of that technique was the unique ability of FIB to prepare site-specific TEM foils (Kirk et al., 1989; Young et al., 1990; Basile et al., 1992; Overwijk et al., 1993). The publications listed describe the procedure: how to remove the foil from the excavation site, the ex situ lift-out technique, which later was improved by Giannuzzi et al. (1997). A summary of the FIB technique was presented by Orloff et al. (2003), and by Giannuzzi and Stevie (2005).
Application of FIB in the geosciences began in the early 2000s (Wirth, 2000, 2001; Dobrzhinetskaya et al., 2001; Dobrzhinetskaya & Green, 2001; Heaney et al., 2001; Dobrzhinetskaya et al., 2002; Wirth, 2002; Lee et al., 2003; Dobrzhinetskaya et al., 2003; Wirth, 2003; Graham et al., 2004; Wirth, 2004, 2005; Smith et al., 2006). At present, the major application of FIB in geosciences is site-specific TEM foil preparation, though the technique is being used increasingly for other purposes such as micromachining of diamonds, specimen preparation for infrared (IR) spectroscopy and 3D cross-sectioning. The hardness contrast in multiphase materials, a major problem with conventional argon ion milling, is overcome with FIB. Interfaces are thinned preferentially by conventional argon ion milling because the interface region deviates in chemical composition and bonding from the bulk crystal structure. Interfaces are not thinned preferentially by the FIB method (Wirth, 2004; Heinemann et al., 2005; Seydoux-Guillaume et al., 2003). The preparation of TEM foils of inclusions in meteorites and of dust particles are extremely challenging, but facilitated tremendously by FIB (Vicenzi & Heaney, 1999; Lee et al., 2003; Graham et al., 2004).
The first FIB device used in a geosciences department, a single-beam machine (FEI FIB200TEM), has operated since late 2002 at the GeoForschungsZentrum, Potsdam, Germany. Site-specific TEM foils were cut to identify micro- and nano-inclusions in different host minerals, to investigate interfaces, to characterize very small samples from high-pressure experiments (microstructure, chemical composition, crystal structure), to study microfossils and to solve particular problems in applied mineralogy such as coatings or thin films on substrates.
Meanwhile, the Dual Beam machines, a combination of FIB and a scanning electron microscope (SEM), have substantially widened the field of application of focused Ga ion beams. They are used for multilayer characterization of thin films, in life sciences, micro- and nanomachining such as tips for Field Ion Microscopy samples and especially for 3D imaging and analysis as well as electron backscattered diffraction (EBSD).
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