Nanoscale Tomographic Imaging using Focused Ion Beam Sputtering, Secondary Electron Imaging and Secondary Ion Mass Spectrometry

Abstract As the importance of nano-scaled structures in both science and engineering increases, techniques for reconstructing three-dimensional structural, crystallographic and chemical relationships become increasingly important. in this paper we described a technique which uses focused ion beam (FIB) sputtering to expose successive layers of a 3D sample, coupled with secondary electron imaging and secondary ion mass spectrometry of each sputtered surface. Computer interpolation of these different slice images then enables reconstruction of the 3D structure and chemistry of the sample. These techniques are applicable to almost any inorganic material, at a spatial resolution of tens of nanometers, and fields of view up to (tens of μm). The FIB instrument used in this study is an FEI 200 with a minimum ion probe diameter < 10 nm, an ion current density ∼ 10 A/cm2, a maximum ion current of 11 nA, and a standard Ga+ ion energy of 30 keV. Our instrument is equipped with a continuous dynode electron multiplies (CDEM) for secondary electron imaging and a quadrupole mass spectrometer for secondary ion mass spectroscopy (SIMS) / element specific mapping. Gallium ions of this energy will ablate any material, with sputter yields typically of order ten, corresponding to a material removal rate of order 1 μm3nA−1s−1.