16 Introduction: The optical nature of a charged particle beam
adequate is remarkable. Third, the fragile graphene structure is
undamaged by the beam. It would not be possible to obtain such
an image without spherical aberration correction.
Figure 1.9: SIMS images of chromosomes.
Alternatively, a beam of ions can be used to perform chemical
analysis of a material. The ion beam is focused and scanned over
the surface of the material to be analyzed. Atoms are removed from
the surface and ionized. These secondary ions then pass through a
spectrometer which separates the various ionic species according to
their masses. An image is formed synchronously, consisting of any
chosen individual chemical species. This is called Secondary Ion
Mass Spectrometry or SIMS. An example is shown in Figure 1.9