3.1.5. Objective Magnetic Lens

The objective or "probe-forming" lens is located at the base of the column just above the sample. This lens focuses the electron beam onto the sample and controls its final size and position. The Cameca MBX microprobe uses a "mincoil" objective lens, which allows the light optical system and scanning coils to fit inside it. The magnet is asymmetrical with less of the magnet located below the air gap to limit the amount of magnetic field at the sample.

Figure C-8. The light optics (4) and scanning coils (1) are located inside the minicoil probe-forming lens (2) at the base of the electron column. The pole piece (7) is one solid piece of metal and protects the sample from stray magnetic fields. The x-ray beams (3) are collimated by small apertures (6), and pass through an electron trap (5) that prevents backscattered electrons from entering the x-ray spectrometers.