5
Introduction: The optical nature of a charged particle beam
tion. The solenoid is surrounded by a shroud of soft iron, which
concentrates the magnetic field. The magnetic field lines bulge into
the region of the electron beam, which is incident from the top of
the figure. The beam is focused to a small probe at the target
plane, shown at the bottom of the figure. Such an arrangement is
used in a scanning electron microscope. The magnetic field lines
and the electron trajectories are generated in a computer simulation by MEBS, Ltd. [63]. The beam path is 100 mm long in the
figure, the beam energy is 10 KeV, and the solenoid carries 550
ampere-turns. In reality, the electrons spiral around the central
optic axis. The figure is plotted in a coordinate system which rotates about the axis with the beam, so that the trajectories appear
not to rotate. This is for clarity.
An example of an electrostatic lens is shown schematically in Figure 1.3. Electrons are emitted from a heated flat surface at zero
Figure 1.3: Electrostatic acceleration and focusing of a beam of
electrons.
volts relative potential on the left of the figure, and are accelerated to the right. An aperture at –10 volts forms a grid to control
Introduction: The optical nature of a charged particle beam
tion. The solenoid is surrounded by a shroud of soft iron, which
concentrates the magnetic field. The magnetic field lines bulge into
the region of the electron beam, which is incident from the top of
the figure. The beam is focused to a small probe at the target
plane, shown at the bottom of the figure. Such an arrangement is
used in a scanning electron microscope. The magnetic field lines
and the electron trajectories are generated in a computer simulation by MEBS, Ltd. [63]. The beam path is 100 mm long in the
figure, the beam energy is 10 KeV, and the solenoid carries 550
ampere-turns. In reality, the electrons spiral around the central
optic axis. The figure is plotted in a coordinate system which rotates about the axis with the beam, so that the trajectories appear
not to rotate. This is for clarity.
An example of an electrostatic lens is shown schematically in Figure 1.3. Electrons are emitted from a heated flat surface at zero
Figure 1.3: Electrostatic acceleration and focusing of a beam of
electrons.
volts relative potential on the left of the figure, and are accelerated to the right. An aperture at –10 volts forms a grid to control