objective lens

The objective lens is a lens that is placed close to a specimen to focus an electron probe onto the surface of the specimen. The diameter of the electron probe can be made smaller when the aberration of the lens is smaller. Three types of objective lenses are available; the out-lens objective lens below which the specimen is placed, the in-lens objective lens inside which the specimen is placed, and the semi-in-lens objective lens whose structure is a compromise of the out-lens- and in-lens-objective lenses.
A magnetic field lens is generally used for the objective lens. Recently, an electromagnetic-and-electrostatic composite lens has been available to acquire a high spatial resolution image at a low accelerating voltage below 1 kV.