semi-in-lens objective lens

One of the objective lenses for the high-resolution SEM.
The semi-in-lens objective lens has been created, so as to improve the disadvantages of the in-lens objective lens. As shown in Figure, the opening of the yoke is located below this lens and thus, a lens magnetic field is created below the objective lens (indicated by yellow region). Since the semi-in-lens objective lens provides a short focal length, this feature achieves small spherical and chromatic aberrations of the semi-in-lens objective lens comparable to those of the in-lens objective lens, and a high-resolution SEM image is obtained. Since the specimen is placed outside the lens, a large specimen can be handled.
However, a magnetic material (magnetic specimen) is placed in a strong magnetic field in the lens, thereby not suitable for observation of the magnetic specimen. To detect secondary electrons emitted from the specimen, the TTL (through-the-lens) detector is used.
For the SEM instrument equipped with the semi-in-lens objective lens, it is possible to attach an EDS detector. Also an EBSD detector can be attached, but a diffraction pattern acquired by EBSD is distorted due to the lens magnetic field, thereby requiring a compensation function for this distortion.
The semi-in-lens objective lens has been installed in a great number of FE-SEMs, so as to meet the needs of SEM users focusing on high-resolution imaging.