Development of an image-forming system for the magnetic field-free electron microscope

The successful development of a magnetic field-free objective lens for high-resolution imaging has enabled the acquisition of atomic-resolution scanning transmission electron microscopy (STEM) images under magnetic field-free conditions around the sample. Utilizing this magnetic field-free objective lens for conventional transmission electron microscopy (TEM) observations is expected to offer advantages for the comprehensive characterization of magnetic materials. This approach is particularly significant in the context of in-situ observations. To obtain conventional TEM images, such as bright- and dark-field images, it is important to position the objective lens aperture in a diffraction plane, typically the back focal plane of the objective lens. However, positioning the objective lens aperture around the back focal plane, which is surrounded by multiple magnetic poles, is not feasible for the magnetic field-free objective lens. In this study, we describe the development of an image-forming system that can position the aperture in a diffraction plane conjugate to the back focal plane. In addition, the development of a wide-gap pole piece for the magnetic field-free objective lens has enabled the use of sample holders with thick tips for in-situ observations. The magnetic field-free electron microscope, which integrates a newly developed pole piece and image-forming system with higher-order aberration correctors, offers not only atomic-resolution TEM/STEM observations but also a versatile approach for the characterization of magnetic materials in a magnetic field-free environment.