Nanoscale electromagnetic field imaging by advanced differential phase-contrast STEM

Nanoscale electromagnetic fields formed at localized structures such as interfaces play a pivotal role in the properties of state-of-the-art electronic and spintronic devices. Direct characterization of such local electromagnetic fields inside devices is thus crucial for propelling their research and development. In recent years, direct electromagnetic field imaging via differential phase-contrast scanning transmission electron microscopy (DPC STEM) has attracted much attention. Recent developments of tilt-scan averaging systems and magnetic-field-free objective lenses have finally enabled the practical application of this technique to electronic and spintronic devices. This progress has led to the nanoscale, quantitative observations of electric fields of p–n junctions, 2D electron gas and quantum wells, as well as magnetic fields of magnetic domains, magnetic tunnel junctions and antiferromagnets. These studies demonstrate that DPC STEM can observe local electromagnetic fields from nanometre to sub-angstrom length scales across a wide range of materials and devices. In this Review, we describe the basic principles of DPC STEM, discuss its recent developments in both hardware and imaging techniques and finally show its practical applications in device characterization. We emphasize the immense potential of advanced DPC STEM for the research and development of future electronic and spintronic devices. Direct characterization of nanoscale electromagnetic fields is crucial for propelling device development. This Review summarizes recent developments and applications of high-resolution electromagnetic field imaging by scanning transmission electron microscopy, demonstrating the real-space electromagnetic field and charge observations at device interfaces.