Cryogenic Electron Holography and Differential Phase Contrast Imaging of Quantum Materials and Electron-Beam-Sensitive Materials

Cryogenic transmission electron microscopy offers new prospects for studying quantum materials and electron-beam-sensitive materials. Here, we describe recent progress in the use of phase contrast techniques in the (scanning) transmission electron microscope, in combination with liquid nitrogen and liquid helium cooling, to obtain quantitative information about electromagnetic fields in nanoscale materials and to generate improved contrast at low electron dose from materials that are affected by irradiation damage.<br/><br/>The first examples involve the use of off-axis electron holography and Lorentz imaging at low temperature to study magnetic skyrmions in crystallographically chiral materials such as FeGe and magnetic flux vortices in superconducting materials such as NbN in focused ion beam milled samples that provide geometrical lateral confinement. The influence on the measurements of sample preparation damage, the direction and strength of an applied magnetic field and electrical current, as well as the presence of electron-beam-induced specimen charging, will be discussed.<br/><br/>The second examples involve the use of (integrated) differential phase contrast imaging in the scanning transmission electron microscope at low temperature to record atomic-resolution images of electron-beam-sensitive materials, including metal-organic frameworks, organic materials and minerals. The use of event-driven detectors, automation of experimental workflows and non-standard electron beam scanning protocols will be discussed.<br/><br/>Finally, new concepts for improved instrumentation for such experiments, including liquid-helium-cooled specimen stages, advanced magnetizing units, specimen holders for high frequency experiments, sample transfer cartridges and capabilities for in situ laser irradiation of the sample in the electron microscope, will be presented.