Time and place
Friday, 2 October 2026, at 13:00, Building. 341, Auditorium 22
Principal supervisor
Associate Professor Paul Kempen, DTU Nanolab
Co-supervisor
Professor Stephan Sylvest Keller, DTU Nanolab
Associate Professor Marco Beleggia, DTU Nanolab
Assessment committee
Senior Researcher Shima Kadkhodazadeh, DTU Nanolab
Associate Professor Thomas Boesen, Aarhus University
Senior Researcher Marek Malac, National Research Council Canada
Moderator at defence
Associate Professor, Ada-Ioana Bunea, DTU Nanolab
Abstract
High-resolution transmission electron microscopy (TEM) is a powerful tool for studying biological structures, but biological materials naturally produce very little image contrast because they scatter electrons weakly. One common solution is to defocus the microscope image, although this reduces resolution. An alternative is the use of phase plates, which can enhance contrast without sacrificing detail. However, their wider use has been limited by issues such as electron-beam-induced charging, operational complexity, and uncertainty in the phase shift they produce.
In this work, chip-based thin-film phase plates were designed, fabricated, and tested, combining experiments with simulations. The devices were made from nanofabricated silicon nitride membranes coated with amorphous carbon, enabling precise and reproducible geometries. Devices in Zernike (ZPP), Hilbert (HPP), and Volta modes (VPP) were investigated. Their performance was evaluated using carbon phase gratings and cryo-TEM imaging of liposomes as biological model systems. Electron holography was also used to measure how the thin films modify electron waves, providing key data for phase plate design.
Simulations and experiments revealed how factors such as phase shift, beam size, hole size, and alignment affect image quality. The results showed that phase plates can significantly improve contrast, but also that even small alignment errors can strongly degrade performance. In fact, alignment was found to be more critical than moderate variations in phase shift or film thickness.
Overall, the study demonstrates that nanofabricated phase plates can reliably enhance contrast in both conventional and cryogenic TEM. It also establishes design and measurement methods that support the development of more robust and practical phase-contrast imaging technologies for biological microscopy.
