Dissertation

Optical Near-Field Electron Microscopy

In this thesis, we develop a novel technique called Optical Near-field Electron Microscopy (ONEM), which aims to combine the advantages of both optical and electron microscopy: the high resolution of electron microscopy and the low sample damage of optical microscopy.

Author

W.G. Stam

Date

04 June 2025

Links

Thesis in Leiden Repository

In ONEM, the sample is illuminated from the backside with visible light. The light passes through the sample, is modified by it, and then reaches a thin photocathode. In this thin layer, the light is converted into electrons. Areas receiving less light, because the light is blocked by an object, such as a virus, generate fewer electrons. The emitted electrons are then accelerated and imaged using the electron optics of a low-energy electron microscope (LEEM). The key idea is that ONEM bypasses the optical diffraction limit by capturing the optical near field in close proximity to the sample using the photocathode. The resulting "snapshot" of the optical near field is thus taken with electrons, which themselves have a much smaller diffraction limit than light.