Electron-beam-induced charging of an Al2O3 nanotip studied using off-axis electron holography

Electrostatic charging of specimens during electron, photon or ion irradiation is a complicated and poorly understood phenomenon, which can affect the acquisition and interpretation of experimental data and alter the functional properties of the constituent materials. It is usually linked to secondary electron emission, but also depends on the geometry and electrical properties of the specimen. Here, we use off-axis electron holography in the transmission electron microscope to study electron-beam-induced charging of an insulating Al2O3 nanotip on a conducting support. The measurements are performed under parallel electron illumination conditions as a function of specimen temperature, electron dose, primary electron energy and surface cleanliness. We observe a lack of reproducibility of charge density measurements after cycling the specimen temperature. Surprisingly, we find both positively and negatively charged regions in closely adjacent parts of the specimen. •Study electrostatic charging of specimens in the TEM by off-axis electron holography.•Varying parameters, including specimen temperature, electron dose, primary electron energy and surface cleanliness.•Understanding charging requires improved control and knowledge of the specimen geometry, surface state, electrical contact and surrounding environment.