Speaker
Description
Electrostatic potential, including both that contributed by electron-beam-induced specimen charging and intrinsic material-related mean inner potential (MIP), is crucial because it is influence the reaction between charged particles, chemical reactivity, and dielectric properties. Off-axis electron holography is a powerful TEM technique that can be used to map local variations in electron optical phase shift, which are in turn sensitive to electrostatic potentials and magnetic fields. In the absence of magnetic contributions to the phase shift, the recorded phase is proportional to the projected electrostatic potential within and outside the specimen. Insulating nanoparticles with simple geometries are ideal objects for the study of specimen charging in the TEM.
Polystyrene latex beads were examined temperature-dependent behavior of the MIP and electron-beam-induced charge from room temperature down to 5.3 K in a FEI Titan G2 TEM at 300 kV. The diameter of latex spheres is in the range of 230 nm to 600 nm. By using a model-independent approach for the quantification of the spatially-dependent projected charge density from a recorded phase image [1,2], the amount of positive charge on the sphere at each temperature was determined. Isolating the electrostatic potential contributed by the electron-beam-induced charge, the MIP was obtained at high precision, revealing a significant increase of 16.8% as temperature decreases from RT to 5 K.
In addition, this talk will present the quantification of electron-beam-induced charge on MgO nanocubes reflecting the amount of oxygen vacancies on the surface, which is essential for catalytical reaction [3].
