Inelastic Phase Contrast Using Electrostatic Zach Phase Plates

Physical phase plates (PP) for transmission electron microscopy (TEM) are intensively studied since the first carbon film-based and electrostatic PPs have been experimentally realized [1,2]. By inducing a phase shift on a part of the electrons in the back focal plane of the objective lens, contrast enhancement can be achieved. Several groups have already demonstrated proof-of-principle experiments using different PP designs. Our approach is based on the electrostatic Zach PP [3] shown in Fig. 1. The Zach PP has a central electrode positioned on a single rod and surrounded by insulating ceramic and shielding metal layers. This design offers reduced obstruction in the back focal plane compared to Boersch PPs [2] and a controllable phase shift induced on the unscattered electrons by the inhomogeneous electrostatic potential created at the tip. To minimize contamination and electrostatic charging, a heating device is implemented and a thin amorphous carbon layer is deposited on the PP.