Phase contrast transmission electron microscopy using phase plates

Transmission electron microscopy of weakly scattering materials like thin sections of cells and polymers often leads to poor image contrast and poor transfer of information with a spatial frequency lower than around 2 nm. In addition, the information contained in the phase of the specimen exit wave is often lost due to an inability to directly record phase changes. Electron Holography, which is difficult and expensive to practice has proven ineffective at significantly improving image contrast in many cases. Another method for generating phase contrast involves the use of phase plates that until now were not practical for routine transmission electron microscopy (TEM). This work describes two phase plates, one employing a contamination spot and the other an electrically compensated electrostatic phase plate that can be routinely used in modern TEM to enhance contrast. This method should prove to be particularily useful where heavy metal stains are ineffective or where they must be avoided to preserve the sample integrity. Examples of the use of these plates to improve images of polymers, biological cells and catalysts are presented. Results show significant contrast improvement for features greater than 2 nm in dimension.