[Seminar] "Physical principles underlying operation of phase plates in a TEM" by Marek Malac

Abstract:

Phase plates can be used to increase contrast in a transmission electron microscope (TEM). The increased contrast leads to reduced irradiation dose needed to detect an object at a desired signal-to-noise ratio. Phase plates can also be used to image materials science samples, such as computer processor chips and magnetic samples. Recently, the use of a particular type of phase plate, the Hole-Free Phase Plate (HFPP) is gaining popularity. The HFPP uses an uniform film placed in focal plane of an imaging lens. The film properties are then locally modified by the high energy electron beam itself thus eliminating the need for complicated alignment of the beam and phase plate hardware.

Several microscopic mechanisms are known to contribute to local modification of the film properties, induce phase shift and increase contrast. The mechanisms include film contamination, positive charge trapping arising from secondary electron emission and negative surface potential due to local removal of adsorbed contaminants.

Example new applications of phase plate imaging will be shown followed by a detailed discussion of electron beam induced charging of thin films.