Development of a real-time wave field reconstruction TEM system (I): incorporation of an auto focus tracking system

We have developed a real-time wave field reconstruction transmission electron microscope system that enables auto focus tracking at a video rate. In the developed system, a high-speed image calculation technique using a graphical processing unit was incorporated along with two techniques facilitating high-speed focus control using high-voltage modulation and weighted image integration using exposure time control. By utilizing these techniques, the sample drift induced in the Z-axis direction can be measured and automatically corrected for every 1/30 of a second. The auto focus tracking system can be operated in the sample drift range of ±150 nm with a precision of ~0.4 nm. In addition to amorphous samples, the system can be used to examine thin crystalline samples, which indicates that atomic structure analysis can be performed in real time with high reliability even when heavy drift occurs in the Z-axis direction.