Development of a 100 MHz scan controller for the electron microscope

We report on the development of a new 100 MHz high-speed scan controller for the electron microscope, using programmable hardware. By using a spiral scan pattern in order to work around the limitations of the scan coils, we show that this controller is able to acquire undistorted images with a frame time of 0.9 ms. The controller's scan signal and timing control is used to optimize regular (sawtooth) scanning, in order to reduce image distortions at high speeds. Finally, we implement a dose-driven acquisition method, which lowers the required dose and optimizes its distribution, while maintaining the contrast mechanism of the detector.