Unlimited acquisition time in electron holography by automated feedback control of transmission electron microscope

Abstract

The signal-to-noise ratio of measurements by electron holography could be considerably improved if longer exposure times were possible: increasing the number of electrons contributing to the hologram improves the counting statistics. However, instrumental instabilities causing drift in the hologram fringes and specimen position make acquisition times of above a few seconds counterproductive. The current approach is to acquire image stacks of holograms, with short exposure times, followed by numerical realignment through sophisticated post-processing. The associated data storage and manipulation make in-situ and tomography experiments extremely cumbersome. Here, we implement dynamic automation of electron holography experiments to overcome these problems. The real-time drift measurement and feedback control of the instrument allow single holograms to be acquired with exposure times of 30 min or more. Indeed, there are no longer any limitations from instrumental instabilities and only those imposed by the specimen itself. Furthermore, automation allows the implementation of sophisticated phase reconstruction techniques based on precise control of the experimental conditions. Smart acquisition of electron holograms preludes future computer-controlled electron microscopy capabilities.

Magnetic flux closure in mutant magnetotactic bacteria elucidates a key signature of magnetofossils

“…The fringe spacing is equal to 1 nm (7 pixels) allowing for a spatial resolution of 1.5 nm for the treated magnetic phase images. The exposure time was set to 1 nm using dynamic automation acquisition for removing instabilities and applying the fringe π-shift method 66,67 . Phase and amplitude images were extracted from the holograms by using homemade software based on fast-Fourier transform approach.…”

Optimization of off-axis electron holography performed with femtosecond electron pulses

“…In this section we will show how the use of image stacks previously introduced in conventional holography experiments [24,25], can contribute to overcome this limitation.…”

“…Data processing has been performed using home- In the Not corrected row, individual holograms in the stack have been summed without applying any fringe drift using the gun tilt coils will be implemented in the future [25]. The future transfer of our technology from the old HF2000 to a recent stateof-the-art TEM, will give us the possibility to move towards this direction and the use of direct electron camera providing a higher DQE should also strongly improve the live-correction process.…”

Software tools for automated transmission electron microscopy

“…In cryo-TEM, feedback from image analysis is employed to identify and judge the quality of particles for acquisition of imaging [10][11][12] or diffraction data [13][14][15] . In material science TEM, similar approaches exist that enable ultrastable imaging [16][17][18] . There is, however, no solution that incorporates advanced image analysis procedures into the various kinds of TEM data acquisition workflows in a generic way.…”