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 then 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. Real-time drift measurement and feedback control of the instrument allows single holograms to be acquired with exposure times of 30 minutes or more. The positions of the hologram fringes and the specimen are corrected in real-time by feedback control of the microscope deflectors and specimen stage. Indeed, there are no longer any limitations from instrumental instabilities, 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. Apart from the necessity of a fast camera and microscope control protocols, the approach presented here is based on software routines and should therefore be widely applicable.

This work was supported by the French National Research Agency under the project IODA (ANR-17-CE24-0, the "Investissement d'Avenir" program reference No. ANR-10-EQPX-38-01 and No. 11-IDEX-0002, the "Conseil Regional Midi-Pyrénées", the European FEDER for financial support within the CPER program. This work was also supported by the international associated laboratory M²OZART.

Reference

Unlimited acquisition time in electron holography by automated feedback control of transmission electron microscope
C. Gatel, J. Dupuy, F. Houdellier and M.J. Hÿtch
Applied Physic Letters 113 , 133102 (2018);
doi: 10.1063/1.5050906

Contact

Dr. Christophe GATEL , CEMES (CNRS)
gatel at cemes.fr

Dr. Martin HYTCH , CEMES (CNRS)
martin.hytch at cemes.fr