Time-resolved Transmission
Electron Microscopy

Work-Package 24

The purpose of this Joint Research Activity aims at stimulating progress in Europe in time-resolved TEM which is not currently available to users. Two time scales have been targeted: the millisecond to second regime which requires the development of novel fast detectors and the pico-second to nanosecond regime which necessitates the developments of an innovative and tunable pulsed electron gun to perform pump probe experiments.

Fast Transmission Electron Microscopy:
We aim at developing new fast detectors for existing TEMs, which could be made available to other consortium members and TA users. Within this, the University of Oxford (UOXF) has initiated a program to develop advanced CMOS detectors with 2048 x 2048 pixels that are fully radiation hardened and which can be used for direct detection without the need for a resolution limiting scintillator and coupling.

Development of an ultrafast field emission electron source for a 200 kV TEM:
The second task is even more ambitious as its goal is to build a new hybrid instrument combining a fs laser source and a TEM based on a field emission source to perform pump/probe TEM experiments on ultrafast dynamical processes that occur in nanostructures. Such project requires the development of experimental TEM techniques with sub-nanometer spatial resolution and femtosecond temporal resolution.

The first step of the project consists in developing the first high-voltage electron gun for pulsed ultra-coherent electron emission. To develop a novel ultrafast TEM based on a high brightness electron source, CNRS CEMES (Toulouse) is developing a new technology allowing generating electron pulses of subpicosecond duration from the interaction of a femtosecond laser source focused on the apex of a cold field emission tungsten (310) tip. To achieve this goal, a dedicated Ultra-High Vacuum Bench allowing for in-depth testing of the modified mechanical parts has been mounted. New HV connections, new mechanical parts have been designed fabricated and installed. In parallel, a femtosecond laser source has been installed together with a characterization set-up based on a pulse autocorrelator. An optical set-up has been designed for the alignment of the femtosecond laser source on the metallic nanotip together with diagnostic tools and alignment procedure. After validation in the near future, the new ultra-short electron source will be installed on a modified commercial TEM column.

TEM pump-probe experiments require combining this novel ultra-short electron probe with a light injector (pump). CNRS ESTEEM2 partner in Orsay
(LPS) is developing the optical pump of the sample based on a light injection system developed for a VG machine. It basically consists in a micro-machined, ultra compact, very high numerical aperture, hole drilled, parabolic mirror put on the electron path, and easily alignable with submicrometer precision from the atmospheric pressure si de of the microscope. The system is designed for injection from a collimated beam or a point source without loss of spatial coherence, allowing for ultimately di ffraction limited spot.

JRA5 - image 1

Image of the mounting of a new tip in the accelerator on the UHV.

 

Deliverable: Progress report on light injection

Partners involved:

CNRS/CEMES Toulouse (Work-Package leader); CNRS/LPS Orsay (WP co-leader); University of Oxford: ER-C Jülich

Contacts:

Etienne Snoeck (CNRS/CEMES Toulouse)
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Mathieu Kociak (CNRS/LPS Orsay)
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