Condensed-Matter Physics & Materials Science Seminar

Ultrafast Transmission Electron Microscopy (U-TEM) has become a very important tool
for the study of ultrafast phenomena at (sub-)nm length scales and (sub-)ps time scales.
U-TEM is usually based on the creation of ultrashort electron pulses by femtosecond
laser photoemission from a flat cathode, with the result that both the beam quality and
the average current are significantly less than in state-of-the-art continuous-beam
TEMs. At Eindhoven University we have developed U-TEM in which ultrashort electron
pulses are produced by using a 3 GHz deflecting microwave cavity in TM110 mode to
sweep a high-brightnes continuous beam across a slit [1]. We have demonstrated
ultrafast beam chopping with conservation of the beam quality and the sub-eV energy
spread of the FEG source of an adapted 200 keV Tecnai TEM, enabling atomic resolution
with sub-ps temporal resolution at 3 GHz rep rate [2]

In addition we have developed a new method for doing Time-of-Flight Electron Energy
Loss Spectroscopy (ToF-EELS) based on the combined use of two TM110 deflecting
cavities and two TM010 (de)compression cavities. The first 'chopping' TM110 cavity
produces ultrashort electron pulses which are sent through a sample. Energy loss in the
sample translates into reduction of the electron velocity and thus into a later arrival
time at the detector, which is measured with a synchronized second TM110 'streak'
cavity. In this way an energy resolution of 12 eV at 30 keV has been demonstrated [3].
By adding a TM010 (de)compression cavity after the sample, the longitudinal phase space
can be manipulated in such a way that the energy resolution is improved to 2 eV (to be
published). By adding a second TM110 cavity before the sample, full control over the
longitudinal phase space can be achieved. Detailed charged particle tracking simulations
show that an energy resolution of 20 meV combined with a temporal resolution of 2 ps
can be achieved; or, alternatively, 2