Scanning low-and very low energy electron microscopy

0450822 - ÚPT 2016 RIV HU eng C - Konferenční příspěvek (zahraniční konf.)
Pokorná, Zuzana - Frank, Luděk - Knápek, Alexandr - Konvalina, Ivo - Mikmeková, Eliška - Mikmeková, Šárka - Walker, Christopher - Müllerová, Ilona
Scanning low-and very low energy electron microscopy.
12th Multinational Congress on Microscopy. Budapest: Akadémiai Kiadó, 2015, s. 218-220. ISBN 978-963-05-9653-4.
[MCM 2015. Multinational Congress on Microscopy /12./. Eger (HU), 23.08.2015-28.08.2015]
Grant CEP: GA TA ČR(CZ) TE01020118
Institucionální podpora: RVO:68081731
Klíčová slova: very low energy * scanning low energy electron microscopy * crystallography, graphene * tissue sections
Kód oboru RIV: JA - Elektronika a optoelektronika, elektrotechnika

Scanning low energy electron microscopy (SLEEM) allows imaging samples with a good lateral resolution using electrons of an arbitrarily low energy. This is achieved by means of the Cathode Lens, which is essentially a decelerating electrostatic field inserted just before the electron beam hits the sample. The technique allows both for a reflection and a transmission mode and energies down to zero electron volts. The region of very low electron energies (below 50 eV) offers some interesting phenomena that are not encountered at the usual energies of a few units to tens of keV that are employed in ordinary scanning electron microscopes. To name but a few: Reflectivity of very slow electrons in the very low energy range can be correlated with the electronic structure of the material which in turn is related to the crystallographic orientation of the sample. This fact has been successfully used for the extraction of crystallographic orientation related information in polycrystalline metals. At around 500 eV, the penetration depth of electrons is roughly equal to the information depth for single elastic scattering, which is sensitive to local crystallinity. This allows visualizing strain in heavily deformed polycrystalline metal. The decelerating electrostatic field of the Cathode Lens in our particular experimental setup influences also the collection efficiency of signal electrons, as stronger field means also larger emission angle of the signal electrons that are collected on the detector. This also plays an important role in interpreting the image contrast. In the very low energy region below 50 eV, the inelastic mean free path of the electrons increases as energy is lowered. This causes the sample transmissivity to increase as well. In this energy region the thickness contrast is well visible, allowing for example to discern the number of graphene sheets present in a layer.
Trvalý link: http://hdl.handle.net/11104/0252034