Graphene examined with very slow electrons

0450825 - ÚPT 2016 RIV HU eng C - Konferenční příspěvek (zahraniční konf.)
Frank, Luděk - Mikmeková, Eliška
Graphene examined with very slow electrons.
12th Multinational Congress on Microscopy. Budapest: Akadémiai Kiadó, 2015, s. 182-183. 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: graphene * 2D crystals * ultra-low-energy STEM * ultra-low-energy SEM
Kód oboru RIV: JA - Elektronika a optoelektronika, elektrotechnika

Electron microscopy of materials composed of light elements suffers from low image contrast, particularly in the transmission microscopy of biomedical specimens. Post-fixation or staining with heavy metal salts that highlight certain structural details is a partially successful aid in routine microscopy. In order to examine mutually overlapped flakes of two-dimensional crystals such as graphene we need to obtain a contrast contribution from a single layer of carbon atoms. This task requires increasing the scattering rate of incident electrons by means of a drastic lowering of their energy to hundreds of eV or less. The cathode lens principle implemented in the SEM, and recently in the STEM mode as well, makes it possible to use an arbitrarily low energy in both reflection and transmission modes. Contrasts between sites differing in thickness by a single graphene layer are demonstrated at 220 eV. The high lateral resolution of ultra-low-energy STEM with a cathode lens enabled us to measure graphene transmissivity accurately down to 1 eV for 1 to 7 graphene layers. Surprisingly, below 50 eV the transmissivity does not increase as one would expect from the usual behaviour of the inelastic mean free path of electrons, but remains within a range of units of percent.
Trvalý link: http://hdl.handle.net/11104/0252038