Examination of Graphene in a Scanning Low Energy Electron Microscope

0450818 - ÚPT 2016 RIV US eng J - Journal Article
Müllerová, Ilona - Mikmeková, Eliška - Frank, Luděk
Examination of Graphene in a Scanning Low Energy Electron Microscope.
Microscopy and Microanalysis. Roč. 21, S3 (2015), s. 29-30. ISSN 1431-9276. E-ISSN 1435-8115
R&D Projects: GA MŠMT(CZ) LO1212
Institutional support: RVO:68081731
Keywords : graphene * LEEM
Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering
Impact factor: 1.730, year: 2015

Although graphene has been available and intensively studied for a full decade, new methods are still required for its examination and diagnostics. Even checking the continuity of layers and the reliable counting of layers of graphene and other 2D crystals should be easier to perform. Scanning low energy electron microscope (SLEEM) equipped with a cathode lens offers an innovative tool enabling one to see graphene samples at nanometer lateral resolution in both transmitted and reflected electrons and to count the number of layers. This diagnostics can be performed on freestanding graphene samples as well as on graphene grown on the surfaces of bulk substrates. The freestanding graphene samples were first examined in the standard vacuum high resolution SLEEM. Fig. 1 shows micrographs taken in the reflected electron (RE) as well as transmitted electron (TE) mode at several energies. The RE signal was composed of both secondary and backscattered electron emission, accelerated in the cathode lens field toward the detector. In the RE frames the maximum contrast between the graphene layers and lacey carbon appears at 1 keV and decreases toward higher and lower energies because of extending and shortening information depth, respectively. These images identify empty holes but do not reveal thicker islands of graphene. In the TE mode we do not see multilayer graphene islands above 100 eV. This fact underlines the suitability of very low energy electron microscopy for examination of 2D crystals. Interpretation challenges are presented by some details inverting their contrast more than once, see the arrow. These probably arise from contaminations that become charged.
Permanent Link: http://hdl.handle.net/11104/0257504