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Pinned and unpinned epitaxial and sublimated graphene on SiC
|Jan A. Błaszczyk 3, Kacper Grodecki 1,2, Adam Dominiak 3, Kamil Boryczko 1, Wlodek Strupinski 2, Andrzej Wysmolek 1, Roman Stępniewski 2, Jacek Baranowski 1,2|
1. University of Warsaw, Institute of Experimental Physics (IFDUW), Hoża 69, Warsaw 00-681, Poland
The Chemical Vapor Deposition (CVD) of epitaxial graphene has been up until recently almost exclusively carried out on metal substrates. This particular type of growth has been known since late nineties, and has recently received a lot of attention. However, the CVD growth of graphene on SiC is an emerging technique, hence it needs to be verified whether it leads to an improvement of graphene fabrication technology.
Raman spectroscopy is one of the standard optical methods providing valuable information about properties of graphene structures. In this communication we focus on temperature induced shift of Raman 2D band in sublimated and CVD graphene structures grown on SiC. It was found that temperature behavior of the 2D band shift, defined as the Thermal Shift Rate (TSR), depends on the growth method, substrate polarity as well as of the thickness of the multilayer graphene structure.
The highest TSR amplitudes were found in graphene structures fabricated by Si sublimation on Si-face of the SiC substrates. For the single graphene layer TSR–0.17cm-1/K. It indicates that the first layer is strongly pinned to the SiC substrate. At the same time the mean positions of the 2D line for Si sublimated samples reaches 2742cm-1, which is extremely blue shifted in comparison with freestanding graphene. This means that graphene layers grown by this method are strongly stained.
The results for CVD grown layers on Si face of SiC are different. The mean position for the 2D line becomes close to 2700 cm-1which indicates much smaller strain. The values of TSR are also smaller. The CVD growth creates a weakly pinned first graphene layer. Succeeding layers have properties similar to freestanding samples and are almost unstrained. The smallest TSR amplitudes were observed in the CVD graphene structures grown on C-face of the SiC substrate, for which value of –0.032cm-1/K was measured, which is comparable with the freestanding graphene TSR = –0.034cm-1/K
The obtained results are discussed in terms of graphene pinning to the SiC substrate. Moreover the mechanisms responsible for the observed difference in pinning between sublimated and CVD grown layers are presented.
Presentation: Poster at Warsaw and Karlsruhe Nanotechnology Day, by Kacper Grodecki
See On-line Journal of Warsaw and Karlsruhe Nanotechnology Day
Submitted: 2011-09-12 22:25 Revised: 2011-09-12 22:25