Regensburg 2013 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 39: Graphene: Characterization and Devices (jointly with DS, HL, MA, and TT)
O 39.2: Vortrag
Mittwoch, 13. März 2013, 09:45–10:00, H17
Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds — Julio Chacon-Torres1, •Ludger Wirtz2, and Thomas Pichler1 — 1Faculty of Physics, University of Vienna, Austria — 2Physics and Material Sciences Unit, University of Luxembourg, Luxembourg
We present recent Raman measurements together with a detailed analysis of potassium graphite intercalation compounds (GICs): stage II to stage VI (where stage n means one intercalant layer after every nth graphene layer). By ab-initio calculations of the charge densities and the electronic band dispersions, we demonstrate that most (but not all) of the charge donated by the K atoms remains on the outer graphene layers, i.e., the once adjacent to the intercalant layer. This leads to an electronic decoupling of the inner (uncharged) from the outer (charged) layers and consequently also to a decoupling of the corresponding Raman spectra: The G-line splits into two peaks and the 2D line is entirely due to the uncharged inner layers while the 2D line of the outer layers is suppressed due to the strong charging. The quantitative interpretation of the peak positions requires that the internal strain of the graphene layers is taken into account. This allows to unambiguously identify the Raman response of strained charged and uncharged graphene layers and to correlate it to the in-plane lattice constant. Raman spectroscopy is thus a very powerful tool to identify internal strain in single and few-layer graphene as well as to to identify the strain in nanoelectronic and optoelectronic devices or the local interfacial strain in other graphene composites.