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We present detailed multi frequency resonant Raman measurements of potassiumgraphite intercalation compounds (GICs). From a well controlled and consecutivein-situ intercalation and high temperature de-intercalation approach theresponse of each stage up to stage VI is identified. The positions of the G and2D lines as a function of staging depend on the charge transfer from K to thegraphite layers and on the lattice expansion. Ab-initio calculations of thedensity and the electronic band-structure demonstrate that most (but not all)of the transferred charge remains on the graphene sheets adjacent to theintercalant layers. This leads to an electronic decoupling of these "outer"layers from the ones sandwiched between carbon layers and consequently to adecoupling of the corresponding Raman spectra. Thus higher stage GICs offer thepossibility to measure the vibrations of single, double, and multi-layergraphene under conditions of biaxial strain. This strain can additionally becorrelated to the in-plane lattice constants of GICs determined by x-raydiffraction. The outcome of this study demonstrates that Raman spectroscopy isa very powerful tool to identify local internal strain in pristine and weaklycharged single and few-layer graphene and their composites, yielding evenabsolute lattice constants.

Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds