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   Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron–phonon coupling in graphene layers; Wirtz, Ludger  ; in Physica Status Solidi B. Basic Research (2014), 251(12), 23372355 Graphite intercalation compounds (GICs) are an interesting and highly studied field since 1970’s. It has gained renewed interest since the discovery of superconductivity at high temperature for CaC6 and ... [more ▼] Graphite intercalation compounds (GICs) are an interesting and highly studied field since 1970’s. It has gained renewed interest since the discovery of superconductivity at high temperature for CaC6 and the rise of graphene. Intercalation is a technique used to introduce atoms or molecules into the structure of a host material. Intercalation of alkali metals in graphite has shown to be a controllable procedure recently used as a scalable technique for bulk production of graphene, and nano-ribbons by induced exfoliation of graphite. It also creates supra-molecular interactions between the host and the intercalant, inducing changes in the electronic, mechanical, and physical properties of the host. GICs are the mother system of intercalation also employed in fullerenes, carbon nanotubes, graphene, and carbon-composites. We will show how a combination of Raman and ab-initio calculations of the density and the electronic band structure in GICs can serve as a tool to elucidate the electronic structure, electron–phonon coupling, charge transfer, and lattice parameters of GICs and the graphene layers within. This knowledge of GICs is of high importance to understand superconductivity and to set the basis for applications with GICs, graphene and other nano-carbon based materials like nanocomposites in batteries and nanoelectronic devices. [less ▲] Detailed reference viewed: 240 (11 UL)Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds.; Wirtz, Ludger ; in ACS Nano (2013), 7(10), 9249 We present detailed multifrequency resonant Raman measurements of potassium graphite intercalation compounds (GICs). From a well-controlled and consecutive in situ intercalation and high-temperature ... [more ▼] We present detailed multifrequency resonant Raman measurements of potassium graphite intercalation compounds (GICs). From a well-controlled and consecutive in situ intercalation and high-temperature deintercalation approach the response of each stage up to stage VI is identified. The positions of the G and 2D lines as a function of staging depend on the charge transfer from K to the graphite layers and on the lattice expansion. Ab initio calculations of the density and the electronic band structure demonstrate that most (but not all) of the transferred charge remains on the graphene sheets adjacent to the intercalant layers. This leads to an electronic decoupling of these "outer" layers from the ones sandwiched between carbon layers and consequently to a decoupling of the corresponding Raman spectra. Thus, higher stage GICs offer the possibility to measure the vibrations of single, double, and multilayer graphene under conditions of biaxial strain. This strain can additionally be correlated to the in-plane lattice constants of GICs determined by X-ray diffraction. The outcome of this study demonstrates that Raman spectroscopy is a very powerful tool to identify local internal strain in pristine and weakly charged single and few-layer graphene and their composites, yielding even absolute lattice constants. [less ▲] Detailed reference viewed: 161 (3 UL)Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compoundsWirtz, Ludger ; ; Scientific Conference (2013) Detailed reference viewed: 119 (2 UL) |
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