De-intercalation process from Stage-1 to Stage-2 graphite intercalation compounds revisited

The identification and contribution of the different phonons present in the G-line Raman response in Stage-1 and Stage-2 graphite intercalation compounds (GIC) is crucial for a correct stage determination. Different factors like laser induced de-intercalation play an important role in the precise stage assignment of these phases, and their intrinsic Raman response. In this contribution, an in situ micro-Raman analysis was conducted under high-vacuum conditions. Local heating of the samples was induced by using a high laser power (8.5?mW) in order to study the de-intercalation process from Stage-1 to Stage-2 GICs. A detailed Raman line-shape analysis was performed from the recorded spectra to determine the changes from the G-line response of KC8, CaC6, and LiC6. We confirmed the assignment of the broad E2g Fano mode at similar to 1510?cm-1 to the intrinsic Stage-1 Raman response in GICs. Additionally, the most evident change from Stage-1 to Stage-2 was observed in an asymmetric Fano mode in the range of 15651610?cm-1. This mode is linked to the first-order stretching Raman mode of Graphite, which tends to increase in frequency and decrease in width as function of de-intercalation. Finally, the response of the Stage-2 phase after de-intercalation was confirmed to be a useful benchmark for the identification of the intercalation stage in highly doped GICs.