Dynamic Study of Intercalation/Deintercalation of Ionic Liquids in Multilayer Graphene Using an Alternating Current Raman Spectroscopy Technique.

We report Raman spectra and infrared (IR) imaging collected during the intercalation-deintercalation half cycles in a multilayer graphene (MLG) device (∼100 layers) operating at 0.2-10 Hz. The device consists of a MLG/alumina membrane/copper stack, in which the alumina membrane is filled with ionic liquid [DEME][TFSI], forming an electrochemical cell. Upon the application of a positive voltage, the TFSI- anions intercalate into the interstitial spaces in the MLG. The incident laser light is modulated using an optical chopper wheel that is synchronized with (and delayed with respect to) a 0.2-10 Hz alternating current (AC) voltage signal. Raman spectra taken just 200 ms apart show the emergence and disappearance of the intercalated G band mode at around 1610 cm-1. By integration of over hundreds of cycles, a significant Raman signal can be obtained. The intercalation/deintercalation is also monitored with thermal imaging via voltage-induced changes in the carrier density, complex dielectric function ε(ω), and thermal emissivity of the device.