Optical Characterization of chemically doped and/or intercalated thin layers graphene

This thesis describes the Raman and Contrast change in chemically doped and/or intercalated thin layers of graphene with halogen gases, FeCl3 and alkali metals. The first chapter introduces graphene and graphite intercalation compounds (GICs). It will also briefly explain Raman of the graphitic compounds including GICs. The second chapter presents doping status of halogen molecules doped graphene. The Raman spectra of the graphene G peak as a function of different number of layers implies the doping structure of few layers graphene. The adsorption-induced electric potential difference between surface and interior layers implies that a band gap opens in the bilayer type bands of I2 doped 3 L and 4 L. The third chapter investigates graphene enhanced raman signal of halogen molecules adsorbed onto and intercalated into graphene. We analyze and model the intramolecular electronic, charge transfer, and multiple reflection electromagnetic mechanisms responsible for the unusual sensitivity. We attribute the large Raman signal from both adsorbed iodine and intercalated bromine species to intramolecular electronic resonance enhancement. The signal evolution with varying graphene thickness is explained by multiple reflection electromagnetic calculations. The fourth chapter explains how the graphene to adjacent graphene layers decouple by expanding lattice distance with insertion of FeCl3 intercalants. Raman measurement proves that adsorbed FeCl3 can easily be washed off by acetone while intercalated FeCl3 is relatively intact by impermeable graphene layers. The fifth chapter considers alkali metal intercalated few layers graphene. We try to understand how the extreme electronic properties of alkali doped bulk graphite develops in few layer thick intercalated graphenes, as a function of the number of layers, starting from a single graphene layer with adsorbed alkali atoms to several graphene layers intercalated with alkali metals. We study both optical reflectivity and Raman scattering, as they reveal different aspects of the electronic structure of peculiar graphene intercalation compounds characters.