Spectroscopic imaging ellipsometry of graphene

Abstract

Graphene, a novel nanomaterial, was first isolated in 2004 by Novoselov and coworkers.1 It is essentially a single atomic layer of carbon, where the atoms are arranged into a hexagonal, honeycomb-like structure. This structure is the reason for graphene’s unique electronic,2 optical,3 and mechanical properties, which have attracted both fundamental and applied research interest in recent years. Graphene shows promise for use in future electronic devices and especially optoelectronics,4 so it is important to fully understand its optical properties. We have used various techniques to investigate these and also the effects of transfer residue and annealing.5–8 Furthermore, we have studied the behavior of graphene in laboratory conditions, when a water layer forms on it.7 Ellipsometry is an optical technique used mainly for investigating the dielectric properties and thicknesses of thin films. It is nondestructive, contactless, and used in many different fields, such as solid-state physics and microelectronics, for both fundamental research and industrial applications.9, 10 Ellipsometry measures the ratio between complex amplitude reflection coefficients for the electric field vector parallel (rp D Erp=Eip) and perpendicular (rs D Ers=Eis) to the plane of incidence: see Figure 1. This ratio is presented as the complex value