Graphene and Plasmonics: The Nanoscale Challenges for Real-Time Spectroscopic Ellipsometry

The improvement of technologies towards a more sustainable development and use of energy resources and devices has received an increasing interest worldwide in recent decades. There is consensus that this improvement needs corroborating materials synthesis and device fabrication processes with in-situ real-time characterization. Elucidating the synthesis-processing-material-functionality interplay is also a key issue in fundamental science, necessary to advance basic knowledge of materials and to manipulate their properties at the nanoscale. Therefore, this contribution overviews how spectroscopic ellipsometry, which is a non-destructive, nonintrusive, noninvasive, and contactless optical technique, has evolved into an efficient characterization tool for graphene-metal based hybrids for plasmonics, optical sensors, and SERS devices. The scope of this contribution is to highlight experimental achievements obtained using real-time spectroscopic ellipsometry on the CVD growth on nickel and copper substrates of graphene, and its interactions with metals. Specifically, it will be shown improvements in the properties of graphene achieved by optimizing CVD growth and establishing correlations between process kinetics and graphene thickness. It will also be provided for the first time the direct evidence of the tunability of the plasmon resonance of graphene coupled to plasmonic metal nanoparticles (NPs). New opportunities for the design of plasmonic graphene/metal (Ga, Au, Ag) systems based on charge transfer are presented exploiting the real time tailoring of the plasmon resonance by spectroscopic ellipsometry. Charge transfer is crucial for characterizing metal/graphene interfaces and understanding plasmon-electron coupling across the materials components. The role of graphene in the charge transfer, between the metal NPs and the substrate, on the plasmon resonance energy and amplitude is discussed and elucidated.