Determination of a refractive index and an extinction coefficient of standard production of CVD-graphene

Abstract

The refractive index and extinction coefficient of chemical vapour deposition grown graphene are determined by ellipsometry analysis. Graphene films were grown on copper substrates and transferred as both monolayers and bilayers onto SiO 2 /Si substrates by using standard manufacturing procedures. The chemical nature and thickness of residual debris formed after the transfer process were elucidated using photoelectron spectroscopy. The real layered structure so deduced has been used instead of the nominal one as the input in the ellipsometry analysis of monolayer and bilayer graphene, transferred onto both native and thermal silicon oxide. The effect of these contamination layers on the optical properties of the stacked structure is noticeable both in the visible and the ultraviolet spectral regions, thus masking the graphene optical response. Finally, the use of heat treatment under a nitrogen atmosphere of the graphene-based stacked structures, as a method to reduce the water content of the sample, and its effect on the optical response of both graphene and the residual debris layer are presented. The Lorentz-Drude model proposed for the optical response of graphene fits fairly well the experimental ellipsometric data for all the analysed graphene-based stacked structures.

Direct synthesized graphene-like film on SiO2: Mechanical and optical properties

“…Combination of the Drude model with the Lorentz line was proposed for description of the optical parameters of graphene [16]. The pure Drude model gave not so satisfactory results in our case, but its accomplishing by one Lorentz line remarkably improved the situation.…”

Nonlinear graphene plasmonics

“…The original intent of Vakil and Engheta's model was to simulate graphene in commercial electromagnetic software; it was emulated with tremendous success by researchers working on device simulations thereafter [37,38,[41][42][43]. Later, experimental optics researchers also successfully adopted this model to fit their experimental measurements of graphene's refractive index [44][45][46][47][48][49]. It should be noted that the rapid development of graphene research has prompted improvement in modern Maxwell solvers to incorporate surface current boundary conditions for simulation of graphene's 2D optical conductivity in 3D devices [50][51][52].…”

Optimization pathways to improve GaInP/GaInAs/Ge triple junction solar cells for CPV applications

“…As it is already known, by using this method, the graphene layer could be damaged or end up unintentionally with a higher doping level due to several agents present at the different steps (such as Cu etchant, dust particles, water molecules or PMMA residues) degrading its final electronic mobility [Capasso et al 2014, Leclercq. J et al 2016 or changing its optical properties [Ochoa-Martinez et al 2015]. Moreover, previous reports indicate that not only PMMA can be a p-type dopant on graphene [Chen et al 2007, Na et al 2006] but it has been also reported that the presence of oxygen may also influence the p-type doping level [Ryu et al 2010].…”

“…With the aim of exploring the evolution of the surface composition on top of and under the graphene layer, measurements were made at three different take-off angles (10º, 45º and 90º, outing photoelectrons pathway measured from the sample surface), changing thus the explored depth. Further information and details on ARXPS measurements can be obtained in [Ochoa-Martinez et al 2015].…”

“…What was observed, is that graphene transfer is directly influenced not only by the different steps of the wet transfer method, but also by the substrate used. Moreover, the presence of water molecules, oxygen at the interface of graphene and the substrate together with PMMA residues are drastically reduced when thermal annealing treatments are carried out [Ochoa-Martinez et al 2015]. Unfortunately, after such treatments the presence of some of this debris is unavoidable and thus the influence on the electrical properties of graphene (mobility, doping, work function…).…”