Hunting micrometer-sized graphene flakes on gold substrate

TL;DR

This study measures the optical contrast of micrometer-sized graphene flakes on gold substrates, demonstrating high sensitivity for detecting contamination and enabling potential applications in ultrasensitive molecular sensing.

Contribution

It provides the first accurate optical contrast spectra for small graphene flakes on gold and shows the technique's capability for detecting sub-monolayer molecular adsorption.

Findings

Optical contrast spectra match theoretical predictions.

High-resolution microscopy can determine micron-scale flake thickness.

Optical contrast spectroscopy detects airborne hydrocarbon contamination.

Abstract

Gold is widely used as the substrate material in many graphene devices, due to its superior optoelectronic properties and chemical stability. However, there has been little experimental investigation on the optical contrast of graphene films on Au substrates. Here we report accurate measurement of the optical contrast spectra of few-layer graphene flakes on bulk Au. We used a high-resolution optical microscopy with a 100x magnification objective, accurately determining the thickness of flakes as small as one micrometer in lateral size, which are highly desired in many applications. The results are in excellent agreement with theoretical calculations and confirmed by Raman and AFM measurements. Furthermore, we demonstrate that the optical contrast spectroscopy is sensitive enough to detect the adsorption of a sub-monolayer airborne hydrocarbon molecules, which can reveal whether graphene is con-taminated and opens the opportunity to develop miniaturized and ultrasensitive molecular sensors.