Direct Optical Characterization of Graphene Growth and Domains on Growth Substrates

Abstract

We detailed a facile detection technique to optically characterize graphene growth and domains directly on growth substrates through a simple thermal annealing process. It was found that thermal annealing transformed the naked Cu to Cu oxides while keeping graphene and graphene-covered Cu intact. This increases the interference color contrast between Cu oxides and Cu, thus making graphene easily visible under an optical microscope. By using this simple method, we studied the factors that affect graphene nucleation and growth and achieved graphene domains with the domain size as large as ~100 μm. The concept of chemically making graphene visible is universal, as demonstrated by the fact that a solution process based on selective H2O2 oxidation has been developed to achieve the similar results in a shorter time. These techniques should be valuable for studies towards elucidating the parameters that control the grains, boundaries, structures and properties of graphene.

Role of residual polymer on chemical vapor grown graphene by Raman spectroscopy

“…As shown in Fig. 1A, optical microscope (OM) image clearly shows HGG after oxidizing the underlying Cu strip at 160°C for 6 min [27]. The average length of HGG was about 25 lm.…”

“…2. In order to visualize the graphene layer, the graphene-grown copper sample was optionally oxidized at $165°C for 6 min on a hot plate in an ambient atmosphere [27].…”

Comparison of graphene growth on arbitrary non-catalytic substrates using low-temperature PECVD

“…In order to verify complete coverage of graphene, Cu samples were heated at 180°C in ambient conditions for 30 min. Graphene, which acts as a passivation barrier, prevents the oxidation of Cu [24] (see Supporting Information for full description of heating test and XPS studies). The heating test was performed on all Cu samples and it was found that even 5 min of growth prevents Cu oxidation, indicating complete coverage of graphene on Cu.…”

Polycrystalline graphene and other two-dimensional materials

“…For example, Kim et al developed a simple method to visualize graphene grains and GBs by imaging the birefringence of a graphene surface covered with nematic liquid crystals, taking advantage of the orientation of the liquid crystals with the underlying graphene lattice (thus mapping the graphene grains and GBs to those of the corresponding liquid crystal domains) 96 . Using optical microscopy, one can also enhance the contrast of grains and make GBs more visible by taking advantage of the more effective oxidation of substrate (Cu) in the region exposed or under GBs (which can be further functionalized to facilitate oxidation) 97,98 . Similar techniques can also be used to facilitate AFM and other types of GB imaging 99 .…”