General Characterization of Graphene

Optical Microscope Images

Graphene crystal size and surface coverage are well known to be key factors in the graphene performance for any application. For that reason, General Graphene has developed the capability to tune the crystal size from a few tens of micrometers to more than 1 mm, while achieving a graphene coverage higher than 98%.

Below are optical microscope images of graphene grown on copper with various graphene crystal sizes. Also shown, are typical examples of the high-coverage graphene coated copper currently supplied to industry.

Optical images showing graphene crystal sizes higher than 1mm:
Graphene crystal sizes > 1mm
Optical images showing graphene crystal sizes higher than 500 μm:
Optical images showing graphene crystal sizes higher than 100 μm:
Optical image of graphene with crystal size lower than 60 μm:
Optical image of high coverage graphene on copper:

Raman Spectroscopy

Graphene defect levels are evaluated using Raman Spectroscopy. This technique is sensitive to changes on the atomic scale and is useful for the study of disorder in graphene films. At General graphene Raman spectroscopy is performed using InVia Renishaw Raman microscope equipped with 50x and 100x·objectives with 514.5 nm laser excitation on 1800-line grating.

Below is shown Raman spectra of graphene grown on copper and an example of graphene transferred to Si/SiO2 substrate. The Raman data of graphene transferred to Si/SiO2 is used to deduce D/G and 2D/G intensity ratios and 2D width. This helps determine graphene properties in terms of defects and monolayer coverage.

Raman spectra of graphene on copper:

The Raman spectra of graphene on copper are not homogeneous. This is due to the underlying polycrystalline copper substrate. Once transferred to Si/SiO2 substrates, the typical Raman spectrum of graphene transferred on Silicon are shown below:

Typical Raman spectrum of monolayer graphene transferred to SiO2/Si wafer:
Multilayer graphene spots may be present on the surface as detected by the Raman spectra:

Scanning Electron Microscopy (SEM)

Our graphene solutions are imaged using Scanning Optical Microscopy to observe crystal homogeneity in terms of monolayer coverage and the presence of defects.

Below are SEM images of high coverage monolayer graphene on copper and graphene crystals grown on copper.

SEM images of high coverage monolayer graphene on copper (top)
SEM images of graphene crystal on copper (bottom)

Sheet Resistance using Four-Point Probes measurement:

The four-point probe measurement is used to evaluate sheet resistance of graphene. Below is a selection of monolayer and multilayer graphene transferred to polyethylene terephthalate (PET) transparent substrates, with the corresponding sheet resistance. These values are for undoped samples.

Reference PET

1 Layer Graphene

5 Layer Graphene

10 Layer Graphene

Sheet resistance Ω/sq. (undoped)
O.L. (∞) 635 120 55
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