General Characterization of Graphene

The following describes examples of graphene produced by General Graphene. In this case the sample substrate is copper with different characteristics. The graphene is characterized in terms of crystal size, coverage, defect density and multilayer coverage.

All our graphene is characterized in our laboratory using optical microscopy, Scanning Electron Microscopy, Raman Spectroscopy and four-point probes measurements.

A summary of our graphene selection is given in the table below and detailed in the following document.

Summary of Graphene Characteristics

*Note that the values below are of a range of properties measured on products made for different customers. General Graphene manufactures application specific graphene sheets, designed for the unique performance needs of the customer. We do not offer standard products.

Example of Graphene Measurements

Crystal size5 - 30 μm
CoverageTypically >98%
Multilayer coverage<10% - <5%
2D width average (Graphene on Si/SiO₂)35 cm-1
2D/G Intensity ratio (Graphene on Si/SiO₂)2.2
D/G Intensity ratio (Graphene on Si/SiO₂)<0.1

Optical Microscopic Images

Below are optical microscope images of graphene grown on copper showing typical examples of the high-coverage graphene coated copper currently supplied to industry.

Optical image of high coverage graphene on copper:

Optical image of low coverage graphene on copper showing graphene crystals:

Optical image of high coverage graphene after transfer to SiO2/Si substrate:

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/SiO substrate. The Raman data of graphene transferred to Si/SiO 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:

Sheet Resistance Range

Our graphene is characterized using four-point probe to evaluate electrical conductivity.

Below are Sheet resistance ranges for graphene after transfer to SiO2/Si substrate using wet etching transfer method.

SEM images of high coverage monolayer graphene on copper

Shows high monolayer coverage with multilayer presence on the surface.