IEC/TS 62607-6-12 Ed. 1.0 En:2024 PDF

This part of IEC TS 62607 establishes a standardized method to determine the key control characteristic
– number of layers
for films consisting of graphene by
– Raman spectroscopy and
– optical reflection.

Criteria for the determination of the number of layers are the G-peak integrated intensity and the optical contrast. Both methods enable to distinguish between graphene and multilayer graphene. However, neither method on its own nor the combination of the two enable a determination of the number of layers in all possible cases (especially regarding all possible stacking angles). But the comparison of the values deduced by each method allows to discriminate whether the determined number of layers is correct and can be specified or not.
– The method is applicable to exfoliated graphene and graphene grown on or transferred to a substrate with a small defect density, low surface contamination (e.g. transfer residue) and number of layers up to 5.
– The method is suitable for the following substrates:
a) glass (soda lime glass or similar with a refractive index between 1,45 and 1,55 at
532 nm);
b) oxidized silicon (SiO2 on silicon, with a SiO2 thickness of 90 nm ± 5 nm).

NOTE 90 nm and 300 nm are the most used SiO2 thicknesses for graphene substrates. Due to the current state of the art, the method can securely be used for 90 nm ± 5 nm thick SiO2 layers and a laser wavelength of 532 nm, but cannot be fulfilled for 300 nm ± 15 nm SiO2 layers even by changing the laser wavelength. It is possible that future editions of IEC TS 62607-6-12 will include thick layers and other substrates also.
– The spatial resolution is in the order of 1 μm given by the spot size of the exciting laser.