Standards Development

Scope

This part of IEC 62607 establishes two standardized methods to determine the structural key control characteristic (KCC)

– number of layers for graphene-based material prepared by mechanical exfoliation with AB stacking and ABC stacking by

– Raman spectroscopy.

Method A:

– The number of layers of graphene-based material is derived by the Raman lineshape of 2D peak. 

– Method A is applicable to mechanical exfoliated graphene -based material with AB stacking and the number of layers is less than 5.

Its lateral size should be at east 2 μm.

– Method A is applicable to graphene-based material on any substrate.

Method B:

– The number of layers of graphene-based material is derived by intensity ratio IG(Si)/I0(Si), where IG(Si) is the intensity of the Raman peak
of silicon substrate underneath the graphene-based material while I0(Si) is that of bare silicon substrate.

Method B is applicable to mechanical exfoliated and chemical vapor deposition grown graphene - based material with AB stacking and ABC stacking and the number of layers up to 10. Its lateral size should be at least 2 μm.

Method B is applicable to graphene-based material on the oxidized silicon substrate (SiO2 on silicon) with the SiO2 thickness around 90nm ± 5 nm.

Method A and Method B are independent from each other and can be mutually authenticated.

Purpose

Graphene-based two-dimensional materials (carbon-based two-dimensional materials with no more than 10 layers, including graphene, double-layer graphene, few-layer graphene, graphene oxide, etc.) have excellent performance in electrical, optical, mechanical and thermal properties, which has aroused widespread interest in both academic and industrial communities. The number of l ayers of graphene-based materials is a key control characteristic affecting their performance. Therefore, the accurate measurement of the number of layers is one of the core issues in related researches and applications. Raman spectroscopy is a fast, non-destructive and highly sensitive characterization method which has been widely used in the measurement of number of layers in graphene-based materials up to 10 layers. Since the graphene-based materials prepared by the mechanical exfoliation method have specific stacking configuration, the Spectral characteristics of their Raman peaks show certain relationship with the number of layers. For example, the 2D peak of graphene-based materials with AB stacking less than 5 layers has specific and distinctive lineshape, which is related to the number of layers but independent of the substrate. Also the Raman peak intensity of silicon substrate underneath the graphene -based materials with AB stacking and ABC stacking is also related to its number of layers. The inten sity ratio of the IG(Si)/I0(Si) decreases linearly with number of layers, where IG(Si) is Raman peak intensity of silicon substrate underneath the graphene layers while I0(Si) is that of bare silicon substrate. The number of layers up to 10 can be determined accordingly. Therefore, the layer number of graphene -based materials can be accurately measured using only Raman spectroscopy based on these Spectral characteristics.

In recent years many advances have been made to determine of the number of layers of graphene- based materials. However, multiple characterization techniques and criteria need to combined and complement each other to confirm the number of layers. There is no standardized method using Raman spectroscopy individually.

This document provides two independent standardized methods on the measurement of the number of layers of graphene-based material using Raman spectroscopy based on the lineshape of 2D peak (Method A) and intensity ratio of the IG(Si)/I0(Si) (Method B). Method A is applicable fo r the characterization of AB stacking graphene-based materials with less than 5 layers. Method B is valid for AB stacking and ABC stacking graphene-based materials with less than 10 layers. The purpose of this document is to provide scientific and reliable reference and technical guidance for the electronic/electrotechnical products and research of graphene -based materials.

Since graphene-based materials prepared by different methods have great differences in crystallinity and microstructure, any existing characterization method is not universal. In practical applications, it is necessary to comprehensively select the appropriate characterization method (or multiple characterization methods) based on the crystallinity and microstructure characteristics of the graphene-based materials under study