Graphene layer number characterization using scanning kelvin probe force microscopy

As the importance of material surfaces and interfaces for industrial applications is ever increasing, a need for accurate measurement of their properties and functionalities with traceability and reproducibility through unbroken chain of measurements and their reference materials for proficiency testing has become very important. Carbon and its allotropes have several industrial applications and recently graphene which is a two dimensional layered material of carbon has proven to have great potential, and its characterization for layer number has become very important. A need for quantitative measurement apart from existing qualitative techniques is very much required for accurate determination of layer number. Under the aegis of Versailles Project on Advanced Materials and Standards (VAMAS), technical working area (TWA-2) an international round robin test is conducted among 13 laboratories for establishing a protocol for accurate measurement of graphene layer number and generating reference material. CSIR-NPL being NMI of India participated and contributed to the project which got recognition from VAMAS for its participation. Scanning Kelvin Probe Force Microscopy (SKPFM) of graphene layers on Au/SiO2/Si and SiO2/Si substrates is performed and their CPD data is compared. Graphene on Au/SiO2/Si has shown consistent CPD data for different modulation voltages with least uncertainty. From the comparative analysis it is found that SKPFM has potential to be an international standard technique to determine graphene layer number and can generate certified reference material.