Good Practice Guide on the electrical characterisation of graphene using non-contact and high throughput methods

The electrical characterisation of graphene, either in plane sheets or in properly geometrised form can be approached using non-contact methods already employed for thin film materials. The extraordinary thinness (and, correspondingly, the volume) of graphene, however, makes the proper application of these methods difficult. The electrical properties of interest (sheet electrical resistivity/conductivity, concentration and mobility of charge carriers) must be indirectly derived from the measurement outcome by geometrical and electrical modelling; the assumptions behind such models (e.g., uniformity and isotropy, effective value of the applied fields, etc.) require careful consideration. The traceability of the measurement to the International System of units and a proper expression of measurement uncertainty is an issue. This guide focuses on non-contact and high-throughput methods, that are methods where the graphene sample surface is not physically contacted with any metallic electrodes at any stage. A companion guide about contact methods is also available. The methods discussed are: Measurement of surface potential and work function using Scanning Kelvin Probe Microscopy (SKPM); Measurement of sheet resistance by Microwave Resonant Cavity; Measurement of sheet resistance by Terahertz time-domain spectroscopy (THz-TDS); For each method, a corresponding measurement protocol is discussed, which describes: The measurement principle; Sample requirements and preparation; A description of the measurement equipment / apparatus; Calibration standards and ways to achieve a traceable measurement; Environmental conditions to be considered; A detailed measurement procedure, with specific hints to achieve a reliable measurement; Modeling and data analysis to determine the electrical property of interest; Considerations about the expression of measurement uncertainty.