Microwave method for high-frequency properties of graphene

Graphene is a remarkable material, which is yet to make the transition from unique laboratory phenomenon to useful industrial material. One missing element in the development process is a quick method of quality control of the electrical properties of graphene which may be applied in, or close to, the graphene growth process on an industrial scale. In this study, the authors describe a non-contact method using microwave resonance which potentially solves this problem. They describe the technique, consider its limitations and accuracy and suggest how the method may have future take up.UK NMS Programme, the EU EMRP project ‘GraphOhm’ and ‘MetNEMS’. The EMRP (European Metrology Research Programme

Graphene optical and microwave molecular sensing platforms

The unique electronic and physical structure of graphene is highly sensitive to its surroundings, producing a promising candidate for future sensor technologies. However, graphene responds equally to perturbations at both sides of its interface, such that tuning the chemical potential of the substrate at the graphene-solid interface impacts the sensor response at the graphene-gas/liquid interface. In this work, two distinct non-contact graphene sensing platforms are studied under various ambient conditions to assess their propensity towards molecular sensing. The different spectral enhancement mechanisms of graphene surface enhanced Raman spectroscopy platforms are studied through interfacing graphene to differently treated gold nanodisc substrates. Using statistical Raman analysis, the influence of the chemical enhancement mechanism with respect to the graphene Raman peaks is assessed. Moreover, Kelvin force microscopy shows that the locally enhanced electromagnetic field can induce surface chemical reactions which are dependent upon the sensor environment. Explicitly, laser illumination in an air/nitrogen ambient, p-/n-dopes the graphene sheet by -0.87 0.05 meV/ +0.75 0.07 meV. By measuring the change of resistivity of graphene upon gas adsorption using a microwave dielectric resonator, a contactless non-invasive gas sensing platform is demonstrated. This large area graphene measurement platform allows evaluation of the real time sorption processes of NO2 with graphene. Using a modified Langmuir adsorption model, the sticking coefficient is exponentially dependent upon NO2 occupancy. Consequently, the possible variation of the NO2 binding energy, which is frequently considered as the main parameter, plays only a secondary role compared to the rising adsorption energy barrier with increasing NO2 coverage. Finally, through preliminary temperature and electrical gating measurements the charge transfer affinity of graphene based NO2 sensors is explored. Interestingly, the sensor response can be hindered and/or enhanced by back gate control of the doping in graphene.Open Acces