In-Liquid Dual-Harmonic KPFM for the Study of Electronic Properties of Single Layer Graphene

Graphene, a biocompatible 2D material with unique properties – electrical, optical, mechanical and chemical- is widely investigated as a key part of electronic devices aimed to perform in the biomedical field. More specifically, electrodes and transistors are fabricated using graphene as the active material for sensing and brain activity recording, among other applications^1,2.<br/>Dual-Harmonic Kelvin probe force microscopy (DH-KPFM) is used in this work to measure the work function of chemically-grown single layer graphene, deposited on different substrates, in contact with an aqueous electrolyte to evaluate its dependence on the electronic nature of the substrate, the pH and the ion strength of the electrolyte. In-liquid DH-KPFM is also used in this project to obtain information about the surface potential distribution along a device (graphene transistor) in a liquid environment, and the measurement of the contact resistance values in that media. Contact resistance in graphene transistors affects its performance and is caused, among other parameters, by the work function differences between graphene and the contacting metals³. Knowing the values of the contact resistance of a standard fabricated device will enable the optimization of the fabrication procedure. To the best of our knowledge, this parameter has never been measured using in-liquid DH-KPFM. Hence, the novelty of this work and its contribution to the field is remarkable.<br/>Other techniques such as Raman spectroscopy, electrochemical impedance spectroscopy, X-ray and ultraviolet photoelectron spectroscopy complement the experimental work, providing information about graphene’s doping level and its dependence on the ionic environment and the substrate; furthermore, we will also discuss the effect of chemical residues present on the graphene surface.<br/><br/><b>References</b><br/>Masvidal-Codina, E., Illa, X., Dasilva, M., et al (2019) High-resolution mapping of infraslow cortical brain activity enabled by graphene microtransistors, Nature Mater.<br/>Garcia-Cortadella, R., Schwesig, G., Jeschke, C., et al (2021) Graphene active sensor arrays for long-term and wireless mapping of wide frequency band epicortical brain activity, Nat Commun.<br/>F. Giubileo, A. Di Bartolomeo (2017) The role of contact resistance in graphene field-effect devices, Prog. Surf. Sci.