Graphene Sensor for Monitoring Electric Charges and Binding Energies on Dielectric Surfaces in Cryogenic Liquids

Dielectric surface charging in cryogenic environments can cause unwanted systematic effects in precision experiments such as the search for a neutron electric dipole moment (nEDM), where unstable or non-uniform electric fields can limit sensitivity. Motivated by these effects, we present experimental studies of charge generation, adsorption, and recombination on polymethyl methacrylate (PMMA) surfaces immersed in liquid nitrogen. Using the electro-optical Kerr effect, we measure field-induced ellipticities to track surface charge dynamics on PMMA, identifying a characteristic binding energy of approximately 0.12 meV and a threshold reversal field near 3 kV/cm—parameters that quantify the strength of surface charge trapping and the field required for recombination. To advance these studies, we are developing a graphene-based field-effect sensor capable of directly detecting electric charge accumulation in real time at cryogenic liquids. Graphene's high carrier sensitivity, low noise, and single-atomic thickness make it uniquely suited for probing charge transfer on dielectric surfaces. This device enables in-situ characterization of ion/electron adsorption and desorption processes, providing new insight into charge stability and control in low-temperature dielectric systems.