Operando Hall Measurement of Covalent Functionalization of a Ag/AgCl Gated Graphene Field Effect Transistor in a Flow Cell

The unique electronic properties of graphene have attracted attention for its applications in sensor technologies. To fully understand and optimize graphene-based sensing and functionalization, it is necessary to quantify the effect of these processes on graphene’s charge carrier density and mobility. Here, we introduce an integrated measurement system that combines Hall effect and field effect measurement techniques with a flow cell, enabling operando, real-time characterization of graphene’s charge carrier density and mobility. The microfluidic cell includes a Ag/AgCl gate electrode, enabling electrolyte gated Hall and field effect measurements, thereby permitting operando monitoring of dynamic processes such as gate-controlled graphene functionalization. Operando measurement of gate-controlled functionalization of graphene with 4-carboxybenzene tetrafluoroborate (CBDT) reveals a real-time decrease of charge carrier mobility with a minimal change in charge carrier density. Our observations are in qualitative agreement with a resonant short-range charge carrier scattering model, appropriate to covalent attachment of CBDT to graphene. Raman spectroscopy independently confirms the covalent attachment of functional groups. The microfluidic Hall measurement technique can be extended to the study of other low-dimensional electronics systems used for sensing liquid phase analytes.