Chemical Vapour Deposition Graphene Hall Probes for High Resolution Scanning Hall Probe Microscopy

Scanning Hall probe microscopy (SHPM) is a non-invasive, quantitative magnetic imaging technique which involves rastering a Hall sensor over a surface to generate a magnetic field map of the sample, as shown in figure 1(a). However, current SHPM systems are reliant on GaAs heterostructure Hall sensors that exhibit outstanding figures-of-merit at low temperatures, but show very poor performance at room temperature. This prevents the technique from being applied under ambient conditions in contemporary industrial and research applications, where the rapid miniaturisation and evolution of modern technologies has created a demand for higher spatial resolution, better sensitivity and lower minimum detectable fields.

We report our recent progress in the development of nanoscale Hall sensors for the next generation of ambient SHPMs that exploit graphene's very high carrier mobility and low carrier density. We demonstrate that chemical vapour deposited graphene is an ideal candidate for such sensors, which surpass all figures-of-merit for Hall sensors based on alternative materials. Our smallest sub-100nm sensors are capable of attaining room temperature minimum detectable fields in the µT/Hz range. We demonstrate the performance of graphene-based SHPMs at room temperature, opening the door to their use in a wide range of new applications. These include, but are by far not limited to, evaluating the effectiveness of vortex pinning in high temperature superconducting tapes, investigating and understanding the behavior of next generation data storage and logic devices based on magnetic skyrmions as well as their use in non-destructive, process control of additive manufacturing technologies, such as powder bed fusion processes, through scanning susceptometry.