Nano-SQUID magnetometers fabricated with focussed ion beam microstructuring on commercial AFM tips*

Scanning probe microscopy is a helpful tool to study many quantum materials, including 2D van der Waals materials and materials that may be useful for quantum information science. Scanning Superconducting QUantum Interference Devices (SQUIDs) are highly sensitive to magnetic field, enabling insights into magnetism, superconductivity, and current distribution. On-chip planar SQUID designs can be fabricated at wafer scale and are highly reliable and reproducible, but their spatial  resolution is limited to sub-micron scale. Nano-scale SQUIDs on force microscopy tips, sometimes called nano-squids or squid-on-tip, have better spatial resolution but as of yet cannot be fabricated in large reproducible batches.

In this talk I will discuss our efforts in fabricating nano-scale SQUID magnetometers with focussed ion beam microstructuring on AFM cantilevers for nano-scale topographic control. We use Ga FIB to fabricate sub-200 nm SQUID magnetometers on commercial AFM tips in a simple one step process. With nano-scale spatial resolution and topographic control, this tip geometry will enable close surface scanning, especially on uneven surfaces, trenches, mechanically fragile samples like 2D van der Waals layered materials, etc.

Technologically, this nanofabrication method can be applied to develop similar sensors in the future on commercially available AFM probes. E-beam lithography, which is the leading fabrication method for achieving nm scale fab resolution, often requires a multi-step fabrication process and only applies to large planar substrates. Comparatively, this is a much simpler one-step process that is not limited to large planar substrates and is applicable to 3D substrates with variable shapes and dimensions.