Optimized Single-Crystal Diamond Scanning Probes for High Sensitivity Magnetometry

TL;DR

This paper presents optimized single-crystal diamond scanning probes with enhanced photoluminescence collection for high-sensitivity magnetometry, achieved through comprehensive simulations of device geometry and fabrication uncertainties.

Contribution

It introduces a detailed simulation-based optimization of diamond scanning probe geometry, significantly improving photoluminescence collection efficiency for NV-based magnetometry.

Findings

Achieved a 13-fold increase in collectible PL rate over bulk diamond.

Optimized device geometry yields a 1.8-fold improvement over previous designs.

Simulations account for fabrication uncertainties like NV position and taper geometry.

Abstract

The negatively-charged nitrogen-vacancy center (NV) in diamond forms a versatile system for quantum sensing applications. Combining the advantageous properties of this atomic-sized defect with scanning probe techniques such as atomic force microscopy (AFM) enables nanoscale imaging of e.g. magnetic fields. To form a scanning probe device, we place single NVs shallowly (i.e. < 20 nm) below the top facet of a diamond nanopillar, which is located on a thin diamond platform of typically below 1 \mu m thickness. This device can be attached to an AFM head, forming an excellent scanning probe tip. Furthermore, it simultaneously influences the collectible photoluminescence (PL) rate of the NV located inside. Especially sensing protocols using continuous optically-detected magnetic resonance (ODMR) benefit from an enhanced collectible PL rate, improving the achievable sensitivity. This work presents a comprehensive set of simulations to quantify the influence of the device geometry on the collectible PL rate for individual NVs. Besides geometric parameters (e.g. pillar length, diameter and platform thickness), we also focus on fabrication uncertainties such as the exact position of the NV or the taper geometry of the pillar introduced by imperfect etching. As a last step, we use these individual results to optimize our current device geometry, yielding a realistic gain in collectible PL rate by a factor of 13 compared to bulk diamond and 1.8 compared to our unoptimized devices.