Optical tuning of the diamond Fermi level measured by correlated scanning probe microscopy and quantum defect spectroscopy

TL;DR

This study demonstrates that laser-induced oxidation can precisely tune the Fermi level of diamond surfaces, enabling control over quantum defect charge states, with potential applications in quantum technology surface engineering.

Contribution

It introduces a method combining optical oxidation with scanning probe microscopy to control and measure the Fermi level and defect charge states in diamond surfaces.

Findings

Laser oxidation tunes the Fermi level over at least 2.00 eV.

Implanted surfaces oxidize faster than unimplanted surfaces.

KPFM effectively maps surface Fermi level changes at high spatial resolution.

Abstract

Quantum technologies based on quantum point defects in crystals require control over the defect charge state. Here we tune the charge state of shallow nitrogen-vacancy and silicon-vacancy centers by locally oxidizing a hydrogenated surface with moderate optical excitation and simultaneous spectral monitoring. The loss of conductivity and change in work function due to oxidation are measured in atmosphere using conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). We correlate these scanning probe measurements with optical spectroscopy of the nitrogen-vacancy and silicon-vacancy centers created via implantation and annealing 15-25 nm beneath the diamond surface. The observed charge state of the defects as a function of optical exposure demonstrates that laser oxidation provides a way to precisely tune the Fermi level over a range of at least 2.00 eV. We also observe a significantly larger oxidation rate for implanted surfaces compared to unimplanted surfaces under ambient conditions. Combined with knowledge of the electron affinity of a surface, these results suggest KPFM is a powerful, high-spatial resolution technique to advance surface Fermi level engineering for charge stabilization of quantum defects.