Diamond Surface Functionalization via Visible Light-Driven C-H Activation for Nanoscale Quantum Sensing

TL;DR

This paper introduces a visible light-driven method for functionalizing diamond surfaces at the nanoscale, enabling improved NV center-based quantum sensing of single molecules without harsh chemical treatments.

Contribution

A novel ambient-condition surface functionalization technique using visible light to activate C-H bonds on single-crystal diamond surfaces, compatible with long-coherence NV centers.

Findings

Functionalization preserves NV spin coherence times.

Enables detection of nuclear spins from surface-attached molecules.

Compatible with high-quality single-crystal diamond surfaces.

Abstract

Nitrogen-vacancy centers in diamond are a promising platform for nanoscale nuclear magnetic resonance sensing. Despite significant progress towards using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. NV molecular sensing requires that target molecules are immobilized within a few nanometers of NV centers with long spin coherence time. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be more readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown to be compatible with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C-H bonds on single-crystal diamond surfaces under ambient conditions using visible light. This functionalization method is compatible with charge stable NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof of principle, we use shallow ensembles of NV centers to detect nuclear spins from functional groups attached to the surface. Our approach to surface functionalization based on visible light-driven C-H bond activation opens the door to deploying NV centers as a broad tool for chemical sensing and single-molecule spectroscopy.