Probing aqueous interfaces with spin defects

TL;DR

This paper demonstrates how spin defects in two-dimensional materials can be used as sensitive probes to study the microscopic properties of aqueous interfaces, revealing insights into water and ion dynamics at the nanoscale.

Contribution

It introduces a novel approach combining molecular dynamics and spin dynamics simulations to probe interfacial water properties using quantum sensors.

Findings

Hahn echo coherence time is sensitive to water and ion dynamics.

Interfacial properties depend on temperature and ion type.

Near-surface qubits can reveal microscopic interfacial phenomena.

Abstract

Understanding the physical and chemical properties of aqueous interfaces is important in diverse fields of science, ranging from biology and chemistry to materials science. In spite of crucial progress in surface sensitive spectroscopic techniques over the past decades, the microscopic properties of aqueous interfaces remain difficult to measure. Here we explore the use of noise spectroscopy to characterize interfacial properties, specifically of quantum sensors hosted in two-dimensional materials in contact with water. We combine molecular dynamics simulations of water/graphene interfaces and the calculations of the spin dynamics of an NV-like color center, and we investigate the impact of interfacial water and simple ions on the decoherence time of the defect. We show that the Hahn echo coherence time of the NV center is sensitive to motional narrowing and to the hydrogen bonding arrangement and the dynamical properties of water and ions at the interface. We present results as a function of the liquid temperature, strength of the water-surface interaction, and for varied mono-valent and di-valent ions, highlighting the broad applicability of near-surface qubits to gain insight into the properties of aqueous interfaces.