Probing molecular dynamics at the nanoscale via an individual paramagnetic center

TL;DR

This paper introduces a novel pulse protocol using individual NV centers in diamond to observe nanoscale molecular dynamics, revealing insights into surface-bound liquid layers and molecular motions.

Contribution

The study presents a new NV center-based method to probe molecular dynamics at the nanoscale, capable of distinguishing rotational and translational diffusion near surfaces.

Findings

Liquid forms a semi-solid 1.5 nm layer on diamond surface

Translational diffusion is suppressed in the surface layer

Rotational diffusion persists within the semi-solid layer

Abstract

Understanding the dynamics of molecules adsorbed to surfaces or confined to small volumes is a matter of increasing scientific and technological importance. Here, we demonstrate a pulse protocol using individual paramagnetic nitrogen vacancy (NV) centers in diamond to observe the time evolution of 1H spins from organic molecules located a few nanometers from the diamond surface. The protocol records temporal correlations among the interacting 1H spins, and thus is sensitive to the local system dynamics via its impact on the nuclear spin relaxation and interaction with the NV. We are able to gather information on the nanoscale rotational and translational diffusion dynamics by carefully analyzing the time dependence of the NMR signal. Applying this technique to various liquid and solid samples, we find evidence that liquid samples form a semi-solid layer of 1.5 nm thickness on the surface of diamond, where translational diffusion is suppressed while rotational diffusion remains present. Extensions of the present technique could be adapted to highlight the chemical composition of molecules tethered to the diamond surface or to investigate thermally or chemically activated dynamical processes such as molecular folding.