Nanoscale magnetic resonance imaging

This part of our research effort is aimed at developing a novel sensing platform for nanoscale spin imaging and spectroscopy (i.e., a form of nanometer-resolution MRI). Building on prior work, the figure below introduces recent experiments with the Wrachtrup group demonstrating the ability to reconstruct the “free-induction-decay” from a small (~100 nm3) ensemble of (unpolarized) protons deposited on the diamond surface. We use this technique to gather valuable information on the nanoscale structure and diffusion dynamics of model fluids in contact with the diamond surface. In particular, we manage to extract the fluid self-diffusion coefficient near the interface and find evidence for the existence of a layer of adsorbed molecules (approximately 2 nm thick). Anticipated extensions articulating the present protocol with NMR-inspired schemes open interesting opportunities for the investigation of chemical or biochemical systems affected by compositional heterogeneity or local aggregation as well as various thermally- or chemically-activated processes.

NV-assisted detection of proton spin resonance at the nanoscale. (a) Pulse sequence integrating optical and microwave control. (b) Experimental setup. (c) Proton spin signal from a 100 nm^3 volume in an organic film overlaid on the diamond crystal. We use a correlation protocol designed to pick-up the random proton spin fluctuations; no nuclear spin polarization or rf manipulation is necessary. The beating results from the precession of proton spins in the applied magnetic field. From Staudacher et al., Nature Commun. (2015).

NV-enabled sensing is not restricted to nuclear spins and extensions to detecting other, “dark” paramagnetic centers are also an important component of the activities we carry out. One example is our work on the detection of P1 centers (i.e., substitutional nitrogen) in a diamond nanocrystal via the use of NVs (Laraoui et al, Nano Letters 2012). Such spins can serve as ‘proxies’ to mediate the interaction between the probe NV and target nuclear spins.