Abstract
Optically detected magnetic resonance using nitrogen-vacancy (NV) colour centres in diamond is a leading modality for nanoscale magnetic field imaging, as it provides single electron spin sensitivity, three-dimensional resolution better than 1 nm (ref. 5) and applicability to a wide range of physical and biological samples under ambient conditions. To date, however, NV-diamond magnetic imaging has been performed using 'real-space' techniques, which are either limited by optical diffraction to ∼250 nm resolution or require slow, point-by-point scanning for nanoscale resolution, for example, using an atomic force microscope, magnetic tip, or super-resolution optical imaging. Here, we introduce an alternative technique of Fourier magnetic imaging using NV-diamond. In analogy with conventional magnetic resonance imaging (MRI), we employ pulsed magnetic field gradients to phase-encode spatial information on NV electronic spins in wavenumber or 'k-space' followed by a fast Fourier transform to yield real-space images with nanoscale resolution, wide field of view and compressed sensing speed-up.
Highlights
Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color centres in diamond is a leading modality for nanoscale magnetic field imaging,[1,2,3] as it provides single electron spin sensitivity,[4] three-dimensional resolution better than 1 nm,[5] and applicability to a wide range of physical[6,7,8] and biological[9] samples under ambient conditions
Key advantages of NV-diamond Fourier magnetic imaging, relative to real-space imaging, are: (i) spatially multiplexed detection,[14] which enhances the signal-to-noise ratio (SNR) for typical NV centre densities; (ii) a high data acquisition rate that can be further boosted with compressed sensing;[15,16] and (iii) simultaneous acquisition of signal from all NV centres in the FOV, which allows probing of temporally correlated dynamics and provides isolation from system drift
NV electronic spin states (Fig. 1c) are optically polarized with green illumination (λ=532 nm), coherently manipulated using resonant microwave fields applied by a microwave loop, and detected via spin-state-dependent fluorescence measurements
Summary
The ground state of the NV centre is a spin-triplet with a 2.87 GHz zero-field splitting between the |0〉 and | ± 1〉 spin states (Fig. 1c). Magnetic field gradients used in the Fourier imaging demonstrations did not significantly affect NV spin coherence properties across the imaging FOV.[30] To fabricate diamond nanopillars, Sample B was spin coated with a 100 nm-thick layer of e-beam resist (XR-1541-006). A tapered-cosine windowing function with taper coefficient set at 0.1 was applied to the k-space data and a symmetric fast Fourier transform algorithm implemented with MATLAB was used to obtain real-space images. The convex optimization routine was implemented using MATLAB library functions made available by CVX Research (www.cvxr.com)
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