Extension of nuclear magnetic resonance (NMR) to nanoscale samples has been a longstanding challenge because of the insensitivity of conventional detection methods. We demonstrated the use of an individual, near-surface nitrogen-vacancy (NV) center in diamond as a sensor to detect proton NMR in an organic sample located external to the diamond. Using a combination of electron spin echoes and proton spin manipulation, we showed that the NV center senses the nanotesla field fluctuations from the protons, enabling both time-domain and spectroscopic NMR measurements on the nanometer scale.

We show that electric field noise from surface charge fluctuations can be a significant source of spin decoherence for near-surface nitrogen-vacancy (NV) centers in diamond. This conclusion is based on the increase in spin coherence observed when the diamond surface is covered with high-dielectric-constant liquids, such as glycerol. Double resonance experiments show that improved coherence occurs even though the coupling to nearby electron spins is unchanged when the liquid is applied. Multipulse spin echo experiments reveal the effect of glycerol on the spectrum of NV frequency noise. 2The negatively charged nitrogen-vacancy (NV) center in diamond is attracting great interest as an atomic-size quantum sensor that is operable at room temperature and has a convenient readout via optical fluorescence. NV centers are finding wide ranging applications due to their responsiveness to local magnetic [1,2], electric [3,4], strain [5,6] and temperature fields [7,8]. In most cases, the sensitivity of the NV center is critically dependent on the long quantum coherence time of its spin state, which in bulk diamond can be greater than 1 ms at room temperature [9].In many nanoscale sensing applications the NV center must be located as close to the surface as possible in order to maximize the detected signal [10][11][12][13][14]. Unfortunately, significant impairment of the spin coherence has been found for NV centers located within a few nanometers of the diamond surface [15][16][17][18]. In the NV-diamond research community, this near-surface decoherence is commonly attributed to magnetic noise emanating from unpaired electron spins in surface dangling bonds [15][16][17][18][19].In this paper we present evidence that near-surface NV decoherence is not solely due to magnetic noise, but instead can be dominated by electric field noise from surface charge fluctuations. This finding is based on the improvement of coherence seen when high-dielectric-constant liquids are applied to the diamond surface. For example, when the diamond is immersed in glycerol, we have found that Hahn echo 2 T times can increase by more than a factor of four. To rule out the influence of magnetic noise due to surface spins, we directly probed the surface electron spin density with a double resonance experiment and found no significant change upon application of the glycerol. With simple electrostatic calculations, combined with the known NV spin Hamiltonian, we show that decoherence due to charge fluctuations is physically reasonable. Finally, we use the results from multipulse dynamic decoupling experiments to estimate the spectral density of the NV frequency noise.Our experiments were performed using an electronic grade (100)-oriented diamond substrate that was capped with a 50 nm thick layer of isotopically pure carbon-12 diamond. Near-surface NV centers were created by 15 N ion implantation at 2.5 keV, followed by annealing in vacuum at 850°C, acid cleaning and heating to 425°C in a pure oxygen atmosphere [20]. This process results in NV c...

Magnetic resonance imaging, with its ability to provide three-dimensional, elementally selective imaging without radiation damage, has had a revolutionary impact in many fields, especially medicine and the neurosciences. Although challenging, its extension to the nanometre scale could provide a powerful new tool for the nanosciences, especially if it can provide a means for non-destructively visualizing the full three-dimensional morphology of complex nanostructures, including biomolecules. To achieve this potential, innovative new detection strategies are required to overcome the severe sensitivity limitations of conventional inductive detection techniques. One successful example is magnetic resonance force microscopy, which has demonstrated three-dimensional imaging of proton NMR with resolution on the order of 10 nm, but with the requirement of operating at cryogenic temperatures. Nitrogen-vacancy (NV) centres in diamond offer an alternative detection strategy for nanoscale magnetic resonance imaging that is operable at room temperature. Here, we demonstrate two-dimensional imaging of (1)H NMR from a polymer test sample using a single NV centre in diamond as the sensor. The NV centre detects the oscillating magnetic field from precessing protons as the sample is scanned past the NV centre. A spatial resolution of ∼12 nm is shown, limited primarily by the scan resolution.