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Register a new userNanoscale Sensing Using Point Defects in Single-Crystal Diamond: Recent Progress on Nitrogen Vacancy Center-Based Sensors
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Individual, luminescent point defects in solids so called color centers are atomic-sized quantum systems enabling sensing and imaging with nanoscale spatial resolution. In this overview, we introduce nanoscale sensing based on individual nitrogen vacancy (NV) centers in diamond. We discuss two central challenges of the field: First, the creation of highly-coherent, shallow NV centers less than 10 nm below the surface of single-crystal diamond. Second, the fabrication of tip-like photonic nanostructures that enable efficient fluorescence collection and can be used for scanning probe imaging based on color centers with nanoscale resolution.
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Detection of AC magnetic fields at the nanoscale is critical in applications ranging from fundamental physics to materials science. Isolated quantum spin defects, such as the nitrogen-vacancy center in diamond, can achieve the desired spatial resolution with high sensitivity. Still, vector AC magnetometry currently relies on using different orientations of an ensemble of sensors, with degraded spatial resolution, and a protocol based on a single NV is lacking. Here we propose and experimentally demonstrate a protocol that exploits a single NV to reconstruct the vectorial components of an AC magnetic field by tuning a continuous driving to distinct resonance conditions. We map the spatial distribution of an AC field generated by a copper wire on the surface of the diamond. The proposed protocol combines high sensitivity, broad dynamic range, and sensitivity to both coherent and stochastic signals, with broad applications in condensed matter physics, such as probing spin fluctuations.
Powered by the mutual developments in instrumentation, materials andtheoretical descriptions, sensing and imaging capabilities of quantum emitters insolids have significantly increased in the past two decades. Quantum emitters insolids, whose properties resemble those of atoms and ions, provide alternative waysto probing natural and artificial nanoscopic systems with minimum disturbance andultimate spatial resolution. Among those emerging quantum emitters, the nitrogen-vacancy (NV) color center in diamond is an outstanding example due to its intrinsicproperties at room temperature (highly-luminescent, photo-stable, biocompatible,highly-coherent spin states). This review article summarizes recent advances andachievements in using NV centers within nano- and single crystal diamonds in sensingand imaging. We also highlight prevalent challenges and material aspects for differenttypes of diamond and outline the main parameters to consider when using color centersas sensors. As a novel sensing resource, we highlight the properties of NV centersas light emitting electrical dipoles and their coupling to other nanoscale dipoles e.g.graphene.
A study of the photophysical properties of nitrogen-vacancy (NV) color centers in diamond nanocrystals of size of 50~nm or below is carried out by means of second-order time-intensity photon correlation and cross-correlation measurements as a function of the excitation power for both pure charge states, neutral and negatively charged, as well as for the photochromic state, where the center switches between both states at any power. A dedicated three-level model implying a shelving level is developed to extract the relevant photophysical parameters coupling all three levels. Our analysis confirms the very existence of the shelving level for the neutral NV center. It is found that it plays a negligible role on the photophysics of this center, whereas it is responsible for an increasing photon bunching behavior of the negative NV center with increasing power. From the photophysical parameters, we infer a quantum efficiency for both centers, showing that it remains close to unity for the neutral center over the entire power range, whereas it drops with increasing power from near unity to approximately 0.5 for the negative center. The photophysics of the photochromic center reveals a rich phenomenology that is to a large extent dominated by that of the negative state, in agreement with the excess charge release of the negative center being much slower than the photon emission process.
The electrical conductivity of a material can feature subtle, nontrivial, and spatially-varying signatures with critical insight into the materials underlying physics. Here we demonstrate a conductivity imaging technique based on the atom-sized nitrogen-vacancy (NV) defect in diamond that offers local, quantitative, and noninvasive conductivity imaging with nanoscale spatial resolution. We monitor the spin relaxation rate of a single NV center in a scanning probe geometry to quantitatively image the magnetic fluctuations produced by thermal electron motion in nanopatterned metallic conductors. We achieve 40-nm scale spatial resolution of the conductivity and realize a 25-fold increase in imaging speed by implementing spin-to-charge conversion readout of a shallow NV center. NV-based conductivity imaging can probe condensed-matter systems in a new regime, and as a model example, we project readily achievable imaging of nanoscale phase separation in complex oxides.
We report an experimental study of the longitudinal relaxation time ($T_1$) of the electron spin associated with single nitrogen-vacancy (NV) defects hosted in nanodiamonds (ND). We first show that $T_1$ decreases over three orders of magnitude when the ND size is reduced from 100 to 10 nm owing to the interaction of the NV electron spin with a bath of paramagnetic centers lying on the ND surface. We next tune the magnetic environment by decorating the ND surface with Gd$^{3+}$ ions and observe an efficient $T_{1}$-quenching, which demonstrates magnetic noise sensing with a single electron spin. We estimate a sensitivity down to $approx 14$ electron spins detected within 10 s, using a single NV defect hosted in a 10-nm-size ND. These results pave the way towards $T_1$-based nanoscale imaging of the spin density in biological samples.
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