Nitrogen-vacancy centers close to surfaces
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ntroduction The precise positioning of defects near semiconductor surfaces is a prerequisite for nanoscale magnetometry (where individual defects are used as atomic-sized magnetic sensors, see Figure 1a), coupling to photonic/plasmonic devices, and for deterministic positioning of qubits to build scalable quantum processors. The first two applications intrinsically require that defects be located near the surface due to physical constraints. In the first, magnetic imaging resolution depends on the sensor-sample distance (in the near field limit) since the magnetic field from single spins decreases as the inverse cube of the separation (Figure 1b). In the second application, efficient optical coupling to plasmonic structures requires that the emitter be located at a distance substantially below the wavelength of light (Figure 1c).1 For the creation of scalable arrays, the restriction to near-surface defects is not a hard limit; however, to date, the most exciting results for controlled implantation and sensing have been obtained with shallow defects.2–6 Nitrogen-vacancy (NV) color centers are particularly interesting in this context owing to the availability of optical readout7,8 of their spin states and the ability to engineer them close to the diamond surface. Such shallow NV centers are of crucial importance for building multi-qubit systems and
sensing applications. Their spin transitions are sensitive to magnetic field fluctuations, and monitoring their energy shifts9,10 or dephasing11 are promising tools for sensing electric and magnetic fields at the nanoscale. This article reviews recent work on the creation of NV centers near the diamond surface and related progress in sensing applications.
Positioning of NV centers near the surface There are currently three avenues for achieving near-surface NV centers: incorporation of a thin layer of NVs into the diamond at the very end of the chemical vapor deposition (CVD) growth process (delta-doping), implantation of nitrogen ions or molecules with low energies, and utilization of small nanodiamonds (see the Introduction article in this issue). Each method has its own advantages and disadvantages. For instance, “as-grown” NV centers created through delta-doping have been shown to possess superior qualities to those created through the damaging implantation processes.12 Here, the defect layer thickness and depth can be remarkably well controlled, and the defect concentration varied over a wide range. However delta-doping only provides control over the NV position in a single dimension; for creation of two-dimensional arrays, implantation using either a focused spot13 or a mask5 is employed (Figure 2a).
Jörg Wrachtrup, Stuttgart University and Max Planck Institute for Solid State Physics; [email protected] Fedor Jelezko, Ulm University; [email protected] Bernhard Grotz, Stuttgart University; [email protected] Liam McGuinness, Ulm University; [email protected] DOI: 10.1557/mrs.2013.22
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