title: Toward Optimized Surface δ-Profiles of Nitrogen-Vacancy Centers Activated by Helium Irradiation in Diamond.
abstract: The negatively charged nitrogen-vacancy (NV) center in diamond has been shown recently as an excellent sensor for external spins. Nevertheless, their optimum engineering in the near-surface region still requires quantitative knowledge in regard to their activation by vacancy capture during thermal annealing. To this aim, we report on the depth profiles of near-surface helium-induced NV centers (and related helium defects) by step-etching with nanometer resolution. This provides insights into the efficiency of vacancy diffusion and recombination paths concurrent to the formation of NV centers. It was found that the range of efficient formation of NV centers is limited only to approximately 10 to 15 nm (radius) around the initial ion track of irradiating helium atoms. Using this information we demonstrate the fabrication of nanometric-thin (δ) profiles of NV centers for sensing external spins at the diamond surface based on a three-step approach, which comprises (i) nitrogen-doped epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy helium irradiation and thermal annealing, and (iii) controlled layer thinning by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to 50 μs are demonstrated at depths of less than 5 nm in material with 1.1% of (13)C (depth estimated by spin relaxation (T1) measurements). At the end, the limits of the helium irradiation technique at high ion fluences are also experimentally investigated.
authors.affiliation: 3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.
authors.forename: Felipe
authors.initials: F
authors.lastname: Fávaro de Oliveira
authors.affiliation: 3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.
authors.forename: S Ali
authors.initials: SA
authors.lastname: Momenzadeh
authors.affiliation: 3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.
authors.forename: Denis
authors.initials: D
authors.lastname: Antonov
authors.affiliation: Institute for Quantum Optics, University of Ulm , 89081 Ulm, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Scharpf
authors.affiliation: Institute for Quantum Optics, University of Ulm , 89081 Ulm, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Osterkamp
authors.affiliation: Institute for Quantum Optics, University of Ulm , 89081 Ulm, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Naydenov
authors.affiliation: Institute for Quantum Optics, University of Ulm , 89081 Ulm, Germany.
authors.forename: Fedor
authors.initials: F
authors.lastname: Jelezko
authors.affiliation: 3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.
authors.forename: Andrej
authors.initials: A
authors.lastname: Denisenko
authors.affiliation: 3. Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart , 70569 Stuttgart, Germany.|Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wrachtrup
keywords: Nitrogen-vacancy center; diamond CVD growth; nitrogen δ-doping; plasma etching; spin coherence times; spin−lattice relaxation