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Diamond and Related Materials

Impact of annealing and nanostructuring on properties of NV centers created by different techniques

Miriam Mendoza Delgado, Lucas Tsunaki, Shaul Michaelson, Mohan Kumar Kuntumalla, Johann Peter Reithmaier, A. Hoffman, Boris Naydenov, Cyril Popov

Published Feb 19, 2025• 11 citations
Publisher

Abstract

Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated by electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation. • Comparative study of optical and spin properties of implanted and δ-doped CVD NVs • Impact of structuring with nanopillars and annealing on the NV properties • Fluorescence enhancement factors of above 30 in 100–150 nm diameter pillars • 3-Fold increase in ODMR contrast of all samples after annealing • Increase of coherence and relaxation times after annealing

DOI
10.1016/j.diamond.2025.112126

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Impact of Annealing and Nanostructuring on Properties of NV Centers Created by Different Techniques

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Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated with electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation.

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Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars

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Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

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The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.

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The Nitrogen-Vacancy (NV) color center is a defect of diamond which behaves as an artificial atom hosted in a solid-state matrix. Due to its electron spin properties which can be read-out and manipulated as an elementary quantum system, the NV center has found a wide panel of applications as a qubit for quantum information and as a magnetic field sensor. However these applications require to control the properties of the NV centers and their localization. This doctoral thesis investigates methods allowing us to tailor the properties of NV centers by combining techniques for the implantation of nitrogen atoms and the plasma-assisted (CVD) synthesis of diamond.The manuscript is divided into six chapters. The first chapter summarizes the properties of the NV center which will set our objectives for the NV engineering. The second chapter will describe how arrays of NV centers can be created using Focused Ion Beam implantation. The results open a wide range of applications for the targeted creation of NV centers in diamond structures such as photonic crystals and tips. However the low kinetic energy which is required for achieving implantation within a spot of 10-nm diameter leads to shallow defects which properties are strongly affected by the sample surface. The third chapter investigates how the overgrowth of a diamond layer over implanted NV centers can remove the detrimental influence of the surface. The fourth and fifth chapters describe effective methods for NV center fabrication through the control of the CVD growth conditions of the hosting crystal. Thin layers with high NV doping can be grown and almost perfect control of the orientation of the NV axis can be achieved. With the goal to optimize the spin coherence properties, the sixth chapter investigates how the electron spin of the NV center can be protected from decoherence effects induced by magnetic noise due to the unpolarized spins in the diamond lattice.

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Generation of NV– Centers in Diamond Nanostructures: PL, ODMR, and Spin Coherence

V. P. Popov, Sergey N. Podlesny, V. A. Antonov +3 more

The nanolayers and nanomembranes with the 30–300 thickness and the 0.5 ppm NV– center content were produced by 50 keV $${\text{H}}_{2}^{ + }$$ ion implantation in Ib type (111) diamond plates and vacuum or high pressure annealing with subsequent lift-off process. The similar NV– content nanolayers were formed by N+ ion implantation in IIa type (111) diamond plates and similar annealings. 〈111〉 oriented nanopillars were produced on both types of nanolayers using focused ion beam (FIB) with Ga+ 30 keV maskless milling. The unusual optically detected magnetic resonances (ODMRs) were measured in a single nanopillars with a height of 500‒700 nm and of 250 nm in diameter covered by an amorphous a-C:Ga nanolayer in the 0‒20 G magnetic field. They demonstrated both a significant decrease in the gyromagnetic ratio and the quenching of photoluminescence (PL) signal from the NV– centers inclined to the nanopillar axis by the conductive a‑C:Ga nanolayer and stresses created by it. The multistep O2 RIE plasma etching restored the normal ODMR resonance frequencies and intensities for all four NV–center orientations in (111) diamond nanopillars.

Journal of Surface Investigation X-ray Synchrotron and Neutron Techniques•Apr 1, 2026•0 citations
Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated by electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation. • Comparative study of optical and spin properties of implanted and δ-doped CVD NVs • Impact of structuring with nanopillars and annealing on the NV properties • Fluorescence enhancement factors of above 30 in 100–150 nm diameter pillars • 3-Fold increase in ODMR contrast of all samples after annealing • Increase of coherence and relaxation times after annealing
Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated with electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation.
Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.
The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.
We present the increase in the nitrogen vacancy center concentration in nitrogen delta-doped layers by almost one order of magnitude. To achieve this, we employ a low-pressure, high-temperature annealing step at 1750 °C in vacuum. We demonstrate an enhancement of the photoluminescence intensity of NV centers compared to annealing steps at lower temperatures of 1200 °C. To achieve this, we fabricate nitrogen-doped thin films with a thickness of 50 nm via chemical vapor deposition. We show that the nitrogen is mainly incorporated in a 6 nm thin film at the layer interface. We link the strong enhancement of the NV concentration to a possible decomposition of NVH centers and the mobility of various species at elevated temperatures, including vacancies and nitrogen in these two-dimensional structures. Additionally, after the high temperature annealing, we observe a Hahn-echo spin coherence time of 7.9 μ s, which is in line with literature data on achievable coherence time in highly nitrogen-doped layers. Our results could pave the way for the precise fabrication of improved diamond elements, e.g., used in magnetic field sensors and offer an alternative route to implantation techniques.
The Nitrogen-Vacancy (NV) color center is a defect of diamond which behaves as an artificial atom hosted in a solid-state matrix. Due to its electron spin properties which can be read-out and manipulated as an elementary quantum system, the NV center has found a wide panel of applications as a qubit for quantum information and as a magnetic field sensor. However these applications require to control the properties of the NV centers and their localization. This doctoral thesis investigates methods allowing us to tailor the properties of NV centers by combining techniques for the implantation of nitrogen atoms and the plasma-assisted (CVD) synthesis of diamond.The manuscript is divided into six chapters. The first chapter summarizes the properties of the NV center which will set our objectives for the NV engineering. The second chapter will describe how arrays of NV centers can be created using Focused Ion Beam implantation. The results open a wide range of applications for the targeted creation of NV centers in diamond structures such as photonic crystals and tips. However the low kinetic energy which is required for achieving implantation within a spot of 10-nm diameter leads to shallow defects which properties are strongly affected by the sample surface. The third chapter investigates how the overgrowth of a diamond layer over implanted NV centers can remove the detrimental influence of the surface. The fourth and fifth chapters describe effective methods for NV center fabrication through the control of the CVD growth conditions of the hosting crystal. Thin layers with high NV doping can be grown and almost perfect control of the orientation of the NV axis can be achieved. With the goal to optimize the spin coherence properties, the sixth chapter investigates how the electron spin of the NV center can be protected from decoherence effects induced by magnetic noise due to the unpolarized spins in the diamond lattice.
The nanolayers and nanomembranes with the 30–300 thickness and the 0.5 ppm NV– center content were produced by 50 keV H2+{\text{H}}_{2}^{ + }H2+​ ion implantation in Ib type (111) diamond plates and vacuum or high pressure annealing with subsequent lift-off process. The similar NV– content nanolayers were formed by N+ ion implantation in IIa type (111) diamond plates and similar annealings. 〈111〉 oriented nanopillars were produced on both types of nanolayers using focused ion beam (FIB) with Ga+ 30 keV maskless milling. The unusual optically detected magnetic resonances (ODMRs) were measured in a single nanopillars with a height of 500‒700 nm and of 250 nm in diameter covered by an amorphous a-C:Ga nanolayer in the 0‒20 G magnetic field. They demonstrated both a significant decrease in the gyromagnetic ratio and the quenching of photoluminescence (PL) signal from the NV– centers inclined to the nanopillar axis by the conductive a‑C:Ga nanolayer and stresses created by it. The multistep O2 RIE plasma etching restored the normal ODMR resonance frequencies and intensities for all four NV–center orientations in (111) diamond nanopillars.