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Journal of Physics D Applied Physics

Screening and engineering of colour centres in diamond

Tobias Lühmann, Nicole Raatz, Roger John, Margarita Lesik, Jasper Rödiger, Marc Portail, Dominik Wildanger, Felix Kleißler, K. Nordlund, Alexander M. Zaitsev, Jean-François Roch, Alexandre Tallaire, Jan Meijer, Sébastien Pezzagna

Published Sep 7, 2018• 92 citations
Publisher

Abstract

Abstract We present a high throughput and systematic method for the screening of colour centres in diamond with the aim of searching for and reproducibly creating new optical centres down to the single defect level, potentially of interest for a wide range of diamond-based quantum applications. The screening method presented here should, moreover, help to identify some already indexed defects among hundreds in diamond (Zaitsev 2001 Optical Properties of Diamond (Berlin: Springer)) but also some promising defects of a still unknown nature, such as the recently discovered ST1 centre (Lee et al 2013 Nat. Nanotechnol . 8 487; John et al 2017 New J. Phys . 19 053008). We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage of addressing single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of producing intrinsic defects. The implanted samples are annealed in vacuum at different temperatures (between 600 °C and 1600 °C with 200 °C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, re-formation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (such as the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of the vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to sub-diffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted for reference, taking advantage of the considerable knowledge on NV centres as a versatile sensor in order to retrieve or deduce the conditions and local environment in which the different implanted chemical elements are embedded. We show here the preliminary promising results of a long-term study and focus on the elements O, Mg, Ca, F and P from which fluorescent centres were found.

DOI
10.1088/1361-6463/aadfab

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Abstract We present a high throughput and systematic method for the screening of colour centres in diamond with the aim of searching for and reproducibly creating new optical centres down to the single defect level, potentially of interest for a wide range of diamond-based quantum applications. The screening method presented here should, moreover, help to identify some already indexed defects among hundreds in diamond (Zaitsev 2001 Optical Properties of Diamond (Berlin: Springer)) but also some promising defects of a still unknown nature, such as the recently discovered ST1 centre (Lee et al 2013 Nat. Nanotechnol . 8 487; John et al 2017 New J. Phys . 19 053008). We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage of addressing single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of producing intrinsic defects. The implanted samples are annealed in vacuum at different temperatures (between 600 °C and 1600 °C with 200 °C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, re-formation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (such as the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of the vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to sub-diffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted for reference, taking advantage of the considerable knowledge on NV centres as a versatile sensor in order to retrieve or deduce the conditions and local environment in which the different implanted chemical elements are embedded. We show here the preliminary promising results of a long-term study and focus on the elements O, Mg, Ca, F and P from which fluorescent centres were found.
A huge variety of optical colour centres can be found in diamond, emitting in its whole wide transparency range. Although several of these centres have been demonstrated as single-photon emitters, none of them meets all of the requirements of an ideal single-photon source. In this view, we discuss the properties of prominent optical centres, such as the nitrogen vacancy, the silicon vacancy or the so-called NE8 centre, as well as recently found centres ascribed to defects containing Ni, Si, Cr and Xe. Besides suitable intrinsic properties, it is necessary for practical applications that optical centres can be created artificially on demand. Of all known methods, only ion implantation allows for the most controlled creation of such defect centres. In this paper, we discuss how nanoscalability, that is, the nanometre placement and the deterministic creation of optical centres, can, could or cannot be achieved by the available ion implantation techniques. A fine analysis of individual optical centres is now possible, thanks to the recently developed subdiffraction optical microscopy methods.
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.
Colour centres in diamonds represent one of the most actively researched areas in the field of quantum technologies. In this work, we investigate a specific colour centre based on sodium (Na), selected due to promising theoretical predictions suggesting its potential for various quantum applications, despite the current lack of experimental studies. To explore this centre, we conducted two complementary experiments at ISOLDE/CERN. First, we employed the electron emission channeling (EC) technique to determine the most probable lattice sites occupied by sodium in a single-crystal lattice of a diamond implanted with radioactive 24Na. We then used a photoluminescence (PL) set-up to obtain the emission spectrum of a similar sample implanted with stable 23Na. EC measurements revealed that sodium likely adopts a combination of substitutional (S) and bond-centre (BC) sites, maximised after an annealing temperature of 600°C, exhibiting approximately 51% NaV split-vacancy (the highest fraction observed) and 17% substitutional Na (which increases slowly and almost linearly with annealing temperature). However, at higher annealing temperatures, the BC configuration decreases rapidly, and the combined fraction of these two sites also drops, suggesting the emergence of another, yet unidentified, configuration. In the PL experiments, we did not observe a direct optical signal attributable to sodium, but we present the optical characterisation of single-crystal diamond samples fabricated by Element Six and implanted with stable sodium at different annealing temperatures. We found the 3H centre consistently present across nearly all samples followingimplantation and annealing, with its zero-phonon line (ZPL) located around 503 nm.
Colour centre defects in diamond are promising candidates for many quantum technologies because they act as isolated two level systems in the solid-state that can be controlled and read-out through photonics [1][2][3]. Realisation of these technologies requires the placement of many highly coherent centres in a regular array with high positional accuracy and high fabrication yield [4]. Previous fabrication techniques have lacked the ability to produce high yields with high positional accuracy without causing irreparable damage to the lattice which reduced the quality of the spin and optical properties [5]. Ultra-fast laser writing has been shown to produce highly coherent nitrogen vacancy (NV) colour centres within the diamond lattice with positional accuracies of order hundreds of nanometers and a stochastic yield. In this case, the yield and positional accuracy is held back by the need to thermally anneal the diamond within a furnace to convert laser generated defects into colour centres; a fabrication step in which there is little to no control over individual site [6]. In this thesis, the ultra-fast pulsed laser writing technique is broached in detail from both a theoretical and experimental standpoint. The theory behind the highly non-linear light-matter interactions is studied and a hypothesis is developed for the energy transfer between photo-excited carriers and the lattice via the non-radiative recombination of self-trapped multi-excitonic states [7]. In addition, this thesis presents an expansion on the laser writing of colour centres through broaching the generation of different colour centres that have some preferential properties over the NV [8], and the development of a new engineering technique involving a local laser anneal [9]. The yield of generated centres is increased from stochastic to deterministic by replacing the global thermal anneal with the local laser anneal in combination with a fluorescence feedback mechanism. In addition, the use of the laser to locally anneal generated centres leads to a factor of five improvement in the positional accuracy due to the highly non-linear interaction of the laser with the material. These results culminate in a key step forward in the development of a large scale quantum device and improved understanding of the highly dynamical processes that occur upon femtosecond laser interaction with a wide bandgap material.
Abstract The negatively charged nitrogen-vacancy centre (so-called NV-centre) in diamond is one of the most promising systems for applications in quantum technologies because of the possibility to optically manipulate and read out the spin state of this defect, even at room temperature. Nevertheless, obtaining high NV densities (>500 ppb) close to the surface (5–20 nm) while maintaining good spin properties remain challenging. In this work we rely on a versatile ion implantation system allowing both implanting nitrogen using N 2 + and creating vacancies with He + ion bombardment at variable energies and fluence to create shallow NV ensembles. By optimizing the ion irradiation conditions as well as the surface preparation prior to treatment we successfully increase the amount of created colour centres while demonstrating narrow magnetic resonance linewidths.
Abstract Spin-photon interfaces based on group-IV colour centres in diamond offer a promising platform for quantum networks. A key challenge in the field is realising precise single-defect positioning and activation, which is crucial for scalable device fabrication. Here we address this problem by demonstrating a two-step fabrication method for tin vacancy (SnV−) centres that uses site-controlled ion implantation followed by local femtosecond laser annealing with in-situ spectral monitoring. The ion implantation is performed with sub-50 nm resolution and a dosage that is controlled from hundreds of ions down to single ions per site, limited by Poissonian statistics. Using this approach, we successfully demonstrate site-selective creation and modification of single SnV− centres. Our in-situ spectral monitoring opens a window onto materials tuning at the single defect level, and provides new insight into defect structures and dynamics during the annealing process. While demonstrated for SnV− centres, this versatile approach can be readily generalised to other implanted colour centres in diamond and wide-bandgap materials.