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arXiv:1901.05728

Surface coating with oxide layers to enhance the spin properties of shallow NV centers in diamond

Wenlong, Zhang, Shengran, Lin, Jian, Zhang, Zhao Jiaxin, Yuanjie, Yang, Changfeng Weng, Haolei, Zhou, Liren Lou, Wei Zhu, Wang Guanzhong

Published Jan 17, 2019• 1 citation
arXivHTMLPDF

Abstract

We present an enhancement of spin properties of the shallow (<5nm) NV centers by using ALD to deposit titanium oxide layer on the diamond surface. With the oxide layer of an appropriate thickness, increases about 2 up to 3.5 times of both relaxation time and evolution time were achieved and the shallow NV center charge states stabilized as well. Moreover, the coherence time kept almost unchanged. This surface coating technique could produce a protective coating layer of controllable thickness without any damages to the solid quantum system surface, making it possible to prolong T1 time and T2* time, which would be a possible approach to the further packaging technique for the applicating solid quantum devices.

DOI
10.48550/arxiv.1901.05728

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We present an enhancement of spin properties of the shallow (<5nm) NV centers by using ALD to deposit titanium oxide layer on the diamond surface. With the oxide layer of an appropriate thickness, increases about 2 up to 3.5 times of both relaxation time and evolution time were achieved and the shallow NV center charge states stabilized as well. Moreover, the coherence time kept almost unchanged. This surface coating technique could produce a protective coating layer of controllable thickness without any damages to the solid quantum system surface, making it possible to prolong T1 time and T2* time, which would be a possible approach to the further packaging technique for the applicating solid quantum devices.
We present an enhancement of the fluorescence of shallow (<10 nm) nitrogen-vacancy (NV−) centers by using atomic layer deposition to deposit titanium oxide layers on the diamond surface. In this way, the shallow NV− center charge states were stabilized, leading to the increasing fluorescence intensity of about 2 times. This surface coating technique could produce a protective layer of controllable thickness without any damages to the solid-state quantum system surface, which might be an approach to the further passivation or packaging techniques for the solid-state quantum devices.
Nitrogen-vacancy (NV) centers in diamond are utilized extensively as quantum sensors for imaging fields at the nanoscale. The ultrahigh sensitivity of NV magnetometers has enabled the detection and spectroscopy of individual electron spins, with potentially far-reaching applications in condensed matter physics, spintronics, and molecular biology. However, the surfaces of these diamond sensors naturally contain electron spins, which create a background signal that can be hard to differentiate from the signal of the target spins. In this study, we develop a surface modification approach that eliminates the unwanted signal of these so-called dark electron spins. Our surface passivation technique, based on coating diamond surfaces with a thin titanium oxide ( Ti O 2 ) layer, reduces the dark spin density. The observed reduction in dark spin density aligns with our findings on the electronic structure of the diamond- Ti O 2 interface. The reduction, from a typical value of 2000 μ m − 2 to a value below that set by the detection limit of our NV sensors ( 200 μ m − 2 ), results in a twofold increase in Hahn-echo coherence time of near surface NV centers. Furthermore, we derive a comprehensive spin model that connects dark spin relaxation with NV coherence, providing additional insights into the mechanisms behind the observed spin dynamics. Our findings are directly transferable to other quantum platforms, including nanoscale solid-state qubits and superconducting qubits.
We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 to 100 nm display long spin coherence times, T2 > 100 μs at d = 5 nm and T2 > 600 μs at d ≥ 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.
The ability to control the charge and spin states of nitrogen-vacancy (NV) centers near the diamond surface is of pivotal importance for quantum applications. Hydrogen-terminated diamond is promising for long spin coherence times and ease of controlling the charge states due to the low density of surface defects. However, it has so far been challenging to create negatively charged single NV centers with controllable spin states beneath a hydrogen-terminated surface because atmospheric adsorbates that act as acceptors induce surface holes. In this study, we optically detected the magnetic resonance of shallow single NV centers in hydrogen-terminated diamond through precise control of the nitrogen implantation fluence. Furthermore, we found that the probability of detecting the resonance was enhanced by reducing the surface acceptor density through passivation of the hydrogen-terminated surface with hexagonal boron nitride without air exposure. This control method opens up new opportunities for using NV centers in quantum applications.
Nitrogen vacancy (NV) color centers in diamond have shown great potential for various applications in quantum technology due to their long coherence times, high sensitivity to magnetic fields and atomic scale resolution. However, one major challenge in utilizing near surface NV centers is the decoherence caused by spins and charges fluctuating on the surface, which affects the spin properties of the sensors. To reduce the induced noise, various oxygen surface treatments such as low power oxygen plasma treatment and annealing under oxygen atmosphere have been explored to terminate the diamond surface and reduce its impact on NV coherence. We showed that the NV center’s coherence time can be enhanced up to a factor of 3 over a large spectral range of noise. Double electron–electron resonance measurements revealed an extra source of decoherence, scaling similarly as the P1 spin bath. The improvement in coherence times is accompanied with an increase in measured ketone/ether content and reduction of sp2 signal in x-ray photoelectron spectroscopy measurements. Finally we compared the performance of different NV ensembles and surface treatments for sensing external proton spins. The oxygen annealing is an effective procedure of enhancing the spin coherence times and reducing broad band spin noise experienced by shallow implanted ensemble NV centers in diamond.
ABSTRACT Shallow nitrogen vacancy (NV) centers with long coherence times are promising candidates for applications in areas such as quantum computing and quantum sensing. However, as the NVs are only a few nanometers below the diamond's surface, it is a challenge to remove the different decoherence sources related to the surface, e.g., charge fluctuations and magnetic impurities. Here, the effect of ozone treatment on the chemical composition of diamond surfaces was correlated with its impact on the spin properties of the same individual shallow NV (depth < 20 nm) by comparing its coherence times, Ramsey and Hahn Echo (T 2 ), before and after the treatment. X‐ray photoelectron spectroscopy (XPS) shows a reduction in sp 2 bonds, and it was reported that an enhancement of the coherence times up to a factor of 3. Additionally, we investigate the effects of Ozone treatment on random single NVs engineered to have a depth of ∼30 nm, where an enhancement up to a factor of 10 on and up to a factor of 3 on T 2 have been observed.