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International Conference on Solid State Devices and Materials (SSDM)

Alignment and Coherence Time of 2D Shallow NV Ensemble Fabricated from (111) Diamond

Kyotaro Kanehisa, Tetsuya Tatsuishi, Takahiro Sonoda, Kazuto Kawakatsu, Yuki Hata, Takashi Tani, Shinobu Onoda, Alastair D. Stacey, Mojtaba Moshkani, Richard Paul Mildren, Junichi Isoya, Shozo Kono, Hiroshi Kawarada

Published Sep 28, 2020• 0 citations
Publisher

Abstract

We established the method to fabricate two-dimensional (2D) shallow NV ensemble. We realized nitrogen-terminated (111) diamond surface with nitrogen radical exposure and grew very thin (approximately 10 nm) diamond film on the surface by microwave plasma-enhanced chemical vapor deposition (MPCVD). We counted the number of NV ensembles aligned in [111] direction of the NV ensembles which we observed. The probability of NV ensemble being aligned in [111] was 42 %. On the other hand, we changed the surface condition of N-terminated (111) diamond by thermal annealing. Then, we grew 10 nm diamond film on the surface. As a result, the probability of NV ensemble being aligned in [111] rose to 60 %. Also, s-factor developed from 0.44 to 0.52.

DOI
10.7567/ssdm.2020.i-2-07

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C-enriched diamond aligned along the [111] crystal axis. The preferentially-aligned NV centres are fabricated by a Plasma Enhanced Chemical Vapour Deposition (PECVD) process and their concentration is quantitatively determined by analysing the confocal microscopy images. We further observe that annealing the samples at high temperature (1500 °C) in vacuum leads to a conversion of substitutional nitrogen into NV centres. This treatment also increases the coherence time of the NV centres electron spins up to 40 μs, which corresponds to enhancement of the sensitivity by a factor of three. However, this procedure also leads to a loss of the preferential alignment by 34%.
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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.