Nitrogen-Terminated Diamond Surface for Nanoscale NMR by

Subscriber access provided by University of Winnipeg Library

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Nitrogen-Terminated Diamond Surface for Nanoscale NMR by Shallow Nitrogen-Vacancy Centers Sora Kawai, Hayate Yamano, Takahiro Sonoda, Kanami Kato, Jorge Juan Buendia, Taisuke Kageura, Ryosuke Fukuda, Takuma Okada, Takashi Tanii, Taisei Higuchi, Moriyoshi Haruyama, Keisuke Yamada, Shinobu Onoda, Takeshi Ohshima, Wataru Kada, Osamu Hanaizumi, Alastair Stacey, Tokuyuki Teraji, Shozo Kono, Junichi Isoya, and Hiroshi Kawarada J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b11274 • Publication Date (Web): 24 Jan 2019 Downloaded from http://pubs.acs.org on January 24, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 49

Nitrogen-Terminated Diamond Surface for Nanoscale NMR by Shallow Nitrogen-Vacancy Centers Sora Kawai1, Hayate Yamano1, Takahiro Sonoda1, Kanami Kato1, Jorge J. Buendia1, Taisuke Kageura1, Ryosuke Fukuda1, Takuma Okada1, Takashi Tanii1, Taisei Higuchi2,3,Moriyoshi Haruyama2,3, Keisuke Yamada2, Shinobu Onoda2, Takeshi Ohshima2, Wataru Kada3, Osamu Hanaizumi3, Alastair Stacey4, Tokuyuki Teraji5, Shozo Kono6, Junichi Isoya7, Hiroshi Kawarada*,1,6 1. Faculty of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan 2. Takasaki Advanced Radiation Research Institute, National Institute for Quantum and Radiological Science and Technology, Takasaki, Gunma 370-1292, Japan 3. Division of Electronics and Informatics, Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515, Japan 4. Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville , Melbourne VIC 3010 , Australia 5. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan


1

Page 3 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6. Kagami Memorial Research Institute for Materials Science and Technology, Waseda University, Shinjuku, Tokyo 169-0051, Japan 7. Research Center for Knowledge Communities, University of Tsukuba, Tsukuba, Ibaraki 3058550, Japan E-mail address for corresponding author: [email protected] Phone number for corresponding author: +81-3-5286-3391


2


Page 4 of 49

Abstract

The nitrogen-vacancy (NV) center in diamond is the most promising candidate for quantum sensing because of its beneficial properties. For quantum-sensing applications, a shallow NV center is critical for approximating the sensing target on diamond surface. Such shallow NV centers are strongly affected by the diamond surface termination. The properties of shallow NV centers in hydrogen-, oxygen- and fluorine-terminated diamond have been well studied. In recent years, silicon-terminated diamond has also been investigated; however, the effect of siliconterminated diamond on the properties of shallow NV centers remains unclear. Recently, the suitability of nitrogen-terminated diamond for shallow NV centers has been theoretically and experimentally examined; however, quantum sensing has not yet been performed. In this work, we evaluated the effect of silicon and nitrogen termination on shallow NV centers. The negatively charged state of shallow NV centers was unstable below silicon termination. In contrast, the properties of shallow NV centers in nitrogen-terminated diamond were satisfactory for quantum sensing and, enabling 1H-nuclear magnetic resonance (NMR) detection. Our results are in good agreement with previous reports on silicon and nitrogen terminations and provide the perspective that the stability of shallow NV centers highly depends on the polarity of electron affinity of diamond surface.


3

Page 5 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction A nitrogen-vacancy (NV) center, which consists of a substitutional nitrogen atom and an adjacent vacancy in a diamond lattice, is the most promising candidate for quantum sensing and quantum information processing because of its beneficial properties (including spin triplet (S = 1),1 zero-field splitting,1 individual addressability, optical initialization2 and readout3 of the spin quantum states, coherent manipulation by microwave pulses, and long coherence time). Recently, NV-based sensing of nuclear magnetic resonance (NMR) of multiple nuclear species was performed.4-7 Furthermore, high spectral resolution of detecting chemical shifts has been achieved by using nitrogen nuclear spin as memory and applying a quantum algorithm8 or synchronized readout.9 This NV center primarily has two charge states: a neutral state, NV0, and a negatively charged state, NV−. In a recent work, the positively charged state, NV+, was also formed by bias voltages and used to protect the nuclear spin coherence.10 Among these charge states, only NV− contributes to the NV-based sensing applications as a probe. In sensing applications such as the detection of NMR signals, the magnetic dipolar interaction contributing to the signal is inversely proportional to r3, where r is the distance between the NV center in diamond and the sensing target on diamond surface. Thus, shallow NV centers are required for sensing applications. However, shallow NV centers tend to exhibit shorter coherence time T2 (the sensitivity of the magnetometer11 η ∝ 1/√𝑇2 ) than bulk diamond.12 Furthermore, shallow NV centers also exhibit instability of the negatively charged state of NV−.13 Thus, improvement of the charge stability and coherence time is necessary for sensing applications. To improve the coherence time, new methods of forming NV centers have been proposed. One such method involves optimization of the thermal annealing conditions after nitrogen ion implantation.14 In addition, tenfold improvement of T2 was achieved by nitrogen ion implantation through a boron-


4


Page 6 of 49

doped p+ diamond layer and subsequent etching of the p+ layer to prevent the formation of vacancy clusters during annealing.15 Oxygen-related surface treatments such as oxygen soft plasma and oxygen annealing have also been applied. For the spin properties, oxygen soft plasma16 and oxygen annealing at 550 °C,17 which etched the diamond surface, have been shown to improve T2 of shallow NV center. For the charge stability, oxygen annealing at 465 °C stabilized the negatively charged state of shallow NV centers.18 These findings indicate that surface treatment or termination strongly affects the properties of shallow NV centers. The effect of surface termination by multiple atoms such as oxygen, hydrogen,19 and fluorine20-23 on the charge stability of shallow NV− has been studied using various methods. In addition, the electronic band structures of these terminations have been calculated using computational methods.24,25 Termination with negative electron affinity (NEA) such as hydrogen termination, induces surface charge transfer and makes the charge state of shallow NV− unstable.19 In contrast, terminations with positive electron affinity (PEA), such as oxygen19 or fluorine26 termination, stabilize shallow NV−.18-23 Thus, a surface with strong PEA appears to be desirable for applications using shallow NV centers. Recently, silicon-terminated (001) diamond was formed by silicon deposition and subsequent annealing in vacuum.27 The silicon-terminated (001) diamond surface exhibited a (3×1) lowenergy electron diffraction (LEED) pattern, and the NEA was estimated to be −0.86 eV using angle resolved photoemission spectroscopy (ARPES), near-edge X-ray absorption fine structure (NEXAFS) analysis, and contact potential difference (CPD) measurements.28 In addition, surface upper band-bending was observed when depositing MoO3 on Si-terminated surface,29 similar to the case for hydrogen termination.30 However, the effect of silicon termination on shallow NV centers has not yet been investigated. Nitrogen-terminated (001) diamond can also be formed


5

Page 7 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


using nitrogen plasma31, 32 or radical beam exposure.33 When using nitrogen plasma, full nitrogen coverage ("full N"), where the N–N bonds are parallel to the (001) surface, and partial nitrogen coverage ("N/H"), where the N–C bonds are parallel to the (001) surface, were observed by NEXAFS analysis.32 In addition, a remarkable decrease of the nitrogen peak intensity of X-ray photoelectron spectroscopy (XPS) spectrum was observed with increasing rate of hydrogen against nitrogen.32 In addition to these nitrogen-related terminations, amino termination ("NH2") can immobilize biomolecules directly on the diamond surface.34 Theoretical calculations indicated that "full N" and "N/H" coverage were associated with PEA of 3.46 and 0.32 eV, respectively.32 In contrast, "NH2" was experimentally estimated to exhibit NEA.35 On (111) diamond, higher nitrogen coverage induces a surface with stronger PEA according to theoretical calculations.36 In the NV-related result, nitrogen radical beam exposure stabilized shallow NV− in 1.0- and 2.0-keV-nitrogen-ion-implanted regions.33 However, the coherence properties of shallow NV centers in nitrogen-terminated diamond have not yet been investigated. We summarize the various terminations and their effect on shallow NV centers in Figure 1. In this study, silicon-terminated diamond was prepared using silicon beam deposition at high temperature, and nitrogen termination was performed using nitrogen radical beam exposure. We used a molecular beam epitaxy (MBE) apparatus (Figure 2(a)) generally used for epitaxial growth of III-nitride with nitrogen weak radicals by RF discharge. For the nitrogen radical beam exposure, hydrogen-containing nitrogen (4% H2/N2) gas was used to clean the surface and obtain a small coverage of "NH2" terminations. A schematic illustration of nitrogen-terminated diamond formed using MBE is shown in Figure 2(b). Silicon termination was also performed at high temperature via sublimation of silicon from a pure silicon rod. Afterwards, we evaluated the


6


Page 8 of 49

properties of the shallow NV centers using a lab-built confocal laser scanning fluorescence microscope (CFM). 2. Methods 2.1. Sample preparation for ODMR measurement In this report, silicon termination was used for sample A and nitrogen termination was used for sample B. First, low-nitrogen 12C-enriched high-purity diamond was grown on a (100) diamond substrate. Detailed information about the diamond growth is provided by Teraji et al.37 Then, the substrate was cleaned by hot acid mixture treatment of sulphuric acid and nitric acid (3:1) at 200 °C for 30 min. To produce a regular array of NV centers, a resist mask consisting of a regular array of holes was fabricated on the substrate of sample B by electron beam lithography. The detailed fabrication method is described by Fukuda et al.38 In the experimental method for sample A, shallow NV centers were formed by 1.2- and 10-keV nitrogen ion implantation with a fluence of 1×109 cm−2. For sample B, shallow NV centers were formed using 2.5-keV nitrogen ion implantation with a fluence of 1×1012 cm−2 through the mask; the mask was then removed using tetrahydrofuran. Subsequent annealing at 1000 °C for 2 h14 in 4% hydrogen-containing argon gas atmosphere for sample A and 10% hydrogen-containing argon gas atmosphere for sample B was performed. For sample A, hot acid mixture treatment at 200 °C for 30 min was performed to clean the surface. Afterwards, silicon termination was formed by silicon evaporation at 950 °C. RHEED analysis entering from [110] was performed during the silicon evaporation. After that, hydrofluoric acid (HF) cleaning was used to remove SiOx. A second hot acid mixture treatment and subsequent silicon evaporation were performed using the same conditions as the first


7

Page 9 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


treatment. The properties of the shallow NV centers were evaluated by continuous wave ODMR and pulsed ODMR using a lab-built confocal laser scanning fluorescence microscope (CFM) with 532 nm laser after each surface treatment. For sample B, hot acid mixture treatment at 200 °C for 30 min and VUV/ozone treatment (wavelength: 172 nm) for 15 min in a 0.3 atm oxygen atmosphere were performed to clean the surface. Nitrogen termination was subsequently formed by nitrogen radical beam exposure. The nitrogen radical was generated by radio frequency (300 W), and the temperature of the stage was set to 200 °C. Nitrogen gas containing 4% hydrogen was used for the radical beam source, and the flow rate was 2 sccm at the time of nitrogen radical beam exposure. For the measurement of NV centers, the properties of shallow NV centers were estimated using continuous wave ODMR and pulsed ODMR using the CFM after each surface treatment. We also measured the 1H NMR signal by XY8 sequence with CFM after nitrogen radical beam exposure. The depth of the NV centers was estimated by the method implemented by Pham et al.39 and noise spectroscopy was performed in accordance with the reports by Myers et al.,12 BarGill et al.40 and Romach et al.41 2.2. Sample preparation for surface analysis A boron-doped diamond layer was grown on the (100) substrate to evaluate the surface nitrogen coverage and surface structure using XPS and NEXAFS analysis. Nitrogen termination was formed using the same process described above for the boron-doped sample. In XPS measurement, an Al Kα (1486.6 eV) source was used. In NEXAFS measurement, the sample was annealed at 400 °C in the exchange chamber before the measurement.


8


Page 10 of 49

3. Results 3.1. Shallow NV centers in silicon-terminated diamond Figure 3(a) presents a schematic illustration of our experiments related to silicon-terminated diamond. First, we formed oxygen-terminated diamond by hot acid mixture treatment. Then, silicon termination was performed by silicon evaporation at high temperature. Each method was repeated, as shown in Figure 3(a), to verify the reproducibility. Figure 3(b) presents the reflection high-energy electron diffraction (RHEED) pattern of the sample after silicon evaporation at 950 °C to form the silicon termination. The pattern corresponded to a (3×1) pattern of silicon-terminated diamond.27 Thus, the successful formation of silicon termination was confirmed. Before the silicon termination, some stable fluorescence spots produced by the NV− in the 1.2keV-ion-implanted region (the average nitrogen ion depth calculated by SRIM42 simulation was 2.6 ± 1.1 nm) and optically detected magnetic resonance (ODMR) were observed in the oxygen termination formed by the hot acid mixture treatment. In addition, pulsed ODMR measurement such as Rabi oscillation measurement and Hahn echo measurement could be carried out on 9 fluorescence spots in 1.2-keV-ion implantation region and 4 spots in 10-keV region although the charge state of all measured NV centers were unstable (see Supporting Information). However, after the silicon evaporation, no stable fluorescence spots were detected with ODMR signatures in 550 μm2 areas although ~20 stable fluorescence spots were observed in each 100 μm2 area under oxygen termination, and the spots that appeared to blink were present in the siliconterminated diamond. To verify whether the instability of the fluorescence spots was attributed to the conversion of the termination from oxygen to silicon, oxygen termination was formed again.


9

Page 11 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3(c) presents a confocal image after the second hot acid mixture treatment, revealing the reappearance of NV−. Silicon termination was formed using the same method for the second time to confirm if the disappearance reoccurred. Figure 3(d) presents a confocal image of the silicon termination at the same position, which revealed the presence of some fluorescence spots in each image. Below silicon termination, the background intensity of the confocal image was a little higher than that below oxygen termination. This might be caused by SiO2 formed by silicon evaporation at high temperature although the origin of the background intensity could not be determined precisely. The right confocal image in Figure 3(d) was measured immediately at the same position as that in the left image (note that Figure 3(c) and 3(d) were measured at different positions in the 1.2-keV-ion-implanted region). However, the position of the fluorescence spots differed between each image in Figure 3(d), and ODMR was not observed at any fluorescence spots. Therefore, the shallow NV centers were very unstable as NV− in the silicon-terminated diamond. 3.2. Charge stability of shallow NV centers in nitrogen-terminated diamond An alternative termination formed using MBE was nitrogen termination, which exhibits PEA and is thus expected to stabilize shallow NV−. To investigate the charge stability of shallow NV centers, the Rabi oscillation contrast can be used as a measure of the charge stability. Since both NV0 and NV− states fluoresce, but only the NV− state shows spin-dependent fluorescence contrast, we introduce a very simple model using Rabi oscillations to evaluate the charge stability. Figure 4(a) presents a schematic illustration of the Rabi oscillation measurement. The practically measured Rabi oscillations are expressed as 2𝜋𝐿

𝐼 = 𝐴 ∙ cos (

𝑇

) + 𝑦0 = (

(𝐹top −𝐹bottom )∙𝑃NV− 2

2𝜋𝐿

) ∙ cos (

𝑇

)+

(𝐹top +𝐹botom )∙𝑃NV− +2𝐹NV0 ∙𝑃NV0 2

, (1)


10


Page 12 of 49

, where A is the amplitude of the Rabi oscillations, y0 is the middle value of the Rabi oscillations, L is the length of the microwave pulse, and T is the period of the Rabi oscillations. In addition, Ftop and Fbottom are the fluorescence intensities of the Rabi oscillations in Figure 4(a) and FNV0 is the detected intensity caused by NV0 during Rabi oscillation measurement. These fluorescence intensities depend on the experimental setup (e.g., the optical filters and the photon detector). In our setup, fluorescence of NV− is brighter than NV0. PNV- and PNV0 are the population of NV− and NV0 respectively at the time of readout. On the other hand, the Rabi oscillation contrast C can be expressed as

𝐶=

2A y0

= (𝐹

2(𝐹top −𝐹bottom )∙𝑃NV−

top +𝐹bottom )∙𝑃NV− +2𝐹NV0 ∙𝑃NV0

(2)

using the parameters in equation (1). Equation (2) shows that the Rabi oscillation contrast decreases if the population of NV0 increases at the time of readout. Figure 4(b) shows the pulse sequence of the Rabi oscillation measurement. The sequence consists of the initialization by the laser pulse, the spin manipulation microwave pulse, and the readout laser pulse. In the initialization laser pulse, NV centers are initialized into the spin sublevel ms=0, while NV0 centers are efficiently converted into NV− via a two-photon ionization process43 whereas NV− are also converted into NV0. Consequently, NV centers are converted into NV− at the rate of about 75 % by the initialization laser pulse of 532-nm.43 However, these photon-ionized NV− may reconvert to NV0 depending on the near-surface charge environment when the laser is off. The Rabi oscillations were measured by changing the length of the microwave pulse in this pulse sequence. In addition, a waiting time (2000 ns) was introduced between the laser initialization and microwave pulses (up to ~100 ns) to complete the initialization. In all ODMR measurement in this paper, we fixed the initialization laser pulse and the waiting time to 5000 ns and 2000 ns,


11

Page 13 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively. The length of waiting time was much longer than that of the microwave pulse. Thus, we can readout the charge state of NV centers as a snapshot in Rabi oscillation measurement. If NV− releases a captured electron and is converted to NV0 during the time without laser irradiation (i.e., the waiting time or microwave pulse irradiation time), the amplitude of the Rabi oscillations and the contrast decrease. Thus, we evaluated the charge stability by monitoring the Rabi oscillation contrast. At the time of the evaluation by Rabi oscillation contrast, we must note that this evaluation of charge stability is valid for only single NV center or multiple NV centers with same orientation. Therefore, pulsed ODMR measurements including Rabi oscillations were carried out on only single NV centers estimated by fluorescence intensity in this study. Figure 4(c) presents the Rabi oscillation measurements in the 2.5-keV-ion-implanted region (the average nitrogen ion depth calculated by SRIM simulation was 4.5 ± 1.9 nm) after each surface treatment (an example of the measured Rabi oscillations is presented in Supporting Information). The average Rabi oscillation contrasts after hot acid mixture treatment and VUV/ozone treatment were 0.22 and 0.25, respectively. These values empirically indicate that the shallow NV centers were unstable as negatively charged state before nitrogen radical beam exposure in our sample. In contrast, the average Rabi oscillation contrast was improved, and the value was 0.38 after nitrogen radical beam exposure. The Rabi oscillation contrast of the stable NV− in the 10-MeV-ion-implanted region (the average nitrogen ion depth calculated by SRIM simulation was 3.79 ± 0.67 μm) was 0.46 in our setup (see Supporting Information). In nitrogen terminated diamond, contrasts exceeding 0.4 were confirmed, despite the NV centers being much shallower. Therefore, nitrogen radical beam exposure stabilized the charge state of the shallow NV−.


12


Page 14 of 49

3.3. Surface analysis of nitrogen-terminated diamond using XPS and NEXAFS XPS and NEXAFS are widely used for surface analysis. XPS can be used to quantify the atomic coverage or identify bonding groups. In addition, NEXAFS can be used to determine the more specific bonding structure. These two methods can be combined to reveal essential surface information. The specific bonding structure using the nitrogen plasma method has already been determined using NEXAFS analysis.32 However, the NEXAFS study of the surface formed by nitrogen radical beam exposure method has not yet been revealed. Hence, we investigated in detail the nitrogen-terminated surface formed using our method, which contributed to the stabilization of shallow NV－. Figure 5(a) presents the XPS wide scan of nitrogen-terminated diamond using an Al Kα (1486.6 eV) source. Figure 5(b) and (c) present the XPS narrow scans of C1s and N1s, respectively, where the coverage of nitrogen on diamond surface was estimated from the peak areas32, 33 in the figures. The evaluation indicated that the nitrogen coverage using the nitrogen radical beam exposure method was ~0.6 monolayer (ML). Figure 5(d) presents the nitrogen Kedge result of the nitrogen-terminated diamond measured by NEXAFS, which shows the remarkable main peaks. The first peak located near 396 eV has been attributed to "Full N" termination, which strongly contributes to stabilizing shallow NV- because of its high PEA.32 The second peak near 399 eV may also be attributed to "N/H" termination.32 As mentioned previously, "N/H" also exhibits PEA and contributes to stabilizing shallow NV−. Thus, the main components of the nitrogen-related termination formed by nitrogen radical beam exposure were determined to be caused by "Full N" and "N/H" termination, which contribute to stabilizing shallow NV− with implications for nuclear spin detection. Both of these nitrogen-related


13

Page 15 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


terminations were modeled to exclude low-lying electron trap states,32 further enhancing their suitability for near-surface NV centers. 3.4. Coherence properties of shallow NV centers in nitrogen-terminated diamond Bulk and surface spins such as 13C nuclear spins and surface electron spins lead to the degradation of the coherence properties of shallow NV centers. Hence, the coherence properties of shallow NV centers can be improved if nitrogen radical beam exposure decreases the surface electron spins or electron trap states as compared with oxygen termination. We used the Hahn echo method to evaluate the coherence properties. Figure 6(a) presents a schematic illustration of the pulse sequence used for the Hahn echo method, and Figure 6(b) presents an example of Hahn echo decays. These decays are generally affected by the instability of NV−. The decays of stable NV− symmetrically converge to the middle value of the Rabi oscillations. However, the decays of unstable NV− unsymmetrically converge because NV− is converted into NV0 during the sequence and the readout fluorescence of NV0 is darker than that of NV− owing to the 647-nmlong pass filter. To prevent incorrect estimation of T2, we applied a normalization procedure (𝐼hahn,π/2 − 𝐼hahn,3π/2 )/(𝐼hahn,π/2 + 𝐼hahn,3π/2 ) to measure the Hahn echo decays and suppress the effect of charge instability. Figure 6(c) presents the normalized result of the Hahn echo decays, which converged at approximately zero. The decay was then fitted using 𝐴 ∙ exp[−(2𝜏/𝑇2 )𝑛 ], where A is the height of decay, and T2 and n were estimated by fitting. In this report, estimating the coherence properties of shallow NV centers in oxygen-terminated diamond was difficult due to very poor charge stability in the 2.5-keV-ion-implanted region. Therefore, we compared the coherence properties to those below oxygen termination in the previous report, in which the shallow NV centers were formed using the same process.38 In the


14


Page 16 of 49

previous report, the T2 value measured using the Hahn echo sequence in oxygen-terminated diamond formed by hot acid mixture treatment mainly ranged from several microseconds to 15 µs in the 2.5-keV-ion-implanted region; however, NV centers for which T2 was over 20 µs also existed.38 Figure 6(d) shows the T2 distribution of the shallow NV centers in the 2.5-keV-ionimplanted region in nitrogen-terminated diamond formed by nitrogen radical beam exposure. The T2 of most NV centers below nitrogen-terminated surface were in the same range as those for the oxygen termination. However, NV centers with T2 over 30 µs may be positioned deeper than other NV centers because of ion channeling at the time of ion implantation. As a result, the spin properties in nitrogen-terminated diamond was found to be comparable to that in oxygenterminated diamond reported by Fukuda et al.38 3.5. Nanoscale NMR detection of 1H nuclear spins in immersion oil As mentioned above, stabilization of shallow NV centers was achieved by nitrogen radical beam exposure, and T2 in nitrogen-terminated diamond was comparable to that for oxygen termination.38 Thus, we performed nanoscale NMR detection of 1H spins in immersion oil (the 1

H density of nuclear spins in immersion oil (OLYMPUS IMMOIL-F30CC) was estimated to be

69.3 ± 0.7/nm3 by elemental analysis) using shallow NV centers in nitrogen-terminated diamond. Figure 7(a) presents the XY8-k pulse sequence used to detect the NMR signal. In this measurement, the NMR signal can be detected when sufficient target spins exist near the NV center and the pulse interval τ is 1/2 fL, where fL is the Larmor frequency of the target nuclear spins. In addition, fL can be expressed as fL = γB, where γ and B represent the gyromagnetic ratio of the target spins and static magnetic field, respectively. Consequently, the signal is considered to be attributed to the target nuclear spins if the position of the signal corresponds to the Larmor frequency of the target spins.


15

Page 17 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7(b) shows the nanoscale NMR detected by XY8-8 sequence corresponding to the 64 πpulses sequence. The applied static magnetic field was estimated using the formula implemented by Balasubramanian et al.44 and ODMR frequencies at the time of this measurement. Figure 7(c) shows the dependence of the NMR signal on the applied static magnetic field, with the slope corresponding to the Larmor frequency of 1H nuclear spins. From these results, NMR detection of 1H nuclear spins in the immersion oil was successful. In Figure 7(b), fitting the NMR signal and subsequent depth estimation of the NV center were performed using the method implemented by Pham et al.39 The depth of the NV center was calculated to be 7.0 ± 1.7 nm by fitting the result of Figure 7(b). Moreover, we defined the number of detected spins N as spins that contribute to 70% of the NMR signal in accordance with the report by Staudacher et al.4 This NV center succeeded in detecting ~6000 1H spins. Contribution of the spins to the NMR signal are expressed as √𝑁 in the range that statistical polarization is dominant over thermal polarization. Therefore, the number of actually contributing spins was estimated to be ~78 spins in Figure 7(b). This number of spins corresponds to 86.5 yL (86.5 × 10−24 L). In addition, eight other NV centers could also detect 1H-NMR of the immersion oil on nitrogen-terminated diamond. Figure 7(d) presents the relation between the depth of NV centers and T2 measured by Hahn echo sequence. Positive correlation in Figure 7(d) implied that decoherence of NV centers in nitrogen-terminated diamond was attributed to the surface-related effects. Furthermore, the estimated depth of NV centers were deeper than the average depth calculated by SRIM simulation. However, these depth of NV centers were reasonable in C-TRIM45 simulation of 2.5keV-ion implantation (see Supporting Information). Consequently, successful detection of 1HNMR indicates that shallow NV centers in nitrogen-terminated diamond can be sufficiently used


16


Page 18 of 49

for quantum sensing applications, whereas our oxygen-terminated diamond formed by hot acid mixture treatment were not sufficiently stable for these applications. 3.6. Noise spectroscopy with shallow NV centers in nitrogen-terminated diamond Recently, noise spectroscopy using NV centers was reported.40,41 The time-dependent coherence decay of a NV center C(t) can be expressed by the general form 𝐶(𝑡) = exp[−χ(𝑡)], where χ(t) describes the time-dependent decoherence process, which is caused by environmental noise. In the noise spectroscopy, C(t) was measured using periodic dynamical decoupling sequences such as Carr-Purcell-Meiboom-Gill (CPMG) and XY8, which works as filter functions (i.e., probing the specific frequency 𝜔 = 𝑘π/𝑡, where k is the number of π-pulses and t is the total length of the dynamical decoupling sequence). Thus, the noise spectrum of the environmental noise S(ω) can be derived from the coherence decay C(t) by spectral decomposition46 because the filter functions of the dynamical decoupling pulse sequences enable to probe the selective frequency components of the environmental noise spectrum. Finally, the spectrum was fitted by the double Lorentzian 𝑆(𝜔) = ∑𝑖=1,2

Δ2𝑖 𝜏c(i)

1

𝜋

1+(𝜔𝜏c(i) )

2

, reflecting an

environmental bath model, where Δ is the average coupling strength of the environment to the NV spin and τc is the correlation time of the environment. To evaluate Δ and τc, a double Lorentzian fit was found to be better than a single Lorentzian fit or 1/ω fit, for fitting the noise spectrum in the system of shallow NV centers.41 In the system of shallow NV centers, the lowfrequency noise of longer correlation time τc(1) was associated with the electron spin bath.41 The high-frequency noise of shorter correlation time τc(2) was ascribed to the noise caused by surfacemodified phonons.41 The coupling strength and the correlation time were determined by the spin 𝑎

density. Furthermore, the coupling strength Δ can be expressed as 𝛥i = 𝑑𝑥ii , where d is the depth


17

Page 19 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of the NV center, and the dependence of Δ on the NV depth indicates whether the decoherence noise is surface related.38,41 In general, a 2D surface spin bath in the vicinity of NV centers, which corresponds to τc(1), yields "𝑥1 = 2".12 Before the fitting, we excluded noisy plots in the high-frequency region in the spectrum and performed an averaging procedure (see Supporting Information). Then, the mean of τc(i) was simply calculated using all the values of τc(i) at different depth to evaluate Δi. The noise spectrum was fitted by a double Lorentzian again using the average value of τc(i) derived from the first fitting, assuming that the noise source contributing to NV decoherence uniformly distributes. In the second fitting, we determined the value of Δi at different depth. Figure 8(a) presents the noise spectrum of the NV centers in nitrogen-terminated diamond. Two noise sources existed in the environment of shallow NV centers below the nitrogen termination, and the measured values of each NV center were summarized into Table 1. Dispersion of estimated τc(i) was found in the NV centers at different depth and similar dispersion was observed in the report by Romach et al.41 In addition, T1 and T2, sat were extremely short as compared to Ref. 41 (T1 and T2, sat of NV center at 2 nm were 430 and 42 μs). These values indicated that NV centers in our sample suffered from high frequency noise. The average τc(1) and τc(2) using the value of Table 1 were 9.0 μs and 143 ns, respectively. These correlation times are reasonable as compared with those in previous reports38,41. Figure 8(b) shows the dependence of Δi on the NV depth evaluated using the noise spectrum. The solid lines associated with x1 (blue) and x2 (red) represent the fitting curves without fixing any parameter. As a result, the evaluated values were 𝑥1 = 1.1 ± 0.08 and 𝑥2 = 0.8 ± 0.1. Especially with respect to x1, the value did not match with the 2D surface spin bath. Assuming that a 2D surface spin bath distributed on nitrogen-terminated diamond, Δ1 was fitted with a fixed value, 𝑥1 = 2 (blue dashed line). The dashed line indicated the possibility that Δ1


18


Page 20 of 49

obeys a 2D surface spin bath. If decoherence of the NV centers in nitrogen-terminated diamond was attributed to the 2D surface spin bath, the density of surface electron spins corresponds to 0.20/nm2. However, we could not conclude that the low-frequency noise was caused by the surface spin bath because of the lack of information for shallower NV centers. Furthermore, estimated Δ2 in this report was much higher than the previous reports38,41 (see Supporting Information). This was in good agreement with short T1 and T2, sat values. As a result, a shallower NV center exhibited higher Δ in the noise spectroscopy, and thus nitrogen-terminated diamond could not sufficiently suppress the surface-related noise, whereas it could stabilize shallow NV−. 4. Discussion In silicon-terminated diamond, ODMR of NV centers was not observed in the 2.5-keV region. In contrast, ODMR of NV centers was observed in the 10-keV region (see Supporting Information), whereas fluorescence blinking also occurred. However, the NV− in the 10-keV region were never stable. This instability can be caused by upward band-bending near the surface due to NEA27, similar to that observed for hydrogen-terminated diamond, because shallower NV− were more unstable. Otherwise, unoccupied states attributing to silicon termination in the bandgap27 may catch the electron of the NV− and cause the instability. In contrast to silicon-terminated diamond, nitrogen-terminated diamond formed by nitrogen radical beam exposure stabilized shallow NV−. From the stabilization of NV− and surface analysis, nitrogen termination formed by nitrogen radical beam exposure consists of large number of PEA terminations such as "Full N" or "N/H" termination and a small number of NEA terminations like "NH2", whereas we did not identify the "NH2" termination using NEXAFS. However, the existence of "NH2" termination was confirmed by the immobilization of


19

Page 21 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


biomolecules such as single-strand DNA terminated by COOH (see Supporting Information), which allows the formation of peptide binding with NH2 on diamond surface through covalent bonding47. In Figure 5(d), the slight peak at higher binding energy than the one relative to "N/H" termination may be caused by "NH2" termination. To identify this "NH2" termination, highresolution electron energy loss spectroscopy (HREELS) is an effective method because HREELS can detect N–H bonding.48 On the other hand, the nitrogen coverage on diamond was not high even though the surface formed by nitrogen radical beam exposure stabilized the shallow NV− sufficiently for quantum sensing. The low coverage was caused by the 4 % hydrogen used to clean the surface, as hydrogen causes a decrease of the N1s peak intensity on diamond for XPS analysis.32 In addition, the higher nitrogen coverage may lead to a higher PEA surface, similar to the theoretical calculation of nitrogen-terminated (111) diamond.36 From the viewpoint of nitrogen coverage, changing hydrogen-containing nitrogen gas to pure nitrogen gas can lead to greater nitrogen coverage and thus a PEA surface although "NH2" terminations may be scarcely obtained. Furthermore, nitrogen radical beam exposure using pure nitrogen gas may yield a nitrogen-rich surface. Therefore, nitrogen radical beam exposure using pure nitrogen gas can construct the system of shallow NV centers on a nitrogen-rich (111) surface for a quantum simulator.36,49 Regarding the coherence properties, nitrogen radical beam exposure may not sufficiently decrease the surface electron spins, as T2 was almost the same as that for oxygenterminated diamond in the previous report38. The coherence properties and noise spectroscopy in nitrogen-terminated diamond indicated that suppression of the spin bath was insufficient. In the noise spectroscopy, the dependence of Δ1 on the depth of NV centers did not indicated that decoherence of shallow NV centers in nitrogen-terminated diamond was caused by a 2D surface spin bath. This might be caused by the lack of information on noise spectroscopy of shallower


20


Page 22 of 49

NV centers. On the other hand, the dependence of Δ1 also implicated that a surface spin bath might distribute non-uniformly. This non-uniformity of a surface spin bath might be caused by 0.6 ML-nitrogen coverage and multiple main nitrogen-related bonding in the surface analysis (i.e., non-uniform surface termination). In addition, dispersion of τc(1) was also consistent with the non-uniformity because correlation time is determined by the spin density. This result indicates the possibility that shallow NV centers can be used for probing the diamond surface. However, further research on the noise spectrum of shallower NV centers induced by lowerenergy-ion implantation is necessary to more precisely evaluate the noise source. In the reports by de Oliveira et al.16 and Kim et al.,17 the oxygen-related surface treatment with etching the diamond surface, improved T2. Therefore, surface treatment with etching may be a more appropriate approach to improve T2 than the gentle surface treatment because not only the surface electron spins but also the spins in diamond attributing to vacancy clusters, can be eliminated. The combination of surface treatment with sub-surface treatments (e.g., surface treatment with etching and subsequent nitrogen radical beam exposure) should be considered to balance the charge stabilization and long T2. 5. Conclusions In summary, we investigated the effect of unconventional surface terminations on shallow NV centers by treating the surface with a molecular beam. We revealed that silicon-terminated diamond induced the formation of unstable NV− because of its NEA surface; therefore, this surface is not suitable for NV-based sensing applications. In contrast, nitrogen-terminated diamond formed by nitrogen radical beam exposure stabilized shallow NV− due to its PEA surface, and the spin properties were comparable to those of oxygen-terminated diamond. Thus, nitrogen-terminated diamond is suitable for NV-based sensing applications. In addition, the


21

Page 23 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surface was examined using XPS and NEXAFS analysis. These measurements revealed that "Full N" and "N/H" terminations were dominant. Consequently, we succeeded in detecting 1HNMR using shallow NV centers in nitrogen-terminated diamond for the first time. These results demonstrate the possibility of terminated 14N- or 15N-NMR detection using the shallow NV center for quantum simulation in nitrogen-rich (111) diamond.


22


Page 24 of 49

Figure 1. Overview of diamond surface terminations Schematic illustration of diamond surface terminations reported thus far. The relation between the shallow NV centers and each surface termination are summarized below the illustrations.


23

Page 25 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Schematic illustrations of nitrogen-terminated diamond formed using MBE (a) Schematic diagram of MBE apparatus. (b) Schematic illustration of surface termination formed by nitrogen radical beam exposure.


24


Page 26 of 49

Figure 3. Investigation of silicon-terminated diamond. (a) Flow chart of experiments related to silicon-terminated diamond. (b) RHEED image of siliconterminated diamond ([110] incident). The right image corresponds to the (3×1) pattern caused by silicon termination. The interval of the pattern corresponds to a third of the strong reflection. (c) 10×10 µm confocal image of 2nd oxygen termination. (d) 10×10 µm confocal image of 2nd silicon termination in the same area. The right confocal image was captured several minutes after the left image. Note that the images in (c) and (d) were captured at different positions in the 1.2-keV-ionimplanted region.


25

Page 27 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. NV center charge stability evaluation based on Rabi oscillations. (a) Schematic illustration of Rabi oscillations. The vertical axis corresponds only to the tendency of the fluorescence intensity, thus, the value of this axis is meaningless. (b) Pulse sequence of Rabi oscillation measurements. The pulse duration corresponds to each plot of the Rabi oscillations. (c) Histograms of Rabi oscillation contrast after each surface treatment.


26


Page 28 of 49

Figure 5. Surface analysis of nitrogen-terminated diamond. (a) XPS wide scan of nitrogen-terminated diamond. (b) XPS C1s narrow scan of nitrogen termination. (c) XPS N1s narrow scan of nitrogen termination. (d) NEXAFS nitrogen K-edge spectrum.


27

Page 29 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Evaluation of spin property by Hahn echo measurement. (a) Pulse sequence of Hahn echo measurement. (b) Example of Hahn echo decays in nitrogenterminated diamond; sequence 1 (red) and sequence 2 (black) from (a), respectively. (c) Normalized Hahn echo decay of (b). (d) T2 distribution in nitrogen-terminated diamond.


28


Page 30 of 49

Figure 7. 1H-NMR detection by NV centers in nitrogen-terminated diamond. (a) Pulse sequence of XY8-k measurement. (b) 1H-NMR detection by XY8-8 sequence. The depth of this NV center was estimated to be 7.0 nm. The plots correspond to each applied static magnetic field, 43.4 mT (red triangles), 45.8 mT (green squares), and 48.3 mT (blue circles). (c) Dependence of dip position on applied static magnetic field; the colored plots correspond to the plots in (c). The 1H-NMR results of another NV are indicated by grey stars. (d) The relation between the NV depth calculated by 1H-NMR measurement and T2 measured by Hahn echo sequence.


29

Page 31 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. Noise spectroscopy of the shallow NV centers in nitrogen-terminated diamond. (a) Noise spectrums measured by the shallow NV centers at different depths, 4.85 nm (orange), 7.97 nm (green), and 10.0 nm (blue), which were evaluated by 1H-NMR detection in nitrogenterminated diamond. The colored region represents the 1σ confidence region. (b) Dependence of 𝑎

the coupling strength Δi on NV depth. The solid lines are fitting curves with 𝛥i = 𝑑𝑥ii and correspond to each noise source, which were distinguished by different values of τc, τc(1) = 9.0 μs (blue) and τc(2) = 143 ns (red). The dashed lines are the fitting curves for "x1 =2".


30


Page 32 of 49

Table 1. The measured values of NV centers in the noise spectroscopy. NV depth [nm]

T2, Hahn [μs]

T2, sat [μs]*

T1 [μs]

τc(1) [μs]

τc(2) [ns]

4.85

2.85

13.4

48.1

4.36

59.9

7.97

5.68

19.1

56.5

7.59

113

10.0

8.74

n/a

242

15.1

257

*

Saturated T2 measured using dynamical decoupling pulse sequences


31

Page 33 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information Available: Continuous wave ODMR measurement below silicon termination in the 10-keV-ion-implanted region, examples of Rabi oscillation measurement, the nitrogen coverage estimation method in XPS measurement, XPS result on nitrogen termination after immobilizing DNA, C-TRIM simulation of 2.5-keV nitrogen ion implantation, and the procedure of data set in noise spectroscopy.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Alastair Stacey: 0000-0002-3794-0317 Takeshi Ohshima: 0000-0002-7850-3164 Hiroshi Kawarada: 0000-0001-7496-4265 Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (S) (Grant Number 26220903), Grant-in-Aid for Scientific Research (A) (Grant Number 26246001), Grant-in-Aid for


32


Page 34 of 49

Scientific Research (B) (Grant Number 15H03980), Grant-in-Aid for Scientific Research (B) (Grant Number 17H02751), and Grant-in-Aid for Scientific Research (B) (Grant Number 17H03526) from the Japan Society for the Promotion of Science (JSPS), and Project of Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development of MEXT. This research was undertaken on the Soft X-ray Spectroscopy beamline at the Australian Synchrotron, part of ANSTO. We thank Dr. Liam P. McGuinness and Professor Fedor Jelezko for their help with setting up the CFM.

REFERENCES 1. Doherty, M. W.; Manson, N. B.; Delaney, P.; Hollenberg, L. C. L. The negatively charged nitrogen-vacancy centre in diamond: the electronic solution New J. Phys. 2011, 13, 025019. 2. Harrison, J.; Sellars, M. J.; Manson, N. B. Optical spin polarisation of the N-V centre in diamond. J. Lumin. 2004, 107, 245-248. 3. Jelezko, F.; Gaebel, T.; Popa, I.; Gruber, A.; Wrachtrup, J. Observation of Coherent Oscillations in a Single Electron Spin. Phys. Rev. Lett. 2004, 92, 076401. 4. Staudacher, T.; Shi, F.; Pezzagna, S.; Meijer, J.; Du, J.; Meriles, C. A.; Reinhard, F.; Wrachtrup, J. Nuclear Magnetic Resonance Spectroscopy on a (5-Nanometer)3 Sample Volume. Science 2013, 339, 561-563. 5. Ishiwata, H.; Nakajima, M.; Tahara, K.; Ozawa, H.; Iwasaki, T.; Hatano, M. Perfectly Aligned Shallow Ensemble Nitrogen-Vacancy centers in (111) Diamond. Appl. Phys. Lett. 2017, 111, 043103.


33

Page 35 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6. Müller, C.; Kong, X.; Cai, J. - M.; Melentijević, K.; Stacey, A.; Markham, M.; Twitchen. D.; Isoya, J.; Pezzagna, S.; Meijer, J.; et al. Nuclear Magnetic Resonance Spectroscopy with Single Spin Sensitivity. Nat. Commun. 2014, 5, 4703. 7. Devience, J. S.; Pham, L. M.; Lovchinsky, I.; Sushkov, A. O.; Bar-Gill, N.; Belthangady, C.; Casola, F.; Corbett, M.; Zhang, H.; Lukin, M.; et al. Nanoscale NMR Spectroscopy and Imaging of Multiple Nuclear Species. Nat. Nanotechnol. 2015, 10, 129-134. 8. Aslam, N.; Pfender, M.; Neumann, P.; Reuter, R.; Zappe, A.; de Oliveira, F. F.; Denisenko, A.; Sumiya, H.; Onoda, S.; Isoya, J.; et al. Nanoscale Nuclear Magnetic Resonance with Chemical Resolution. Science 2017, 357, 67-71. 9. Glenn, D. R.; Bucher, D. B.; Lee, J.; Lukin, M. D.; Park, H.; Walsworth, R. L. High-Resolution Magnetic Resonance Spectroscopy Using a Solid-State Spin Sensor. Nature 2017, 555, 351-354. 10. Pfender, M.; Aslam, N.; Simon, P.; Antonov, D.; Thiering, G.; Burk, S.; de Oliveira, F. F.; Denisenko, A.; Fedder, H.; Meijer, J.; et al. Protecting a Diamond Quantum Memory by Charge State Control. Nano Lett. 2017, 17, 5931-5937. 11. Maze, J. R.; Stanwix, P. L.; Hodges, J. S.; Hong, S.; Taylor, J. M.; Cappellaro, P.; Jiang, L.; Gurudev Dutt, M. V.; Togan, E.; Zibrov, A. S.; et al. Nanoscale Magnetic Sensing with an Individual Electronic Spin in Diamond. Nature 2008, 455, 644-647. 12. Myers, B. A.; Das, A.; Dartiailh, M. C.; Ohno, K.; Awschalom, D. D.; Bleszynski Jayich, A. C. Probing Surface Noise with Depth-Calibrated Spins in Diamond. Phys. Rev. Lett. 2014, 113, 027602. 13. Ofori-Okai, B. K.; Pezzagna, S.; Chang, K.; Loretz, M.; Schirhagl, R.; Tao, Y.; Moores, B. A.; Groot-Berning, K.; Meijer, J.; Degen, C. L. Spin Properties of Very Shallow Nitrogen Vacancy Defects in Diamond. Phys. Rev. B 2012, 86, 081406(R).


34


Page 36 of 49

14. Yamamoto, T.; Umeda, T.; Watanabe, K.; Onoda, S.; Markham, M. L.; Twitchen, D. J.; Naydenov, B.; McGuinness, L. P.; Teraji, T.; Koizumi, S.; et al. Extending Spin Coherence Times of Diamond Qubits by High-Temperature Annealing. Phys. Rev. B 2013, 88, 075206. 15. de Oliveira, F. F.; Antonov, D.; Wang, Y.; Neumann, P.; Ali Momenzadeh, S.; Häußermann, T.; Pasquarelli, A.; Denisenko, A.; Wrachtrup, J. Tailoring Spin Defects in Diamond by Lattice Charging. Nat. Commun. 2017, 8, 15409. 16. de Oliveira, F. F.; Ali Momenzadeh, S.; Wang, Y.; Konuma, M.; Markham, M.; Edmonds, A. M.; Denisenko, A.; Wrachtrup, J. Effect of Low-Damage Inductively Coupled Plasma on Shallow Nitrogen-Vacancy Centers in Diamond. Appl. Phys. Lett. 2015, 107, 073107. 17. Kim, M.; Mamin, H. J.; Sherwood, M. H.; Rettner, C. T.; Frommer, J.; Rugar, D. Effect of Oxygen Plasma and Thermal Oxidation on Shallow Nitrogen-Vacancy Centers in Diamond. Appl. Phys. Lett. 2014, 105, 042406. 18. Yamano, H.; Kawai, S.; Kato, K.; Kageura, T.; Inaba, M.; Okada, T.; Higashimata, I.; Haruyama, M.; Tanii, T.; Yamada, K.; et al. Charge State Stabilization of Shallow Nitrogen Vacancy Centers in Diamond by Oxygen Surface Modification. Jpn. J. Appl. Phys. 2017, 56, 04CK08. 19. Hauf, M. V.; Grotz, B.; Naydenov, B.; Dankerl, M.; Pezzagna, S.; Meijer, J.; Jelezko, F.; Wrachtrup, J.; Stutzmann, M.; Reinhard, F.; et al. Chemical Control of the Charge State of Nitrogen-Vacancy Centers in Diamond. Phys. Rev. B 2011, 83, 081304(R). 20. Cui, S.; Hu, E. L. Increased Negatively Charged Nitrogen-Vacancy Centers in Fluorinated Diamond. Appl. Phys. Lett. 2013, 103, 051603.


35

Page 37 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21. Osterkamp, C.; Scharpf, J.; Pezzagna, S.; Meijer, J.; Diemant, T.; Behm, R. J.; Naydenov, B.; Jelezko, F. Increasing the Creation Yield of Shallow Single Defects in Diamond by Surface Plasma Treatment. Appl. Phys. Lett. 2013, 103, 193118. 22. Shanley, T. W.; Martin, A. A.; Aharonovich, I.; Toth, M. Localized Chemical Switching of the Charge State of Nitrogen-Vacancy Luminescence Centers in Diamond. Appl. Phys. Lett. 2014, 105, 063103. 23. Osterkamp, C.; Lang, J.; Scharpf, J.; Müller, C.; McGuinness, L. P.; Diemant, T.; Behm, R. J.; Naydenov, B.; Jelezko, F. Stabilizing Shallow Color Centers in Diamond Created by Nitrogen Delta-Doping Using SF6 Plasma Treatment. Appl. Phys. Lett. 2015, 106, 113109. 24. Kaviani, K.; Deak, P.; Aradi, B.; Frauenheim, T.; Chou, JP.; Gali, A. Proper Surface Termination for Luminescent Near-Surface NV Centers in Diamond. Nano Lett. 2014, 14, 47724777. 25. Chou, JP.; Gali, A. Nitrogen-vacancy Diamond Sensor: Novel Diamond Surfaces from ab initio Simulations. MRS Commun. 2017, 7, 551-562. 26. Rietwyk, K. J.; Wong, L.; Cao, L.; O'Donnell, K. M.; Ley, L.; Wee, A. T. S.; Pakes, C. I. Work Function and Electron Affinity of the Fluorine-Terminated (100) Diamond Surface. Appl. Phys. Lett. 2013, 102, 091604. 27. Schenk, A.; Tadich, A.; Sear, M.; O'Donnell, K. M.; Ley, L.; Stacey, A.; Pakes, C. Formation of a Silicon Terminated (100) Diamond Surface. Appl. Phys. Lett. 2015, 106, 191603. 28. Schenk, A. K.; Tadich, A.; Sear, M. J.; Qi, D.; Wee, A. T. S.; Stacey, A.; Pakes, C. I. The Surface Electronic Structure of Silicon Terminated (100) Diamond. Nanotechnology 2016, 27, 275201.


36


Page 38 of 49

29. Sear, M. J.; Schenk, A. K.; Tadich, A.; Stacey, A.; Pakes, C. I. P-Type Surface Transfer Doping of Oxidised Silicon Terminated (100) Diamond. Appl. Phys. Lett. 2017, 110, 011605. 30. Strobel, P.; Riedel, M.; Ristein J.; Ley, L. Surface Transfer Doping of Diamond. Nature 2004, 430, 439-441. 31. Chandran, M.; Shasha, M.; Michaelson, S.; Hoffman, A. Nitrogen Termination of Single Crystal (100) Diamond Surface by Radio Frequency N2 Plasma Process: An in-situ X-Ray Photoemission Spectroscopy and Secondary Electron Emission Studies. Appl. Phys. Lett. 2015, 107, 111602. 32. Stacey, A.; O'Donnell, K. M.; Chou, JP.; Schenk, A.; Tadich, A.; Dontschuk, N.; Cervenka, J.; Pakes, C.; Hoffman, A.; Prawer, S. Nitrogen Terminated Diamond. Adv. Mater. Interfaces 2015, 2, 1500079. 33. Kageura, T.; Kato, K.; Yamano, H.; Suaebah, E.; Kajiya, M.; Kawai, S.; Inaba, M.; Tanii, T.; Haruyama, M.; Yamada, K.; et al. Effect of a Radical Exposure Nitridation Surface on the Charge Stability of Shallow Nitrogen-Vacancy Centers in Diamond. Appl. Phys. Express 2017, 10, 055503. 34. Kawarada, H.; Ruslinda, A. R. Diamond Electrolyte Solution Gate FETs for DNA and Protein Sensors Using DNA/RNA Aptamers. Phys. Status Solidi A 2011, 208, 2005-2016. 35. Zhu, D.; Bandy, J. A.; Li, S.; Hamers, R. J. Amino-Terminated Diamond Surfaces: Photoelectron Emission and Photocatalytic Properties. Surf. Sci. 2016, 650, 295. 36. Chou. JP.; Retzker, A.; Gali, A. Nitrogen-Terminated Diamond (111) Surface for RoomTemperature Quantum Sensing and Simulation. Nano Lett. 2017, 17, 2294−2298. 37. Teraji, T. High-Quality and High-Purity Homoepitaxial Diamond (100) Film Growth under High Oxygen Concentration Condition. J. Appl. Phys. 2015, 118, 115304.


37

Page 39 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


38. Fukuda, R.; Balasubramanian, P.; Higashimata, I.; Koike, G.; Okada, T.; Kagami, R.; Teraji, T.; Onoda, S.; Haruyama, M.; Yamada, K.; et al. Lithographically Engineered Shallow NitrogenVacancy Centers in Diamond for External Nuclear Spin Sensing. New J. Phys. 2018, 20, 083029. 39. Pham, L. M.; DeVience, S. J.; Casola, F.; Lovchinsky, I.; Sushkov, A. O.; Bersin, E.; Lee, J.; Urbach, E.; Cappellaro, P.; Park, H.; et al. NMR Technique for Determining the Depth of Shallow Nitrogen-Vacancy Centers in Diamond. Phys. Lev. B 2016, 93, 045425. 40. Bar-Gill, N.; Pham, L. M.; Belthangady, C.; Le Sage, D.; Cappellaro, P.; Maze, J. R.; Lukin, M. D.; Yacoby, A.; Walsworth, R. L. Suppression of Spin-Bath Dynamics for Improved Coherence of Multi-Spin-Qubit Systems. Nat. Commun. 2012, 3, 858. 41. Romach, Y.; Müller, C.; Unden, T.; Rogers, L. J.; Isoda, T.; Itoh, K. M.; Markham, M.; Stacey, A.; Meijer, J.; Pezzagna, S.; et al. Spectroscopy of Surface-Induced Noise Using Shallow Spins in Diamond. Phys. Lev. Lett. 2015, 114, 017601. 42. Ziegler, J. F.; Biersack J. P.; M. D.; SRIM - The Stopping and Range of Ions in Matter; SRIM Co., 2008. 43. Aslam, N.; Waldherr G.; Neumann, P.; Jelezko, F.; Wrachtrup J. Photo-Induced Ionization Dynamics of the Nitrogen Vacancy Defect in Diamond Investigated by Single-Shot Charge State Detection. New J. Phys. 2013, 15, 013064. 44. Balasubramanian, G.; Chan, I. Y.; Kolesov, R.; Al-Hmoud, M.; Tisler, J.; Shin, C.; Kim, C.; Wojcik, A.; Hemmer, P. R.; Krueger, A.; et al. Nanoscale Imaging Magnetometry with Diamond Spins under Ambient Conditions. Nature 2008, 455, 648–651. 45. Crystal-TRIM, M. Posselt, Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Material Research, 1991-2014.


38


Page 40 of 49

46. Álvarez, G. A.; Suter. D. Measuring the Spectrum of Colored Noise by Dynamical Decoupling. Phys. Lev. Lett. 2011, 107, 230501. 47. Suaebah, E.; Seshimo , Y.; Shibata, M.; Kono, S.; Hasegawa, M.; Kawarada, H. Aptamer strategy for ATP detection on nanocrystalline diamond functionalized by a nitrogen and hydrogen radical beam system. J. Appl. Phys. 2017, 121, 044506. 48. Chandran, M.; Shasha , M.; Michaelson, S.; Akhvlediani, R.; Hoffman, A. Incorporation of Nitrogen into Polycrystalline Diamond Surfaces by RF Plasma Nitridation Process at Different Temperatures: Bonding Configuration and Thermal Stabilty Studies by in situ XPS and HREELS. Phys. Status Solidi A. 2015, 11, 2487-2495. 49. Cai, J.; Retzker, A.; Jelezko, F.; Plenio, M. B. A Large-Scale Quantum Simulator on a Diamond Surface at Room Temperature. Nat. Phys. 2013, 9, 168-173.


39

Page 41 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Image


40


Figure 1. Overview of diamond surface terminationsSchematic illustration of diamond surface terminations reported thus far. The relation between the shallow NV centers and each surface termination are summarized below the illustrations. 254x173mm (150 x 150 DPI)


Page 42 of 49

Page 43 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Schematic illustrations of nitrogen-terminated diamond formed using MBE(a) Schematic diagram of MBE apparatus. (b) Schematic illustration of surface termination formed by nitrogen radical beam exposure. 254x111mm (150 x 150 DPI)



Figure 3. Investigation of silicon-terminated diamond.(a) Flow chart of experiments related to siliconterminated diamond. (b) RHEED image of silicon-terminated diamond ([110] incident). The right image corresponds to the (3×1) pattern caused by silicon termination. The interval of the pattern corresponds to a third of the strong reflection. (c) 10×10 µm confocal image of 2nd oxygen termination. (d) 10×10 µm confocal image of 2nd silicon termination in the same area. The right confocal image was captured several minutes after the left image. Note that the images in (c) and (d) were captured at different positions in the 1.2-keV-ion-implanted region. 254x155mm (150 x 150 DPI)


Page 44 of 49

Page 45 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. NV center charge stability evaluation based on Rabi oscillations.(a) Schematic illustration of Rabi oscillations. The vertical axis corresponds only to the tendency of the fluorescence intensity, thus, the value of this axis is meaningless. (b) Pulse sequence of Rabi oscillation measurements. The pulse duration corresponds to each plot of the Rabi oscillations. (c) Histograms of Rabi oscillation contrast after each surface treatment. 254x155mm (150 x 150 DPI)



Figure 5. Surface analysis of nitrogen-terminated diamond.(a) XPS wide scan of nitrogen-terminated diamond. (b) XPS C1s narrow scan of nitrogen termination. (c) XPS N1s narrow scan of nitrogen termination. (d) NEXAFS nitrogen K-edge spectrum. 245x185mm (150 x 150 DPI)


Page 46 of 49

Page 47 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Evaluation of spin property by Hahn echo measurement.(a) Pulse sequence of Hahn echo measurement. (b) Example of Hahn echo decays in nitrogen-terminated diamond; sequence 1 (red) and sequence 2 (black) from (a), respectively. (c) Normalized Hahn echo decay of (b). (d) T2 distribution in nitrogen-terminated diamond. 228x172mm (150 x 150 DPI)



Figure 7. 1H-NMR detection by NV centers in nitrogen-terminated diamond.(a) Pulse sequence of XY8-k measurement. (b) 1H-NMR detection by XY8-8 sequence. The depth of this NV center was estimated to be 7.0 nm. The plots correspond to each applied static magnetic field, 43.4 mT (red triangles), 45.8 mT (green squares), and 48.3 mT (blue circles). (c) Dependence of dip position on applied static magnetic field; the colored plots correspond to the plots in (c). The 1H-NMR results of another NV are indicated by grey stars. (d) The relation between the NV depth calculated by 1H-NMR measurement and T2 measured by Hahn echo sequence. 254x177mm (150 x 150 DPI)


Page 48 of 49

Page 49 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. Noise spectroscopy of the shallow NV centers in nitrogen-terminated diamond. (a) Noise spectrums measured by the shallow NV centers at different depths, 4.85 nm (orange), 7.97 nm (green), and 10.0 nm (blue), which were evaluated by 1H-NMR detection in nitrogen-terminated diamond. The colored region represents the 1σ confidence region. (b) Dependence of the coupling strength Δi on NV depth. The solid lines are fitting curves with Δi=ai/dxi and correspond to each noise source, which were distinguished by different values of τc, τc(1) = 9.0 μs (blue) and τc(2) = 143 ns (red). The dashed lines are the fitting curves for "x1 =2". 254x108mm (150 x 150 DPI)



Table of contents 83x25mm (300 x 300 DPI)


Page 50 of 49

Nitrogen-Terminated Diamond Surface for Nanoscale NMR by

Recommend Documents