Wafer-scale integration of single nanodiamonds via electrostatic-trapping

Domain: physics
Published: 2026-02-11
Editorial outcome: minor_revision

Abstract
Nanodiamonds (NDs) are key materials for building nanoscale quantum sensing, imaging and communication devices. Scalable configuration of single NDs on heterogeneous platforms, forming quantum emitter arrays, will be an essential solution towards realizing next-generation scalable quantum devices. However, NDs are challenging to manipulate because their size, shape and surface chemistry vary substantially. Here, we show a simple method based on electrostatic-trapping to rapidly and reliably pattern single ND arrays on arbitrary substrates at scale. Our method, which uses carefully engineered microscale hole templates and electrostatic force, captures single NDs across 8-inch wafers with 82.5% yields within 5 min. Systematic experimental and theoretical studies show the number of deposited NDs primarily depends on the diameter of the hole trap. The method is compatible with mature CMOS technologies, enabling the mass production of scalable and integrable quantum devices. This advancement is expected to accelerate the commercialization and industrial adoption of ND-based technologies.

Introduction
Diamond’s ability to host quantum defects – most notably nitrogen-vacancy (NV) centers – makes it an exceptional material for advancing quantum technologies 1–4. Nanodiamonds (ND), in particular, are ideal for quantum metrology, sensing and imaging 5–8, because they are small (typically 1-200 nm) 9, hard 10, chemically stable 11, and biocompatible 12. As heterogenous integration becomes more popular in advanced microelectronics and photonic integrated systems (PICs) 13–17, the ability to add arrays of single NDs into these systems on-demand and at scale will be an essential step towards realizing next-generation monolithic quantum devices that are multifunctional and programmable 18–20.

Manipulating NDs, however, is challenging. Their size, shape and surface chemistry are inherently heterogenous, unlike spherical silicon dioxide (SiO 2), polystyrene (PS) and metallic nanoparticles 21–23. Template-assisted methods 24–26, electrostatic self-assembly 27–30, three-dimensional (3D) printing 31, 32 and atomic force microscope (AFM) tip-based transfer 33, 34 are currently used to pattern ordered single NDs. However, these methods are tedious and can only yield a few single ND across millimeter-scale areas. Moreover, producing miniature hole and disk templates for confining NDs require time-consuming and expensive electron beam lithography setups, which are incompatible with complementary metal-oxide semiconductor (CMOS) technology.

Here, we report a simple CMOS-compatible method based on electrostatic-trapping to reliably integrate single ND arrays onto arbitrary substrates at scale, filling a long-term gap between laboratory and industrial scale production of ND-based quantum devices. Inspired by template-assisted patterning, where NDs are confined within holes or disks, and concepts in optical tweezers, where optical field gradient force is used to confine miniature objects within the narrow waist of a laser beam 35–37, we constructed an electrostatic field force gradient inside a template hole to electrostatically anchor single-NDs at the center of the hole. To ensure the electrostatic field force is distributed within the narrow space inside the template hole, we introduced positive charges on the template surface and maintained negatively charged template sidewalls. The resulting spatial electrostatic field distribution gradient allows only electronegative NDs, which are typically functionalized with -COOH groups, to pass through the hole and anchor to the positively charged template surface at the bottom of the hole (Fig. 1a).

Results
For our experiments, we used NDs with an average diameter of 150 nm (Fig. 1b and Supplementary Fig. 1). The NDs were processed via salt-assisted air oxidation to remove surface-adsorbed impurities, such as ultrasmall NDs and disordered carbons, and dispersed in an aqueous solution (Methods). The typical diamond Raman peak at 1333 cm⁻¹ with a narrow full width at half maximum (FWHM), indicates the high crystalline quality of the nanodiamonds (Supplementary Fig. 2). The photoluminescence (PL) emitted from nitrogen-vacancy (NV) centers in the nanodiamonds, demonstrates their quantum functionality. To obtain the trapping template, we treated a silicon (Si) substrate in oxygen plasma for 10 min to increase its hydrophilicity (Supplementary Fig. 3) and chemically modified the resulting hydroxylated surface with positively charged amino (NH 3+) functional groups by immersing the substrate in 5% 3-aminopropyltriethoxysilane (APTES) solution for 3 hours (Supplementary Fig. 4 and Methods). The corresponding chemical reaction are displayed as follows:

(C 2H 5O) 3Si(CH 2) 3NH 2+3H 2O ! (OH) 3Si(CH 2) 3NH 2+3C 2H 5OH (1)

(OH) 3Si(CH 2) 3NH 2+OH-surface ! surface-O-Si(CH 2) 3NH 2+H 2O (2)

A layer of negatively charged photoresist is then spin-coated onto the modified substrate and circular holes are patterned using photolithography (Fig. 1c). Trapping involves covering the holes with aqueous ND (0.1 mg/mL) and letting it sit at room temperature for 5 minutes (Supplementary Fig. 5 and Movie 1).

Single ND arrays formed after the 5-min incubation (Fig. 1b), and the remaining aqueous ND is collected with a pipette for reuse. Immersing the substrate in acetone removes the template in one minute. ND concentrations that are either too low or too high caused insufficient trapping, indicating that the number of NDs matter and overly high numbers of NDs can interfere with the trapping electrostatic field (Supplementary Fig. 6). Trapping single NDs in the holes depends on the incubation time and hole diameter (Supplementary Fig. 7). For a 3.6 µm diameter hole, a single ND is typically trapped after about 5 min—within the observed onset range of 3-6 min—and remained single for about 3 hours, with an estimated uncertainty of ±0.5 hours before additional NDs populated the hole (Supplementary Fig. 8). Longer incubation times can damage the photoresist and compromise the internal electrostatic field. Larger holes (≥6 µm) trapped multiple NDs and became saturated over time.

Our method is scalable and tunable. Large-area ND arrays observable with naked eyes can be easily obtained on an 8-inch Si wafer (Fig. 1d). Dark-field optical images of arrays from different regions of the Si wafer show the ND patterns are highly uniform and clean (Fig. 1e). Timely collection of the aqueous ND with the pipette is key. Residues form on the patterned arrays when the ND solution is allowed to self-evaporate (Supplementary Note. 1 and Supplementary Fig. 9). Additionally, the small ND arrays and large mark ‘HKU’ on the wafer illustrate the flexibility of our method, enabling the ND patterning from micro to macro scale.

We show ND trapping through electrostatic absorption is feasible in our setup. Kelvin probe force microscopy (KPFM) measurements show that amino-modified holes displayed significantly higher surface electrostatic potential (~112 mV) than bare, unmodified ones (~40 mV) (Fig. 2a). Notably, surface electrostatic potential saturates easily for substrates that were incubated for longer than 3 hours in APTES (Supplementary Fig. 10). The photoresist template performed an electrostatic potential of −13 mV relative to the bare substrate. Additionally, NDs subjected to salt-assisted air oxidation displayed high zeta potential with an average value of −35 mV (Fig. 2b). These negatively charged NDs were trapped only in positively charged amino-modified holes (Fig. 2c), regardless of hole diameter (Supplementary Fig. 11). No NDs were seen in all sizes of bare, unmodified holes. Furthermore, when other ions that could break down the trapping electrostatic field such as Na+ and Cl- ions were introduced into the aqueous ND solution, no trapping was observed (Supplementary Fig. 12). These results together strongly suggest that ND trapping occurred through electrostatic absorption.

We further verified that the hourglass shape trapping method proposed in Fig. 1a is not influenced by poor aqueous infiltration in the template hole. Our experiments show water completely infiltrated 3-µm wide holes after 10 min (Supplementary Fig. 13). To determine the trapping conditions and configuration in the template hole (Fig. 3a), we used finite element method (COMSOL Multiphysics) and mean-field Poisson-Boltzmann (PB) theory 38, 39 to calculate the spatial distribution of electrostatic potential in the template hole (Methods). Applying appropriate boundary conditions and solving the non-linear PB equations in the model, we find that the electrostatic potential ψ inside the hole is non-uniform, decaying either from top to bottom or from the edge to the center of the hole (Fig. 3b). This condition naturally causes a negatively charged particle to move towards a location with lower potential, that is, to the center and bottom of the hole as observed in our experiments. Based on standard electric potential threshold values for triggering the movement of charged particles, we further identified the center of the hourglass shape as the region most likely to trap a ND (Supplementary Fig. 14). These theoretical results are consistent with the experimental results and the proposed trapping model in Fig. 1a.

Because hole diameter affects the number of trapped NDs, we also calculated the effective trapping region for holes of different diameters (Supplementary Fig. 14). By quantitatively comparing the minimal horizontal width of the effective trapping volume marked in Fig. 3b, we found that the trapping width enlarges linearly with hole diameter, D (Fig. 3c), but not hole depth, h (Fig. 3d). For a 3 µm diameter hole, the trapping width at different h was consistently around 0.4 µm. In agreement with these calculations, our experimental results show that trapping single ND is more sensitive to D than h (Fig. 3e and Supplementary Fig. 15). Consequently, the number and size of trapped NDs can be easily tailored through D. Our trapping method is universal and can be used to capture other types of particles, including silica, polystyrene and gold nanoparticles (Supplementary Fig. 16). The method is also versatile and can be applied to arbitrary substrates, such as glass, sapphire, and gold (Supplementary Fig. 17).

We repeated each ND trapping experiment 5 times and confirmed the method is highly reproducible even for a 25 × 25 array (Fig. 4a-d). Examining the distributed position of trapped NDs, we found that most NDs were concentrated within 500 nm from the hole’s center (Fig. 4e and Supplementary Fig. 18). Particularly, based on the minimum displacement from the target center, the achievable highest resolution was estimated to be approximately 13 nm. This concentrated area is consistent with the calculated minimal trapping width in Fig. 3 and shows that the trapping is highly accurate. Counting the number of single ND in the entire array after template removal, we found that up to 82.5% of the array had a single ND (Fig. 4c, d, f and Supplementary Fig. 19). This single ND yield and 8-inch wafer patterning area is highest amongst other single ND placement methods (Fig. 4g and Supplementary Table 1) 24, 27, 31. In principle, our approach can be extended to the largest commercially available Si wafer (12-inch), and the single ND yield can be further improved through more precise photolithography setups.

The electrostatic-trapping method is compatible with hybrid platforms and current CMOS technology. We fabricated scalable heterogenous platforms such as silicon waveguides, gallium nitride (GaN) pillars, and gold microwave antennas through mature CMOS technology and used our electrostatic-trapping method to integrate single ND arrays (Fig. 5a and Supplementary Note. 2). After template removal, the trapped NDs remained in position (Fig. 5b and c). Notably, they remain positionally stable even after long-term high-temperature processing, which is vital for subsequent device fabrication (Supplementary Fig. 20). Compatibility with CMOS technology means that our method can be broadly applied to a host of other heterogenous platforms and devices. In addition, for future implementations that require optimized light-matter interaction (e.g., nanocavity), achieving tighter control over ND size uniformity would further enhance device performance. Normally, the size uniformity of ND is crucial because it determines surface-to-volume ratio, local strain, and light–matter interaction. Although the main properties of quantum photonics, such as single-photon emission, antibunching behavior, and overall photoluminescence stability, are primarily governed by the quality of the color center and its local environment, rather than by small variations in ND diameter. However, ND size can influence the local photonic environment and thus affect emission rate, coupling efficiency to photonic structures, and collection efficiency.

In conclusion, we have developed an electrostatic-trapping method to rapidly integrate single ND array with CMOS-compatible platforms at scale. Using standard photolithography and electrostatic field force, we realized reliable trapping of single ND array across large areas (8-inch wafer scale) with high single ND yields (82.5%). Unlike current strategies, our method is simple, highly reproducible, CMOS-compatible and scalable to any commercially available platform. The experiment and simulation results show that trapping is made possible by the non-uniform distribution of electrostatic potential inside the trapping template hole. An hourglass-like trapping channel within the hole controls the passage of single ND. We show the method can be used to place single ND arrays on heterogenous platforms fabricated using standard CMOS technology. The ability to reliably order single NDs at scale on any platform through such a simple method is expected to impact the development and commercialization of various ND-based quantum sensing, imaging, communication and computing technologies.

Methods
ND processing via salt-assisted air oxidation
NDs with an average size of 150 nm (HPHT, PolyQolor, China) were first mixed with sodium chloride (NaCl, 99.5%, Sigma-Aldrich) at a ratio of 1:5, followed by heating at 500 °C for 5 h in air. Next, the mixtures of ND and NaCl were dispersed in deionized (DI) water and sonicated for 1 h, and then NDs were purified with DI water for 3 times by centrifugation (first: 1000 rcf, 5 min; second: 3000 rcf, 5 min; third: 8000 rcf, 10 min). Finally, the purified NDs were re-dispersed in DI water and sonicated for 10 min to obtain well-dispersed ND suspension for further use.

Template preparation
The employed silicon (Si) wafer was first cleaning in ultrasound bath in acetone, isopropyl alcohol (IPA), DI water for 10 min, respectively, followed by drying with nitrogen gas. Then, the clean Si wafer was treated by oxygen plasma for 10 min to increase surface hydrophilicity. After that, the Si wafer was immersed in the solution of ethanol and silane agent (3-Aminopropyltriethoxysilane) with a ratio of 1:30 for 3 hours at room temperature.

After completion of surface modification on Si wafer, the standard micro/nanofabrication process was utilized to generate the template pattern. First, the photoresist AZ5214 was spin-coated on Si wafer at a rate of 4500 r/min for 50 s, followed by post-baking at 90 °C for 60 s. Then, the template pattern was defined by photolithography at a UV dose of 300 mJ/cm2 and then developed for 60 s. The preparation of trapping template was therefore well achieved.

ND trapping processes
After preparation of ND aqueous and trapping template, the ND aqueous was diluted to 0.1 mg/mL and sonicated for 20 min to realize sufficient dispersion. Then, using a pipette to control a certain volume of ND solution and drop on the template, in which the solution should completely cover the template pattern. Next, keeping the coverage for 5 min at room temperature, followed by collection of ND solution from the template by the pipette. To further remove the template, the wafer after completion of ND trapping should be immersed in acetone solution for 1 min, followed by drying with nitrogen gas.

Calculating the spatial distribution of electrostatic potential in template holes
According to the geometrically induced electrostatic trapping mechanism in fluids, the corresponding model in our case was built based on the practical measurements in Fig. 2. As shown in Fig. 3a, the bottom layer represents a Si substrate, while the holes on its top are formed by a layer of photoresist. When in contact with DI water, the surface of the holes can ionize and dissociate chemical groups, resulting in electrostatic potentials on both the Si substrate and the photoresist walls, referred to as φ bottom and φ wall, respectively. Using the mean-field Poisson-Boltzmann (PB) theory 38, 39, we can calculate the electrostatic potential free energy of the ND particles in this system. By analyzing the distribution of the electrostatic potential, we can understand why ND particles tend to deposit at the center of the holes and the relationship between the deposition distribution and the size of the holes.

By setting appropriate boundary conditions, we can solve the nonlinear PB equation and obtain the spatial distribution of the electrostatic potential by using COMSOL Multiphysics 38–40. Near an isolated ionized surface, the electrostatic potential ψ decays exponentially with distance, following the relationship 41:

ψ(z) = ψ 0 exp(-κz) (3)

Among them ψ 0 is the surface value, κ-1 represents the Debye length, in electrolyte solution 42,

κ-1 = (ε ε 0 k B T / 2 c 0 e 2) 1/2 (4)

c 0 represents the salt concentration in the electrolyte, ε ε 0 is the dielectric constant of the medium, and e is the elementary charge. In a cylindrical hole-shaped hole with a diameter of 2r, the electrostatic potential decays monotonically from the circular hole wall and reaches a minimum at the center when the fluid fills the entire hole. We define a dimensionless PB equation and assume that the electrostatic potential can be expressed as:

∇2ψ = (κr) 2 sinh(ψ) (5)

where r represents the radius of the trap and κ-1 represents the inverse Debye length based on the condition of the solution. We assume that the interior of nanodiamonds is a uniform dielectric environment, with a dielectric constant of ε p, namely, ∇2ψ = 0. Because the electrostatic potential of wall is constant, we set the Dirichlet boundary condition:

ψ s = ψ w (6)

By measuring surface potential using KPFM, the surface potential of the photoresist in solution with pH=7 ψ wall ≈ -13 mV, while surface potential of silicon in DI water is positive, ψ bottom ≈ +72 mV (after silanization processing). Setting the dimensionless electrostatic potential u to facilitate calculation, which is also one of the parameters required for simulation results:

u = eψ / k B T (7)

For the particle properties, measurements have shown that the surface potential is approximately -35 mV, and the diameter is around 150 nm. Based on previous statistical measurements and data analysis 43, 44, the particle charge q is estimated to be approximately -120 e. The simulation results are shown in Fig. 3b, where the cross-sectional electrostatic potential is represented as qψ in units of k B T. It is generally believed that when qΔψ is approximately 10 k B T, the particle can acquire sufficient trapping force to remain in a relatively stable position within the hole. From Fig. 3b, it can be observed that at the center of the same horizontal cross-section, the electrostatic potential is the lowest. The dashed lines represent the positions where qΔψ is equal to 10 k B T at each height, and the regions between them can be referred to as traps for capturing particles (Fig. 3b and Supplementary Fig. 14). When the hole diameter is 2 μm, the trap region is the smallest, which facilitates the convergence and deposition of particles towards the center of the bottom. As the hole diameter increases, the trap gradually widens, leading to the gradual dispersion of particles at the bottom and an increase in the deposition radius. Since the particles carry charges of the same sign and repel each other, when the trap diameter is small, fewer particles can fit inside, resulting in a reduced number of deposited nanoparticles. Conversely, when the trap is wide enough, more particles can pass through it, leading to an increased number of particles at the bottom. This explains why a smaller hole diameter corresponds to fewer deposited particles, which are more prone to converge towards the center, while a larger hole diameter leads to more deposited particles and a wider deposition area.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "General\nIn this paper from Jixiang Jing et al. the authors develop and demonstrate a novel approach based on electrostatic trapping to integrate arrays of nanodiamonds onto a substrate at a relatively large scale. The methods uses a combination of a patterned (dissolvable) template, an electrostatic field force and functionalization of the nanodiamonds surface to make them electronegatively charged. The authors show both theoretical and experimental results demonstrating the effectiveness of the technique.\nThe mechanism seems clean, neat and effective, and the results of patterned nanodiamonds shown in figures 1, 4 and 5 are convincing. The method is compatible with other fabrication techniques and in fact it shines for placing NDs on top of other electronic and photonic structures (as nicely shown in figure 5).\nThe paper is well written, the results are convincing, and both presented and discussed well. The paper is short but to the point, which is commendable. My only concern regards the statistical analysis: most figures of merit are quoted (I guess) as average values, but the uncertainties are missing (see specific comments below).\nI recommend the paper for publication in Nature Communications provided the authors address a few comments specified below, in particular points (b) and (c).\nSpecific comments\na) Across the whole paper the referencing is not done properly. The superscript should appear after punctuation, for instance instead of “…for advancing quantum technologies 1, 2, 3, 4.” It should be “… for advancing quantum technologies.1, 2, 3, 4” (with the number obviously superscript).\nb) On lines 88 and 89 of page 2, the authors make a claim that a single ND is trapped in a hole after 5 minutes and stays single for up to 3 hours (after which the hole gets populated with more NDs). These estimates are too vague; I suspect these are average values so the authors should specify uncertainties on them.\nc) The authors discuss the relation between hole diameter in the template and number of trapped NDs. This is fine, but there is no mention of what is the ultimate resolution with which they can position a single ND. There is mention on page 6, line 177 that each ND sits ~500 nm from the hole center but the authors must include a discussion about what is the highest precision and resolution they can achieve. That is, how far the ND is from where they want to put it (i.e. the accuracy/precision) and how reliable that is (i.e. the resolution, calculated, for instance, as the standard deviation over many repetitions).", "reviewer_2": "The manuscript presents a scalable electrostatic-trapping method for positioning single nanodiamonds (NDs) on heterogeneous substrates to form ordered arrays. The authors report an impressive yield of 82.5% for single-ND capture across 8-inch wafers within 5 minutes, supported by both experimental validation and theoretical modeling. The proposed electrostatic-trapping approach is conceptually simple yet highly effective, representing a practical route toward large-scale integration of quantum emitters. The study addresses an important bottleneck in quantum photonics—the deterministic placement of nanoscale emitters—and could have significant implications for scalable quantum device fabrication. The work is overall interesting. The demonstration on an 8-inch wafer highlights the method’s scalability and industrial relevance, aligning well with the applied-physics and materials focus of Nature Communications.\nThe long-term stability of the electrostatically trapped NDs under thermal stress should be examined, especially if the technique is intended for practical device fabrication.\nAdditional discussion on the uniformity of ND size and its potential impact on optical and quantum performance would strengthen the paper’s relevance to quantum photonics applications.\nFor a fair comparison with other ND placement methods, the particle sizes of the NDs in this work and previous work should be listed in a table (ND sizes, yields, scalability, etc).\nThe intrinsic properties of the NDs should be characterized, for example through Raman spectroscopy and photoluminescence measurements, to confirm material quality and optical functionality.\nWhen referring to “arbitrary substrates,” please clarify whether both conductive and insulating substrates are included. If applicable, it would be valuable to demonstrate patterning on distinct materials such as glass, sapphire, or metals (e.g., Cu) to confirm the versatility of the approach."}, "author_response": "Point-by-point response:\nWe would like to express our gratitude to all the reviewers for evaluating our manuscript and providing valuable feedback. We have made the necessary revisions to the manuscript in accordance with the suggestions provided. Please find our point-by-point response to each comment below:\nReferee#1:\nIn this paper from Jixiang Jing et al. the authors develop and demonstrate a novel approach based on electrostatic trapping to integrate arrays of nanodiamonds onto a substrate at a relatively large scale. The methods use a combination of a patterned (dissolvable) template, an electrostatic field force and functionalization of the nanodiamonds surface to make them electronegatively charged. The authors show both theoretical and experimental results demonstrating the effectiveness of the technique.\nThe mechanism seems clean, neat and effective, and the results of patterned nanodiamonds shown in figures 1, 4 and 5 are convincing. The method is compatible with other fabrication techniques and in fact it shines for placing NDs on top of other electronic and photonic structures (as nicely shown in figure 5). The paper is well written, the results are convincing, and both presented and discussed well. The paper is short but to the point, which is commendable. My only concern regards the statistical analysis: most figures of merit are quoted (I guess) as average values, but the uncertainties are missing (see specific comments below). I recommend the paper for publication in Nature Communications provided the authors address a few comments specified below, in particular points (b) and (c).\nSpecific comments\na) Across the whole paper the referencing is not done properly. The superscript should appear after punctuation, for instance instead of “…for advancing quantum technologies 1, 2, 3, 4.” It should be “… for advancing quantum technologies.1, 2, 3, 4” (with the number obviously superscript).\nResponse: We acknowledge the reviewer for pointing out this format issue. As suggested, we have conducted revisions accordingly.\nb) On lines 88 and 89 of page 2, the authors make a claim that a single ND is trapped in a hole after 5 minutes and stays single for up to 3 hours (after which the hole gets populated with more NDs). These estimates are too vague; I suspect these are average values so the authors should specify uncertainties on them.\nResponse: We highly appreciate the reviewer’s concern here, which reflects a rigorous scientific attitude. To more accurately determine the onset and termination times of single-ND trapping, we have conducted detailed observations from five experiments (Fig. R1). The results show that the trapping onset for a single ND ranges from 3 to 6 minutes, and the corresponding trapping duration extends from 2.5 to 4 hours.\nModification:\nWe have added Fig. R1 as Supplementary Fig. 8 in the revised supporting materials.\nBefore: “For a 3.6 µm diameter hole, a single ND is trapped after 5 min and remained single for 3 hours before additional NDs populated the hole.”\nAfter: “For a 3.6 µm diameter hole, a single ND is typically trapped after about 5 min—within the observed onset range of 3-6 min—and remained single for about 3 hours, with an estimated uncertainty of ±0.5 hours before additional NDs populated the hole (Supplementary Fig. 8)” (Page 3, line 1-3, Main text)\nFig. R1\nThe trapping performance as times for 3 µm-diameter template holes from five experiments.\nc) The authors discuss the relation between hole diameter in the template and number of trapped NDs. This is fine, but there is no mention of what is the ultimate resolution with which they can position a single ND. There is mention on page 6, line 177 that each ND sits ~500 nm from the hole center but the authors must include a discussion about what is the highest precision and resolution they can achieve. That is, how far the ND is from where they want to put it (i.e. the accuracy/precision) and how reliable that is (i.e. the resolution, calculated, for instance, as the standard deviation over many repetitions).\nResponse: We sincerely admire the rigorous academic attitude of the reviewer. To clarify the ultimate resolution of our method for positioning single ND, we analyzed the statistical data in Fig. 4e to estimate their displacement from the target center. As shown in Fig. R2, the achievable highest resolution is estimated to be approximately 13 nm.\nModification:\nBefore: “, we found that most NDs were concentrated within 500 nm from the hole’s center (Fig. 4e and Supplementary Fig. 18).”\nAfter: “, we found that most NDs were concentrated within 500 nm from the hole’s center (Fig. 4e and Supplementary Fig. 18). Particularly, based on the minimum displacement from the target center, the achievable highest resolution was estimated to be approximately 13 nm.” (Page 6, line 14-17, Main text)\nFig. R2\na, Statistics of the relative positions of NDs within the template holes of a 25 × 25 array. b, The distribution of NDs within the displacement range of 100 nm × 100 nm, where the cross in red indicates the target center.\nReferee#2:\nThe manuscript presents a scalable electrostatic-trapping method for positioning single nanodiamonds (NDs) on heterogeneous substrates to form ordered arrays. The authors report an impressive yield of 82.5% for single-ND capture across 8-inch wafers within 5 minutes, supported by both experimental validation and theoretical modeling. The proposed electrostatic-trapping approach is conceptually simple yet highly effective, representing a practical route toward large-scale integration of quantum emitters. The study addresses an important bottleneck in quantum photonics—the deterministic placement of nanoscale emitters—and could have significant implications for scalable quantum device fabrication. The work is overall interesting. The demonstration on an 8-inch wafer highlights the method’s scalability and industrial relevance, aligning well with the applied-physics and materials focus of Nature Communications.\n1. The long-term stability of the electrostatically trapped NDs under thermal stress should be examined, especially if the technique is intended for practical device fabrication.\nResponse: We highly appreciate the reviewer’s concern here. To demonstrate the long-term positional stability of the trapped NDs, we first integrated the ND array on top of silicon pillars, which serve as position references. We then heated the sample at 300 °C for 1, 2, and 3 hours, respectively. From the results in Fig. R3, we can see there is no loss of NDs and no obvious positional shift even after long-term high-temperature processing.\nModification:\nWe have added Fig. R3 as Supplementary Fig. 20 in the revised supporting materials.\nBefore: “After template removal, the trapped NDs remained in position (Fig. 5b and 5c).”\nAfter: “After template removal, the trapped NDs remained in position (Fig. 5b and 5c). Notably, they remain positionally stable even after long-term high-temperature processing, which is vital for subsequent device fabrication (Supplementary Fig. 20).” (Page 8, line 3-4, Main text)\nFig. R3\nLong-term positional stability of trapped nanodiamonds under 300 ℃ heating for different durations.\n2. Additional discussion on the uniformity of ND size and its potential impact on optical and quantum performance would strengthen the paper’s relevance to quantum photonics applications.\nResponse: We thank the reviewer for raising this important point. We have carefully reviewed relevant works and summarized the potential influence as follows:\n“The size uniformity of ND is crucial because it determines surface-to-volume ratio, local strain, and light–matter interaction. Particularly, the main properties of quantum photonics, such as single-photon emission, antibunching behavior, and overall photoluminescence stability, are primarily governed by the quality of the color center and its local environment, rather than by small variations in ND diameter. However, ND size can influence the local photonic environment and thus affect emission rate, coupling efficiency to photonic structures, and collection efficiency. Thus, achieving tighter control over ND size uniformity would enhance device performance especially for applications that require precise light–matter coupling engineering (e.g., integration with nanophotonic cavities or waveguides).”\nModification:\nWe have added this discussion in the revised manuscript.\nBefore: “Compatibility with CMOS technology means that our method can be broadly applied to a host of other heterogenous platforms and devices.”\nAfter: “Compatibility with CMOS technology means that our method can be broadly applied to a host of other heterogenous platforms and devices. In addition, for future implementations that require optimized light-matter interaction (e.g., nanocavity), achieving tighter control over ND size uniformity would further enhance device performance. Normally, the size uniformity of ND is crucial because it determines surface-to-volume ratio, local strain, and light–matter interaction. Although the main properties of quantum photonics, such as single-photon emission, antibunching behavior, and overall photoluminescence stability, are primarily governed by the quality of the color center and its local environment, rather than by small variations in ND diameter. However, ND size can influence the local photonic environment and thus affect emission rate, coupling efficiency to photonic structures, and collection efficiency.” (Page 8, line 6-13, Main text)\n3. For a fair comparison with other ND placement methods, the particle sizes of the NDs in this work and previous work should be listed in a table (ND sizes, yields, scalability, etc).\nResponse: We sincerely admire the rigorous academic attitude of the reviewer. As suggested, we have included a comparison of various methods with respect to ND size, single-ND yield, and scalability, which is summarized in Table R1.\nModification:\nWe have added Table R1 as Supplementary Table. 1 in the revised supporting materials.\nBefore: “This single ND yield and 8-inch wafer patterning area is highest amongst other single ND placement methods (Fig. 4g)”\nAfter: “This single ND yield and 8-inch wafer patterning area is highest amongst other single ND placement methods (Fig. 4g and Supplementary Table. 1)” (Page 7, line 1, Main text)\nTable R1. Comparison of different methods for ND placement\nMethod ND size (nm) Single ND yield (%) Scalability (cm2) Reference\nElectrostatic self-assembly 40 48 1.6 × 10-5 1\nPMMA template 40 76 4.2 × 10-5 2\n3D print 40 40 3.6 × 10-6 3\nPMMA template 50 42.8 1 × 10-4 4\n‘dip-pen’ nanolithography 60 N/A 4.3× 10-5 5\nElectrostatic trapping 100-150 82.5 324 This work\nReferences:\n1. Jiang M, Kurvits JA, Lu Y, Nurmikko AV, Zia R. Reusable inorganic templates for electrostatic self-assembly of individual quantum dots, nanodiamonds, and lanthanide-doped nanoparticles. Nano Lett 15, 5010-5016 (2015).\n2. Shulevitz HJ, et al. Template-assisted self-assembly of fluorescent nanodiamonds for scalable quantum technologies. Acs Nano 16, 1847-1856 (2022).\n3. Xu Z, et al. On‐Demand, Direct Printing of Nanodiamonds at the Quantum Level. Advanced Science 9, 2103598 (2022).\n4. Komrakova S, et al. CMOS compatible nanoantenna-nanodiamond integration. In: Journal of Physics: Conference Series). IOP Publishing (2019).\n5. Singh S, Thomas V, Martyshkin D, Kozlovskaya V, Kharlampieva E, Catledge SA. Spatially controlled fabrication of a bright fluorescent nanodiamond-array with enhanced far-red Si-V luminescence. Nanotechnology 25, 045302 (2014).\n4. The intrinsic properties of the NDs should be characterized, for example through Raman spectroscopy and photoluminescence measurements, to confirm material quality and optical functionality.\nResponse: We appreciate the reviewer’s insightful suggestion. To better demonstrate the properties of the nanodiamonds used in our work, we have added Raman and photoluminescence (PL) characterizations. The typical diamond Raman peak at 1333 cm⁻¹ with a narrow full width at half maximum (FWHM), as shown in Fig. R4a, indicates the high crystalline quality of the nanodiamonds. The PL spectrum in Fig. R4b, together with the PL image of the nanodiamond arrays in Fig. R4c, confirms the emission from nitrogen-vacancy (NV) centers in the nanodiamonds.\nModification:\nWe have added Fig. R4 as Supplementary Fig. 2 in the revised supporting materials.\nBefore: “The NDs were processed via salt-assisted air oxidation to remove surface-adsorbed impurities, such as ultrasmall NDs and disordered carbons, and dispersed in an aqueous solution (Methods).”\nAfter: “The NDs were processed via salt-assisted air oxidation to remove surface-adsorbed impurities, such as ultrasmall NDs and disordered carbons, and dispersed in an aqueous solution (Methods). The typical diamond Raman peak at 1333 cm⁻¹ with a narrow full width at half maximum (FWHM), indicates the high crystalline quality of the nanodiamonds (Supplementary Fig. 2). The photoluminescence (PL) emitted from nitrogen-vacancy (NV) centers in the nanodiamonds, demonstrates their quantum functionality.” (Page 2, line 28-31, Main text)\nFig. R4\na, Raman spectrum of the nanodiamonds used in this work. b, Photoluminescence spectrum of NV centers in the nanodiamonds. c, Photoluminescence image of patterned nanodiamond arrays.\nExperimental parameter: 532 nm laser excitation laser, 100 µW power, collection with a 0.95 NA air objective.\n5. When referring to “arbitrary substrates,” please clarify whether both conductive and insulating substrates are included. If applicable, it would be valuable to demonstrate patterning on distinct materials such as glass, sapphire, or metals (e.g., Cu) to confirm the versatility of the approach.\nResponse: The reviewer’s concern about the versatility of the approach reflects a rigorous scientific attitude. To demonstrate this, we patterned nanodiamonds on different substrates, including glass, sapphire, and gold. As shown in Fig. R5, by adjusting the size of the template holes, we can achieve nanodiamond trapping from single to multiple particles on all three substrates. Owing to differences in surface chemistry, the trapping performance varies between substrates. For example, the hole size required for single nanodiamond trapping is smaller on glass than on the other substrates.\nModification:\nWe have added Fig. R5 as Supplementary Fig. 17 in the revised supporting materials.\nBefore: “Our trapping method is universal and can be used to capture other types of particles, including silica, polystyrene and gold nanoparticles (Supplementary Fig. 16).”\nAfter: “Our trapping method is universal and can be used to capture other types of particles, including silica, polystyrene and gold nanoparticles (Supplementary Fig. 16). The method is also versatile and can be applied to arbitrary substrates, such as glass, sapphire, and gold (Supplementary Fig. 17).” (Page 5, line 29-30, Main text)\nFig. R5\nTrapping performance for holes of different sizes on glass, sapphire, and gold substrates. All scale bars are 10 µm."}, {"round": 2, "reviewer_comments": {"reviewer_1": "All my comments have been addressed in a satisfactory manner. I recommend publication of the updated manuscript", "reviewer_2": "The comments were all addressed. The paper is acceptable."}, "author_response": ""}]

Decision letter