Method for forming bonded diamond film heterostructures

Abstract

A method for forming a bonded diamond film heterostructure and a bonded diamond film heterostructure are provided that do not have the drawbacks of the prior art. A method for forming a bonded diamond film heterostructure includes the steps of: (a) subjecting a surface of a target substrate to plasma ashing to provide a plasma-treated target substrate having a plasma-treated surface; and (b) contacting the plasma-treated surface of the plasma-treated target substrate with a surface of a diamond film to form a bonded diamond film heterostructure, the bonded diamond film heterostructure comprising the target substrate covalently bonded to the diamond film at a bonding interface formed between the plasma-treated surface of the plasma-treated target substrate and the surface of the diamond film. Also provided is a bonded diamond film heterostructure formed using this method.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 428,236, filed November 28, 2022, the entire contents of which are incorporated herein by reference.

[0002] Reference to government rights This invention was made with government support under DE FOA-0002253 awarded by the U.S. Department of Energy. The U.S. Government has certain rights in this invention. [Background technology]

[0003] Diamond is a key material platform in quantum information science, enabling numerous groundbreaking demonstrations in quantum sensing and quantum communication. These demonstrations rely on devices fabricated directly in monolithic bulk diamond, which presents high costs, low throughput, and low yields, limiting scalability and device functionality. For example, millimeter-scale electronic-grade diamond is limited in availability and costs thousands of dollars. Additionally, device functionality is highly limited by the diamond material. Diamond material lacks any significant nonlinear optical response and is difficult to fabricate at the nanoscale without degradation of optical and spin qubit properties. While color centers in diamond can be used to probe biological and chemical phenomena, integrating diamond substrates with nondiamond materials used in quantum applications is challenging. Summary of the Invention [Problem to be solved by the invention]

[0004] A method for forming bonded diamond film heterostructures is provided. The method uses a diamond film (e.g., an ultrathin single-crystal (100) diamond) and a non-diamond target substrate (e.g., lithium niobate) to achieve a strongly bonded (e.g., covalent) dissimilar material bond between the diamond film and the target substrate without the use of an intervening material. This contrasts with existing methods that use non-covalent interactions (e.g., van der Waals forces) or intermediate bonding layers such as epoxy or hydrogen silsesquioxane. Additionally, the bonded interface of the bonded diamond film heterostructure is highly crystalline and extremely thin, in contrast to the amorphous and / or thick bonded interfaces produced using existing methods. This method enables the integration of diamond films into a variety of devices, including non-diamond materials, such as those used in quantum sensing and quantum communication applications. [Means for solving the problem]

[0005] Embodiment 1 is a method of forming a bonded diamond film heterostructure, the method comprising the steps of: (a) subjecting a surface of a target substrate to plasma ashing to provide a plasma-treated target substrate having a plasma-treated surface; and (b) contacting the plasma-treated surface of the plasma-treated target substrate with a surface of a diamond film to form a bonded diamond film heterostructure, the bonded diamond film heterostructure comprising the target substrate covalently bonded to the diamond film at a bonding interface formed between the plasma-treated surface of the plasma-treated target substrate and the surface of the diamond film.

[0006] Embodiment 2 is the method of embodiment 1, further comprising subjecting the surface of the diamond film to plasma ashing before step (b) to provide a plasma-treated surface of the diamond film.

[0007] Embodiment 3 is the method according to any one of embodiments 1 to 2, wherein the plasma ashing is carried out using O2 plasma.

[0008] Embodiment 4 is the method of any of embodiments 1-3, wherein the plasma ashing provides an oxygen termination to the plasma-treated surface of the plasma-treated target substrate.

[0009] Embodiment 5 is the method of embodiment 1, wherein the surface of the diamond film is an untreated surface.

[0010] Embodiment 6 is the method of any one of embodiments 1 to 5, wherein the diamond film is single crystalline and the surface of the diamond film is (100).

[0011] Embodiment 7 is the method of any one of embodiments 1 to 6, wherein the diamond film has a thickness of 500 nm or less.

[0012] Embodiment 8 is the method of any of embodiments 1-7, wherein step (b) provides the diamond film contacted with the target substrate on an intermediate substrate, wherein the diamond film is adhered to the intermediate substrate by a layer of photoresist directly interposed between and in contact with the diamond film and the intermediate substrate. Embodiment 9 is the method of embodiment 8, wherein the photoresist is a positive photoresist. Embodiment 10 is the method of embodiment 10, wherein the photoresist is a T g is 200°C or less, and T g The method of any one of embodiments 8-9, wherein the range of is 20° C. or less. Embodiment 11 is the method of any one of embodiments 8-10, wherein the positive photoresist comprises a cresol novolac resin or polymethyl methacrylate.

[0013] Example 12 is the method of any of Examples 1-11, wherein the target substrate is fused silica, thermal silicon oxide, sapphire, lithium niobate, silicon, or yttrium iron garnet.

[0014] Embodiment 13 is any of embodiments 1-12, wherein step (b) comprises heating in a first heating step and a second heating step.Embodiment 14 is the method of embodiment 13, wherein the first heating step comprises heating to an intermediate temperature selected to soften the layer of photoresist in contact with the diamond film, and wherein the second heating step comprises heating in a non-oxidizing atmosphere to a final temperature higher than the intermediate temperature.Embodiment 15 is the method of embodiment 14, wherein the final temperature is at least 500°C.

[0015] Embodiment 16 is any of embodiments 1-15, wherein the bonded interface is crystalline throughout its thickness as measured using high-resolution transmission electron microscopy (HRTEM).Embodiment 17 is the method of embodiment 16, wherein the bonded interface has a thickness of 0.5 nm or less as measured using HRTEM.

[0016] Embodiment 18 is any of embodiments 1-17, wherein the diamond film is provided on an intermediate substrate, wherein the diamond film is adhered to the intermediate substrate by a layer of photoresist directly interposed between and in contact with the diamond film and the intermediate substrate, and further wherein the method includes, prior to step (b), subjecting a surface of the diamond film to plasma ashing to provide a plasma-treated surface of the diamond film.

[0017] Embodiment 19 is a bonded diamond film heterostructure comprising a plasma-treated target substrate having a plasma-treated surface and a diamond film having a surface, wherein the plasma-treated target substrate is covalently bonded to the diamond film at a bonding interface formed between the plasma-treated surface of the plasma-treated target substrate and the surface of the diamond film, and wherein the bonding interface is crystalline throughout its thickness as measured using HRTEM.

[0018] Embodiment 20 is the bonded diamond film heterostructure of embodiment 18, wherein the bonded interface has a thickness of 0.5 nm or less as measured using HRTEM.

[0019] Embodiment 21 is the bonded diamond heterostructure according to any one of Embodiments 19 to 20, wherein the surface of the diamond film is a plasma-treated surface.

[0020] Embodiment 22 is the bonded diamond film heterostructure according to any one of Embodiments 19 to 21, wherein the diamond film is single crystalline and the surface of the diamond film is (100).

[0021] Embodiment 23 is the bonded diamond film heterostructure according to any one of Embodiments 19 to 22, wherein the diamond film has a thickness of 500 nm or less.

[0022] Embodiment 24 is the bonded diamond film heterostructure of any of embodiments 19-23, wherein the plasma-treated target substrate is fused silica, thermal silicon oxide, sapphire, lithium niobate, silicon, or yttrium iron garnet.

[0023] Other principal features and advantages of the present disclosure will become apparent to those skilled in the art upon review of the following drawings, detailed description, and appended claims. [Brief explanation of the drawings]

[0024] Exemplary embodiments of the present disclosure will now be described with reference to the accompanying drawings.

[0025] [Figure 1A] Schematic diagram of the steps in the transfer of a diamond film onto a photoresist-coated intermediate wafer using two patterned stamps, PDMS1 and PDMS2. Images corresponding to the three steps in Figure 1A are shown in Figures 1B-1D. [Figure 1B]FIG. 10 shows an image of the alignment and pick-up of the diamond film by PDMS1 (four small squares touching the corners of the film). [Figure 1C] FIG. 10 shows images of membrane inversion by transferring the membrane from PDMS1 to PDMS2 (larger outer square). [Figure 1D] Figure 1 shows an image of the deposition of a membrane by PDMS2 onto a photoresist-coated intermediate wafer, where the intermediate wafer is a fused silica substrate with a support elevated 5 μm above the surrounding substrate.

[0026] [Figure 2A] 2B-2E are schematic diagrams of steps in a method for forming a bonded diamond film heterostructure according to an exemplary embodiment. Images corresponding to the four steps in FIG. 2A are shown in FIGS. [Figure 2B] 10 shows an image of the alignment of the film to the target wafer. Rainbow colors were observed due to optical interference from using a non-zero approach angle. [Figure 2C] 1 shows the film after contact with a target wafer during heating. The image shows the heated photoresist flowing onto the film and surrounding the entire surface of the film. [Figure 2D] 10 shows the film on the target wafer after the intermediate wafer has been pulled and lifted, leaving residual photoresist. [Figure 2E] FIG. 1 shows the final bonded diamond film heterostructure after annealing and photoresist removal.

[0027] 3A-3B show the longitudinal strain in the transferred diamond film. [Figure 3A] FIG. 1 shows Raman images of the original film and the grown layer. [Figure 3B] Figure 1 shows an image of a curved diamond film, with the arrow indicating the presence of rainbow colors representing the curved film on the PDMS stamp.

[0028] Figures 4A to 4H show the He phase of diamond films under various conditions. + AFM images of a small area (200 nm range) and a large area (10 μm range) of the damaged surface are shown. The root mean square roughness value (Rq) is shown in the images. [Figure 4A] FIG. 1 shows an image obtained after Ar / Cl etching as described in the "Multi-cycle ICP etching" section of the Examples. [Figure 4B] FIG. 1 shows an image obtained after Ar / Cl etching as described in the "Multi-cycle ICP etching" section of the Examples. [Figure 4C] FIG. 10 shows an image obtained after O2 etching without the addition of plasma. [Figure 4D] FIG. 10 shows an image obtained after O2 etching without the addition of plasma. [Figure 4E] FIG. 1 shows images obtained after O2 plasma treatment according to the first group of conditions ("O2 descum") described in the "Plasma Treatment" section of the Examples. [Figure 4F] FIG. 1 shows images obtained after O2 plasma treatment according to the first group of conditions ("O2 descum") described in the "Plasma Treatment" section of the Examples. [Figure 4G] 1 shows an image obtained after O plasma treatment according to the second group of conditions ("High Power") described in the "Plasma Treatment" section of the Examples. The defect-free area has a surface roughness of 0.29 nm. [Figure 4H] 1 shows an image obtained after O plasma treatment according to the second group of conditions ("High Power") described in the "Plasma Treatment" section of the Examples. The defect-free area has a surface roughness of 0.35 nm.

[0029] [Figure 5A]Figure 1 shows an image of a bonded diamond film heterostructure formed according to an exemplary embodiment of the present method, consisting of a diamond film (smaller, lighter squares) bonded to an underlying thermally oxidized silicon wafer (larger, darker squares) without any intervening layers between them. [Figure 5B] Microscope images of a 155 nm thick diamond film bonded to a marked thermally oxidized silicon substrate (left) and to a fused silica substrate with a 5 mm deep trench etched before bonding (right).

[0030] [Figure 6] 1 is a schematic diagram of a method for forming a bonded diamond film heterostructure according to an exemplary embodiment;

[0031] [Figure 7] 1 is a schematic diagram of a device incorporating a bonded diamond film heterostructure according to an exemplary embodiment;

[0032] 8A-8E show the characterization of the bonded diamond film heterostructure. [Figure 8A] Figure 1 shows AFM images of the diamond bonded interface (etched surface) after ICP etching. Atomically flat surfaces with Rq≦0.3 nm were observed in both small scan areas (200 nm × 100 nm, top) and large scan areas (10 μm × 5 μm, bottom). [Figure 8B]Contact angle and XPS plots of high-power plasma pre- and post-treatment of diamond and sapphire are shown. The improved hydrophilicity was confirmed by the decrease in contact angle, and the effect of oxygen termination was observed by the decrease in carbon sp2, as determined by C KLL extrapolation of the sp2 / sp3 ratio, and the increase in the sapphire-O signal, as determined by quantification of the O 1s peak. GeV-centered PL maps were obtained within films bonded to DBR mirrors but are not shown. The signal-to-background ratio near the zero phonon line (ZPL) was as high as 65, with the signal exceeding 65 kcs-1. [Figure 8C] Figure 1 shows the profilometry of the membrane silicon heterostructure. The membrane area is indicated by two dashed lines. The membrane thickness is 493.7 nm with a standard deviation of 1.1 nm. [Figure 8D] HRTEM image of a 10 nm thick film bonded to a c-plane sapphire substrate. The top 2 nm layer of diamond is due to a lack of surface control prior to gold deposition. [Figure 8E] (Top): Magnified HRTEM image of the diamond-sapphire bonded interface. The dashed rectangular area in Figure 8D indicates a thickness of less than 0.5 nm at the bonded interface. (Bottom): EDS elemental analysis at the bonded interface.

[0033] [Figure 9A] Schematic of TiO2-based (top) and diamond-based (bottom) nanophotonic devices on a bonded diamond film heterostructure. A fused silica (thermal silicon oxide) wafer was used as a carrier wafer for the TiO2 (diamond)-based demonstration. A grating coupler for excitation (light collection) is shown. [Figure 9B] Schematic of a flow channel device fabricated using a diamond membrane bonded heterostructure (diamond membrane bonded to a fused silica coverslip), and its use for imaging cells illuminated by total internal reflection within the diamond membrane is also shown. DETAILED DESCRIPTION OF THE INVENTION

[0034] In one aspect, a method for forming a bonded diamond film heterostructure is provided. The method includes generating a plasma containing plasma-activated species, exposing a surface of a target substrate to the plasma-activated species to provide a plasma-treated target substrate having a plasma-treated surface, and contacting the plasma-treated surface of the plasma-treated target substrate with a surface of a diamond film under various conditions to form a bonded diamond film heterostructure. As further described below, the plasma treatment can be "plasma ashing." The bonded diamond film heterostructure includes a target substrate, which is bonded to the diamond film, for example, by a covalent bond, at a bonded interface formed between the plasma-treated surface and the surface of the diamond film.

[0035] The composition of the diamond film is that of a solid carbon matrix, in which the carbon atoms are substantially sp 3 The diamond film may be characterized by a generally high degree of crystallinity. In an embodiment, the diamond of the diamond film is monocrystalline, i.e., the diamond film is a single crystal diamond film. The diamond film may be characterized by the crystal lattice structure of the diamond film at the surface of the diamond being in contact with the plasma treated surface of the plasma treated target substrate. In an embodiment, this surface is (100) diamond. In addition to carbon, the diamond film may be doped such that the diamond film may contain other elements (including ions or isotopes thereof), such as N, Ge, Si, Sn, etc. In an embodiment, the diamond film may be 12 C isotope-purified diamond film.

[0036] The diamond film is characterized by a thickness that is much smaller than the other two dimensions of the diamond film. The thickness is generally nanoscale, i.e., 1 μm or less. This includes thicknesses of 750 nm or less, 500 nm or less, 250 nm or less, or in the ranges of 3 nm to 250 nm, 100 nm to 200 nm, or 5 nm to 50 nm. Ultrathin diamond films, including those with thicknesses in the range of 10 nm to 15 nm, can be used. The thickness of the diamond film can be measured from atomic force microscopy (AFM) images and a profilometer. The thickness value may refer to an average value determined from such AFM images / profilometry. The other two dimensions of the diamond film are not particularly limited, but are larger than the thickness, e.g., in the range of 10 μm to 10 mm. Therefore, the diamond film can be characterized as having a planar, two-dimensional morphology. The shape of the diamond film, defined by the two dimensions perpendicular to the thickness, is not particularly limited.

[0037] The diamond film used in the present method is further characterized by low surface roughness and low surface curvature. Surface roughness can be quantified by reference to the root mean square roughness value (Rq) determined, for example, using atomic force microscopy (AFM). In embodiments, the diamond film has a roughness of 0.04 to 100 μm. 2 The Rq values ​​range from 0.2 nm to 0.9 nm when measured over an AFM area of ​​1000 nm, including 0.2 nm to 0.6 nm and 0.2 nm to 0.4 nm.

[0038] The present diamond films are distinguished from bulk diamond, which refers to diamonds with much greater thicknesses than those described above, including thicknesses greater than about 50 μm. Bulk diamonds are also generally characterized by a surface curvature greater than that of diamond films due to the surface polish required for bulk diamond. For example, the diamonds used in the following references were bulk diamonds: Matsumae, T., et al., Scripta Materialia 175 (2020) 24-28; Matsumae, T., et al., Scientific reports 11.1 (2021): 11109; Liang, J. et al., Applied Physics Express 12.1 (2018): 016501; and Liang, J. et al., Applied Physics Letters 110.11 (2017).

[0039] The diamond film synthesis techniques used in this method include those described in X. Guo, et al., Nano Letters 21, 10392 (2021), the entire contents of which are incorporated herein by reference. Briefly, such methods involve the deposition of He on a single-crystal, optical-grade diamond substrate. + This involves implantation and annealing processes, growing diamond by plasma-enhanced chemical vapor deposition (PE-CVD), in situ doping (if necessary), and undercutting the diamond film by electrochemical etching (EC). Diamond films synthesized using this method can be grown using He + The film may be characterized by having regions of the crystal lattice damaged by He due to implantation.Other methods for synthesizing diamond films are also possible.

[0040] The diamond film used in this method can be provided on an intermediate substrate (the terms "substrate" and "wafer" can be used interchangeably in this phrase). This is shown in box 104 of FIG. 1A, where a diamond film 116 is shown connected to an intermediate substrate 118 via a layer of photoresist 120. The diamond film 116 is connected on the surface opposite the surface that contacts the target substrate. Boxes 100 and 102 of FIG. 1A show how the diamond film 116 was synthesized from a diamond substrate 122 using the diamond film synthesis technique described above. Box 102 shows the transfer of the diamond film 116 from the diamond substrate 122 to the photoresist-coated intermediate substrate 118 using polydimethylsiloxane (PDMS) stamps PDMS1 and PDMS2. Any visually transparent material can be used as the intermediate substrate.

[0041] A positive photoresist can be used to provide the layer of photoresist 118. Suitable such positive photoresists include cresol novolac resins, such as AZ 1505 photoresist (available from EMD Performance Materials Corp.), Microposit™ S1805™ photoresist (available from The Dow Chemical Company), and AZ MiR 703 photoresist (available from EMD Performance Materials). Other suitable such positive photoresists include those comprising polymethyl methacrylate (PMMA), such as PMMA A4 photoresists (e.g., 950 PMMA A4, 495 PMMA A4). These positive photoresists, particularly AZ 1505, have a glass transition temperature T g It has been found to be useful in this process because it has a relatively low and well-defined temperature range and exhibits a relatively low viscosity over this temperature range. For example, AZ 1505 has a T g AZ MiR 703 has a T of approximately 130°C to approximately 135°C.g The PMMA A4 photoresist has a T range of approximately 95°C to approximately 106°C. g In embodiments, the photoresist exhibits a T g is less than about 200° C. (e.g., less than about 150° C. or less than about 140° C.), and the photoresist exhibits a T g is about 20°C or less (e.g., about 15°C or about 10°C). In embodiments, the photoresist is not a negative photoresist. In embodiments, the photoresist does not include hydrogen silsesquioxane, and hydrogen silsesquioxane is not used in the present method. Various thin film coating techniques can be used to coat the intermediate substrate with a layer of photoresist. Generally, the layer of photoresist is very thin, for example, between 80 nm and 500 nm, including between 100 nm and 400 nm and between 150 nm and 300 nm.

[0042] This method can be used to bond diamond films to a variety of target substrates (the terms "substrate" and "wafer" can be used interchangeably in this phrase). However, the target substrate has a composition different from that of the diamond film. The composition of the target substrate generally depends on the application of the bonded diamond film heterostructure. However, exemplary materials include optically nonlinear materials, piezoelectric materials, superconducting materials, materials that are effective in thermal management, magnetic materials, biocompatible materials (glasses, oxides), and metals that are compatible with oxygen-terminated interfaces and are resistant to stamping processes. Specific exemplary such materials include fused silica, thermally oxidized silicon, sapphire, lithium niobate, silicon, and yttrium iron garnet (YIG). The shape and dimensions of the target substrate are not particularly limited and depend on the application.

[0043] As described above, the method includes plasma-treating the surface of the target substrate to be bonded to the diamond film. Plasma treatment is a dry functionalization process, which is distinct from wet chemical functionalization processes using wet chemicals such as H2SO4, HO2, and NH3. Plasma treatment is performed by generating a plasma in a gas (which may be a gas mixture), which generates plasma-activated species, including ions, free radicals, and the like, derived from one or more gases. The plasma, and therefore the plasma-activated species, can also be generated at a location remote from the target substrate. Such a configuration includes subsequent transport of the plasma-activated species to the target substrate at the remote location. For example, the plasma can be generated in a first chamber and the plasma-activated species can be transported to a target substrate located in another chamber downstream from the first chamber. This and other embodiments of the plasma treatment can include filtering the plasma-activated species and exposing the surface of the target substrate to the filtered plasma-activated species. Both of these embodiments prevent more energetic / reactive plasma-activated species from impinging on the surface of the target substrate, instead favoring less energetic / reactive plasma-activated species (including electrically neutral plasma-activated species). Each of these characteristics indicates that the plasma process is "plasma ashing," which is distinguishable from "plasma etching" and "reactive ion etching." Accordingly, in embodiments, the method includes subjecting the surface of the target substrate to plasma ashing using a plasma including the plasma-activated species to provide a plasma-treated target substrate having a plasma-treated surface, and contacting the plasma-treated surface of the plasma-treated target substrate with a surface of a diamond film under respective conditions to form a bonded diamond film heterostructure.

[0044] With respect to plasma etching and reactive ion etching, these techniques involve placing the substrate to be treated in the same chamber where plasma is generated, not filtering plasma-activated species, and / or allowing more energetic / reactive plasma-activated species (including charged plasma-activated species) to impinge on the exposed surface. For example, the following references use surface treatments that involve one or more of plasma etching, reactive ion etching, and wet functionalization, all of which are distinct from plasma ashing: Matsumae, T., et al., Scripta Materialia 175 (2020) 24-28; Matsumae, T., et al., Scientific reports 11.1 (2021): 11109; Wang, F., et al., Applied Sciences 12.7 (2022): 3261. The surface treatments used in the following references use high-velocity Ar beams rather than plasma: Liang, J. et al., Applied Physics Express 12.1 (2018): 016501; and Liang, J. et al., Applied Physics Letters 110.11 (2017).

[0045] A variety of gases can be used to generate the plasma used, including when the plasma is used in plasma ashing. However, in embodiments, the plasma is an O2 plasma. In such embodiments, the plasma-activated species that impinge on the surface of the target substrate can include or consist of monoatomic oxygen. While not wishing to be bound by any particular theory, it is believed that O2 plasma treatment (including O2 plasma ashing) performed as described herein produces an oxygen-terminated plasma-treated surface. Oxygen termination refers to termination by oxygen atoms and is distinct from hydroxyl termination. Oxygen termination can be confirmed using X-ray photoelectron spectroscopy (XPS), as described in the Examples below. (See also FIG. 8B.)

[0046] Plasma processing (including plasma ashing) can be characterized by the conditions used to generate the plasma, including gas flow rate, power (which may be radio frequency (RF) power), process temperature, and process time (i.e., the length of time the target substrate is exposed to the plasma-activated species). These conditions can be adjusted to promote bonding between the plasma-treated surface of the target substrate and the diamond film. This may include promoting oxygen termination, as discussed above. Exemplary values ​​for these parameters include gas flow rates of 5 sccm to 250 sccm, RF power of 100 W to 650 W, process temperatures from room temperature (20°C to 25°C) to 150°C, and process times from a few seconds to a few minutes. Included are gas flow rates of 75 sccm to 150 sccm and 175 sccm to 225 sccm. Included are RF powers of 150 W to 250 W and 575 W to 625 W. In an embodiment, the process temperature is room temperature. As described in the examples below, room temperature has been found to improve the bonding process. Treatment times of 10 to 60 seconds and 95 to 175 seconds are included. The plasma treatment can be carried out once (i.e., once) or multiple times (e.g., twice, three times, etc.).

[0047] In embodiments, the surface of the diamond film to be bonded to the plasma-treated surface of the plasma-treated target substrate is untreated. By "untreated" is meant that the surface of the diamond film has not been exposed to the plasma treatments described herein. It further means that the surface has not been exposed to wet chemical functionalization, for example, using sulfuric acid, ammonia, or peroxide. However, the term "untreated" does not exclude treatment of the diamond film that may occur in conjunction with the formation of the diamond film itself, for example, using the synthesis techniques described above. Furthermore, the term "untreated" does not exclude treatment that may occur after the formation of the bonded diamond film heterostructure.

[0048] In another embodiment, the surface of the diamond film bonded to the plasma-treated surface of the plasma-treated target substrate is also plasma-treated, i.e., exposed to plasma-activated species from the generated plasma. The plasma gas and plasma conditions used may be the same or different from the plasma gas and plasma conditions used to treat the target substrate. However, in an embodiment, the plasma is O2 plasma. In an embodiment, the surface of the diamond film is subjected to plasma ashing, which includes the use of O2 plasma.

[0049] If the diamond film contains regions of the crystal lattice damaged by He as described above, these regions can be removed before the diamond film is brought into contact with the target substrate to induce bonding. If the diamond film is to be plasma-treated, the plasma treatment can be performed after the He-damaged crystal lattice is removed. This removal can be performed using an inductively coupled plasma (ICP) etching process, as described in the Examples below.

[0050] After plasma treatment (including plasma ashing) of the target substrate (and optionally plasma treatment (including plasma ashing) of the diamond film), the plasma-treated surface of the target substrate and the (plasma-treated) surface of the diamond film are brought close together until they contact each other over their entire surfaces, thereby forming a bonded interface. The bonded interface is formed by bringing the target substrate and the diamond film into direct contact with each other without any intervening material therebetween. Without wishing to be bound by any particular theory, it is believed that covalent bonds can occur between individual atoms of the target substrate and individual carbon atoms of the diamond film. Also, without wishing to be bound by any particular theory, covalent bonds can include those represented by the formula (-O-), where each "-" represents a covalent bond to an atom of the target substrate and a carbon atom of the diamond film, respectively ("O" represents oxygen). Bonded interfaces are further described below.

[0051] The contacting step is performed under conditions that promote bonding between the plasma-treated surface of the target substrate and the (plasma-treated) diamond film. This may include the formation of covalent bonds as described above. For example, the contacting step generally includes heating. Heating can be performed in two or more stages, which is useful for embodiments in which the diamond film is provided on a photoresist-coated intermediate substrate, as shown in FIG. 2A. For example, as shown in box 200, the target substrate 224 and the diamond film 216 are brought into contact with each other over their entire surfaces 224a and 216a. In this embodiment, both surfaces 224a and 216a are plasma-treated, as indicated by the thick dashed lines. In the first heating stage, as shown in box 202, heat is applied to increase the temperature from an initial temperature (e.g., room temperature) to an intermediate temperature. The intermediate temperature is selected to soften the layer of photoresist 220. The specific intermediate temperature will therefore depend on the type of photoresist used. The heating rate, heating time (i.e., the length of time for which heating is performed), and the use of one or more isothermal holds during heating can be adjusted as desired to, for example, ensure uniform reflow of the softened photoresist 220 throughout the diamond film 216 and subsequently facilitate removal of the intermediate substrate as shown in box 204. By way of example, when AZ 1505 was used as the photoresist layer, as described in the Examples below, heat was applied to increase the temperature from room temperature to 125°C, including holds at 75°C and 95°C. The first heating step can be performed without the application of any mechanical force (other than that exerted by the overlying photoresist-coated intermediate film). The first heating step can be performed at atmospheric pressure.

[0052] As shown in box 206, after removing the intermediate substrate, additional heat can be applied in a second heating step (which may be referred to as an annealing step) to a final temperature, which is generally higher than the intermediate temperature of the first heating step. The diamond film heterostructure can be cooled to room temperature before the second heating step, so that the second heating step can begin at room temperature. The second heating step can be performed in a non-oxidizing atmosphere (e.g., an Ar / H gas mixture) selected to prevent oxidation of the diamond film during annealing and at the final temperature. The final temperature, heating rate, heating time, use of one or more isothermal holds, and atmosphere can be adjusted as desired to promote bonding without inducing oxidation, for example. However, in embodiments, the final temperature is at least 450°C, at least 500°C, at least 525°C, at least 550°C, or in the range of 500°C to 550°C. As described in the examples below, bonding may not be achieved at relatively low temperatures, or bonding may be lost after a final cleaning step. The second heating step can be carried out without the application of any mechanical force.

[0053] The application of heat to bring the target substrate and diamond film into contact as described above results in a bonded diamond film heterostructure 226, as shown in box 206 of FIG. 2A. Any residual photoresist present on the heterostructure 226 can be removed, for example, by application of a cleaning composition. In an embodiment, the cleaning composition is a dual acid cleaning composition comprising H2SO4:HNO3. The use of a cleaning composition is not necessarily required for all types of photoresist, such as is the case with PMMA.

[0054] An exemplary embodiment of the method is further illustrated in Figure 6. Box 600 corresponds to the steps shown in boxes 100-104 of Figure 1A. However, in this embodiment, the He-damaged regions of the diamond film are explicitly labeled 628. This embodiment also illustrates the removal of He-damaged regions 628 in box 602. Box 604 corresponds to the steps shown in boxes 200-206 of Figure 2A.

[0055] The plasma-treated (including plasma-ashed) surfaces provided by the present method can be characterized by various properties, including Rq value, water contact angle, and oxygen termination. Regarding Rq, this value can be less than 0.35, less than 0.33, less than 0.30, or less than 0.28. (See also Figures 4A-4H and 8A.) Non-diamond plasma-treated surfaces can have higher Rq values, such as less than 0.53, less than 0.40, or less than 0.30. Rq values ​​can be determined by AFM as described in the Examples below, and can cover both small areas (e.g., 200 nm × 100 nm) and large areas (e.g., 10 mm × 5 mm). Regarding water contact angles, they can be less than 40°, less than 35°, less than 30°, less than 28°, less than 25°, less than 22°, or less than 20°. (See Figure 8B.) Water contact angles can be determined using techniques described in the Examples below. As mentioned above and in the Examples below, oxygen termination can be confirmed using XPS. When diamond is plasma treated, oxygen termination can be confirmed by (sp 2 / sp 3 Carbon sp in atomic (at.) % (obtained by C KLL extrapolation of the ratio 2 This can be confirmed by a decrease in the amount of O, which can be a decrease of at least 2 or 3. If the non-diamond surface has been plasma treated, oxygen termination can be confirmed by an increase in the amount of non-diamond-O signal (obtained by quantification of the O 1s peak), which can be an increase of at least 2 or 3.

[0056] The present disclosure further encompasses bonded diamond film heterostructures formed using the present methods. As described above, there is provided a bonded diamond film heterostructure comprising a target substrate covalently bonded (e.g., by an -O- bond) to a diamond film at a bonded interface formed between a plasma-treated surface and a surface of the diamond film.

[0057] An exemplary bonded diamond film heterostructure formed by this method is shown in Figure 5A. In this embodiment, the diamond film (smaller, lighter squares) is covalently bonded to the thermal silicon dioxide target substrate (larger, darker squares) without any intervening material between them.

[0058] The bonded diamond film heterostructures fabricated using this method are characterized by high quality, as evidenced by high-resolution transmission electron microscopy (HRTEM) images, which are further discussed in the Examples section below. Briefly, the HRTEM images reveal that the diamond film maintains uniform crystallinity and morphology throughout its thickness. Specifically, HRTEM images such as those shown in Figures 8D-8E demonstrate that the diamond film maintains its single-crystallinity after bonding. In this embodiment, the non-diamond target substrate is sapphire, and the HRTEM images further reveal that the crystallinity of the sapphire is maintained after bonding. The HRTEM image shown in Figure 8E also demonstrates that the bonded interface is also crystalline (rather than amorphous), meaning the region formed between the surface of the diamond film and the surface of the contacting non-diamond target substrate. This is supported by the crystal lattice image obtained by HRTEM throughout the entire thickness of the bonded interface. This contrasts with the dark HRTEM image of the bonded interface, which suggests an amorphous rather than crystalline atomic structure. Finally, the HRTEM image, as shown in Figure 8E, also shows that the bonded interface is extremely thin, less than 0.5 nm in this embodiment. From such an HRTEM image, the thickness of the bonded interface can be measured, which corresponds to the thickness of the transition region in the crystal lattice image of the bonded diamond film heterostructure (marked with an arrow in Figure 8E).

[0059] Thus, the bonded diamond film heterostructure can be characterized as having a crystalline bonded interface, which can be further characterized as having a thickness of 0.5 nm or less, 0.4 nm or less, or 0.3 nm or less.

[0060] In contrast, existing techniques result in amorphous bonding interfaces, much thicker bonding interfaces, or both. See Matsumae, T., et al., Scripta Materialia 175 (2020) 24-28; Matsumae, T., et al., Scientific reports 11.1 (2021): 11109; Wang, F., et al., Applied Sciences 12.7 (2022): 3261; Liang, J. et al., Applied Physics Express 12.1 (2018): 016501; and Liang, J. et al., Applied Physics Letters 110.11 (2017).

[0061] Finally, the high quality of the present bonded diamond film heterostructures fabricated using this method is due to the presence of color centers (e.g., GeV - , N.V. - ), which indicates a high signal-to-noise ratio by photoluminescence spectroscopy. These results are further discussed in the Examples below.

[0062] Devices incorporating bonded diamond film heterostructures fabricated using the present method are also provided. Any device in which high-quality diamond is typically used is encompassed by the present disclosure. However, an exemplary device is the electrically reconfigurable multiplexed quantum photonic device 700 shown in FIG. 7. The device comprises a lithium niobate substrate 724 (target substrate) and a patterned diamond film 716 directly bonded using the present method. The device 700 further comprises electrodes 730 (two of which are labeled) in electrical communication with the lithium niobate for phase shifting. Another exemplary photonic device is shown in FIG. 9A, and an exemplary flow channel device is shown in FIG. 9B, each of which is further described in the Examples below. Example

[0063] Introduction

[0064] Diamond possesses exceptional material properties for a wide range of quantum and electronic technologies. However, heteroepitaxial growth of single-crystal diamond remains limited, hindering the integration and advancement of diamond-based technologies. In this example, single-crystal diamond films are directly bonded to a wide variety of materials, including silicon, fused silica, sapphire, thermal silicon oxide, and lithium niobate. The bonding process combines customized film synthesis, transfer, and dry surface functionalization based on specific plasma treatments, providing a route to near-perfect yield and scalability with minimal contamination. As further described below, we have demonstrated the ability to fabricate diamond-based films with thicknesses on the order of 10 nm, sub-nanometer interface areas, and dimensions of 200 × 200 μm. 2 We have produced bonded crystalline films with nanometer-scale thickness variations over a range of 100 nm. Furthermore, we have integrated the resulting bonded diamond film heterostructures into high-quality-factor nanophotonic resonators, demonstrating the versatility of this platform for quantum photonics applications. Furthermore, we have found that the bonded diamond film heterostructures are compatible with total internal reflection fluorescence (TIRF) microscopy, enabling the construction of interfaces between coherent diamond quantum sensors and living cells while suppressing undesired background luminescence. The process presented below provides a comprehensive toolkit for synthesizing diamond-based heterogeneous hybrid systems for quantum and electronic technologies.

[0065] Manufacturing process

[0066] Synthesis and patterning of diamond films

[0067] Diamond films were synthesized according to the method described in the paper by X. Guo et al., Nano Letters 21, 10392 (2021). Briefly, a single-crystal optical-grade diamond substrate was heated at 1000 K for 1 hour. +Injection (injection amount 5×10 16 cm -2 The diamond was subjected to a 150 keV (energy 150 keV) annealing treatment followed by an annealing treatment in an argon forming gas environment (24% H, 96% Ar). The annealing treatment included three isothermal holds: 400°C for 8 hours, 800°C for 8 hours, and 1200°C for 2 hours. Diamond growth was performed in a microwave plasma chemical vapor deposition (MPCVD) chamber at Argonne National Laboratory. Four films were used in this example, with diamond growth layers grown to thicknesses of 185 nm, 260 nm, 400 nm, and 660 nm, respectively. After growth, the samples were ion-implanted (Si + , Ge + , Sn + or N + )or 15 The samples were delta-doped with N. The samples were then patterned to form individual 200 μm × 200 μm membranes by lithography, inductively coupled plasma (ICP) etching, and undercutting by electrochemical (EC) etching in deionized (DI) water.

[0068] Transfer of membranes onto intermediate wafers with patterned PDMS stamps

[0069] A patterned PDMS stamp was used to transfer the film to the intermediate substrate. Two different PDMS patterns were transferred from inverted SU-8 (3050, 55 μm thick) structures lithographically formed on a 4-inch silicon wafer. The first pattern consisted of four squares for picking up the diamond film from its diamond substrate (see Figure 1A, box 100, and Figure 1B), while the second pattern contained a single large square to achieve film inversion by utilizing a larger adhesive area (see Figure 2A, box 102, and Figure 2C). Film pick-up, inversion, and placement were performed using a probe station (Signatone S1160).

[0070] The diamond film transfer process shown in Figures 1A–1D had several advantages. The first PDMS stamp (PDMS1) cut its tether to the diamond substrate and only picked up the film from its corner. This effectively reduced the contact area and therefore contamination of the growth surface due to transfer. In addition, protecting the adjacent, partially etched film on the diamond substrate effectively improved the overall transfer yield to 100%. This process also enabled EC etching and transfer of multiple films in a single cycle, with six films achieved to date. The second PDMS stamp (PDMS2) was 300 μm × 300 μm, which preserved the existing structures on the intermediate wafer outside the transfer area. Overall, the patterned PDMS method achieved full yield, protected both the substrate and the intermediate wafer, and significantly improved scalability.

[0071] Preparation of intermediate wafer

[0072] The intermediate wafer used in this example was a 13 mm x 13 mm substrate diced from a 4-inch fused silica wafer. However, other transparent substrates can also be used as the intermediate wafer. Prior to the dicing process, the 4-inch wafer was patterned and ICP etched to create a 400 μm x 400 μm square with a height of 5 μm in the center of each chip to provide a support. The creation of the support was useful for compensating for the residual tilt angle between the intermediate wafer and the final (target) wafer. In addition, the creation of the support also limited the contact area and protected existing structures on the final (target) wafer. A wafer bonder may also be used.

[0073] Prior to transferring the film to the intermediate wafer, the patterned intermediate wafer was spin-coated with a thin layer of positive photoresist (AZ 1505, approximately 500 nm) or e-beam resist (950 K PMMA A4, MicroChem, approximately 250 nm). AZ 1505 is particularly suitable because it softens over a well-defined temperature range (100–110 °C) and has a relatively low viscosity over this temperature range, resulting in minimal contamination. As shown in box 104 in Figure 1A, after the film was inverted and placed on the photoresist-coated intermediate wafer support, the adhesion of the film to the photoresist exceeded the adhesion to the PDMS2 stamp, so the film remained attached to the intermediate wafer and was ready for multi-cycle ICP etching.

[0074] Multi-cycle ICP etching

[0075] After transfer to the intermediate wafer, the helium-damaged diamond film surface was subjected to ICP etching to thin the grown diamond layer to the target film thickness. The target film thickness (and therefore the total etch depth) was variable and tailored to the intended application (e.g., to match the desired photonics wavelength). The minimum etch depth was set solely by the thickness of the helium-damaged diamond layer. This process also relieved out-of-plane strain caused by the crystal lattice mismatch between the damaged and grown layers. Because the film thinning step was performed on the intermediate wafer, the existing structures on the final (target) wafer were effectively protected. To prevent photoresist crosslinking at high temperatures, a multi-cycle Ar / Cl2-O2 / Cl2-O2 etching sequence was used, with an etching time of only 15 seconds per cycle. Multi-cycle ICP etching also maintained a higher quality chamber environment compared to continuous etching by utilizing more pump-purge cycles between etching cycles. Multi-cycle ICP etching also provided improved control of the etch rate and, therefore, film thickness.

[0076] Plasma treatment of film and target wafer

[0077] A downstream plasma asher (YES-CV200 RFS Plasma Strip / Descum System, Yield Engineering Systems Inc.) was used to activate the surfaces before bonding. O2 was used to generate the plasma, but other gases (e.g., N2, Ar) could also be used. Two different groups of plasma conditions were used to treat the ICP-etched diamond film and target wafer. The first group of plasma conditions (sometimes referred to herein as "O2 descum") were as follows: O2 gas flow rate of 100 sccm, RF power of 200 W, temperature at room temperature, and exposure time of 25 seconds. The second group of plasma conditions (sometimes referred to herein as "high power") were as follows: O2 gas flow rate of 200 sccm, RF power of 600 W, temperature at room temperature, and exposure time of 150 seconds. Room temperature conditions were used because a decrease in hydrophilicity was observed after a short post-plasma baking period (1 minute at 90°C on a hot plate) (discussed below). Some target wafers, eg, LiNbO3 wafers, were subjected to plasma treatment more than once, eg, three times.

[0078] The two treatment conditions were compared based on three metrics measured on the resulting products: surface morphology, surface hydrophilicity, and GeV - and N.V. -The comparison was made according to the optical performance of the centers. The effects on both the surface of the carrier (i.e., target) wafer and the surface of the diamond film were evaluated. The results are described below. For the selection of carrier wafers, fused silica and thermally oxidized silicon were tested. Both treatment conditions resulted in improved surface hydrophilicity while maintaining good surface morphology, which is favorable for the subsequent bonding process. High-power treatment conditions were used for all carrier substrates because better hydrophilicity was achieved. For diamond films, both treatment conditions improved the signal-to-background ratio for the optical characterization of color centers. However, an increased number of particle-like contaminants was observed by atomic force microscopy (AFM) on the surface after treatment with the high-power treatment conditions. Therefore, O2 descum treatment conditions were used for the diamond films (NVs require better charge state adjustment). - (Excluding sensing applications.) However, contaminants can be eliminated by using dedicated equipment configurations.

[0079] It should be noted that plasma treatment of only the target substrate (without plasma treatment of the diamond film) is sufficient to achieve a high quality bond, although plasma treatment of the diamond film is desirable in other embodiments.

[0080] Bonding of the film to the target wafer

[0081] Bonding of the film to the target wafer was performed using the same probe station described above. Figure 2A shows a schematic of the process steps, and Figures 2B–2E show images corresponding to these steps. The thick dashed lines in Figure 2A indicate the plasma-treated surface. First, the intermediate wafer was placed on a glass slide with a large PDMS stamp, while the final (target) wafer was placed on a temperature-controlled stage and held by vacuum. Because the micropositioner (Signatone CAP-946) lacks full angular control, the approach angle was set to 0° along the y direction, and the angle along the x direction was a small but poorly defined value. The diamond film was aligned by observing through the transparent PDMS stamp and intermediate wafer with a microscope. Because the approach angle was not well-defined, alignment accuracy was limited to 30 μm and 0.1°. Alignment accuracy can be improved by using a wafer bonder. Once the target location was identified, as shown in box 200 of Figure 2A, the intermediate wafer was slowly lowered until the film contacted the final (target) wafer. Next, heating was applied to initiate bonding and soften the photoresist (PR), as shown in box 202 of Figure 2A. The temperature was increased stepwise from room temperature (75 °C, 95 °C, and 125 °C for AZ 1505; 90 °C, 130 °C, and 170 °C for PMMA), allowing the resist to reach thermal equilibrium at each step. No mechanical force (other than that exerted by the overlying photoresist-coated intermediate film) was applied during heating. Once the flow pattern reached equilibrium, the film was completely covered and surrounded by photoresist. The intermediate wafer exhibited a slight shift relative to the film, which was due to the non-zero contact angle and softening of the photoresist. Next, as shown in box 204 of Figure 2A, the intermediate wafer was slowly pulled and lifted from the film area, leaving the film on the target wafer along with some residual photoresist. Finally, after cooling to room temperature, the diamond film heterostructure is annealed to complete the bonding, as shown in box 206 of FIG. 2A and further described below.

[0082] Annealing and photoresist removal

[0083] Annealing was used to promote bonding between the diamond film and the target wafer. Argon forming gas (96% Ar, 4% H, approximately 1 atm) was used during annealing to prevent oxidation of the diamond surface at high temperatures. After annealing, the remaining cross-linked photoresist was removed by a two-acid wash (H2SO4:HNO3 = 1:1, 225 °C for 2 h).

[0084] Two annealing temperatures were used: 450°C and 550°C. The film annealed at 450°C eventually delaminated from the underlying target wafer during the acid wash. In contrast, the film annealed at 550°C remained bonded after the acid wash.

[0085] When PMMA was used as the resist, the residual resist was fully baked out after annealing, and the bonded diamond film heterostructures were cleaned using only a short O2 descum clean. However, when AZ 1505 was used, the residual photoresist was crosslinked, making removal difficult. However, a cleaning process using two boiling acids was found to remove the crosslinked AZ 1505. This was performed using H2SO4:HNO3 = 1:1 at the boiling point of nitric acid for 2 hours. Because AZ 1505 has a lower viscosity compared to PMMA, PMMA-based bonding was used for structured surfaces and acid-sensitive substrates, while AZ 1505 was used for other substrates. The bonded diamond film heterostructures were found to be compatible with isopropyl alcohol, acetone, potassium hydroxide- or tetramethylammonium hydroxide (TMAH)-based developers (e.g., AZ 300 MIF or AZ 400K), heated (80 °C) N-methyl-2-pyrrolidone (NMP), and room-temperature NanoStrip. However, triple acid cleaning (H2SO4:HNO3:HClO4 = 1:1:1 at reflux temperature), high temperature (≥ 80 °C) piranha (H2SO4:H2O2 = 3:1), and high temperature NanoStrip can damage the bond and cause the diamond film to delaminate from the target wafer.

[0086] Materials characterization

[0087] Out-of-plane strain of smart cut membrane

[0088] Unlike isotropically etched diamond frames or ICP-etched diamond slabs, Smart Cut diamond films are +Diamond naturally contains out-of-plane strain due to the crystal lattice mismatch between the damage layer created by implantation and the subsequent growth layer. This strain causes the free-standing film to curve, which is due to the large geometric aspect ratio of the free-standing film (typically greater than 500). To roughly estimate the magnitude of the strain, Raman spectroscopy was performed on a transferred diamond film with a 100 nm growth layer before ICP etching. The experimental data are shown as individual points in Figure 3A, which can be fitted to two Lorentzian curves. The original film (He + The damage layer is 1326 cm -1 The growth layer is shown as the dashed curve with a central wavenumber of 1332 cm, while the growth layer is shown as the other dashed curve with a central wavenumber of 1332 cm. -1 The difference in wavenumber indicates a crystal lattice mismatch of approximately 0.5%.

[0089] Figure 3B shows a test membrane partially attached to the PDMS2 stamp, with the top and bottom portions floating as indicated by the arrows. The interference pattern reveals tension in the original layer and compression in the grown layer, which contributes to the upward curvature of the membrane. The elimination of strain by ICP etching was previously described.

[0090] Surface morphology of diamond wafer and final wafer

[0091] The success of plasma-enhanced bonding depends on the surface morphology of the diamond film and the target substrate. AFM was performed to characterize the surface roughness during the fabrication process. Both small-scale (200 nm × 200 nm) and large-scale (10 μm × 10 μm) scans were applied to capture features of various sizes.

[0092] Regarding the diamond film surface, only the etched surface will be described in this example because the growth surface retained excellent surface morphology. Prior to ICP etching, the etched surface was etched with He + R due to implantation and EC etching qThe polishing effect was confirmed by applying the above-mentioned Ar / Cl2 etching for 15 cycles, and as shown in Figures 4A and 4B, the R q was reduced to 0.54 nm (0.44 nm). It was observed that small area scans usually detect larger roughness compared to large area scans, which may indicate Cl-based contaminants on the diamond surface. Such contaminants can be removed by O2 / Cl2-O2 ICP cycling, which reduces the R q = 0.25 nm (0.34 nm) (Figure 4C-4D). As shown in Figure 4E-4F, the R after O2 descum treatment q No change in R (0.28 nm and 0.34 nm in small and large area scans) was observed. In contrast, the high-power treatment conditions resulted in an R of up to 0.84 nm (1.09 nm) in small (large) area scans. q It was found that an increase in R has a negative effect on the surface morphology, which can be interpreted as the appearance of particulate dust, because in areas without contaminants, R q This is because the thickness remains ≦0.35 nm. Such contaminants can be reduced by using process-specific equipment configurations.

[0093] The effect of two downstream plasma asher processing conditions was also analyzed on two carrier substrates: fused silica wafers and thermally oxidized silicon wafers. q The values ​​of R are shown in Table 1 below. Both wafers have sub-nanometer R in the unprocessed state. q The surface morphology of these carrier wafers was maintained after ashing, regardless of the power or duration settings. Therefore, it was concluded that the plasma treatment conditions did not significantly affect the surface morphology of these carrier wafers.

[0094] [Table 1]

[0095] Height deviation across the diamond film

[0096] One-dimensional (1D) height detection by profilometry

[0097] In this example, two methods were applied to characterize the global flatness. For the presented 1D characterization, the entire film was scanned using a profilometer (Dektak XT). The scan range was 350 μm, with a height detection limit of 6.5 μm. The film exhibited a height deviation σ of approximately 1 nm, which was one-tenth of the value measured for HSQ-bonded films with the same instrument. This σ was also below the tool's minimum detection height (10 nm) and the instrument resolution (1.5 nm) for large-scale scanning.

[0098] Two-dimensional (2D) height mapping by confocal laser scanning microscopy (CLSM)

[0099] The 2D film height map and surface topology were measured using an Olympus LEXT OLS4100 405 nm laser confocal microscope. A microscopic image of the measured film-thermal silicon oxide heterostructure was obtained along with its height map. The bonded film profile revealed a uniform height of 309 ± 8 nm across the entire film, with a standard deviation σ below the height resolution of CLSM (approximately 10 nm). The primary causes of the height nonuniformity are currently believed to be due to crystal growth defects in the diamond film and contaminants in the transfer process. These can be minimized by performing the entire process in a clean environment (e.g., a clean room).

[0100] Characterization of hydrophilicity of the bonded interface

[0101] Contact angle measurement setup

[0102] Water contact angles were measured to characterize the surface hydrophilicity of the diamond and target substrate. Measurements were performed using a Kruss DSA100A drop shape analyzer. Deionized water was dispensed from a sterile syringe (14-817-25, Fisher Scientific) through a fine needle (75165A761, McMaster-Carr). The dispensing rate was 2.67 μL s -1 The contact angle was measured on a 3 mm × 3 mm single-crystal, high-precision polished diamond substrate (R q The results showed that the surface hydrophilicity of diamond and thermally oxidized silicon substrates was improved by contact angle analysis before and after high-power plasma ashing. The milder O2 descum treatment conditions had minimal effect on the hydrophilicity of diamond, with contact angles exceeding 40°.

[0103] Changes in surface hydrophilicity over time and temperature dependence

[0104] Surface hydrophilicity positively correlates with the quality of plasma-activated bonding. Here, the decay of hydrophilicity was characterized by repeated contact angle measurements on various substrates, including diamond, fused silica, thermally oxidized silicon, sapphire, and lithium niobate-oxide insulator. The time-dependent hydrophilicity trend revealed a decrease in hydrophilicity over a time scale of 3 to 24 hours, demonstrating the benefits of timely bonding. We also tested the temperature dependence of hydrophilicity by baking plasma-treated diamond samples on a hot plate at 90 °C for 30 seconds prior to contact angle measurements. A decay in hydrophilicity was observed, likely due to the loss of surface-absorbed water molecules.

[0105] Due in part to the strong correlation between high temperature and reduced hydrophilicity, resist AZ 1505 was selected as a suitable resist material for the bonding process due to its relatively low glass transition temperature (softening temperature) and significantly reduced viscosity.

[0106] High-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS)

[0107] To characterize the bonded interface at the atomic level, HRTEM was performed on cross-sectional samples of the diamond-sapphire heterostructure. The sapphire substrate was c-axis (0001) manufactured by University Wafer. First, a 200-nm-thick gold mask was deposited on the surface to prevent damage to the diamond film by the Ga ion beam. Cross-sectional TEM samples with thicknesses of several tens of nanometers were prepared by a standard FIB lift-out technique using a Zeiss NVision 40 system. HRTEM images were acquired using an FEI Titan microscope operating at 200 kV with aberration and chromatic aberration correction. Scanning transmission electron microscope (STEM) images were acquired using a high-angle annular dark-field (HAADF) detector. An FEI Talos S / TEM equipped with a Super X energy-dispersive spectrometer (EDS) was used for STEM-EDS elemental mapping. The results confirmed the presence of carbon at the location of the diamond film and oxygen and aluminum at the location of the sapphire target substrate.

[0108] X-ray photoelectron spectroscopy (XPS)

[0109] The experimental samples were identical to those used in other demonstrations: diamond, fused silica, and sapphire. One group was left untreated to serve as a control, while the other group underwent a surface activation treatment using oxygen plasma ashing approximately 90 minutes before being introduced into the XPS chamber. Two different incidence angles were used for XPS analysis to confirm that the observed effects were due to near-surface species. One group was characterized at 0° incidence, while the other group was characterized at 35° incidence. Since no significant differences were observed between the two data sets, only the 0° incidence data set is shown. Consistent with contact angle measurements, the surfaces were found to have degraded somewhat over the time period, but remained "bondable." Therefore, all quantitative XPS analyses provide a lower limit for species associated with surface activation.

[0110] XPS characterization was performed at both normal and 35° incidence using an Al-Kα source mounted on a Thermo Scientific ESCALAB 250Xi. Elemental peaks were acquired at a pass energy of 50 eV, a dwell time of 50 ms, and a step size of 0.1 eV, while C KLL peaks were acquired at a pass energy of 100 eV and a step size of 0.5 eV. For all scans, an electron flood gun was used for charge compensation, maintaining an X-ray spot size of approximately 200 μm. C 1s, C KLL, Al 2p, Si 2p, O 1s, and N 1s peaks were all acquired in high-resolution mode, and the presence of other unexpected contaminants was verified by a survey scan. All scans were acquired using a C-sp at 284.8 eV binding energy (BE). 3 The peaks were used as the reference peaks. Elemental analysis was performed by quantitative comparison of high-resolution component fits (taking into account appropriate sensitivity factors). The C 1s KLL signature was used to calculate and fit the peak spacing of the first derivative of the KLL signal, resulting in the sp 1s line fit. 2 vs. SP 3The ratios were extrapolated and verified. All peak fitting parameters were taken from the NIST XPS database, based on commonly agreed-upon values ​​for comparable materials and systems. High-resolution XPS spectra of relevant lines, along with fitting parameters, were obtained for untreated diamond, ashed diamond, untreated sapphire, ashed sapphire, untreated silica, and ashed silica. This analysis is consistent with the conclusions of this work. However, unexplained anomalies were observed, specifically the presence of an unidentified third component in the O 1s peak in the fused silica sample. This peak is tentatively identified as organic. The appearance of an intermediate SiO2-silicate peak in the Si 2p quantification of the fused silica suggests that these are likely oxygen species derived from undercoordinated quartz. In any case, these are in the low atomic percent range (approximately 2 atomic percent) and do not affect any of the conclusions of this work. Table 2 provides a general overview of the quantification of the XPS experiments.

[0111] [Table 2-1] [Table 2-2]

[0112] GeV - and optical characterization of NV centers

[0113] Optical setup

[0114] In this example, the film sample was placed in a closed-loop cryostation (Montana S200) and cooled to 4 K for cryogenic measurements. The film position was controlled by three closed-loop piezo micropositioners (Attocube ANC 350). The light beam was guided by a fast steering mirror (Newport FSM-300). For photoluminescence (PL) measurements, either a 519 nm green diode (Thorlabs LP520-SF15) or a 532 nm continuous-wave (CW) laser (Lighthouse Photonics Sprout-G) was used as the excitation source. GeV - For photoluminescence excitation (PLE) measurements, the excitation laser was generated by a wavelength mixing module (AdvR Inc.) combining a tunable CW Ti:sapphire laser (M Squared Solstis) with a monochromatic CW laser (Thorlabs, SFL 1550P). A single-photon counting module (SPCM) (Excelitas Technologies) was applied to plot PL maps, while a spectrometer (Princeton Instruments, SpectraPro HRS) was used to measure the color center spectra. Two bandpass filters (Semrock FF01-615 / 24-25, Semrock FF01-600 / 14-25) were used to measure the luminescence intensity at 1 GeV. - For PL measurements, a combined bandpass filter (2 × Semrock FF01-647 / 57-25) was used for PLE measurements. For NV measurements, a single longpass filter (Semrock LP02-561RE-25) was used for NV measurements. 0 Signal and NV - Both signals were captured.

[0115] Plasma processing is GeV - Effect on central optical coherence

[0116] As mentioned above, plasma treatment of the diamond film is not necessarily required to achieve bonding. In this section of the example, the plasma is -The influence of the center on the PL and PLE characteristics was investigated. Each was about 200 nm thick and implanted at a depth of 40 nm from the top surface. - The two films, including the center, were transferred to a single thermally oxidized silicon wafer. Film 1 was not plasma treated before bonding, while film 2 was subjected to a strong plasma ashing treatment as described above. - The central 4K PL map clearly shows the improvement in signal to background due to plasma treatment. The average background is reduced from about 7000 to about 1900, which improves the signal to background from about 4.5 to about 11. The slightly lower signal for the plasma-treated diamond film indicates the presence of slight oxygen termination, which shifts the Fermi level to about 11 GeV. - The linewidths shift from the center optimum. Single (2.5 min average) ZPL linewidth plots were obtained by resonant excitation. For Film 1 (Film 2), the average linewidth of the single scan was 97 MHz (85 MHz), and the average linewidth of the average scan was 212 MHz (196 MHz), with no statistically significant difference in the linewidth distribution. The measured linewidths may be broader than the actual values ​​due to the resolution limit of the wavemeter (High Finesse WS6-600, measurement resolution 20 MHz, wavelength accuracy 500 MHz).

[0117] GeV - Characterization of center-dependent strain

[0118] Group IV element centers in diamond have a relatively large strain sensitivity, making them excellent sensors for detecting the local strain environment. The magnitude of the strain is measured by a relative shift in wavelength.

number

number

[0119] For films bonded to fused silica (thermal silicon oxide) wafers, GeV - The mean central ZPL wavelength was 602.68 (20) nm (602.53 (8) nm), and the mean ground-state splitting was 307 (158) GHz (224 (75) GHz). These ZPL wavelength distributions are comparable to those obtained with bulk diamond. A slight positive strain was observed in the diamond-fused silica heterostructure, which can be explained by the lower thermal expansion ratio of fused silica. Thermally induced negative strain was barely visible in the diamond film-thermal silicon oxide substrate, which may be attributed to the fact that films with such high aspect ratios (≥1000) may deform rather than develop negative strain under compressive stress. The mean strain level in the diamond film was approximately 2.9 × 10 for the fused silica (thermal silicon oxide) carrier wafer. -4 (approx. -1.7×10 -4 ) was estimated.

[0120] NV centered at 4K

[0121] Due to the low optical background of the direct bonding method, individual NV centers were discernible in the diamond film heterostructure. Typical NV PL maps obtained at 4 K showed a signal-to-background ratio of more than 1.4, which enables NV sensing applications as further explained below. Furthermore, the charge stability of NV centers is a good indicator of the surface termination of the film with respect to various plasma treatments at the diamond bonded interface. Here, NV spectral characterization was performed on three bonded films. These were in situ characterized. 15 The films were taken from a single N-doped mother substrate and therefore had the same NV density. They were bonded to SiO2 surfaces with diamond bonding surfaces that were (1) untreated, (2) treated with O2 descum, and (3) subjected to high-power plasma ashing. NV spectra and statistical data were obtained. It was confirmed that without plasma treatment, the NV centers remained charge-neutral due to the hydrogen termination effect of the Ar / H2 annealing process. However, the plasma-treated films had significantly higher NV - / NV 0 This ratio had a positive correlation with the intensity of the O2 ashing process, suggesting that the oxygen termination performance was improved, which contributed to maintaining the NV centers in a negative charge state. - This paper supports the use of dry O-termination methods to control the near-surface Fermi level of diamond for silicon-based applications.

[0122] Diamond-based nanophotonic devices were fabricated using the bonded diamond film heterostructures prepared as described above. The devices are shown schematically in Figure 9A. The devices include a TiO2-based device formed on a diamond film bonded to fused silica (top) and a diamond-based device in which the diamond film is bonded to thermal silicon oxide (bottom). The results are summarized below.

[0123] NVs in a diamond film bonded to a fused silica coverslip (prepared as described above) - The centers were also characterized, including after chemical functionalization of the diamond films with labeled biomolecules. The results are summarized below.

[0124] A flow channel device was fabricated using the bonded diamond film heterostructure (diamond film bonded to a fused silica coverslip) prepared as described above. The device is shown schematically in Figure 9B, which also illustrates the use of the device to image cells illuminated by total internal reflection within the diamond film. The device and its use are further described below.

[0125] Results and Discussion

[0126] This example demonstrates the feasibility of surface plasma activation-based synthesis of diamond heterostructures for direct bonding of diamond films to industrially important materials, such as silicon, fused silica, thermal silicon oxide, sapphire, and lithium niobate (LiNbO), while preserving the functionality of existing on-chip structures. The fabrication process begins with film synthesis by SmartCut, followed by homoepitaxial diamond growth and ex situ or in situ color center formation. The substrate is then patterned by either photolithography or electron beam lithography to define the geometry of the individual films. The target films are then etched by electrochemical (EC) etching to form sp 2 Undercutting by selective carbon removal leaves small tethers connected to the diamond substrate, enabling deterministic manipulation. The film size was limited to a 200 μm × 200 μm square. However, by extending the EC etching time and slightly modifying the patterning step in the process flow, larger and more complex film geometries can be generated.

[0127] After EC etching, we utilized a templated, area-controlled polydimethylsiloxane (PDMS) stamp to transfer and manipulate the film, improving the yield and scalability of the process. The PDMS stamps had two distinct patterns, allowing for smaller (PDMS1 stamp) and larger (PDMS2 stamp) contact areas and increased adhesion strength. The PDMS1 stamp was used to break the diamond tether and pick up the film, while the PDMS2 stamp was used to flip the diamond film from the PDMS1 stamp and then place it. In both cases, the raised adhesion area, 50 μm higher than the rest of the stamp, ensured that only the target film was in contact. This method allows for multiple film transfers following EC etching, which can ultimately be automated as a single process for the entire diamond substrate.

[0128] Next, He +The underlying diamond layer, damaged by implantation, was removed. This improved the overall crystallographic quality and completely separated the final isotopically purified and controlled-doped film from the low-cost type IIa diamond substrate. This thinning was achieved by inductively coupled plasma (ICP) reactive ion etching (RIE). To protect the final bonded substrate from etching, the film was thinned by placement on an intermediate fused silica carrier wafer. The intermediate wafer was coated with photoresist (AZ 1505) or electron beam resist (PMMA). This photoresist softens at temperatures between 100 and 130 °C, reducing its viscosity during subsequent processing. In this additional step, the film was again flipped so that the growth surface was facing up (exposed) on the target substrate. This eliminated constraints on the growth surface morphology during bonding and allowed for precise depth control of the near-surface and δ-doped color centers. To prevent overheating and crosslinking of the resist, a multi-cycle etching process was developed with a short plasma duration of 15 seconds or less per cycle. Using this technique, we achieved precise thickness control from 10 nm to 500 nm. The maximum thickness was determined by the homoepitaxial growth process, but can be modified to meet application requirements.

[0129] Downstream O2 plasma ashing was used to activate the surfaces of both the diamond film and the target substrate, enabling subsequent bonding. The target substrate was subjected to high-power ashing conditions (gas flow rate 200 sccm, RF power 600 W, 150 seconds), with extended processing times for inert substrates such as sapphire and LiNbO3. The diamond film was subjected to either the high-power processing conditions or an O2 descum clean (gas flow rate 100 sccm, RF power 200 W, 25 seconds), which did not result in etching or roughening of the diamond surface. The downstream O2 plasma cleaned and oxygen-terminated the film and carrier material surfaces without the use or need for any wet processing. All ashing conditions were performed at room temperature to prevent degradation of the functionalization at high temperatures.

[0130] The film was then bonded to a target substrate. The patterned intermediate wafer was placed on a glass slide using a flat, chip-sized PDMS stamp, controlled by a micropositioner. The target substrate was vacuum-mounted on a temperature-controlled stage. Using optical access through the transparent intermediate wafer for alignment, the film was moved to the desired position and brought into contact with the target substrate. Upon contact, film-scale interference fringes / patterns appeared. Using this method, alignment accuracy of 30 μm and 0.1° was achieved. The heterostructure was then heated by increasing the stage temperature in multiple steps. After reaching the resist softening point, the intermediate wafer was slid away, leaving the bonded structure. Future use of dedicated wafer bonding equipment will significantly improve the accuracy and tolerance of all transfer steps.

[0131] Finally, to ensure the formation of a strong covalent interface between the film and the target wafer, the heterostructure was annealed at 550 °C under argon forming gas to minimize undesired oxidation. This annealing also removed any polymethyl methacrylate (PMMA) residue, leaving a clean, directly bonded film as the final product (for PMMA-based transfer). In several cases, diamond films were bonded to fused silica with patterned trenches in it, highlighting the potential for film bonding to structured materials. Overall process yields exceeded 95%, limited only by unstable plasma ashing chamber conditions and limited control of the transfer station's approach angle. However, both can be easily improved by transitioning to process-specific equipment configurations.

[0132] Depth characterization of the material revealed that diamond quality was maintained throughout the bonding process. Atomic force microscopy (AFM) was used to characterize the film surface morphology, which is important not only for the success of the plasma-activated bonding but also for the coherence and stability of the color centers near the surface. As shown in Figure 8A, both the small-area scan and the large-area scan showed that R q Atomically flat surface profiles of ≦0.3 nm were obtained. Furthermore, the target substrates were characterized by AFM to ensure sub-nanometer roughness after plasma treatment as detailed in Table 1 above.

[0133] The bonded films exhibited an overall flatness of approximately 1 nm as characterized by profilometry, excluding local height deviations. The film thickness profile, shown in Figure 8C, exhibited a uniform height of 493.7 ± 1.1 nm, with a standard deviation below the instrument resolution (1.5 nm) for large-scale scans. In addition to linear scans, two-dimensional flatness maps of the films were analyzed by confocal laser scanning microscopy, as described above. The effectiveness of plasma surface activation was also characterized by tracking the change in surface hydrophilicity at the bonded interface through contact angle measurements, as shown in Figure 8B. For the diamond surface, the contact angle decreased from 52.4° ± 0.7° to 6.1° after high-power plasma treatment, indicating a substantial increase in hydrophilicity. This was confirmed by quantitative X-ray photoelectron spectroscopy (XPS) characterization of surface species, also shown in Figure 8B. Surface hydrophilicity was quantified by the more reliable D-parameter extrapolation of the C KLL line, suggesting the presence of surface amorphous carbon sputtering. 2 The results showed a direct correlation with the decrease in bond density. Furthermore, the decrease from the raw C 1s quantification (presumably due to an increase in ether-like terminations) and the increase in available sapphire-O bonds at the surface indicated effective surface treatment and oxygen termination for both surfaces. Similar behavior was observed for all target bonding materials, with post-treatment contact angles of less than 20°.

[0134] The quality of the bonded diamond heterostructure was directly analyzed by high-resolution transmission electron microscopy (HRTEM). Figures 8D–8E show an ICP-thinned (approximately 309 nm–10 ± 0.3 nm) diamond film bonded to a sapphire substrate. This thinness and uniformity reflect a high degree of process control, allowing us to characterize both interfaces of the diamond film within a single field of view. HRTEM images revealed several important features. First, the film exhibited uniform crystallinity and morphology throughout its thickness. Second, a distinct interface between the crystalline diamond and sapphire was observed, measuring less than 0.5 nm. Third, a repeating atomic sequence was observed throughout the interface profile, confirming that the interface was covalently bridged. Energy-dispersive X-ray spectroscopy (EDS) analysis of the elements involved at the interface (C, Al, and O) (see bottom of Figure 8E) established an upper limit of the bonded interface thickness of less than 2 nm. EDS analysis confirmed that the interface was artificially widened due to a slight angular mismatch between the electron beam depth projection and the actual physical interface.

[0135] Furthermore, the optical properties of the color centers in the bonded film were characterized. By confocal imaging, the germanium vacancies (GeV - ) has been shown to have high signal-to-background and sufficient optical coherence for applications in quantum technology. - From a typical photoluminescence (PL) map of the center, - It was found that the signal-to-background ratio can be up to about 65, with an average value of about 40. This is a significant improvement over suspended HSQ-based films (5-30) and bulk diamond (about 25). The bonding process also requires GeV - The central optical coherence was preserved and the introduced distortion was minimized.

[0136] This example further demonstrates that the fabricated bonded diamond film heterostructure is suitable as a platform for quantum technologies. First, we explore nanophotonic integration, which is widely used in quantum photonics to improve qubit addressability. Photonic integration is typically achieved by patterning diamond into undercut suspended structures, but such structures impose geometric constraints and complicate further multiplexing and integration with on-chip single-photon detectors, electronic circuits, or other devices that can enhance quantum network functionality. This example demonstrates that bonded diamond film heterostructures enable multiple approaches to photonic integration.

[0137] Briefly, we used templated atomic layer deposition (ALD) of TiO to fabricate nanophotonic devices on the surface of a 50 nm-thick diamond film bonded to a fused silica substrate. A schematic diagram is shown in the upper image of Figure 9A, where the excitation and collection ports (grating couplers) are depicted. In these devices, optical modes are effectively hybridized between TiO and diamond. Microscope images of TiO fishbone and ring resonators were acquired at the same location from different fabrication lots, demonstrating the robustness of the bonded diamond film to cleanroom processing and the recyclability of photonic integration.

[0138] Transmittance measurements of the resonators also revealed a significant improvement in quality factor. We obtained a transmission spectrum of a typical fishbone resonator at the target wavelength of 737 nm (SiV emission wavelength). The highest measured quality factor, Q, was 10,640, with an average of 10,150 ± 350 for three devices. These values ​​are 2.5 times higher than previous demonstrations and are attributed to the elimination of the intermediate bonding layer and improved diamond crystal quality. Based on the updated Q factors, the maximum Purcell enhancement factor in diamond is estimated to be 270. These metrics are suitable for state-of-the-art experiments in resonator quantum electrodynamics. Similarly, a ring resonator measured through a drop port showed a quality factor of Q = 16319 (Q = 12620) for the transverse magnetic field, i.e., TM mode (transverse electric, i.e., TE mode).

[0139] To verify the robustness of the bonded diamond film heterostructure platform, nanophotonic ring resonators were etched directly into diamond using a lithographically defined hard mask and RIE. A schematic is shown in the lower image of Figure 9A. Bright-field and dark-field images of the devices demonstrated the high quality and uniformity of the fabrication process. These ring resonators also exhibited a quality factor, Q, of 21,883 while possessing strong electric field confinement within the diamond. The adaptability and versatility of these high-aspect-ratio structures make them ideal for integration with other materials, paving the way for hybrid quantum technologies.

[0140] Diamond heterostructures also offer unique advantages in quantum metrology, such as sensing nanoscale magnetic and electric fields and temperature. In these applications, diamond sensors are typically placed in close proximity to the target. The most sensitive diamond sensors are based on high-purity single crystals, with the target immobilized on the top surface of the diamond. Due to the large thickness and refractive index of conventional bulk diamond, optical initialization and readout of the sensing qubit must be performed from the top surface. This geometry requires the target system to possess optical transparency, low autofluorescence, and high photostability, which presents significant limitations in studying biological systems. The present bonded diamond film heterostructure overcomes these challenges by enabling optical addressability from the backside of the diamond film, without the need for access to the top surface and the target.

[0141] First, individual nitrogen vacancies (NV) in the bonded diamond film - The stability and addressability of the NV centers (i.e., qubit sensors) were investigated. Wide-field and confocal images revealed individually identifiable and photostable NVs in a diamond film bonded to a fused silica coverslip. - These emitters are NV - The presence of NV centers was confirmed by the presence of a unique 2.87 GHz zero-field splitting peak using optically detected magnetic resonance (ODMR) spectroscopy. - The center is known to exhibit excellent spin coherence. Next, the diamond surface of the bonded diamond film heterostructure was chemically functionalized. Using backside illumination, it was found that the fluorescence of individual streptavidin molecules labeled with Alexa 488 and streptavidin-conjugated Qdot-525 quantum dots could be detected. This allowed the NV - This makes it possible to image not only the center but also the position of the target protein attached to the diamond film surface. -The ability to detect the center and protein location with fluorescence is important for NV-based single-molecule nuclear magnetic resonance and electron paramagnetic resonance spectroscopy because it allows the detection of NVs with desired molecular targets within the sensing range. - This is because it becomes possible to efficiently identify the center.

[0142] We further demonstrated the feasibility of imaging with reduced background fluorescence by combining the bonded diamond membrane heterostructure with TIRF microscopy. Figure 9B shows a schematic diagram of the setup, in which the bonded diamond membrane was integrated into a flow channel and macrophage-like RAW cells were grown on the diamond surface. Optical excitation above the critical angle ensured that only a very narrow region above the diamond membrane was excited by the optical field. By staining Toll-like receptor 2 (TLR2) with an Alexa488-conjugated anti-TLR2 antibody, TIRF imaging revealed the location of individual proteins distributed on the cell surface. This is in stark contrast to epiluminescence imaging, in which background luminescence prevents the imaging of individual molecules. It is noteworthy that diamond has a higher refractive index (n = 2.4) compared with a typical glass microscope coverslip (n = 1.5), resulting in a 1.6-fold faster decay of the evanescent field. Similarly, we observed the sedimentation of live Escherichia coli bacteria introduced through a flow channel onto the diamond membrane in real time. The experiments enabled by the flow channel demonstrated remarkable flexibility in constructing the interface between the target sample and the quantum diamond sensor, a task that has been extremely difficult to achieve with existing technologies.

[0143] conclusion

[0144] This example demonstrates the viability of a complete process flow for creating diamond-based heterogeneous materials and technologies. Bonded diamond film heterostructures combine isotopic engineering, in situ doping, and precise film thickness control while maintaining the surface morphology, flatness, and crystalline quality required for quantum technologies. Continuous, bonded crystalline diamond films as thin as 10 nm were fabricated, far below previous demonstrations and comparable to material geometries in state-of-the-art microelectronics. HRTEM results confirmed an ordered, subnanometer-scale bonded interface, while PL measurements demonstrated high signal-to-background ratios for all incorporated color centers. The process is compatible with nanostructured substrates, with a small device footprint and no post-bonding etching required, ensuring the integrity of existing target substrate structures. The bonded diamond films are highly robust to multiple subsequent nanofabrication steps, making the process compatible with standard semiconductor manufacturing techniques, including wafer bonding. Importantly, the elimination of intermediate adhesive materials produces material heterostructures that are ideally suited for quantum photonics and quantum biosensing applications. Their technological suitability for quantum photonics was demonstrated through the integration of high-quality factor nanophotonics, either by TiO2 deposition or by direct diamond patterning and etching. These diamond-based heterostructures, with minimal optical losses, are ideal choices for on-chip nanophotonics integration and spin-photon coupling devices. Furthermore, the bonding of diamond films was demonstrated to open up new experimental possibilities for quantum biosensing and imaging by integrating flow channels with diamond films. The bonding of fluorescent molecules and NV - Simultaneous resolution with center allows NV close to the desired sensing target - The ultrathin diamond membrane also enables TIRF illumination, which significantly improves signal contrast for localized sensing targets while minimizing unwanted laser excitation.

[0145] The disclosed fabrication process opens up a broad heterogeneous diamond-based platform for quantum technologies. The integration of diamond with electro-optic and piezoelectric materials such as LiNbO3 enables on-chip, electrically reconfigurable nonlinear quantum photonics and also allows the study of quantum spin-phonon interactions. The diamond junctions disclosed herein open up further coupling possibilities with other solid-state qubits, magnonic hybrid systems, and superconducting platforms. Furthermore, the bonded diamond films can be integrated with highly coherent near-surface NVs. - Combined with established techniques for generating diamond centers, this technology enables ultrasensitive diamond probes optimized for molecular binding assays, two-dimensional dichalcogenides (TMDs), and thin-film magnetic materials studies. Finally, bonded diamond films with high thermal conductivity, wide band gaps, and high critical fields have diverse applications in high-power electronics.

[0146] The word "exemplary" is used herein to mean something that serves as an example, instance, or illustration. Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure, unless expressly stated otherwise, "a" or "an" means "one or more."

[0147] The foregoing description of exemplary embodiments of the present disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to be limited to the particular forms disclosed. Many modifications and variations are possible in light of the above teachings and may be acquired from practice of the present disclosure. The embodiments were chosen and described to explain the principles of the present disclosure and to enable those skilled in the art to utilize the disclosure in various embodiments and with various modifications depending on the particular use contemplated. It is intended that the scope of the present disclosure be defined by the claims appended hereto and their equivalents.

[0148] Unless otherwise expressly stated, all numerical values ​​of various parameters in this disclosure are preceded by the term "about," which means approximately. This encompasses the inherent variability in measuring the parameter, as understood by one of ordinary skill in the art. This includes the exact value of the disclosed numerical value and values ​​that are rounded to the disclosed numerical value.

Claims

1. 1. A method for forming a bonded diamond film heterostructure, comprising: (a) subjecting a surface of a target substrate to plasma ashing to provide a plasma-treated target substrate having a plasma-treated surface; (b) contacting the plasma-treated surface of the plasma-treated target substrate with a surface of a diamond film to form a bonded diamond film heterostructure, the bonded diamond film heterostructure comprising the target substrate covalently bonded to the diamond film at a bond interface formed between the plasma-treated surface of the plasma-treated target substrate and the surface of the diamond film; A method comprising:

2. 10. The method of claim 1, further comprising the step of subjecting the surface of the diamond film to plasma ashing prior to step (b) to provide a plasma-treated surface of the diamond film.

3. The plasma ashing is carried out by ２ The method of claim 1 carried out using a plasma.

4. The method of claim 1 , wherein the plasma ashing provides an oxygen termination to the plasma-treated surface of the plasma-treated target substrate.

5. The method of claim 1 , wherein the surface of the diamond film is an untreated surface.

6. 2. The method of claim 1, wherein the diamond film is single crystalline and the surface of the diamond film is (100).

7. The method of claim 1 , wherein the diamond film has a thickness of 500 nm or less.

8. 2. The method of claim 1, wherein the diamond film in contact with the target substrate in step (b) is provided on an intermediate substrate, and the diamond film is adhered to the intermediate substrate by a layer of photoresist directly interposed between and in contact with the diamond film and the intermediate substrate.

9. The method of claim 8 wherein the photoresist is a positive photoresist.

10. The photoresist is T ｇ is 200°C or less, and T ｇ The method according to claim 8, characterized in that the width of is 20°C or less.

11. 9. The method of claim 8, wherein the positive photoresist comprises a cresol novolac resin or polymethyl methacrylate.

12. The method of claim 1 , wherein the target substrate is fused silica, thermal silicon oxide, sapphire, lithium niobate, silicon, or yttrium iron garnet.

13. 10. The method of claim 1, wherein step (b) comprises heating in a first heating stage and a second heating stage.

14. 14. The method of claim 13, wherein the first heating step comprises heating to an intermediate temperature selected to soften a layer of photoresist in contact with the diamond film, and wherein the second heating step comprises heating in a non-oxidizing atmosphere to a final temperature higher than the intermediate temperature.

15. 15. The method of claim 14, wherein the final temperature is at least 500°C.

16. The method of claim 1 , wherein the bond interface is crystalline throughout its thickness as measured using high-resolution transmission electron microscopy (HRTEM).

17. 17. The method of claim 16, wherein the bond interface has a thickness of 0.5 nm or less as measured using HRTEM.

18. 2. The method of claim 1, wherein the diamond film is provided on an intermediate substrate, wherein the diamond film is adhered to the intermediate substrate by a layer of photoresist directly interposed between and in contact with the diamond film and the intermediate substrate, and further comprising the step of subjecting the surface of the diamond film to plasma ashing prior to step (b) to provide a plasma-treated surface of the diamond film.

19. 1. A bonded diamond film heterostructure comprising: a plasma-treated target substrate having a plasma-treated surface; and a diamond film having a surface, wherein the plasma-treated target substrate is covalently bonded to the diamond film at a bonding interface formed between the plasma-treated surface of the plasma-treated target substrate and the surface of the diamond film, the bonding interface being crystalline throughout its thickness as measured using HRTEM.

20. 20. The bonded diamond film heterostructure of claim 19, wherein the bonded interface has a thickness of 0.5 nm or less as measured using HRTEM.

21. 20. The bonded diamond film heterostructure of claim 19, wherein said surface of said diamond film is a plasma treated surface.

22. 20. The bonded diamond film heterostructure of claim 19, wherein said diamond film is single crystalline and said surface of said diamond film is (100).

23. 20. The bonded diamond film heterostructure of claim 19, wherein said diamond film has a thickness of 500 nm or less.

24. 20. The bonded diamond film heterostructure of claim 19, wherein the plasma treated target substrate is fused silica, thermal silicon oxide, sapphire, lithium niobate, silicon, or yttrium iron garnet.

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