Method for manufacturing super-flat polycrystalline diamond film on large scale

Abstract

The invention provides a method for manufacturing a super-flat polycrystalline diamond film on a large scale. The method comprises the following steps: (1) growing a layer of polycrystalline diamond film on a growth substrate with a diamond seed crystal on the surface by adopting a chemical vapor deposition method; (2) cutting off at least one part of the substrate after growth to form a boundary for jointing the polycrystalline diamond film and the growth substrate; (3) sticking a stripping adhesive tape; and (4) the stripping adhesive tape is pulled to strip the polycrystalline diamond film from the surface of the growth substrate, so that the nucleation surface of the polycrystalline diamond film is exposed, and the roughness of the exposed nucleation surface is smaller than that of the growth surface. According to the method, the nucleation surface of the grown polycrystalline diamond film is turned over, the novel and simple method is developed to manufacture the polycrystalline diamond film which is reasonable in price, capable of growing on a large scale, super-flat and transferable, and the method has huge potential in practical application.

Description

Technical Field

[0001] The invention belongs to the technical field of polycrystalline diamond film preparation technology, and particularly relates to a method for large-scale manufacturing of polycrystalline diamond films with ultra-flat surfaces. Background Art

[0002] High-quality synthetic diamond materials have been considered as ideal candidates for applications in mechanical, electronic and optical fields due to their excellent physical and chemical properties. To date, diamond materials have been successfully synthesized, but obtaining large-scale, high-quality and ultra-thin diamond films remains a considerable challenge.

[0003] Doping diamond can further expand its applications in electronic devices, such as boron-doped p-type semiconductors and superconductors, as well as quantum photonics materials based on atomic defects such as nitrogen-doped silicon, especially those materials called next-generation diamond substrates, such as membranes, which are expected to play an important role in the efficient heat dissipation of circuits and high-power electronic devices, especially for emerging soft / flexible electronic devices.

[0004] Realizing these diamond-based functional components inevitably involves standard nanofabrication and seamless integration, all of which place high demands on the surface roughness of the diamond material. Furthermore, a flat surface is a prerequisite for many testing and characterization methods widely used in related fields, such as thermal conductivity measurements and bonding in the semiconductor industry.

[0005] However, unlike other materials such as silicon, planarization of diamond is very difficult and requires a lot of time and energy through traditional methods such as polishing.

[0006] Diamond films are primarily produced through homogeneous and heterogeneous growth using chemical vapor deposition (CVD) techniques. Single-crystal diamond (SCD) films, primarily obtained by homogeneous growth on bulk diamond substrates, represent the highest quality required for many applications. For example, their high electron and hole mobility and excellent radiation resistance make them highly valuable for detectors in nuclear and high-energy physics experiments. However, the expensive growth process, limited fabrication scale, and complex processing of CVD-grown SCD have hindered its widespread application.

[0007] Although heterogeneous growth of SCD on iridium has been demonstrated in a limited number of laboratories worldwide, it remains difficult to control the quality of the resulting diamond, which tends to form polycrystalline diamond (PCD) films due to lattice mismatch. Therefore, the construction of large-area SCD films on arbitrary substrates remains a significant challenge.

[0008] In contrast, scalable, inexpensive, and easy-to-grow polycrystalline diamond (PCD) films can be readily obtained on a variety of common substrates, such as Si, SiC, TiC, Co, Pt, Al2O3, Ni, and Re. In particular, with a sufficiently high nucleus density, they can form a continuous film, and the quality of the film is closely related to the directionality of the nuclei. To optimize PCD films, researchers have proposed the concepts of nanocrystalline and ultra-nanocrystalline diamond films, which form continuous nuclei by depositing diamond seeds. However, the surface smoothness of PCD films is less than satisfactory, which is one of the biggest bottlenecks in promoting such an excellent platform.

[0009] In summary, the extremely stringent growth conditions of single-crystal diamond (SCD) have greatly hindered the application of diamond materials in large-scale, cost-acceptable fields; and the poor surface morphology and high roughness caused by the uneven profile of polycrystalline diamond (PCD) have seriously limited its further construction of high-precision photonic structures at the nano / micrometer scale. Summary of the Invention

[0010] Therefore, the purpose of the present invention is to overcome the problems of poor surface morphology and high roughness of polycrystalline diamond (PCD) films and to provide a simple method to prepare large-area, ultra-flat and transferable PCD films in a scalable and controllable manner.

[0011] A first aspect of the present invention provides a method for large-scale production of ultra-flat polycrystalline diamond films, the method comprising:

[0012] (1) growing a polycrystalline diamond film on a growth substrate having a diamond seed on its surface by chemical vapor deposition, wherein the polycrystalline diamond film comprises: a growth surface (or referred to as a "growth surface") having a first roughness and a nucleation surface (or referred to as a "nucleation surface") bonded to the growth substrate;

[0013] (2) cutting at least a portion of the growth substrate on which the polycrystalline diamond film is grown, wherein the cutting operation forms a boundary line where the polycrystalline diamond film is bonded to the growth substrate at the cutting portion;

[0014] (3) attaching a stripping tape to the growth surface of the polycrystalline diamond film, wherein the stripping tape extends beyond the polycrystalline diamond film at least at an edge of the cut portion to form a stripping operation end;

[0015] (4) Pulling the stripping operation end to strip the polycrystalline diamond film from the surface of the growth substrate to expose the nucleation surface of the polycrystalline diamond film, wherein the exposed nucleation surface has a second roughness, and the second roughness is smaller than the first roughness.

[0016] According to the method provided by the present invention, the first roughness may be 10-200 nm, such as 20-50 nm. In a preferred embodiment of the present invention, the second roughness may be 0.5-5 nm, preferably 0.5-2 nm, more preferably 0.5-1 nm.

[0017] According to the method provided by the present invention, the particle size of the diamond seed crystal described in step (1) can be 2-10 nm. In some embodiments of the present invention, the growth substrate can be selected from one or more of Si, SiC, TiC, Co, Pt, Al2O3, Ni, Re, Ir, SiO2 and Mo. In a preferred embodiment of the present invention, the surface roughness of the growth substrate is less than 2 nm, preferably less than 1 nm, and more preferably less than 0.5 nm. Preferably, a microwave plasma assisted chemical vapor deposition (MPCVD) device is used to grow the polycrystalline diamond film in step (1). In some embodiments of the present invention, the thickness of the polycrystalline diamond film can be 200 nm-100 μm, preferably 200 nm-10 μm, and more preferably 400 nm-5 μm.

[0018] According to the method provided by the present invention, the deposition temperature of the chemical vapor deposition method in step (1) can be 800-1000°C, preferably 850-950°C.

[0019] According to the method provided by the present invention, the trimming operation in step (2) is preferably performed perpendicular to the growth surface of the polycrystalline diamond film. The trimming operation can be performed along a straight line, a curve, or an arc. In a preferred embodiment of the present invention, the trimming operation is performed so that the length of the boundary line where the formed polycrystalline diamond film is bonded to the growth substrate is at least 1% of the circumference of the growth surface of the polycrystalline diamond film, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, preferably 5%-20%, preferably 10%-12%.

[0020] In a preferred embodiment of the present invention, to facilitate large-scale production, the cutting operation described in step (2) can be performed along a straight line. When the growth substrate is circular, the length of the boundary line where the polycrystalline diamond film formed by cutting is bonded to the growth substrate is preferably 20%-50% of the substrate diameter.

[0021] The inventors of the present invention have found through extensive experimental research that the cutting operation described in step (2) can reduce the adhesion force caused by the excessive coverage of the polycrystalline diamond film on the side wall of the growth substrate. Starting from the cutting point, the polycrystalline diamond film can be gradually separated from the growth substrate with the help of the stripping tape, thereby obtaining a complete polycrystalline diamond film, and the growth substrate after stripping can be recycled.

[0022] According to the method provided by the present invention, the stripping tape in step (3) can be 3M tape, PVC tape, PE tape, etc. In an embodiment of the present invention, the stripping tape completely covers the polycrystalline diamond film remaining after the cutting operation, and leaves a margin at least at the cutting edge to facilitate the subsequent stripping operation.

[0023] After extensive experimental research, the inventors discovered that while the peeling performance of PCD films of varying thickness is related to their mechanical strength, different peeling operations (such as speed and peeling angle) also have an impact. Proper peeling within the permitted mechanical strength range is a prerequisite for obtaining large, intact films with minimal cracks.

[0024] In the present invention, the peel angle refers to the angle between the peeling force required to separate the polycrystalline diamond film from the growth substrate by pulling the peeling end and the growth surface of the polycrystalline diamond film (the starting position of the peeling end of the stripping tape is defined as 0°). The peel angle range that produces a complete polycrystalline diamond film with minimal cracks is referred to as the safe peel angle.

[0025] In the present invention, integrity refers to the percentage of the area of ​​the polycrystalline diamond film obtained by stripping to the area of ​​the growth substrate after stripping.

[0026] According to the method provided by the present invention, in step (4), the speed at which the polycrystalline diamond film is pulled off the growth substrate surface by pulling the stripping operation end can be 1-10 mm / s. In a preferred embodiment of the present invention, the stripping angle of the stripping operation in step (4) can be 10-90°.

[0027] According to the method provided by the present invention, the nucleation surface has a higher refractive index than the growth surface. Preferably, the nucleation surface has a lower extinction coefficient than the growth surface.

[0028] The optical parameters of the polycrystalline diamond film produced by the method of the present invention are at levels comparable to those of SCD grown by CVD.

[0029] According to the method provided by the present invention, the position of the XRD diffraction peak of the (111) crystal plane of the nucleation surface is closer to the standard (111) crystal plane XRD diffraction peak of single crystal diamond than the position of the (111) crystal plane XRD diffraction peak of the growth surface; and the full width at half maximum (FWHM) of the Raman spectrum of the (111) crystal plane of the nucleation surface is less than the full width at half maximum (FWHM) of the (111) crystal plane of the growth surface. The shift of the XRD diffraction peak indicates an improvement in the crystallization quality, and the narrowing of the full width at half maximum of the Raman spectrum means that the internal crystallization of the film has been improved.

[0030] According to the method provided by the present invention, the method may further include using a solvent to reduce the viscosity of the stripping tape to release the polycrystalline diamond film; or a thermal release stripping tape may be used to release the polycrystalline diamond film from the stripping tape by heating.

[0031] The second aspect of the present invention also provides a method for regulating the energy band of a diamond film, the method comprising attaching the polycrystalline diamond film prepared by the present invention to the surface of a flexible substrate, stretching and / or compressing the polycrystalline diamond film by bending the flexible substrate, and regulating the energy band structure of the polycrystalline diamond film through the strain generated by the polycrystalline diamond film during the stretching and / or compression process.

[0032] While the growth surface of polycrystalline diamond films has been extensively studied, the nucleation surface is rarely explored due to its limited public exposure. This paper presents a novel and simple method for in situ generation of polycrystalline diamond nucleation surfaces without introducing any damage. This method enables the large-scale, controllable production of large-area, ultra-flat, and transferable polycrystalline diamond films. The effectiveness of this method is demonstrated through detailed characterization of the surface morphology and material properties of the nucleation surface.

[0033] Compared to other methods of exposing the nucleation surface (such as the sacrificial growth substrate described in prior application 202310540694.7), the present method reduces impurities introduced by multiple operations (such as grinding and etching). Therefore, this exfoliation method preserves the pristine state of the nucleation surface without causing any damage. Characterization of the roughness of the growth and nucleation surfaces of polycrystalline diamond films of varying thicknesses revealed that the nucleation surface roughness was less than 1 nm for all thicknesses, while the growth surface roughness increased with thickness. Compared to previously reported studies optimizing diamond film surface roughness, the present exfoliation method offers significant advantages in both thickness range and film size. Therefore, the present method is considered to be the best approach to obtain polycrystalline diamond films with the largest size, smoothest surface, and widest thickness range. The novel, scalable, and controllable strategy proposed in this invention paves the way for the development of high-quality and cost-effective polycrystalline diamond films, making them promising building blocks for a variety of high-performance structures and devices in diverse applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

[0035] Figure 1 Schematic diagram of the method for preparing a polycrystalline diamond film according to the present invention.

[0036] Figure 2 Figures (a), (b) and (c) are photos of a 2-inch silicon wafer with a polycrystalline diamond film grown on its surface in Example 1 (a), the peeling process (b), the polycrystalline diamond film after peeling, and the silicon wafer after peeling (c).

[0037] Figure 3 The following are photos of the nucleation surfaces of polycrystalline diamond films of different thicknesses prepared in Examples 2-5.

[0038] Figure 4 Statistical diagrams of cracks and integrity of polycrystalline diamond films of different thicknesses prepared in Examples 2-5.

[0039] Figure 5 SEM images of the growth surface (a), nucleation surface (b) and cross section (c) of the polycrystalline diamond film with a thickness of 1000 nm prepared in Example 5.

[0040] Figure 6 SEM images of the growth surface (top) and nucleation surface (bottom) of polycrystalline diamond films of different thicknesses prepared in Examples 2-5.

[0041] Figure 7 AFM images of the growth surface (a) and nucleation surface (b) of the 1000 nm thick polycrystalline diamond film prepared in Example 5, and the nucleation surface (c) of the 1000 nm thick polycrystalline diamond film prepared in Example 6.

[0042] Figure 8 (a) Roughness statistics of growth surfaces and nucleation surfaces of PCD films of different thicknesses prepared in Examples 2-5 (statistical area 20 μm × 20 μm); (b) Comparison of film thickness and roughness between the method of the present invention and other reported methods; and (c) Comparison of film size and roughness between the method of the present invention and other methods.

[0043] Figure 9 Comparison of the refractive indices of the growth surface (a) and the nucleation surface (b) of the polycrystalline diamond film prepared in Example 1.

[0044] Figure 10 2 are the XRD results of the growth surface (a) and the nucleation surface (b) of the polycrystalline diamond film prepared in Example 1.

[0045] Figure 11 Raman spectra of the growth surface (a) and nucleation surface (b) of the polycrystalline diamond film prepared in Example 1.

[0046] Figure 12 The following are photos of the 360-degree bending of the 4 μm thick polycrystalline diamond film prepared in Example 7 (a) and the winding of the film on cylinders with different radii (b).

[0047] Figure 13 Different bending modes (a) and corresponding strain distribution on the surface (b) of the 4 μm thick polycrystalline diamond film prepared in Example 7 on a flexible PDMS substrate.

[0048] Figure 14 The conductivity changes of the 4 μm thick polycrystalline diamond film prepared in Example 7 under different strains (a) and bending cycles (b).

[0049] Figure 15 The Raman spectrum (a) and XPS measurement results (b and c) of the polycrystalline diamond film prepared in Example 5 are shown.

[0050] Figure 16 Summary of experimental photos and data of contact angles on the growth surface and nucleation surface of PCD films of different thicknesses.

[0051] Figure 17 The friction coefficients of the growth surface and the nucleation surface of the polycrystalline diamond film prepared in Example 5 (a) and the relationship curve between the external force applied to the growth surface and the nucleation surface and the depth of the indentation formed (b) are shown.

[0052] Figure 18 Refractive index (a) and extinction coefficient (b) of the growth and nucleation surfaces of a polycrystalline diamond film with a thickness of 500 nm; and refractive index (c) and extinction coefficient (d) of the growth and nucleation surfaces of a polycrystalline diamond film with a thickness of 1000 nm.

[0053] Figure 19 These are the fatigue test results of the polycrystalline diamond film of the present invention, where (a) is a photograph after undergoing >10,000 deformation cycles at 2% strain; (b) is a 5x magnified optical image corresponding to areas 1 and 2 in (a).

[0054] Figure 20 1. The experimental statistics (a) of the microcrack density on films of different thicknesses peeled at different peeling angles in Example 9 of the present invention are compared with the probability of crack extension on films of different thicknesses at different peeling angles calculated by simulation (b).

[0055] Figure 21 These are photos of a chip array fabricated on a 2-inch polycrystalline diamond film before (a) and after (b) peeling in Example 10 of the present invention, as well as the resistance change before and after peeling (c).

[0056] Figure 22 These are scanning electron microscope images of micro / nano fabrication performed on the growth surface and nucleation surface of the polycrystalline diamond film in Example 11 of the present invention.

[0057] Figure 23(a) is the fluorescence spectrum of the NV color center in the polycrystalline diamond film prepared in Example 12 of the present invention; and (b) is the optically detected magnetic resonance (ODMR) test result of the polycrystalline diamond film having NV color centers. DETAILED DESCRIPTION

[0058] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0059] Figure 1 Schematic diagram of the method for preparing a polycrystalline diamond film of the present invention, the preparation process includes:

[0060] I. CVD growth of polycrystalline diamond films;

[0061] II. cutting a portion of the grown substrate and polycrystalline diamond film to form a new boundary;

[0062] III. Applying a peeling tape to perform mechanical peeling to separate the polycrystalline diamond film from the substrate.

[0063] Example 1

[0064] Fabrication of polycrystalline diamond films

[0065] (1) Growth of polycrystalline diamond films on silicon substrates

[0066] Diamond heteroepitaxial growth on silicon substrates includes three steps: substrate pretreatment, deposition of diamond seeds, and CVD growth of polycrystalline diamond films.

[0067] Substrate pretreatment: The silicon surface was pretreated with hydrogen plasma. A 2-inch silicon wafer was placed in a microwave plasma-assisted chemical vapor deposition (MPCVD) device under the conditions of 1300 W power, 35 Torr chamber pressure and 300 sccm H2 gas flow for 10 minutes.

[0068] Diamond seed crystal deposition: Diamond seed crystals less than 10 nm in size (purchased from Tokyo Chemical Industry Co., Ltd.) were mixed with dimethyl sulfoxide (DMSO), anhydrous ethanol, and acetone in a mass ratio of 1:5000:250:250. The mixture was ultrasonically dispersed for 12 hours and then centrifuged at 1000 rpm for 20 minutes to remove impurities. The suspension was spin-coated onto a silicon wafer using the following deposition parameters: 3 drops were added over 15 seconds at 500 rpm, followed by increasing the speed to 4500 rpm for 110 seconds. This process was repeated three times.

[0069] CVD growth of diamond films: A silicon wafer with diamond seeds deposited on it was placed in an MPCVD apparatus (Seki 6350) to grow diamond films. The main growth parameters included: 3400W microwave power, 900°C temperature, 15sccm methane flow rate, and 40 minutes of growth time. A PCD film approximately 447 mm thick was grown on the silicon substrate.

[0070] (2) Cutting of polycrystalline diamond film and growth substrate

[0071] Using a silicon wafer cutter or a diamond knife, cut the 2-inch silicon wafer with the polycrystalline diamond film grown on the surface obtained in step (1) along a straight line 2-5 mm from the edge of the back side of the growth substrate to form a new boundary, so that a clear boundary line of the polycrystalline diamond film and the growth substrate is formed at the cutting point.

[0072] (3) Sticking of peeling tape

[0073] A stripping tape of 10 cm × 6 cm is attached to the growth surface of the polycrystalline diamond film so that it completely covers the growth surface of the polycrystalline diamond film and extends out from the edge of the cut portion of the polycrystalline diamond film to form a stripping operation end (stripping pull handle).

[0074] (4) Stripping of polycrystalline diamond film

[0075] The polycrystalline diamond film is peeled off from the surface of the silicon wafer by pulling the peeling operation end reserved in step (3) at a peeling angle of 40-60 degrees and a speed of 5 mm / s, so as to expose the nucleation surface of the polycrystalline diamond film.

[0076] Figure 2 are photos taken during the operation of this embodiment. Figure 2 Figures (a), (b) and (c) are photos of a 2-inch silicon wafer with a polycrystalline diamond film grown on the surface, the peeling process, the polycrystalline diamond film after peeling, and the silicon wafer after peeling, respectively.

[0077] Examples 2-5

[0078] Fabrication of polycrystalline diamond films of different thicknesses

[0079] According to a method similar to that of Example 1, polycrystalline diamond films having thicknesses of 200 nm, 400 nm, 800 nm, and 1000 nm were produced, respectively. Figure 3 The following are photos of the nucleation surfaces of polycrystalline diamond films of different thicknesses after exfoliation. As can be seen from the figures, polycrystalline diamond films of different thicknesses can almost be completely exfoliated from the substrate, demonstrating the effectiveness of the exfoliation method of the present invention.

[0080] In order to effectively evaluate their performance, the number of microcracks (generated during the peeling process) and the integrity (proportion of the growth substrate size) of these polycrystalline diamond films were counted. Figure 4 The following are statistical graphs of cracks and integrity for polycrystalline diamond films of varying thicknesses produced in Examples 2-5. The figures on the right show 50x magnified optical images of polycrystalline diamond films with thicknesses of 200 nm (top) and 1000 nm (bottom), respectively. As can be seen from the figures, the crack density corresponding to the 200 nm film is significantly higher than that of the 1000 nm film. These results show that the number of cracks increases with decreasing thickness, indicating that when the thickness is reduced to 200 nm, the PCD film exhibits exfoliation properties similar to those of two-dimensional materials. Furthermore, as the thickness decreases to 200 nm, the integrity of the exfoliated film decreases from 100% to 99.43%, primarily due to varying adhesion to the growth substrate.

[0081] Example 6

[0082] Fabrication of optimized polycrystalline diamond films

[0083] A polycrystalline diamond film with a thickness of 1000 nm was manufactured in a manner similar to that of Example 1, except that the surface of the silicon wafer was polished to reduce its roughness from 1 nm to 0.5 nm before substrate pretreatment.

[0084] Morphology and property characterization of polycrystalline diamond films

[0085] 1. The growth surface, nucleation surface and cross section of the polycrystalline diamond films of different thicknesses prepared in Examples 2-6 were characterized by SEM.

[0086] Figure 5 Shown are typical SEM images of the growth surface, nucleation surface, and cross section of a 1000 nm thick polycrystalline diamond film prepared in Example 5. Figure 6 Shown are SEM images of the growth surface (top) and nucleation surface (bottom) of polycrystalline diamond films of different thicknesses prepared in Examples 2-5. Figure 5 It can be seen that there are various large grains (hundreds of nanometers) on the growth surface, but the nucleation surface is flat without any visible grains; this gradient change in grain size can also be seen from the cross section. Figure 6The SEM images also show that the grains on the growth surface increase with increasing thickness, in stark contrast to the nucleation surface, where the surface morphology remains unchanged. This significant difference in growth surface morphology is primarily related to the growth method of the PCD film. Specifically, before CVD growth, diamond particles no larger than 10 nm are deposited as seeds on a silicon substrate. During the subsequent growth process, the silicon substrate hinders the diamond growth towards the bottom, so the diamond particles can only grow randomly in an upward and horizontal direction. In particular, the morphology of the nucleation surface depends on the surface of the growth substrate, the size of the seed crystals, and the nucleation density.

[0087] 2. Atomic force microscopy (AFM) was used to characterize the growth surface and nucleation surface of the polycrystalline diamond films of different thicknesses prepared in Examples 2-6.

[0088] Figure 7 Shown are AFM images of the growth surface (a) and nucleation surface (b) of a 1000 nm thick polycrystalline diamond film prepared in Example 5, and the nucleation surface (c) of a 1000 nm thick polycrystalline diamond film prepared in Example 6.

[0089] pass Figure 7 AFM images show that the surface roughness (Ra) of the polycrystalline diamond film in Example 5 is reduced from 36.2 nm (growth surface) to 0.952 nm (nucleation surface). When a smoother growth substrate is used in Example 6, the surface roughness is further reduced to 0.612 nm. This ultra-flat surface is comparable to polished single-crystal diamond, meeting the requirements of high-precision nanofabrication. Furthermore, compared with other strategies for exposing the nucleation surface, such as sacrificial growth substrates, the present method avoids impurities introduced by multiple operations. Therefore, this exfoliation method preserves the nucleation surface in its pristine state without causing any damage.

[0090] Figure 8Figures 2-3 show (a) roughness statistics of the growth and nucleation surfaces of PCD films of varying thicknesses produced in Examples 2-5 (statistical area 20 μm × 20 μm); (b) comparison of the present method with other reported methods in terms of film thickness and roughness; and (c) comparison of the present method with other methods in terms of film size and roughness. Comparison of the roughness of the growth and nucleation surfaces of PCD films of varying thickness reveals that the nucleation surface roughness is less than 1 nm for both thicknesses, while the roughness of the growth surface increases. Compared to previously reported studies on optimizing diamond film surface roughness, the present exfoliation method offers significant advantages in both thickness range and PCD film size. Therefore, it is currently considered the optimal method for obtaining PCD films with the largest size, smoothest surface, and widest thickness range. Furthermore, by extending the growth time and using a larger growth substrate, even thicker and larger PCD films can be obtained.

[0091] 3. The refractive index of the growth surface and the nucleation surface of the polycrystalline diamond film of Example 1 was measured using an optical ellipsometer. Figure 9 As shown in the figure, n represents the refractive index and k represents the extinction coefficient. Figure 9 The measurements show that the nucleation surface has a higher refractive index and a lower extinction coefficient than the growth surface, and the levels of these optical parameters of the nucleation surface are found to be comparable to those of SCD grown by CVD method.

[0092] 4. X-ray diffraction (XRD) technology was used to characterize the crystallization characteristics of the polycrystalline diamond film obtained in Example 1, such as Figure 10 As shown in the figure, obvious diffraction peaks are obtained at 43.96°, 75.14° and 91.52°, corresponding to the (111), (220) and (311) crystal planes, respectively, confirming that the nucleation surface has the properties of diamond. The strong diffraction peak of the (111) crystal plane indicates its dominance, which is consistent with other reports. In addition, the full width at half maximum (FWHM) of the (111) crystal plane diffraction peak of the nucleation surface is 0.64° narrower than that of the growth surface. In addition to the change in FWHM, the position of the diffraction peak of the (111) crystal plane shows a significant shift ( Figure 10 , inset), from 44.36° (growth surface) to 43.96° (nucleation surface), which is close to the position of the SCD (43.95°) for the standard (111) orientation. The shift of the diffraction peak indicates an improvement in crystal quality, which may be related to the release of internal stress. Typically, due to the lattice mismatch between diamond and the foreign substrate, residual stress will be introduced into the film, which will further induce lattice distortion and lead to abnormal shifts in the diffraction peak. By adopting the manufacturing method of the present invention, the residual stress has the opportunity to be released after removing the growth substrate.

[0093] 5. Raman spectroscopy was used to further characterize the crystallization characteristics of the polycrystalline diamond film obtained in Example 1. Figure 11 From the Raman spectrum, at 1332.8 cm -1 An obvious diamond scattering peak was observed at , which further proved the state of the film. Figure 11 From the illustration, the FWHM of the nucleation surface (7.43 cm -1 ) than the FWHM of the growth surface (7.67 cm -1 ) is narrower than that of the nucleation surface, indicating that the internal crystallization of the film measured from the nucleation surface is improved.

[0094] In addition to the reduced roughness of the nucleation surface, the crystallization quality was also improved compared to the growth surface, as shown by Raman shift and X-ray diffraction properties. Furthermore, the refractive index of the nucleation surface was lower than that of the growth surface, comparable to single crystals in terms of optical properties.

[0095] Table 1 summarizes the comparison of the surface roughness, thickness range and size (area of ​​the film) of the polycrystalline diamond films prepared by the method of the present invention and previously reported polycrystalline diamond films.

[0096]

[0097] It can be seen from the data in Table 1 that the polycrystalline diamond film obtained by the method of the present invention has a very low surface roughness, close to the level of polished single crystal diamond blocks. In addition, the obtained film is superior to previously reported work in size and thickness.

[0098] Example 7

[0099] Fabrication and characterization of 4 μm thick polycrystalline diamond films

[0100] A polycrystalline diamond film with a thickness of 4 μm was manufactured in a similar manner to Example 1, and then the polycrystalline diamond film was directly attached to a flexible PDMS substrate for bending and conductive performance tests.

[0101] Bending properties of polycrystalline diamond films

[0102] The polycrystalline diamond film stripped by the method of the present invention can be deformed arbitrarily without being restricted by the rigid growth substrate. Figure 12 A photo of a 4 μm thick PCD film showing its 360-degree bending (A) and its wrapping around cylinders of different radii (B).

[0103] like Figure 12As shown in Figure 2, the 4 μm thick film prepared in Example 7 can support 360° bending, with a tolerable curvature radius as small as 2 mm. Furthermore, the film remains stable after more than 2,500 bending cycles.

[0104] Fatigue test of polycrystalline diamond films

[0105] A polycrystalline diamond film with a thickness of 4 μm manufactured according to the method of Example 1 was attached to a flexible PDMS substrate and subjected to a 2% deformation cycle. Figure 19 Figure (a) shows a photograph of the film after >10,000 deformation cycles at 2% strain; Figure (b) shows a 5x magnified optical image of regions 1 and 2 in (a). This demonstrates that the polycrystalline diamond film of the present invention can withstand >10,000 deformation cycles at 2% strain without any damage.

[0106] While previously reported polycrystalline diamond films exhibited maximum strain at the microscale, these incredible diamond bending and fatigue properties are the first to be observed at the macroscale. Previous theoretical predictions for single-crystal diamond nanopillars predicted that the energy bands would gradually decrease with increasing strain. However, due to the complex internal crystal structure of diamond, this principle has rarely been confirmed in both theory and experiment. Fortunately, the present invention, through a simple exfoliation strategy, allows observation of the dynamic properties of freestanding polycrystalline diamond films.

[0107] Conductive properties of polycrystalline diamond films and their energy band control

[0108] In order to investigate the conductive properties of the polycrystalline diamond film under different bending degrees, the inventors adhered the 4μm thick polycrystalline diamond film prepared in Example 7 to a 1mm thick flexible PDMS (polydimethylsiloxane) substrate, and then attached soft conductive tape. By controlling the deformation of the PDMS substrate, the polycrystalline diamond film can be bent. In addition, by bending the PDMS substrate in different directions, the deformation of the polycrystalline diamond film under tensile and compressive strain can be observed respectively. Figure 13 From the calculation results shown, it can be seen that the strain distribution is uneven. Whether it is the top surface or the bottom surface of PDMS, the maximum deformation occurs in the center.

[0109] Figure 14 The conductivity of a 4μm-thick polycrystalline diamond film prepared in Example 7 changes under different strains (a) and bending cycles (b). The film's significant piezoresistive properties are observed by measuring its resistance under dynamic strain. In both bending modes, the resistance decreases with increasing strain, but the magnitude of the resistance change in the push-down mode is greater than that in the pull-up mode. Furthermore, the resistance fully recovers during load-unload cycles.

[0110] The above results show that the band structure of polycrystalline diamond films can be regulated by strain. As the degree of strain increases, the energy band of diamond gradually decreases, and thus the conductivity increases. Generally speaking, the regulation of diamond band is mainly achieved through element doping, but diamond doping has high process requirements and is difficult to complete in ordinary laboratories. The method of strain regulation of diamond band proposed in this invention greatly reduces the difficulty of preparation and production cost, providing convenience for the development of flexible diamond semiconductor devices and diamond-based sensor devices.

[0111] Example 8

[0112] Material properties of polycrystalline diamond films

[0113] Figure 15 (a) Raman spectrum and (b) and (c) XPS measurement results of the polycrystalline diamond film prepared in Example 5 above.

[0114] Figure 16 Summary of experimental photos and data of contact angles on the growth surface and nucleation surface of PCD films of different thicknesses.

[0115] Figure 17 The friction coefficients of the growth surface and the nucleation surface of the polycrystalline diamond film prepared in Example 5 (a) and the relationship curve between the external force applied to the growth surface and the nucleation surface and the depth of the indentation formed (b) are shown.

[0116] Figure 18 Refractive index (A) and extinction coefficient (B) of the growth and nucleation surfaces of a polycrystalline diamond film with a thickness of 500 nm; and refractive index (C) and extinction coefficient (D) of the growth and nucleation surfaces of a polycrystalline diamond film with a thickness of 1000 nm.

[0117] These results demonstrate that the nucleation surface has a higher refractive index and lower extinction coefficient than the growth surface. The refractive index of the nucleation surface is comparable to that of single-crystal bulk diamond. Furthermore, as thickness increases, the refractive index of both the growth and nucleation surfaces decreases, while the extinction coefficient increases. This high-refractive-index, low-absorption-coefficient diamond film offers the potential for the development of diamond-based micro- and nano-optical devices, such as optical superlenses and optical modulators.

[0118] Example 9

[0119] Effect of different peeling angles

[0120] Polycrystalline diamond films of varying thicknesses were fabricated using a method similar to that used in Example 1. These films were peeled at a constant rate (10 mm / min) and varying peel angles (20°-90°). Furthermore, potential crack propagation was simulated using the phase field method. For a detailed description of the phase field method, please refer to the following two references:

[0121] Miehe, C., Hofacker, M. & Welschinger, F. A phase field model forrate-independent crack propagation: Robust algorithmic implementation based on operator splits. Computer Methods in Applied Mechanics and Engineering199, 2765-2778 (2010).

[0122] Spatschek, R., Brener, E. & Karma, A. Phase field modeling of crackpropagation. Philosophical Magazine 91, 75-95 (2011).

[0123] Calculation of crack density on the peeled films revealed that peeling quality depends on the peel angle and film thickness. For thicker films (800 nm and 1000 nm), crack-free films can be obtained over a wide range of peel angles (20°-90°). However, for films with a thickness of 600 nm, the peel angle range with minimal cracking narrows to 40°-70°. As the film becomes thinner, the operating window further narrows.

[0124] Phase-field simulations were performed on a 600 nm thick polycrystalline diamond film peeled at various peel angles of 30°, 60°, and 90°. Initial crack sizes were set at 56 nm (upper surface) and 1.2 nm (lower surface), respectively, with 95% of cracks smaller than these sizes. Simulation results show that at a low peel angle of 30°, the separated film undergoes slight bending deformation, placing tensile stress on both the lower and upper surfaces, ultimately leading to large crack propagation from the upper surface. In contrast, at a higher peel angle (90°), the upper (concave) side of the film is compressed, preventing potential crack growth. However, on the highly deformed lower (convex) side of the film, elevated tensile stress triggers the propagation of small initial cracks. Consequently, crack propagation does not occur within the 600 nm thick film when peeled at a moderate peel angle (60°).

[0125] For thicker films (700 nm to 1000 nm), simulations indicate that peel angles between approximately 30° and 90° can prevent crack propagation. These results are consistent with the observed crack densities of various peeled films and can therefore be used to guide the large-scale production of crack-free films.

[0126] Example 10

[0127] Integrity and quality evaluation of polycrystalline diamond films

[0128] The initial resistance of the growth surface of the polycrystalline diamond film prepared in Example 1 was measured to be approximately 10<4> Ω.

[0129] Since the resistance of a diamond film is determined by its integrity and quality, to evaluate the potential impact of the stripping process on film quality, a chip array was fabricated on a 2-inch diamond film. Each chip in the array contained a pair of gold electrodes, and the resistance change before and after stripping was measured. Figure 21 Photos of chip arrays fabricated on a 2-inch polycrystalline diamond film before (a) and after (b) peeling, as well as the resistance changes before and after peeling (c).

[0130] from Figure 21 Figure (c) shows a relatively uniform resistance distribution, demonstrating the consistency of the film across the entire 2-inch diamond film. After stripping, the resistance remains nearly constant at all locations (the overall resistance decrease is likely related to the separation from the silicon substrate). This result demonstrates the good integrity and high quality of the polycrystalline diamond film of the present invention.

[0131] Example 11

[0132] Micro / nanofabrication on polycrystalline diamond films

[0133] Diamond micro / nano structures were prepared on the growth surface and nucleation surface of the polycrystalline diamond film prepared in Example 1 using electron beam lithography (EBL) and plasma etching techniques, respectively. Figure 22 shown.

[0134] By comparing the micro / nanostructures prepared on the growth surface and the nucleation surface, it can be seen that the nucleation surface has significantly less residue and higher structural accuracy.

[0135] Example 12

[0136] Application of polycrystalline diamond films as quantum platforms

[0137] A polycrystalline diamond film was produced in a manner similar to that of Example 1, except that nitrogen gas was introduced during the CVD growth process to generate special atomic defects in the film, called nitrogen vacancy (NV) color centers.

[0138] The diamond film was excited with a 532 nm laser (Changchun New Industry Corporation, MGL-FN-5321W). The laser was focused on the diamond film through a 40× air objective lens. The excited NV fluorescence was filtered with a 605 nm long-pass filter and imaged on an EMCCD (Teledyne Photometrics, Evolve 512 Delta). Figure 23 (a) The inset of the fluorescence image shows the bright spot corresponding to the emission of the NV color center. The peak at about 640 nm represents the zero-phonon line of NV-.

[0139] Optically detected magnetic resonance (ODMR) measurements were performed with the 532 nm laser kept constant throughout the measurement. The MW (microwave) frequency was linearly swept from 2800 to 2940 MHz using an external pulse trigger. Figure 23 The ODMR spectrum results shown in Figure (b) indicate that the spin states (±1) of the NV color center can be effectively separated under the action of an external magnetic field. Therefore, the polycrystalline diamond film provided by the present invention has great application potential in quantum technology.

Claims

1. A method for large-scale production of ultra-flat polycrystalline diamond films, the method comprising: (1) Growing a polycrystalline diamond film on a growth substrate having a diamond seed crystal on its surface by chemical vapor deposition, wherein the polycrystalline diamond film comprises: a growth surface having a first roughness and a nucleation surface bonded to the growth substrate; (2) cutting at least a portion of the growth substrate on which the polycrystalline diamond film is grown, wherein the cutting operation forms a boundary line where the polycrystalline diamond film is bonded to the growth substrate at the cutting portion; (3) attaching a stripping tape to the growth surface of the polycrystalline diamond film, wherein the stripping tape extends beyond the polycrystalline diamond film at least at an edge of the cut portion to form a stripping operation end; (4) Pulling the stripping operation end to strip the polycrystalline diamond film from the surface of the growth substrate to expose the nucleation surface of the polycrystalline diamond film, wherein the exposed nucleation surface has a second roughness, and the second roughness is smaller than the first roughness.

2. The method according to claim 1, wherein The first roughness is 10-200 nm, preferably 20-50 nm; preferably, the second roughness is 0.5-5 nm, preferably 0.5-2 nm, more preferably 0.5-1 nm.

3. The method according to claim 1 or 2, wherein: The particle size of the diamond seed crystals described in step (1) is 2-10 nm.

4. The method according to any one of claims 1 to 3, wherein In step (1), a microwave plasma assisted chemical vapor deposition device is used to grow a polycrystalline diamond film; Preferably, the deposition temperature of the chemical vapor deposition method in step (1) is 800-1000°C, more preferably 850-950°C.

5. The method according to any one of claims 1 to 4, wherein The growth substrate is selected from one or more of Si, SiC, TiC, Co, Pt, Al2O3, Ni, Re, Ir, SiO2 and Mo; preferably, the surface roughness of the growth substrate is less than 2 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

6. The method according to any one of claims 1 to 5, wherein The thickness of the polycrystalline diamond film is 200 nm-100 μm, preferably 200 nm-10 μm, and more preferably 400 nm-5 μm.

7. The method according to any one of claims 1 to 6, wherein The trimming operation in step (2) is performed perpendicularly to the growth surface of the polycrystalline diamond film; preferably, the trimming operation is performed so that the length of the boundary line where the formed polycrystalline diamond film is bonded to the growth substrate is at least 1% of the circumference of the growth surface of the polycrystalline diamond film, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, preferably 5%-20%, more preferably 10%-12%; Preferably, the growth substrate is circular, and the length of the boundary line between the polycrystalline diamond film cut in step (2) and the growth substrate is 20%-50% of the diameter of the growth substrate.

8. The method according to any one of claims 1 to 7, wherein In step (4), the speed of pulling the stripping operation end to strip the polycrystalline diamond film from the surface of the growth substrate is 1-10 mm / s; preferably, the stripping angle of the stripping operation in step (4) is 10-90 degrees.

9. The method according to any one of claims 1 to 8, wherein The nucleation surface has a higher refractive index than the growth surface; preferably, the nucleation surface has a lower extinction coefficient than the growth surface; Preferably, compared with the position of the (111) crystal plane XRD diffraction peak of the growth surface, the position of the (111) crystal plane XRD diffraction peak of the nucleation surface is closer to the standard (111) crystal plane XRD diffraction peak of single crystal diamond; and the half-maximum full width of the (111) crystal plane XRD diffraction peak of the nucleation surface is smaller than the half-maximum full width of the (111) crystal plane XRD diffraction peak of the growth surface.

10. A method for regulating the energy band structure of a diamond film, the method comprising attaching a polycrystalline diamond film manufactured by the method of any one of claims 1 to 9 to the surface of a flexible substrate, stretching and / or compressing the polycrystalline diamond film by bending the flexible substrate, and regulating the energy band structure of the polycrystalline diamond film through the strain generated in the polycrystalline diamond film during the stretching and / or compression process.

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