Heat treatment of nanodiamond particles with controlled powder layer depth

Abstract

Luminescent diamonds are manufactured by creating vacancies in diamond grains and heat treating the diamond grains by controlling the thickness of the diamond grains on a substrate. The heat treatment may be performed within a temperature range that does not burn the diamond grains, and the controlled thickness results in uniform color changes and / or promotes oxygen termination on the surface of the diamond particles.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 366,439, filed on June 15, 2022, entitled “HEAT TREATMENT OF NANODIAMONDPARTICLES WITH CONTROLLED POWDER LAYER DEPTH,” the disclosure of which is hereby incorporated herein by reference. Background Art

[0003] Laser injected fluorescence is a known technique used to better understand how biological systems function at the cellular, subcellular or molecular level by individually probing tissues, cells and biomolecules for observation. In an example, laser injected fluorescence can be applied to imaging and tracking individual molecules or particles in biological cells or the like, for example, in vivo biosensors for visceral mapping, cell imaging and the like. One material used for laser injected fluorescence is luminescent nanodiamonds, which are nanometer-sized diamond particles or grains that have been developed to emit light when excited by a light source within a desired wavelength as required by the end-use application. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] These and other features and aspects of the luminescent nanodiamonds and methods of making the same as disclosed herein will be appreciated as they will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0005] Figure 1-1 is a photograph of nanodiamond particles coated on a glass slide before heat treatment;

[0006] Figure 1-2 When coated on a glass slide after heat treatment Figure 1-1 Photo of nanodiamond particles;

[0007] Figure 2 shows the measurement of the layer thickness of diamond nanoparticles before heat treatment using a 3D imaging method; and

[0008] Figure 3 A method for enhancing the photoluminescent properties of diamond nanoparticles by heat treatment is shown. DETAILED DESCRIPTION

[0009] Some embodiments of the present disclosure relate to luminescent diamonds, which may also be referred to as photoluminescent diamonds. In some additional embodiments, methods and apparatus are described that can be used to produce luminescent diamonds, including producing diamond pellets having an enhanced degree of plastic deformation and an increased amount of vacancy centers (nitrogen, silicon, etc.). The increase in vacancy centers can result in an increased degree of luminescence in one or more light spectrums. For example, the increased luminescence may occur in one or more of the following: the red, blue, green, or violet visible wavelength spectrum; the ultraviolet spectrum; the infrared spectrum; or the near infrared spectrum.

[0010] In some embodiments, luminescent diamonds (e.g., photoluminescent diamonds) and methods of making the same as disclosed herein are designed in a manner that improves manufacturing efficiency and throughput, thereby increasing affordability and availability of the material for end-use applications, including but not limited to biological uses. In such embodiments, luminescent diamonds may be produced with less expense, energy, time, or any combination thereof, thereby potentially increasing the availability of such luminescent diamonds.

[0011] In addition, in some embodiments, the luminescent diamond prepared according to the principles disclosed herein exhibits luminescent intensity levels similar to or greater than those of conventional luminescent diamonds, thereby providing an opportunity to expand the range of potential end-use applications of such materials. For the sake of clarity, in some embodiments, the luminescent diamond of some embodiments of the present invention is initially formed by consolidation and compaction of pre-existing diamond grains, forming a luminescent active sintered body or block (characterized by a high degree of intercrystalline diamond bonding) or forming a mechanically combined semi-sintered body or block (characterized by a lower degree of intercrystalline diamond bonding or substantially no intercrystalline diamond bonding). Under such conditions, the consolidated material is referred to as luminescent diamond herein. During subsequent processing, the luminescent diamond can be heat treated and / or reduced in size as required by a specific end use, and in some embodiments, the size of the resulting diamond particles or grains is nanoscale. In some examples, the size-reduced luminescent diamond can be only nano-sized particles, or can include a combination of nano-sized particles with coarser diamond particles. The term "nanodiamond" as used herein is understood to refer to luminescent diamond comprising nano-sized diamond particles, for example having an average size of at most 1000 nm (eg, between 1 nm and 1000 nm).

[0012] In some embodiments, luminescent diamonds as disclosed herein may be formed by combining a volume of precursor diamond grains, which may be in the form of natural and / or synthetic diamond grains, and placing the volume of diamond grains into a unit, can or container typically used for diamond grain consolidation. In examples, the diamond grains may have an average grain size of 1 μm to 1000 μm, 1 μm to 100 μm or 10 μm to 50 μm. In other embodiments, the initial diamond grain or powder size may extend to the submicron or nanodiamond range, as described herein. In some embodiments, nano-sized powders formed by mechanical crushing or explosion processes of conventional diamond powders may be used in a similar manner. Conventional diamond powders may be synthetic or natural, however, in some cases, synthetic diamond powders have a higher intrinsic nitrogen content, which together with adjacent vacancy centers makes the diamond luminescently active. In examples, the starting diamond material has an intrinsic nitrogen impurity amount consistent with the intrinsic nitrogen impurity amount found in diamonds designated as type 1b (e.g., 50 ppm nitrogen or more). Nanosized powders synthesized by impact synthesis will also have a high inherent nitrogen content.

[0013] In an example embodiment, the cell, tank or container (each cell or pressure cell) is specially configured to apply differential or asymmetric pressure to its contents when subjected to a high pressure / high temperature (HPHT) consolidation process using conventional stamping equipment for making polycrystalline diamond. Systems and methods for making luminescent diamond using differential or asymmetric pressure as described in International Patent Application PCT / US2022 / 052223 are hereby incorporated by reference in their entirety for all purposes. As described in more detail herein, the differential pressure applied by the cells as disclosed herein can cause a greater degree of plastic deformation to occur and thereby generate more nitrogen vacancy centers, which helps to increase the number of defects / optical centers (e.g., NV, NVN or N3 in the case of nitrogen defects) formed in the resulting luminescent diamond pellets and correspondingly increase the amount of luminescence. In example embodiments, a stamping device or apparatus for applying pressure to a cell, can or container may be specially configured to apply differential or asymmetric pressure (e.g., axial pressure as opposed to radial pressure) to the cell and the contents within the cell when subjected to an HPHT consolidation process using such specially configured stamping device for making polycrystalline diamond. As described in more detail herein, the differential pressure applied by the stamping device as disclosed herein may result in a greater degree of plastic deformation and thus more vacancy centers, which helps to increase the amount of centers formed in the resulting luminescent diamond pellets to increase the amount of luminescence.

[0014] As described herein, the luminescent diamonds may be heat treated and / or reduced in size as required for a particular end use. According to some aspects, heat treatment or other treatments may be used to provide desired surface properties that may be beneficial to the end use. For example, luminescent nanodiamonds may be used as biomaterials, bioimaging materials, etc. as drug delivery vehicles, and heat treatments may be used to provide different surface terminations.

[0015] According to some aspects, the heat treatment can be performed in air below 550°C, which can promote oxygen termination on the surface, thereby affecting the optical properties of the luminescent diamond. In some embodiments, heat treatment in air at 550°C or 650°C or below is essential for improving the photoluminescence intensity of nanodiamonds. However, it is worth noting that when the temperature is below 550°C, it is also difficult to uniformly treat the nanodiamond particles within the powder bed. In addition, if the temperature is too high, the nanodiamond powder will burn out.

[0016] For the convenience of heat treatment, consider applying coating method to control the powder layer depth during the heat treatment process. In an exemplary embodiment, nano diamond powder is dispersed in a liquid. In this way, disperse nano diamond powder and stable suspension can be prepared. Particles can be well dispersed in a variety of liquid solvents (including water).

[0017] The suspension can then be coated on the surface to form a nano diamond layer. In some embodiments, the surface is a glass surface, but other materials that can withstand the temperature of heat treatment can also be used. For example, various metals and metal alloys, composite materials, ceramics, cermets and other materials can be used.

[0018] Figure 1 (including Figure 1-1 and Figure 1-2 ) shows an example embodiment of a nanodiamond material coated on a glass slide before and after heat treatment. In the example, after heat treatment in air at 450°C to 550°C for one hour, the color of the diamond particles changes and the color changes from dark to bright milky white. Figure 1-1 In the present invention, the nanodiamond particles are coated before heat treatment, and Figure 1-2 Nanodiamond particles are shown after heat treatment at 500°C for one hour. As shown, the change in color can be quite dramatic. The lighter color corresponds to an increase in oxygen terminations of the diamond particles, resulting in an increase in photoluminescence intensity.

[0019] The color change can also depend on factors other than temperature, duration of heat treatment, and the substrate the material is applied on. For example, the color of nanodiamonds after heat treatment can depend on the layer thickness. Figure 2The layer thickness measurements before heat treatment are shown. It is noteworthy that when the layer thickness is ≈13 μm, the diamond particles are all bright milky white after treatment. However, when the layer thickness is increased to ≈30 μm (reflected by the ridge area), the diamond particles remain darker in color.

[0020] Any suitable method can be used to coat diamond nanoparticles on glass, ceramic or other slides. Example methods can include dip coating, spin coating, dry coating and slip casting. In at least some embodiments, the thickness coating is within the range of having a lower limit, an upper limit or a lower limit and an upper limit, and the value includes 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm and the value therebetween. For example, the thickness of the coating can be controlled to be at least 1 μm, no more than 25 μm or within the range between 1 μm and 25 μm. In some embodiments, the layer is controlled to have a thickness between 3 μm and 15 μm or between 5 μm and 15 μm. In at least some embodiments, a thickness below 15 μm or below 20 μm may be critical for obtaining consistent color changes.

[0021] Layer thickness can also depend on heat treatment length and temperature. Generally speaking, layer thickness can increase with heat treatment time, temperature or both time and temperature. Reducing layer thickness can be beneficial to shorten heat treatment time, reduce temperature or shorten heat treatment time and reduce temperature.

[0022] In one or more embodiments, the method for coating the substrate includes dry coating with diamond particles at a concentration between 0.1% and 10% by weight. However, due to the surface tension of the water or other liquid in which the particles are suspended, it may be difficult to obtain a uniform layer thickness. In some embodiments, alcohol or another material that suppresses or reduces the surface tension of the suspension can be used. For example, a nanodiamond suspension in which the liquid is composed of a surface tension inhibitor (e.g., alcohol) of 10% to 100% can be spread well on a glass substrate. After the suspension is placed on the substrate surface, the suspension can be dried (e.g., air-dried, oven-dried, dried with a hot plate, etc.). Drying can be performed at a temperature below the boiling point of the liquid of the suspension. After drying, the coating can be highly uniform. In the case where some areas have a larger thickness (e.g., more than 25 μm or 30 μm), these areas can be scraped off before or after heat treatment, which particularly promotes oxygen termination on the surface of the diamond particles.

[0023] Figure 3A method 300 for enhancing the photoluminescent properties of diamond nanoparticles by heat treatment is shown. As described above, a volume of precursor diamond grains may be subjected (block 302) to a HPHT process in a pressure chamber to form diamond grains having luminescent centers (e.g., Nv, NVN, or N3 centers). In some embodiments, the HPHT process may be in the range of about 1300° C. to 2500° C., and the process pressure may be about 3.0 GPa to about 10 GPa. The resulting diamond grains may be separated into a powder and combined with a liquid (block 304) to form a suspension. As described above, the liquid may include water, a surface tension inhibitor (e.g., alcohol), or other liquids. The diamond grains may have a concentration of between 0.1% and 10% by weight in the suspension. The suspension is adhered (block 306) to a substrate such as glass or ceramic. The suspension may be adhered by one or more of dip coating, spin coating, dry coating, or slip casting. The suspension and substrate are heat treated at a heat treatment temperature for a period of time (block 310). In some embodiments, the heat treatment temperature is less than 650° C., 600° C., 550° C., 500° C., or 450° C. In some embodiments, the heat treatment temperature is greater than 400° C., greater than 450° C., or greater than 500° C., such as 525° C. The heat treatment duration may be between 30 minutes and 300 minutes, between 30 minutes and 120 minutes, between 45 minutes and 90 minutes, or about 60 minutes. One or more liquids of the suspension may evaporate before or during the heat treatment.

[0024] During the heat treatment, oxygen termination and / or vacancy formation may occur on the diamond grains arranged on the substrate. The heat treatment may change the color of the suspension on the substrate. For example, a dark, opaque or slightly translucent suspension before the heat treatment may become a light, transparent or more translucent suspension after the heat treatment. In some embodiments, the adhered suspension may change from black, gray or dark to a yellow, light gray, white or translucent suspension. As appropriate, some diamond grains may be removed from the substrate before or after the heat treatment (block 310) (block 308). The diamond grains may be removed to facilitate the diamond material on the substrate to reach a desired thickness, such as less than 30 μm, less than 25 μm, less than 20 μm, less than 15 μm or between 1 μm and 15 μm. Keeping the thickness of the diamond material on the substrate less than about 15 μm can increase the yield of oxygen termination on the diamond grains.

[0025] After the heat treatment at block 310, the diamond grains may be removed from the substrate and separated (block 312) into desired grain sizes. In some embodiments, portions of method 300 may be repeated, wherein some or all of the removed diamond grains are combined with a liquid (block 304) to form a suspension for subsequent adhesion (block 306) to a substrate and heat treatment (block 310). In some embodiments, the diamond grains may repeat the suspension and heat treatment process 3, 4, 6, 8, 10, 12, 15, or more times.

[0026] Although several example embodiments of luminescent diamonds have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the scope of the claims and the present disclosure. For example, luminescent diamonds as disclosed herein already exist in the context of biological end-use applications. It should be understood that luminescent diamonds as disclosed herein can be used in end-use applications other than biological, where the desired level of improvement in luminescence intensity is useful or beneficial. Other potential uses of luminescent diamonds (e.g., luminescent diamonds containing nitrogen vacancy centers) include, but are not limited to, use in magnetic sensors, high-resolution thermal imaging, microscopic sensor arrays, anti-counterfeiting measures, ion concentration monitoring, membrane potential measurements, light trapping, and strain / pressure sensors. Therefore, it should be understood that luminescent diamonds as disclosed herein are not intended to be limited to one particular end-use application.

[0027] In other embodiments, HPHT or heat treatment conditions are described, but are illustrative only, as different conditions may be used. For example, the materials described herein may be formed using different pressing techniques in the presence of different catalyst materials, suspended in different liquids, used with different surface tension inhibitors, adhered to different substrates, heat treated in different atmospheres, treated at different temperatures or time periods, or varied in a variety of ways. Thus, in different embodiments, the conditions may vary. Systems and methods for making luminescent diamonds are described in U.S. Patent Application Publication No. US2022 / 0056337, U.S. Patent Application No. 18 / 005,115, and International Patent Application No. PCT / US2023 / 023697, each of which is incorporated herein by reference in its entirety for all purposes.

[0028] In the description herein, various relational terms may be used to facilitate understanding of various aspects of some embodiments of the present disclosure. Relational terms such as "top," "bottom," "above," "below," "left," "right," and the like may be used to describe various components, including the operational or pictorial positions of the components relative to one or more other components. The relational terms do not indicate a particular orientation of each embodiment within the scope of the specification or claims, but are intended to facilitate reference to the various components. Thus, such relational aspects may be reversed, flipped, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly modified.

[0029] Certain component descriptions or designations such as "first," "second," "third," and the like may be used in the specification or claims to distinguish between identical components or to distinguish between components that are similar in use, structure, or operation. Such language is not intended to limit a component to a single designation or to require multiple components. Thus, a component referenced as a "first" component in the specification may be the same as or different from a component referenced as a "first" component in a claim, and a claim may include a "first" component without requiring the presence of a "second" component.

[0030] In addition, although the specification or claims may mention "additional" or "other" elements, features, aspects, parts or the like, this does not exclude the presence of a single element or more than one additional element. Where the claims or specification mention "one" or "an" element, such reference should not be interpreted as only one of the elements, but should include other components and be understood as "at least one" of the elements. It should be understood that where the specification indicates that "may", "perhaps", "can" or "can" include a certain component, feature, structure, function or characteristic, the specific component, feature, structure or characteristic is provided in certain embodiments, but is optional for other embodiments of the present disclosure. The terms "couple", "coupled", "connect", "connection", "connected", "connected with..." and "connecting" refer to "directly connected with..." or "connected with..." via one or more intermediate elements or members. "Integrally" or "integrally" formed components include components that are made from the same piece of material or a group of materials, such as by being formed or cast together from the same material, in the same forming or casting process, or processed together from the same piece of material stock. "Integrally" components should also be understood to be "coupled" together.

[0031] In addition, it should be understood that reference to "one embodiment," "an embodiment," or "an example" of the present disclosure is not intended to be interpreted as excluding the existence of additional embodiments or examples that also incorporate the recited features. For example, any element described with respect to an embodiment herein may be combined with any element of any other embodiment described herein.

[0032] As will be appreciated by those of ordinary skill in the art encompassed by the embodiments of the present disclosure, the numbers, percentages, ratios, or other values ​​stated herein are intended to include the values, and also include other values ​​that are "about" or "approximately" the stated values. Thus, the values ​​should be interpreted broadly enough to include values ​​that are at least close enough to the stated values ​​to perform the desired function or achieve the desired result. The values ​​include at least the variations expected in suitable manufacturing or production processes, and may include values ​​within 5%, within 1%, within 0.1%, or within 0.01% of the stated values.

[0033] As used herein, the terms "approximately," "about," and "substantially" refer to an amount that is close to a stated amount within standard manufacturing or process tolerances or that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is less than 5% of the stated amount, less than 1% of the stated amount, less than 0.1% of the stated amount, and less than 0.01% of the stated amount. In addition, it should be understood that any directions or reference frames in the foregoing description are relative directions or movements only. For example, any reference to "up" and "down" or "above" or "below" merely describes the relative position or movement of the relevant elements.

[0034] Although various example embodiments have been described in detail herein, it will be readily apparent to those skilled in the art, in view of the present disclosure, that many modifications are possible in the example embodiments without departing substantially from the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure. Similarly, although the disclosure herein contains many details, these details should not be interpreted as limiting the scope of the disclosure or any appended claims, but only provide information related to one or more specific embodiments that may fall within the scope of the disclosure and the appended claims. All claims and evidence are incorporated herein. Any of the described features from the various embodiments disclosed and incorporated may be used in combination.

[0035] In the claims, means-plus-function clauses are intended to include structures described herein as performing the recited function and include not only structural equivalents but also equivalent structures. Thus, while a nail and a screw may not be structural equivalents because a nail employs a cylindrical surface to fasten wooden parts together while a screw employs a helical surface, in the context of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intent of the applicant not to limit any claim herein by invoking a means-plus-function requirement unless the claim expressly uses the phrase "means for..." and an associated function.

[0036] The Abstract at the end of this disclosure is provided to allow the reader to quickly ascertain the general nature of some embodiments of the disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. A method for producing a luminescent diamond, comprising: subjecting a volume of precursor diamond grains to high pressure / high temperature conditions in a pressure chamber and thereby forming diamond grains having luminescent centers; forming a suspension by suspending the diamond grains in a liquid; causing the suspension to adhere to a substrate and controlling the thickness of the suspension on the substrate; as well as The suspension on the substrate is heat treated and thereby changes at least one of the color of the suspension or oxygen terminations on diamond particles of the suspension. 2 . The method of claim 1 , wherein the luminescent center comprises at least one of a nitrogen vacancy or a silicon vacancy.

3. The method of claim 1, wherein the liquid comprises water.

4. The method of claim 3, wherein the liquid comprises a surface tension suppressant.

5. The method of claim 4, wherein the surface tension suppressant comprises alcohol.

6. The method of claim 1, wherein the liquid is 10% to 100% alcohol.

7. The method of claim 1, wherein the substrate is glass. The method of claim 1 , wherein the thickness is controlled to be less than 30 μm.

9. The method of claim 8, wherein the thickness is controlled to be less than 25 μm.

10. The method of claim 8, wherein the thickness is controlled to be between 1 μm and 15 μm.

11. The method of claim 1 , wherein controlling the thickness comprises removing material above a threshold thickness.

12. The method of claim 1, wherein causing the suspension to adhere to the substrate comprises drying the suspension.

13. The method of claim 1, wherein causing the suspension to adhere to the substrate comprises coating the suspension on the substrate using one or more of dip coating, spin coating, dry coating, or slip casting.

14. The method of claim 12, wherein drying the suspension is performed at a temperature below the boiling point of the liquid and prior to subjecting the suspension to a heat treatment.

15. The method of claim 1, wherein heat treating the suspension comprises heat treating at a temperature not exceeding 650°C.

16. The method of claim 15, wherein heat treating the suspension comprises heat treating at a temperature not exceeding 600°C.

17. The method of claim 15, wherein heat treating the suspension comprises heat treating at a temperature not exceeding 550°C.

18. The method of claim 17, wherein heat treating the suspension comprises heat treating at a temperature ranging between 450°C and 550°C.

19. The method of claim 1, wherein heat treating the suspension is performed for a duration of up to two hours.

20. The method of claim 1, wherein heat treating the suspension is performed for a duration between 30 minutes and 90 minutes.

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