Heat treatment of nanodiamond particles with controlled powder bed depth

Abstract

Luminescent diamonds are produced by forming voids in the diamond grains, controlling the thickness of the diamond grains on the substrate, and then heat-treating the diamond grains. The heat treatment can be carried out at a temperature range that does not burn the diamond grains, and the controlled thickness results in a uniform color change and promotes oxygen termination on the diamond grain surface.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 366,439, filed June 15, 2022, entitled "HEAT TREATMENT OF NANODIAMOND PARTICLES WITH CONTROLLED POWDER LAYER DEPTH," the disclosure of which is incorporated herein by reference. [Background technology]

[0002] Laser-infused fluorescence (LAF) is a well-known technique employed to better understand how biological systems function at the cellular, subcellular, or molecular level through the individual exploration and observation of tissues, cells, and biomolecules. In one example, LAF can be applied to image and track single molecules or particles within living cells, for example, in vivo biosensors for organ mapping, cellular imaging, and the like. One material used in LAF is luminescent nanodiamonds, which are nanosized diamond particles or grains engineered to emit light when excited by a light source within the desired wavelength required for the end application.

[0003] These and other features and aspects of the luminescent nanodiamonds and methods for making same disclosed herein will be appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0004] [Figure 1-1] 1 is a photograph of nanodiamond particles coated on a glass slide before heat treatment. [Figure 1-2] 1-1 is a photograph of the nanodiamond particles of FIG. 1-1 when coated on a glass slide after heat treatment. [Figure 2] 3D imaging is used to measure the layer thickness of diamond nanoparticles before heat treatment. [Figure 3] We demonstrate how heat treatment can enhance the photoluminescence properties of diamond nanoparticles. DETAILED DESCRIPTION OF THE INVENTION

[0005] Some embodiments of the present disclosure relate to luminescent diamond, which may also be called photoluminescent diamond.In some additional embodiments, methods and devices useful for producing luminescent diamond are described, including producing diamond pellets with enhanced plastic deformation and increased amount of vacancy centers (nitrogen, silicon, etc.).The increase in vacancy centers can increase the luminescence in one or more spectra.For example, the increase in luminescence can occur in one or more of the visible wavelength spectrum of red, blue, green, or purple, ultraviolet spectrum, infrared spectrum, or near-infrared spectrum.

[0006] In some embodiments, the luminescent diamonds (e.g., photoluminescent diamonds) and methods for making them disclosed herein are designed in a way that increases production efficiency and production volume, thereby improving the availability and usability of the material in end uses, including but not limited to biological applications. Luminescent diamonds, in such embodiments, can be produced with less cost, energy, time, or any combination thereof, potentially increasing the usability of such luminescent diamonds.

[0007] Furthermore, in some embodiments, luminescent diamonds prepared according to the principles disclosed herein exhibit similar or higher levels of luminescence intensity than conventional luminescent diamonds, thereby offering the opportunity to expand the range of potential end-use applications for such materials. For clarity, in some embodiments, the luminescent diamonds of some embodiments herein are first formed by compaction and consolidation of existing diamond grains, forming a luminescence-active sintered body or slug (characterized by a high degree of intercrystalline diamond bonding) or a mechanically bonded semi-sintered body or slug (characterized by a low degree or substantially no intercrystalline diamond bonding). In this state, this compacted material is referred to herein as luminescent diamond. During subsequent processing, the luminescent diamond may be heat-treated and / or reduced in size, depending on the specific end-use application; in some embodiments, the resulting diamond grains or grains may be nanoscale in size. In some instances, the reduced-size luminescent diamond may be exclusively nano-sized grains or may include a combination of nano-sized grains and coarser diamond grains. The term "nanodiamond" as used herein is understood to refer to luminescent diamond, including nano-sized diamond particles, for example, having an average size of up to 1000 nm (e.g., between 1 nm and 1000 nm).

[0008] In some embodiments, the luminescent diamond disclosed herein can be formed by combining a quantity of precursor diamond grains, which can be in the form of natural and / or synthetic diamond grains, and placing the quantity of diamond grains in a cell, can, or container conventionally used for compacting diamond grains. In one example, the diamond grains can 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 size of the initial diamond grains or powder can range from submicron to nanodiamond, as described herein. In some embodiments, nano-sized powders formed by either mechanical crushing of conventional diamond powder or by detonation processes can be used in a similar manner. Conventional diamond powders can be of either synthetic or natural origin, although in some cases, synthetic diamond powders have a higher intrinsic nitrogen content, which, along with adjacent vacancy centers, activates the diamond's luminescence. In one example, the starting diamond material has an intrinsic amount of nitrogen impurity consistent with the nitrogen impurity found in diamond designated as Type 1b (e.g., 50 ppm or more nitrogen). Nano-sized powders synthesized by impact synthesis can also have high intrinsic nitrogen content.

[0009] In exemplary embodiments, the cell, can, or container (respectively, cell or pressure cell) is specially configured to apply differential or asymmetric pressure, for example, axial pressure different from radial pressure, to its contents when subjected to a high-pressure / high-temperature (HPHT) compaction deformation process using conventional press equipment to produce polycrystalline diamond. The system and method for producing luminescent diamond using differential or asymmetric pressure described in International Patent Application PCT / US2022 / 052223 is incorporated herein by reference in its entirety for all purposes. As described in more detail herein, the differential pressure applied by the cell disclosed herein can cause a greater degree of plastic deformation, thereby increasing the amount of defect / optical centers (e.g., in the case of nitrogen defects, NV, NVN, or N3) formed in the resulting luminescent diamond pellet, and correspondingly creating more nitrogen vacancy centers, which are useful for increasing the amount of luminescence. In exemplary embodiments, the press equipment or device used to apply pressure to the cells, cans, or containers may be specially configured to apply differential or asymmetric pressure (e.g., axial pressure that is different from radial pressure) to the cells and contents therein when subjected to a HPHT compaction deformation process using such specially configured press equipment to create polycrystalline diamond. As explained in more detail herein, the differential pressure applied by the press equipment disclosed herein results in a greater degree of plastic deformation, which can create more vacancy centers that are useful for increasing the amount of centers formed in the resulting luminescent diamond pellets and increasing the amount of light emitted.

[0010] As discussed herein, luminescent diamonds may be heat-treated and / or reduced in size depending on the particular end use. According to some embodiments, heat treatment or other treatments may be used to provide desirable surface properties that may be beneficial to the end use. For example, luminescent nanodiamonds can be used as biomaterials, such as drug delivery carriers and bioimaging materials, and heat treatments can be used to provide various surface terminations.

[0011] According to some aspects, heat treatment may be carried out in air at temperatures below 550°C, which may promote oxygen termination on the surface, which affects the optical properties of the luminescent diamond. In some embodiments, heat treatment in air at temperatures below 550°C or 650°C may be important for enhancing the photoluminescence intensity of nanodiamonds. However, it should be noted that temperatures below 550°C may make it difficult to uniformly treat the nanodiamond particles in the powder bed. Furthermore, temperatures that are too high may cause the nanodiamond powder to burn out.

[0012] To facilitate the heat treatment, a coating method is considered for controlling the depth of the powder layer during the heat treatment process. In an exemplary embodiment, the nanodiamond powder is dispersed in a liquid. By dispersing the nanodiamond powder in this manner, a stable suspension can be prepared. The particles can be well dispersed in various liquid solvents, including water.

[0013] The suspension can then be applied to a surface to form a nanodiamond layer. In some embodiments, the surface is a glass surface, although other materials that can withstand the temperatures of the heat treatment can be used. For example, various metals and metal alloys, composites, ceramics, cermets, and other materials can be used.

[0014] Figure 1 (including Figures 1-1 and 1-2) shows an example of an embodiment where nanodiamond material is coated onto a glass slide before and after heat treatment. In one example, after heat treatment in air at 450°C to 550°C for 1 hour, the color of the diamond particles can change from dark to a light milky white. Figure 1-1 shows the coated nanodiamond particles before heat treatment, while Figure 1-2 shows the nanodiamond particles after heat treatment at 500°C for 1 hour. As shown in the figures, the color change can be significant. The brightness of the color corresponds to an increase in oxygen termination of the diamond particles, which increases the emission intensity.

[0015] The color change may depend on factors other than the temperature, duration of the heat treatment, and the substrate on which the material is coated. For example, the color of nanodiamonds after heat treatment may depend on the layer thickness. Figure 2 shows the layer thickness measurement results before heat treatment. In particular, when the layer thickness is about 13 μm, all diamond particles after treatment become a light milky white. However, when the layer thickness increases to about 30 μm (reflected in the ridge region), the diamond particles remain darker in color.

[0016] Any suitable method can be used to coat diamond nanoparticles on glass, ceramic, or other slides. Examples of methods include dip coating, spin coating, dry coating, and slip casting. In at least some embodiments, the coating thickness is within a range having a lower limit, an upper limit, or a lower and upper limit, including 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and values ​​therebetween. For example, the coating thickness can be controlled to be at least 1 μm and not exceed 25 μm, or to be in the range of 1 μm to 25 μm. In some embodiments, the layer thickness is controlled to be between 3 μm and 15 μm, or between 5 μm and 15 μm. In at least some embodiments, a thickness of less than 15 μm or less than 20 μm may be important to obtain a consistent color change.

[0017] The thickness of the layer may also vary depending on the length and temperature of the heat treatment. Generally, the thickness of the layer may increase with the heat treatment time, temperature, or both. Reducing the thickness of the layer may facilitate shorter heat treatment times, lower temperatures, or both shorter and lower heat treatment times.

[0018] In one or more embodiments, the method for coating a substrate involves dry coating a diamond particle concentration of 0.1% to 10% by weight. However, achieving a uniform layer thickness can be difficult due to the surface tension of the water or other liquid that keeps the particles suspended. In some embodiments, alcohol or other substances that suppress or reduce the surface tension of the suspension can be used. For example, nanodiamond suspensions in which the liquid is composed of 10% to 100% surface tension suppressing agent (e.g., alcohol) can spread well on glass substrates. After the suspension is applied to the substrate surface, it can be dried (e.g., air-dried, oven-dried, hotplate-dried, etc.). Drying can occur at a temperature below the boiling point of the suspension liquid. After drying, the coating can be very uniform. If some areas have a thicker thickness (e.g., greater than 25 μm or 30 μm), these areas can be ground away before or after heat treatment, which, among other things, promotes oxygen termination of the diamond particle surfaces.

[0019] FIG. 3 illustrates a method 300 for enhancing the photoluminescence properties of diamond nanoparticles through heat treatment. As described above, a quantity of precursor diamond grains can be subjected to a HPHT process in a pressure cell (block 302) to form diamond grains with luminescent centers (e.g., Nv, NVN, or N3 centers). In some embodiments, the HPHT process can be in the range of about 1300-2500°C, and the process pressure can be about 3.0 GPa to about 10 GPa. The resulting diamond grains can be separated into a powder and mixed with a liquid (block 304) to form a suspension. As described above, the liquid can include water, a surface tension reducer (e.g., alcohol), or other liquids. The concentration of the diamond grains in the suspension can range from 0.1% to 10% by weight. The suspension is then applied to a substrate, such as glass or ceramic (block 306). The suspension can be applied 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 time may be 30-300 minutes, 30-120 minutes, 45-90 minutes, or about 60 minutes. One or more liquids in the suspension may evaporate before or during the heat-treatment.

[0020] During the heat treatment, oxygen termination and / or vacancy formation may occur on the diamond grains disposed on the substrate. The heat treatment can change the color of the suspension on the substrate. For example, a dark, opaque, or slightly translucent suspension before the heat treatment may change to a light, clear, or more translucent suspension after the heat treatment. In some embodiments, the deposited suspension may change from a black, gray, or dark color to a yellow, light gray, white, or translucent suspension. If desired, a portion of the diamond grains may be removed from the substrate (block 308) before or after the heat treatment (block 310). The diamond grains may be removed to facilitate a desired thickness of diamond material on the substrate, such as less than 30 μm, less than 25 μm, less than 20 μm, less than 15 μm, or between 1 and 15 μm. Maintaining the thickness of the diamond material on the substrate to less than about 15 μm may improve the yield of oxygen termination on the diamond grains.

[0021] After heat treatment at block 310, the diamond particles may be removed from the substrate and separated into a desired grain size (block 312). In some embodiments, portions of method 300 may be repeated to mix some or all of the removed diamond grains with a liquid (block 304) to form a suspension for subsequent deposition on the substrate (block 306) and heat treatment (block 310). In some embodiments, the diamond grains may be subjected to the suspension and heat treatment process 3, 4, 6, 8, 10, 12, 15, or more times.

[0022] Although several exemplary embodiments of luminescent diamonds have been described in detail above, those skilled in the art will readily understand that many modifications can be made to the exemplary embodiments without substantially departing from the scope of the claims and the present disclosure. For example, the luminescent diamonds disclosed herein are presented in the context of biological end-use applications. It should be understood that the luminescent diamonds disclosed herein may also be used in non-biological end-use applications where a desired improved level of luminescence intensity is useful or beneficial. Other potential applications of luminescent diamonds (e.g., those containing nitrogen vacancy centers) include, but are not limited to, magnetic sensors, high-resolution thermography, microscope sensor arrays, anti-counterfeiting measures, ion concentration monitoring, membrane potential measurement, optical traps, and strain / pressure sensors. Therefore, it is understood that the luminescent diamonds disclosed herein are not intended to be limited to one particular end-use application.

[0023] In other embodiments, the conditions of HPHT or heat treatment are described, but are merely exemplary, because 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 suppressing agents, attached to different substrates, heat-treated in different atmospheres, treated at different temperatures or for different periods, or may be varied in countless ways.Therefore, the conditions may vary in different embodiments.Systems and methods for producing luminescent diamonds are described in U.S. Patent Application Publication US2022 / 0056337, U.S. Patent Application No. 18 / 005,115, and International Patent Application PCT / US2023 / 023697, each of which is incorporated herein by reference in its entirety for all purposes.

[0024] 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," "upper," "lower," "left," and "right" may be used to describe various components, including their operational or illustrated positions relative to one or more other components. The relational terms do not dictate a particular orientation for each embodiment within the scope of the specification or claims, but are intended for convenience in facilitating reference to the various components. Accordingly, aspects of such relationships may be reversed, flipped, rotated, moved in space, oriented or positioned diagonally, horizontally or vertically, or similarly altered.

[0025] A specific description or designation of an element as "first," "second," "third," etc. may be used in the specification or claims to distinguish between identical elements or elements similar in use, structure, or operation. Such language is not intended to limit an element to singular designation or to require a plurality of elements. Thus, an element referred to herein as a "first" element may be the same as or different from an element referred to as a "first" element in a claim, and a claim may include a "first" element without requiring the presence of a "second" element.

[0026] Furthermore, the specification or claims may refer to "additional" or "other" elements, features, aspects, components, etc., without excluding the presence of one or more of the additional elements. When a claim or the specification refers to "a" or "an" element, such reference is not to be construed as referring to only one of that element, but instead encompasses other elements and is understood as "at least one" of that element. When a component, feature, structure, function, or characteristic is described herein as "may include," "may include," "can include," or "potentially include," the particular component, feature, structure, or characteristic is provided in one particular embodiment but is optional in other embodiments of the disclosure. The terms "couple," "coupled," "connect," "connected," "connected," "connected with," and "connecting" refer to either "directly connected with" or "connected with via one or more intermediate elements or members." "Integral" or "integrally" formed components include components made from the same piece or set of materials, such as by being generally molded or cast from the same material in the same molding or casting process, or generally machined from the same stock material. Components that are "integral" are also understood to be "bonded" together.

[0027] Furthermore, it should be understood that references to "one embodiment," "one embodiment," or "one example" in the present disclosure are 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 in connection with an embodiment herein may be combinable with any element of any other embodiment described herein.

[0028] Any number, percentage, ratio, or other value described herein is intended to include not only that value, but also other values ​​that are "about" or "approximately" the described value, as understood by those of ordinary skill in the art, and are encompassed by embodiments of the present disclosure. Thus, a described value should be interpreted broadly enough to encompass values ​​that are at least close enough to the described value to perform the desired function or achieve the desired result. The described value will at least include expected variation during a suitable manufacturing or production process, and may include values ​​within 5%, 1%, 0.1%, or 0.01% of the described value.

[0029] 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 within less than 5%, less than 1%, less than 0.1%, and less than 0.01% of the stated amount. Furthermore, it should be understood that any directions or frames of reference in the foregoing specification are relative directions or movements only. For example, any reference to "top" and "bottom," or "above" or "below," merely describes the relative positions or movements of the associated elements.

[0030] Although various exemplary embodiments have been described in detail herein, those skilled in the art will readily appreciate in light of the present disclosure that many modifications are possible in the exemplary embodiments without substantially departing from the present disclosure. Accordingly, any such modifications are intended to be included within the scope of the present disclosure. Similarly, while the present disclosure herein contains many details, these details should not be construed as limiting either the scope of the present disclosure or the scope of the appended claims, but merely as providing information regarding one or more specific embodiments that may be included within the scope of the present disclosure and the appended claims. All claims and appendices are incorporated herein. Any described features from the various embodiments disclosed and incorporated may be used in combination.

[0031] In the claims, means-plus-function clauses are intended to cover equivalent structures, as well as the structures described herein as performing the described function and structural equivalents. Thus, while nails and screws may not be structural equivalents in that nails use cylindrical surfaces to fasten wooden parts together while screws use helical surfaces, in the context of fastening wooden parts, nails and screws may be equivalent structures. It is Applicant's express intention not to invoke the claimed means-plus-function type for any limitation of any of the claims herein, except where the claim expressly uses the words "means for" with the relevant function.

[0032] The Abstract at the end of this disclosure is provided to enable the reader to quickly grasp the general nature of some embodiments of the disclosure, and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. 1. A method of making a luminescent diamond, comprising: subjecting a quantity of precursor diamond grains to high pressure / temperature conditions in a pressure cell, thereby forming diamond grains having luminescent centers; suspending the diamond grains in a liquid to form a suspension; depositing the suspension on a substrate and controlling the thickness of the suspension on the substrate; heat treating the suspension on the substrate, thereby changing at least one of the color of the suspension or the oxygen termination on the diamond particles of the suspension; The method comprising:

2. The method of claim 1 , wherein the luminescent centers include at least one of nitrogen vacancies or silicon vacancies.

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

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

5. The method of claim 4 , wherein the surface tension reducing agent comprises an alcohol.

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

7. The method of claim 1 , wherein the substrate is glass.

8. 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 applying the suspension to the substrate comprises drying the suspension.

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

14. 13. The method of claim 12, wherein drying the suspension occurs before heat treating the suspension at a temperature below the boiling point of the liquid.

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

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

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

18. 18. The method of claim 17, wherein heat treating the suspension comprises heat treating at a temperature in the range of 450°C to 550°C.

19. 10. The method of claim 1, wherein heat treating the suspension is carried out for a period of up to 2 hours.

20. 10. The method of claim 1, wherein heat treating the suspension is performed for a period of 30 to 90 minutes.

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