Preparation method of diamond film

Abstract

The invention relates to the field of diamond film materials, in particular to a preparation method of a diamond film, which specifically comprises the following steps of: firstly, attaching nano-diamond suspension containing ionic liquid to a substrate, and then carrying out hot filament chemical vapor deposition on the substrate to obtain the diamond film. The diamond film is compact in structure and can meet application requirements of more scenes, acetone is not used in the process of preparing the diamond film, environmental pollution cannot be caused, and the diamond film is more friendly to operators.

Description

Technical Field

[0001] The present invention relates to the field of diamond thin film materials, and specifically to a method for preparing diamond thin films. Background Art

[0002] In recent years, synthetic diamond thin films have become one of the most popular new materials. The reason why diamond thin films are so favored is that they have many excellent properties in chemistry, mechanics, thermotics, optics, and electricity, making them have a very broad application prospect in the fields of industry, national defense, and high technology.

[0003] The method of growing diamond films by seeding is an efficient process that uses nanodiamond particles as nucleation centers to promote the growth of diamond crystals. It avoids the damage to the substrate caused by traditional diamond selective growth methods such as grinding, plasma etching, and anodic oxidation. However, in the prior art, low-boiling-point acetone is often used as the seeding solvent. During the process of substrate attachment and drying, acetone is likely to volatilize, causing environmental pollution and harm to the health of operators. Summary of the Invention

[0004] Object of the Invention: Aiming at the above technical problems, the present invention proposes a method for preparing diamond thin films.

[0005] The technical solution adopted is as follows: A method for preparing diamond thin films: Attach a nanodiamond suspension containing an ionic liquid to a substrate, and then perform hot filament chemical vapor deposition on the substrate to obtain a diamond thin film.

[0006] Further, the ionic liquid is an ionic liquid containing an unsaturated double bond.

[0007] Further, the ionic liquid is 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate.

[0008] Still further, the ionic liquid is any one or any combination of 1-butylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-pentylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-hexylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-heptylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-octylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-nonylsulfonic acid-4-vinylimidazole tetrafluoroborate, 1-decylsulfonic acid-4-vinylimidazole tetrafluoroborate, and is preferably 1-butylsulfonic acid-4-vinylimidazole tetrafluoroborate.

[0009] Further, the preparation method of the 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate is as follows: Add alkylsulfonic acid lactone and 1-vinylimidazole into ethyl acetate, react at 30 - 60 °C for 12 - 72 h. After the reaction, collect the precipitate, wash it, and after drying, mix it with aqueous tetrafluoroboric acid solution, react at 70 - 90 °C for 5 - 10 h. After removing water by reduced pressure distillation of the reaction product, wash it with ethyl acetate and dry it to obtain the product.

[0010] Further, the nano-diamond suspension consists of water, ionic liquid and diamond nanopowder.

[0011] Further, the mass ratio of the water, ionic liquid and diamond nanopowder is 1:0.01 - 0.1:0.1 - 0.2.

[0012] Further, the particle size of the diamond nanopowder is ≤10 nm.

[0013] Even further, the diamond nanopowder is synthesized by the explosion method and is successively washed with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution to remove metal contamination, unsaturated hydrocarbons, residual metal ions and silicate components.

[0014] Further, the nano-diamond suspension is attached to the substrate by spraying, brushing or dipping.

[0015] Further, the substrate is irradiated with ultraviolet light at 100 - 200 °C before hot filament chemical vapor deposition.

[0016] The purpose of ultraviolet light irradiation is to crosslink and cure the ionic liquid containing unsaturated double bonds at high temperature, thereby further improving the density of the seed layer. The high-density seed layer can provide more uniformly distributed active sites, significantly enhance the nucleation density, and the dense seeds can also reduce the grain spacing and inhibit the merging of grains in the initial growth stage, thus forming a more uniform thin film structure.

[0017] Further, in order to further improve the density of the seed layer, the operations of spraying, brushing or dipping and ultraviolet light irradiation at 100 - 200 °C can be repeated multiple times.

[0018] Further, the parameters of hot filament chemical vapor deposition are as follows: the hydrogen flow rate is 100 - 200 mL / s, the methane flow rate is 1 - 10 mL / s, the pressure in the reaction chamber is 5000 - 6000 Pa, the filament temperature is 1500 - 2000 °C, the substrate temperature is 800 - 1000 °C, the distance between the filament and the substrate is 1 - 10 mm, and the time is 30 - 60 min.

[0019] The technical solution of the present invention has the following beneficial effects: Acetone is selected as the solvent in the method for preparing diamond thin films by the crystal seeding method because it has a large dipole moment and a small surface tension, which are very necessary for the stability of the colloid and the effect of crystal seeding. In the method for preparing diamond thin films provided by the present invention, water is used as the solvent and an ionic liquid is used as a co-solvent. The diamond nanopowder synthesized by the explosion method carries groups such as hydroxyl groups and carboxyl groups on its surface after being washed with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution. The sulfonic acid group in the ionic liquid can form hydrogen bonds with the hydroxyl groups and carboxyl groups on the surface of the diamond nanopowder. The hydrogen bonds significantly improve the stability of the nanodiamond suspension and reduce the surface tension by enhancing the liquid phase viscosity, forming a structured network and an interfacial hydration film, so that a uniform nucleation layer can be formed on the surface of the substrate. When irradiated with ultraviolet light, the double bonds of the ionic liquid crosslink, further improving the density of the seed layer. The highly dense seed layer can provide more uniformly distributed active sites, significantly increasing the nucleation density. The dense seeds can also reduce the grain spacing and inhibit the merging of grains in the initial stage of growth, thus forming a more uniform thin film structure. When hot filament chemical vapor deposition is carried out, the boron element generated by the decomposition of the ionic liquid at high temperature will dope the diamond thin film, thus affecting its electrical conductivity and enabling it to meet the application requirements of more scenarios. Moreover, acetone is not used in the process of preparing diamond thin films in the present invention, which will not cause environmental pollution and is more friendly to operators. Description of the Drawings

[0020] Figure 1 Photograph of the diamond thin film prepared in Example 1 under an optical microscope; Figure 2 Photograph of the diamond thin film prepared in Example 11 under an optical microscope; Figure 3 Photograph of the diamond thin film prepared in Example 12 under an optical microscope; Figure 4 Resistivity characteristic curve of the diamond thin films prepared in Examples 1-10. Detailed Description of the Invention

[0021] For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase. Technologies not mentioned in the present invention refer to the prior art. Unless otherwise specified, the following examples and comparative examples are parallel experiments and adopt the same treatment steps and parameters.

[0022] Example 1: A method for preparing a diamond thin film: Add 0.1 mol of 1,4-butanesultone and 0.1 mol of 1-vinylimidazole into 100 ml of ethyl acetate, stir and react at 40 °C for 48 h. After the reaction is completed, restore to room temperature, filter under reduced pressure, collect the precipitate, wash the precipitate with ethyl acetate, and dry it under vacuum to obtain 1-sulfobutyl-4-vinylimidazolium salt. Mix 0.01 mol of 1-sulfobutyl-4-vinylimidazolium salt with 2 ml of 50% aqueous solution of tetrafluoroboric acid, react at 80 °C for 8 h. After removing water by distillation under reduced pressure for the reaction product, wash it with ethyl acetate and dry it under vacuum to obtain 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate. Mix diamond nanopowder (particle size 1 - 5 nm, synthesized by explosion method and successively washed with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate with a mass ratio of 0.15:1:0.01, and obtain a nanodiamond suspension after ultrasonic oscillation for 30 min. Ultrasonically clean a P-type single-crystalline silicon wafer in acetone and dry it in air as a substrate. Spray the nanodiamond suspension on the substrate, then place the substrate on an electric heating plate at 120 °C and irradiate it with ultraviolet light for 10 min. Repeat the spraying-ultraviolet light irradiation step 4 times, and then put the substrate into the chamber of a hot filament chemical vapor deposition device for hot filament chemical vapor deposition. The hot filament chemical vapor deposition parameters are as follows: the hydrogen flow rate is 120 mL / s, the methane flow rate is 1 mL / s, the reaction chamber pressure is 5333 Pa, the filament temperature is 1800 °C, the substrate temperature is 870 °C, the distance between the filament and the substrate is 7 mm, and the time is 30 min. Use an optical microscope to observe the surface morphology of the diamond film prepared in this example, and it can be seen that the grain size is delicate, uniform, and the structure is dense. For details, see Figure 1 。

[0023] Example 2: Basically the same as Example 1, the difference is that the mass ratio of diamond nanopowder (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.02.

[0024] Example 3: Basically the same as Example 1, the difference is that the mass ratio of diamond nanopowder (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.03.

[0025] Example 4: Basically the same as Example 1, the difference is that the mass ratio of diamond nanopowder (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.04.

[0026] Example 5: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.05.

[0027] Example 6: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.06.

[0028] Example 7: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.07.

[0029] Example 8: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.08.

[0030] Example 9: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.09.

[0031] Example 10: Basically the same as Example 1, except that the mass ratio of diamond nanoflakes (particle size 1 - 5 nm, synthesized by explosion method and successively washed with hydrochloric acid, aqua regia, potassium permanganate solution, and hydrofluoric acid solution), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate is 0.15:1:0.1.

[0032] The resistivity of the diamond films prepared in Examples 1 - 10 was measured using the Van der Pauw method, and the test results are as Figure 4 shown. It can be seen from Figure 4 that as the content of 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate in the nanodiamond suspension increases, the resistivity of the diamond film first decreases and then increases. The reason may be that the boron element generated by the thermal decomposition of 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate dopes with the diamond film, and the resistivity of the diamond film changes due to the influence of the boron element.

[0033] Example 11: A method for preparing a diamond film: 0.1 mol of 1,4-butanesultone and 0.1 mol of 1-vinylimidazole were added to 100 ml of ethyl acetate, and the mixture was stirred at 30 °C for 12 h. After the reaction, the temperature was restored to room temperature, and the mixture was filtered under reduced pressure. The precipitate was collected, washed with ethyl acetate, and dried in vacuo to obtain 1-sulfobutyl-4-vinylimidazolium salt. 0.01 mol of 1-sulfobutyl-4-vinylimidazolium salt was mixed with 2 ml of an aqueous solution of 50% tetrafluoroboric acid, and the mixture was reacted at 70 °C for 5 h. After the reaction product was distilled under reduced pressure to remove water, it was washed with ethyl acetate and dried in vacuo to obtain 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate. Diamond nanopowder (particle size 1 - 5 nm, synthesized by the explosion method and successively washed with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution), deionized water, and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate with a mass ratio of 0.1:1:0.01 were mixed, and the mixture was ultrasonically oscillated for 30 min to obtain a nanodiamond suspension. The P-type single crystal silicon wafer was ultrasonically cleaned in acetone and then dried in air as the substrate. The nanodiamond suspension was sprayed on the substrate, and then the substrate was placed on an electric heating plate at 100 °C and irradiated with ultraviolet light for 10 min. After repeating the spraying-ultraviolet light irradiation step 4 times, the substrate was placed in the chamber of a hot filament chemical vapor deposition apparatus for hot filament chemical vapor deposition. The hot filament chemical vapor deposition parameters were as follows: the hydrogen flow rate was 100 mL / s, the methane flow rate was 1 mL / s, the reaction chamber pressure was 5000 Pa, the filament temperature was 1500 °C, the substrate temperature was 800 °C, the distance between the filament and the substrate was 1 mm, and the time was 30 min. The surface morphology of the diamond film prepared in this example was observed using an optical microscope, and it could be seen that the grain size was fine, uniform, and the structure was dense. For details, see Figure 2 。

[0034] The resistivity of the diamond film prepared in this example was measured by the four-point probe method, and its resistivity was 0.72 Ω·cm.

[0035] Example 12: A method for preparing a diamond film: 0.1 mol of 1,4-butanesultone and 0.1 mol of 1-vinylimidazole were added to 100 ml of ethyl acetate, and the mixture was stirred at 60 °C for 72 h. After the reaction, the temperature was restored to room temperature, and the mixture was filtered under reduced pressure. The precipitate was collected, washed with ethyl acetate, and dried in vacuo to obtain 1-sulfobutyl-4-vinylimidazolium salt. 0.01 mol of 1-sulfobutyl-4-vinylimidazolium salt was mixed with 2 ml of 50% aqueous tetrafluoroboric acid solution, and the mixture was reacted at 90 °C for 10 h. After the reaction product was distilled under reduced pressure to remove water, it was washed with ethyl acetate and dried in vacuo to obtain 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate. Diamond nanopowder (particle size 1-5 nm, synthesized by explosion method and sequentially washed with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution), deionized water and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate with a mass ratio of 0.2:1:0.1 were mixed, and ultrasonic oscillation was carried out for 30 min to obtain a nanodiamond suspension. The P-type monocrystalline silicon wafer was ultrasonically cleaned in acetone and then dried as a substrate. The nanodiamond suspension was sprayed on the substrate, and then the substrate was placed on an electric heating plate at 200 °C and irradiated with ultraviolet light for 10 min. After repeating the spraying-ultraviolet light irradiation step 4 times, the substrate was placed in the chamber of a hot filament chemical vapor deposition device for hot filament chemical vapor deposition. The hot filament chemical vapor deposition parameters were as follows: the hydrogen flow rate was 200 mL / s, the methane flow rate was 10 mL / s, the reaction chamber pressure was 6000 Pa, the filament temperature was 2000 °C, the substrate temperature was 1000 °C, the distance between the filament and the substrate was 10 mm, and the time was 60 min. The surface morphology of the diamond film prepared in this example was observed by an optical microscope, and it could be seen that the grain size was fine, uniform, and the structure was dense. For details, see Figure 3 。

[0036] The resistivity of the diamond film prepared in this example was measured by the four-point probe method, and its resistivity was 0.79 Ω·cm.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a diamond film, characterized in that: The nano-diamond suspension containing ionic liquid is attached to a substrate, and then hot-wire chemical vapor deposition is performed on the substrate to obtain a diamond film.

2. The method for preparing a diamond film according to claim 1, wherein: The ionic liquid is an ionic liquid containing unsaturated double bonds.

3. The method for preparing a diamond film according to claim 2, wherein: The ionic liquid is 1-sulfonic acid alkyl-4-vinyl imidazole tetrafluoroborate.

4. The method for preparing a diamond thin film according to claim 3, characterized in that: The preparation method of the 1-sulfonic acid alkyl-4-vinyl imidazole tetrafluoroborate is as follows: Add alkyl sultone and 1-vinyl imidazole to ethyl acetate, react at 30-60°C for 12-72 hours, collect the precipitate after the reaction, wash, dry and mix with tetrafluoroboric acid aqueous solution, react at 70-90°C for 5-10 hours, distill the reaction product under reduced pressure to remove water, wash with ethyl acetate and dry.

5. The method for preparing a diamond thin film according to claim 1, wherein: The nano-diamond suspension consists of water, ionic liquid and diamond nano-powder.

6. The method for preparing a diamond thin film according to claim 5, characterized in that: The mass ratio of water, ionic liquid and diamond nanopowder is 1:0.01-0.1:0.1-0.

2.

7. The method for preparing a diamond thin film according to claim 6, characterized in that: The particle size of the diamond nanopowder is ≤10nm.

8. The method for preparing a diamond thin film according to claim 1, characterized in that: The nano-diamond suspension is attached to the substrate by spraying, brushing or dipping.

9. The method for preparing a diamond thin film according to claim 1, characterized in that: The substrate was also irradiated with UV light at 100-200°C before hot-wire chemical vapor deposition.

10. The method for preparing a diamond thin film according to claim 1, characterized in that: The hot filament chemical vapor deposition parameters are as follows: hydrogen flow rate is 100-200mL / s, methane flow rate is 1-10mL / s, reaction chamber pressure is 5000-6000Pa, filament temperature is 1500-2000℃, substrate temperature is 800-1000℃, distance between filament and substrate is 1-10mm, and time is 30-60min.

Images