A method for preparing diamond thin films

Abstract

The present invention relates to the field of diamond thin film materials, and specifically to a method for preparing diamond thin films. Specifically, a nano-diamond suspension containing ionic liquid is first attached to a substrate, and then the substrate is subjected to hot filament chemical vapor deposition to obtain a diamond thin film. The diamond thin film prepared by the present invention has fine and uniform crystal grain size and a dense structure, which can meet the application requirements of more scenarios. Moreover, acetone is not used in the process of preparing the diamond thin film in the present invention, which will not cause environmental pollution and is more user-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, thermology, 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 preparing diamond thin films by seeding is an efficient process that uses nano-diamond particles as nucleation centers to promote the growth of diamond crystals. It avoids the damage to the substrate used in traditional diamond selective growth methods such as grinding, plasma etching, and anodic oxidation. However, in the prior art, low-boiling-point acetone is often selected 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:

[0006] A method for preparing diamond thin films:

[0007] Attach a nano-diamond 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.

[0008] Further, the ionic liquid is an ionic liquid containing an unsaturated double bond.

[0009] Further, the ionic liquid is 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate.

[0010] Furthermore, the ionic liquid is any one or a combination of any one or more 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, and 1-decylsulfonic acid-4-vinylimidazole tetrafluoroborate, preferably 1-butylsulfonic acid-4-vinylimidazole tetrafluoroborate.

[0011] Further, the preparation method of the 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate is as follows:

[0012] 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, dry it, then mix it with aqueous tetrafluoroboric acid solution, react at 70-90 °C for 5-10 h. After removing water by vacuum distillation of the reaction product, wash it with ethyl acetate and dry it to obtain the product.

[0013] Further, the nanodiamond suspension consists of water, ionic liquid and diamond nanopowder.

[0014] Further, the mass ratio of the water, ionic liquid and diamond nanopowder is 1: 0.01-0.1: 0.1-0.2.

[0015] Further, the particle size of the diamond nanopowder is ≤10 nm.

[0016] Furthermore, the diamond nanopowder is synthesized by the explosion method and is successively cleaned with hydrochloric acid, aqua regia, potassium permanganate solution and hydrofluoric acid solution to remove metal contamination, unsaturated hydrocarbons, residual metal ions and silicate components.

[0017] Further, the nanodiamond suspension is attached to the substrate by spraying, brushing or dipping.

[0018] Further, the substrate is also irradiated with ultraviolet light at 100-200 °C before hot filament chemical vapor deposition.

[0019] 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 improve the nucleation density, and the dense seed layer can also reduce the grain spacing and inhibit the merger of grains in the initial growth stage, thus forming a more uniform thin film structure.

[0020] 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.

[0021] 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.

[0022] The technical solution of the present invention has the following beneficial effects:

[0023] 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 ionic liquid is used as the co-solvent. The diamond nanopowder synthesized by the explosion method carries groups such as hydroxyl and carboxyl 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 and carboxyl groups on the surface of the diamond nanopowder. The hydrogen bonds can 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 substrate surface. 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

[0024] Figure 1 It is a photograph of the diamond thin film prepared in Example 1 under an optical microscope;

[0025] Figure 2 It is a photograph of the diamond thin film prepared in Example 11 under an optical microscope;

[0026] Figure 3 It is a photograph of the diamond thin film prepared in Example 12 under an optical microscope;

[0027] Figure 4 It is the resistivity characteristic curve of the diamond thin films prepared in Examples 1-10. Detailed Embodiments

[0028] For those not specified in the examples, they are carried out according to the 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. The technologies not mentioned in the present invention refer to the prior art. Unless otherwise specified, the following examples and comparative examples are parallel tests and adopt the same treatment steps and parameters.

[0029] Example 1:

[0030] A method for preparing a diamond thin film:

[0031] 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 40 °C for 48 h. After the reaction, the mixture was returned to room temperature, filtered under reduced pressure, and the precipitate was collected. The precipitate was 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 solution of tetrafluoroboric acid, and the mixture was reacted at 80 °C for 8 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 nanopowders (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 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 in air as a substrate. The nanodiamond suspension was sprayed on the substrate, and then the substrate was placed on an electric heating plate at 120 °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 120 mL / s, the methane flow rate was 1 mL / s, the reaction chamber pressure was 5333 Pa, the filament temperature was 1800 °C, the substrate temperature was 870 °C, the distance between the filament and the substrate was 7 mm, and the time was 30 min. The surface morphology of the diamond film prepared in this example was observed by optical microscope, and it could be seen that the grain size was fine, uniform, and the structure was dense. For details, see Figure 1 。

[0032] Example 2:

[0033] It was basically the same as Example 1, except that the mass ratio of diamond nanopowders (particle size 1-5 nm), deionized water and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate was 0.15:1:0.02.

[0034] Example 3:

[0035] It was basically the same as Example 1, except that the mass ratio of diamond nanopowders (particle size 1-5 nm), deionized water and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate was 0.15:1:0.03.

[0036] Example 4:

[0037] It was basically the same as Example 1, except that the mass ratio of diamond nanopowders (particle size 1-5 nm), deionized water and 1-sulfobutyl-4-vinylimidazolium tetrafluoroborate was 0.15:1:0.04.

[0038] Example 5:

[0039] It is 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 - vinylimidazole tetrafluoroborate is 0.15:1:0.05.

[0040] Example 6:

[0041] It is 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 - vinylimidazole tetrafluoroborate is 0.15:1:0.06.

[0042] Example 7:

[0043] It is 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 - vinylimidazole tetrafluoroborate is 0.15:1:0.07.

[0044] Example 8:

[0045] It is 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 - vinylimidazole tetrafluoroborate is 0.15:1:0.08.

[0046] Example 9:

[0047] It is 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 - vinylimidazole tetrafluoroborate is 0.15:1:0.09.

[0048] Example 10:

[0049] It is 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 cleaned with hydrochloric acid, aqua regia, potassium permanganate solution, and hydrofluoric acid solution), deionized water, and 1 - sulfobutyl - 4 - vinylimidazole tetrafluoroborate is 0.15:1:0.1.

[0050] The resistivity of the diamond films prepared in Examples 1 - 10 was measured by the Van der Pauw method, and the test results are as Figure 4 shown, from Figure 4It can be seen that as the content of 1-butylsulfonate-4-vinylimidazole 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-butylsulfonate-4-vinylimidazole tetrafluoroborate is doped into the diamond film, and the resistivity of the diamond film changes under the influence of the boron element.

[0051] Example 11:

[0052] A method for preparing a diamond film:

[0053] Add 0.1 mol of 1,4-butanesultone and 0.1 mol of 1-vinylimidazole to 100 ml of ethyl acetate, stir and react at 30 °C for 12 h. After the reaction, restore to room temperature, filter under reduced pressure, collect the precipitate, wash the precipitate with ethyl acetate, and dry it in vacuo to obtain 1-butylsulfonate-4-vinylimidazole salt. Mix 0.01 mol of 1-butylsulfonate-4-vinylimidazole salt with 2 ml of 50% aqueous solution of tetrafluoroboric acid, react at 70 °C for 5 h. After removing water by distillation under reduced pressure for the reaction product, wash it with ethyl acetate and dry it in vacuo to obtain 1-butylsulfonate-4-vinylimidazole tetrafluoroborate. Mix 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-butylsulfonate-4-vinylimidazole tetrafluoroborate with a mass ratio of 0.1:1:0.01, and obtain a nanodiamond suspension after ultrasonic oscillation for 30 min. Ultrasonically clean a P-type single crystal 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 100 °C and irradiate it with ultraviolet light for 10 min. Repeat the spraying-ultraviolet light irradiation step 4 times, and then place 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 100 mL / s, the methane flow rate is 1 mL / s, the reaction chamber pressure is 5000 Pa, the filament temperature is 1500 °C, the substrate temperature is 800 °C, the distance between the filament and the substrate is 1 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 fine, uniform, and the structure is dense. For details, see Figure 2 .

[0054] The resistivity of the diamond film prepared in this example was measured by the Van der Pauw method, and its resistivity was 0.72 Ω·cm.

[0055] Example 12:

[0056] A method for preparing a diamond film:

[0057] 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 an aqueous solution of 50% tetrafluoroboric acid, 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 the 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 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 to be used 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 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 3 。

[0058] 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.

[0059] 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 present invention in each embodiment.

Claims

1. A method for preparing a diamond thin film, characterized in that, Attach the ionic liquid-containing nanodiamond suspension to a substrate, and then perform hot filament chemical vapor deposition on the substrate to obtain a diamond film; The ionic liquid is 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate; Before hot filament chemical vapor deposition, the substrate is also irradiated with ultraviolet light at 100-200 °C.

2. The method for preparing a diamond film according to claim 1, wherein The preparation method of the 1-alkylsulfonic acid-4-vinylimidazole tetrafluoroborate is as follows: Add alkylsulfonic acid lactone and 1-vinylimidazole to ethyl acetate, react at 30-60 °C for 12-72 h, collect the precipitate after the reaction, wash, dry, and then mix with an aqueous solution of tetrafluoroboric acid, react at 70-90 °C for 5-10 h, distill off water under reduced pressure for the reaction product, wash with ethyl acetate, and dry.

3. The method for preparing a diamond thin film according to claim 1, characterized in that, The nanodiamond suspension is composed of water, an ionic liquid, and diamond nanopowder.

4. The method for preparing a diamond thin film according to claim 3, wherein, The mass ratio of the water, the ionic liquid, and the diamond nanopowder is 1:0.01-0.1:0.1-0.

2.

5. The method for preparing a diamond thin film according to claim 4, wherein The particle size of the diamond nanopowder is ≤10 nm.

6. The method for preparing a diamond film according to claim 1, wherein, The nanodiamond suspension is attached to the substrate by spraying, brushing, or dipping.

7. The method for preparing a diamond thin film according to claim 1, wherein The hot filament chemical vapor deposition parameters are as follows: the hydrogen flow rate is 100-200 mL / s, the methane flow rate is 1-10 mL / s, the reaction chamber pressure 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.

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