A process for preparing a nitrogen-doped carbon thin film that modifies the modification of a substrate surface

Abstract

The application relates to the technical field of thin film preparation, in particular to a nitrogen-doped carbon thin film preparation process for modifying the surface modification of a substrate, which comprises the following preparation steps: S1. substrate pretreatment; S2. composite etching treatment; S3. dynamic surface modification; S4. magnetron co-sputtering deposition; and S5. gradient annealing treatment. By introducing an electroactive monomer and adjusting the substrate bias during the deposition process and the annealing temperature after the deposition, the chemical bond state of N is controlled, the ORR catalytic activity is optimized, it is proved that the catalytic activity of the nitrogen-doped carbon thin film for ORR directly depends on the content of pyridine N in the thin film, and it is indicated that the pyridine N is an effective catalytic active site for ORR.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film preparation, in particular to a preparation process of nitrogen-doped carbon thin film for modifying the surface modification of a substrate. BACKGROUND

[0002] The ORR (oxygen reduction reaction) occurring at the cathode of a fuel cell has a very important influence on the actual working efficiency of the fuel cell. A platinum-based catalyst with high catalytic activity and stability in acid and alkaline solutions is usually used to accelerate the ORR. However, since platinum is a noble metal, it has a high cost, a limited yield and is prone to methanol poisoning, so that the current fuel cell still cannot be widely commercialized. In recent years, nitrogen-doped carbon-based catalysts (such as nitrogen-doped carbon nanotubes and graphene) have attracted great interest, because the doping of nitrogen can effectively adjust the electrical properties of carbon-based nanomaterials, thereby obtaining high catalytic performance, which is expected to replace platinum-based catalysts. However, in the currently reported preparation methods of nitrogen-doped carbon-based catalysts, transition metals (such as Fe) are usually added as catalysts for growing carbon-based nanomaterials, and then they are removed by dissolving in an acidic solution, which makes it difficult to determine whether the catalytic activity is derived from the nitrogen-doped carbon material itself or some metal residues. In addition, in the process of removing the metal with an acidic solution, the pyridine N, which is suspected to be the active site, can be protonated into inactive pyridine N-hydrogen, thereby reducing the catalytic activity of the material.

[0003] Therefore, it has become an urgent problem to develop a method for preparing a nitrogen-doped carbon-based catalyst without any metal. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a preparation process of nitrogen-doped carbon thin film for modifying the surface modification of a substrate.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A preparation process of nitrogen-doped carbon thin film for modifying the surface modification of a substrate, comprising the following preparation steps:

[0007] S1. Substrate pretreatment: cleaning the substrate material to remove surface impurities to obtain a pretreated substrate;

[0008] S2. Composite etching treatment: using a modified etching solution to coat the pretreated substrate for etching, the etching time being 1-4 min, and then performing ultrasonic cleaning with ultrapure water for 20-30 min to obtain an etched substrate;

[0009] S3. Dynamic surface modification: the etched substrate is immersed in the electroactive monomer base solution for surface modification, the immersion time is 3-8 min, and then gradient temperature drying is performed to obtain the surface modified substrate material;

[0010] S4. Magnetron co-sputtering deposition: after the pressure in the vacuum chamber reaches 5×10 -4 Pa, ionized gas Ar, reaction gas N2 and CH4 are introduced into the vacuum chamber, and auxiliary gas He is introduced, and nitrogen-doped carbon film is deposited on the substrate material by magnetron sputtering process to obtain a substrate material with deposited nitrogen-doped carbon film;

[0011] S5. Gradient annealing treatment: the substrate material with deposited nitrogen-doped carbon film obtained in step S4 is placed in a high-temperature vacuum annealing furnace, and after the pressure in the vacuum chamber reaches 5×10 -4 Pa, protective gas Ar is introduced, and annealing is performed at a segmented heating rate to obtain a nitrogen-doped carbon film modified for surface modification of the substrate;

[0012] The mass ratio of the surface modification modifier to the electroactive monomer base solution in the mixed solution is 3-5:1;

[0013] The preparation of the surface modification modifier comprises the following steps:

[0014] S41. 2-4 parts of polyvinylpyrrolidone and 1-3 parts of 3-aminopropyltriethoxysilane are dissolved in 50-60 parts of deionized water, and stirred at a speed of 400-500 r / min for 8-10 min;

[0015] S42. 5-8 parts of pyridine-3-carboxylic acid is added to the solution obtained in step S41, and stirred in a 60°C water bath for 18-20 min until completely dissolved to obtain a preliminary surface modification solution;

[0016] S43. 0.1-0.3 parts of ammonium persulfate is added to the preliminary surface modification solution, and ultrasonic treatment is performed under nitrogen protection at a power of 200W for 12-15 min to obtain a surface modification modifier.

[0017] Preferably, the substrate material is one of single crystal silicon or polycrystalline titanium.

[0018] Preferably, in step S1, when the substrate material is single crystal silicon, the cleaning method is specifically: sequentially using acetone, ethanol and ultrapure water to ultrasonically clean it for 20-30 min to remove the stains on its surface;

[0019] When the substrate material is polycrystalline titanium, the cleaning method is specifically: placing it in a hydrochloric acid solution with a volume ratio of hydrogen chloride to water of 1:3 for 30-40 min to remove the oxides on its surface, and then ultrasonically cleaning it with ultrapure water for 20-30 min.

[0020] Preferably, the preparation of the electroactive monomer base solution comprises the following steps:

[0021] S31. 10-13 parts of acrylic acid and 8-11 parts of acrylamide are dissolved in deionized water, stirred at a speed of 400-500 r / min until completely dissolved, and the pH is controlled to 6.5-7.0 to obtain a transparent solution;

[0022] S32. 0.1-0.5 parts of graphene quantum dots are dissolved in deionized water, and ultrasonic treatment is carried out at a power of 200-250 W for 20-30 min until no visible agglomeration is observed, to obtain a dispersion liquid;

[0023] S33. 5-8 parts of vinyl isocyanate and the dispersion liquid prepared in step S32 are added to the transparent solution under a nitrogen atmosphere, and stirred at a speed of 700-800 r / min for 20-30 min, to finally obtain an electroactive monomer base solution.

[0024] Preferably, the flow rates of the ionized gas Ar, the reaction gas N2, the auxiliary gas He and the CH4 introduced in step S4 are 30-35 sccm, 20-25 sccm, 5-10 sccm, and 5-8 sccm, respectively.

[0025] Preferably, the magnetron sputtering process parameters in step S4 are: a radio frequency power of 160-170 W; a substrate bias of -12.3 V to -200 V; a sputtering time of 40-50 min; and a sputtering pressure of 0.5-1 Pa.

[0026] Preferably, the sputtering target used in the magnetron sputtering process in step S4 is a high-purity carbon target with a diameter of 6 cm and a thickness of 1 mm, and a purity of 99.95%.

[0027] Preferably, the annealing in step S5 is carried out at a segmented heating rate, the initial stage is heated at a rate of 5 ℃ / min to 600 ℃, the second stage is heated at a rate of 10 ℃ / min to 800-1000 ℃, and after holding for 10-15 min, the furnace is slowly cooled to room temperature.

[0028] Preferably, the preparation of the modified etching solution comprises the following steps:

[0029] S21. Deionized water is added to a container, nitric acid is slowly added, and the mixture is stirred until uniform to obtain a nitric acid solution;

[0030] S22. Hydrofluoric acid is gradually added under continuous stirring, and the temperature is controlled not to exceed 40 ℃ to obtain an acid mixture;

[0031] S23. The modified liquid is added to the acid mixture obtained in step S22, and the stirring is continued for 15-20 min to finally obtain a modified etching solution.

[0032] The mass ratio of nitric acid, hydrofluoric acid and modified liquid is 3:1:0.5-1.

[0033] The preparation of the modified liquid comprises the following steps:

[0034] S231. 1-3 parts of citric acid are added into a proper amount of deionized water, and stirred until completely dissolved to obtain a citric acid solution;

[0035] S232. 0.5-0.8 parts of urea are added into the citric acid solution, and continue to stir until completely dissolved to obtain a mixed solution;

[0036] S233. 7-10 parts of polyethylene glycol and 0.3-0.6 parts of sodium dodecyl sulfate are added into the mixed solution, and stirred for 10-20 min under the condition of a water bath at 40℃ to obtain a modified liquid.

[0037] Compared with the prior art, the beneficial effects of the present application are:

[0038] 1. The present application controls the chemical bond state of N through the synergistic effect of surface modification modifier and electroactive monomer base solution, optimizes the ORR catalytic activity, proves that the catalytic activity of nitrogen-doped carbon film on ORR directly depends on the content of pyridine N in the film, and indicates that pyridine N is an effective catalytic active site for ORR.

[0039] 2. The nitrogen-doped carbon film with the highest pyridine N content not only shows the best ORR catalytic activity, but also has better stability and methanol resistance than the commercial Pt / C catalyst in alkaline solution. This pyridine N-rich amorphous nitrogen-doped carbon film catalyst, which does not contain metal, is expected to replace platinum-based catalyst and be used as a cathode catalyst for direct methanol fuel cells and alkaline fuel cells, and has obvious application value.

[0040] 3. The carboxyl groups in the modified etching liquid in the present application can form hydrogen bonds or chemical bonds with the subsequent modified electroactive monomer (such as acrylic acid, vinyl isocyanate), and the two cooperate with each other to improve the adsorption capacity of the monomer on the substrate surface. At the same time, the carboxyl groups form a hydrogen bond network with the amino groups (NH2-) generated by the decomposition of urea, enhance the stability of the etching liquid, complex metal ions with citric acid, and avoid impurities interfering with the subsequent magnetron sputtering process. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The preparation process flow chart of the nitrogen-doped carbon film modified by the surface modification of the present application;

[0042] Figure 2 The preparation process flow chart of the modified etching liquid of the present application;

[0043] Figure 3This is a flow chart of the preparation process of the modified liquid of the present invention;

[0044] Figure 4 This is a process flow diagram for preparing the electroactive monomer base solution of the present invention;

[0045] Figure 5 This is a flow chart illustrating the preparation process of the surface modification agent of the present invention;

[0046] Figure 6 This is a bar chart showing the pyridine N and pyrrole N content on the surface of nitrogen-doped carbon thin films deposited under different substrate biases in Example 1 of the present invention;

[0047] Figure 7 The LSV diagrams of the ORR of nitrogen-doped carbon films deposited under different substrate biases in Example 1 of the present invention, and the nitrogen-doped carbon films obtained in Comparative Example 1 and Comparative Example 2 are shown.

[0048] Figure 8 The KL diagrams of nitrogen-doped carbon films deposited under different substrate biases in Example 1 of the present invention, and nitrogen-doped carbon films obtained in Comparative Example 1 and Comparative Example 2, are shown at -0.60V.

[0049] Figure 9 The graph shows the performance test results of anion exchange membrane fuel cells using nitrogen-doped carbon films as cathode catalysts, obtained in Example 1 and Comparative Example 2 of this invention.

[0050] Figure 10 The chronoamperometry diagrams of the nitrogen-doped carbon thin films obtained in Example 1 and Comparative Example 2 of this invention are shown (wherein, the electrolyte used is a 0.1 MkOH solution saturated with O2).

[0051] Figure 11 The chronoamperometry (COP) of nitrogen-doped carbon films obtained in Example 1 and Comparative Example 2 of this invention is shown in the figure (wherein, the electrolyte used is 0.1 M KOH, saturated with N2 for 0-1000s, saturated with O2 for 1000-2000s, and saturated with O2 and injected with 3 M CH3OH for 2000-3000s). Detailed Implementation

[0052] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] Please see Figures 1-11 The present invention provides a technical solution:

[0054] Example 1

[0055] A preparation process of nitrogen-doped carbon film for modifying the surface modification of a substrate:

[0056] S1. Substrate pretreatment: before use, the polycrystalline titanium substrate material is cleaned by placing it in a 10ml hydrogen chloride and 30ml water hydrochloric acid solution for 30min to remove the oxides on its surface, and then ultrasonic cleaning with ultrapure water for 20min to obtain a pretreated substrate;

[0057] Before the composite etching treatment, the modified etching solution is prepared, which includes the following steps:

[0058] S21. Add deionized water to the container, slowly add 30g nitric acid, stir and mix uniformly to obtain a nitric acid solution;

[0059] S22. Under continuous stirring, gradually add 10g hydrofluoric acid, control the temperature not to exceed 40℃, and obtain an acid mixture;

[0060] S23. Add 5g of modified liquid to the acid mixture obtained in step S22, continue stirring for 15min, and finally obtain a modified etching solution;

[0061] The preparation of the modified liquid includes the following steps:

[0062] S231. Add 10g of citric acid to an appropriate amount of deionized water, stir until completely dissolved, and obtain a citric acid solution;

[0063] S232. Add 5g of urea to the citric acid solution, continue stirring until completely dissolved, and obtain a mixture;

[0064] S233. Add 70g of polyethylene glycol and 3g of sodium dodecyl sulfate to the mixture, stir for 10min under the condition of a 40℃ water bath, and obtain a modified liquid;

[0065] S2. Composite etching treatment: use the 30g of modified etching solution prepared above to coat the pretreated substrate for etching, the etching time is 1min, and then ultrasonic cleaning with ultrapure water for 20min to obtain an etched substrate;

[0066] Before the dynamic surface modification, the preparation of the electroactive monomer base solution and the surface modification modifier is carried out, which includes the following steps:

[0067] S31. Dissolve 100g of acrylic acid and 80g of acrylamide in deionized water, stir at a speed of 400r / min until completely dissolved and control the pH to 6.5, and obtain a transparent solution;

[0068] S32. 1-5 g graphene quantum dots were dissolved in deionized water, and ultrasonic treatment was performed at a power of 200 W for 20 min until no visible agglomeration was observed, to obtain a dispersion liquid;

[0069] S33. 50 g of vinyl isocyanate and the dispersion liquid prepared in step S32 were added to a transparent solution under a nitrogen atmosphere, and stirring was performed at a rotation speed of 700 r / min for 20 min, to finally obtain an electroactive monomer base solution;

[0070] The preparation of the surface modification modifier includes the following steps:

[0071] S41. 8 g of polyvinylpyrrolidone and 4 g of 3-aminopropyltriethoxysilane were dissolved in 200 ml of deionized water, and stirring was performed at a rotation speed of 400 r / min for 8 min;

[0072] S42. 20 g of pyridine-3-carboxylic acid was added to the solution obtained in step S41, and stirring was performed in a 60℃ water bath for 18 min until complete dissolution, to obtain a preliminary surface modification liquid;

[0073] S43. 0.4 g of ammonium persulfate was added to the preliminary surface modification liquid, and ultrasonic treatment was performed at a power of 200 W for 12 min under nitrogen protection, to obtain a surface modification modifier;

[0074] S3. Dynamic surface modification: the etched substrate was immersed in a mixed liquid of 40 g of the electroactive monomer base solution and 120 g of the surface modification modifier prepared above for surface modification, and the immersion time was 3 min, and then gradient temperature drying was performed, to obtain a surface-modified substrate material;

[0075] S4. Magnetron co-sputtering deposition: after the pressure in the vacuum chamber reached 5×10 -4 Pa, ionized gas Ar, reaction gas N2 and CH4 were introduced into the vacuum chamber, and auxiliary gas He was introduced (flow ratio Ar:N2:CH4:He=30:20:5:5 sccm), and nitrogen-doped carbon film was deposited on the substrate material by magnetron sputtering process, to obtain a substrate material with deposited nitrogen-doped carbon film, the radio frequency power was 160 W, the substrate bias was -12.3 V, the sputtering time was 40 min, and the sputtering pressure was 0.5 Pa;

[0076] S5. Gradient annealing treatment: the substrate material with deposited nitrogen-doped carbon film obtained in step S4 was placed in a high-temperature vacuum annealing furnace, ionized gas Ar was introduced into the vacuum chamber after the pressure in the vacuum chamber reached 5×10 -4 Pa, and annealing was performed at a segmented heating rate, the initial stage heating rate was 5℃ / min to 600℃, the second stage heating rate was 10℃ / min to 800℃, and after holding for 10 min, the furnace was slowly cooled to room temperature, to obtain a nitrogen-doped carbon film modified by surface modification of the substrate.

[0077] Example 2

[0078] Example 2 differs from Example 1 only in that in Example 2, the substrate bias is -50 V, and the rest of the steps are exactly the same in Example 1 and Example 2.

[0079] Example 3

[0080] Example 3 differs from Example 1 only in that in Example 3, the substrate bias is -150 V, and the rest of the steps are exactly the same in Example 1 and Example 3.

[0081] Example 4

[0082] Example 4 differs from Example 1 only in that in Example 4, the substrate bias is -200 V, and the rest of the steps are exactly the same in Example 1 and Example 4.

[0083] Comparative Example 1

[0084] Comparative Example 1 differs from Example 1 only in that in Comparative Example 1, the surface modification modifier and the modification liquid are omitted, and the composite etching treatment step is only etched with nitric acid and hydrofluoric acid, and the rest of the steps are exactly the same in Comparative Example 1 and Example 1.

[0085] Comparative Example 2

[0086] A commercially available Pt / C catalyst purchased from Hunan Sinozirconium Technology Co., Ltd. is used as Comparative Example 2.

[0087] Performance test:

[0088] The ORR electrocatalytic activity and stability of the thin film catalyst are characterized in a three-electrode electrochemical cell using a PARSTAT 2273 type electrochemical workstation. The nitrogen-doped carbon thin film obtained by modifying the surface modification of the substrate is used as the cathode catalyst of the anion exchange membrane fuel cell, and a single cell is prepared to test the discharge performance of the cell to characterize the catalytic activity of the catalyst in the actual working environment of the fuel cell.

[0089] Through experiments, when the absolute value of the substrate bias in Example 3 is increased to 100 V, the content of pyridine N reaches a maximum, and at this time the content of pyridine N in the thin film is about 3 times the content of pyrrole N. Generally speaking, pyridine N and pyrrole N are the most common types of N doped in carbon matrix, and since pyridine N has one lone pair of electrons, it can increase the electron donation ability, which is beneficial to the adsorption of O2 molecules and the rupture of O-O bond, so it is considered to promote a 4-electron transfer ORR, and has high ORR catalytic activity.

[0090] Appendix Figure 8The KL diagrams for nitrogen-doped carbon films deposited under different substrate biases in Example 1 of this invention, as well as nitrogen-doped carbon films obtained in Comparative Examples 1 and 2, are shown at -0.60V. According to the KL formula, ω can be plotted at a fixed potential (-0.60V). -1 / 2 and J -1 The relationship curve, i.e., the KL diagram (attached) Figure 8 The electron transfer number and kinetic current density of the catalyst in the ORR process can be calculated from the intercept and slope of the curve in the KL plot. The results are shown in Table 1 below:

[0091] Table 1. Total N, pyridine N, and pyrrole N content on the surface of nitrogen-doped carbon films deposited under different substrate bias voltages, and the electrocatalytic performance parameters of nitrogen-doped carbon films, pure carbon films, and Pt / C catalysts on ORR.

[0092]

[0093] As the absolute value of the substrate bias voltage increased from the floating voltage to 100V, the total N content gradually increased from 6.0 at.% to 15.3 at.%. Further increases in the absolute value of the substrate bias voltage led to a decrease in the total N content. This change is because increasing the absolute value of the substrate bias voltage enhances the energy of the bombarding ions during deposition, promoting the doping of nitrogen atoms into the carbon matrix and thus increasing the total N content in the carbon film. However, when the absolute value of the substrate bias voltage continues to increase, excessively high bombarding ion energy can easily induce preferential etching of N atoms deposited on the film surface, i.e., backsputtering, resulting in a decrease in the total N content in the film. Meanwhile, compared to Example 1, Comparative Example 1 without the added modified liquid showed a gap in electrocatalytic performance, indicating that the carboxylic acid groups in the modified etching solution prepared with the modified liquid can form hydrogen bonds or chemical bonds with subsequent modified electroactive monomers (such as acrylic acid and vinyl isocyanate). These two components work together to enhance the adsorption capacity of the monomers on the substrate surface and improve electrocatalytic performance.

[0094] Appendix Figure 6 This is a bar chart showing the pyridine N and pyrrole N content on the surface of nitrogen-doped carbon films deposited under different substrate bias voltages in Example 1 of the present invention. As can be seen from the figure, the pyridine nitrogen content reaches its maximum when the absolute value of the substrate bias voltage increases to 100V. Generally, pyridine nitrogen and pyrrole nitrogen are the most common types of nitrogen doped in carbon matrices. Since pyridine nitrogen has a lone pair of electrons, it can increase electron-donating ability, which is beneficial for adsorbing O2 molecules and breaking OO bonds. Therefore, it is considered to promote a 4-electron transfer ORR and has high ORR catalytic activity.

[0095] Appendix Figure 7The LSV diagrams for ORR of nitrogen-doped carbon films deposited under different substrate biases in Example 1 of this invention, as well as those obtained in Comparative Examples 1 and 2, are shown. When the absolute value of the substrate bias increases from the floating voltage to 200V, the turn-on potential and limiting current density of the nitrogen-doped carbon film for ORR first increase and then decrease. When the substrate bias is -100V, the nitrogen-doped carbon film exhibits the highest catalytic activity, with a turn-on potential identical to that of the Pt / C catalyst (-0.02V) and a limiting current density of 5.86 mA cm⁻¹. -2 .

[0096] Appendix Figure 9 The figures show the performance test results of anion exchange membrane fuel cells using nitrogen-doped carbon films obtained in Examples 1 and 2 of this invention as cathode catalysts. The performance of the anion exchange membrane fuel cells was tested using the nitrogen-doped carbon films obtained in Examples 1 and 2 as cathode catalysts to evaluate the catalyst's catalytic activity for ORR under actual fuel cell operating conditions. Figure 9 As shown, when nitrogen-doped carbon thin films and Pt / C are used as catalysts, the nitrogen-doped carbon thin film catalyst exhibits the same catalytic activity as commercial Pt / C catalysts under actual fuel cell operating conditions.

[0097] Appendix Figure 10 The figures show the chronoamperometry (CMT) curves of the nitrogen-doped carbon thin films obtained in Examples 1 and 2 of this invention for ORR. The test conditions were: electrode potential -0.26 V, electrode rotation speed 1600 rpm; electrolyte was O2-saturated 0.1 M KOH solution. The CMT curves in O2-saturated 0.1 M KOH solution at a fixed electrode potential (-0.26 V) show that during the 18000 s CMT test, the nitrogen-doped carbon thin film catalyst exhibited superior stability compared to commercial Pt / C catalysts.

[0098] Appendix Figure 11 The figures show the chronoamperometry (COP) of the nitrogen-doped carbon films obtained in Examples 1 and 2 of this invention. The test conditions were: electrode potential -0.26V; electrode rotation speed 1600rpm; electrolyte 0.1M KOH, saturated with N2 for 0-1000s, saturated with O2 for 1000-2000s, and saturated with O2 followed by injection of 3M CH3OH for 2000-3000s. The figures show that the nitrogen-doped carbon film exhibits better methanol resistance compared to the Pt / C catalyst.

[0099] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for producing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate, characterized by, The preparation steps include: S1. Substrate pretreatment: clean the substrate material to remove surface impurities to obtain a pretreated substrate; S2. Composite etching treatment: use a modified etching solution to coat the pretreated substrate for etching for 1-4 min, and then ultrasonic clean with ultrapure water for 20-30 min to obtain an etched substrate; S3. Dynamic surface modification: immerse the etched substrate in a mixed solution containing a surface modification modifier and an electroactive monomer base solution for surface modification for 3-8 min, and then dry by gradient heating to obtain a surface modified substrate material; S4. Magnetron co-sputtering deposition: After the pressure in the vacuum chamber reaches 5x10 -4 Pa, ionized gas Ar, reaction gas N2 and CH4 are introduced into the vacuum chamber, auxiliary gas He is introduced, and nitrogen-doped carbon film is deposited on the substrate material by magnetron sputtering process, and the magnetron sputtering process parameters are as follows: radio frequency power is 160-170 W; The substrate bias is -100 V; the sputtering time is 40-50 min; the sputtering pressure is 0.5-1 Pa, and a substrate material with a deposited nitrogen-doped carbon film is obtained; S5. Gradient annealing treatment: the substrate material with the deposited nitrogen-doped carbon film obtained in step S4 is placed in a high-temperature vacuum annealing furnace, the pressure in the vacuum chamber is brought to 5x10 -4 Pa, and then the protective gas Ar is introduced to anneal at a segmented heating rate, so as to obtain a nitrogen-doped carbon film modified for surface modification of the substrate; The mass ratio of the surface modification modifier to the electroactive monomer base solution in the mixed solution is 3-5:1; The preparation of the surface modification modifier includes the following steps: S41. Dissolve 2-4 parts of polyvinylpyrrolidone and 1-3 parts of 3-aminopropyltriethoxysilane in 50-60 parts of deionized water, and stir at a speed of 400-500 r / min for 8-10 min; S42. Add 5-8 parts of pyridine-3-carboxylic acid to the solution obtained in step S41, stir in a 60°C water bath for 18-20 min until completely dissolved, and obtain a preliminary surface modification solution; S43. Add 0.1-0.3 parts of ammonium persulfate to the preliminary surface modification solution, and ultrasonically treat under nitrogen protection at a power of 200 W for 12-15 min to obtain a surface modification modifier; The preparation of the electroactive monomer base solution includes the following steps: S31. Dissolve 10-13 parts of acrylic acid and 8-11 parts of acrylamide in deionized water, stir at a speed of 400-500 r / min until completely dissolved, and control the pH to 6.5-7.0 to obtain a transparent solution; S32. Take 0.1-0.5 parts of graphene quantum dot solution in deionized water, and ultrasonically treat at a power of 200-250 W for 20-30 min until no visible agglomeration is observed to obtain a dispersion liquid; S33. Under a nitrogen atmosphere, add 5-8 parts of vinyl isocyanate and the dispersion liquid prepared in step S32 to the transparent solution obtained in S31, and stir at a speed of 700-800 r / min for 20-30 min to finally obtain an electroactive monomer base solution; The preparation of the modified etching solution includes the following steps: S21. Add deionized water to a container, slowly add nitric acid, and stir to mix uniformly to obtain a nitric acid solution; S22. Under continuous stirring, gradually add hydrofluoric acid, and control the temperature not to exceed 40°C to obtain an acid mixture; S23. Add a modified solution to the acid mixture obtained in step S22, and continuously stir for 15-20 min to finally obtain a modified etching solution; The mass ratio of the nitric acid, hydrofluoric acid, and modified solution is 3:1:0.5-1; The preparation of the modified solution includes the following steps: S231. Add 1-3 parts of citric acid to an appropriate amount of deionized water, and stir until completely dissolved to obtain a citric acid solution; S232. 0.5-0.8 parts of urea is added into the citric acid solution, and stirring is continued until complete dissolution, to obtain a mixed solution; S233. 7-10 parts of polyethylene glycol and 0.3-0.6 parts of sodium dodecyl sulfate are added into the mixed solution, and stirring is continued for 10-20 min under the condition of a water bath at 40℃, to obtain a modified solution.

2. The process for preparing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate according to claim 1, wherein The base material is one of single crystal silicon or polycrystalline titanium.

3. The process for preparing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate according to claim 1, wherein In step S1, when the base material is single crystal silicon, the cleaning method is specifically as follows: the single crystal silicon is sequentially cleaned with acetone, ethanol and ultrapure water by ultrasonic cleaning for 20-30 min, to remove the stains on the surface thereof. When the base material is polycrystalline titanium, the cleaning method is specifically as follows: the polycrystalline titanium is boiled in a hydrochloric acid solution with a volume ratio of hydrogen chloride to water of 1:3 for 30-40 min to remove the oxides on the surface thereof, and then ultrasonic cleaning is performed with ultrapure water for 20-30 min.

4. The process for preparing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate according to claim 1, wherein In step S4, the flow rates of the ionized gas Ar, the reaction gas N2 and CH4 and the auxiliary gas He are respectively 30-35 sccm, 20-25 sccm, 5-10 sccm and 5-8 sccm.

5. The process for preparing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate according to claim 1, wherein In step S4, the sputtering target used in the magnetron sputtering process is a high-purity carbon target with a diameter of 6 cm, a thickness of 1 mm and a purity of 99.95%.

6. The process for preparing a nitrogen-doped carbon thin film for modifying a surface finish of a substrate according to claim 1, wherein, In step S5, the initial stage of annealing is performed at a temperature increasing rate of 5℃ / min to 600℃, and the second stage is performed at a temperature increasing rate of 10℃ / min to 800-1000℃, and then the furnace is slowly cooled to room temperature after holding for 10-15 min.

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