CN1260411C - Method for modifying planar mono-crystal silicon surface - Google Patents

Abstract

A method for modifying the surface of flat monocrystalline silicon, consisting of the following steps: 1. 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl radical (HTEMPO) and azobis Dissolve isobutyronitrile (AIBN) in styrene and 4-vinylpyridine, heat at 95°C for 2 hours, then polymerize at 130±2°C for 5-48 hours, then cool at -20°C to terminate the reaction. Separation by precipitation method to obtain random copolymers of styrene and 4-vinylpyridine containing hydroxyl groups and narrow molecular weight distribution. 2. Ultrasonic cleaning the flat monocrystalline silicon with water for 30 minutes, and then putting it into concentrated sulfuric acid and 30% A mixed solution composed of hydrogen peroxide was heated at 90°C for 2 hours, washed and dried. 3. The obtained copolymer was formulated into a DMF solution, which was coated on the surface of the obtained flat single crystal silicon, and dried in a vacuum oven , heating at 120° C. for 6-122 hours, so that the polymer is grafted onto the surface of the flat monocrystalline silicon to form a polymer brush layer. The molecular weight and thickness of the polymer brush layer prepared by the method are controllable, and the preparation method is simple and convenient.

Description

Modification method of flat single crystal silicon surface

1. Technical field

The present invention relates to the modification of the surface of flat single crystal silicon, specifically, it is a method of grafting styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer on the surface of flat single crystal silicon .

2. Background technology

The method of grafting random copolymers containing reactive end groups, narrow molecular weight distribution, and controllable molecular weight on the surface of flat single crystal silicon was developed in the 1990s. The polymer layer is also called: polymerized brushes. Many studies have proved that grafting random copolymers on the surface of single crystal silicon can effectively control the wetting behavior of the surface of single crystal silicon, thereby inducing the self-assembly of organic matter on the surface of single crystal silicon, or inducing the ordering of polymer materials on the surface. Phase separation, so as to prepare ordered films, this ordered film will be widely used in the fields of microelectronics, cell growth control, biomimetic material preparation, microreactor and controlled drug release, and has high application and theoretical research value , is one of the high technologies that are widely valued at present.

The current technology is to use 2,2,6,6-tetramethylpiperidine-1-oxyl free radical (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO) nitroxide free radical as raw material, first synthesize Containing terminal group 2,2,6,6-tetramethylpiperidine-1-oxyl radical derivatives, and then synthesizing random copolymers with reactive terminal groups, narrow molecular weight distribution, and controllable molecular weight, and finally reacting A polymer brush layer is prepared by grafting random copolymers with permanent end groups, narrow molecular weight distribution and controllable molecular weight to the silicon surface.

The prior art generally uses aromatic hydrocarbon alkylated 2,2,6,6-tetramethylpiperidine-1-oxyl radical (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO) as nitrogen oxygen free radical base, due to the high price of 2,2,6,6-concave methylpiperidine-1-oxyl radicals, in addition, in the preparation of aromatic hydrocarbon alkylation 2,2,6,6-tetramethylpiperidine-1 -Oxygen free radicals have undergone a multi-step synthesis and separation process, and the yield is low. Therefore, this technology is greatly limited in practical applications.

3. Contents of the invention

The present invention uses cheap 4-hydroxyl-2,2,6,6-tetramethylpiperidine as raw material to prepare 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1 through one-step oxidation -Oxygen free radicals (T.Kurosaki, K.W.Lee, M.OkawaraJ.Polym.Sci., Polym.Chem.Ed.1972,10,3295), use this as nitrogen oxide free radicals to initiate styrene and 4-vinylpyridine or styrene and methyl methacrylate monomers for "living" free radical polymerization to prepare styrene and 4-vinylpyridine and styrene and methyl methacrylate containing hydroxyl or carboxyl groups, narrow distribution, molecular weight controllable ester random copolymers, and then grafted them on the surface of single crystal silicon. The technology has the advantages of low preparation cost, readily available raw materials, simple separation and purification, and easy control.

The method of the present invention synthesizes hydroxyl or carboxyl, narrow distribution, controlled molecular weight styrene and 4-vinylpyridine and styrene and methyl methacrylate random copolymer synthetic route is:

Note: When synthesizing random copolymers of styrene and 4-vinylpyridine, styrene and methyl methacrylate with hydroxyl group, narrow distribution and controllable molecular weight: I is azobisisobutyronitrile;

When synthesizing random copolymers of styrene and 4-vinylpyridine and styrene and methyl methacrylate containing carboxyl groups, narrow distribution, molecular weight controllable: I is 4,4'-azobis(4-cyano Valeric acid) (4,4'-Azobis (4-Cyanovaleric Acid, ACA))

In the present invention, the synthesis route of grafting random copolymers of styrene and 4-vinylpyridine or styrene and methyl methacrylate containing hydroxyl groups, narrow molecular weight distribution, and molecular weight controllable on the surface of single crystal silicon is as follows:

The present invention grafts carboxyl-containing, narrowly distributed, molecular weight-controllable styrene and 4-vinylpyridine and methyl methacrylate random copolymers on the surface of single crystal silicon:

Technical scheme of the present invention is as follows:

A method for modifying the surface of flat monocrystalline silicon, which consists of the following steps:

Step 1. Prepare hydroxyl-containing, narrow molecular weight distribution, molecular weight controlled styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer:

Step 1.1. Dissolve 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (HTEMPO) and azobisisobutyronitrile (AIBN) in styrene and 4-vinylpyridine or In styrene and methyl methacrylate, the ratio of the amount of styrene/4-vinylpyridine or methyl methacrylate is in the range of 0.2 to 0.8, and the total monomer and 4-hydroxyl-2,2,6,6- The mass ratio of tetramethylpiperidine-1-oxyl radical and azobisisobutyronitrile is: 500-1,000:1.8-3:1, put them into a single-necked flask fully dehydrated and deoxygenated, at 90 Heating at ℃～100℃ for 2～4 hours can obtain the “covalent dormant species” compound,

Step 1.2. After the "covalent dormant species" obtained in step 1.1 is polymerized at 130±2°C for 5 to 48 hours, it is cooled in an ice-salt bath (-20°C) to stop the polymerization reaction.

Step 1.3. The reaction mixture of stopping the polymerization reaction is separated by precipitation to obtain random copolymers of styrene and 4-vinylpyridine or styrene and methyl methacrylate containing hydroxyl groups, narrow molecular weight distribution, and molecular weight controllable.

Step 2 Functionalization of flat monocrystalline silicon surface

Place the flat monocrystalline silicon into twice distilled water, ultrasonically clean it for 30 minutes, and then put it into a mixed solution of concentrated sulfuric acid and 30% hydrogen peroxide (the volume ratio of concentrated sulfuric acid and hydrogen peroxide is 70:30) , heated at 80°C to 90°C for 1.5 to 2.5 hours, washed with diethyl ether and double distilled water, dried with high-purity argon,

Step 3. Graft random copolymers of styrene and 4-vinylpyridine or styrene and methyl methacrylate containing hydroxyl or carboxyl end groups, narrow molecular weight distribution, and molecular weight controllable on the surface of single crystal silicon

Step 3.1. The polystyrene, poly4-vinylpyridine, styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer containing hydroxyl or carboxyl end groups obtained in step 1 are formulated into 1.5% ~4% N, N-dimethylformamide (DMF) solution, which is coated on the surface of the flat silicon monocrystalline silicon prepared in step 2 by spin coating, and the monocrystalline silicon coated with the polymer layer The crystalline silicon wafer is placed in a vacuum oven, and heated at 120° C. to 122° C. for 6 to 122 hours under vacuum conditions (according to Example 9), so that the polymer is grafted onto the surface of the flat monocrystalline silicon to form a polymer brush layer.

Step 3.2. Quench the flat monocrystalline silicon with a polymer brush layer formed on the surface at room temperature, soak it with N, N-dimethylformamide for 24 hours to remove the ungrafted polymer from the silicon substrate, and then remove the ungrafted polymer from the silicon substrate. and dry below 60°C to obtain flat monocrystalline silicon with a uniform polymer brush layer of a certain thickness on the surface.

The method for modifying the surface of the above-mentioned flat monocrystalline silicon can use 4,4'-azobis(4-cyanovaleric acid) instead of azobisisobutyronitrile as an initiator, so that carboxyl-containing, narrow molecular weight distribution can be obtained. Styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer with controllable molecular weight, so the method for modifying the surface of the above-mentioned flat single crystal silicon, steps 1.1 and 1.2 can also be carried out as follows:

Step 1. Preparation of carboxyl-containing, narrow molecular weight distribution, molecular weight controlled styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer:

Step 1.1. Dissolve 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (HTEMPO) and 4,4'-azobis(4-cyanovaleric acid) in benzene In ethylene and 4-vinylpyridine or styrene and methyl methacrylate, the ratio of the amount of styrene to the total monomer substance is between 0.2 and 0.8, and the total monomer to 4-hydroxyl-2,2,6, 6-tetramethylpiperidine-1-oxygen free radical and 4,4'-azobis(4-cyanovaleric acid) have a ratio of 500-1,000:1.8-3:1, and they are Put it into a fully dehydrated and deoxygenated single-necked flask, and heat it at 90°C to 100°C for 1.5 to 3 hours to obtain the "covalent dormant species" compound.

Step 1.2. After the "covalent dormant species" obtained in step 1.1 is polymerized at 130±2°C for 5 to 60 hours, it is cooled in an ice-salt bath (-20°C) to stop the polymerization reaction.

In this way, step 2 is correspondingly changed as follows:

Step 2 Functionalization of flat monocrystalline silicon surface

Place the flat monocrystalline silicon into twice distilled water, ultrasonically clean it for 30 minutes, and soak the monocrystalline silicon in 2% 3-aminopropene in anhydrous toluene solution for 24 hours under the protection of argon, and then soak it in 2% heptane acid methanol solution for 24 hours, and finally rinsed with methanol three times to obtain flat monocrystalline silicon with carboxyl groups on the surface.

Other steps remain unchanged.

In the method for modifying the surface of flat single crystal silicon mentioned above, the number average molecular weight (Mn) of the polymer can be controlled between 6,000-60,000 g/mol by adjusting the reaction time in step 1.2.

In the method for modifying the surface of flat single crystal silicon mentioned above, the thickness of the polymer brush layer can be controlled between 2.5-9.1 nm by adjusting the heating time in step 3.1.

Compared with the existing technology for preparing polymers with narrow molecular weight distribution, the present invention adopts the method of "living" free radical polymerization in the preparation process to prepare a series of polystyrene, poly-4-vinylpyridine, styrene and 4 - random copolymers of vinylpyridine or styrene and methyl methacrylate. In the preparation process, the raw materials of the initiation system used are easily available, the synthesis method is simple and convenient, and the operation and control are easy. The polymer prepared by this process can have end groups, narrow molecular weight distribution, and the molecular weight can be controlled by controlling the reaction time. The number average molecular weight can be controlled from 6,000g/mol to 60,000g/mol, the molecular weight distribution index is between 1.15 and 1.30 (M _w /M _n ), and the thickness of the polymer brush layer can be adjusted by adjusting the single crystal coated with polymer The heating time of the silicon wafer is controlled, and the thickness of the polymer brush layer can be between 2.5 and 9.1 nm.

Compared with the existing technology for preparing polymer brushes, the present invention adopts the method of "living" free radical polymerization to control the preparation process of polymer brushes in the preparation process, and uses the HTEMPO initiation system in the preparation to make the polymer brushes The thickness and grafting density of the brush layer are easy to control, and the synthesis method is simple. The problem of complicated preparation, separation and purification and high synthesis cost in the prior art is well solved. The synthesized polymer brush has a thickness of 2.5nm-9.1nm and a surface coverage of 90-95%.

4. Description of drawings

Fig. 1 is the ¹ H-NMR spectrogram of the sample prepared in embodiment 1;

Fig. 2 is the GPC graph of the sample containing hydroxyl group prepared in Example 3,  reaction time is 24 hours, ■ reaction time is 48 hours, ● reaction time is 60 hours, ▲ reaction time is 70 hours.

Fig. 3 is the XPS spectrogram of the sample prepared in embodiment 7, wherein, take-off angle: (a) 90 ° (b) 75 ° (c) 60 ° (d) 45 ° (e) 30 ° (f) 10 °; C _1s : 285eV, N _1s : 400eV, O _1s : 532eV, Si _2s : 152eV, Si ₂₉ : 100eV.

Figure 4: A is the atomic force microscope topography of the sample prepared in Example 7, and B is the atomic force microscope side view of the sample prepared in Example 7.

Figure 5: A is the atomic force microscope topography of the sample prepared in Example 8, and B is the atomic force microscope side view of the sample prepared in Example 8.

5. Specific implementation

The technical solution of the present invention will be further described below through examples.

Example 1: Preparation of poly(styrene-r-4-vinylpyridine) random copolymer containing hydroxyl end groups and having a styrene content fraction of 0.66

The polymerization reaction was carried out in a single-necked flask after three cycles of evacuation-baking-argon gas circulation. 0.61g 4-hydroxyl-2,2,6,6-tetramethylpiperidinyloxy radical (HTEMPO·) and 0.287g azobisisobutyronitrile (AIBN) mixture were dissolved in 63.7g styrene and 27.6g 4- Vinylpyridine mixed solution (the ratio of their substances is 500:2:1), inject it into a single-necked flask under the protection of argon. Under the protection of argon, first stir and heat at 90°C-95°C for 1.5-3 hours, then control the reaction temperature to 130±2°C, after 48 hours of reaction, cool with ice-salt bath to stop the polymerization reaction. After the reaction was terminated, the polymer was dissolved in a mixed solvent of absolute ethanol and toluene (volume ratio 1/1), treated with n-hexane as a precipitating agent, the polymer was precipitated, and dried to obtain 62 g of the polymer.

The molecular weight and the molecular weight distribution of poly(styrene-r-4-vinylpyridine) random copolymer adopt GPC instrument (Waters244) to measure, and polystyrene standard sample is standard, and tetrahydrofuran (THF) is mobile phase (the same below), The measured weight average molecular weight is 76,400 g/mol, the number average molecular weight is 58,768 g/mol, and the molecular weight distribution index is 1.20 (M _w /Mn). The composition of copolymer is characterized by Broker A (CE)-300 nuclear magnetic resonance instrument (DMSO-d ₆ is a solvent), see accompanying drawing 1, the composition (mass fraction of 4-vinylpyridine) of copolymer is used 8.3ppm (pyridine The ratio of the peak area at 2H _A ) at position 2 and 6 on the ring to the peak area at 6.3 ppm (3.5 position on the pyridine ring, 2H; 2H at position 2 and 6 on the benzene ring) was calculated. The 12 Hs on the terminal HTEMPO correspond to 1.1 ppm (G).

Juice was calculated to have a styrene content of 0.66.

Embodiment two: the preparation of poly(styrene-r-4-vinylpyridine) random copolymer containing carboxyl end group, the amount fraction of styrene substance is 0.52

The polymerization reaction was carried out in a single-necked flask after three cycles of evacuation-baking-argon gas circulation. 0.61g 4-hydroxyl-2,2,6,6-tetramethylpiperidinyloxy radical (HTEMPO·) and 0.327g 4,4'-azobis(4-cyanovaleric acid) mixture were dissolved in 88.4g benzene Ethylene and 89.25g of 4-vinylpyridine in a mixed solution (the ratio of their substances is 1,000:3:1), and injected into a single-necked flask under the protection of argon. Under the protection of argon, first stir at 90°C-95°C for 1.5-3 hours, then control the reaction temperature to 130±2°C, and after 5 hours of reaction, cool with an ice-salt bath to stop the polymerization reaction. After the reaction was terminated, the polymer was dissolved in a mixed solvent of absolute ethanol and toluene (volume ratio was 1/1), and n-hexane was precipitated as a precipitating agent to obtain 35g of a copolymer with a weight-average molecular weight of 6,800g/mol and a number-average molecular weight of 6,800g/mol. is 6,018 g/mol, the molecular weight distribution index is 1.30 (M _w /Mn), and the amount fraction of styrene substances is 0.52.

Embodiment Three: Preparation of poly(styrene-r-4-vinylpyridine) random copolymers containing hydroxyl or carboxyl end groups, different compositions and different molecular weights

Using a synthetic method similar to Example 1 and Example 2, by changing the molar ratio of styrene and 4-vinylpyridine in the monomer, poly(styrene-r-4-vinylpyridine) of different compositions can be prepared without Regular copolymer, when the ratio of the amount of styrene and 4-vinylpyridine in the monomer is 8/2, 6/4, 4/6, 3/7 and 2/8 respectively, in the prepared copolymer The amount fractions of styrene species were 0.72, 0.58, 0.43, 0.28 and 0.2, respectively. By controlling the polymerization time, copolymers with different molecular weights can be prepared. When the polymerization time is in the range of 5 hours to 48 hours, the weight average molecular weight of the prepared copolymer can be controlled in the range of 6,800g/mol-76,400g/mol. The average molecular weight is in the range of 6,018g/mol-58,768g/mol, and the molecular weight distribution index is in the range of 1.13-1.30 (M _w /Mn), as shown in Figure 2. As can be seen from Figure 2, as the polymerization time prolongs, the The molecular weight increases. The poly(styrene-r-4-vinylpyridine) random copolymers containing hydroxyl end groups, different compositions and different molecular weights can be obtained by the similar synthetic method of Example 1; can be obtained by the similar synthetic method of Example 2 Poly(styrene-r-4-vinylpyridine) random copolymers containing carboxyl end groups with different compositions and molecular weights.

Embodiment four: the preparation of poly(styrene-r-methyl methacrylate) random copolymer containing hydroxyl end groups and having a styrene content fraction of 0.55

The polymerization reaction was carried out in a single-necked flask after three cycles of evacuation-baking-argon gas circulation. 0.61g 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy radical and 0.32g azobisisobutyronitrile mixture were dissolved in a solution composed of 50.6g styrene and 49.7g methyl methacrylate (the ratio of their substances is 500:1.8:1), inject it into a single-necked flask under the protection of argon. Under the protection of argon, first stir at 90° C. for 2 hours, and then control the reaction temperature to 130±2° C. for 5 hours. Polymerization was stopped by cooling with an ice-salt bath. After the reaction was terminated, the polymer was dissolved in anhydrous toluene, treated with n-hexane as a precipitating agent, and 21 g of the polymer was precipitated. The weight average molecular weight of the copolymer was 10,000 g/mol, the number average molecular weight was 8,700 g/mol, the molecular weight distribution index was 1.15 (M _w /Mn), and the amount fraction of styrene was 0.55.

Embodiment five: the preparation of the poly(styrene-r-methyl methacrylate) random copolymer that contains carboxyl end group, the amount fraction of styrene substance is 0.41

The polymerization reaction was carried out in a single-necked flask after three cycles of evacuation-baking-argon gas circulation. 0.61g 4-hydroxyl-2,2,6,6-tetramethylpiperidinyloxy free radical (HTEMPO·) and 0.446g 4,4'-azobis(4-cyanovaleric acid) mixture was dissolved in 33.2 g of styrene and 48.8 g of methyl methacrylate (the ratio of the amount of their substances is 500:2.2:1), injected into a single-necked flask under the protection of argon. Under the protection of argon, first heat at 100°C for 3 hours, then control the reaction temperature at 130±2°C, and react for 48 hours. Polymerization was stopped by cooling with an ice-salt bath. After the reaction was terminated, the polymer was dissolved in anhydrous toluene, treated with n-hexane as a precipitant, and 57 g of the polymer was precipitated. The weight average molecular weight of the copolymer was 68,000 g/mol, the number average molecular weight was 53,968 g/mol, the molecular weight distribution index was 1.26 (M _w /Mn), and the amount fraction of styrene was 0.41.

Embodiment 6: Preparation of poly(styrene-r-methyl methacrylate) random copolymers containing hydroxyl or carboxyl end groups, different compositions and different molecular weights

Adopt and embodiment four, the synthetic method similar to five, by changing the material ratio of styrene and 4-methyl methacrylate in the monomer, can prepare the poly(styrene-r-methyl methacrylate of different composition ) random copolymers, when the ratio of the amount of styrene and methyl methacrylate in the monomer is 8/2, 7/3, 6/4, 4/6, 3/7 and 2/8, The fractions of styrene species in the prepared copolymers were 0.75, 0.68, 0.61, 0.41, 0.33 and 0.25, respectively. By controlling the polymerization reaction time, copolymers with different molecular weights can be prepared. When the polymerization time is in the range of 5 hours to 48 hours, the weight average molecular weight of the prepared copolymer can be controlled in the range of 10,000g/mol-68,000g/mol. The number average molecular weight is in the range of 8,700g/mol-53,968g/mol, and the molecular weight distribution index is in the range of 1.13-1.26 (M _w /Mn). Can obtain the poly(styrene-r-methyl methacrylate) random copolymer that contains hydroxyl end group, different compositions and different molecular weight size with the similar synthetic method of embodiment four; Can obtain with the similar synthetic method of embodiment five Poly(styrene-r-methyl methacrylate) random copolymers containing carboxyl end groups, different compositions and different molecular weights were obtained.

Embodiment 7: Hydroxylation treatment on the surface of flat monocrystalline silicon

Place the flat monocrystalline silicon into twice distilled water, ultrasonically clean it for 30 minutes, and then put it into a mixed solution of concentrated sulfuric acid and 30% hydrogen peroxide (the volume ratio of concentrated sulfuric acid and hydrogen peroxide is 70:30) , heated at 80°C to 90°C for 1.5 to 2.5 hours, washed with diethyl ether and double distilled water, and dried with high-purity argon.

Embodiment 8: Carboxylation treatment on the surface of flat monocrystalline silicon

Place the flat monocrystalline silicon into twice distilled water, ultrasonically clean it for 30 minutes, and soak the monocrystalline silicon in 2% 3-aminopropene in anhydrous toluene solution for 24 hours under the protection of argon, and then soak it in 2% heptane acid methanol solution for 24 hours, and finally rinsed with methanol three times to obtain flat single crystal silicon with carboxyl groups on the surface.

Example 9: Grafting hydroxyl-containing poly(styrene-r-4-vinylpyridine) random copolymer on the surface of single crystal silicon

A 2% N,N-dimethylformamide (DMF) solution of poly(styrene-r-4-vinylpyridine) random copolymer containing hydroxyl or carboxyl groups was spin-coated at 3,500 rpm on On the surface of flat monocrystalline silicon containing hydroxyl or carboxyl groups, place the monocrystalline silicon wafer coated with a polymer layer in a vacuum oven, and heat it at 120°C for 48 hours under vacuum conditions to allow the hydroxyl groups on the polymer to diffuse to The surface of the flat single crystal silicon reacts with the hydroxyl groups on it, so that the polymer is grafted onto the surface of the flat single crystal silicon to form a polymer brush layer. Then, the silicon substrate was quenched at room temperature. Ungrafted polymer was removed from the silicon substrate by immersion in N,N-dimethylformamide for 24 hours, and dried in vacuo.

Through the above steps, a uniform polymer brush layer with a certain thickness on the surface of the flat monocrystalline silicon can be prepared.

The element composition of polymer brush layer is measured with X-ray photoelectron spectrometer (XPS), and film thickness is measured with variable angle X-ray photoelectron spectrometer (XPS) or ellipsometer, and the result is as shown in Figure 3, and its surface Morphology and rough mean square noise were determined by atomic force microscope (AFM) (Nanoscope III MultiMode atomic force microscope of Digital Company). The probe uses Si ₃ N ₄ , at room temperature and in the atmosphere, with contact mode measurement, the results are shown in Figure 4. Explanation: 1. Formula for mean square rough noise: $\mathrm{roughness}=\sqrt{\frac{\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{(Z_i-Z_{\mathrm{ave}})}^2}{N}}$ Calculate, Z _ave the average height within a given area; the height value of a certain point in Z _i ; the total number of points in a given area of N.

2. The surface coverage [Γ(mg/m ² )] is calculated by the formula, Γ=hρ, ρ is the density of the polymer, and h is the thickness of the brush layer.

Embodiment 10: Preparation of poly(styrene-r-methyl methacrylate) random copolymer brushes

A 2% N,N-dimethylformamide (DMF) solution of poly(styrene-r-methyl methacrylate) random copolymer containing hydroxyl or carboxyl groups was spin-coated at a speed of 3,500 rpm Covered on the surface of flat monocrystalline silicon containing hydroxyl or carboxyl groups, the single crystal silicon wafer coated with a polymer layer is placed in a vacuum oven, and heated at 120°C for 48 hours under vacuum conditions to allow the hydroxyl groups on the polymer to diffuse to the surface of the flat single crystal silicon and react with the hydroxyl groups on it, so that the polymer is grafted onto the surface of the flat single crystal silicon to form a polymer brush layer. Then, the silicon substrate was quenched at room temperature. Ungrafted polymer was removed from the silicon substrate by immersion in N,N-dimethylformamide for 24 hours, and dried in vacuo.

The elemental composition of the polymer brush layer is measured by X-ray photoelectron spectroscopy (XPS), and the thickness of the film is measured by variable-angle X-ray photoelectron spectroscopy (XPS) or ellipsometer. Poly(styrene-r-methyl Methyl acrylate) random copolymer brush surface morphology and root mean square roughness were measured by atomic force microscope (AFM) (Digital company Nanoscope III MultiMode type atomic force microscope), the probe used Si ₃ N ₄ , at room temperature, under large atmosphere , measured in contact mode, the results are shown in Figure 5.

Embodiment eleven: the preparation of the copolymer brush layer of different thickness

Adopt the similar method of embodiment seven, eight, by controlling heating time, can prepare the copolymer brush layer of different graft density and different thickness, when heating time is controlled at 6 hours to 122 hours, can prepare graft layer thickness in Copolymer brush layers ranging from 2.5nm to 9.1nm.

Example 12: Poly(styrene-r-4-vinylpyridine) random copolymers with different compositions were grafted onto the surface of flat single crystal silicon to control the interfacial energy of the silicon surface.

By grafting copolymers with different styrene fractions on the surface of single crystal silicon, modified single crystal silicon surfaces with different surface energies can be prepared, and the surface energy can be controlled between 42mJ/cm2 and 51mJ/cm2.

By measuring three kinds of liquids: water, diiodomethane and glycerin contact angle (see table 1) on each polymer surface, with Young-Good-Girifalco-Fowkes equation:

${\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; Lv</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}^{\mathrm{<span\; class="notranslate">\; LW</span>}}{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}^{\mathrm{<span\; class="notranslate">\; LW</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}^{<span\; class="notranslate">\; -</span>}{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}^{<span\; class="notranslate">\; +</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}}^{<span\; class="notranslate">\; +</span>}{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}^{<span\; class="notranslate">\; -</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>$

Calculate the interfacial energy of the polymer brush layer. Table 2 lists the interfacial energy of poly(styrene-r-4-vinylpyridine) random copolymer brush layers with different compositions.

Table 1 The contact angles of water, glycerol and diiodomethane on the surface of poly(styrene-r-4-vinylpyridine) graft layer with different compositions Polymer brushes (volume fraction of styrene substances) water Glycerol Diiodomethane 1.000.780.690.610.550.380.320.220.00 92.088.486.584.482.280.178.276.272.5 76.072.670.467.965.663.661.358.555.0 37.034.431.830.128.226.324.823.020.5

Table 2, the surface energy of poly(styrene-r-4-vinylpyridine) grafted layer Polymer brushes (volume fraction of styrene substances) gamma γ ^LW γ ^AB gamma ⁺ gamma ^- 1.000.780.690.610.550.380.320.220.00 41.0042.5743.9345.0646.1447.1748.1949.4351.00 41.0042.3143.4744.1844.9545.6846.2346.8447.60 0.000.260.460.881.191.491.962.593.40 0.000.010.030.090.130.180.270.450.58 1.101.691.922.172.643.183.543.725.01

Description: 1, according to the Young-Good-Girifalco-Fowkes equation:

${\mathrm{\&gamma;}}_{\mathrm{Lv}}(1+\cos {\mathrm{\&theta;}}_e)=2[{\left({{\mathrm{\&gamma;}}_L}^{\mathrm{LW}}{{\mathrm{\&gamma;}}_{\mathrm{the\; s}}}^{\mathrm{LW}}\right)}^{1/2}+{\left({{\mathrm{\&gamma;}}_L}^{-}{{\mathrm{\&gamma;}}_{\mathrm{the\; s}}}^{+}\right)}^{1/2}+{\left({{\mathrm{\&gamma;}}_l}^{+}{{\mathrm{\&gamma;}}_{\mathrm{the\; s}}}^{-}\right)}^{1/2}]$ Calculate the interfacial energy of the polymer brush layer.

2. The known parameters of water are: γ ^LW = 21.8, γ = 72.8, and γ ⁺ = γ ^- = 25.5mJ/m ² . The individual parameters for glycerol are: γ ^LW =34, γ =64, γ ⁺ =5.3, and γ ⁻ =42.5 mJ/m ² . The individual parameters of diiodomethane are: γ ^LW = 50.8, γ = 50.8, γ ⁺ = 0, and γ ⁻ = 0 mJ/m ² .

Claims (4)

1. a method for modifying the surface of flat monocrystalline silicon is characterized in that it is made up of the following steps: Step 1. Prepare hydroxyl-containing, narrow molecular weight distribution, molecular weight controlled styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer: Step 1.1. Dissolve 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (HTEMPO) and azobisisobutyronitrile (AIBN) in styrene and 4-vinylpyridine or In styrene and methyl methacrylate, the material fraction ratio of styrene and total monomer is in the range of 0.2 to 0.8, and the total monomer and 4-hydroxyl-2,2,6,6-tetramethylpiperidine- The ratio of the amount of 1-oxyl radicals to azobisisobutyronitrile is: 500-1,000:1.8-3:1, put them into a single-necked flask fully dehydrated and deoxygenated, at 90-100°C Heating at low temperature for 1.5 to 3 hours can obtain the "covalent dormant species" compound, Step 1.2. After the "covalent dormant species" obtained in step 1.1 is polymerized at 130±2°C for 5-48 hours, it is cooled in an ice-salt bath at -20°C to stop the polymerization reaction. Step 1.3. stop the reaction mixture of the polymerization reaction, and separate by precipitation to obtain hydroxyl-containing, narrow molecular weight distribution, molecular weight controllable styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer, Step 2 Functionalization of flat monocrystalline silicon surface Put the flat monocrystalline silicon into twice distilled water, ultrasonically clean it for 30 minutes, then put it into a mixed solution composed of concentrated sulfuric acid and 30% hydrogen peroxide, the volume ratio of the mixed solution concentrated sulfuric acid to hydrogen peroxide is 70: 30, heated at 80°C to 90°C for 1.5 to 2.5 hours, washed with diethyl ether and double distilled water, dried with high-purity argon, Step 3. Graft random copolymers of styrene and 4-vinylpyridine or styrene and methyl methacrylate with narrow molecular weight distribution and controllable molecular weight on the surface of single crystal silicon Step 3.1. The polystyrene obtained in step 1, poly 4-vinylpyridine, styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer are formulated into 1 to 4% N, N-di Methylformamide solution, which is coated on the surface of the flat monocrystalline silicon prepared in step 2 by spin coating, and the monocrystalline silicon wafer coated with the polymer layer is placed in a vacuum oven, under vacuum condition , heating at 120°C to 122°C for 6 to 122 hours, so that the polymer is grafted onto the surface of the flat monocrystalline silicon to form a polymer brush layer, Step 3.2. Quench the flat monocrystalline silicon with a polymer brush layer formed on the surface at room temperature, soak it with N, N-dimethylformamide for 24 hours to remove the ungrafted polymer from the silicon substrate, and then remove the ungrafted polymer from the silicon substrate. Drying at a temperature below 60°C can produce flat monocrystalline silicon with a uniform polymer brush layer of a certain thickness on the surface. 2. A method for modifying the surface of flat monocrystalline silicon, characterized in that: Step 1. Preparation of carboxyl-containing, narrow molecular weight distribution, molecular weight controlled styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer: Step 1.1. Dissolve 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (HTEMPO) and 4,4'-azobis(4-cyanovaleric acid) in benzene In ethylene and 4-vinylpyridine or styrene and methyl methacrylate, the ratio of the amount of styrene to the total monomer substance is between 0.2 and 0.8, and the total monomer to 4-hydroxyl-2,2,6, 6-tetramethylpiperidine-1-oxygen free radical and 4,4'-azobis(4-cyanovaleric acid) have a ratio of 500-1,000:1.8-3:1, and they are Put it into a fully dehydrated and deoxygenated single-necked flask, and heat it at 90°C to 100°C for 1.5 to 3 hours to obtain the "covalent dormant species" compound. Step 1.2. After the "covalent dormant species" obtained in step 1.1 is polymerized at 130±2°C for 5 to 60 hours, it is cooled in an ice-salt bath at -20°C to stop the polymerization reaction. Step 2 Functionalization of flat monocrystalline silicon surface Place the flat monocrystalline silicon into double distilled water, ultrasonically clean it for 30 minutes, and soak the monocrystalline silicon in 2% 3-aminopropene in anhydrous toluene solution for 24 hours under the protection of argon, and then soak it in 2% heptane acid methanol solution for 24 hours, and finally rinsed with methanol three times to obtain flat monocrystalline silicon with carboxyl groups on the surface. Step 3. Graft random copolymers of styrene and 4-vinylpyridine or styrene and methyl methacrylate with narrow molecular weight distribution and controllable molecular weight on the surface of single crystal silicon Step 3.1. The polystyrene obtained in step 1, poly 4-vinylpyridine, styrene and 4-vinylpyridine or styrene and methyl methacrylate random copolymer are formulated into 1 to 4% N, N-di Methylformamide solution, which is coated on the surface of the flat monocrystalline silicon prepared in step 2 by spin coating, and the monocrystalline silicon wafer coated with the polymer layer is placed in a vacuum oven, under vacuum condition , heating at 120°C to 122°C for 6 to 122 hours, so that the polymer is grafted onto the surface of the flat monocrystalline silicon to form a polymer brush layer, Step 3.2. Quench the flat monocrystalline silicon with a polymer brush layer formed on the surface at room temperature, soak it with N, N-dimethylformamide for 24 hours to remove the ungrafted polymer from the silicon substrate, and then remove the ungrafted polymer from the silicon substrate. and dry below 60°C to obtain flat monocrystalline silicon with a uniform polymer brush layer of a certain thickness on the surface. 3. The method for modifying the surface of flat single crystal silicon according to claim 1 or 2, characterized in that the number average molecular weight of the polymer is controlled between 6,000-60,000 g/mol by adjusting the reaction time in step 1.2. 4. The method for modifying the surface of flat single crystal silicon according to claim 1 or 2, characterized in that: by adjusting the heating time in step 3.1, the thickness of the polymer brush layer is controlled between 2.5-9.1 nm.

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