A method for processing an ultra-smooth sheet

Abstract

The application provides a processing method of super-slip sheet, which comprises the following steps: patterning a graphite island pattern on the surface of a graphite material; etching the graphite material according to the graphite island pattern to form a graphite island; heating the graphite island and introducing an oxidizing gas to make the side wall outer edge of the graphite island contact with the oxidizing gas; pushing the upper layer of the graphite island, and if the graphite island of the upper layer is self-recovered, transferring the graphite island of the upper layer into a super-slip sheet. The processing method can effectively improve the performance of the graphite island, increase the self-recovery rate of the graphite island, greatly reduce the super-slip contact friction force of the graphite island, and greatly improve the super-slip performance of the graphite island.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of super-slippery materials, and relates to a processing method of a super-slippery sheet. BACKGROUND

[0002] The "self-recovery" phenomenon is a super-slippery phenomenon of the graphite island. When a micro probe pushes away the graphite island and drives the upper sheet slider to slide on the lower sheet base, the slider will spontaneously return to the initial position under the driving of the tendency, which is the "self-recovery" phenomenon of the graphite island. The probability of the "self-recovery" phenomenon of the graphite island, i.e. the self-recovery rate, can determine the super-slippery performance of the graphite island.

[0003] Therefore, how to improve the probability of the "self-recovery" phenomenon of the graphite island is a key means to improve the success rate of the processing of the super-slippery sheet. In the prior art, the graphite island is generally prepared by adopting a mechanical peeling method to peel the highly oriented pyrolytic graphite (HOPG) to obtain a new graphite surface. The new graphite surface is coated with glue, and then exposed and developed by a laser direct writing, an ultraviolet exposure machine, an electron beam exposure machine and other photolithography technologies to form a corresponding graphite island pattern. Then, the etching process is adopted to etch and prepare a plurality of separate graphite islands according to the graphite island pattern.

[0004] However, the super-slippery performance of the graphite island prepared by the above two methods is poor. Therefore, how to improve the super-slippery performance of the graphite island prepared by the dry etching method has become a problem to be solved in the prior art. SUMMARY

[0005] To solve the technical problems in the prior art, the application provides a processing method of a super-slippery sheet. The processing method can effectively improve the performance of the graphite island, improve the self-recovery rate of the graphite island, greatly reduce the super-slippery contact friction force, and greatly improve the super-slippery performance of the graphite island.

[0006] The static friction force of the graphite island, also known as the initial cleavage force, is the minimum force when the graphite island is first pushed away from the graphite layer. The force mainly consists of the force of internal step fracture and the force of edge physical and chemical bond fracture. The latter force is much larger than the former force. It is found through research that the edge physical and chemical bond fracture is mainly caused by the amorphous carbon of the edge, and the amorphous carbon of the edge is caused by the side of the graphite island during etching. Therefore, how to control the generation of the amorphous carbon is an important problem for optimizing the super-slippery performance of the graphite island.

[0007] To achieve the above technical effects, the application adopts the following technical solutions:

[0008] The application provides a processing method of a super-slippery sheet, which comprises the following steps:

[0009] patterning a surface of the graphite material to form a graphite island pattern;

[0010] etching the graphite material according to the graphite island pattern to form a graphite island;

[0011] heating the graphite island and introducing an oxidizing gas to make the sidewall outer edge of the graphite island contact the oxidizing gas;

[0012] pushing the upper layer of the graphite island, and if the graphite island of the upper layer is self-recovered, transferring the graphite island of the upper layer to a super-slip piece.

[0013] The present application analyzes the graphite island by X-ray photoelectron spectroscopy (XPS) and finds that the edge of the graphite island prepared by a common method is rich in sp 3 -C, sp 3 -C is mainly due to the existence of carbon elements with poor crystalline quality such as amorphous carbon, and sp 2 -C is the peak corresponding to graphite, and it is also observed by transmission electron microscopy (TEM) that there is an amorphous carbon region of more than 20 nm at the edge of the graphite island. Related research shows that the interlayer friction of the graphite island is mostly contributed by the edge, so the existence of amorphous carbon at the edge of the graphite island has an adverse effect on the super-slip performance of the graphite island.

[0014] In the present application, the super-slip performance of the graphite island is improved by removing or thinning the amorphous carbon at the edge of the graphite island. Amorphous carbon has a higher defect density and a higher reactivity of carbon-carbon bond, so compared with a perfect graphite lattice structure, amorphous carbon is more easily etched. According to the difference in chemical reactivity between amorphous carbon and graphite lattice, CO2 gas with appropriate oxidation ability can be used to efficiently etch the amorphous carbon contaminants on the surface of the graphite lattice at a suitable reaction temperature window, without damaging the original perfect graphite lattice structure.

[0015] As a preferred technical solution of the present application, the oxidizing gas includes any one or a combination of at least two of carbon dioxide, water vapor or oxygen, and preferably carbon dioxide.

[0016] As a preferred technical solution of the present application, the graphite island heating is located in a heating device, and the heating device is filled with carbon dioxide.

[0017] In the present application, the heating device includes a tube furnace, a muffle furnace or a sealed drying box.

[0018] As a preferred technical solution of the present application, the pressure of the carbon dioxide atmosphere is not less than 0.001 MPa, such as 0.002 MPa, 0.005 MPa, 0.01 MPa, 0.02 MPa, 0.05 MPa, 0.1 MPa, 0.12 MPa, 0.15 MPa or 0.2 MPa, etc., but not limited to the listed values, and other values not listed in the range are also applicable, preferably 0.1-0.11 MPa, and further preferably normal pressure.

[0019] In the present application, the carbon dioxide atmosphere can be formed by replacing the air in the heating device with carbon dioxide, or by first pumping the air in the heating device to a low pressure, and then introducing carbon dioxide gas to the desired pressure, etc. The carbon dioxide atmosphere can be formed before the graphite islands are placed in the heating device, or the graphite islands can be placed in the heating device first, and then the carbon dioxide atmosphere is formed.

[0020] As a preferred technical solution of the present application, the heating temperature is 400-700℃, such as 450℃, 500℃, 550℃, 600℃ or 650℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0021] As a preferred technical solution of the present application, the heating time is 0.5-24 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h or 23 h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0022] In the present application, the pressure of the carbon dioxide atmosphere, the heating temperature and time, etc. can be controlled to control the thinning degree of the amorphous carbon at the edges of the graphite islands, and thus graphite islands with different super-slip properties can be obtained.

[0023] As a preferred technical solution of the present application, the method comprises: placing the graphite islands prepared by a dry etching process in a heating device with a carbon dioxide atmosphere inside, the pressure of the carbon dioxide atmosphere being not less than 0.1 MPa; and treating the graphite islands with carbon dioxide at 400-700℃ for 0.5-24 h.

[0024] As a preferred technical solution of the present application, the graphite material comprises a mechanically exfoliated highly oriented pyrolytic graphite and a large-area single-crystal graphite material processed by a graphene growth process.

[0025] In the present application, the material of the graphite island is preferably HOPG (Highly Oriented Pyrolytic Graphite), which is a new type of high-purity carbon material prepared by high-temperature and high-pressure treatment of pyrolytic graphite. Its performance is close to that of single crystal graphite, and its surface and interior are relatively perfect graphite lattices without amorphous carbon. The amorphous carbon on the edge of the graphite island comes from the subsequent top-down plasma etching or reactive ion etching, which destroys the perfect graphite lattice of the sidewall of the graphite island. On the other hand, a certain amount of amorphous carbon is also sputtered onto the sidewall during the dry etching process of the bottom of the graphite. These amorphous carbons are mainly caused by physical bombardment and chemical reaction etching of oxygen plasma, which is different from the amorphous carbon formed on the surface during the preparation of traditional graphene or carbon nanotubes.

[0026] As a preferred technical solution of the present application, the graphite island is prepared by a dry etching lift-off process.

[0027] As a preferred technical solution of the present application, in the lift-off process, the photoresist includes a lower layer of glue and an upper layer of glue, the lower layer of glue is bonded with the graphite material, and the length of the patterned upper layer of glue is greater than the length of the lower layer of glue.

[0028] In the present application, the lift-off process includes the steps of flattening, coating photoresist, patterning, sputtering / metal layer evaporation, stripping photoresist and etching in sequence, but is not limited to the above process. The process steps can be adjusted according to the specific preparation requirements. At the same time, the parameters of the above process can be selected according to the preparation requirements, which are not limited here.

[0029] In the present application, the graphite island is prepared by a lift-off process. Compared with the traditional metal etching process, since the photoresist is patterned, the metal layer can be directly prepared on the surface of the exposed graphite material after patterning. Therefore, the required metal mask structure can be formed after the photoresist is stripped, reducing the step of patterning the metal film by IBE etching in the traditional process, reducing the manufacturing cost of the graphite island, and shortening the preparation time of the graphite island. Using the lift-off process, the final etching will also be carried out in the presence of a metal mask to obtain a graphite island of a target size. During the etching process, the top-down etching destroys the perfect graphite lattice of the sidewall of the graphite island, thereby forming amorphous carbon and reducing the super-slip performance of the graphite island. Therefore, after the graphite island is processed by the lift-off process, the obtained graphite island is treated with an oxidizing gas to thin or even remove the amorphous carbon formed on the edge of the graphite island, thereby improving the super-slip performance of the graphite island.

[0030] In the present application, the photoresist in the lift-off process comprises a lower glue and an upper glue connected in sequence, the lower glue is bonded with the graphite material, the lower glue can be set as a peel-off glue without photosensitivity, the upper glue can be set as a photosensitive glue, a window is opened in the photoresist by using the upper glue after exposure and development, the developing solution enters the inside of the photoresist structure, the bottom glue continues to corrode in the developing solution, and transverse expansion is generated to form an undercut structure, that is, the length of the upper glue after patterning is greater than the length of the lower glue. Therefore, compared with the single-layer glue structure, the double-layer glue structure is more conducive to forming the undercut structure required in the lift-off process in the patterning process. However, in the patterning process, the photoresist needs to be corroded by using the developing solution, and since the photoresist of the patterned part needs to be completely removed in the developing process, the developing solution will inevitably contact the graphite surface, and the chemical corrosion will also cause the formation of amorphous carbon on the surface of the graphite island. Therefore, the effect of using the oxidizing gas to treat the obtained graphite island in the present application is more embodied.

[0031] Compared with the prior art, the present application has at least the following beneficial effects:

[0032] (1) The present application provides a processing method of super slippery sheet, which can effectively improve the performance of graphite islands, increase the self-recovery rate of graphite islands, and greatly reduce the super slippery contact friction force and the initial cleavage force of graphite islands, so that the super slippery performance of graphite islands is greatly improved.

[0033] (2) The present application provides a processing method of super slippery sheet, which is simple and convenient to operate, low in cost, and suitable for batch processing and industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a schematic diagram for testing the static friction force of the graphite island treated in embodiment 4 of the present application.

[0035] Figure 2 It is a transmission electron microscope test diagram of the graphite island treated in embodiment 4 of the present application.

[0036] Figure 3 It is a transmission electron microscope test diagram of the graphite island treated in embodiment 5 of the present application.

[0037] Figure 4 It is a schematic diagram of the processing flow of the lift-off process in the specific embodiment of the present application.

[0038] The present application will be further described below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims. DETAILED DESCRIPTION

[0039] In order to better illustrate the present application, facilitate understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0040] Embodiment 1

[0041] The embodiment provides a processing method of a super-smooth sheet, and the method comprises the following steps:

[0042] The surface of the graphite material is subjected to a flattening treatment, a photoresist is spin-coated, the photoresist comprises a lower layer of glue and an upper layer of glue, the lower layer of glue is bonded to the graphite material, a developing solution is used to patternize the photoresist to form a graphite island pattern;

[0043] A metal layer is prepared by sputtering according to the graphite island pattern, ICP etching is performed after stripping the photoresist, and a graphite island is formed;

[0044] The graphite island sample is placed in a tube furnace, the tube furnace is vacuumized to a bottom pressure, carbon dioxide gas is introduced into the above equipment, the pressure in the system is kept at 1000 Pa, the temperature is raised to 500 DEG C, the reaction is heated at this temperature for 3h, the heating is turned off, the temperature is lowered to room temperature, the carbon dioxide is turned off, and the sample is taken out;

[0045] The upper layer of the graphite island is pushed, if the graphite island of the upper layer self-recoveries, the graphite island of the upper layer is transferred to a super-smooth sheet.

[0046] Embodiment 2

[0047] The embodiment provides a processing method of a super-smooth sheet, and the processing method is the same as the processing method of embodiment 1, and the difference is only that:

[0048] The graphite island sample is placed in a tube furnace, the tube furnace is vacuumized to a bottom pressure, carbon dioxide gas is introduced into the above equipment to normal pressure (0.101 MPa), the temperature is raised to 500 DEG C, the reaction is heated at this temperature for 3h, the heating is turned off, the temperature is lowered to room temperature, the carbon dioxide is turned off, and the sample is taken out.

[0049] Embodiment 3

[0050] The embodiment provides a processing method of a super-smooth sheet, and the processing method is the same as the processing method of embodiment 1, and the difference is only that:

[0051] The graphite island sample is placed in a tube furnace, the tube furnace is vacuumized to a bottom pressure, carbon dioxide gas is introduced into the above equipment to normal pressure (0.101 MPa), the temperature is raised to 550 DEG C, the reaction is heated at this temperature for 3h, the heating is turned off, the temperature is lowered to room temperature, the carbon dioxide is turned off, and the sample is taken out.

[0052] Embodiment 4

[0053] The embodiment provides a processing method of a super-smooth sheet, and the processing method is the same as the processing method of embodiment 1, and the difference is only that:

[0054] The graphite island sample was placed in a tube furnace, the tube furnace was vacuumed to the bottom pressure, carbon dioxide gas was introduced into the above equipment to the normal pressure (0.101 MPa), the temperature was raised to 550°C, the reaction was heated at this temperature for 6h, the heating was turned off, the temperature was lowered to normal temperature, the carbon dioxide was turned off, and the sample was taken out.

[0055] Example 5

[0056] This example provides a processing method of super slippery sheet, which is the same as the processing method of Example 1, and the difference is only that:

[0057] The graphite island sample was placed in a tube furnace, the tube furnace was vacuumed to the bottom pressure, carbon dioxide gas was introduced into the above equipment to the normal pressure (0.101 MPa), the temperature was raised to 550°C, the reaction was heated at this temperature for 13h, the heating was turned off, the temperature was lowered to normal temperature, the carbon dioxide was turned off, and the sample was taken out.

[0058] This example is the same as Example 5 except that the heating time is 24h.

[0059] The graphite material used in Examples 1-5 is HOPG.

[0060] Comparative Example 1

[0061] The graphite island in this comparative example is not treated by carbon dioxide, but the preparation method is the same as Examples 1-5. Its super slippery performance is not as good as the sample after CO2 treatment, and the self-recovery rate is higher than the sample after CO2 treatment, and the super slippery contact friction and the initial cleavage force are greater than the sample after CO2 treatment.

[0062] Comparative Example 2

[0063] This comparative example is the same as Example 5 except that HOPG is replaced by ordinary graphite. The graphite island sample using ordinary graphite does not have super slippery performance and cannot self-recover.

[0064] Comparative Example 3

[0065] This comparative example is the same as Example 5 except that CO2 is replaced by inert gas argon. The self-recovery rate and friction of the graphite island sample in this comparative example are not much different from the sample without this treatment. That is, simply increasing the temperature cannot improve the super slippery performance of the graphite island.

[0066] The thickness of the amorphous carbon layer was characterized by TEM, and the amorphous carbon thickness of the edge of the graphite island treated by CO2 and not treated by CO2 was characterized respectively.

[0067] The test method for the sliding friction and static friction of super-slick contact is to use the NT-AFM (produced by NT-MDT, Russia) instrument, press the needle tip on a graphite island of a certain size (such as 6 μm*6 μm), apply a certain positive pressure to drag the graphite island to slide between the graphite layers, the sliding range is 1 μm, the sliding frequency is 1 Hz, and the friction size before and after CO2 treatment is tested.

[0068] The test method for the self-recovery rate is to use the self-made island rotating equipment, press the needle tip on a graphite island of a certain size (such as 8 μm*8 μm), apply a certain positive pressure to drag the graphite island to displace a certain distance (for example, 2 μm), then release the positive pressure, and the graphite island will return to the original position. This phenomenon is called self-recovery phenomenon. The graphite island has a certain probability of self-recovery phenomenon. More than 20 samples are tested, and the number of samples that can self-recover is calculated, so as to obtain the self-recovery rate of the sample.

[0069] The thickness of the amorphous carbon layer at the edge of the graphite island, the friction of super-slick contact and the self-recovery rate of the graphite island after treatment of examples 1-5 and comparative examples 1-3 are tested, and the results are shown in the table. The thickness of the amorphous carbon layer at the edge of the graphite island after CO2 treatment under a certain pressure, temperature and time is reduced to a certain extent or completely removed, and the super-slick performance of the graphite island is improved to a certain extent. For example, the super-slick effect that can be achieved according to example 4 is as follows:

[0070] Figure 1 The test results of the static friction (i.e. the initial cleavage force) in the table show that according to example 4, the static friction of the graphite island of 6 μm*6 μm after treatment is 0.123 μN, which is only one twelfth of the static friction of 1.53 μN before treatment, i.e. reduced by 92.0%, and the static friction is greatly reduced. The sliding friction between the layers of the graphite island after treatment is 0.0637 μN, which is only one third of the sliding friction of 0.213 μN before treatment, i.e. reduced by about 70.00%, and the sliding friction is greatly reduced.

[0071] Figure 2 According to the characterization results of the comparative transmission electron microscope, according to example 4, the thickness of the amorphous carbon at the edge of the graphite island is reduced from 22 nm before treatment to 7 nm after treatment, and the etching rate of the amorphous carbon of the example is about 2.5 nm / hour. Example 4 is a partial removal of amorphous carbon.

[0072] For the self-recovery test of the graphite island, the self-recovery rates of the same sample at similar positions before and after CO2 treatment are tested, according to example 4, 20 samples are tested respectively, and the self-recovery rates of the 8 μm and 10 μm graphite islands before and after CO2 treatment are increased from 25% and 20% to 85% and 65% respectively.

[0073] Figure 3According to the characterization results of the contrast transmission electron microscope, the thickness of the amorphous carbon at the edge of the graphite island is reduced from 22 nm for the untreated sample to 0 nm after the treatment according to this embodiment 5. Embodiment 5 is the complete removal of amorphous carbon.

[0074] The applicant declares that the present application is illustrated by the above embodiments to show the detailed structural features of the present application, but the present application is not limited to the above detailed structural features, i.e. it does not mean that the present application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the components selected by the present application, addition of auxiliary components, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.

[0075] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above embodiments, and within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0076] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combination manners.

[0077] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for processing a superslipper, characterized in that, The processing method includes: Graphite island patterns are formed on the surface of graphite materials; The graphite material is etched according to the graphite island pattern to form graphite islands; The graphite island is heated and an oxidizing gas is introduced so that the outer edge of the sidewall of the graphite island comes into contact with the oxidizing gas, thereby controlling the degree of thinning of amorphous carbon at the edge of the graphite island. Push the upper layer of the graphite island; if the upper graphite island self-recovers, then transfer the upper graphite island to a super-slippery sheet. The graphite islands were prepared using a dry etching lift-off process. The heating temperature is 400~700℃; The oxidizing gas is carbon dioxide.

2. The processing method according to claim 1, characterized in that, The graphite island heating is located in a heating device, which is filled with carbon dioxide.

3. The processing method according to claim 2, characterized in that, The pressure of the carbon dioxide atmosphere is not less than 0.001 MPa.

4. The processing method according to claim 3, characterized in that, The pressure of the carbon dioxide atmosphere is 0.1~0.11 MPa.

5. The processing method according to claim 1, characterized in that, The heating time is 0.5 to 24 hours.

6. The processing method according to claim 1, characterized in that, The method includes: placing the graphite islands prepared by dry etching process in a heating device with an internal carbon dioxide atmosphere, the pressure of which is not less than 0.1 MPa; and treating the graphite islands with carbon dioxide at 400~700℃ for 0.5~24 h.

7. The processing method according to claim 1, characterized in that, The graphite material includes mechanically exfoliated highly oriented pyrolytic graphite and large-area single-crystal graphite material processed using graphene growth technology.

8. The processing method according to claim 1, characterized in that, In the lift-off process, the photoresist includes a lower layer and an upper layer. The lower layer is bonded to the graphite material, and the length of the patterned upper layer is greater than the length of the lower layer.

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