A method for preparing controllable nanowire composite micro-channel by microsphere template assisted etching

Abstract

The application discloses a preparation method of controllable nanowire composite micro-flow channel by microsphere template assisted etching, belongs to the field of micro-nano structure surface preparation and reinforced heat dissipation structure, and adopts the liquid lowering method to prepare a single-layer polystyrene microsphere template, adopts plasma etching to regulate the size of the single-layer polystyrene microsphere template, and obtains the controllable nanowire composite micro-flow channel through magnetic control sputtering and water bath etching. The preparation method of the application effectively makes up for the defects of the existing single-layer template prepared by the pulling method, and simultaneously proposes that the plasma etching method is used to replace the commonly used reactive ion etching method to regulate the size of the template, so that the nanowire structure is prepared by the microsphere template assistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano structure surface preparation and enhanced heat dissipation structure, and in particular relates to a method for preparing a controllable nanowire composite microchannel assisted by microsphere template etching. Background Art

[0002] Microfluidic cooling technology has attracted widespread attention and research due to its ultra-high heat transfer efficiency and compact design. Microfluidic heat sinks utilize the advantages of microscale effects and phase change latent heat to achieve high heat flux density heat dissipation. Due to the extremely small size of the microchannel structure, the heat exchange area between the working fluid and the flow channel is increased, resulting in an extremely rapid rise in the working fluid temperature, greatly improving heat dissipation efficiency. Due to its advantages such as good temperature uniformity, simple equipment system structure, low mass, and stable operation, microfluidic cooling systems are expected to become one of the future solutions for dissipating heat from high-density heat-generating electronic devices, with broad application prospects in computer chip cooling, aerospace, phased array radar antenna cooling, and other fields.

[0003] Currently, the widespread application of microchannel heat sinks faces some challenges: high pressure drop and flow boiling instability lead to low heat transfer coefficient and critical heat flux (CHF). Flow boiling instability can seriously affect the heat transfer performance of the working fluid in the microchannel. The pressure drop, wall temperature and mass flux in the microchannel oscillate during flow boiling. Transient flow pattern alternation may cause backflow, rapid bubble growth and expansion, and even backflow. The existence of system pressure leads to instability of flow boiling in the microchannel, resulting in temperature oscillations, which in turn affects the stability of the system pressure, creating a vicious cycle. In addition, the size of the microchannel, volume compressibility and unstable flow of the heat dissipating medium will also affect the pressure. As the heat dissipation flux increases, the steam gradually increases, and then the vapor phase will occupy the entire flow channel, and even reverse flow may occur.

[0004] Based on the current research status, the use of micro-nanostructures to modify the microfluidic channel wall to enhance heat transfer performance has certain research prospects. By modifying the super-wetting micro-nanostructure in the microfluidic channel, the heat transfer area of ​​the microfluidic channel can be significantly increased. At the same time, the flow and thermal boundary layer can be interrupted and redeveloped, thereby improving the two-phase convection heat transfer. On the other hand, the enhanced structure can also increase the effective nucleation sites of bubbles, promote bubble nucleation, thereby promoting two-phase flow behavior and reducing severe two-phase flow instability. At present, the material of the chip is mainly silicon. The use of nanostructures to modify the microfluidic channel wall is superior to other structures in terms of manufacturing difficulty. It can also change the properties of the wall at the microscopic level and has excellent stability.

[0005] Currently, silicon nanowire fabrication processes are well-established, including chemical vapor deposition (CVD), molecular beam epitaxy (MEB), laser ablation (LA), oxide-assisted, solution-based, and etching methods. Growth modes are broadly categorized into bottom-up incremental and top-down subtractive methods. The bottom-up growth mode utilizes silicon or silicon compounds as a source, decomposing them through high-temperature decomposition to form nanoclusters and molecular / atomic clusters. This, combined with phase transitions, allows the transition from a vapor / liquid silicon source to a solid-state silicon nanowire. Key fabrication processes for this mode include metal-catalyzed vapor-liquid-solid (VLS) synthesis, supercritical solution-liquid-solid (SFLS) synthesis, solid-liquid-solid (SLS) growth, and oxide-assisted growth. Top-down growth uses bulk silicon as a base material, utilizing chemical reactions or physical processes to reduce the silicon material from the macroscopic to the nanoscale, resulting in the fabrication of nanowire arrays. Key fabrication processes for this mode include plasma etching, reactive ion etching (RIE), and metal-assisted chemical etching (MACE). Bottom-up nanowire preparation methods can selectively produce nanowires of appropriate sizes, with greater controllability over parameters such as diameter and length. However, such methods are extremely demanding on equipment and are very costly, making them only suitable for the preparation of single nanowires. Top-down nanowire preparation methods are not fully controllable.

[0006] The controllable preparation of micro-nanostructures is closely linked to the distribution of metal catalysts in metal-assisted methods. The microsphere template-assisted method effectively addresses the issue of uniform and controllable template distribution, enabling the controllable preparation of micro-nanostructures such as nanowires. The most critical step in the template-assisted preparation process is the preparation of a single-layer microsphere template. Currently, the most common methods for preparing single-layer templates include spin coating and Czochralski methods.

[0007] Spin coating is a common surface preparation method used in experiments. It is widely used due to its controllable and efficient characteristics. The operation of spin coating is also very simple, and the corresponding parameters can be controlled. When using this method, attention should be paid to the amount of dripping, the rotation speed, and the rotation time. If too much dripping is added, multiple layers will form, while too little dripping will cause the surface microspheres to be too dispersed. If the rotation is too fast, the microspheres will gather at the edge or even be thrown off the surface due to centrifugal force. If the rotation is too slow, the microspheres will not reach the edge of the surface and will only spread in the center. The same applies to the rotation time and speed. Too long will result in too much at the edge, while too short will only spread in the center.

[0008] The pulling method is very common in template self-assembly. The operation steps are simple, but it is difficult to implement successfully. The most important thing to pay attention to in the pulling method is the speed of adding the microsphere solution and the pulling speed. The needle of the syringe should not be too thick, and the solution must be added slowly along the wall. Too fast will cause the microspheres to rush into the interior of the solution and will not be able to fully spread on the surface to form a continuous microsphere film. Secondly, the pulling speed and stability are also the key to the experiment. The pulling should not be too fast, which will cause the surface to be unable to fully contact the microsphere film and be pulled out of the liquid surface. Secondly, the pulling process must maintain a uniform speed so that the surface template is uniform. Stability is also a very important point but it is difficult to control. Slight shaking during the pulling process will cause the microsphere film on the surface to be destroyed by vibration, and the resulting template will be uneven.

[0009] The preparation of templates in microfluidic channels has more limitations than that on a flat surface, and the simple and fast spin coating method is not applicable in microfluidic channels. Summary of the Invention

[0010] To address the above-mentioned technical problems, the present invention proposes a method for preparing a controllable nanowire composite microfluidic channel using microsphere template-assisted etching. The present invention utilizes a drop-in method to prepare a single-layer polystyrene microsphere template, plasma etching to control the size of the single-layer polystyrene microsphere template, and magnetron sputtering and water-bath etching to obtain the controllable nanowire composite microfluidic channel. This preparation method effectively overcomes the shortcomings of the existing Czochralski method for preparing a single-layer template. It also proposes the use of plasma etching instead of the commonly used reactive ion etching method for template size adjustment, achieving microsphere template-assisted preparation of nanowire structures.

[0011] To achieve the above objectives, the present invention provides the following technical solutions:

[0012] A method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching comprises the following steps: preparing a single-layer polystyrene (PS) microsphere template by a drop-in method, regulating the size of the single-layer polystyrene microsphere template by plasma etching, and obtaining the controllable nanowire composite microfluidic channel by magnetron sputtering and water bath etching.

[0013] Preferably, the method for preparing the controllable nanowire composite microfluidic channel by microsphere template-assisted etching comprises the following steps:

[0014] Pre-treating the substrate material;

[0015] The PS microsphere solution was diluted, centrifuged, and the supernatant was mixed with anhydrous ethanol, and ultrasonicated in ice water to obtain a mixed solution;

[0016] The downcomer is fixed vertically on an iron stand, the mixed liquid is sucked into a syringe, and the syringe containing the mixed liquid is fixed vertically on the iron stand, the syringe is located above the downcomer, the needle tip of the syringe is close to the inner wall of the downcomer, and a container is provided below the downcomer for holding the solution dripping from the downcomer;

[0017] The piston of the downcomer is closed, a silicon wafer is placed in the downcomer, and water is poured into the downcomer until the silicon wafer is submerged. The piston of the syringe is pulled out to allow the PS microsphere solution to move downward under the action of gravity, so that the mixed solution can slide toward the water surface along a fixed path. The dripping speed of the mixed solution at the needle tip of the syringe is controlled so that continuous ripples can be formed on the water surface. After the mixed solution is added dropwise, it is allowed to stand to allow the PS microspheres to fully spread on the liquid surface (the liquid surface here refers to the interface formed by the mixed solution sliding from the syringe and the water in the downcomer). After the liquid surface stabilizes, the piston of the downcomer is opened to allow water to drip into the container. The liquid surface is kept from fluctuating and descending until the liquid level is lower than the silicon wafer, and the PS microspheres remain on the silicon wafer. After standing, it is dried to obtain a single-layer PS microsphere template.

[0018] The single-layer PS microsphere template is etched by plasma etching, and then a layer of noble metal catalyst is sputtered at the gaps of the PS microsphere template by magnetron sputtering. Etching is performed under water bath conditions to obtain the controllable nanowire composite microchannel.

[0019] Considering the difficulty of addressing speed and stability issues during the Czochralski process, the present invention employs reverse engineering, allowing the liquid level to decrease at a uniform rate before attaching the PS microspheres to the surface—a process known as the liquid-falling method. The present invention employs this method to prepare controllable nanowire composite microfluidics. This method replaces the Czochralski method for template preparation, effectively resolving the difficulties and unevenness of template preparation caused by operational stability in the Czochralski method. Furthermore, the present invention utilizes plasma etching to control template size, resulting in lower costs, shorter experimental cycles, and a more streamlined preparation process.

[0020] Preferably, the method for pre-treating the base material comprises the following steps: cleaning the base material, drying it with nitrogen, and then performing surface hydrophilic treatment.

[0021] More preferably, the method for pretreating the substrate material is:

[0022] (1) Ultrasonic treatment with acetone for 10 min to remove surface organic impurities;

[0023] (2) Clean the silicon wafer with dilute hydrofluoric acid (HF with a mass concentration of 40% and H2O in a volume ratio of 1:2) using ultrasonic cleaning for 15 minutes to remove the native oxide layer on the surface of the silicon wafer;

[0024] (3) Ultrasonic cleaning with deionized water for 10 min to remove residual solution;

[0025] (4) heating a mixture of hydrochloric acid and hydrogen peroxide (36-38% HCl, 30% H2O2, and H2O in a volume ratio of 1:1:5) in a 70°C water bath for 25 min;

[0026] (5) Ultrasonic cleaning with deionized water to remove residual solution;

[0027] (6) Soak in anhydrous ethanol to prevent oxidation.

[0028] Preferably, the substrate material is a material having semiconductor properties, high thermal conductivity, good chemical stability, high mechanical strength and hardness, such as silicon wafer, silicon nitride or gallium nitride.

[0029] Preferably, the concentration of the PS microsphere solution is 25 mg / mL, and the diameter of the PS microspheres is 400 nm.

[0030] Preferably, the PS microsphere solution is diluted with anhydrous ethanol. When diluting the PS microsphere solution with anhydrous ethanol, ensure that the supernatant after centrifugation is mixed with anhydrous ethanol so that the PS microsphere monolayer can be spread on the liquid surface of the downcomer.

[0031] Preferably, the centrifugal speed is 3000-7000 rpm. To solve the problem of impurities and PS microsphere aggregation in the solution, the present invention adds a centrifugation step after obtaining the PS microsphere ethanol solution. It was found that the centrifugal speed has a significant effect on the microsphere content in the supernatant. At a speed of 3000-12000 rpm, centrifugation is carried out for 10 minutes, and the supernatant is taken. Analysis of the surface electron microscopy image obtained from the descending liquid shows that the centrifugal speed should not be too high. At 11000 rpm, the PS microsphere content in the supernatant is too low. At 3000-7000 rpm, a large number of PS microspheres are retained in the supernatant, which can meet the requirements of removing impurities and agglomerates and retaining independent PS microspheres.

[0032] Preferably, in the step of obtaining the mixed solution after ultrasonication in ice water, the frequency of the ultrasonication is 40 kHz, and the ultrasonication time is 5-10 min.

[0033] Preferably, pouring water until the silicon wafer is submerged comprises pouring deionized water until the water level is 5 mm higher than the silicon wafer.

[0034] More preferably, the downcomer used in the present invention is made entirely of glass, and the funnel portion is a cylindrical and conical structure. A pointed conduit is connected to the lower portion of the cone, and a honeycomb leak plate is fixedly connected to the connection between the cylinder and the cone. The honeycomb leak plate can achieve stable placement of the substrate material and can achieve uniform drop of the liquid level. The pointed conduit is equipped with a piston. First, the PS microsphere solution is diluted 2 times with anhydrous ethanol, then centrifuged at a speed of 3000-7000 rpm, the supernatant is mixed with anhydrous ethanol in a volume ratio of 1:1, and the mixture is obtained after ultrasonication in ice water. Anhydrous ethanol can serve as a spreading agent, allowing the PS microspheres to spread fully on the surface, effectively reducing the probability of overlap. At the same time, the high volatility of anhydrous ethanol is conducive to surface drying. The prepared solution is placed in ice water for ultrasonication to prevent the deposition and aggregation of the PS microspheres. The ice water can prevent the solution from heating up during ultrasonication, which may cause the microsphere morphology to be destroyed. The ultrasonic frequency should not be too high to prevent the microspheres from being shattered.

[0035] Preferably, the downcomer of the present invention is equipped with a piston and a flat-bottomed sieve hole. The flat-bottomed sieve hole can realize the stable placement of the silicon wafer sample and ensure the consistent and stable flow rate of the liquid near the silicon wafer; the piston can realize the control of the liquid downcomer speed, ensuring that the liquid surface falls steadily at a uniform speed, so that the surface PS microsphere film (referring to the film formed by the PS microspheres tightly and evenly arranged on the liquid surface) is not disturbed.

[0036] PS microspheres are insoluble in water. When an ethanol solution of PS microspheres is injected into deionized water, ethanol and water dissolve, and the PS microspheres float on the water surface. This creates a thin film of PS microspheres on the liquid surface, which then falls onto the silicon wafer surface. However, when placing the silicon wafer, be sure to tilt it at a certain angle. Do not place it directly on a flat-bottomed sieve. Placing the wafer parallel to the surface will block some of the pores, forcing the liquid to flow only through unobstructed pores near the wafer. This can cause disturbances in the liquid flow near the wafer, resulting in ripples in the resulting liquid flow. The preferred tilt angle for the wafer is 10-15°.

[0037] Preferably, during plasma etching, the oxygen flow rate is 0.2-0.6 mL / s and the etching time is 8-12 min. The present invention adopts plasma etching to regulate the size of PS microspheres. Plasma etching is a technology commonly used in micro-nano processing, which uses ion beams to induce chemical reactions and physical erosion on the surface of materials, thereby achieving precise etching of materials. In general, plasma etching is a complex process involving plasma physics and chemical reaction kinetics. By controlling the energy, flow rate and composition of the ion beam, high-precision etching of the material surface can be achieved, thus having a wide range of applications in the field of micro-nano processing. The present invention adopts plasma etching to etch PS microspheres, reducing the diameter of the PS microspheres and creating gaps between the microspheres. This step is a key step in template preparation and is the key to controllable nanowires. This process can achieve regulation of the size of the PS template, thereby affecting the distribution of nanowires. The present invention etches a silicon wafer surface with a single-layer PS microsphere template through a plasma cleaner using a constant oxygen flow rate (0.2-0.6 mL / s) for a period of time (8-12 minutes) to produce single-layer PS microsphere templates of varying sizes. Longer treatment times and higher oxygen flow rates result in greater changes in PS microsphere diameter. However, excessive oxygen flow rates are not recommended, as excessive reduction in the diameter of the single-layer PS microspheres can lead to deformation and affect the micro-nanostructure morphology. The single-layer PS microsphere template after plasma treatment realizes the control of the microsphere diameter, thereby controlling the spacing and diameter of the nanowires formed by subsequent etching. Secondly, theoretically, by changing the initial PS microsphere diameter, the center distance of the nanowires can be regulated after plasma etching treatment, thereby expanding the nanowire size controllable range (the diameter of the PS microsphere affects the diameter of the nanowire. The surface nanowires prepared by PS microspheres with a diameter of 400nm must be less than 400nm, and the theoretical center distance between nanowires is also 400nm. Replacing with PS microspheres of other sizes can theoretically adjust the diameter range of the nanowires and also realize the regulation of the center distance).

[0038] Preferably, when etching is performed under water bath conditions, it is performed in an etching solution, which is a mixed solution of HF (hydrofluoric acid), H2O2 (hydrogen peroxide) and water, wherein the mass concentration of HF is 40%, the mass concentration of H2O2 is 30%, and the volume ratio of HF, H2O2 and deionized water is 5:1:15.

[0039] Preferably, the etching time in a water bath is 10-30 min, and the etching temperature in a water bath is 30-70°C.

[0040] Preferably, the etching time in a water bath is 20 min, and the etching temperature in a water bath is 70° C.

[0041] Preferably, the noble metal catalyst is silver, platinum or gold.

[0042] Compared with the prior art, the present invention has the following advantages and technical effects:

[0043] To address the stability issues of the Czochralski method in template preparation, the present invention designs a liquid-falling method to replace the common Czochralski method for the preparation of PS microsphere monolayer templates, and designs a corresponding liquid-falling funnel. At the same time, in terms of template control, plasma etching is used instead of the common reactive ion etching method. Plasma etching is simple to operate, has low cost, and a shorter cycle. The method of the present invention utilizes the liquid-falling method to assist the plasma etching method in preparing a monolayer microsphere template and then controls the distribution of the metal catalyst, thereby realizing the preparation of nanowire structures on silicon-based surfaces. In addition, it can also be extended to other new material surfaces such as silicon nitride, gallium nitride, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0045] Figure 1 This is a schematic structural diagram of the downcomer funnel used in the downcomer method of the present invention.

[0046] Figure 2 Schematic diagram of the experimental device of the liquid reduction method in the method of the present invention.

[0047] Figure 3 This is a SEM image of the surface obtained after precipitation of a solution prepared by centrifuging the supernatant and anhydrous ethanol in a volume ratio of 1:1 in Example 1.

[0048] Figure 4 These are SEM images of the silicon wafer surface after plasma etching of the single-layer PS microsphere template in Example 1 at different magnifications, where a is 2000 times, b is 5000 times, and c is 20000 times.

[0049] Figure 5 These are SEM images of the surface of the template with a single layer of PS microspheres after magnetron sputtering and water bath etching in Example 1 at different magnifications, a is 1000 times, b is 3000 times, and c is 4000 times.

[0050] Figure 6 These are SEM images of the spreading results of PS microspheres in the flow channel in Example 6 at different magnifications, where a and b are the liquid drop conditions in the flow channel, and c and d are partial enlarged images of a and b, respectively.

[0051] Figure 7 These are SEM images at different magnifications of the flow channel surface after plasma etching in Example 6.

[0052] Figure 8These are SEM images of the flow channel surface at different magnifications after magnetron sputtering and water bath etching in Example 6, where a is 1500 times and b is 6500 times. DETAILED DESCRIPTION

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0055] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0056] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0057] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0058] All raw materials used in the examples of the present invention are commercially available.

[0059] In the present invention, the base material is a material having semiconductor properties, high thermal conductivity, good chemical stability, high mechanical strength and hardness, such as a silicon wafer, silicon nitride or gallium nitride. The embodiments of the present invention are described with the base material being a silicon wafer and a microchannel heat sink (which is also a silicon material).

[0060] In the present invention, the noble metal catalyst is silver, platinum or gold. Plasma etching can be performed using the above noble metal catalysts. Taking all factors into consideration, the embodiments of the present invention are described using silver as the noble metal catalyst.

[0061] In the present invention, it should be noted that the diameter of the nanowires is not equal to the diameter of the PS microspheres after plasma treatment. This is because the magnetron sputtering process is not vertical sputtering, and during the etching process, the noble metal catalyst (such as Ag) + ) will diffuse freely, and some areas that are not sputtered to Ag and not covered by PS microspheres will also be etched, so the diameter of the nanowires formed by etching is smaller than the diameter of the treated PS microspheres.

[0062] In an embodiment of the present invention, the microchannel heat sink is independently designed and outsourced, and is a silicon wafer of 18.14*16.14 mm in size, with a set of channels etched internally with a width of 300 μm, a length of 11.14 mm, and a depth of 300 μm.

[0063] The structural diagram of the downcomer used in the method of the present invention is shown in FIG. Figure 1 The liquid-dropping funnel is made of glass as a whole. The funnel part is a column plus cone structure. The inner diameter of the column is 5 cm. The lower part of the cone is connected to a pointed tube. The connection between the column and the cone is fixedly connected with a honeycomb leak plate. The honeycomb leak plate can realize the stable placement of the base material and can realize the uniform drop of the liquid level. The pointed tube is equipped with a piston to adjust the liquid drop rate.

[0064] The schematic diagram of the experimental device of the liquid reduction method of the present invention is shown in Figure 2 .

[0065] The materials required in the examples and comparative examples of the present invention are shown in Table 1.

[0066] Table 1 Materials required for the preparation of micro-nanostructures by microsphere-assisted method

[0067]

[0068]

[0069] Note: In Table 1, “%” refers to mass percentage.

[0070] The technical solution of the present invention is further illustrated by the following examples.

[0071] Example 1

[0072] (1) Pre-treat the silicon wafer: Clean the silicon wafer as follows: (1) Ultrasonic treatment with acetone for 10 minutes to remove organic impurities on the surface; (2) Ultrasonic treatment with dilute hydrofluoric acid (HF with a mass concentration of 40% and H2O mixed in a volume ratio of 1:2) for 15 minutes to remove the native oxide layer on the surface of the silicon wafer; (3) Ultrasonic cleaning with deionized water for 10 minutes to remove the residual solution; (4) Heating a mixture of hydrochloric acid and hydrogen peroxide (HCl with a mass concentration of 36%, H2O2 with a mass concentration of 30% and H2O mixed in a volume ratio of 1:1:5) in a 70°C water bath for 25 minutes; (5) Ultrasonic cleaning with deionized water to remove the residual solution; (6) Soak in anhydrous ethanol for later use to prevent oxidation. After drying with nitrogen, perform surface hydrophilic treatment, i.e., plasma treatment for 1 minute to make the silicon wafer surface temporarily hydrophilic;

[0073] (2) A 25 mg / mL PS microsphere solution was diluted 2-fold with anhydrous ethanol and centrifuged at 5000 rpm for 10 min. The supernatant was mixed with anhydrous ethanol at a volume ratio of 1:1 (to facilitate the spreading of PS microspheres). The mixture was sonicated in ice water at a low frequency (specifically 40 kHz) for 8 min to obtain a mixture for subsequent liquid drop experiments.

[0074] (3) A downcomer with a piston and a flat-bottomed sieve hole is fixed vertically on an iron stand, the mixed liquid is sucked into a syringe, and the syringe containing the mixed liquid is fixed vertically on the iron stand. The syringe is located above the downcomer, and the needle tip of the syringe is close to the inner wall of the downcomer. A beaker is placed below the downcomer to hold the solution dripping from the downcomer. The piston of the downcomer is closed, and the pretreated silicon wafer is placed in the downcomer with the silicon wafer tilted at an angle of 10°. Deionized water is poured in until the silicon wafer is submerged (the water surface is 5 mm higher than the silicon wafer surface); the piston of the syringe is pulled out to allow the PS microsphere solution to move downward under the action of gravity, so that the mixed solution can slide to the water surface along a fixed path, and the dripping speed of the mixed solution at the needle tip of the syringe is controlled so that it can form continuous ripples on the water surface. After the mixed solution is added dropwise, it is allowed to stand to allow the PS microspheres to spread completely on the liquid surface. After the liquid level stabilizes, the piston of the downcomer is opened and the solution is allowed to drip into the beaker, and the liquid level is kept from fluctuating and falling until it is lower than the silicon wafer. The PS microspheres remain on the silicon wafer. After standing for 3 minutes, it is dried in an oven to obtain a single-layer PS microsphere template. The SEM image of the surface of the solution prepared by centrifuging the supernatant and anhydrous ethanol in a volume ratio of 1:1 after the downcomer is shown in FIG. Figure 3 , it can be seen that the PS microspheres are evenly spread on the surface, achieving a single layer of dense arrangement within a large area;

[0075] (4) Plasma etching was used to regulate the single-layer PS microsphere template: a silicon wafer with a single-layer PS microsphere template was placed in a plasma cleaning chamber and bombarded with pure oxygen in a vacuum environment for 10 min (i.e., the etching time was 10 min). The oxygen flow rate was 0.2 mL / s to achieve the etching effect. After etching, the diameter of the PS microspheres in the single-layer PS microsphere template was 270 nm. The SEM images of the silicon wafer surface at different magnifications after plasma etching of the single-layer PS microsphere template are shown in FIG. Figure 4 It can be seen that the PS microspheres are evenly distributed on the silicon wafer surface after plasma treatment. After magnification, it can be observed that the etched PS microspheres are proportionally reduced, maintaining the original spherical shape and neat specifications.

[0076] (5) Then, a layer of silver (Ag) catalyst is sputtered in the gap of the single-layer PS microsphere template by magnetron sputtering (the upper limit of the thickness of the catalyst is ensured not to exceed the radius of the PS microsphere after plasma treatment. In this embodiment, the thickness of the catalyst layer is 30 nm). Although the surface of the PS microsphere is covered with a silver layer after magnetron sputtering, its distribution is not affected. The sample after magnetron sputtering is placed in an etching solution (a mixed solution obtained by mixing HF, H2O2 and deionized water in a volume ratio of 5:1:15) and etched in a 70°C water bath for 20 minutes. After etching, it is soaked in dilute nitric acid (mass concentration of 65%) for 3 hours, rinsed with deionized water, and dried with nitrogen to obtain a controllable nanowire composite microchannel. In this embodiment, the SEM images of the surface of the single-layer PS microsphere template after magnetron sputtering and water bath etching at different magnifications are shown as follows. Figure 5 As shown, it can be seen that the nanowire structure is more obvious, there is less silver catalyst residue at the tip, and the nanowire structure can be clearly observed.

[0077] Example 2

[0078] The same as Example 1, except that the flow rate of oxygen in step (4) is 0.6 mL / s and the etching time is 8 min.

[0079] In this embodiment, the diameter of the PS microspheres in the single-layer PS microsphere template after etching is 140 nm.

[0080] Example 3

[0081] The same as Example 1, except that the flow rate of oxygen in step (4) is 0.6 mL / s and the etching time is 12 min.

[0082] In this embodiment, the diameter of the PS microspheres in the single-layer PS microsphere template after etching is 90 nm.

[0083] It can be seen from Examples 1 to 3 that after 8 minutes of plasma treatment with an oxygen flow of 0.6 mL / s, the diameter of the PS microspheres decreased from 400 nm to 140 nm, and after 12 minutes of treatment, it decreased from 400 nm to 90 nm. After 10 minutes of treatment at an oxygen flow rate of 0.2 mL / s, the diameter of the PS microspheres decreased from 400 nm to 270 nm. If the etching time continues to increase, the PS microspheres will be deformed or even washed away if the etching time exceeds 15 minutes.

[0084] From the above experimental results, it can be seen that plasma treatment should control two conditions: treatment time and oxygen flow rate. The longer the treatment time and the greater the oxygen flow rate, the greater the change in the diameter of the PS microspheres. The oxygen flow rate should not be too high. Excessive reduction in the diameter of the PS microspheres will cause the PS microspheres to deform and affect the micro-nanostructure morphology.

[0085] The PS microsphere template after plasma treatment realizes the control of the microsphere diameter, thereby controlling the spacing and diameter of the nanowires formed after subsequent etching. Secondly, theoretically, by changing the initial PS microsphere diameter, the center distance of the nanowires can be regulated after plasma etching treatment, thereby expanding the controllable range of nanowire size.

[0086] Example 4

[0087] (1) Pre-treating the silicon wafer: same as in Example 1;

[0088] (2) A 25 mg / mL PS microsphere solution was diluted 2-fold with anhydrous ethanol and centrifuged at 3000 rpm for 10 min. The supernatant was mixed with anhydrous ethanol at a volume ratio of 1:1 and sonicated at a low frequency (40 kHz) in ice water for 5 min to obtain a mixed solution.

[0089] (3) A downcomer with a piston and a flat-bottomed sieve hole is fixed vertically on an iron stand, the mixed liquid is sucked into a syringe, and the syringe containing the mixed liquid is fixed vertically on the iron stand. The syringe is located above the downcomer, and the needle tip of the syringe is close to the inner wall of the downcomer. A beaker is placed below the downcomer to hold the solution dripping from the downcomer. Close the piston of the downcomer, place the pretreated silicon wafer into the downcomer, tilt the silicon wafer at an angle of 15°, and pour deionized water until the silicon wafer is submerged (the water surface is 5 mm higher than the silicon wafer surface); pull out the piston of the syringe to allow the PS microsphere solution to move downward under the action of gravity, so that the mixed solution can slide toward the water surface along a fixed path, and control the dripping speed of the mixed solution at the needle tip of the syringe so that it can form continuous ripples on the water surface. After the mixed solution is added dropwise, let it stand to allow the PS microspheres to spread completely on the liquid surface. After the liquid level stabilizes, open the piston of the downcomer and let the solution drip into the beaker, keeping the liquid level from fluctuating and falling until it is lower than the silicon wafer. The PS microspheres remain on the silicon wafer. After standing for 3 minutes, use an oven to dry to obtain a single-layer PS microsphere template. The PS microspheres are evenly spread on the surface, achieving a dense single-layer arrangement over a large area.

[0090] (4) Plasma etching was used to control the single-layer PS microsphere template: the silicon wafer with the single-layer PS microsphere template was placed in the chamber of a plasma cleaning machine and bombarded with pure oxygen in a vacuum environment for 10 min at a flow rate of 0.2 mL / s to achieve the etching effect;

[0091] (5) Then, a layer of Ag catalyst was sputtered in the gap of the single-layer PS microsphere template by magnetron sputtering. Although the surface of the PS microsphere was covered with the Ag layer after magnetron sputtering, its distribution was not affected. The sample after magnetron sputtering was placed in an etching solution (a mixed solution of HF, H2O2 and deionized water in a volume ratio of 5:1:15) and etched for 30 minutes in a 30°C water bath. After etching, it was soaked in dilute nitric acid (mass concentration of 65%) for 3 hours and then rinsed with deionized water and dried with nitrogen to obtain a controllable nanowire composite microchannel. The nanowire structure can be clearly observed from the SEM image, and there is less silver catalyst residue at the tip.

[0092] Example 5

[0093] (1) Pre-treating the silicon wafer: same as in Example 1;

[0094] (2) A 25 mg / mL PS microsphere solution was diluted 2-fold with anhydrous ethanol and centrifuged at 7000 rpm for 10 min. The supernatant was mixed with anhydrous ethanol at a volume ratio of 1:1 and sonicated at a low frequency (40 kHz) in ice water for 10 min to obtain a mixed solution.

[0095] (3) A downcomer with a piston and a flat-bottomed sieve hole is fixed vertically on an iron stand, the mixed liquid is sucked into a syringe, and the syringe containing the mixed liquid is fixed vertically on the iron stand. The syringe is located above the downcomer, and the needle tip of the syringe is close to the inner wall of the downcomer. A beaker is placed below the downcomer to hold the solution dripping from the downcomer. Close the piston of the downcomer, place the pretreated silicon wafer into the downcomer, tilt the silicon wafer at an angle of 12°, and pour deionized water until the silicon wafer is submerged (the water surface is 5 mm higher than the silicon wafer surface); pull out the piston of the syringe to allow the PS microsphere solution to move downward under the action of gravity, so that the mixed solution can slide toward the water surface along a fixed path, and control the dripping speed of the mixed solution at the needle tip of the syringe so that it can form continuous ripples on the water surface. After the mixed solution is added dropwise, let it stand to allow the PS microspheres to spread completely on the liquid surface. After the liquid level stabilizes, open the piston of the downcomer and let the solution drip into the beaker, keeping the liquid level from fluctuating and falling until it is lower than the silicon wafer. The PS microspheres remain on the silicon wafer. After standing for 3 minutes, use an oven to dry to obtain a single-layer PS microsphere template. The PS microspheres are evenly spread on the surface, achieving a dense single-layer arrangement over a large area.

[0096] (4) Plasma etching was used to control the single-layer PS microsphere template: the silicon wafer with the single-layer PS microsphere template was placed in the chamber of a plasma cleaning machine and bombarded with pure oxygen in a vacuum environment for 10 min at a flow rate of 0.2 mL / s to achieve the etching effect;

[0097] (5) Then, a layer of Ag catalyst was sputtered in the gaps of the single-layer PS microsphere template by magnetron sputtering. Although the surface of the PS microsphere was covered with an Ag layer after magnetron sputtering, its distribution was not affected. The sample after magnetron sputtering was placed in an etching solution (a mixed solution of HF, H2O2 and deionized water in a volume ratio of 5:1:15) and etched for 10 minutes in a 60°C water bath. After etching, it was soaked in dilute nitric acid (mass concentration of 65%) for 3 hours and then rinsed with deionized water and dried with nitrogen to obtain a controllable nanowire composite microchannel. The nanowire structure can be clearly observed from the SEM image, and there is less residual silver catalyst at the tip.

[0098] Example 6

[0099] The same as Example 1, except that the silicon wafer is replaced with a microchannel radiator. When the microchannel radiator is placed in step (3), the flow channel is ensured to be in an up-down structure. During the liquid drop method, the liquid level is allowed to fall along the flow channel to ensure that the bottom of the flow channel can contact the microsphere film formed on the liquid surface. The spreading results of the PS microspheres in the flow channel after step (3) at different magnifications are shown in FIG. Figure 6, it can be seen that the PS microspheres are indeed distributed inside the flow channel obtained in step (3), with a large area spreading in some areas and a local monolayer tightly arranged; after 10 minutes of plasma treatment in step (4), the diameter of the PS microspheres in the flow channel is reduced to 270nm, and the PS microsphere monolayer spacing is locally controlled inside the flow channel ( Figure 7 ); After step (5), the surface structure of the flow channel at different magnifications is shown Figure 8 , the existence of nanowire structure can be observed from the inside of the flow channel.

[0100] Comparative Example 1

[0101] The same as Example 1, except that in step (2), the 25 mg / mL PS microsphere solution was directly diluted 2-fold with anhydrous ethanol, centrifuged at 5000 rpm for 10 min, and the supernatant was sonicated at low frequency (40 kHz) in ice water for 8 min before the liquid drop experiment.

[0102] Since anhydrous ethanol was not added to the supernatant in this comparative example, the PS microspheres were not fully spread, and some were not spread or were spread in multiple layers, making it impossible to proceed to the subsequent steps.

[0103] Comparative Example 2

[0104] The same as Example 1, except that step (2) is as follows: a 25 mg / mL PS microsphere solution is diluted 3 times with anhydrous ethanol, placed in a centrifuge and centrifuged at 5000 rpm for 10 min, and then the supernatant is mixed with anhydrous ethanol in a volume ratio of 1:1. After low-frequency (40 kHz) sonication in ice water for 8 min, the mixed solution is obtained and the subsequent liquid reduction experiment is carried out.

[0105] Since the concentration of PS microspheres in the supernatant obtained by centrifugation was low after 3-fold dilution in this comparative example, the PS microspheres were spread more evenly after liquid precipitation and were distributed in a single layer, but there were many local blanks, and the subsequent steps could not be carried out.

[0106] Comparative Example 3

[0107] The same as Example 1, except that step (2) is as follows: a 25 mg / mL PS microsphere solution is diluted 5 times with anhydrous ethanol, placed in a centrifuge and centrifuged at 5000 rpm for 10 min, the supernatant is mixed with anhydrous ethanol in a volume ratio of 1:1, and the mixture is ultrasonicated in ice water at a low frequency (40 kHz) for 8 min to obtain a mixed solution, which is then subjected to subsequent liquid reduction experiments.

[0108] Since the concentration of PS microspheres in the supernatant obtained by centrifugation was too low after 5-fold dilution in this comparative example, the PS microspheres on the surface were loosely and disorderly distributed after precipitation, making it impossible to proceed to the subsequent steps.

[0109] Comparative Example 4

[0110] Same as Example 1, except that the centrifugal speed in step (2) is 11000 rpm.

[0111] In this comparative example, the centrifugal speed was too high, and the content of PS microspheres in the supernatant was too low to proceed to the subsequent steps.

[0112] Comparative Example 5

[0113] The same as Example 1, except that after centrifugation in step (2), the supernatant is mixed with anhydrous ethanol in a volume ratio of 1:2.

[0114] In this comparative example, a large amount of anhydrous ethanol was added after centrifugation, and the content of PS microspheres in the mixed solution was too small. The PS microspheres could not be fully spread on the liquid surface, and subsequent steps could not be performed.

[0115] In summary, in the preparation method of the controllable nanowire composite microfluidic channel assisted by microsphere template etching of the present invention, in order to solve the problems of impurities and PS microsphere aggregation in the solution, a centrifugation step is added. The solution is centrifuged at a speed of 3000-12000 rpm for 10 minutes, and the supernatant is taken. From the surface electron microscopy analysis of the liquid obtained, it can be seen that the centrifugal speed should not be too high. At 11000 rpm, the content of PS microspheres in the supernatant is too small. At 3000-7000 rpm, the number of PS microspheres retained in the supernatant is relatively large, which can meet the requirements of removing impurities and agglomerates and retaining independent PS microspheres. Therefore, the present invention preferably centrifuges at a speed of 3000-7000 rpm.

[0116] Comparison of the liquid deposition and spin coating of PS microsphere solutions at different dilution ratios (Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3) was made. After dilution by 5 times, 3 times, and 2 times, the supernatant was removed and anhydrous ethanol was added at a volume ratio of 1:1 to degas. After 5-fold dilution and centrifugation, the concentration of the PS microsphere solution was too low. After degassing, the PS microspheres on the surface were loosely and disorderly distributed. After 3-fold dilution, the PS microsphere concentration was high, but the spreading was uneven. After 2-fold dilution, the concentration of the PS microspheres was appropriate, and the surface was spread more evenly, but there were still some local unspread and multi-layered areas. In order to improve the situation of local unspread and multi-layered areas after 2-fold dilution, anhydrous ethanol was added again. After the PS microsphere solution was diluted by 2 times, the supernatant was taken and mixed with anhydrous ethanol at a volume ratio of 1:1 after centrifugation. From the SEM image, it can be seen that the PS microspheres were evenly spread on the surface, and a single layer was tightly arranged over a large area.

[0117] In the preparation method of the controllable nanowire composite microchannel assisted by microsphere template etching of the present invention, two conditions should be controlled during plasma etching: the treatment time and the oxygen flow rate. The longer the treatment time and the greater the oxygen flow rate, the greater the change in the diameter of the PS microspheres. The oxygen flow rate should not be too high. Excessive reduction in the diameter of the PS microspheres will cause deformation of the PS microspheres, affecting the morphology of the micro-nanostructure.

[0118] The plasma-treated PS microsphere template allows for control of the microsphere diameter, thereby controlling the spacing and diameter of the nanowires formed after subsequent etching. Furthermore, by varying the initial PS microsphere diameter, the center-to-center distance of the nanowires after plasma etching can be adjusted. Furthermore, the oxygen flow rate and duration of the plasma treatment can be used to control the nanowire diameter, enabling controlled fabrication.

[0119] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching, characterized in that: The following steps are involved: Pre-treating the substrate material; The polystyrene microsphere solution was diluted, centrifuged, and the supernatant was mixed with anhydrous ethanol, and ultrasonicated in ice water to obtain a mixed solution. The centrifugal speed was 3000-7000 rpm; The downcomer is fixed vertically on an iron stand, the mixed liquid is sucked into a syringe, and the syringe containing the mixed liquid is fixed vertically on the iron stand, the syringe is located above the downcomer, the needle tip of the syringe is close to the inner wall of the downcomer, and a container is provided below the downcomer for holding the solution dripping from the downcomer; The downcomer is made of glass as a whole. The funnel part is a column and cone structure. The lower part of the cone is connected to a pointed nozzle conduit. The connection between the column and the cone is fixedly connected to a honeycomb leak plate. The honeycomb leak plate can achieve a stable placement of the base material and can achieve a uniform drop of the liquid level. The pointed nozzle conduit is equipped with a piston. The piston of the downcomer is closed, a silicon wafer is placed in the downcomer, and water is poured into the downcomer until the silicon wafer is submerged; the piston of the syringe is pulled out to allow the polystyrene microsphere solution to move downward under the action of gravity, so that the mixed liquid can slide toward the water surface along a fixed path, and the dripping speed of the mixed liquid at the needle tip of the syringe is controlled so that continuous ripples can be formed on the water surface. After the mixed liquid is added dropwise, it is allowed to stand to allow the polystyrene microspheres to fully spread on the liquid surface. After the liquid level stabilizes, the piston of the downcomer is opened to allow the solution in the downcomer to drip into the container, and the liquid level is kept from fluctuating and falling until the liquid level is lower than the silicon wafer, and the polystyrene microspheres remain on the silicon wafer. After standing, it is dried to obtain a single-layer polystyrene microsphere template; The single-layer polystyrene microsphere template is etched by plasma etching, and then a layer of noble metal catalyst is sputtered at the gaps of the single-layer polystyrene microsphere template by magnetron sputtering, and etching is performed under water bath conditions to obtain the controllable nanowire composite microchannel; The substrate material is a microchannel heat sink, which is a silicon wafer of 18.14*16.14mm in size, with a set of channels etched inside with a width of 300μm, a length of 11.14mm, and a depth of 300μm; When placing the microchannel heat sink, ensure that the flow channel is in an up-and-down structure, so that the liquid level drops along the flow channel during the liquid drop method, ensuring that the bottom of the flow channel can contact the microsphere film formed on the liquid surface.

2. The method for preparing a controllable nanowire composite microchannel by microsphere template-assisted etching according to claim 1, characterized in that: The method for pre-treating the base material comprises the following steps: cleaning the base material, drying it with nitrogen, and then performing surface hydrophilic treatment.

3. The method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching according to claim 1, characterized in that: The polystyrene microsphere solution is diluted with anhydrous ethanol.

4. The method for preparing a controllable nanowire composite microchannel by microsphere template-assisted etching according to claim 1, characterized in that: The frequency of the ultrasound is 20-40 kHz.

5. The method for preparing a controllable nanowire composite microchannel by microsphere template-assisted etching according to claim 1, characterized in that: During plasma etching, the oxygen flow rate is 0.2-0.6 mL / s, and the etching time is 8-12 min.

6. The method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching according to claim 1, characterized in that: When etching is performed under water bath conditions, it is performed in an etching solution, which is a mixed solution of HF, H2O2 and water.

7. The method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching according to claim 1, characterized in that: The etching time under water bath conditions is 10-30 min, and the etching temperature under water bath conditions is 30-70°C.

8. The method for preparing a controllable nanowire composite microfluidic channel by microsphere template-assisted etching according to claim 7, characterized in that: The etching time in the water bath was 20 min, and the etching temperature in the water bath was 70 °C.

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