Growth of Vertically Aligned Nanowires on a Conductive Surface

Abstract

A method for manufacturing a nanowire array on a surface having irregularities or a curved surface is disclosed herein. A flexible porous scaffold is used to hold a liquid electrolyte and create a semi-solid electrolyte that is used to transfer pressure to a template placed on a target surface. By aligning and adhering the template to the target surface to substantially remove the voids therebetween, robust and controllable growth of the nanowire array can be achieved.

Description

Technical Field

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 341,796, filed May 13, 2022, the content of which is incorporated herein in its entirety.

Background Art

[0002] Vertically aligned metal nanowire arrays have attracted significant interest due to their exceptional thermal, mechanical, electrical, optical, and chemical properties. Considerable efforts driven by diverse applications in batteries, thermal management, electronics, and solar energy conversion have been invested in developing simple, inexpensive, and robust manufacturing methods. Among them, electrochemical deposition methods based on anodic aluminum oxide or track-etched polycarbonate templates are the most commonly adopted approaches, and free-standing nanowires grow on either a conductive seed layer pre-deposited on one side of the template or a flat conductive substrate to which the template can be firmly bonded.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Growing nanowires directly on an existing object having a curved surface or a rough conductive surface remains a challenge even when the roughness is only a few microns. As shown in FIG. 1A, if the template remains flat as it is and is not pre-deformed to follow the morphology of the rough surface 100, even when the template is closely joined to the surface, there is a risk that voids 104 will remain between the surface and the template 102. Especially for hard / brittle templates (e.g., anodic aluminum oxide), since they cannot be pre-deformed / bent to follow a surface with a rough / curved surface inherently, there is always a risk of leaving voids. In such an example, before the electrodeposited material grows in the pores of the template, a thick parasitic metal film is usually electrochemically deposited to fill the void 104 between the template 102 of the non-flat region and the target surface 100. This process requires a lot of time investment and leads to non-uniform growth of nanowires. On the other hand, as shown in FIG. 1B, even when the template 102 is flexible (e.g., track-etched polycarbonate), has already been pre-pressurized and deformed to follow the rough morphology together with the target surface 100, and leaves small voids, it cannot be kept joined to the target surface 100 when released from the external pressure. Alternatively, the template 102 tends to expand and detach from the surface after being impregnated with the electrolyte during the electrodeposition process, which forms even larger voids to be filled before the electrodeposited material grows in the pores of the template.

Means for Solving the Problem

[0004] (Summary of the Invention) To address the above specific issues, this specification discloses a robust manufacturing method that uses a pressure-applied semi-solid electrolyte to directly grow an array of metal nanowires on a surface with unevenness, aligning the template with the target surface and keeping it joined during the electrodeposition process. The above method can be applied regardless of the size, shape, or roughness of the substrate surface. The above method can also be used to grow nanowires on a surface having a curved surface.

[0005] As an example, specific exemplary embodiments of the systems and methods of the present disclosure will be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0007] The novel manufacturing method of the present disclosure usually has three steps. In the first step, as shown in FIG. 2A, a flexible and bendable porous scaffold material contains an electrolyte and forms a semi-solid electrolyte 208. The scaffold material may be, for example, a sponge, foam, fabric, paper, hydrogel, or any other material that can act as a scaffold for a liquid electrolyte, which is flexible and bendable. In a preferred embodiment where the nanowire array is composed of copper nanowires, the electrolyte is copper sulfate (CuSO 4 ) or copper tetrafluoroborate (Cu(BF 4 ) 2 ) or may be based on any other electrolyte suitable for the electrolytic deposition of copper. However, other electrolytes may be used when growing nanowires composed of materials different from copper. For example, when depositing nickel nanowires, related electrolytes such as nickel sulfate (NiSO 4 ), nickel chloride (NiCl 2 ) and nickel sulfamate (Ni(SO 3 NH 2 ) 2 ) can be used. Other materials may also include, but are not limited to, metals such as silver, gold, brass, cadmium, chromium, iron, etc. that can be electrodeposited through a solution process, and semiconductors such as ZnS, ZnO, ZnSe, CdMnTe, CdS, ZnTe, GaSe, InSe, CdSe, CuInGaSe 2 , CdTe, CuInSe 2 , Ni(OH) 2 , etc.

[0008] As shown in FIG. 2A, the stacked structure 200 is fabricated in the form including a substrate 202 having a target surface 204 defined thereon, a template 206, a semi-solid electrolyte 208, and a negative electrode 210. Preferably, the substrate 202 having the target surface 204 defined thereon is a conductive material that acts as a positive electrode during the growth of the nanowires. In a preferred embodiment, the substrate and the target surface are composed of copper, but other conductive materials may be used, such as any other conductive metal or alloy such as Fe, Ti, Ni, Zn, Ag, Au, CuZn, etc., conductive semiconductors such as indium-doped tin oxide (ITO), fluorine-doped tin oxide (FTO), etc., and other conductive materials such as graphene, carbon nanotubes, carbon fibers, etc., and conductive polymer materials such as PEDOT:PSS, PH1000, etc.

[0009] Thereafter, a pressure 212 is applied between the target surface 204 of the substrate 202 and the metal negative electrode 210. When the pressure is continuously applied, the semi-solid electrolyte 208 deforms together with the template 206 so that the template 206 can conformally cover the rough or curved target surface 202. After an electrochemical deposition time (i.e., on the order of tens of seconds) that enables the nanowires to grow in the pores defined within the template 206, a substantially complete adhesion can be formed between the template 206 and the target surface 204.

[0010] The second step of the process is shown in FIG. 2B. In this step, the nanowire 212 grows within the template 206 by circulating an electrolyte within the porous scaffold 208 or by transferring the adhered template 206 and substrate 202 to a conventional electroplating bath to achieve more controllable and high-quality deposition. The length of the resulting nanowire can be precisely controlled by adjusting the electroplating time. The template 206 defines its plurality of nanopores through which the nanowire 212 grows. The template 206 may be a commercially available article including, but not limited to, anodic aluminum oxide (AAO) and various types of track-etched polymer films such as track-etched polycarbonate (TEPC), track-etched polyester (TEPET), track-etched polyimide (TEPI), track-etched polypropylene (TEPP), track-etched polystyrene (TEPS), etc.

[0011] The last step of the process is shown in FIG. 2C where the nanowire array (schematically shown as reference 214) is released by dissolving the template 206 using a corresponding solvent or solution without damaging or dissolving the nanowire array 214 or the substrate 202.

[0012] The use of the semi-solid electrolyte 208 allows for the continuous application of a constant pressure across the entire template film such that the template 206 adheres to the target surface 204 during the electrochemical deposition process. This is achieved without limiting the morphology of the target surface 204. Based on this novel method, the electroplated material grows directly within the template 206 substantially eliminating the formation of parasitic metal films (see FIG. 1A), leading to a well-controlled process. FIG. 3 is an SEM image of a double-sided nanowire array grown according to the process described immediately above.

[0013] Various processes described can be used to locally grow a nanowire array at any desired spot on the conductive surface shown in FIG. 4. In this process, the cover 402 is placed on the desired spot. Preferably, the cover 402 is composed of a material such as PLA, PEG, PVC, although other materials may be used. Thereafter, the cover 402 is sealed to the target surface 204 using a sealant 404. The sealant 404 may be composed of a general material used in an O-ring configuration, such as rubber or silicone. The port 406 is provided in the cover 402 to enable the circulation of the electrolyte. The connection part 408 of the negative electrode 210 extends through the cover 402. This same process also enables the growth of vertically aligned nanowire arrays on various surfaces with different curvatures and roughnesses. Some examples are shown in FIG. 5. In addition, since the above method does not limit the size of the target surface, it is an industrial-oriented and mass-producible technology. Furthermore, the above process can be used to grow a nanowire array on the opposing surface of a conductive film and a conductive sheet to produce a double-sided nanowire array with a substrate disposed between the double-sided nanowire arrays.

[0014] The nanowire arrays fabricated by the process of the present disclosure have many potential applications. For example, the nanowire arrays can be used as thermal interface materials, battery electrodes, supercapacitor electrodes, sensors, LEDs, triboelectric nanogenerators, catalysts, etc. Many other applications are also possible.

[0015] As can be realized by those skilled in the art, many modifications to the implementations discussed herein that fall within the scope of the present invention are possible. For example, in the above method, various materials having various shapes can be used as the substrate, and various electrolytes can be used to grow nanowires of various materials. The nanowires may have different heights, diameters, and ratios of diameter to height. The density of the nanowires may vary depending on the template used. In addition, the parameters of the manufacturing process can be changed. For example, the pressure applied to the negative and positive electrodes to keep the template aligned with the target substrate may be changed according to the application. The length of time for growing the nanowires may also be changed according to the application. Furthermore, the nanowire array can be grown on substrates of any size. A variety of modifications are possible both to the manufactured nanowire array and to the manufacturing process, and they are intended to be within the scope of the present invention.

[0016] Furthermore, the features of the various embodiments herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not explicitly stated herein, without departing from the spirit and scope of the present invention. Therefore, the exemplary methods of the present disclosure are not intended to limit the present invention but should be regarded as examples thereof. The scope of the present invention is defined by the claims that follow.

Claims

1. A method for manufacturing a nanowire array, A process for preparing a deformable semi-solid electrolyte containing a flexible material containing a liquid electrolyte, A process for creating a laminated structure comprising a substrate having a target surface having irregularities, a template placed on the target surface, a semi-solid electrolyte placed on the template, and a metal negative electrode placed on the semi-solid electrolyte, A step of applying pressure to the laminated structure to align the template with the target surface and leave it bonded. The process involves growing multiple nanowires through voids defined in the template, bonding the template and the substrate to form a bonding template-substrate structure for further nanowire growth, The process involves transferring the bonding template-substrate structure to an electrolytic plating bath and growing nanowires of a desired length. Includes, A method wherein the substrate is a conductive material, and the substrate acts as a positive electrode for the growth of the plurality of nanowires.

2. The nanowires are ZnS, ZnO, ZnSe, CdMnTe, CdS, ZnTe, Gase, InSe, CdSe, CuInGaSe ２ , CdTe, CuInSe ２ , and Ni(OH) ２ The method according to claim 1, comprising a semiconductor material selected from the group consisting of the following.

3. The method according to claim 1, further comprising the step of circulating the liquid electrolyte in the flexible material.

4. The method according to claim 1, further comprising the step of dissolving the template to release the plurality of nanowires.

5. The method according to claim 1, wherein the flexible material is selected from the group consisting of sponge, cloth, foam, paper, and hydrogel.

6. The method according to claim 1, wherein the nanowire is formed by electrolysis.

7. The method according to claim 6, wherein the liquid electrolyte is suitable for electrolysis.

8. The method according to claim 1, further comprising a second template and a second semi-solid electrolyte disposed on the opposing surface of the substrate such that the laminated structure grows simultaneously on both sides of the substrate.

9. The method according to claim 1, wherein the target surface is curved.

10. The method according to claim 1, wherein the layered structure can be patterned to grow a nanowire array having a customizable shape and / or size.

11. The method according to claim 1, wherein the laminated structure covers only a part of the substrate, A step of covering the laminated structure by covering a part of the substrate, The process further includes the step of sealing the cover onto the substrate, The cover is provided with a port for circulating the electrolyte, The method involves the metal negative electrode for depositing the nanowires extending through the cover.

12. The method according to claim 1, wherein the nanowire is made of a material selected from the group consisting of copper, nickel, silver, gold, brass, cadmium, chromium, iron, etc.

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