Growth of vertically aligned nanowires on conductive surfaces

Abstract

A method of fabricating an array of nanowires on an uneven or curved surface is disclosed. A flexible porous scaffold is used to hold a liquid electrolyte, creating a semi-solid electrolyte for transferring pressure to a template disposed on a target surface to conform the template to and bind to the target surface to substantially eliminate gaps therebetween, and to form a semi-solid electrolyte on the target surface. And the stable and controllable growth of the nanowire array can be realized.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 341,796, filed on May 13, 2022, the contents of which are incorporated herein in their entirety. Background Art

[0003] Vertically aligned metal nanowire arrays have attracted great attention due to their extraordinary thermal, mechanical, electrical, optical and chemical properties. Driven by various applications in batteries, thermal management, electronics and solar energy conversion, a lot of effort has been invested in developing simple, cheap and robust manufacturing methods. Among them, electrochemical deposition methods based on anodized aluminum or track-etched polycarbonate templates are the most commonly used methods, in which free-standing nanowires are grown on a conductive seed layer pre-deposited on one side of the template or on a flat conductive substrate to which the template can be closely attached.

[0004] Growing nanowires directly on existing objects with curved or rough conductive surfaces, even if the roughness is only a few microns, remains challenging. As shown in FIG. 1A , when the template remains originally flat and is not pre-deformed to follow the morphology of the rough surface 100, a gap 104 will remain between the surface and the template 102 even if the template has been closely attached to the surface. Especially for rigid / fragile templates (e.g., anodized aluminum), which are inherently unable to be pre-deformed / bent to follow the rough / curved surface, gaps will inevitably remain. In this case, a thick parasitic metal film is usually electrochemically deposited to fill the gap 104 between the template 102 and the target surface 100 in the non-planar region before the electrodeposited material grows into the pores of the template. This process requires a large amount of time investment and results in non-uniform growth of nanowires. On the other hand, as shown in FIG1B , even if the template 102 is soft (e.g., track-etched polycarbonate) and has been pre-compressed and deformed to conform to the rough topography of the target surface 100, leaving tiny gaps, when the external pressure is released, the template 102 cannot remain attached to the target surface 100. Instead, the template 102 tends to swell and separate from the surface after being immersed in the electrolyte during the electrodeposition process, forming even larger gaps to be filled before the electrodeposited material grows into the pores of the template. Summary of the invention

[0005] To address the above problems, a robust manufacturing method is disclosed herein, which directly grows metal nanowire arrays on uneven surfaces using a semi-solid electrolyte applied to the uneven surface, the semi-solid electrolyte having pressure applied thereto to conform and remain attached to the target surface during the electrodeposition process. The method is applicable regardless of the size, shape or roughness of the substrate surface. The method can also be used to grow nanowires on curved surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] By way of example, certain exemplary embodiments of the disclosed systems and methods will now be described with reference to the accompanying drawings, in which:

[0007] Figure 1A is a diagram illustrating challenges associated with growing nanowires on uneven surfaces, where a thick parasitic metal film is electrochemically deposited to fill the gap between the template and the target surface in non-planar regions prior to nanowire growth. Figure 1B is a schematic diagram illustrating a prior art solution, where the template is pre-deformed to conform to the uneven surface, showing separation of the template after immersion in an electrolyte.

[0008] Figure 2A -C is an illustration of the steps of growing a metal nanowire array according to the method disclosed herein.

[0009] Figure 3 is a scanning electron microscope (SEM) image showing a nanowire array grown on an uneven surface, showing that there is almost no parasitic layer between the nanowires and the original surface.

[0010] Figure 4 Shows Figure 2A A variation of the process of -C is used to locally produce nanowire arrays at desired points on the substrate.

[0011] Figure 5 A is a photograph of a nanowire array grown on a copper pillar with a rough and curved surface. Figure 5 B is a photograph showing a nanowire array grown on a larger curved or flexible surface. DETAILED DESCRIPTION

[0012] There are generally three steps in the new manufacturing process disclosed herein. In the first step, Figure 2AAs shown, a soft, flexible, porous scaffold material contains an electrolyte to form a semi-solid electrolyte 208. The scaffold material can be, for example, a sponge, foam, fabric, paper, hydrogel, or any other soft and flexible material that can serve as a support for a liquid electrolyte. In a preferred embodiment in which the nanowire array is composed of copper nanowires, the electrolyte can be based on copper sulfate (CuSO4) or copper tetrafluoroborate (Cu(BF4)2) or any other electrolyte suitable for copper electrodeposition. However, other electrolytes can be used when growing nanowires composed of materials other than copper. For example, when nickel nanowires are to be deposited, relevant electrolytes such as nickel sulfate (NiSO4), nickel chloride (NiCl2) and nickel sulfamate ((Ni(SO3NH2)2)) can be used. Other materials may also include but are not limited to metals such as silver, gold, brass, cadmium, chromium, iron, etc., and semiconductors such as ZnS, ZnO, ZnSe, CdMnTe, CdS, ZnTe, GaSe, InSe, CdSe, CuInGaSe2, CdTe, CuInSe2, Ni(OH)2, etc., which can be electrodeposited by solution methods.

[0013] like Figure 2A As shown, a stacked structure 200 including a substrate 202 having a target surface 204 defined thereon, a template 206, a semi-solid electrolyte 208, and an anode 210 is formed. Preferably, the substrate 202 having the target surface 204 defined thereon is a conductive material, which serves as a cathode during the growth of the nanowires. In a preferred embodiment, the substrate and the target surface are composed of copper, although other conductive materials may be used, for example, 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.

[0014] Pressure 212 is then applied between the target surface 204 of the substrate 202 and the metal anode 210. As the pressure continues to be applied, the semi-solid electrolyte 208 and the template 206 deform together so that the template 206 can conformally cover the rough or curved target surface 202. After electrochemical deposition for a period of time (i.e., on the order of tens of seconds) to allow the nanowires to grow into the pores defined in the template 206, an almost perfect bond can be formed between the template 206 and the target surface 204.

[0015] Figure 2BThe second step of the method is shown. In this step, nanowires 212 grow into template 206 by circulating the electrolyte in porous support 208 or by transferring the combined template 206 and substrate 202 to a conventional electroplating bath to achieve more controlled and high-quality deposition. The length of the resulting nanowires can be precisely controlled by adjusting the electroplating time. Template 206 defines a plurality of nanopores therein, and nanowires 212 grow through these nanopores. Template 206 can be a commercially available item, including but not limited to anodized 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.

[0016] Figure 2C The final step of the process is shown in , where the nanowire array (schematically shown as reference numeral 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 .

[0017] The use of a semi-solid electrolyte 208 allows for the continuous application of a constant pressure across the template film, allowing the template 206 to bond to the target surface 204 during the electrochemical deposition process. This is achieved without constraining the morphology of the target surface 204. Based on this new approach, the electroplated material grows directly into the template 206, essentially eliminating the formation of parasitic metal films (see FIG. 1A ), resulting in a well-controlled process. Figure 3 is a SEM image of a double-sided nanowire array grown according to the process just described.

[0018] like Figure 4 As shown, a variation of the process can be used to locally grow nanowire arrays at any desired point on a conductive surface. In this process, a cover 402 is placed above the desired point. Preferably, the cover 402 is made of materials such as PLA, PEG, PVC, although other materials can also be used. The cover 402 is then sealed to the target surface 204 using a seal 404. The seal 404 can be made of common materials used for O-ring construction, such as rubber or silicone. A port 406 is provided in the cover 402 to allow the circulation of an electrolyte. A connector 408 for the anode 210 extends through the cover 402. This same process also allows the growth of vertically arranged nanowire arrays on various surfaces with different curvatures and roughnesses. Figure 5 Some examples are shown in . In addition, this method has no restrictions on the size of the target surface, making it an industrially friendly and scalable technology. In addition, this process can be used to grow nanowire arrays on opposite sides of a conductive film or sheet to produce double-sided nanowire arrays with a substrate disposed therebetween.

[0019] The nanowire arrays produced by the disclosed process 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.

[0020] As will be appreciated by those skilled in the art, many variations of the implementations discussed herein that fall within the scope of the invention are possible. For example, the method may use different materials with different shapes as substrates, and different electrolytes may be used to grow nanowires of different materials. The nanowires may have different heights, diameters, and ratios of height to diameter. The density of the nanowires may vary depending on the template used. In addition, the parameters of the manufacturing process may vary. For example, the pressure applied to the anode and cathode to keep the template conformal to the target substrate may vary depending on the application. The length of time for the nanowire growth may also vary depending on the application. In addition, nanowire arrays may be grown on substrates of any size. Many variations of the nanowire arrays and manufacturing processes manufactured are possible and are expected to fall within the scope of the invention.

[0021] In addition, it should be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and arrangements without departing from the spirit and scope of the present invention, even if such combinations or arrangements are not explicitly made herein. Therefore, the exemplary methods disclosed herein should not be considered as limitations of the present invention, but rather as illustrations of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for manufacturing a nanowire array, comprising: preparing a semisolid electrolyte comprising a flexible material that serves as a porous scaffold for a liquid electrolyte; generating a stacked structure comprising a substrate having a target surface, a template disposed on the target surface, the semisolid electrolyte disposed on the template, and a metal anode disposed on the semisolid electrolyte; as well as Pressure is applied to the stack to cause the template to conform to and remain attached to the target surface.

2. The method according to claim 1, further comprising: A plurality of nanowires are grown through the holes defined in the template.

3. The method of claim 1, wherein the nanowires are composed of a material selected from copper, nickel, silver, gold, brass, cadmium, chromium, iron, etc. and semiconductors such as ZnS, ZnO, ZnSe, CdMnTe, CdS, ZnTe, GaSe, InSe, CdSe, CuInGaSe2, CdTe, CuInSe2, Ni(OH)2.

4. The method according to claim 2, further comprising: The liquid electrolyte is circulated in the porous support.

5. The method according to claim 2, further comprising: Transfer the template and substrate to the plating tank.

6. The method according to claim 2, further comprising: The template is dissolved to release the plurality of nanowires.

7. The method of claim 1, wherein the pliable material is selected from the group consisting of sponges, fabrics, foams, paper, and hydrogels. The method of claim 1 , wherein the nanowires are formed via electrodeposition.

9. The method of claim 8, wherein the target surface is a conductive surface, and further wherein the liquid electrolyte is suitable for electrodeposition.

10. The method of claim 1, wherein the substrate is a conductive surface regardless of shape and roughness.

11. The method of claim 1, wherein the stacked structure further comprises templates and semi-solid electrolytes disposed on opposite surfaces of the substrate so as to simultaneously grow nanowire arrays on opposite sides of the substrate.

12. The method of claim 1, wherein the target surface is non-planar, and wherein the template conforms to the non-planar target surface by applying pressure.

13. The method of claim 1, wherein the target surface is curved.

14. The method of claim 2, wherein the substrate is conductive and acts as a cathode during the growth of the nanowires.

15. The method of claim 1, wherein the stacked structure can be patterned to grow nanowire arrays having customizable shapes and / or sizes.

16. The method according to claim 1, wherein the stacked structure covers only a portion of the substrate, the method further comprising: providing a cover over the portion of the substrate to cover the stacked structure; as well as sealing the cover to the substrate; wherein the cover is provided with a port to allow the semi-solid electrolyte to flow; and The anode for nanowire deposition extends through the cover.

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