A method for preparing one-dimensional metal nanowires

Abstract

The present invention discloses a method for efficiently preparing one-dimensional metal nanowires. This method involves surface-modifying a mold with a micro-nanostructured surface. The metal is then pressed into the modified mold cavity under specific pressure and temperature conditions to replicate the micro-nanostructure pattern in the mold. The advantage of this method is that the surface modification reduces the sliding barrier of the metal on the mold cavity surface, significantly increasing the growth rate of the metal in the modified mold compared to the untreated mold under the same molding conditions. Importantly, this method is effective for most metals, metallic glasses, and polymers.

Description

Technical Field

[0001] The present invention relates to the field of nanomanufacturing technology, and in particular to a method for efficiently preparing one-dimensional nanowires. Background Art

[0002] Nanostructures play a vital role in numerous fields (for details, see the paper titled "Nanofabrication through molding," published in Progress in Materials Science, April 2022). For example, silver nanostructures are widely used in surface-enhanced Raman spectroscopy, and copper nanostructures exhibit remarkable catalytic efficiency. Metal nanowires with high aspect ratios, in particular, are essential raw materials for applications such as flexible electronics and conductive inks. Currently, methods for preparing one-dimensional nanowires primarily include chemical growth, photolithography, self-assembly processes, and scanning probe-based dip-pen techniques (for details, see the paper titled "Dip-pen nanolithography," published in Science, January 1999). These methods allow for the fabrication of uniform metal nanopatterns, but are costly due to the time-consuming, multi-step process and are also limited in their ability to prepare nanostructures with high aspect ratios.

[0003] In 2017, Liu Ze's research group at Wuhan University developed a nanomolding technique based on plastic deformation (for details, see the paper titled "One-step fabrication of crystalline metal nanostructures by direct nanoimprinting below melting temperatures," published in Nature Communications in March 2017, and the invention patent CN107572476B, titled "A method for preparing metal micro-nanostructures"). This method is, in principle, suitable for the rapid fabrication of various metal nanostructures. However, because interfacial friction is a surface force whose effect becomes more pronounced as the feature size decreases, the flow resistance of metal in nanopores increases significantly as the pore size decreases. Although the efficiency of molding can be improved by superimposing microvibrations on the molding pressure (for details, see the paper titled “Observation of speeding growth of metal nanowires by ultra-low frequency micro-vibration assisted superplastic nanomolding” published in Materials Letters in January 2021, and the paper titled “Rapid fabrication of complex nanostructures using room-temperature ultrasonic nanoimprinting” published in Nature Communications in May 2021), the efficiency improvement is limited. In order to quickly prepare metal nanowires with a large aspect ratio, the most effective method previously was to increase the temperature or molding pressure of nanomolding. However, increasing the temperature increases energy consumption, and increasing the molding pressure is limited by the strength of the mold. Therefore, finding methods and developing processes to improve the manufacturing efficiency of metal nanostructures is a challenge that needs to be addressed urgently. Summary of the Invention

[0004] The present invention aims to provide a method for efficiently preparing one-dimensional metal nanowires. By modifying the surface of the nanomold, the method reduces the metal's sliding barrier on the nanomold's pore surfaces, enabling boundary slip within the nanopores, thereby significantly improving the efficiency of preparing one-dimensional nanowires.

[0005] The technical solutions provided by the present invention are as follows:

[0006] A method for efficiently preparing one-dimensional metal nanowires comprises the following steps:

[0007] (1) Surface modification of molds with one-dimensional micron or nanopores;

[0008] (2) stacking the material to be molded and the surface-modified mold on a heated press plate;

[0009] (3) applying a load to press the material to be molded into the mold to obtain a composite structure of the material to be molded and the mold;

[0010] (4) The mold is removed to obtain a molded material with a nanowire structure replicated on the surface.

[0011] Furthermore, the surface modification treatment method is to deposit a coating on the mold surface by chemical vapor deposition or physical vapor deposition.

[0012] Furthermore, the thickness of the coating ranges from a single atomic layer to tens of nanometers.

[0013] Furthermore, the coating includes a polymer coating, a carbon material, a metal and a ceramic layer.

[0014] Furthermore, the polymer coating includes fluorosilane and octadecyltrichlorosilane.

[0015] Furthermore, the material to be molded is a metal element or alloy having a melting point lower than 1800°C under atmospheric conditions.

[0016] Furthermore, the material to be molded is a metal element or alloy with a melting point lower than 1200°C under atmospheric conditions.

[0017] Furthermore, the mold material is a material with a higher melting point and greater hardness than the material to be molded.

[0018] Furthermore, the mold material includes metal, silicon, silicon nitride, silicon oxide and aluminum oxide.

[0019] Furthermore, the load application speed is 1-1000 N / s, the peak load is 0.1-50 kN, and the load unloading speed is 0.001-5 kN / s.

[0020] Principle of the present invention: Figure 1 As shown in the figure, when the mold surface is modified to reduce the sliding barrier of the metal on the mold surface, the speed of the metal at the mold interface may not be zero during the die casting process ( Figure 1 In the figure on the right, the slip length b For viscous fluids such as metallic glass, the velocity profile during the casting process is as follows: Figure 1 As shown in the middle right figure, v zis the flow rate of the viscous fluid in the pipe. Obviously, the flow rate is the largest at the center of the pipe. Compared with the case where the metal-mold interface is adhesive but not slipping, under the same conditions, when there is slip at the interface, the length of the prepared metal nanowire will be greater:

[0021] (1)

[0022] In the above formula R is the radius of the nanopore cavity, L 1 and L 2 are the lengths of nanowires obtained after casting using untreated and surface-modified nanomolds. For crystalline metals, a similar effect will occur when the casting temperature is in the diffusion-dominated temperature range.

[0023] The beneficial effects of the present invention are as follows:

[0024] The method described herein reduces the sliding barrier of metal on the mold cavity surface through surface modification of the mold, resulting in a significantly higher growth rate of metal in the surface-modified mold compared to the untreated mold under the same molding conditions. The surface modification method of the present invention can increase metal molding efficiency by two orders of magnitude, far exceeding previously reported technologies. Furthermore, the present invention is also applicable to materials such as polymers and metallic glasses, and has broad application prospects in the field of micro- and nano-fabrication. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of hot embossing of a mold for surface modification and a combination of the material to be molded.

[0026] In the figure: 1. Hot pressing plate; 2. Material to be molded; 3. Surface-modified mold; 4. Modified layer on the mold cavity surface.

[0027] Figure 2 These are optical microscope images of the sample surface after metallic glass casting (the left is the sample surface after casting using an untreated mold, and the right is the sample surface after casting using a mold treated with octadecyltrichlorosilane (OTS)).

[0028] Figure 3 Scanning electron microscope (SEM) images of the cross section of the sample after metallic glass was molded at 265°C (the left is the sample molded using an untreated mold, and the right is the sample molded using an OTS-treated mold).

[0029] Figure 4 0.68 T m ( T mCross-sectional SEM images of bismuth metal molded at (Kelvin) temperature (left: sample molded using an untreated mold; right: sample molded using an OTS-treated mold).

[0030] Figure 5 0.87 T m Cross-sectional SEM images of bismuth metal after die casting at 370°C (the left is the sample after die casting using an untreated mold, and the right is the sample after die casting using an OTS-treated mold).

[0031] Figure 6 0.67 T m Cross-sectional SEM images of metallic silver after molding at 370°C (the left is the sample molded using an untreated mold, and the right is the sample molded using a mold with carbon deposited on the surface by chemical vapor deposition).

[0032] Figure 7 In order to compare the use of AAO molds with unmodified and modified surfaces to cast various metals, under the same conditions (0.6T m and 300MPa), the length of the prepared nanowires was significantly improved using the modified AAO mold. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings:

[0034] In order to more clearly illustrate the present invention, the following examples are provided:

[0035] Example 1

[0036] Efficient preparation of metallic glass nanowires. First, platinum-based metallic glass (Pt 57.5 Cu 14.7 Ni 5.3 P 22.5 , hereinafter referred to as Pt-BMG) were cut from platinum blocks of similar weight (0.05 g) and then thermoplastic molded at 250 ° C. The maximum load and molding time were 6 kN and 30 s, respectively, to obtain thin discs of similar area size. The surface oxide layer was then removed by grinding with 4000 grit sandpaper and the samples were cleaned with ethanol and deionized water. The anodic aluminum oxide (AAO) template was placed in an octadecyltrichlorosilane (OTS) environment and kept at 100 ° C for 2 h. Under the same conditions, the Pt-BMG / AAO template combination with and without OTS treatment was molded ( Figure 1 The molding temperature was 265℃, and the molding load was loaded at 100N / s to 5 kN and then quickly unloaded (5 kN / s). The optical photograph of the sample surface after molding is shown in the figure. Figure 2 The sample was cut and the length of the Pt-BMG nanowires in the central area was measured as shown in Figure 3 Compared with the untreated AAO mold, the length of the Pt-BMG nanowires prepared using the OTS surface-modified AAO mold increased by about 3 times under the same conditions ( Figure 3 ).

[0037] Example 2

[0038] Metal nanowires were prepared by nanomolding at a lower temperature. First, bismuth blocks of approximately the same weight (0.07 g) were cut from the same base material and then pre-pressed at 200°C to obtain bismuth sheets that were approximately circular. The pre-pressing load was increased from 0 to 1.5 kN at a loading rate of 100 N / s and then quickly unloaded (5 kN / s). The surface oxide layer was then removed by grinding with 4000-grit sandpaper and the sample was cleaned with ethanol and deionized water. The AAO template was placed in an OTS environment at 100°C for 2 h. Finally, the Bi / AAO template combination without and with OTS treatment was nanomolded at 100°C ( Figure 1 ), the molding load is loaded from 0 to 3 kN at a loading speed of 100 N / s and then quickly unloaded (5 kN / s). The length of the nanowires in the center area of the sample after molding is measured, as shown in Figure 4 As shown, Figure 4 The left image shows nanowires cast using an untreated AAO template, and the right image shows nanowires cast using an OTS-treated AAO template. Clearly, the OTS-treated template increases the length of the nanowires cast by nearly an order of magnitude compared to the untreated template (Figure 4).

[0039] Example 3

[0040] Preparation of metal nanowires at high temperature. First, bismuth blocks of approximately the same weight (0.07 g) were cut from the same parent material and then pre-pressed at 200°C to obtain approximately circular bismuth flakes. The pre-pressing load was increased from 0 to 1.5 kN at a loading rate of 100 N / s and then rapidly unloaded (5 kN / s). The surface oxide layer was then removed by grinding with 4000-grit sandpaper and the sample was cleaned with ethanol and deionized water. The AAO template was placed in an OTS environment at 100°C for 2 h. Finally, the Bi / AAO template combination without and with OTS treatment was molded at 200°C ( Figure 1 The casting load was loaded from 0 to 3 kN at a loading rate of 100 N / s and then quickly unloaded (5 kN / s). The length of the nanowires in the center area of the sample after casting was measured, as shown in Figure 5 As shown, Figure 5The left image shows nanowires cast using an untreated AAO template, and the right image shows nanowires cast using an OTS-treated AAO template. Clearly, the OTS-treated template increases the length of the nanowires cast by nearly two orders of magnitude compared to the untreated template.

[0041] Example 4

[0042] Carbon was used as a modification layer. First, silver blocks of approximately the same weight (0.015 g) were cut from the same base material and then pre-pressed at 400°C to obtain thin sheets approximately in the shape of discs. The pre-pressing load was increased from 0 to 3 kN at a loading rate of 100 N / s and then rapidly unloaded (5 kN / s). The surface oxide layer was then removed by grinding with 4000-grit sandpaper and the sample was cleaned with ethanol and deionized water. A layer of carbon material was deposited on the surface of the AAO pores at any temperature in the temperature range of 450°C-650°C using the chemical vapor deposition (CVD) method. The AAO / Ag template combination without and with carbon deposition was molded at 550°C ( Figure 1 ), the casting load is loaded from 0 to 4 kN at a loading rate of 100 N / s and then quickly unloaded (5 kN / s). The length of the nanowires in the center area of the sample after casting is measured, as shown in Figure 6 As shown, Figure 6 The left picture shows the nanowires after casting using an untreated AAO template, and the right picture shows the nanowires after casting using an AAO template with CVD deposited carbon material. Obviously, compared to using an untreated mold, the length of the nanowires after casting using a CVD deposited carbon material mold increased several times ( Figure 6 ).

[0043] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent replacements and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention should be included in the scope of protection of the invention.

Claims

1. A method for preparing one-dimensional metal nanowires, characterized in that: The following steps are involved: (1) performing surface modification on a mold having one-dimensional micron or nanopores; the surface modification method comprises depositing a coating on the mold surface by chemical vapor deposition or physical vapor deposition; The coating is fluorosilane, octadecyltrichlorosilane or carbon material; the thickness of the coating ranges from a single atomic layer to tens of nanometers; the surface modification treatment is used to reduce the sliding barrier of the metal on the surface of the nano mold cavity; (2) stacking the material to be molded and the surface-modified mold on a heated press plate; (3) applying a load to press the material to be molded into the mold to obtain a composite structure of the material to be molded and the mold; (4) The mold is removed to obtain a molded material with a nanowire structure replicated on the surface.

2. The method according to claim 1, wherein: The material to be molded is a metal element or alloy having a melting point lower than 1800°C under atmospheric conditions.

3. The method according to claim 2, wherein: The material to be molded is a metal element or alloy having a melting point lower than 1200°C under atmospheric conditions.

4. The method according to claim 1, wherein: The mold material is a material with a higher melting point and greater hardness than the material to be molded.

5. The method according to claim 4, characterized in that: The mold material is metal, silicon, silicon nitride, silicon oxide or aluminum oxide.

6. The method according to claim 1, wherein: The load application speed is 1-1000 N / s, the peak load is 0.1-50 kN, and the load unloading speed is 0.001-5 kN / s.

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