A general method and device for preparing metal micro-nano structures

Abstract

This application belongs to the field of nanofabrication technology, and more specifically, relates to a general method and apparatus for preparing metal micro / nanostructures. This invention employs pulsed current to control the heating and holding processes in nanomolding. Through non-thermal effects such as electromigration and electron wind induced by the current input, the diffusion rate of metal within the nanomold channels is significantly enhanced, promoting dislocation slip behavior and thus greatly improving the forming efficiency of high aspect ratio nanowires. Based on the current-induced non-thermal effect enhancing the forming mechanism, this invention can also achieve the direct and controllable preparation of refractory metal nanowires at relatively low temperatures, expanding the material application range and process window of nanomolding technology.

Description

Technical Field

[0001] This application belongs to the field of nanofabrication technology, and more specifically, relates to a general method and apparatus for preparing metal micro / nano structures. Background Technology

[0002] Micro- and nano-sized structural materials exhibit significantly superior performance compared to conventional bulk materials in optics, electronics, magnetism, and catalysis due to their unique surface effects, small size effects, and quantum size effects, thus showing broad application prospects in many cutting-edge fields. For example, platinum nanomaterials, due to their high specific surface area and abundant surface active sites, exhibit extremely high catalytic efficiency in reactions such as automotive exhaust purification, petrochemicals, and fuel cells. Gold, silver, and copper nanostructures, due to their surface plasmon resonance effects, have wide applications in photocatalysis, nano-integrated photonics, optical sensing, biological labeling, medical imaging, and surface-enhanced Raman spectroscopy. In particular, silver nanowires with high aspect ratios are a fundamental raw material for applications such as flexible electronic devices and conductive inks.

[0003] Methods for preparing micro / nano structures can be divided into two categories: one is the "bottom-up" method, which involves assembling nanostructures from tiny building blocks, and the other is the method itself.

[0004] a) Liquid-phase synthesis. This is currently the most widely used strategy for preparing nanomaterials. Its core lies in inducing nucleation and further growth into the target nanostructure through the controlled decomposition or reduction of the metal precursor. Examples include patent documents CN103540995A "A method for liquid-phase synthesis of germanium nanowires", CN109014237A "A platinum-non-noble metal alloy nanowire and its aqueous-phase synthesis method and application", and patent document CN120551414A "An ultralong silver nanowire and its preparation method and application". However, this method has complex nucleation and growth mechanisms, poor process controllability, and the synthesized nanomaterials are prone to aggregation.

[0005] b) Chemical vapor deposition (CVD). This method is also a widely used strategy for preparing micro / nanostructured materials. Its classic approach relies on highly volatile, thermally stable organometallic compounds. These substances need to be precisely vaporized at controlled temperatures and guided onto the substrate, as illustrated in patent document CN120384271A, "A Chemical Vapor Deposition Method for Preparing Naturally Bending VO2 Nanowires with Controllable Curvature Radius." This method can achieve controllable growth of micro / nano metal structures to a certain extent and effectively avoids the agglomeration problem encountered in liquid-phase methods. The main disadvantages of this method are the expensive equipment and complex process steps.

[0006] c) Electrodeposition. Also known as electrolytic deposition, this method involves reducing, nucleating, and growing metal or alloy ions into micro / nano structures on a conductive substrate surface under an applied electric field. Examples include patent documents CN109576735A "A Method for Preparing Indium Nanowires by DC Electrodeposition", CN119859827A "A Ligand-Free Electrodeposition Method for Synthesizing Platinum Nanowire Arrays on a Substrate", and CN118996538A "An Electrochemical Deposition Preparation Method and Application of Silver Nanowires". All of these patent documents suffer from difficulties in depositing nanomaterials in small-diameter template pores, and the preparation of micro / nano structures with large aspect ratios is extremely time-consuming.

[0007] d) Sputtering methods. These include ion beam sputtering deposition, magnetron sputtering, molecular beam epitaxy, etc., as exemplified by patent documents CN103572374A "A method for preparing silicon nanowires using sputtering deposition of metal", CN104805409A "A method for preparing Ag nanowire array electrodes using magnetron sputtering-mask assisted deposition", and CN116536628A "A method and product for preparing nanoscale amorphous superconducting thin films using magnetron sputtering". It can be observed that this method is difficult to prepare micro / nano structures with large aspect ratios, and the prepared metal nanostructures resemble nanoparticle stacking, exhibiting poor compactness. However, it is more suitable for preparing nanofilms or coating materials.

[0008] Another type is the "top-down" method of processing nanoscale materials. Current mainstream methods include laser micromachining, photolithography, and superplastic nanomolding, among others.

[0009] a) Laser micromachining technology. This method utilizes high-energy photon beams to remove, melt, or modify materials, and is currently widely used in the three major fields of microelectronics, micromechanics, and microoptics, especially adept at the precision processing of polymers and high-melting-point materials. Based on differences in laser pulse width, lasers can be categorized into nanosecond, picosecond, and femtosecond lasers. Among these, ultrafast lasers (picosecond / femtosecond level) have become the mainstream technology due to their small heat-affected zone, as seen in patent documents CN109079314A "A method for fabricating array micro / nano structures using ultrafast laser combined pulse sequences" and CN118720426A "A method for preparing functionalized self-arrayed micro / nano-hole surfaces using femtosecond laser direct writing." However, this method clearly requires high-power lasers, consumes a lot of energy, and is limited by the laser beam size, making it difficult to fabricate micro / nano structures with large aspect ratios and higher density.

[0010] b) Photolithography. This method involves transferring a pattern from a photomask to a substrate using a photoresist under illumination. Its fabrication range is typically from 1 to 100 nanometers. Unlike other processes, photolithography provides controllable "sculpting" capabilities for metal nanostructures. Currently, the controllable fabrication of uniform and regular metal nanostructures still relies on photolithography, especially for nanostructures with a specific aspect ratio, as illustrated in patent documents CN111453692A "Nanopillar Array and its Fabrication Method," CN118969600A "Method for Fabricating Planar Ultrafine Dense-Panel Trenches and Nanowires without High-Precision Photolithography," and CN119365061A "Amorphous Tungsten Superconducting Nanowire Single-Photon Detector." However, this method also has significant drawbacks: low efficiency and high cost, making large-scale application difficult.

[0011] c) Superplastic nanomolding technology. This method was developed in 2017 by Professor Liu Ze's research group at Wuhan University (see patent document CN107572476A, "A Method for Preparing Metal Micro / Nano Structures"). In principle, it is applicable to the controllable, low-cost, and rapid fabrication of various metal nanostructures. However, due to interfacial friction, the flow resistance of the metal in the nanopores increases significantly as the pore size decreases. Previously, the most effective method for rapidly preparing metal nanowires with large aspect ratios was to increase the nanomolding temperature or molding pressure. However, increasing the temperature increases energy consumption, while increasing the molding pressure is limited by the mold strength. Furthermore, due to limitations in the high-temperature resistance of the template and experimental conditions, this method still faces significant challenges in preparing refractory metal nanostructures such as tungsten, tantalum, and molybdenum.

[0012] In summary, apart from superplastic nanomolding technology, existing technologies generally face the challenge of high cost or difficulty in rapidly fabricating high aspect ratio structures. Although superplastic nanomolding technology is considered a cheap, efficient, and controllable fabrication method, it still falls short in meeting the requirements for fabricating ultra-high aspect ratio nanowires. Existing research has attempted to improve molding efficiency by superimposing micro-vibrations during molding pressure (see the papers "Observation of speeding growth of metal nanowires by ultra-low frequency micro-vibration assisted superplastic nanomolding" published in Materials Letters in January 2021 and "Rapid fabrication of complex nanostructures using room-temperature ultrasonic nanoimprinting" published in Nature Communications in May 2021) or by modifying the surface of the nanotemplate (see patent document CN115846673A "A method for efficiently preparing one-dimensional metal nanowires"), but the actual improvement effect is relatively limited. Specifically, applying micro-vibrations can only increase the nanowire length by about 20%. Modifying the template, which involves introducing boundary slip, often requires higher pressure and temperature conditions to effectively increase the aspect ratio, especially for metals with few slip systems. Furthermore, current superplastic nanomolding technology is limited by equipment capabilities and template materials, and is only suitable for metals with melting points below 1800 °C. This technology relies on heat conduction to heat the surface of the metal to be molded; if the metal volume is large, it significantly slows down the overall fabrication efficiency and easily causes upsetting during molding, affecting structural accuracy. The oxygen content and contamination issues during molding, particularly when the metal is easily oxidized, also warrant attention. Therefore, developing novel fabrication processes to significantly improve the manufacturing efficiency of high aspect ratio metal nanostructures and extend to the efficient and controllable fabrication of higher melting point metal nanowires, while simultaneously achieving the direct construction of nanowire structures on the surface of bulk materials, remains a critical challenge that urgently needs to be overcome. Summary of the Invention

[0013] In view of the shortcomings of the prior art, the purpose of this application is to provide a general preparation method and apparatus for metal micro and nanostructures, aiming to solve the technical problems of low preparation efficiency and difficulty in controllable preparation of metal nanowires with large aspect ratio in the prior art.

[0014] To achieve the above objectives, in a first aspect, this application provides a general method for preparing metal micro / nano structures, comprising the following steps:

[0015] (1) The metal material to be molded and the template with micro-nano structure are stacked in the cavity of the conductive mold; and the width of the metal material to be molded and the width of the conductive mold are adapted to each other, so that the side of the metal material to be molded is in contact with the conductive mold;

[0016] (2) In a vacuum environment, the conductive mold is heated by a pulsed current, and then the metal material to be molded is heated to a certain temperature through heat conduction. T , of which 0.3 T m < T < T m , T Represents absolute temperature. T m This represents the melting point temperature of the metal material to be molded according to the absolute temperature scale;

[0017] (3) Apply a load to bring the temperature to a T The metal material to be molded is pressed into the template with micro-nano structure, and after holding the pressure and removing the mold, the metal material with micro-nano structure is obtained.

[0018] The metal material to be molded is a metallic element or alloy with a melting point below 3600℃ in atmospheric environment; the conductive mold is a graphite mold or a cemented carbide mold.

[0019] The temperature T Less than or equal to 1400 °C; according to the metal material to be molded T m Select the appropriate mold type and pulse current parameters. The specific process parameters are configured as follows:

[0020] when T m At temperatures below 300 ℃, a carbide mold is selected, the pulse waveform is a trapezoidal pulse, the pulse current rise time and fall time are set to 2-5 ms, the pulse current flat-top holding time is 10-15 ms, and the pulse interval is 10-15 ms, in order to achieve flexible heating;

[0021] When 300 ℃ ≤ T m When the temperature is ≤ 1800 ℃, a graphite mold or a cemented carbide mold shall be selected. The pulse waveform shall be a rectangular pulse. The duty cycle of the pulse width and the pulse interval shall be set to (5-7):1, where the pulse width is 20-80 ms.

[0022] whenT m At >1800 ℃, a graphite mold is used, the pulse waveform is a rectangular pulse, and the duty cycle of the pulse width and pulse interval is set to (5-7):1, where the pulse width is 40-160 ms.

[0023] More preferably, when using a graphite mold, the applied load pressure is less than or equal to 50 MPa; when using the cemented carbide mold, the applied load pressure is less than or equal to 600 MPa.

[0024] Preferably, the template with micro / nano structure is made of silicon, silicon oxide, or aluminum oxide.

[0025] Preferably, the pulse current source is equipped with a waveform parameter adjustment module and adopts a stepped current control strategy, specifically: the initial current peak value and current increase amplitude are set according to the mold type, the metal material to be molded is heated according to the preset heating rate, after reaching the target temperature, the current value is reduced to the current value during heat preservation, and the power is cut off and unloaded after heat preservation, so as to achieve stable heating according to the preset heating rate and suppress local overheating.

[0026] According to another aspect of the present invention, an apparatus for preparing metal micro / nano structures using the general preparation method described above is provided, comprising a pulsed current source, a vacuum chamber, electrodes, conductive pads, a conductive mold, an infrared temperature measurement module, and a pressurization module;

[0027] The pulsed current source is connected to the electrode, the conductive mold is placed in the vacuum chamber, and the electrode is electrically connected to the conductive mold through a conductive pad;

[0028] During operation, the metal material to be molded and the template with micro / nano structures are stacked in the cavity of the conductive mold. The pulsed current source applies a pulsed current to the conductive mold through the electrodes and conductive pads, heating the metal material to be molded to a certain temperature. T The pressurization module is used to apply a load to press the metal material to be molded at a temperature of T into the template with micro-nano structure, and after maintaining the pressure and removing the mold, the metal material with micro-nano structure is obtained.

[0029] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0030] (1) This invention employs pulsed current to control the heating and holding processes in nanomolding. Through non-thermal effects such as electromigration and electron wind induced by the current input, the diffusion rate of metal within the nanomold channels is significantly enhanced, promoting dislocation slip behavior and thus greatly improving the molding efficiency of high aspect ratio nanowires. Based on the enhancement mechanism of current-induced non-thermal effects on molding, this invention can also be applied at relatively low temperatures (T < 0.5 T m ,in T Represents absolute temperature. T m This represents the direct and controllable fabrication of refractory metal nanowires (based on the melting point temperature of the metal on an absolute temperature scale).

[0031] (2) This invention is used in conjunction with a conductive graphite mold or a hard alloy mold capable of stably bearing high pressure of 600 MPa or above, which can simultaneously apply pressure and pulse current to various metal and micro / nano structure template combinations, effectively overcoming the problem of current application caused by the insulation of some templates. In addition, the close fit between the side of the sample and the inner wall of the mold can significantly suppress the upsetting deformation of the material during the nanomolding process, ensuring the dimensional accuracy and shape integrity of the molded material body.

[0032] (3) Traditional thermomechanical nanomolding technology relies on heat conduction heating, which is easily limited to thin sheet materials due to problems such as slow heating and uneven temperature. The present invention adopts a pulsed current direct heating method, which can make the material uniformly rise to the target temperature in a very short time, realize rapid and uniform energy input, and thus break through the limitations of the size and shape of the material to be molded.

[0033] (4) By introducing pulsed current, additional driving forces such as electron wind and Joule thermal stress are excited inside the material, effectively reducing the energy barrier for dislocation slip and atomic diffusion. Compared with traditional thermomechanical nanomolding technology, this invention can increase the aspect ratio of metal nanowires by tens of times under the same temperature and pressure conditions, realizing the fabrication of micro-nano structures with ultra-high specific surface area in one step. At the same time, this invention uses an adjustable pulsed current waveform. For example, when nanomolding high-melting-point metals, a high-peak rectangular pulse is used to give stronger driving forces to atomic diffusion and dislocation movement, so that metals can be nanomolded at lower temperatures, providing a feasible path for the efficient and controllable nanomanufacturing of refractory metals.

[0034] (5) For metals that are easily oxidized, the inherent oxide film on the material surface and its growth during heating can create certain obstacles in the nanomolding process. This invention utilizes pulsed current to induce a self-cleaning effect at the interface between the template and the metal, which can dynamically remove the oxide layer, fundamentally overcoming the limitation and pollution problems of oxygen on the molding process, and ensuring high-fidelity replication of the nanostructure. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the metal micro / nanostructure fabrication device of the present invention and details of local nanomolding.

[0036] Figure 2 The Zn nanowires prepared in Example 1 of this invention.

[0037] Figure 3 Zn nanowires were prepared under the same conditions as in Example 1 using conventional thermomechanical nanomolding.

[0038] Figure 4 Zn nanowires were prepared by reducing the pulse current conduction time based on Example 1.

[0039] Figure 5 This describes the situation where the template breaks after excessively increasing the current amplitude based on Example 1.

[0040] Figure 6 The Mo nanowires prepared in Example 2 of this invention.

[0041] Figure 7 The W nanowires prepared in Example 3 of this invention.

[0042] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0043] 1-Pulse current source; 2-Vacuum chamber; 3-Electrode; 4-Conductive pad; 5-Conductive mold; 51-Punch; 52-Die; 6-Infrared temperature measurement module; 61-Infrared thermometer; 62-Infrared thermometer bracket; 7-Pressure module; 8-Template with micro-nano structure; 9-Graphite pad; 10-Metal material to be molded. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0045] In existing superplastic nanomolding technologies, to prepare high aspect ratio nanowires, a double-channel AAO template with a high melting point is typically selected from among many micro / nanostructure templates. The surface metal to be molded is then heated via heat conduction using an external heat source, which suffers from low thermal efficiency and slow response speed. This invention proposes to use electric heating instead of traditional heating methods. Electric heating can effectively overcome this limitation; however, the inherent insulating properties of the double-channel AAO template block the current path, making it difficult to apply direct and efficient electric heating to the template itself. To address this problem, this invention specifically incorporates a conductive mold in the device. The metal material to be molded and the insulating template with micro / nanostructures are stacked in the cavity of this conductive mold. The mold constructs new conductive channels, and pulsed current is used to efficiently heat the mold and the closely contacting metal material. Furthermore, a graphite sheet can be placed around the surface of the metal material to be molded, making the newly constructed conductive channels even more effective. This conductive mold design effectively solves the problem of current application caused by the template's insulation. Simultaneously, the concave-convex mating structure of the conductive mold facilitates the simultaneous application of molding pressure during heating.

[0046] Furthermore, in existing technologies, due to limitations in equipment and process conditions, nanoforming methods are generally only applicable to metallic materials with melting points below 1800 °C. This is primarily because its experimental temperature limit is approximately 900 °C. The reason for this is that current technologies mainly rely on heating a metal pressure plate, which itself has a limited melting point; surface forming or deformation may occur at temperatures around 900 °C. Although theoretically, metals with higher melting points (e.g., 3000-4000 °C) could be used to make the pressure plate to increase the operating temperature, this method is still limited by the material of the forming template—common templates fail at around 1400 °C. For high-melting-point metals such as tungsten, tantalum, and molybdenum (whose melting points are generally above 2500 °C), the required temperature for nanoforming typically needs to reach above 1400 °C. Under these conditions, not only can existing templates not withstand the heat, but even if a pressure plate with a higher melting point is used, thermal deformation is still inevitable on the surface, leading to a loss of forming accuracy. Therefore, existing nanomolding technologies are difficult to effectively process such high-melting-point metals.

[0047] Therefore, the present invention provides a general method for preparing metal micro / nano structures, which can overcome the above-mentioned technical problems. The preparation method includes the following steps:

[0048] (1) The metal material to be molded and the template with micro-nano structure are stacked in the cavity of the conductive mold; and the width of the metal material to be molded is adapted to the width of the conductive mold, so that the side of the metal material to be molded is in contact with the conductive mold;

[0049] (2) In a vacuum environment, the conductive mold is heated by a pulsed current, and then the metal material to be molded is heated to a certain temperature through heat conduction. T , of which 0.3 T m < T < T m , T Represents absolute temperature. T m This represents the melting point temperature of the metal material to be molded according to the absolute temperature scale;

[0050] (3) Apply a load to press the metal to be molded at a temperature of T into the template with micro-nano structure, maintain the pressure and remove the mold to obtain a metal material with micro-nano structure.

[0051] The metal material to be molded in this invention is mainly a metallic element or alloy with a melting point below 3600 °C in atmospheric environment. In some embodiments, the metal material to be molded is any one pure metal selected from In, Ge, Sn, Bi, Pb, Zn, Al, Cu, Au, Ag, Pt, Pd, Mo, Ta, and W, or an alloy of two or more of these elements.

[0052] While existing graphite molds can withstand extreme temperatures above 2000 °C, their mechanical strength is relatively low, typically only able to withstand pressures below 50 MPa. Conversely, cemented carbide molds, although capable of withstanding pressures of only 600 MPa, have limited temperature resistance, usually requiring temperatures below 650 °C to prevent failure. To address this difference in material properties, this invention employs a classification and matching strategy, selecting the appropriate mold type based on the melting point characteristics of the metal material to be molded, and accordingly finely controlling the pulse parameters. In setting the pulse current parameters, this invention balances heating rate and temperature control accuracy, avoiding both slow heating and low fabrication efficiency caused by excessively small current amplitudes, and preventing localized overheating or material damage caused by excessively large current amplitudes. This ensures stable fabrication of high aspect ratio micro / nano structures under different mold systems.

[0053] In some embodiments of the present invention, the conductive mold is a graphite mold or a cemented carbide mold.

[0054] The metal material to be molded in this invention is generally in sheet or block form. In order to suppress upsetting deformation of the block metal material to be molded during the surface nanowire forming process, this invention uses graphite mold or cemented carbide mold to effectively ensure the dimensional accuracy and shape integrity of the molded structure.

[0055] In some embodiments, the vacuum environment is a vacuum environment of less than or equal to 40 Pa.

[0056] In some embodiments, the temperatureT Less than or equal to 1400 ℃; and temperature T Use graphite molds or carbide molds when the temperature is less than or equal to 650 ℃. T For temperatures above 650 °C, use a graphite mold. When using a graphite mold, the applied load pressure is less than or equal to 50 MPa; when using the aforementioned cemented carbide mold, the applied load pressure is less than or equal to 600 MPa.

[0057] In some embodiments, the template with micro / nano structures is made of silicon, silicon oxide, aluminum oxide, or other inorganic oxides; when the temperature T At temperatures above 1000 °C, the template with micro-nano structures is made of alumina.

[0058] In some embodiments, the characteristic size of the micro / nano structure is 1 nm-50 µm. When the metal material to be molded is a refractory metal such as Mo, Ta, or W, the preparation temperature is below 1400 °C, and the template material is alumina.

[0059] In a preferred embodiment, the current source of the pulse current is equipped with a waveform parameter adjustment module and is programmed to adopt a stepped current control strategy. Specifically, the initial current peak value and current increase amplitude are set according to the mold type, the metal material to be molded is heated according to a preset heating rate, and after reaching the target temperature, the current decreases according to the set current amplitude, down to the current value during heat preservation, and the power is cut off and unloaded after heat preservation; so as to achieve stable heating at a preset rate and suppress local overheating.

[0060] In some embodiments, to obtain high aspect ratio micro / nano structures, it is necessary to determine the specific requirements of the metal material to be molded. T m Select the appropriate mold type and pulse current parameters. The specific process parameters are configured as follows:

[0061] like T m At temperatures below 300 ℃, to apply higher pressure, it is preferable to select a cemented carbide mold, such as the YG series cemented carbide mold. The pulse waveform is preferably a trapezoidal pulse. The pulse current rise time and fall time are set to 2-5 ms, the pulse current flat-top holding time is 10-15 ms, and the pulse interval is 10-15 ms to achieve flexible heating.

[0062] When 300 ℃ ≤ T m For temperatures ≤ 1800 ℃, graphite molds or cemented carbide molds can be used (depending on the actual temperature). T (Confirmed), preferably a rectangular pulse, pulse width ( t on ) and pulse interval ( toff The duty cycle of the pulse is set to (5-7):1, where the pulse width is 20-80 ms.

[0063] when T m When the temperature is >1800℃, a graphite mold is selected. The pulse waveform is preferably a rectangular pulse. The duty cycle of the pulse width and the pulse interval is set to (5-7):1, where the pulse width is 40-160 ms.

[0064] In some embodiments, the pulse current source employs a stepped current regulation strategy, specifically:

[0065] When using graphite molds, a proportionality coefficient is set to meet the preset heating rate requirement of 50-200 ℃ / min. , No. The current is set at the minute:

[0066]

[0067] The equilibrium current after reaching the target temperature, i.e., the current during heat preservation, is as follows:

[0068]

[0069] in This is the initial peak current. ;

[0070] To increase the amplitude of the current, ;

[0071] This is the current value when the target temperature is reached;

[0072] To reduce the amplitude of the current, ;

[0073] The inner diameter of the mold is in mm, and the outer diameter is... The proportionality coefficient ;

[0074] When using carbide molds, if the pressure is less than 200 MPa, a current increment correction value is set to meet the preset heating rate requirement of 50-100 ℃ / min. The unit is A, the first The current is set at the minute:

[0075]

[0076] The equilibrium current after reaching the target temperature, i.e., the current during heat preservation, is as follows:

[0077]

[0078] in This is the initial peak current. ;

[0079] To increase the amplitude of the current, ;

[0080] To prevent severe overheating at the contact point between the die and punch, which could lead to localized upsetting of the punch, the maximum allowable current value is specified. (Priority should be given to protecting the mold, rather than pursuing a stable heating rate).

[0081] This is the current value when the target temperature is reached;

[0082] To reduce the amplitude of the current, ;

[0083] The inner diameter of the mold is in mm; its outer diameter is... , For mold wall thickness, The unit is mm. 。

[0084] When using carbide molds, the suitable metal forming temperature is less than or equal to 650 ℃. To prevent these bulk metals from undergoing severe plastic flow due to overheating under extremely high pressure, which could damage the mold, the heating rate can be slowed down to reduce the degree of overheating. For example, if the pressure is greater than 200 MPa, to avoid severe plastic deformation of the material due to severe local overheating, the preset heating rate should be less than 50 ℃ / min, and the current should be increased accordingly. The upper limit should also be reduced at this time. For metals with melting points below 300 °C, the preset heating rate value should be further reduced. The remaining parameters remain unchanged.

[0085] After the current value drops to the holding current value, theoretically, the longer the holding time, the longer the nanowires will be. In a preferred embodiment, the holding time is not less than 30 s, for example, 30-600 s.

[0086] This invention also provides an apparatus for preparing metal micro / nano structures using the aforementioned general preparation method, also known as an electrically assisted nanomolding device, such as... Figure 1 As shown, it includes a pulse current source 1, a vacuum chamber 2, electrodes 3, conductive pads 4, a conductive mold 5, an infrared temperature measurement module 6, and a pressurization module 7;

[0087] The pulse current source 1 is connected to the electrode 3, the conductive mold 5 is placed in the vacuum chamber 2, and the electrode 3 is electrically connected to the conductive mold 5 through the conductive pad 4; the conductive pad 4 can prevent heat concentration on the electrode and also avoid pressure concentration on the electrode.

[0088] During operation, the metal material 10 to be molded and the template 8 with micro-nano structures are stacked in the cavity of the conductive mold 5. The pulsed current source 1 applies a pulsed current to the conductive mold 5 through the electrode 3 and the conductive pad 4 to heat the metal material to be molded to a certain temperature. T The pressurization module 7 is used to apply a load to press the metal to be molded at a temperature of T into the template 8 with micro-nano structure, and after holding the pressure and removing the mold, a metal material with micro-nano structure is obtained.

[0089] In some embodiments, the conductive pad 4 is made of graphite or hard alloy.

[0090] The conductive mold 5 includes a punch 51 and a die 52, and the infrared temperature measurement module 6 includes an infrared thermometer 61 and an infrared thermometer bracket 62.

[0091] In some embodiments, a graphite gasket 9 is also provided between the template 8 with micro-nano structure and the cavity wall of the conductive mold 5 to facilitate demolding.

[0092] Furthermore, the inherent oxide film on easily oxidized metal surfaces and its regrowth during heating pose certain obstacles to the nanomolding process. Traditional mechanical nanomolding techniques typically require meticulous pre-treatment steps such as grinding, polishing, or even chemical treatment (e.g., acid pickling) to remove this oxide film, especially to avoid "secondary oxidation" between processes. This invention cleverly utilizes the unique "self-cleaning" effect of pulsed current, allowing for nanomolding after only simple polishing without concerns about secondary oxidation. It also enables the preparation of multiple samples at once, greatly simplifying the process.

[0093] The principle of this invention is as follows: During the nanomolding process, by introducing pulsed current assistance, the migration and diffusion capabilities of atoms and defects (such as dislocations) within the metal or metal alloy are enhanced, thereby significantly improving the replication efficiency and molding accuracy of the mold structure at the micro- and nano-scale. Without loss of generality, taking a mold with columnar nanopores as an example, denoted as d, we consider the length L of the metal or metal alloy material pressed into the pore under constant stress. Clearly, L can be generally expressed as a function of temperature T, constant stress σ, pore diameter d, time t, and current density J.

[0094]

[0095] Applying the classic Norton-Bailey power law, neglecting the current, we have:

[0096]

[0097] Considering the coupling effect of current, phenomenological models that introduce the current density variable include:

[0098]

[0099] Here, L0 represents the length of material that can flow into the pore under a constant stress σ, which generally depends on the pore size, temperature, and constant stress value; the constant A depends on temperature, pore size, and the mechanical parameters of the material; and the constant α depends on resistivity, dislocation density, charge, and electron concentration. Therefore, under the same temperature and pressure conditions, applying a pulsed current can significantly increase the forming length of metal nanowires. Simultaneously, the introduction of current enables the efficient fabrication of high aspect ratio nanostructures even under lower temperature and lower stress conditions.

[0100] This invention discloses a highly efficient method for fabricating universal metal micro / nano structures. The method employs pulsed current-assisted nanomolding technology, using either a graphite mold or a hard alloy mold capable of stably withstanding 600 MPa high pressure. Pressure and pulsed current are simultaneously applied to the metal and a template with micro / nano structures. Under preset process conditions, the metal material rapidly fills the micro / nano pores in the template under the synergistic effect of current and pressure, thereby accurately replicating the structural pattern in the mold. The main advantages of this invention are that the use of a mold simply solves the technical problem of applying current directly to the sample, bypassing an insulating template (such as alumina), under high pressure. Furthermore, the sample adheres tightly to the designed inner wall of the mold, preventing lateral flow under high pressure and suppressing upsetting deformation of the material during the molding process. The non-thermal effects such as electromigration and electron wind introduced by the pulsed current provide additional driving force for atomic diffusion and dislocation movement, significantly improving the efficiency of micro / nano molding. Compared to traditional thermomechanical nanomolding, this invention eliminates the dependence on thin sheet materials, making it suitable for the fabrication of micro / nano structures on the surface of bulk materials. Furthermore, the growth rate of metal nanowires is significantly improved in this invention; under the same temperature and pressure conditions, the aspect ratio of nanowires fabricated on metal surfaces with fewer slip systems can be increased by tens of times. Simultaneously, by utilizing pulsed current to induce a self-cleaning effect at the template-metal interface, the oxide layer can be dynamically removed, fundamentally overcoming the limitations and contamination problems caused by oxygen in the molding process, ensuring high-fidelity replication of nanostructures. In addition, this invention can be applied at relatively low temperatures (… T <0.5 T m This technology enables the direct and controllable forming of nanostructures from refractory metals, expanding the material applicability and process window of nanomolding technology.

[0101] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0102] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0103] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0104] The embodiments of this application are described below with reference to the accompanying drawings.

[0105] Example 1

[0106] 1) Take a Zn block with a diameter of 10 mm and a thickness of 2 mm as the metal material to be molded, and place it together with an AAO template (anodic aluminum oxide template) with a pore size of 200-300 nm in the cavity of a cemented carbide conductive mold.

[0107] 2) Place the assembled cemented carbide mold (YG6) (mold inner diameter D is 10 mm, outer diameter is 40 mm) into an electrically assisted nanomolding device ( Figure 1 In the process, a vacuum is drawn down to below 40 Pa, and a pressure of 23.5 kN is applied. After the vacuum level reaches below 40 Pa, a rectangular pulse is set. t on 40 ms t off The initial peak current was set to 300 A, and then increased by 200 A per minute to control the heating rate at 50-100 ℃ / min, reaching the target temperature of 250 ℃ (0.6 ms) in about 5 minutes. T m Then, reduce the current to about 750 A (the current reduction is 150 A), keep it warm for 100 seconds, and then quickly disconnect the power and unload the load.

[0108] 3) The sample was removed, and the aspect ratio of the prepared Zn nanowires was approximately 38 ( ). Figure 2 ).

[0109] As a representative of low-melting-point metals with fewer slip systems, in conventional thermomechanical nanomolding techniques, at the same heating rate, at 0.6... T mThe aspect ratio of Zn nanowires prepared at 200 MPa is only about 1. Figure 3 The result is far lower than that of this embodiment.

[0110] Comparative Example 1

[0111] This embodiment is basically the same as embodiment 1, except that in step 2... t on Reducing the heating time to 20 ms decreases the heating rate to approximately 10 °C / min, requiring 25-30 min to reach the target temperature. The resulting Zn nanowires have an aspect ratio of approximately 15. Figure 4 The preparation efficiency is greatly reduced.

[0112] Comparative Example 2

[0113] This embodiment is basically the same as embodiment 1, except that in step 2, without adjusting the On and Off times of the pulse current, if the original increase of 200 A per minute is changed to an increase of 350 A per minute, severe local overheating will occur, forcing the template to crack due to uneven stress. Figure 5 ).

[0114] Example 2

[0115] 1) Take a Mo block with a diameter of 10 mm and a thickness of 2 mm as the metal material to be molded, and place it together with an AAO template with a pore size of about 160-200 nm in the cavity of the graphite conductive mold.

[0116] 2) Place the assembled graphite conductive mold (inner diameter D is 10 mm, outer diameter is 30 mm) into an electro-assisted nanomolding device. Figure 1 In the process, a vacuum is drawn and a pressure of 3.9 kN is applied. After the vacuum level reaches below 40 Pa, a rectangular pulse is set. t on 40 ms t off (7 ms), the initial current is set to 150 A, and then 100 A is added per minute to control the heating rate of 150 ℃ / min until the target temperature of 1200 ℃ is reached. Then the current is reduced to 900 A (the current reduction is 50 A), the temperature is held for 300 s, and then the power is quickly cut off and the load is unloaded.

[0117] 3) The sample was removed and successfully measured at 0.45. T m Refractory metal Mo nanowires with an aspect ratio of approximately 7 were prepared at a specific temperature. Figure 6 ).

[0118] Example 3

[0119] 1) Take a W block with a diameter of 10 mm and a thickness of 2 mm, and place it together with an AAO template with a pore size of about 160-200 nm in a graphite mold;

[0120] 2) Place the assembled graphite mold (inner diameter D = 10mm, outer diameter = 30mm) into the electrically assisted nanomolding equipment. Figure 1 In the process, a vacuum is drawn and a pressure of 3.9 kN is applied. After the vacuum level reaches below 40 Pa, a rectangular pulse is set. t on 40 ms t off (7 ms), the initial current is set to 150 A, and then 100 A is added per minute to control the heating rate of 150 ℃ / min until the target temperature of 1300 ℃ is reached. Then the current is reduced to 980 A (the current reduction is 70 A), the temperature is held for 600 s, and then the power is quickly cut off and the load is unloaded.

[0121] 3) The sample was removed and successfully measured at 0.38. T m Refractory metal W nanowires with an aspect ratio of approximately 5 were prepared at a specific temperature. Figure 7 This is something that conventional thermomechanical nanomolding technology cannot achieve.

[0122] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A general method for preparing metal micro- and nano-structures, characterized in that, Includes the following steps: (1) The metal material to be molded and the template with micro-nano structure are stacked in the cavity of the conductive mold; and the width of the metal material to be molded and the width of the conductive mold are adapted to each other, so that the side of the metal material to be molded is in contact with the conductive mold; (2) In a vacuum environment, the conductive mold is heated by a pulsed current, and then the metal material to be molded is heated to a certain temperature through heat conduction. T , of which 0.3 T m < T < T m , T Represents absolute temperature. T m This represents the melting point temperature of the metal material to be molded according to the absolute temperature scale; (3) Apply a load to bring the temperature to a certain level. T The metal material to be molded is pressed into the template with micro-nano structure, and after holding the pressure and removing the mold, the metal material with micro-nano structure is obtained. The metal material to be molded is a metallic element or alloy with a melting point below 3600℃ in atmospheric environment; the conductive mold is a graphite mold or a cemented carbide mold. the temperature T less than or equal to 1400 °C; according to the metal material to be molded T m The mold type and pulse current parameters are selected and adapted, and the specific process parameter configuration is as follows: When T m When the temperature is less than 300 ℃, a hard alloy die is selected, a trapezoidal pulse is used as the pulse waveform, the pulse current rise time and fall time are set to 2-5 ms, the pulse current flat top holding time is 10-15 ms, and the pulse interval is 10-15 ms to realize flexible heating. When 300 ℃ ≤ T m ≤ 1800 ℃, a graphite mold or a hard alloy mold is selected, a pulse waveform is a rectangular pulse, and a duty cycle of a pulse width and a pulse interval is set to (5-7):1, wherein the pulse width is 20-80 ms. When T m At 1800 °C, a graphite mold was used, the pulse waveform was a rectangular pulse, and the duty ratio of the pulse width to the pulse interval was set to (5-7): 1, wherein the pulse width was 40-160 ms.

2. The general preparation method according to claim 1, characterized in that, The vacuum environment is a vacuum environment less than or equal to 40 Pa.

3. The general preparation method according to claim 1, wherein, When using the graphite mold, the applied load pressure is less than or equal to 50 MPa; when using the cemented carbide mold, the applied load pressure is less than or equal to 600 MPa.

4. The general preparation method according to claim 1, wherein, The template with micro / nano structures is made of silicon, silicon oxide, or aluminum oxide.

5. The production method according to claim 1, wherein The pulse current source is equipped with a waveform parameter adjustment module and adopts a stepped current control strategy. Specifically, the initial current peak value and current increase amplitude are set according to the mold type, the metal material to be molded is heated according to the preset heating rate, and after reaching the target temperature, the current value is reduced to the current value during heat preservation. After heat preservation, the power is cut off and the current is unloaded, so as to achieve stable heating according to the preset heating rate and suppress local overheating.

6. The general preparation method according to claim 5, wherein, The pulse current source employs a stepped current regulation strategy, specifically: When the graphite mold is used, the preset heating rate is 50-200 ℃ / min, and a proportional coefficient is set , the current is set at min The equilibrium current after reaching the target temperature, i.e., the current value during heat preservation, is: wherein is the initial current peak value, ; to increase the amplitude of the current, ; Iup the current value when the target temperature is reached; reducing the magnitude of the current, ; Dinner is the inner diameter of the mold, in mm, and Douter is the outer diameter where the proportionality factor is ; When the hard alloy die is used, if the pressure is less than 200 MPa, the preset heating rate is 50-100 ℃ / min, the current increment correction value is set , unit: A, the current is set at the first minute . The equilibrium current after reaching the target temperature, i.e., the current during heat preservation, is as follows: wherein is the initial current peak value, ; to increase the amplitude of the current, ; to allow the maximum current value to be applied, ; Iup the current value when the target temperature is reached; reducing the magnitude of the current, ; is the inner diameter of the mold in mm; its outer diameter is , is the wall thickness of the mold, in mm; When using a cemented carbide die, if the pressure is greater than 200 MPa, the preset heating rate is less than 50 ℃ / min, and the current increase amplitude ; for metals with a melting point lower than 300 ℃, .

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