CN113634743B

CN113634743B - Ostwald nano welding method

Info

Publication number: CN113634743B
Application number: CN202110890827.4A
Authority: CN
Inventors: 胡家文; 李末霞; 段曦东; 徐姚梦丽; 刘炳武
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2021-08-04
Filing date: 2021-08-04
Publication date: 2022-08-26
Anticipated expiration: 2041-08-04
Also published as: CN113634743A

Abstract

The invention belongs to the field of nano welding, and particularly discloses an Oerstwald nano welding method, which is used for carrying out surface electronic localization treatment on a metal nanoparticle film to be treated so as to strengthen the Oerstwald nano welding. The method has mild and controllable conditions, can efficiently realize nano welding, and has excellent performances of conductivity, electrochemical sensing and the like of the nano film obtained by welding and good application prospect.

Description

Ostwald nano welding method

Technical Field

The invention relates to the technical field of nano film materials, in particular to a method for welding a nano film material by Ostwald nano welding with the advantages of external field strengthening, low temperature, solution-diffusion, mildness and controllable speed.

Background

Nano-soldering is one of the key technologies for manufacturing single, independent nano-materials with unique size, morphology, composition and lattice orientation into functional units, elements and nano-devices. Based on nano-soldering, good solid phase interconnections can be created between the nanomaterials themselves or between them and the external environment, while not damaging the morphology of the nanomaterials themselves. The method can not only improve the conductivity and mechanical flexibility of the nano material, increase the electrocatalytic active sites, reduce the contact resistance of the contact points, but also generate rectification characteristic in the metal-semiconductor heterojunction. Based on the above characteristics of the nano-welding technology, nano-welding has been widely applied in the fields of nano-devices, electrocatalysis, nano-sensing, surface raman enhanced substrates, electronic packaging, and the like.

The existing relatively mature methods of nano welding are heat welding, joule heat welding, pressure welding, electron beam welding, plasma welding, ultrasonic welding, chemical welding, etc. However, these welding methods either have the potential to damage the original morphology of the nanomaterials being welded, or require expensive operating equipment, special welding environments, as they typically require high energy inputs to achieve the "solid-liquid-solid" phase transformation process. In particular, the thermal welding process, which requires high temperature, has a high possibility of damaging the morphology and structure of the nanomaterial being welded and the flexible substrate supporting the nanomaterial, which greatly limits the application of thermal welding to flexible electronic devices.

On the other hand, ostwald ripening is a surface energy driven, usually occurring in solution, characterized by large particle growth at the expense of small particles. Furthermore, some prior reports have shown that ostwald ripening can weld nanoparticles with nanogaps together, i.e., achieve ostwald nano-welding in solution. However, the mechanism of the welding is not fully explained, and the ostwald ripening itself is a very slow (requiring tens or even hundreds of hours) process, which greatly limits the application of ostwald ripening to practical welding.

Disclosure of Invention

The first purpose of the invention is to provide an Ostwald nano-welding method with external field strengthening, low temperature, solution-diffusion, mildness and controllable speed; aims to provide a rapid and practical low-temperature nano welding method.

The second purpose of the invention is to provide the membrane material prepared by the nano welding method.

The third purpose of the invention is to provide the application of the membrane material prepared by the nano welding method in preparing at least one device of optics, electricity, electrochemistry and sensing.

A method for Ostwald nano welding, which carries out surface electronic localization treatment on a metal nanoparticle film to be treated, thereby strengthening Ostwald nano welding.

The invention innovatively discovers that the localized treatment of the surface electrons of the metal nano particles can strengthen the Ostwald nano welding effect, can realize high-efficiency nano welding under mild and controllable conditions, and can improve the performance of the nano welding material.

In the preferred scheme of the invention, the metal nanoparticle film to be treated is placed in an aqueous solution, and the electronic localization of the surface of the metal nanoparticles is induced under the electric strengthening, so that the Ostwald nano welding is strengthened.

The research of the invention finds that the surface electron localization of the metal nano particles can be effectively induced under the electric strengthening, and the Ostwald nano welding effect can be strengthened.

In the invention, the electricity is at least one of direct current electricity and alternating square wave pulse electricity (alternating current).

In the present invention, the intensity of the applied electricity is less than or equal to the intensity of the electrolysis of water;

preferably, the current intensity of the direct current is 10-70 mA; for example, 10, 25, 50, 55, 70 mA.

Preferably, the pulse frequency of the alternating square wave pulse electricity is 0.01-5000 Hz; for example, 0.01, 1, 50, 500, 5000 Hz.

The aqueous solution is preferably pure water or an electrolyte aqueous solution with the concentration less than or equal to 1M, preferably 0.25-1M;

preferably, the electrolyte is a compound capable of maintaining a stable phase under electric strengthening, and does not react with metal nano-ions chemically and electrochemically; preferably NaClO ₄ 。

The metal nanoparticle film provided by the invention meets the common requirements in the field of nano welding. For example, the metal nanoparticle film is a nano film formed by adjacent metal nanoparticles. The size of the metal nano-particles is 4-250nm, and preferably 20-100 nm. The gaps among the metal nano particles are less than or equal to 10 nm;

the metal nanoparticle film may be prepared based on an existing method, for example, by preparing an aqueous suspension in which metal nanoparticles are dispersed in advance, mixing the aqueous suspension with a hydrophobic solvent, performing self-assembly (interfacial rearrangement) of the metal particles at a water-hydrophobic solvent interface, and collecting a metal nanoparticle layer obtained by the interfacial self-assembly, i.e., the metal nanoparticle film.

Preferably, the metal nanoparticles are at least one of gold, silver, palladium and platinum.

The substrate used to support the metal nanoparticle film to be treated is a non-conductive substrate, preferably a non-conductive glass substrate.

In the present invention, the time of the surface electron localization treatment can be adjusted according to the application requirements of the material, for example, the time of the surface electron localization treatment is less than or equal to 60 min.

The invention also provides an Ostwald nano welding film prepared by the method.

The invention also provides an application of the Ostwald nano-welding film in at least one device of optics, electrics, electrochemistry and sensing.

Has the advantages that:

1. the invention discovers for the first time that the Ostwald nano-welding effect can be effectively improved by carrying out surface electronic localization treatment on metal nano-particles, for example, nano-welding can be efficiently realized under mild and controllable conditions, and the method is also beneficial to improving the performance of a film material obtained by welding.

2. The Ostwald nano welding method adopted in the invention is a spontaneous and mild process based on Ostwald ripening, which not only can effectively reduce the damage to the original shape and structure of the welded nano material and the substrate material, the equipment cost and the requirement on the welding environment, but also does not need to input high energy to realize the solid-liquid-solid phase state conversion process. However, the oswald nano welding process is a very slow process, so the invention can strengthen the oswald nano welding process by an external field induced surface electron localization treatment means, flexibly regulate and control the welding efficiency and speed, thereby realizing the method for welding the nano film material by the oswald nano welding with external field strengthening, low temperature, solution-diffusion, mildness and controllable speed.

3. The method is simple, effective, rapid, strong in adjustability and wide in application range, can be widely applied to welding of the conductive nano material, and can be operated under the conditions of atmospheric environment, room temperature, pure water or low-concentration electrolyte solution.

4. The Au particle (NP) film prepared by the method has good conductivity, a plurality of electrochemical active sites and a plurality of surface plasmon active hot spots, so the Au particle (NP) film has good application prospect in the fields of nano devices, electrocatalysis, nano sensing, surface Raman enhancement and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the technical solutions in the prior art will be briefly described below.

FIG. 1: the preparation process schematic diagram and the morphology characterization of the Au NP thin film are shown.

Wherein, in fig. 1, a is a schematic diagram of the interface self-assembly and transfer of Au NP to the supporting substrate and its nano-soldering in the homemade nano-soldering apparatus; b is a digital photo of the Au NP film obtained by interface self-assembly; c is an optical photograph of the Au NP film obtained by interface self-assembly under an optical microscope; d is a Scanning Electron Microscope (SEM) image of the Au NP film obtained by interface self-assembly; and e is a Transmission Electron Microscope (TEM) image of the Au NP thin film obtained by interfacial self-assembly.

FIG. 2 shows the electrical and morphological characteristics of Au NP thin film on glass substrate under the condition of direct current and alternating current pulse electrically enhanced Ostwald nano welding.

Wherein, in FIG. 2, a is the change of the relative resistance change rate of the Au NP film in pure water under different DC intensities along with the continuous energization time; c. d and e are SEM images of the Au NP film after being welded for 60min under the direct current strength of 10 mA, 55 mA and 70mA respectively; b is the change of the relative resistance change rate of the Au NP film in pure water under the alternating current intensity of 70mA along with the continuous electrifying time under different pulse frequencies; f. g and h are SEM images of the Au NP thin film after welding for 60min at pulse frequencies of 1Hz, 50Hz and 5000Hz respectively.

FIG. 3 is an electrical and morphological characterization of Au NP films on different substrates or under direct current enhanced Ostwald nano-welding conditions in an atmosphere of electrolytic concentration.

In fig. 3, a is the change of the relative resistance change rate on different substrates with the continuous energization time of the Au NP thin film in a pure water atmosphere at a current intensity of 70 mA; c. d and e are SEM images of the Au NP film welded on the Au substrate, the FTO substrate and the glass substrate for 60min in a pure water atmosphere; b is Au NP film under the current intensity of 70mAOn a glass substrate, NaClO at different concentrations ₄ The change in the relative rate of resistance change in the atmosphere of the solution with the duration of energization; f. g and h are respectively 1.0, 0.25 and 0M NaClO of Au NP thin film ₄ SEM characterization after 60min soldering in an atmosphere of solution. c-h, shows the Au NP thin film and the solid substrate or NaClO under the corresponding conditions ₄ Equivalent circuit diagram between solutions.

FIG. 4 is a morphology and electrochemical characterization of an interdigital electrode made of an Au NP thin film after welding of alternating current pulse electrically enhanced Ostwald nano for 60 min;

wherein, in fig. 4, a is an SEM representation of an unwelded gold NP thin film; b is an SEM picture after welding for 60min by an Alternating Current (AC) of 70mA and 50Hz, and an inset is a digital picture of the manufactured interdigital electrode; c is the commercial interdigital electrode, the interdigital electrode which is not welded and is welded at 5mM K ₄ Fe(CN) ₆ +5mM K ₃ Fe(CN) ₆ The sweep rate of the cyclic voltammogram in a PBS buffer solution (pH 7.4) was 10 mV/s.

FIG. 5 is a schematic representation of Ostwald ripening, conventional thermodynamic Ostwald nano-welding and external field enhanced Ostwald nano-welding and a schematic representation of equilibrium electrode potential versus surface charge density for metal nanoparticles;

wherein, in FIG. 5, A is a schematic diagram of a classical Ostwald ripening; b is a traditional thermodynamic Ostwald nano welding schematic diagram; c is a direct current reinforced Ostwald nano welding schematic diagram; d is a schematic diagram of alternating current reinforced Ostwald nano welding; e, connection schematic diagram of the metal nanoparticles after welding; f is a relationship diagram of the balance electrode potential of the single metal nano-particle and the surface charge density thereof described according to the formula (2).

Detailed description of the preferred embodiments

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The method provided by the invention is characterized in that 50nm gold nanoparticles (Au NP) obtained by a classical Frens method (namely, gold chloride acid is reduced in an environment with trisodium citrate as a stabilizing agent and a reducing agent) are assembled into a compact Au NP film by an interface self-assembly method, and then Ostwald nano welding with external field strengthening, low temperature, solution-diffusion, mildness and controllable speed is carried out, so that the original shape and structure of the welded Au NP are prevented from being damaged, and the conductivity and the electrocatalytic activity of the Au NP film are enhanced.

The specific steps of the method can be referred to as follows:

(a) the concentration of the Au NP dispersion obtained by the Frens method was about 57.91. mu.g of NPs/mL;

wherein, the solvent for dispersing the Au NP is water, and the stabilizer is trisodium citrate added before the synthesis reaction.

(b) Assembling Au NP into a compact Au NP film by adopting an interface self-assembly mode, transferring the Au NP film to a glass substrate with two ends respectively plated with 2 multiplied by 3mm gold electrodes, wherein the middle exposed size is 2 multiplied by 4mm, and the actual total size is 2 multiplied by 10mm, and naturally drying to obtain the compact Au NP film;

preferably, the main details of interfacial self-assembly are that the prepared 20mL Au NP dispersion is first placed in a 50mL beaker; followed by the addition of about 5mL of cyclohexane to form a clear water-oil interface; then, 5mL of ethanol is injected quickly to initiate the Au NP to self-assemble into a compact Au NP film on a water-oil interface; finally, cyclohexane on the upper layer of the Au NP film on the water-oil interface was removed and the Au NP film was transferred onto a corresponding solid substrate (e.g., a glass substrate).

The Au NP thin film formed in the above way is the object to be welded in the invention.

(c) The Au NP thin film prepared as above was placed in a welding apparatus to perform dc and ac pulse electric welding, and the resistance of the gold film during the welding was measured and recorded with a precision test power supply B2912A (Keysight, United States), and then the change of the relative resistance change rate with the welding time was calculated.

Preferably, in the direct current welding process, the direct current intensity is 10 mA, 25 mA, 40 mA, 55 mA and 70mA, and the welding effect and the welding rate of the Au NP film are adjusted by adjusting the current intensity.

Preferably, in the direct current welding process, the fixed input current intensity is 70mA, and the welding effect of the Au NP film is adjusted by adjusting the conductivity of the substrate material, namely a vacuum evaporation 50nm thick gold film substrate, an FTO substrate and a glass substrate.

Preferably, in the direct current welding process, the fixed input current intensity is 70mA, and NaClO with the concentration of 1.0, 0.75, 0.5, 0.25 and 0mol/L is respectively adopted by adjusting the concentration of the electrolyte solution in the atmosphere of the Au NP film ₄ And adjusting the welding effect of the Au NP film by using the solution.

Preferably, in the process of the AC pulse electric welding, the intensity of the fixedly input current is 70mA, and the welding effect of the Au NP film is adjusted by adjusting the frequency of the AC pulse electricity, wherein the AC current with the pulse frequency of 0.01, 1, 50, 500 and 5000Hz is respectively adopted.

Preferably, the welding time of the Au NP film is 0-60min both in direct current and alternating current pulse electric welding.

Example 1

The interfacial self-assembly and transfer of Au NPs were performed as follows:

step 1: the prepared 20mL Au NP dispersion was placed in a 50mL beaker, followed by the addition of about 5mL cyclohexane to form a clear water-oil interface.

Step 2: and (3) rapidly injecting 5mL of ethanol to trigger the Au NP to self-assemble into a compact Au NP film at the water-oil interface, then removing cyclohexane on the upper layer of the Au NP film on the water-oil interface, transferring the Au NP film to a corresponding substrate, and naturally drying.

The interfacial self-assembly and transfer of Au NPs in example 1, the schematic diagram of their nano-soldering in the homemade nano-soldering device, and the morphological characterization of the Au NP thin film obtained by assembly are shown in fig. 1.

Au NP films described in the following cases were prepared by the methods of this case, unless otherwise stated.

Example 2

The direct current enhanced oswald nano welding of the Au NP thin film under different current intensities was performed as follows:

step 1: the precision test power supply B2912A is used to set parameters corresponding to the current intensities outputted.

Step 2: and placing the Au NP thin film transferred to the glass substrate into a welding device, welding the Au NP thin film for 0-60min in a pure water atmosphere under the conditions that the current intensity is 10 mA, 25 mA, 40 mA, 55 mA and 70mA respectively, and monitoring the resistance change of the Au NP thin film in the welding process in real time.

And step 3: and according to the rule that the resistance changes along with time, selectively taking the Au NP thin film welded under various conditions, and carrying out shape representation.

In example 2, please refer to fig. 2, which shows the relative resistance change rate of the Au NP film with respect to the bonding time under different current intensity conditions during the enhanced oswald nano-bonding process under different current intensity conditions, and the related SEM characterization chart.

Example 3

The ac-enhanced oswald nano-soldering of the Au NP film was performed at different ac pulse frequencies as follows:

step 1: the fixed current intensity was 70mA and different ac pulse frequencies were set.

Step 2: and placing the Au NP thin film transferred to the glass substrate into a welding device, welding the Au NP thin film for 0-60min in a pure water atmosphere under the conditions that the alternating current pulse frequency is 0.01 Hz, 1Hz, 50Hz, 500 Hz and 5000Hz respectively, and monitoring the resistance change of the Au NP thin film in the welding process in real time.

In example 3, please refer to fig. 2, which shows the relative resistance change rate of the Au NP film with respect to the bonding time under different current intensity conditions during the ac-enhanced oswald nano-bonding process under different ac pulse frequencies, and the related SEM images.

Example 4

The Au NP film is subjected to direct current enhanced Ostwald nano welding on substrates with different conductive capacities according to the following method:

step 1: the Au NP films were transferred to a gold film substrate (i.e., a vacuum-evaporated 50nm thick gold film substrate), an FTO substrate, and a glass substrate, respectively.

Step 2: and respectively placing the Au NP films transferred to different substrates into a welding device, welding the Au NP films for 0-60min in a pure water atmosphere under the direct current condition of 70mA current intensity, and monitoring the resistance change of the Au NP films in the welding process in real time.

In example 4, the dc enhanced oswald nano-soldering is performed on substrates with different conductive capabilities, and the curve of the relative resistance change rate of the Au NP film on the substrate with different conductive capabilities with the soldering time, the related SEM characterization chart, and the corresponding equivalent circuit diagram are shown in fig. 3.

Example 5

NaClO was applied to Au NP thin films at different concentrations as follows ₄ D, direct current enhanced Ostwald nano welding under the electrolyte solution atmosphere condition:

step 1: NaClO with the preparation concentrations of 1.0, 0.75, 0.5, 0.25 and 0mol/L respectively ₄ An electrolyte solution.

Step 2: the Au NP thin film transferred onto the glass substrate was placed in a soldering apparatus and subjected to NaClO treatment at different concentrations ₄ And in the electrolyte solution atmosphere, welding the Au NP film for 0-60min under the direct current condition with the current intensity of 70mA, and monitoring the resistance change of the Au NP film in the welding process in real time.

And 3, step 3: and according to the rule that the resistance changes along with time, selectively taking the Au NP thin film welded under various conditions, and carrying out shape representation.

Example 6

In example 3, the Au NP thin films before and after soldering were used as experimental materials to perform characterization of the electrical, scanning electron microscope, electrocatalytic properties, and the formed interdigital electrode, and the results are shown in fig. 4.

As can be seen from the curve of the relative resistance change rate with the duration of the soldering process in fig. 2, the relative resistance change rate of the Au NP thin film increases with the duration of the soldering process at all frequencies at the same current intensity (fig. 2 b); under the same current intensity and the same welding duration, the relative resistance change rate of the Au NP film is firstly increased along with the increase of the frequency, is reduced along with the increase of the frequency after the frequency is more than 50Hz, and is even smaller than that after the Au NP film is welded under the direct current condition with the same current intensity after the frequency reaches 5000Hz (figure 2b), and the rule can be obtained from SEM pictures after welding for 60min under the frequencies of 1Hz, 50Hz and 5000Hz (figures 2 f-h).

From the SEM comparison results of fig. 4, it is understood that Au nanoparticles in the Au NP thin film (Au NP thin film before bonding) not subjected to the ac pulse bonding are independent of each other, are not connected, and have a certain nanogap (fig. 4 a); the Au nanoparticles in the Au NP thin film after the welding treatment are mutually connected to form a mutually communicated porous network structure (figure 4 b); the experimental results further microscopically verify that the reduction of the resistance of the Au NP thin film after the soldering process is due to the formation of solid-state connections between isolated Au nanoparticles, thereby enhancing the electron transport properties of the Au NP thin film.

As can be seen from the cyclic voltammogram of FIG. 4, the cyclic voltammogram of the interdigital electrode made of the Au NP thin film after soldering had a pair of distinct oxidation peaks and reduction peaks, which were assigned to Fe (CN) ₆ ^3-/4- Redox reaction of redox couple on the surface of Au NP thin film (Fe (CN)) ₆ ^3- +e ^- ＝Fe(CN) ₆ ^4- ) And the redox peak of the interdigital electrode made of the Au NP thin film which is not welded is sharply weakened(FIG. 4 c). This data demonstrates that the gaps between Au nanoparticles in the unsoldered Au NP film inhibit the transport of electrons on the surface of the Au NP film, and thus the Fe (CN) ₆ ^3-/4- And (3) carrying out redox reaction on the surface of the Au NP thin film by using a redox couple.

As can be seen from the schematic diagram of the welding mechanism in fig. 5, in the classical ostwald ripening process (fig. 5A), large particles grow gradually while small particles coexist, and the small particles become smaller until disappear, thereby resulting in a decrease in the total surface energy of the system. One potential precursor to this classical ostwald ripening is that the ability of large particles to grow gradually relies essentially on the macroscopic inter-particle spacing to provide sufficient free growth space. Once the inter-particle spacing is reduced to nano-spacing, the ostwald ripening-driven particle growth is confined to a very limited space; at this time, even minute grain growth easily fills and solidifies the nano-pitch, resulting in spontaneous thermodynamic oswald nano-welding (fig. 5B). However, Ostwald ripening is itself a very slow thermodynamic process, and thus the rate of spontaneous Ostwald nano-welding is thermodynamically limited. To address this issue, the present invention develops an external field enhanced oswald nano-welding strategy (fig. 5C and 5D) and further proposes an electronic localization mechanism to understand it. As shown in fig. 5C and 5D, since the metal particles themselves have better electrical conductivity, when two particles are adjacent to each other (at a nano-scale interval) to constitute a dimeric conductor, the resistance of the conductor is mainly derived from the contact resistance between the particles. When current flows, the voltage drop distributed at the higher place of the resistance of the dimer conductor is larger according to ohm's law; from the viewpoint of electron density, the higher the resistance, the higher the electron density is concentrated. Thus, when a current is passed through the Au NP thin film, the current (i.e., the external field) causes an uneven distribution of electrons in the thin film, more concentrated at the nano-spacing, which is what the present invention calls as charge localization.

FIG. 5F schematically reveals the dissolution and redeposition of localized electrons induced by the external field to the Au nanoparticle surface atoms (general electric field)Au after over-dissolution ³⁺ Reduction of ions), i.e., the process of mass supply during the oswald nano-soldering process. In general, the equilibrium electrode potential of metal nanoparticles with radius r in the zero charge state

Balancing electrode potentials with respect to their respective metal masses

Is composed of

Wherein v _m 、σ ^max Z and F are the molar volume of the metal nanoparticles, the surface tension of the metal in the zero charge state, the number of electrons transferred in the electrochemical reaction and the faraday constant, respectively. Thus, to enhance the effective mass supply of metal nanoparticles in an electrochemical ostwald process, one feasible approach is to adjust their equilibrium electrode potential by a variable r. For the synthesized metal nanoparticles, r is a fixed value and cannot be modulated, so the invention adjusts the equilibrium potential of the nanoparticles by means of another variable sigma. This can be achieved by introducing an excess charge q (relative to the zero charge state) on the metal nanoparticles. From the electrocapillary phenomenon, it is known that the introduction of an excessive charge on the metal nanoparticles generates a strong electrostatic repulsion between its surface atoms, thereby offsetting its σ to some extent. Considering the influence of the excess charge q, the invention deduces the equilibrium electrode potential of the Au nano-particles with excess charge

As follows

Here, C is a double bond around the gold nanoparticleAnd (4) electric layer capacitance. For simplicity, the present invention assumes that C is constant, so that the effect of excess q on the charged Au NP balanced electrode potential can be plotted schematically (fig. 4). For positively charged Au nanoparticles, as q increases, it balances the oxidation electrode potential (i.e., reaction)

Relative to

Is/are as follows

) Tends to be more positive, indicating that the surface atoms of the Au nanoparticles have a stronger tendency to dissolve. For negatively charged Au nanoparticles, it balances the reduction electrode potential (i.e., reaction)

Relative to

Is/are as follows

) And also tends to be more positive with the increase of q, which indicates that the dissolved metal ions have a stronger tendency to be reduced. The same applies to Au nanoparticles that are globally electrically neutral, but highly electron localized. In this case, the local electrons induced by the external field can also greatly polarize specific surface locations with high electron affinity (e.g., the apex of the particle in the nanogap and sharp protrusions on the surface of the particle), thereby enhancing electrochemical dissolution and deposition, and thus enhancing the supply of material in the oswald nano-welding.

It can also be seen from fig. 5C and 5D that, because the size of the nano-spacers is very small, the local charges at the two ends of the spacers form a strong local electric field in the nano-spacers. For the metal ions dissolved electrochemically, the local electric field (together with the solvent water molecules distributed in an orientation induced by the electric field) has a significant binding effect on the metal ions, so that the ions cannot overflow the nano-gap and can only be transmitted in a limited region of the nano-gap. Therefore, localized electrons can not only enhance the dissolution and redeposition of atoms on the surface of the particles (i.e., enhance the supply of species), but also confine the transport of dissolved species in the nano-space (i.e., enhance the transport of species), thereby actively enhancing the electrochemical ostwald ripening process of the nanoparticles. This is the physical mechanism of external field enhanced oswald nano-welding.

While particular embodiments of the present invention have been illustrated and described, it would be obvious that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A method of Ostwald nano-welding is characterized in that the surface electron localization treatment is carried out on the metal nano-particle film to be treated, so that electrons are concentrated in the nano-interval area of the particles, thereby strengthening the Ostwald nano-welding.

2. The method of oswald nano welding as set forth in claim 1, wherein the oswald nano welding is strengthened by placing a metal nanoparticle film to be treated in an aqueous solution and inducing electron localization of the surface of the metal nanoparticles under electrical strengthening.

3. The method of oswald welding as recited in claim 2, wherein the electricity is at least one of direct current, alternating square wave pulsed electricity.

4. The method of oswald nano welding as set forth in claim 3, wherein the intensity of the applied electricity is less than or equal to the intensity of the water to be electrolyzed.

5. The Ostwald nano-welding method of claim 4, wherein the direct current has a current intensity of 10 to 70 mA.

6. The Ostwald nano-welding method of claim 4, wherein the pulse frequency of the alternating square wave pulse electricity is 0.01 to 5000 Hz.

7. The method of oswald nano welding as set forth in claim 2, wherein said aqueous solution is pure water or an aqueous electrolyte solution having a concentration of 1M or less.

8. The method of oswald nano welding as set forth in claim 7, wherein the electrolyte is a compound capable of maintaining a stable phase under the passage of current and not chemically and electrochemically reacting with the metal nanoparticles.

9. The method of oswald nano welding as recited in claim 8, wherein said electrolyte is NaClO ₄ 。

10. The method of oswald nano welding as set forth in claim 1, wherein the metal nanoparticle film is a nano film composed of metal nanoparticles adjacently arranged;

the size of the metal nano-particles is 4-250 nm;

the gaps among the metal nano particles are less than or equal to 10 nm.

11. The method of oswald nano-soldering of claim 10, wherein the metal nanoparticles are at least one of gold, silver, palladium, and platinum.

12. The method of oswald nano welding as set forth in claim 1, wherein the substrate for supporting the metal nanoparticle film to be welded is a non-conductive substrate.

13. The method of oswald nano-soldering of claim 12, wherein the substrate is a non-conductive glass substrate.

14. The method of oswald nano welding as set forth in any one of claims 1 to 13, wherein a time of the surface electron localization treatment is less than or equal to 60 min.

15. An oswald nano-solder film prepared by the method of any one of claims 1 to 14.

16. Use of the oswald nano-soldering film according to claim 15 for at least one device of optical, electrical, electrochemical, sensing.