A method for the in-situ controlled preparation of metal nanoneedle tips by high-energy electron beam irradiation

Abstract

This invention discloses a controllable in-situ irradiation method for preparing metal nanoneedles using high-energy electron beams. Amorphous nanowires with a layer of metal nanoparticles sprayed onto their surface are fabricated as transmission electron microscopy (TEM) samples. In the TEM, a high-energy electron beam is used to focus and irradiate the nanowires, inducing preferential melting and radial shrinkage of the amorphous nanowire material within the irradiated region. Simultaneously, this causes the metal nanoparticles on the nanowire surface to aggregate, fuse, and elongate linearly, ultimately yielding a metal nanoneedle structure. This invention utilizes a high-energy electron beam in the TEM to not only non-thermally activate and induce nanostructural transformations but also to allow for high-resolution in-situ observation of the nanofabrication process. Furthermore, the irradiation process is performed at room temperature, requiring no external assistance such as light, heat, electricity, or force, making the entire irradiation preparation process simple and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial processing technology, specifically relating to a method for the in-situ controllable preparation of metal nanoneedles using high-energy electron beams. Background Technology

[0002] Nanofabrication technology, as a crucial component driving the development of nanotechnology, plays a vital role in realizing novel micro- and nanoscale structures and devices in optics, electronics, semiconductors, and sensors. As one of the most powerful energy beams, the high-energy electron beam in transmission electron microscopy (TEM) allows for both high-resolution in-situ observation of low-dimensional nanomaterials and precise, controllable nanofabrication, demonstrating significant advantages. Nanowires, a typical one-dimensional nanomaterial with a large aspect ratio, show broad application prospects in micro- and nanoelectronic devices, chemical and biological sensors, and other fields. However, the conventional cylindrical nanowire structure and related properties often fail to meet the performance requirements of all types of devices, necessitating precise and controllable fabrication of nanowires at the nanoscale to improve their performance.

[0003] With the development of electron microscopy (TEM) technology, high-energy electron beams in TEM can now be used to modify the morphology of nanowires in situ, including length, diameter, and curvature, as well as perform fine nanofabrication such as cutting, drilling, and welding. In addition, a type of metal nanowire with needle-like tips of different thicknesses at both ends—the metal nanoneedle structure—has promising applications in scanning electron microscopy (SEM) and field emission technologies. In existing literature, some researchers have used high-energy focused electron beam irradiation to achieve the fabrication of amorphous SiO₂. x The sharpening, hooking, and welding of nanowires. However, due to the lower stability of crystalline metallic nanowires compared to amorphous SiO2... x Nanowires are much better; it is difficult to prepare metal nanoneedle structures using the same method, and no one has been found in the existing literature to have successfully prepared them using high-energy electron beam focusing irradiation in transmission electron microscopy. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the above-mentioned problems and those existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a method for the in-situ controllable preparation of metal nanoneedles using high-energy electron beams.

[0007] To solve the above-mentioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution: a method for controllable in-situ irradiation preparation of metal nanoneedles by high-energy electron beam, comprising,

[0008] A layer of metal nanoparticles is sprayed onto the surface of amorphous nanowires. The nanowires are then dispersed onto an electron microscope microgrid to form a TEM sample. The sample is then placed in a TEM. Nanowire segments with both ends resting in the microgrid holes are selected, and an electron beam is focused on the radial center of the nanowire segment for continuous irradiation. This induces the amorphous nanowire material in the irradiated area to melt and shrink radially. At the same time, the linear aggregation, fusion, and elongation of the metal nanoparticles are gradually achieved, ultimately resulting in a metal nanoneedle structure.

[0009] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoneedle tip described in this invention, the amorphous nanowire includes, but is not limited to, amorphous metal nanowires, amorphous semiconductor nanowires, amorphous insulator nanowires, and amorphous composite nanowires.

[0010] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoneedle tip described in this invention, the amorphous nanowire has a diameter of 20-100 nm, is axially straight and radially uniform in thickness, and does not adsorb other impurities.

[0011] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoparticle tip described in this invention, the metal nanoparticles include, but are not limited to, various common Au, Ag, Cu, and Fe crystalline metal nanoparticles.

[0012] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoneedle tip described in this invention, the amorphous nanowire has lower stability than the metal nanoparticles.

[0013] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoparticle tip described in this invention, the metal nanoparticles have a diameter of 3-8 nm, and their amorphous nanowires are arranged in a gradient in the radial direction, with one side being loose and the other side being relatively dense.

[0014] As a preferred embodiment of the high-energy electron beam in-situ controlled preparation method of the metal nanoneedle tip described in this invention, the spot size of the electron beam is slightly smaller than the diameter of the amorphous nanowire.

[0015] In a preferred embodiment of the high-energy electron beam in-situ controlled preparation method for the metal nanoneedle tip described in this invention, the accelerating voltage of the electron beam is 200-300 kV; the irradiation current density is (0.2-12.5) × 10⁻⁶. 3 A / cm 2 .

[0016] The beneficial effects of this invention are:

[0017] This invention employs a high-energy electron beam in a TEM to perform in-situ focused irradiation on amorphous nanowires modified with metal nanoparticles. Utilizing the structural instability difference between amorphous nanowires and crystalline metal nanoparticles, the non-thermally induced amorphous nanowire material preferentially melts and radially shrinks. Simultaneously, it causes the metal nanoparticles on the nanowire surface to continuously aggregate, fuse, and elongate linearly towards the irradiation center, ultimately yielding a metal nanoneedle structure. By adjusting parameters such as the diameter of the amorphous nanowires, the type, size, and distribution of the metal nanoparticles, the beam spot size of the electron beam, and the irradiation current density, this invention can effectively control the fabrication process of the metal nanoneedle structure.

[0018] The high-energy electron beam in-situ irradiation controllable preparation method of the present invention has the advantages of non-thermal activation-induced nanostructure transformation and high-resolution in-situ observation of the preparation process of nanoneedle structures. In addition, the irradiation processing is carried out at room temperature without the need for external assistance such as light, heat, electricity, or force, and the entire irradiation preparation process is simple and easy to operate. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0020] Figure 1 The SiO2 modified with Au nanoparticles selected in Example 1 x TEM images of nanowire fragments and the location and beam size of high-energy electron beam irradiation (see circled locations in the figure);

[0021] Figure 2 This is a standard TEM image of Au nanoneedle tips obtained after in-situ irradiation of the nanowire fragments selected in Example 1 with a high-energy electron beam.

[0022] Figure 3 The image shows a high-resolution TEM image of an Au nanoneedle tip obtained by in-situ irradiation of the nanowire fragment selected in Example 1 with a high-energy electron beam. The inset in the upper right corner is the Fast Fourier Transform (FFT) image of the tip structure when the high resolution is captured. Detailed Implementation

[0023] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] This embodiment selects amorphous SiO2. x Nanowires, where x is 2 to 3.

[0027] Example 1:

[0028] (1) TEM sample preparation: Amorphous SiO2 was prepared using the SCD 005 sputtering equipment manufactured by BAL-TEC. x A layer of Au nanoparticles was deposited on the surface of the nanowires over a period of 5 seconds. Then, a small amount of modified SiO₂ was added. x Nanowire powder (<<1mg) was ultrasonically dispersed in anhydrous ethanol with a mass fraction ≥99.7%, and then two drops of the suspension containing nanowires were aspirated onto an electron microscope microgrid using a dropper. After drying, a TEM sample was obtained.

[0029] (2) Nanowire Sample Screening: TEM samples were loaded into a Tecnai F30 field emission TEM for sample screening. For example... Figure 1 As shown, the nanowires selected in this embodiment have a diameter of 45 nm, are straight along the axis and have uniform radial thickness, with both ends resting on the microgrid holes (the edges of the holes are not visible in the figure). The surface of the nanowires is modified with a layer of Au nanoparticles with a size of 3-8 nm distributed radially, exhibiting an overall surface morphology of sparse on one side and relatively dense on the other.

[0030] (3) Electron beam irradiation processing: First, adjust the electron beam spot size to 25 nm and the irradiation current density to 2.0 × 10⁻⁶. 3 A / cm 2 The accelerating voltage is 300kV, and then the nanowire is focused on the radial center for in-situ irradiation processing (see...). Figure 1 Within the irradiation range, the nanowires gradually contract radially and eventually break, while the Au nanoparticles on the surface of the nanowires gradually aggregate, fuse, and elongate into Au nanoneedle-like structures (see...). Figure 2 To characterize the microstructure of the Au nanoneedle tip, high-resolution TEM images and corresponding FFT images of the Au nanoneedle tip were further captured, such as... Figure 3 As shown, the Au nanoneedle tip is confirmed to have a crystalline structure.

[0031] Example 2:

[0032] (1) TEM sample preparation: Amorphous SiO2 was prepared using the SCD 005 sputtering equipment manufactured by BAL-TEC. x A layer of different metal nanoparticles was deposited on the surface of the nanowires over a period of 5 seconds. Then, a small amount of modified SiO₂ was added. x Nanowire powder (<<1mg) was ultrasonically dispersed in anhydrous ethanol with a mass fraction ≥99.7%, and then two drops of the suspension containing nanowires were aspirated onto an electron microscope microgrid using a dropper. After drying, a TEM sample was obtained.

[0033] (2) Nanowire sample screening: The TEM sample was loaded into a Tecnai F30 field emission TEM for sample screening. The nanowires selected in this embodiment have a diameter of 45 nm and the surface of the nanowires is modified with a layer of metal nanoparticles with a size of 3-8 nm distributed radially.

[0034] (3) Electron beam irradiation processing: First, adjust the electron beam spot size to 25 nm and the irradiation current density to 2.0 × 10⁻⁶. 3 A / cm 2 An accelerating voltage of 300 kV was used, followed by in-situ irradiation focusing on the radial center of the nanowire. Within the irradiation range, the nanowire gradually contracted radially and eventually broke. Simultaneously, the metal nanoparticles on the nanowire surface gradually aggregated, fused, and elongated into a metal nanoneedle structure. The nanoneedle structures prepared from different metal nanoparticles are shown in Table 1.

[0035] Table 1. Nanoneedle tip structures prepared from different metal nanoparticles

[0036]

[0037] The type of metal nanoparticles determines the type of nanotip. As shown in Table 1, it can be various common crystalline metal nanoparticles such as Au, Ag, Cu, and Fe, which are more stable than amorphous nanowires. Therefore, while the amorphous nanowire material is continuously melted and evaporated by the electron beam, the relative stability of the metal nanoparticles can be maintained, and they can aggregate together through diffusion and migration to form a linear structure.

[0038] Example 3:

[0039] (1) TEM sample preparation: Amorphous SiO2 was prepared using the SCD 005 sputtering equipment manufactured by BAL-TEC. x A layer of Au nanoparticles was deposited on the surface of the nanowires over a period of 5 seconds. Then, a small amount of modified SiO₂ was added. xNanowire powder (<<1mg) was ultrasonically dispersed in anhydrous ethanol with a mass fraction ≥99.7%, and then two drops of the suspension containing nanowires were aspirated onto an electron microscope microgrid using a dropper. After drying, a TEM sample was obtained.

[0040] (2) Nanowire sample screening: The TEM sample was loaded into a Tecnai F30 field emission TEM for sample screening. The nanowires selected in this embodiment have diameters of 45 nm and 60 nm, and the nanowire surface is modified with a layer of Au nanoparticles with a size of 3-8 nm that are distributed radially in a gradient or uniform manner.

[0041] (3) Electron beam irradiation processing: The size of the electron beam spot and the corresponding irradiation current density are adjusted as shown in Table 2. The accelerating voltage is 300kV. Then, the nanowire is focused on the radial center for in-situ irradiation processing. Within the irradiation range, the nanowire gradually shrinks radially and eventually breaks. At the same time, the Au nanoparticles on the surface of the nanowire gradually aggregate, fuse, and elongate into Au nanoneedle tip structure.

[0042] Table 2. Effect of different electron beam spot sizes on the structure of metal nanoneedles

[0043]

[0044]

[0045] As shown in Table 2, the electron beam spot size should be slightly smaller than the diameter of the amorphous nanowire. If the spot size is too small, perforation of the nanowire is likely to occur. This is because when the electron beam spot is too small, the irradiation current density is very high. The electron beam induces rapid melting and evaporation of the amorphous nanowire material in the small irradiation area, while the surrounding unirradiated area can maintain its structural stability and not collapse due to the passivation effect of the metal nanoparticles, thus obtaining a porous structure. Conversely, if the electron beam spot size is slightly larger than the nanowire diameter and the particles are uniformly distributed, a dumbbell-shaped structure is more likely to be obtained, rather than a needle-like structure. This is because when the spot size is slightly larger than the nanowire diameter and focused on the center of the nanowire, the irradiation effect at the center is stronger than at the edge. Symmetrical necking will occur on both sides of the nanowire, with faster necking at the center and slower necking at the edge. At the same time, the uniformly distributed metal particles on both sides will continuously gather and merge towards the central axis of the nanowire, ultimately forming a dumbbell-shaped structure.

[0046] Example 4:

[0047] (1) TEM sample preparation: Amorphous SiO2 was prepared using the SCD 005 sputtering equipment manufactured by BAL-TEC. x A layer of Au nanoparticles was deposited on the surface of the nanowires over a period of 5 seconds. Then, a small amount of modified SiO₂ was added. xNanowire powder (<<1mg) was ultrasonically dispersed in anhydrous ethanol with a mass fraction ≥99.7%, and then two drops of the suspension containing nanowires were aspirated onto an electron microscope microgrid using a dropper. After drying, a TEM sample was obtained.

[0048] (2) Nanowire Sample Screening: The TEM sample was loaded into a Tecnai F30 field emission TEM for sample screening. The nanowire diameters selected in this embodiment are shown in Table 3, which are straight along the axis and have uniform radial thickness. The nanowire surface is modified with a layer of Au nanoparticles with a size of 3-8 nm distributed radially.

[0049] (3) Electron beam irradiation processing: The size of the electron beam spot and the corresponding irradiation current density are adjusted according to the diameter of the nanowire as shown in Table 3. The accelerating voltage is 300kV. Then, the nanowire is focused on the radial center for in-situ irradiation processing. Within the irradiation range, the nanowire gradually shrinks radially and eventually breaks. At the same time, the Au nanoparticles on the surface of the nanowire gradually aggregate, fuse, and elongate into Au nanoneedle tip structure.

[0050] Table 3 Different amorphous SiO x Influence of nanowire diameter on the structure of metal nanoneedle tips

[0051]

[0052]

[0053] Table 3 shows that for amorphous SiO x For nanowires, the ideal diameter is between 20-100 nm; nanowires that are too thick or too thin are unsuitable. When nanowires are too thin, i.e., below 20 nm, it becomes difficult for metallic nanoparticles to achieve gradient alignment, and amorphous nanowire materials cannot be stably ordered during the continuous melting and evaporation process by the electron beam, making it impossible to fabricate suitable nanoneedle-like structures. On the other hand, nanowires that are too thick exceed the linearity requirements of nanostructures (0.1-100 nm), and will not be studied or discussed here.

[0054] The type of metal nanoparticles determines the type of nanoneedle. Various common crystalline metal nanoparticles such as Au, Ag, Cu, and Fe can be used, all of which are more stable than amorphous nanowires. Therefore, while the amorphous nanowire material is continuously melted by the electron beam, the relative stability of the metal nanoparticles can be maintained, allowing them to diffuse, migrate, and aggregate together to form a linear structure. The size of the metal nanoparticles affects their diffusion and migration capabilities, as well as the fusion process closely related to surface energy; a suitable particle diameter is 3-8 nm. Furthermore, the distribution of metal nanoparticles on the surface of the amorphous nanowires requires a certain gradient arrangement along the radial direction of the nanowire, with one side sparse and the other relatively dense. This facilitates their directional diffusion and migration from the sparse side to the dense side, ultimately arranging them into a linear structure on the denser side. As irradiation continues, the amorphous nanowires will accelerate radial contraction and breakage. During this process, the nanowires will experience axial stretching, causing the "softened" metal linear structure under high-energy electron beam irradiation to elongate into a nanoneedle structure.

[0055] The electron beam spot size needs to be slightly smaller than the diameter of the amorphous nanowires. If the electron beam spot size is slightly larger than the nanowire diameter and the particles are uniformly distributed, it is easier to obtain a dumbbell-shaped structure rather than a needle-like structure. Additionally, the accelerating voltage of the electron beam is 200-300 kV, and the irradiation current density is (0.2-12.5) × 10⁻⁶. 3 A / cm 2 Under these conditions, the melting and radial shrinkage of amorphous nanowire materials, as well as structural transformations such as aggregation, fusion, and elongation of metal nanoparticles, can be guaranteed.

[0056] In summary, this invention can control the fabrication process and final morphology of metal nanoneedle structures by adjusting parameters such as the diameter of the amorphous nanowires, the type, size and distribution of the surface-modified metal nanoparticles, and the beam spot size, accelerating voltage and irradiation current density of the electron beam.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for controllable in-situ irradiation preparation of metal nanoneedles using high-energy electron beams, characterized in that: include, A layer of metal nanoparticles is sprayed onto the surface of amorphous nanowires, and the nanowires are dispersed onto an electron microscope microgrid to form a TEM sample. The sample is then placed in a TEM, and nanowire segments with both ends attached to the microgrid holes are selected. An electron beam is focused on the radial center of the nanowire segment for continuous irradiation, inducing the amorphous nanowire material in the irradiated area to melt and shrink radially. At the same time, the linear aggregation, fusion, and elongation of metal nanoparticles are gradually achieved, and finally a metal nanoneedle structure is obtained. The amorphous nanowires have a diameter of 20-100 nm, are straight in the axial direction and have uniform thickness in the radial direction, and do not adsorb other impurities. The spot size of the electron beam is smaller than the diameter of the amorphous nanowire; The accelerating voltage of the electron beam is 200-300 kV; the irradiation current density is (0.2-12.5)×10⁻⁶. 3 A / cm 2 ; The metal nanoparticles have a diameter of 3-8 nm and are arranged in a gradient along the radial direction of the amorphous nanowires, with one side being loose and the other side being relatively dense.

2. The method for controllable preparation of metal nanoneedles by in-situ high-energy electron beam irradiation as described in claim 1, characterized in that: The amorphous nanowires include one of amorphous metal nanowires, amorphous semiconductor nanowires, amorphous insulator nanowires, and amorphous composite nanowires.

3. The method for controllable in-situ irradiation preparation of metal nanoneedles by high-energy electron beam as described in claim 1, characterized in that: The metal nanoparticles include one of Au, Ag, Cu, and Fe crystalline metal nanoparticles.

4. The method for controllable in-situ irradiation preparation of metal nanoneedles by high-energy electron beam as described in claim 1, characterized in that: The stability of the amorphous nanowires is worse than that of the metallic nanoparticles.

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