TWI400192B - Core - shell structure nanowires and their production methods - Google Patents

Description

Core-shell structure nanowire and manufacturing method thereof

The invention relates to a nanowire and a preparation method thereof, in particular to a core-shell structure nanowire and a preparation method thereof.

The nanowire is a nanomaterial that is generally called 100 nm or less and is limited in two dimensions. At this time, since the electrons are discontinuous in the lateral direction, the quantum binding energy level is discontinuous, and special physical properties such as non-continuous resistance values are exhibited. Therefore, it has important applications in, for example, nanoelectronic components, nano-optical components, micro-semiconductor components, and nano-motor components, and is widely known as a wiring and field emitter in quantum instruments. And biomolecular nanosensors, etc., and in recent years, due to the application of nanoelectronic components, research on the field emission characteristics of nanostructures has received increasing attention.

For example, "Synthesis and growth mechanism of pentagonal Cu nanobats with field emission characteristics" (J-H Wang et al.; Nanotechnology 17, 2006, 719-722) discloses an organic chemical vapor deposition method (MOCVD). The copper nanowire and the obtained copper nanowire exhibit an electronic characteristic of a turn-on field of 4 V/μm at a current dendity of 1 μA/cm ² ; Field emission properties of electrochemistry deposited gold nanowires" (A. Dangwal et al.; Applied Physics Letters 92, 063115, 2008) discloses an electrochemically deposited method with a length of 6-15 μm and a diameter of 120-265 nm. The technique of the gold nanowire and the produced gold nanowire have a conduction electric field of 4 V/μm under the condition of a current density of 0.1 μA/cm ² .

It can be seen from the above documents that nanowires composed of different materials and having field emission characteristics can be obtained through different growth methods, but how to regulate and dope the overall structure of the nanowires to achieve better field emission performance and how Simplify the process, and produce a large number of nanowires with field emission performance, so that it can be practically used for component production, which is the direction of active research and development in this field.

Accordingly, it is an object of the present invention to provide a core-shell structured nanowire.

Further, another object of the present invention is to provide a method for producing a core-shell structured nanowire.

Thus, a core-shell structured nanowire of the present invention comprises a convex end and an extension extending downward from the bottom of the convex end.

The convex end is composed of a precious metal of a single crystal structure having a linear core and a shell surrounding the core, the core being composed of a precious metal of a single crystal structure, the shell being composed of a single crystal Made up of metal oxides.

In addition, the method for fabricating a core-shell structured nanowire of the present invention comprises the following two steps.

First, the complex average particle size distribution is uniform, and the precious metal particles in the nanometer scale range are dispersed on a carrier plate having amorphous ceria.

Next, the carrier plate with precious metal particles and a plurality of high-purity metal powders having a melting point of not higher than 400 ° C are placed in a low-pressure environment and heated to a temperature of not less than 700 ° C at a predetermined heating rate. Holding the temperature at the reaction temperature for at least 15 minutes, the metal powder is reacted with the carrier to form a linear single crystal metal oxide, and at the same time, the precious metal particles are from one end of the linear metal oxide to the other end. The axially perpendicular flow extends to form a linear core and a convex end located outside the linear single crystal metal oxide, thereby preparing the core-shell structured nanowire. The invention has the advantages of providing a method which is easy to control, simple in process, and can be mass-produced, and a heterogeneous core-shell nanowire having a structure of a convex end and an extended section, and a heterogeneous core-shell nanowire prepared. The shell layer of the extended section reduces the electron scattering effect when the electron is turned on, and concentrates the current conducted through the core with the convex end to be emitted outward, and has a superior field emission characteristic than the current nanowire.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to Figure 1, a preferred embodiment of a core-shell nanowire of the present invention comprises a convex end 2 and an extension 3 extending downward from the bottom surface of the convex end 2, the extension 3 having a linear shape. The core 31 and a shell 32 surrounding the core 31.

The convex end 2 is made of a precious metal selected from a single crystal structure such as gold or silver; the core 31 is composed of the same precious metal material as the convex end 2; the shell 32 is selected from a low melting point. A metal oxide composed of a metal, for example, gallium dioxide (Ga ₂ O ₃ ), tin dioxide (SnO ₂ ), or indium trioxide (In ₂ O ₃ ).

When an electric field is applied, the current is conducted by the core 31, and the shell 32 surrounding the core 31 can be regarded as an isolation layer, thereby avoiding the electron scattering effect when the current is turned on by the core 31, thereby allowing the generated current to follow The core 31 is concentrated to the convex end 2 and is emitted outward, so that excellent field emission is obtained. Sex.

The core-shell nanowires described above can be more clearly understood after being described in conjunction with a preferred embodiment of the core-shell nanowire fabrication method.

Referring to FIG. 2, step 101 is first performed, and a solution containing precious metal particles is dripped on a crucible plate coated with amorphous ceria, and after the solvent is volatilized, the precious metal particles are uniformly disposed on the carrier. The average particle size of the precious metal particles ranges from 80 nm to 250 nm, and has similar surface Plasmon Resonance Effects (SPR Effects). Preferably, the precious metals The microparticles are composed of gold having an average particle diameter of 80 to 250 nm or silver.

Next, in step 102, the amorphous ceria carrier plate provided with the precious metal particles and the metal powder having a purity of not less than 99.99% and a melting point of not higher than 400 ° C are placed at a low pressure (not more than 10 ^-2 Torr). In a heated environment, the temperature is maintained at a temperature of 700 ° C to 800 ° C for not less than 15 minutes. At this time, the vapor generated by the metal powder reacts with the amorphous ceria carrier to form a first metal oxide, and then the first metal oxide is along the majority of the precious metal particles and the amorphous ceria carrier The periphery of the boundary is converted into a single crystal metal oxide in a nanowire form through a non-uniform supersaturation process to form the shell layer, and simultaneously pushes the precious metal particles away from the ceria carrier plate. And the precious metal particles are vertically extended in the direction of the amorphous ceria carrier plate to form the linear core, and the residual precious metal particle portion forms the convex end to obtain the core-shell structure nanowire.

The preferred embodiment of the above-described core-shell structured nanowire of the present invention will be more clearly understood in conjunction with the following description of specific examples.

[Specific example]

In this embodiment, the precious metal fine particles 4 are selected from gold having an average particle diameter of 200 to 250 nm, and the solution containing the precious metal fine particles 4 having an average particle diameter of 250 nm is dropped on an amorphous cerium oxide plate. On the crucible plate 51 of 52, after the solvent is volatilized, the precious metal particles 4 are uniformly disposed on the amorphous ceria 52.

Referring to FIG. 3 and FIG. 4, the crucible carrier 51 of the amorphous ceria 52 provided with the precious metal particles 4 is placed in a quartz tube with a plurality of gallium powders having a purity of not less than 99.9999%, and placed in a quartz tube. Into the heating furnace, under the condition of a vacuum degree of 10 ^-2 Torr, heated to 800 ° C at a heating rate of 20 ° C / min, and then held at a temperature of 800 ° C for 30 minutes; at this time, the vapor generated by the gallium powder 6 Reacting with the amorphous ceria 52 to form digallium monoxide (4Ga _(g) + SiO _2(s) → 2Ga ₂ O _(g) + Si _(s) ), the gallium monoxide further along the precious metals The periphery of the boundary between the fine particles 4 and the amorphous ceria 52 forms a solid single crystal metal oxide of gallium oxide (7Ga ₂ O _(g) → Ga ₂ O _{3 (s)} + 4Ga _{(s, 1)} ) And stacking the precious metal particles 4 away from the buffer plate 51, and the single crystal metal oxide 7 of the gallium trioxide is stacked in a monoclinic form to form a shell structure and generate a twin boundary, at the same time, at this temperature, the precious metal particles 4 will be in a similar molten state along the twin boundary to the amorphous dioxygen The 垂52 direction of the vertical flow extends, gradually forming a linear core structure, and finally the remaining portion of the non-recumbent precious metal particles protrudes out of the shell structure, that is, as shown in FIG. 4, including a convex end 2, and A core 31 extending downward from the bottom surface of the convex end 2 and forming a line, and a core-shell nanowire surrounding the shell layer 32 of the core 31.

Referring to FIG. 5, FIG. 5 is a high angle annular dark field (HAADF) image of the transmission electron microscope (hereinafter referred to as TEM) of the specific example. From the image analysis, the core diameter of the core-shell nanowire is about It is 60-100 nm, the shell diameter is about 250 nm, and the convex end has a diameter of about 100-200 nm.

Referring to FIG. 6 and FIG. 7, the structure of the core-shell nanowire and the detailed image of the convex end of the core-shell nanowire are confirmed by the TEM image of the specific example.

Referring to Fig. 8, Fig. 9, and Annex 1, Fig. 8 and Fig. 9 are energy dispersive spectroscopy (EDX) elemental analysis diagrams of the dot-framed area in Fig. 6, and high-resolution transmissive electron microscope images, respectively. In the color picture of FIG. 8, the distribution of oxygen, gallium, and gold in the marked area can be more clearly seen from FIG. 8 and Annex I, wherein oxygen and gallium are more distributed in the shell layer, and gold is The elements are more distributed in the middle core. A high-resolution electron micrograph of the core and the shell layer can be clearly seen in Figure 9. The inner core is gold and the outer layer is covered with a gallium trioxide shell.

Referring to FIG. 10, FIG. 11, FIG. 10 and FIG. 11 respectively, fast Fourier transformation (FFT) for the lower dotted frame of FIG. 9, and inverse fast Fourier transformation (IFFT) The analysis image map, the microstructure along the [112] zone axis can be clearly seen from the microstructure image in the figure, and the shell layer is confirmed to be monoclinic. β-Ga ₂ O ₃ , and the pitches of the (201) and (110) planes were 0.46 nm and 0.29 nm, respectively.

A brief description of the field emission characteristics of this specific example is as follows.

The core-shell nanowire prepared by the specific example and the pure aluminum oxide nanowire as a control experiment were respectively placed in a vacuum chamber, and the core-shell structure was measured while maintaining the pressure at 10 ^-6 torr. The nanowire, and the field emission characteristics of the gallium trioxide nanowire.

Referring to FIG. 12 and FIG. 13, FIG. 12 is an applied electric field of the core-shell structure nanowire and the emission surface of the gallium trioxide nanowire and the electrode spacing of 100 nm, respectively. The emission current density curve, and FIG. 13 is a partial enlarged view of FIG. It is known from the graph that the conduction electric field of the core-shell nanowire prepared by the specific example is 0.12~2.4V/μm, and the currently developing nanowire (for example, the nanowire (the conduction electric field is: 7.4~11.5V/μm), copper nanostructure (conduction electric field: 4V/μm), gold nanowire (conduction electric field: 4V/μm), and carbon nanotubes (conduction electric field: 0.94~2.77V) /μm) has better field emission characteristics than field emission characteristics.

In summary, the present invention provides a one-stage growth method with simple process, which is easy to control, simple in process, and can be produced in a mass production process to produce a heterogeneous core-shell nanowire. Conducting current through a core made of a single crystal structure metal, and utilizing a shell surrounding the core to reduce the electron scattering effect when the electron is turned on, and using the convex end of the single crystal metal to concentrate the conduction current and then outward The field emission characteristics superior to the currently developed nanowires are obtained, and the inventive object of the present invention is indeed achieved.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention cannot be limited thereto, that is, the scope of patent application according to the present invention. And the simple equivalent changes and modifications made by the description of the invention are still within the scope of the invention.

101‧‧‧Steps

102‧‧‧Steps

2‧‧‧ convex end

3‧‧‧Extension

31‧‧‧ core

32‧‧‧ Shell

4‧‧‧ precious metal particles

51‧‧‧矽carrier board

52‧‧‧Amorphous cerium oxide

6‧‧‧Gallium powder

7‧‧‧Dioxide-series single crystal metal oxide

1 is a schematic view showing a preferred embodiment of the core-shell structure nanowire of the present invention; FIG. 2 is a flow chart showing the manufacturing method of the preferred embodiment of the present invention; FIG. 3 is a schematic view showing a gallium powder The process of reacting with amorphous ceria; FIG. 4 is a schematic diagram showing the reaction of gallium powder with amorphous ceria to form the core-shell nanowire of the present invention; FIG. 5 is a TEM (HAADF) image, illustrating The core-shell structured nanowire prepared by the specific example is shown in FIG. 6; FIG. 6 is a transmission electron microscope image illustrating the core-shell structure nanowire prepared by the specific example; FIG. 7 is a transmission electron microscope image. 5 is an end view of the core-shell nanowire prepared in the specific example; FIG. 8 is an EDX image, which supplements the elemental analysis image at the point frame of FIG. 6; FIG. 9 is a high-resolution transmissive image. The electron microscope image supplements the detailed structure analysis image at the point frame of Fig. 6; Fig. 10 is a fast Fourier transform analysis image, which supplements the detailed structure analysis image at the point frame of Fig. 9; Fig. 11 is an inverse fast Fourier transform analysis Image, supplementary explanation Figure 9 The detailed structure analysis image at the point frame; FIG. 12 is a graph of applied electric field and emission current density, illustrating the field emission characteristics of the core-shell structure nanowire prepared by the specific example of the present invention; and FIG. 13 is an applied electric field and The emission current density curve is a partial enlarged view of FIG.

Annex 1: Description of the color picture of Figure 8EDX.

101‧‧‧Steps

102‧‧‧Steps

Claims (6)

A method for fabricating a core-shell nanowire comprises: (a) uniformly distributing a plurality of average particle diameters, and dispersing precious metal particles in a nanometer scale range on a carrier having amorphous ceria; a carrier plate in which precious metal particles are dispersed and a metal powder having a high purity and a melting point of not higher than 400 ° C are placed in a low pressure environment, and heated at a predetermined heating rate to a reaction temperature of not lower than 700 ° C. At least 15 minutes, the metal powder is reacted with the carrier to form a linear single crystal metal oxide, and at the same time, the precious metal particles extend axially from one end of the linear metal oxide to the other end to form a linear core and a The hetero-core-shell nanowire is prepared by a convex end located outside the linear single crystal metal oxide. The method for producing a core-shell nanowire according to claim 1, wherein the reaction temperature of the step (b) is 700 to 800 °C. The method for fabricating a core-shell nanowire according to claim 2, wherein the step (b) is in a low pressure environment of not more than 10 ^-2 torr. The method for producing a core-shell structured nanowire according to claim 3, wherein the precious metal particles have an average particle diameter of 80 to 250 nm. The method for producing a core-shell nanowire according to claim 4, wherein the metal powder is selected from the group consisting of gallium, indium, and tin. The method for producing a core-shell nanowire according to claim 5, wherein the step (b) is holding the temperature for 15 to 30 minutes.