CN110844876A - A process method for graphene-assisted preparation of large-area metal nanoparticle arrays - Google Patents

Abstract

A process method for graphene-assisted preparation of large-area metal nanoparticle arrays belongs to the field of micro-nano processing. On the basis of the traditional process, the present invention firstly adopts the surface periodic treatment process to prepare nano-columns 106 on the surface of the substrate 101, the purpose of which is to separate the implanted regions of the metal atoms 102, transfer the graphene 105 and anneal , the metal atoms 102 agglomerate into metal nanoparticles 103 during the annealing process. The graphene 105 acts as a perfect barrier to prevent the metal atoms 102 from evaporating. Therefore, the annealing temperature can be much higher than that in the conventional process. In addition, the periodic surface treatment makes the metal nanoparticles exhibit regular arrangement, which can obtain metal nanoparticle arrays with tunable structural arrangement. At the same time, the prepared graphene is protected by metal nanoparticles, blocking its contact with the air, effectively ensuring the long-term stability of the metal nanoparticles.

Description

A process method for graphene-assisted preparation of large-area metal nanoparticle arrays

technical field

The invention relates to a preparation process of a metal nanoparticle array, which belongs to the field of micro-nano processing.

Background technique

Metal nanostructures have surface plasmon effect, which is mainly due to the existence of a large number of free electrons inside and on the surface of the metal, forming a free electron air mass, namely plasmon. Surface plasmon optics of metal nanostructures have broad application prospects in the fields of photocatalysis, optical sensing, biomarkers, medical imaging, solar cells, and surface-enhanced Raman spectroscopy. These functions also interact with metal nanostructures and light. are closely related to the surface plasmon resonance generated when

Metal nanoparticles are one of metal nanostructures, and some corresponding optical functions can be realized by designing the diameter, spacing and period of metal nanoparticles. At present, there are many preparation methods for metal nanoparticles, such as: nanoimprinting, electron beam exposure, sputtering annealing, chemical synthesis, metal ion implantation and annealing. Among them, metal ion implantation and annealing is one of the commonly used preparation methods of metal nanoparticles. Its process flow is generally as follows: Step 1, as shown in Figure 1, prepare a substrate 101 required for metal ion implantation, which can be an insulating substrate or a semiconductor substrate; Step 2, as shown in Figure 2, perform Metal ions are implanted, and metal atoms 102 are implanted into the interior of the substrate 101; Step 3, as shown in FIG. 3, obtain the implanted substrate 101, which has metal atoms 102 inside; Step 4, as shown in FIG. 4, perform annealing , during the annealing process, the metal atoms 102 will agglomerate to form metal nanoparticles 103 ; step 5, as shown in FIG. 5 , finally obtain metal nanoparticles 103 inside and on the surface of the substrate 101 . The method can realize the preparation of large-area metal nanoparticles, and at the same time, due to the introduction of an annealing process in the preparation process, the crystal lattice quality of the obtained metal nanoparticles will be better. However, this method still has the following problems:

1) The annealing temperature should not be too high, otherwise it will cause metal atoms to evaporate on the surface of the substrate after precipitation, resulting in the loss of metal atoms. The result of the low annealing temperature is that the diameter of the obtained metal nanoparticles is too small, and it is difficult to obtain large-sized metal nanoparticles.

2) The arrangement of the obtained metal nanoparticles is disordered and random, which makes it difficult to realize the controllable preparation of metal nanoparticles.

3) For some easily oxidized metals, such as copper, silver, etc., the prepared metal nanoparticles lack effective protection and are easily oxidized, resulting in the failure of the metal nanoparticles.

At present, there is no effective solution for the above problem.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a process method for graphene-assisted preparation of large-area metal nanoparticle arrays. This method is based on the method of preparing metal nanoparticles by ion implantation and annealing. First, a method called "surface periodic treatment" is used to dry-etch the surface of the substrate after implanting metal atoms. The bottom surface is prepared with periodic and densely arranged nanopillars, the purpose of which is to separate the implanted regions of metal atoms. After that, we transferred a layer of graphene on the surface of the substrate (graphene is a single-atom layer two-dimensional thin film material composed of carbon atoms with sp2 hybridization), and introduced graphene as a metal atom blocking layer to prevent the metal atoms from annealing during the annealing process. evaporation. Finally, periodic arrays of regular metal nanoparticles can be obtained on the substrate surface by annealing. The diameter and arrangement period of the obtained metal nanoparticles can be adjusted. The method solves all the problems existing in the current metal ion implantation and annealing to prepare metal nanoparticles, and realizes the controllable large-area periodic preparation of metal nanoparticles.

The specific process steps are as follows:

S1, prepare the substrate 101 required for metal ion implantation; as shown in FIG. 1 .

S2, by means of metal ion implantation, metal atoms 102 are implanted into the superficial layer inside the surface of the substrate 101, and the implantation depth of the metal atoms 102 is controlled so that the height of the superficial layer of the substrate from the surface is less than 100 nm; as shown in FIG. 2 ;

Steps S3-S5 are collectively referred to as performing periodic surface treatment on the substrate.

S3, using a transfer method of silica nanospheres, the silica nanospheres 104 are transferred to the surface of the substrate 101 in step S2; as shown in FIG. After being transferred to the surface of the substrate 101, due to the transfer mechanism, a tight periodic arrangement will appear on the surface of the substrate 101, as shown in FIG. 12;

S4, using the silicon dioxide nanospheres 104 as a mask, vertical dry etching is performed on the surface of the substrate, and the etching depth is greater than the implantation depth of the metal atoms 102, and finally nano-pillars 106 that are closely and regularly arranged on the surface of the substrate are obtained. The purpose of the etching is to separate the injection area of the metal atoms 102, the top surface of each nano-pillar 106 is a silicon dioxide nano-sphere 104, and the diameter of each nano-pillar 106 is approximately equal to the diameter of the silicon dioxide nano-ball 104. diameter, each nanopillar 106 contains metal atoms 102; as shown in FIG. 7;

S5, removing the silicon dioxide nanospheres 104 on the top surfaces of the nanopillars 106 from the surface of the substrate 101 by ultrasonic deionized water, as shown in FIG. 8 ;

S6, a layer of graphene 105 is transferred on the surface of the substrate 101 by a wet transfer method; as shown in FIG. 9 .

S7, by annealing, the metal atoms 102 are precipitated from the nano-pillars 106 on the surface of the substrate 101 to the top surface of the nano-pillars 106 and agglomerated. During the annealing process, the metal atoms 102 inside each nano-pillar 106 will be heated and agglomerated And a metal nano-particle 103 is formed on the top surface of the nano-pillar 106. As shown in FIG. 10, the arrangement of the obtained metal nano-particle 103 is consistent with that of the nano-pillar 106, and is also consistent with the arrangement of the silica nano-spheres 104;

S8, finally, periodically arranged metal nanoparticles 103 are obtained on the surface of the substrate 101; as shown in FIG. 11 .

The substrate used in the present invention may be a silicon substrate with a silicon dioxide layer on the surface, a quartz substrate, or other insulating substrates.

In the present invention, the metal formed by the implantation of metal ions may be noble metals such as gold, platinum, silver, and copper, or may be other metals such as aluminum and iron.

The annealing temperature is equal to or greater than the melting point temperature of the corresponding metal of the metal atom.

In the present invention, compared with the traditional method of metal ion implantation and annealing to prepare metal nanoparticles, the main differences are as follows: Difference (1) After the metal atoms are implanted into the surface of the substrate, a surface periodic treatment process is introduced. The transfer method of silica nanospheres is a common wet transfer method, which is characterized in that after being transferred to the surface of the substrate, the silica nanospheres will show a regular equilateral triangle arrangement, as shown in Figure 12. After that, the substrate is dry-etched to obtain nano-pillars on the surface of the substrate, in order to separate the implanted regions of metal atoms to form small regions. Each nanopillar and the silica nanospheres present a regular arrangement of equilateral triangles. The surface periodic treatment process is to prepare for the subsequent annealing to obtain periodically arranged metal nanoparticles. After annealing, the metal nanoparticles obtained by precipitation will maintain the same arrangement as the nanopillars. Surface periodicity is very important, as shown in Figure 17, taking metallic silver as an example, the white origin in the figure is silver nanoparticles, the left picture is the silver nanoparticles obtained by surface periodic treatment, the right picture is without surface The resulting silver nanoparticles were processed periodically. It can be seen that the silver metal nanoparticles on the left show a regular and orderly arrangement, but not on the right. Difference (2) Transfer a layer of graphene 105 on the surface of the etched substrate as a barrier layer. The purpose of this is to stop the evaporation of metal atoms. Current research has found that for graphene with a complete lattice, metal atoms cannot pass through, and at the same time, graphene has super mechanical properties. The above two properties make graphene very suitable as a barrier for the evaporation of metal atoms. After the graphene is transferred to the surface of the substrate, during the annealing process, once the metal atoms are precipitated to the surface of the substrate, due to the barrier of the graphene, the metal atoms will not evaporate, but will be bound by the graphene and stay on the surface of the substrate, This reduces the loss of metal atoms due to evaporation. Therefore, the annealing temperature can be greatly increased without worrying about the evaporation of metal atoms. Experiments have shown that in the absence of graphene, all the metal atoms deposited on the surface will evaporate during annealing, and no metal nanoparticles will be obtained on the surface of the substrate.

In the present invention, the mask for periodic surface treatment of the substrate can be made by transferring silicon dioxide nanospheres as a mask, or by nanoimprinting or transferring nanospheres of other materials to make a periodic mask.

Advantages of the present invention:

1. The use of graphene as a barrier for the evaporation of metal atoms can effectively prevent the loss of metal atoms, so the annealing temperature can be greatly increased, and larger-sized metal nanoparticles can be obtained.

2. After the metal nanoparticles are formed on the surface of the substrate, they are wrapped by graphene, and the graphene protects the metal nanoparticles and prevents them from contacting with the air. Therefore, the present invention is suitable for preparing nanoparticles of easily oxidizable metals, such as silver, copper, etc., and can realize long-term storage thereof.

3. Through the periodic treatment of the surface of the substrate, the periodic regular arrangement of the metal nanoparticles can be realized, so that the whole preparation method is more controllable.

4. Since it is found in experiments that each etched nano-column surface is fixed to form a metal nano-particle, the diameter of the metal nano-particle is affected by the number of metal atoms in each nano-column. Therefore, the size of the final metal nanoparticles can be adjusted by changing the dose of ion implantation or the diameter of the nanopillars.

5. By preparing periodic etching masks by other methods such as nano-imprinting, nano-pillars with different arrangements can be etched, and metal nanoparticles with different arrangements can be obtained.

Description of drawings

Figure 1: Schematic diagram of the substrate used for metal ion implantation;

Figure 2: Schematic diagram of metal ion implantation process;

Figure 3: Schematic diagram of the distribution of metal atoms inside the substrate after metal ion implantation;

Figure 4: Schematic diagram of the process of agglomeration of metal atoms to form metal nanoparticles during annealing;

Figure 5: Schematic diagram of the distribution and structure of the metal nanoparticles obtained during the annealing process inside the substrate;

Figure 6: Schematic diagram of the sample structure after metal ion implantation and transfer of silica nanospheres on the surface of the substrate;

Figure 7: Process schematic diagram of dry etching;

Figure 8: Schematic diagram of the sample structure after removing the silica nanospheres by ultrasonic deionized water;

Figure 9: Schematic diagram of the sample structure after transferring a layer of graphene on the surface of the sample;

Figure 10: Schematic diagram of the process of annealing, the agglomeration of metal atoms on the surface of the substrate to form metal nanoparticles;

Figure 11: Schematic diagram of the structure of the regularly arranged metal nanoparticle sample finally obtained on the surface of the substrate;

FIG. 12 is a scanning electron microscope (SEM) top view of the structural sample shown in FIG. 6 , that is, a top view of the SEM of the surface of the sample after the silica nanospheres are transferred. The circle circled by the black dotted line in the figure is the silica nanosphere, and its diameter is about 600 nm.

Figure 13: The SEM top view of the structural sample shown in Figure 8 at a tilt angle of 70 degrees, that is, the SEM top view of the sample at a tilt angle of 70 degrees after the nanopillars are etched and the silica nanospheres are removed.

Figure 14: SEM top view of the prepared silver nanoparticles, the white dots indicated by the black arrows in the figure are silver nanoparticles.

Figure 15: SEM top view of the sample after removing graphene, the circle circled by the black dotted line in the figure is the top view of the nanopillar, and the white dots in the figure are silver nanoparticles.

Figure 16: Schematic diagram of the structure of silver nanoparticles on the surface of circular nanopillars.

Figure 17: Optical microscope image of the real silver nanoparticles, the white origin in the figure is the silver nanoparticles. The picture on the left is the silver nanoparticles obtained by the surface periodic treatment, and the picture on the right is the silver nanoparticles obtained without the surface periodic treatment.

Detailed ways

The practice of the present invention is illustrated by the following examples, but the present invention is not limited to the following examples.

Example 1: Large-area preparation of silver nanoparticles

Taking the preparation of silver nanoparticles as an example, the method of the present invention is used to prepare:

S1 After cleaning the silicon wafer with a 300nm silicon dioxide layer, the ion implantation technique is used to implant silver atoms into the superficial layer of the substrate, the implantation dose is 5×10 ¹⁵ /cm ² , and the implantation energy is 30keV. , the implantation depth of silver atoms is about 22 nm.

S2 transfers silica nanospheres on the surface of the substrate implanted with silver atoms, and the diameter of the silica nanospheres is about 600 nm. The transfer method of silica nanospheres is a common wet transfer method, that is, firstly disperse the silica nanospheres uniformly in the solution, and then drop the solution mixed with the silica nanospheres on the surface of deionized water. Due to the surface tension of water (which can increase the surface tension of other solutes), the silica nanospheres will float on the surface of deionized water and form a regular arrangement of equilateral triangles. Finally, the silica nanospheres are pulled out from the deionized water by moving the substrate parallel to the water surface, and the silica nanospheres will be attached to the surface of the substrate and keep the original equilateral triangle shape. Regular arrangement. FIG. 12 is an SEM top view of the silica nanospheres on the surface of the substrate.

S3 uses a reactive ion etching (RIE) system to dry-etch the substrate with silicon dioxide nanospheres as a mask. The etching conditions are: power 300W, trifluoromethane: 100sccm, and etching time: 50s. Under this etching condition, the etching depth is about 40 nm (>22 nm for the implantation depth of silver atoms), which can separate the implanted regions of silver atoms. After etching, the silica nanospheres were removed from the surface of the substrate by ultrasonic deionized water. FIG. 13 is an SEM image of the substrate surface after etching at an inclination angle of 70 degrees. It can be seen that one by one circular nano-pillars are formed on the substrate surface.

S4 uses a wet transfer method to transfer a single layer of graphene on the surface of the substrate.

S5 anneals the substrate. Annealing conditions: 1050 degrees Celsius, 15 minutes, argon/hydrogen (960 sccm/40 sccm) atmosphere. The annealing temperature is much higher than the melting point of nano-silver. During the annealing process, silver atoms will be precipitated from the substrate. Due to the barrier of graphene, the silver atoms will not evaporate from the surface of the substrate, but will be bound between the interface between the graphene and the substrate. Finally, the silver atoms will agglomerate to form silver nanoparticles. The diameter of the silver nanoparticles is around 144 nm. 14 is a top view of the SEM of the silver nanoparticles obtained after annealing. It can be seen that the size of the silver nanoparticles is uniform, and the regular arrangement of the equilateral triangle is presented, and the arrangement is consistent with the silica nanospheres.

After etching the graphene with oxygen plasma at S6, the relative positional relationship between the silver nanoparticles and the circular nanopillars can be visually observed. As can be seen from Figure 15, the silver nanoparticles are in the center of the circular nanopillars, and each nanometer A silver nanoparticle is formed on the surface of the pillar. FIG. 16 is a schematic diagram of the structure of silver nanoparticles on the surface of circular nanopillars.

Claims (6)

1. A process method for preparing a large-area metal nanoparticle array with the assistance of graphene is characterized by comprising the following steps:

s1, preparing a substrate 101 required for metal ion implantation;

s2, injecting metal atoms 102 into the shallow surface layer inside the surface of the substrate 101 in a metal ion injection mode;

the steps S3-S5 are collectively referred to as surface periodic processing of the substrate;

s3, transferring the silica nanospheres 104 to the surface of the substrate 101 in the step S2 by a silica nanosphere transferring method; by adopting a solution transfer method, after the silicon dioxide nanospheres 104 are transferred to the surface of the substrate 101, the silicon dioxide nanospheres can be in close periodic arrangement on the surface of the substrate 101 due to the transfer mechanism;

s4, using the silicon dioxide nanospheres 104 as a mask, performing vertical dry etching on the surface of the substrate, wherein the etching depth is greater than the injection depth of the metal atoms 102, and finally obtaining the individual nano-columns 106 which are closely and regularly arranged on the surface of the substrate; the purpose of the etching is to separate the implanted regions of metal atoms 102, and the top surface of each nano-pillar 106 is a silicon dioxide nanosphere 104;

s5, removing the silicon dioxide nanospheres 104 on the top surfaces of the nano-pillars 106 from the surface of the substrate 101 by using a deionized water ultrasonic method;

s6, transferring a layer of graphene 105 on the surface of the substrate 101 through a wet transfer method;

s7, separating out the metal atoms 102 from the nano-pillars 106 on the surface of the substrate 101 to the top surfaces of the nano-pillars 106 by annealing and agglomerating, wherein the metal atoms 102 inside each nano-pillar 106 are thermally agglomerated and form a metal nanoparticle 103 on the top surfaces of the nano-pillars 106 during the annealing process, and the obtained metal nanoparticles 103 are arranged in the same manner as the nano-pillars 106 and the silicon dioxide nanospheres 104;

s8, finally, the metal nanoparticles 103 are periodically arranged on the surface of the substrate 101.

2. The method of claim 1, wherein the depth of implantation of the metal atoms 102 is controlled to be < 100nm from the surface at a shallow surface of the substrate.

3. The method of claim 1, wherein each of the nanopillars 106 has a diameter approximately equal to a diameter of the silica nanospheres 104, and each of the nanopillars 106 contains metal atoms 102.

4. A method as claimed in claim 1, characterized in that a silicon substrate is used which is covered with a silicon dioxide layer, or a quartz substrate, or another insulating substrate.

5. The method of claim 1, wherein the metal is selected from one or more of noble metals, aluminum, iron, and other metals.

6. The method of claim 1, wherein the annealing is at a temperature greater than or equal to the melting point temperature of the corresponding metal of the metal atom.

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