CN117144361A

CN117144361A - Method for integrating carbon nano tube and SnZn alloy to realize controllable thermal management

Info

Publication number: CN117144361A
Application number: CN202311126312.2A
Authority: CN
Inventors: 朱敏敏; 赵安文; 杨丹; 张海忠
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2023-09-04
Filing date: 2023-09-04
Publication date: 2023-12-01

Abstract

The application discloses a method for integrating carbon nanotubes with SnZn alloy to realize controllable thermal management. The method adopts Atomic Layer Deposition (ALD) technology to deposit SiO-containing material ₂ Iron and aluminum oxide films are prepared on the silicon wafer with the oxide layer as the carbon nanoThe catalyst for the growth of the nanotubes is then used to prepare a carbon nanotube wafer array on a silicon wafer using a Chemical Vapor Deposition (CVD) technique with iron/alumina as the catalyst. The method can control the microstructure, dielectric constant and other electrical properties of the carbon nanotube film. Meanwhile, the control of the working temperature from 200 ℃ to 400 ℃ is successfully realized by integrating the carbon nano tube and the SnZn alloy. The application provides a complete flow from catalyst preparation to film growth of the carbon nanotubes and a method for integrating the carbon nanotubes with SnZn alloy to realize controllable thermal management, which can be used for manufacturing devices based on carbon nanotube composite materials and having wide operating temperature requirements.

Description

Method for integrating carbon nano tube and SnZn alloy to realize controllable thermal management

Technical Field

The application belongs to the technical field of two-dimensional material growth, and particularly relates to a method for growing carbon nanotubes by using an iron/aluminum oxide catalyst and integrating the carbon nanotubes with SnZn alloy to realize controllable thermal management.

Background

In recent years, with the vigorous development of the electronic information industry, portable electronic equipment and new energy industry in China, the demand for new materials is also increased. The carbon nano tube has very good mechanical, electrical and optical characteristics, has very considerable application value in the fields of microwave absorption, anti-corrosion materials, electromagnetic shielding, energy storage, solar cells, chemical sensors, field emission materials and the like, and is considered to be one of the most important nano materials in the twenty-first century. The carbon nanotube composite material can effectively improve the performance of the target material.

The preparation of the carbon nano tube requires the use of a catalyst, the current mainstream preparation methods of the catalyst comprise spin coating, spray coating, ion sputtering and the like, the modes have certain requirements on the substrate material and the shape, the catalyst preparation of the substrate with any shape can not be met, and the size distribution of catalyst particles can not be accurately controlled, so that the quality of the carbon nano tube is affected.

The narrow thermal management window severely limits the reliability and performance of today's high-speed, high-energy-consumption micro-nano-scale electronics. The thermal rectification effect is similar to the modulation of electron flow in an electron diode and is an effect that varies in opposite directions along the heat flow capacity of the medium. Because of its ability to modulate phonon transport, the thermal rectifying effect has great potential in future passive thermal regulation devices, including thermal memories, thermal transistors, and thermal logic circuits. It is well known that the thermal rectifying effect in these bulk systems is related to surface properties such as metal/insulator effects, thermal strain at the interface, thermal conductivity at the interface, and thermal barriers. Although the thermal rectification effect has been theoretically predicted in carbon nanotubes, little effort has been made in carbon nanotube array experiments.

Many studies have shown in theory that experimental verification on the nanoscale has been successful by only a few in the case of different diameters and contact interfaces, and in the case of defective and strained carbon nanotubes, and that practical experimental implementation remains a technical challenge due to the complexity of phonon transport coupling between individual atoms and the surrounding environment in thermal rectification effects.

Disclosure of Invention

In view of the above state of the art, it is an object of the present application to provide a method for growing carbon nanotubes with iron/alumina catalysts and integrating the carbon nanotubes with SnZn alloys for controlled thermal management.

To achieve this object, the present application provides a method for growing carbon nanotubes using the prepared iron/alumina catalyst, and a method for integrating carbon nanotubes with SnZn alloy to achieve controlled thermal management.

The method for growing the carbon nano tube by using the prepared iron/aluminum oxide catalyst provided by the application comprises the following steps: in the presence of SiO ₂ Standard 4 inch silicon wafer with oxide layer is used as substrate, and Atomic Layer Deposition (ALD) technology is used for SiO on the substrate ₂ Sequentially depositing an alumina film and an iron film on the surface to prepare a catalyst iron/alumina composite film, wherein alumina is used as a buffer layer; and catalyzing and growing the thin-walled carbon nano tube by using the prepared iron/aluminum oxide catalyst. The preparation method comprises the following steps:

(1) SiO-containing with melting point higher than 450 DEG C ₂ The standard 4-inch silicon wafer of the oxide layer is taken as a substrate, and ethanol is firstly used for carrying out ultrasonic cleaning on the substrate for 5-10 minutes so as to remove organic and inorganic compounds on the surface of the substrate; reuse forWashing the substrate with ionized water to clean the substrate; plating an iron/aluminum oxide catalyst film on the surface of the substrate by utilizing an atomic layer deposition system; annealing the iron/aluminum oxide film in the presence of argon, hydrogen and water;

(2) Adopting a chemical vapor deposition technology, taking ethylene steam as a carbon source, taking argon and hydrogen as atmosphere gases, and synthesizing carbon nanotubes on the substrate after the treatment in the step (1); after 10-30 minutes of growth, a uniform and dense carbon nano tube array grows on the surface of the substrate, so that the preparation of the carbon nano tube material is carried out, and the total growth time is set to be unequal from 1h to 6h for researching the growth speed.

And (3) when atomic layer deposition is carried out in the step (1), the temperature is 200-300 ℃ and the pressure is 10-200 Pa.

In the step (1), the volume ratio of the carrier gas to the atomic layer deposition vacuum reaction cavity is 1 (5-50).

In the step (1), the repeated times of alumina deposition are 20-100 times; the iron deposition repetition number is 5-50. And during atomic layer deposition, the quality of iron and aluminum oxide is further adjusted by adjusting the cycle times.

In the step (1), in the iron/aluminum oxide catalyst, the mass percentage of aluminum oxide is 1-15%, the mass percentage of iron element is 1-3%, and the rest is silicon dioxide. When the alumina and iron content are in the above ranges, the catalytic performance of the iron/alumina catalyst can be further optimized.

In the step (1), the annealing treatment temperature is 600 ℃ and the time is 15 minutes.

In the step (2), the method for growing the carbon nanotubes by using the chemical vapor deposition technology is to determine that the bubbler system is kept at 50-100 ℃, and the purpose of the bubbler system is mainly to improve the activity of the catalyst.

In the step (2), the chamber is depressurized to 5-20 mTorr before CVD growth. And then turning off the pump and injecting 4000-6000 sccm argon.

In the step (2), the temperature is increased to 500-700 ℃ before the growth process, and 3000-5000 sccm argon and 1000-2000 sccm hydrogen are used for treating on the catalyst for 10-20 minutes.

In the step (2), a reaction furnace is heated to 700-800 ℃ in the growth process, and then ethylene with 500-1500 cubic centimeters is introduced for growth.

In the step (2), the growth time is controlled to be 0.5-6 hours respectively, and the maximum growth length of the carbon nano tube is tested.

The application prepares the SnZn alloy film on the prepared carbon nano tube by adopting an electron beam deposition technology, and realizes controllable thermal management within the working temperature range of 200-400 ℃ by controlling the stoichiometric ratio of Sn and Zn.

The preparation process of the SnZn alloy film adopts an electron beam deposition technology to prepare a series of Sn _x Zn _1-x Alloy thin films (x=0%, 10%, 20%, 25%, 50% and 90%). The chamber pump was reduced to 1.0X10 before depositing the alloy film ^-6 ~2.0×10 ^-6 Low pressure of the tray. During this process, the sample holder is rotated to obtain a uniform film. The applied current and operating voltage are about 10-30 mA and 5-10 kV, respectively. The growth time is about 30-60 minutes. The thickness of the prepared alloy film is 400-600 nm.

The SnZn alloy is utilized to realize the control of the working temperature of the carbon nano tube from 200 ℃ to 400 ℃. With the change of the stoichiometric ratio of the two elements in the SnZn alloy, the melting point of the SnZn is changed within the range of 200-400 ℃. The method is shown that the device can work within a wide range of 200-400 ℃ conveniently by adjusting the stoichiometric ratio of Sn and Zn.

More importantly, this structure can produce a strong thermal rectifying effect at the interface due to the disruption of the mass and thermal conductivity mismatch. And a thermal rectifying device based on the mixed materials is also realized, and the thermal rectifying coefficient is between 0.49 and 0.66.

Compared with the prior art, the application has the following technical advantages:

(1) The preparation method of the application has the advantages of low cost, simple and easy operation, good uniformity, simpler operation compared with other methods, less operation conditions, safe preparation process and no pollution to the environment.

(2) Can be used for preparing silicon wafer materialThe catalyst with uniform size and space distribution is prepared on the surface and used for catalyzing and growing the carbon nano tube, thereby realizing the simple and rapid preparation of various carbon nano tube composite materials. In the iron/alumina catalyst prepared by the method, the film formed by atomic layer deposition is reduced to form active centers in situ, and the active centers have the characteristics of controllable particle size and uniform size, and FeO _X The iron environmental atoms formed after reduction have high dispersion singleness, so that the iron/aluminum oxide catalyst has good catalytic activity.

(3) The application realizes the control of the working temperature of the device from 200 ℃ to 400 ℃ by combining with the SnZn alloy, and the rectification coefficient is between 0.49 and 0.66. Through experiments, a solid-state thermal circuit of the carbon nano tube and the SnZn alloy is realized, and the thermal rectification effect in the metal or alloy integrated carbon nano tube array is clarified, so that the carbon nano tube composite material can be applied to devices with wider thermal working ranges.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present application, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.

Fig. 1 shows a schematic diagram of a design of a Fe catalyst synthesized carbon nanotube array. (I) Synthesizing catalyst by Atomic Layer Deposition (ALD), (II) forming bubble-assisted FeO by annealing _x Nanoparticles, (III) growing carbon nanotubes.

Fig. 2 shows a schematic view of synthesis temperature distribution and precursor gas introduction process of the carbon nanotubes of example 1. (I) Heating to 600 ℃, annealing the catalyst, (III) growing the carbon nano tube, and (IV) cooling.

Fig. 3 is a graph showing the length change of the carbon nanotubes grown over time according to example 1.

Fig. 4 is a scanning electron microscope image of the pure carbon nanotube array of example 1.

Fig. 5 is a scanning electron microscope image of the combination of the carbon nanotube array and the SnZn alloy of example 1.

Fig. 6 shows a schematic diagram of a thermal rectification measuring apparatus of example 1. The heat insulation part is composed of a copper belt, a heater/cooler, a heat insulation layer and a supporting hard plate from top to bottom in sequence. A carbon nanotube based device is mounted between two insulating portions.

The melting behavior of the sample and composite material of the carbon nanotube array combined with the SnZn alloy is shown in fig. 7 (a). (b) SnZn alloy experimental samples showing different SnZn ratios were compared with the melting points of differential scanning calorimetric analysis.

Detailed Description

The application will be further described with reference to the accompanying drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

Example 1

A method for growing carbon nanotubes and integrating the carbon nanotubes with SnZn alloy using an iron/alumina catalyst to achieve controlled thermal management, comprising the steps of:

1) Will be ready to contain SiO ₂ And placing the silicon substrate of the oxide layer in a cleaning frame, sequentially performing ultrasonic cleaning for 10min by using acetone, absolute ethyl alcohol and deionized water, removing pollutants on the substrate, and preventing residual impurities on the substrate from affecting the subsequent film growth. Atomic layer deposition technique is adopted to deposit SiO ₂ And sequentially depositing an aluminum oxide film and an iron film on the oxide layer to prepare an iron/aluminum oxide composite film serving as a catalyst for the growth of the carbon nano tube. The thickness of the aluminum oxide film was 5nm, and the thickness of the iron film was 1nm.

2) Adopting a chemical vapor deposition technology, taking ethylene steam as a carbon source, taking argon and hydrogen as atmosphere gases, and synthesizing carbon nanotubes on the substrate after the catalyst treatment in the step 1); the method specifically comprises the following steps: and (3) placing the silicon wafer after the catalyst coating is completed in a quartz boat, placing the silicon wafer in the central position of a tube furnace, heating to 800 ℃ at the speed of 10 ℃/min, taking 100sccm argon and hydrogen as carrier gas to load ethylene as a carbon source, and growing for 30 minutes to grow a uniform and dense carbon nanotube array on the surface of the substrate, thereby completing the preparation of the carbon nanotube material. The chamber is depressurized to 5-20 mTorr prior to CVD growth. In the growth process, the reactor was heated to 800℃and then 1000 cubic centimeters of ethylene was introduced for growth.

3) A series of Sn are prepared by adopting an electron beam deposition technology _x Zn _1-x Alloy film (x=10%). The method specifically comprises the following steps: the deposition is carried out by taking Sn-Zn alloy with fixed proportion as evaporation film material, and the mole ratio of Sn-Zn component of the film material is 1:9, pumping down the chamber to 1.2X10 before depositing the alloy film ^-6 The low pressure of the holder, during which the sample holder is rotated to obtain a uniform film; the applied current and operating voltage were about 20mA and 5kV, respectively; the growth time was 30 minutes, and the thickness of the alloy film was about 500 a nm a.

Example 2

3) A series of Sn are prepared by adopting an electron beam deposition technology _x Zn _1-x Alloy film (x=50%). The method specifically comprises the following steps: the deposition is carried out by taking Sn-Zn alloy with fixed proportion as evaporation film material, and the mole ratio of Sn-Zn component of the film material is 5:5, pumping down the chamber to 1.2X10 before depositing the alloy film ^-6 The low pressure of the holder, during which the sample holder is rotated to obtain a uniform film; the applied current and operating voltage were about 20mA and 5kV, respectively; the growth time was 30 minutes, and the thickness of the alloy film was about 500 a nm a.

Example 3

1) Will be ready to contain SiO ₂ And placing the silicon substrate of the oxide layer in a cleaning frame, sequentially performing ultrasonic cleaning for 30min by using acetone, absolute ethyl alcohol and deionized water, removing pollutants on the substrate, and preventing residual impurities on the substrate from affecting the subsequent film growth. Atomic layer deposition technique is adopted to deposit SiO ₂ And sequentially depositing an aluminum oxide film and an iron film on the oxide layer to prepare an iron/aluminum oxide composite film serving as a catalyst for the growth of the carbon nano tube. The thickness of the aluminum oxide film was 5nm, and the thickness of the iron film was 1nm.

3) A series of Sn are prepared by adopting an electron beam deposition technology _x Zn _1-x Alloy film (x=90%). The method specifically comprises the following steps: the deposition is carried out by taking Sn-Zn alloy with fixed proportion as evaporation film material, and the mole ratio of Sn-Zn component of the film material is 9:1, pumping down the chamber to 1.2X10 before depositing the alloy film ^-6 The low pressure of the holder, during which the sample holder is rotated to obtain a uniform film; the applied current and operating voltage were about 20mA and 5kV, respectively; the growth time was 30 minutes, and the thickness of the alloy film was about 500 a nm a.

Fig. 1 shows a schematic diagram of a design of a Fe catalyst synthesized carbon nanotube array. Throughout the CVD process, the Fe catalyst undergoes three distinct phases: (i) Synthesizing a catalyst by an Atomic Layer Deposition (ALD), in an atomic layer deposition vacuum reaction cavity, pulsing an alumina precursor to the surface of the NG substrate, then holding the gas, enabling the alumina precursor to be adsorbed on the surface of the NG substrate, and then carrying out gas extraction to remove the unadsorbed alumina precursor; in an atomic layer deposition vacuum reaction cavity, pulse an iron precursor to the surface of the obtained alumina deposition layer, then hold breath, enable the iron precursor to be adsorbed on the surface of the NG substrate, and then carry out air suction to remove the unadsorbed iron precursor; when atomic layer deposition is carried out, the temperature is 250 ℃, the pressure is 200Pa, and the volume ratio of carrier gas to atomic layer deposition vacuum reaction cavity is 1 (50) min ^-1 The method comprises the steps of carrying out a first treatment on the surface of the (ii) Bubble assisted FeO formation by annealing _x Nanoparticles, (iii) growing carbon nanotubes. The formation of iron catalyst nanoparticles under a hydrogen atmosphere prior to the growth step is a critical process for the production of high quality carbon nanotubes. Thus, the key process of the present application is the treatment of the prepared iron catalyst film in hydrogen in the second stage. Preparing a VACNT wafer array with the thickness of more than 4mm on a Si wafer by adopting a thermal Chemical Vapor Deposition (CVD) technology and taking Fe as a catalystColumns. The bubbler hood was first heated to 56.5 ℃ while the bubbler tube was maintained at 80 ℃ and the water in the bubbler was deionized water. The purpose of the bubbler system is primarily to increase the activity of the catalyst. Prior to CVD growth, the chamber is pumped down to around 10 mTorr. The pump was then turned off and 5000sccm Ar was injected. Subsequently, the temperature was increased to 600℃with 3920sccm Ar and 1324 sccm H ₂ The Fe catalyst was treated for 15 minutes. Due to H ₂ The presence of O provides oxygen atoms for Fe, forming oxidized nano-iron particles (FeO _x ). Finally, the furnace was heated to 750℃and 1000 cc of C was introduced ₂ H ₄ And (5) growing. The method can reduce the consumption of the iron catalyst, thereby promoting the growth of the ultra-long carbon nano tube. Unlike the significance of the diffusion of the Fe catalyst into the Al film, al ₂ O ₃ The presence of a layer can significantly reduce the loss of Fe catalyst due to its lower diffusion coefficient. Notably, the conversion of Fe catalysts is strongly dependent on the surrounding environment, such as temperature and pressure.

Other factors include catalyst-washcoat interactions and gas-catalyst reactions. In addition, the flow rate of the bubbler has a certain effect on the uniformity and alignment of the carbon nanotubes. Therefore, controlling the Fe catalyst loss due to diffusion during the pretreatment stage is critical for growing millimeter-long carbon nanotubes on wafer-level substrates. The alumina support can significantly inhibit the diffusion of iron, thereby forming small iron nanoparticles. At the same time, iron oxide nanoparticles (FeO _x ) The mobility is lower than that of metallic Fe catalyst. By this combination, the length of the CNT can reach 4.5mm after 6 hours of growth.

Fig. 2 shows a schematic diagram of the synthesis temperature distribution of carbon nanotubes and the precursor gas introduction process. After loading the prepared catalyst film, the chamber temperature was increased to 600 ℃ with Ar gas (5000 sccm). Subsequently, 4 inch Fe/Al ₂ O ₃ /SiO ₂ Si wafer at Ar/H ₂ (3920 sccm:1000 sccm) annealing at 600℃for 15 minutes in a mixed gas atmosphere and under aqueous conditions, resulting in a catalyst FeO _x Nanoparticle formation. For carbon nanotube growth, the temperature was increased to 750℃and C ₂ H ₄ (1000 sccm) gas was added as a carbon source to chamber (III). After growth, the reactor was closed and the sample was allowed to cool (IV). Notably, the growth rate from 0.5 to 4 hours was almost linear at around 1 mm/hour. However, after 4 hours of growth, the growth rate was significantly decreased, mainly due to the consumption of the Fe catalyst (fig. 3).

The influence of the SnZn alloy film on the microstructure of the carbon nano tube is studied. Fig. 4 shows a scanning electron microscope image of a pure carbon nanotube array. The results show that the grown samples have high density of carbon nanotubes. The color of the SnZn deposited samples turned grey compared to the original black of the carbon nanotube samples (fig. 5). After the SnZn alloy is deposited, the surface of the carbon nano tube is covered with a thick film. The film consists of SnZn nanoparticles, and has a size of hundreds of nanometers. The SnZn layer forms a distinct thermal interface on top of the carbon nanotube sample.

The custom setup was used to measure the thermal rectification effect using a bottom-up symmetrical design. The device consists of two supporting hard plates, two insulators, two heaters, two coolers and a circulating cooling water system. The carbon nanotube-based sample is fixed in a central position. The temperature of the cooling water is kept at 0-10 ℃. Meanwhile, the flow rate is about 0.2mL/min. The chamber pump should be reduced to a low pressure of 30mTorr during measurement, which can effectively reduce heat loss.

Fig. 6 shows a schematic diagram of a thermal rectification measuring device which is of symmetrical structure and is convenient to heat from top to bottom. The carbon nanotube-based device is mounted between two insulators, and heat loss can be effectively reduced. In this setup, there are two models: fixed current and segmented current. The former can be used to determine the melting behavior of SnZn alloys and the latter can be used to study heat transfer over different temperature ranges.

Control of the operating temperature of the carbon nanotubes from 200 ℃ to 400 ℃ was achieved using SnZn alloy (fig. 7). More importantly, such a structure can produce a strong thermal rectifying effect at the interface due to the disruption of the mass and thermal conductivity mismatch. In addition, a thermal rectifying device based on the mixed materials is also realized, and the thermal rectifying coefficient is between 0.49 and 0.66 (table 1).

TABLE 1 thermal boundary resistance and thermal rectification coefficient of carbon nanotube arrays and SnZn alloys in different proportions at 120℃forward temperature

The above description is only a preferred embodiment of the present application, and is not intended to limit the application in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present application still fall within the protection scope of the technical solution of the present application.

Claims

1. A method for integrating carbon nanotubes and SnZn alloy to realize controllable thermal management is characterized in that the carbon nanotubes are prepared by adopting a chemical vapor deposition technology, and the carbon nanotubes are integrated with the SnZn alloy by adopting an electron beam deposition technology; the method specifically comprises the following steps:

step one: cleaning the substrate, and depositing on SiO-containing substrate by atomic layer deposition ₂ Sequentially depositing an aluminum oxide film and an iron film on a silicon wafer of the oxide layer to prepare the iron/aluminum oxide film as a catalyst for the growth of the carbon nano tube; annealing the iron/aluminum oxide film in the presence of argon, hydrogen and water;

step two: synthesizing carbon nano tubes on a substrate of the growth catalyst in the first step by adopting a chemical vapor deposition technology and taking ethylene steam as a carbon source and argon and hydrogen as atmosphere, and growing a uniform and dense carbon nano tube array on the surface of the substrate after 10-30 minutes of growth, thereby completing the preparation of carbon nano tube materials;

step three: and (3) depositing an SnZn alloy film on the carbon nano tube prepared in the second step by adopting an electron beam deposition technology, and controlling the stoichiometric ratio of Sn to Zn to realize controllable thermal management within the working temperature range of 200-400 ℃.

2. The method of claim 1, wherein the iron/alumina catalyst is prepared by an atomic layer deposition technique in step one, wherein the number of repetitions of alumina deposition is 20-100 and the number of repetitions of iron deposition is 5-50; the thickness of the aluminum oxide film is 5-15 nm, and the thickness of the iron film is 1-5 nm; the annealing temperature was 600℃and the time was 15 minutes.

3. The method of claim 1, wherein the chamber is depressurized to 5-20 mtorr before growing the carbon nanotubes by chemical vapor deposition, and then the pump is turned off and 4000-6000 sccm argon is injected.

4. The method of claim 1, wherein the step two chemical vapor deposition process is performed by raising the temperature to 500-700 ℃ and treating the carbon nanotubes with 3000-5000 sccm argon and 1000-2000 sccm hydrogen over the catalyst for 10-20 minutes.

5. The method according to claim 1, wherein in the second growth step, the chemical vapor deposition reaction furnace is heated to 700-800 ℃, and then ethylene of 500-1500 cubic centimeters is introduced for growth.

6. The method of claim 1, wherein the chamber pump is lowered to 1.0 x 10 before depositing the alloy film in step three ^-6 ~2.0 ×10 ^-6 Low pressure of the tray.

7. The method of claim 1, wherein the sample holder is rotated during the step three deposition to obtain a uniform film.

8. The method of claim 1, wherein the current and the operating voltage applied during the third deposition step are 10-30 ma and 5-10 kv, respectively.

9. The method according to claim 1, wherein the growth time in the third step is 30-60 minutes, and the thickness of the prepared alloy film is 400-600 nm.

10. The method according to claim 1, wherein the SnZn alloy thin film prepared in the third step has a chemical formula of Sn _x Zn _1-x ，x=0.1-0.9。