CN103172059B - The preparation method of Graphene - Google Patents

Abstract

The invention discloses a method for preparing graphene. The method comprises: preparing a graphene layer on a first-type metal catalyst layer; and doping a second-type metal into the first-type metal catalyst layer to form an alloy so that the The melting point of the alloy is lower than the melting point of the first type of metal; the alloy is formed by doping the second type of metal in the first type of metal catalyst layer to reduce the melting point of the catalyst layer; at a temperature that does not destroy the graphene structure, the catalyst layer Volatilization can occur, and the metal catalyst layer below the prepared graphene layer becomes a series of discontinuous metal points. The graphene layer is only in contact with a part of the metal points of the underlying substrate, and is basically in a suspended state, so it is very easy to transfer.

Description

The preparation method of graphene

technical field

The invention relates to a method for preparing graphene materials, in particular to a method for preparing graphene which is easy to transfer.

Background technique

Since Geim successfully obtained single-layer graphene through mechanical separation in 2004, graphene has set off an extensive research boom. Graphene is a two-dimensional honeycomb structure formed by a single layer of carbon atoms tightly packed. It has extraordinary optical, electrical, thermal and mechanical properties, and has shown great application potential in the fields of nanoelectronic devices, sensors and optoelectronic devices. At present, the main means of preparing graphene are: mechanical separation method, redox method and chemical vapor deposition method (Chemical Vapor Deposition, CVD). The CVD method is a method in which hydrocarbon gases such as methane and ethylene are adsorbed on the surface of a metal catalyst substrate at high temperature, and decomposed and recombined to form graphene under the action of metal catalysis. Compared with mechanical separation and redox method, CVD method can prepare graphene with larger area, so it has attracted special attention of scientists.

But this method itself also has great flaws. Generally, CVD methods use transition metals such as Cu and Ni as catalysts. Since the melting points of Cu and Ni metals are very high, they are 1083°C and 1453°C respectively, and the commonly used temperature for growing graphene is 900~1000°C, so after the growth is over, There is basically no loss of the metal catalyst, and the grown graphene is completely attached to the metal catalyst. An additional transfer step is required for practical use of graphene produced in this way in devices. The transfer usually needs to be soaked in FeCl ₃ solution for nearly ten hours to etch off the metal substrate, and then pick up and dry with the target substrate. This process is time-consuming, labor-intensive, and difficult to control. It also introduces foreign impurities and even causes damage to the graphene structure. These impurities and defects are likely to be the culprits that lead to the degradation of graphene's electrical properties. Therefore, scientists are trying to find ways to grow easily transferable graphene or directly grow graphene on the target substrate.

Contents of the invention

Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a kind of method for preparing graphene that is easy to transfer.

To achieve the above object, the present invention provides the following technical solutions:

A method for preparing graphene, the method comprising: S1, preparing a carbon film on a first-type metal catalyst layer; S2, evaporating a second-type metal to make it doped into the first-type metal catalyst layer to form an alloy, The melting point of the alloy is lower than the melting point of the first type of metal catalyst; S3, evaporating the alloy to obtain a graphene layer.

Wherein, the material of the first type of metal catalyst layer is selected from one of Ni, Cu, Co, Pt, Ir, Ru and Fe, and the second type of metal is selected from Ga, Bi, Sn, Pb and In one of them.

By doping the second metal catalyst layer into the first metal catalyst layer to form an alloy to reduce the melting point of the catalyst layer; at a temperature that does not destroy the graphene structure, the catalyst layer can be volatilized, and the metal under the graphene layer after preparation is The catalyst layer becomes a series of discontinuous metal points, and the graphene is only in contact with part of the underlying metal points, and is basically in a suspended state, so it is very easy to transfer.

The graphene prepared by the present invention does not require nearly ten hours _of FeCl3 solution etching process, and only needs to be ultrasonicated in deionized water for 30s, and the graphene will fall off from the substrate; The graphene can be transferred to a target substrate. The method provided by the invention simplifies the cumbersome transfer steps brought about by the traditional preparation method, and at the same time, compared with the traditional method, the transferred graphene provided by the invention can maintain the integrity of the shape and structure, and alleviate the damage and pollution of graphene during the transfer process .

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments described in this application, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the schematic flow sheet of the preparation method of graphene of a specific embodiment of the present invention;

Fig. 2 is the scanning electron micrograph of the graphene that a specific embodiment of the present invention prepares;

Fig. 3 is the scanning electron microscope top view of graphene rotation 80 degrees as shown in Fig. 2;

Fig. 4 is the scanning electron microscope image after graphene as shown in Fig. 2 is transferred on the silicon chip;

FIG. 5 is a Raman spectrum image of the graphene shown in FIG. 2 .

Detailed ways

The object of the present invention is to provide a method for preparing easily transferable graphene.

To achieve the above object, the present invention provides the following technical solutions:

A method for preparing graphene, the method comprising: S1, preparing a carbon film on a first-type metal catalyst layer; S2, evaporating a second-type metal to make it doped into the first-type metal catalyst layer to form an alloy, The melting point of the alloy is lower than the melting point of the first type of metal catalyst; S3, evaporating the alloy to obtain a graphene layer.

Wherein, the material of the first type of metal catalyst layer is selected from one of Ni, Cu, Co, Pt, Ir, Ru and Fe, and the second type of metal is selected from Ga, Bi, Sn, Pb and In one of them.

By doping the second metal catalyst layer into the first metal catalyst layer to form an alloy to reduce the melting point of the catalyst layer; at a temperature that does not destroy the graphene structure, the catalyst layer can be volatilized, and the metal under the graphene layer after preparation is The catalyst layer becomes a series of discontinuous metal points, and the graphene is only in contact with part of the underlying metal points, and is basically in a suspended state, so it is very easy to transfer.

Fig. 1 shows the schematic flow sheet of the preparation graphene of this specific embodiment; Concrete preparation method is:

S101, preparation of metal catalyst layer: prepare a first type metal catalyst layer on a first substrate; wherein the substrate is a SiO ₂ /Si substrate; the material of the first type metal catalyst layer in this embodiment is Ni ; The method for preparing the first-type metal catalyst layer includes one of electron beam evaporation, magnetron sputtering and pulsed laser deposition; the thickness of the prepared first-type metal catalyst layer is 100-500nm;

S102, preparation of a carbon thin film: sputtering a layer of carbon thin film on the metal catalyst layer by using a vacuum sputter coater; the thickness of the carbon thin film is 2-10 nm;

S103, preparation of the second type of metal source: drop the second type of metal liquid droplets on the second substrate; wherein the substrate is a SiO ₂ /Si substrate; the material of the second type of metal in this embodiment is Ga; the metal droplet Ga is used as the gallium source to form the Ga-Ni alloy, and the Ga vapor formed at high temperature forms an alloy with the catalyst metal Ni on the substrate;

S104, sample placement: place the first substrate and the second substrate in the reaction furnace; the order of placement is: along the airflow direction, the second substrate is located in front of the first substrate;

S105, gas purging: pass inert gas and hydrogen to purge the reaction chamber and maintain the air flow; wherein, the flow range of inert gas is 1000~2000 ml/min under standard conditions; the flow range of hydrogen is 100~500 ml/min under standard conditions ;

S106, annealing: raising the temperature in the reaction chamber to a specific temperature, and holding for a period of time; wherein, the specific temperature range is 700-1000°C, and the holding time range is 5-30 minutes;

S107, cooling down: rapidly cooling the reaction chamber to room temperature;

S108, ultrasonic treatment: put the sample with the graphene film in deionized water for 0.5-5 minutes, so that the graphene layer is separated from the alloy layer below;

S109, scooping: scooping with a clean target substrate.

The following will further explain some of the above steps.

The purpose of plating metal Ni on the substrate in the step S101 is that Ni acts as a catalyst for carbon atom recombination to form graphene at high temperature; carbon atoms first dissolve into metal Ni at high temperature, and then carbon atoms re-precipitate when the temperature is lowered, and Graphene is formed under the catalytic action of Ni.

The amorphous carbon film sputtered in the step S102 is used as a carbon source for growing graphene, and provides carbon atoms constituting graphene; here, the sputtered amorphous carbon film cannot exceed 10 nm. Because too many carbon atoms are provided, the graphene layers grown are too thick, and the characteristics of graphene will be lost.

The metal Ga dropped in the step S103 is used as a gallium source for forming a Ga-Ni alloy, and the Ga vapor formed at high temperature forms an alloy with the catalyst metal Ni on the substrate.

In the step S104, attention should be paid to the position of the sample. The sample with the Ga source must be placed first along the direction of the air flow, and then the sample with the metal Ni, so that the Ga vapor can form with the metal Ni in the downwind direction. Alloy, otherwise Ga vapor will be taken away by the air flow and cannot fully contact with Ni metal.

In the step S106, during the high-temperature annealing process, the amorphous carbon decomposes, dissolves, and reorganizes to form graphene under the catalysis of the metal, and the catalytic alloy evaporates and disappears continuously while the graphene is formed. The temperature here should not be too low, ranging from 700 to 1000 degrees, and the metal cannot evaporate effectively if the temperature is too low.

The purpose of ultrasound in deionized water in the step S108 is to separate the graphene film from the alloy substrate below; due to the basic evaporation of the alloy, only some metal points are left, and the graphene is only in contact with some metal points, basically in a suspended state ; Therefore, it can be separated from the underlying alloy by ultrasonic treatment for 0.5~5min.

In the step S109, as long as a clean target substrate is used for fishing, the graphene will be attached to the target substrate.

The graphene provided by the present invention does not require nearly ten hours _of FeCl3 solution etching process, only needs to be ultrasonicated in deionized water for 30s, and the graphene will fall off from the substrate; Transfer the graphene to the target substrate. The method provided by the invention simplifies the cumbersome transfer steps brought about by the traditional preparation method, and at the same time, compared with the traditional method, the transferred graphene provided by the invention can maintain the integrity of the shape and structure, and alleviate the damage and pollution of graphene during the transfer process .

Next, provide a specific implementation example of the present invention, referring to Fig. 1, the specific operation steps of this implementation example are:

1) Take a SiO ₂ /Si wafer and record it as No. 1 silicon wafer, and use electron beam evaporation to evaporate a layer of 300nm metal nickel catalyst on the surface of SiO ₂ ;

2) Use a sputter coater to sputter an amorphous carbon film with a thickness of 6nm on the metal nickel catalyst layer;

3) Take another SiO ₂ /Si wafer, denoted as No. 2 silicon wafer, and drop a drop of liquid gallium metal on it;

4) Put the samples into the reaction chamber in the order of No. 2 and No. 1 along the airflow direction;

5) Infuse 2 slm Ar gas and 0.2 slm H ₂ into the reaction chamber under normal pressure, and raise the temperature at a rate of 5°C/min;

6) After reaching 950°C, keep warm at 950°C for 20 minutes;

7) Cool down to room temperature; finally obtain a circular graphene sheet with a diameter of 200-500um.

Fig. 2 is the scanning electron micrograph of the graphene prepared by the specific examples above; it can be seen from Fig. 2 that the continuous metal catalyst layer has become a series of discontinuous metal points.

Figure 3 is a top view of a scanning electron microscope with graphene rotated 80 degrees as shown in Figure 2; it can be seen from Figure 3 that graphene is basically separated from the underlying metal, and only part of it is in contact with the underlying metal, so it is very easy to transfer.

To transfer the prepared graphene to the target substrate, the following processing is also carried out:

8) Ultrasonic treatment in deionized water for 30s to make the graphene fall off;

9) Pick up and dry with a clean SiO ₂ /Si sheet.

The scanning electron microscope image after transfer is shown in Figure 4. Graphene can maintain a perfect circular shape; this transfer method greatly simplifies the cumbersome steps of traditional methods and reduces the damage and pollution to graphene.

Fig. 5 is the Raman spectrum image of the graphene prepared by the specific examples above, and it can be judged from the peak position, peak shape, and peak intensity that the prepared graphene has about 5 layers.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or order between them. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or device. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

The above is only a specific implementation method listed by the application. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the application, some improvements and modifications can also be made. These improvements and Retouching should also be considered as the scope of protection of this application.

Claims (8)

1. a preparation method of graphene, the method comprising: S1, prepare carbon thin film by sputtering method on the first type metal catalyst layer, the material of described first type metal catalyst layer is selected from wherein one of Ni, Cu, Co, Pt, Ir, Ru and Fe; S2. Evaporate the second type of metal to be doped into the first type of metal catalyst layer to form an alloy, the melting point of the alloy is lower than the melting point of the first type of metal catalyst, and the second type of metal is selected from Ga, One of Bi, Sn, Pb and In; S3. Evaporating the alloy at a temperature of 700-1000°C to obtain a graphene layer, the evaporation adopts a chemical vapor deposition process, and the process conditions are: in a mixed atmosphere of inert gas and hydrogen, and at a high temperature of 700-1000 ° C Carry out heat preservation annealing for 5~30 minutes. 2. the preparation method of graphene according to claim 1 is characterized in that, the flow range of inert gas is 1000～2000 slm; The flow range of hydrogen is 100～500 slm. 3. the preparation method of graphene according to claim 1, is characterized in that, described first type metal catalyst layer is Ni. 4. The preparation method of graphene according to claim 1 or 3, characterized in that, the second type of metal is Ga. 5. the preparation method of graphene according to claim 1, is characterized in that, the thickness of described first type metal catalyst layer is 100～500nm. 6. The method for preparing graphene according to claim 1 or 5, wherein the method for preparing the first type metal catalyst layer comprises one of electron beam evaporation, magnetron sputtering and pulsed laser deposition. 7. the preparation method of graphene according to claim 4, is characterized in that, the thickness of described carbon thin film is 2～10nm. 8. The preparation method of graphene according to claim 1, characterized in that, the method further comprises the step of: ultrasonicating the graphene layer in deionized water for 0.5 to 5 minutes to separate the graphene layer from the alloy layer below it.