CN112830479B - Method for preparing easy-to-strip near-free graphene by using sulfur beam decoupling technology - Google Patents

Method for preparing easy-to-strip near-free graphene by using sulfur beam decoupling technology Download PDF

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CN112830479B
CN112830479B CN202110210910.2A CN202110210910A CN112830479B CN 112830479 B CN112830479 B CN 112830479B CN 202110210910 A CN202110210910 A CN 202110210910A CN 112830479 B CN112830479 B CN 112830479B
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李妍璐
孙秀彩
张雪
国星
孙丽
程秀凤
于法鹏
赵显�
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Shandong University
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Abstract

The invention relates to a method for preparing graphene in an easily-stripped near-free state by utilizing a sulfur beam decoupling technology, which is implemented on the basis of a traditional method for preparing graphene by CVD (chemical vapor deposition), and comprises the steps of adopting a double-temperature-zone CVD (chemical vapor deposition) tube furnace, placing a sulfur source in a low-temperature zone of the tube furnace to evaporate sulfur so as to provide a sulfur beam, forming a vulcanized layer on the graphene in a high-temperature zone and a metal interface by controlling reaction temperature and reaction time, weakening the coupling effect of the graphene and a substrate by forming the vulcanized layer, realizing the decoupling of the graphene on the metal substrate, and easily stripping the graphene from the substrate, thereby preparing the high-quality graphene in the near-free state.

Description

Method for preparing easy-to-strip near-free graphene by using sulfur beam decoupling technology
Technical Field
The invention relates to a method for preparing easy-to-strip near-free state graphene by using a sulfur beam decoupling technology, and belongs to the technical field of graphene preparation.
Background
Graphene is a two-dimensional crystalline material consisting of carbon atoms in sp 2 The unique structure determines that the graphene has excellent electrical, mechanical and thermal properties, and has wide application prospects in the fields of novel micro-nano electronic devices, weak photoelectric detector devices and the like. Various methods for preparing graphene have been developed, and among them, the widely used Chemical Vapor Deposition (CVD) method utilizes a carbon-containing compound such as methane as a carbon source, dehydrogenates the compound on the surface of a transition metal having catalytic activity, deposits free activated carbon groups, and then realizes sp on a substrate 2 And reconstructing to obtain high-quality graphene.
At present, the preparation of graphene by a CVD method can be mainly divided into two types in terms of growth mechanism: (1) dissolution mechanism: taking metals with high carbon-dissolving capacity such as Ni, Co and the like as representatives, carbon atoms generated by dehydrogenation of carbon-containing compounds permeate into a metal matrix at high temperature, and are separated out and nucleated from the interior of the metal matrix when the temperature is rapidly reduced, so that graphene grows on the surface of the substrate; (2) the surface catalysis mechanism is as follows: the method is characterized in that metals with low carbon dissolving amount such as Cu, Mo and Pt are taken as representatives, active carbon groups generated by dehydrogenation of carbon-containing compounds at high temperature reach a certain supersaturation degree on the metal surface, further nucleation growth is carried out to form a graphene crystal domain, and finally continuous graphene is obtained through two-dimensional growth and combination.
However, due to the mismatch of the graphene lattice and the metal substrate, strong interactions between the two materials can compromise the near-free state structure and electronic properties of graphene. In addition, the method for preparing graphene by CVD is not compatible with the conventional semiconductor process, so that the CVD-synthesized graphene must be subjected to a complicated transfer operation to recover the independent characteristics of the graphene and the replacement of a target substrate in practical application. In recent years, the graphene transfer methods widely used mainly include wet transfer, electrochemical delamination, and the like. The wet transfer is to release the two-dimensional graphene material by etching and dissolving the entire catalyst substrate thin film. The method is complex to operate, and can cause pollution of transferred graphene chemicals or metals, so that the performance of the graphene is negatively influenced. Moreover, since the substrate material is completely dissolved during the transfer process, this greatly increases the material cost for the industrial preparation of graphene. The electrochemical layering transfer technology does not need to dissolve a catalytic substrate, and H is generated on the interface of graphene and transition metal mainly through electrochemical reaction 2 Bubbling, thereby peeling off the graphene. But the electrochemical production of H by this process 2 Efficiency is easily limited by electrode material, otherwise difficult to control H 2 Bubbling can result in excessive surface tension and even severely damage the structural integrity of the graphene film. In recent years, some relatively direct mechanical peeling methods have been developed to transfer graphene, for example, chinese patent document CN109516454A discloses a method for transferring graphene, which includes spin-coating a polymer solution on the surface of graphene to form a polymer film on the surface of graphene; the graphene is then peeled off the growth substrate and transferred to a target substrate. The method uses mechanical stripping means to remove the metal substrateThe graphene delaminates. At present, although the method is convenient and fast, due to strong interaction between graphene and transition metal, the graphene is easily torn and damaged obviously by direct stripping, a large-area complete graphene film is difficult to obtain, and the obtained graphene is difficult to ensure to present electronic structure characteristics of a near-free state. Therefore, before direct mechanical stripping, a certain technical means is adopted to sufficiently weaken the interaction between the graphene synthesized by CVD and the substrate so as to prepare the near-free-state graphene, which is a prerequisite and a key step for realizing large-area complete transfer and application of the subsequent graphene.
In view of the current defects and shortcomings, it is necessary to develop a method for preparing near-free graphene, which weakens the coupling effect between graphene and a substrate.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for preparing easy-to-strip near-free state graphene by using a sulfur beam decoupling technology.
According to the method, on the basis of a traditional method for preparing graphene by CVD, a double-temperature-zone CVD tubular furnace is adopted, a sulfur source is placed in a low-temperature zone of the tubular furnace to evaporate sulfur so as to provide a sulfur beam, a vulcanized layer is formed on the interface between graphene and metal in a high-temperature zone by controlling the reaction temperature and the reaction time, the coupling effect of the graphene and a substrate is weakened by the formation of the vulcanized layer, the decoupling of the graphene on the metal substrate is realized, the graphene is easily stripped from the substrate, and the high-quality graphene in a near-free state is prepared.
The invention is realized by the following technical scheme:
a method for preparing easy-to-strip near-free state graphene by using a sulfur beam decoupling technology comprises the following steps:
(1) providing a metal substrate;
(2) placing the substrate in a high-temperature area of a dual-temperature-area CVD tube furnace, vacuumizing the tube furnace, and carrying out temperature gradient annealing on the substrate in the atmosphere of high-purity argon and high-purity hydrogen;
(3) keeping the flow rate of hydrogen and argon unchanged, introducing a carbon source gas, heating to a growth temperature, keeping the temperature for 30-240 min to grow graphene, and quickly cooling to room temperature after the growth is finished;
(4) placing a substrate for growing graphene in a high-temperature area of a dual-temperature-area CVD tube furnace, placing a sulfur source in a quartz boat in a low-temperature area, heating the high-temperature area to 400-800 ℃, heating the low-temperature area to 100-400 ℃ to evaporate the sulfur source to generate sulfur beams, introducing the sulfur beams into the high-temperature area, vulcanizing the interface of the graphene substrate, and preserving heat for 1-30 min to form stable sulfides on the interface of the graphene and the substrate;
(5) and turning off all gases, pumping out, and naturally cooling in an inert atmosphere to obtain the large-size easy-to-strip near-free graphene on the surface of the substrate.
According to the invention, the metal substrate is a single crystal substrate or a polycrystalline substrate, and is selected from one of a copper foil substrate, a platinum substrate or a nickel substrate.
According to the present invention, the metal substrate is preferably shaped like a foil, a plate, a block, a tube, or a bag.
According to the invention, the substrate in the step (1) is polished and cleaned before use, wherein the polishing is carried out by adopting an electrochemical polishing or chemical mechanical polishing mode, and the cleaning is carried out by adopting wet chemistry; finally obtaining the substrate with clean surface and roughness less than or equal to 10 nm.
The electrochemical polishing, the chemical mechanical polishing and the wet chemical cleaning are all conventional technologies in the field.
Preferably, in step (2), the vacuum degree of the tube furnace chamber after vacuum pumping is 1mbar to 4 x 10 - 5 mbar。
Preferably, in step (2), the annealing with temperature gradient of the substrate is specifically: introducing high-purity argon, heating to 950-1000 ℃, then introducing high-purity hydrogen, slowly heating to 1030-1070 ℃, preserving heat for 30-90 min, and then slowly cooling to finish annealing of the substrate.
Further preferably, the heating rate of heating to 950-1000 ℃ is 5-20 ℃/min, and the flow of high-purity argon is 300-500 sccm; heating to 1030-1070 ℃, wherein the heating rate is 1-5 ℃/min, and the flow of high-purity hydrogen is 10-50 sccm; the high-purity argon and the high-purity hydrogen are argon and hydrogen with the purity of more than 5N; the slow cooling rate is 1-5 ℃/min, and the temperature is reduced to 900-980 ℃.
According to the invention, in the step (3), the carbon source gas is a mixed gas of methane and argon, and the volume ratio of methane is 0.1-0.3%. Argon is the diluent gas.
Further preferably, the carbon source gas is introduced in a manner that: firstly, introducing a carbon source gas at a flow rate of 5-10 sccm, keeping the temperature constant for 15-30 min, and then increasing the flow rate of methane to 15-50 sccm within 5 min.
Preferably, in the step (3), the growth temperature is 980-1070 ℃, and the heating rate is 1-5 ℃/min.
Preferably, in step (4), the sulfur source is elemental sulfur powder, and the amount of elemental sulfur powder is as follows: 0mg or less per cm 2 The surface area of the metal substrate is less than or equal to 20.0 mg.
According to the invention, in the step (4), the temperature rising rate of the high-temperature area is 5-30 ℃/min, and the temperature rising rate of the low-temperature area is 5-30 ℃/min.
Further preferably, the temperature of the high-temperature area is 400-800 ℃, and the temperature of the low-temperature area is 100-400 ℃.
According to the invention, in the step (5), the inert atmosphere is argon, the pressure is controlled to be-0.1 MPa to-0.05 MPa, and the temperature is naturally reduced along with the furnace.
All equipment and raw materials in the method are commercially available products. Reference is made to the prior art without any particular limitation.
According to the method, a sulfur beam is utilized to enable the interface of the graphene and the substrate to generate a vulcanization layer, the formation of the vulcanization layer weakens the coupling effect of the graphene and the substrate, and the decoupling of the graphene on the metal substrate is realized; on one hand, the gasification temperature of the S simple substance is lower (the sublimation temperature of sulfur is about 95 ℃), so that a low-temperature heating sulfur source can form a gaseous sulfur beam flow in a low-temperature region and is transmitted to a high-temperature region from the low-temperature region through a tubular furnace gas flow channel to participate in the interface reaction of graphene and the substrate; on the other hand, the CVD synthesized graphene can form a unique two-dimensional structure with the substrateThe height of the two-dimensional interface is about that of the interface space, in terms of space size, taking a Cu substrate as an example
Figure BDA0002952258550000041
Atomic radius [ E ] significantly greater than S
Figure BDA0002952258550000042
Steric hindrance effects, which indicate the insertion and migration of the S atom at the interface, are almost negligible. Furthermore, the highest energy barrier for insertion of S atoms at the interface is 0.87eV from an energy point of view, meaning that insertion of S occurs relatively easily under appropriate high temperature catalytic conditions. Under different temperature and pressure conditions, it was found that the inserted S atoms react with the substrate to form a stable two-dimensional vulcanizate at the interface between the two, according to thermodynamic and kinetic criteria. Therefore, after the graphene is synthesized by CVD, sulfide intercalation can be realized at the interface by a sulfur beam method, and the coupling effect between the graphene and the substrate is weakened, so that the strippability of the graphene is greatly improved, and the near-free-state graphene is finally prepared.
In conclusion, according to the S element, the sulfuration intercalation of the interface of the graphene and the metal substrate is easily realized, the method for preparing the near-free-state graphene by the sulfur beam technology in the CVD process weakens the coupling effect between the CVD graphene and the substrate, can obtain the high-quality near-free-state graphene, and is beneficial to the subsequent transfer of a graphene film and the development of a graphene-based microelectronic device. Under the optimized conditions, high-quality graphene materials in a near-free state can be obtained.
The invention has the technical characteristics and excellent effects that:
1. the method is used for preparing the graphene material based on the dual-temperature-zone CVD tube furnace, and sulfur is evaporated in the low-temperature zone to generate a sulfur beam flow so as to vulcanize the interface of the graphene and the substrate in the high-temperature zone. The whole experiment has simple operation process, and can effectively avoid the pollution problem of the graphene.
2. According to the method, a sulfuration reaction is carried out on the interface of the graphene and the substrate by using the sulfur beam, so that sulfide can be formed on the interface, the coupling effect of the graphene and the substrate is weakened, and the electronic structure characteristics of the graphene in a near-free state are recovered. On the basis of ensuring the completeness of graphene preparation, the bonding energy of the substrate and the graphene is obviously reduced, and the subsequent improvement of the transfer characteristic of the graphene is facilitated.
Drawings
Fig. 1 is an atomic mechanism diagram of sulfurizing an interface of a graphene substrate with a sulfur beam in embodiment 1 of the present invention.
Fig. 2 is a graph comparing the peeling energies of graphene before and after the sulfidation interface calculated in example 1 of the present invention.
Fig. 3 is a graph showing stability analysis of a vulcanized graphene substrate interface by molecular dynamics calculation in example 1 of the present invention.
Figure 4 is a calculated STM image of CVD graphene in the free state and after interfacial sulfidation of example 1 of the present invention.
Fig. 5 is a graphene object image prepared in embodiment 1 of the present invention.
Fig. 6 is an optical microscope image of near-free graphene prepared in example 1 of the present invention.
Fig. 7 is an optical microscope image of graphene prepared by a conventional CVD method according to a comparative example.
FIG. 8 shows the transfer of graphene prepared in example 1 of the present invention to SiO 2 Optical microscope images on Si wafers.
Fig. 9 is a Raman spectrum of the transferred graphene prepared in example 1 of the present invention.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The method is a conventional method unless otherwise specified. The starting materials are commercially available from the open literature unless otherwise specified.
The dual temperature zone controlled CVD furnace is an existing device.
Examples 1,
A method for preparing easily stripped near-free graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) Will be pretreatedThe copper foil is placed in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum pumping the CVD furnace chamber to a vacuum degree of 3.4 × 10 -5 Introducing argon with high purity of 500sccm at a pressure of-0.5 MPa at a flow rate of-980 ℃, introducing 10sccm hydrogen at a temperature rise rate of 10 ℃/min, raising the temperature to 1050 ℃ within 30min, keeping the temperature for 30min, and cooling to 980 ℃ within 30min to complete the temperature gradient annealing of the substrate;
(3) and after the annealing is finished, introducing mixed gas of 15sccm methane and argon, wherein the volume ratio of methane is 0.1%, keeping hydrogen unchanged, heating to 1050 ℃ within 30min, keeping the temperature unchanged, increasing the flow of the mixed gas to 40sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to cool the quartz tube at the position of the quartz boat in the air.
(4) Placing a substrate for growing graphene in a high-temperature area of a dual-temperature-area CVD tubular furnace, placing a sulfur simple substance in a low-temperature-area quartz boat, introducing argon of 300sccm, and using amount of simple substance sulfur powder: per cm 2 The surface area of the metal substrate was 1.5 mg. Keeping the air pressure at-0.5 MPa, heating the high-temperature area to 600 ℃ within 20min, simultaneously heating the low-temperature area to 200 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature area, vulcanizing the interface of the graphene substrate, and keeping the temperature for 5min to form an interface stable sulfide.
(5) And finally, turning off argon, and naturally cooling to obtain a free-state graphene crystal domain with the size of 450 mu m.
The sulfidation mechanism of the CVD graphene and substrate interface of the present invention is shown in fig. 1; the comparison of the peeling energy of graphene before and after the interface vulcanization of the graphene substrate is shown in fig. 2; the stability of the MD simulated CVD cure system is shown in figure 3; fig. 4 shows images of the STM image of the graphene and the free-state graphene on the vulcanized substrate prepared by the CVD method, fig. 5 and 6 show physical photographs and optical microscope photographs of the graphene prepared by the present invention, fig. 7 shows photographs of the graphene prepared by the conventional CVD method, and fig. 8 and 9 show optical microscope images and Raman spectra of the graphene prepared and transferred by the present invention. Researches show that the boundary of graphene on the substrate has obvious capture advantages on active S and H atoms in the atmosphere, and the graphene edge is caused by atom captureThe apparent lifting of the boundary allows the insertion of the S atom through the boundary. And then, S atoms freely migrate in the interface and react with the substrate to form a stable vulcanized layer, so that the electronic coupling effect between the graphene and the substrate is effectively weakened, and the graphene has obvious free-state structural characteristics. In addition, the stripping performance of the graphene prepared by the method is obviously reduced, and the graphene is easier to strip. In FIG. 9, I 2D /I G The peak is larger than 2, which indicates that the obtained graphene is a single layer, and the full width at half maximum of the 2D peak is about 33cm -1 Also approaching the eigenvalues of the monolayer.
Examples 2,
A method for preparing easy-to-strip near-free state graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (4) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 Introducing argon with high purity of 500sccm at a pressure of-0.5 MPa, heating to 980 deg.C at a heating rate of 10 deg.C/min, introducing 10sccm hydrogen, heating to 1050 deg.C within 30min, maintaining for 30min, and cooling to 980 deg.C within 30min to complete temperature gradient annealing of the substrate.
(3) After the annealing is finished, mixed gas of 15sccm methane and argon is introduced, the volume ratio of methane is 0.1%, hydrogen is kept unchanged, and the temperature is raised to 1035 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 40sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Placing the substrate after graphene growth in a high-temperature area of a dual-temperature-area CVD tube furnace, placing elemental sulfur in a quartz boat in the low-temperature area, and using the amount of elemental sulfur powder: per cm 2 The surface area of the metal substrate was 2.5 mg. Introducing 300sccm argon gas to keep the pressure at-0.5 MPa, heating the high-temperature region to 600 ℃ within 20min, simultaneously heating the low-temperature region to 200 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and keeping the temperature for 5min forms interface-stable sulfides.
(5) And finally, turning off argon, and naturally cooling to obtain a free-state graphene crystal domain with the size of 400 mu m.
Examples 3,
A method for preparing easy-to-strip near-free state graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (3) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 And mbar, introducing argon with high purity of 320sccm, controlling the pressure at-0.5 MPa, heating to 980 ℃, heating at a rate of 10 ℃/min, introducing 10sccm hydrogen, heating to 1050 ℃ within 30min, keeping the temperature for 60min, and cooling to 980 ℃ within 30min to complete the temperature gradient annealing of the substrate.
(3) And after the annealing is finished, introducing mixed gas of 5sccm methane and argon, keeping the volume ratio of methane at 0.1 percent and hydrogen unchanged, and heating to 1050 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 30sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Placing the substrate after graphene growth in a high-temperature area of a dual-temperature-area CVD tube furnace, placing elemental sulfur in a quartz boat in the low-temperature area, and using the amount of elemental sulfur powder: per cm 2 The surface area of the metal substrate was 3.5 mg. And introducing argon of 300sccm to keep the air pressure at-0.5 MPa, heating the high-temperature region to 500 ℃ within 20min, simultaneously heating the low-temperature region to 150 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and preserving the heat for 10min to form an interface stable sulfide.
(5) And finally, turning off argon, and naturally cooling to obtain a free-state graphene crystal domain with the size of 300 mu m.
Examples 4,
A method for preparing easy-to-strip near-free state graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (3) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 Introducing argon with high purity of 500sccm at mbar, controlling the pressure at-0.5 MPa, heating to 980 ℃ at a heating rate of 10 ℃/min, introducing 21sccm hydrogen, heating to 1050 ℃ within 30min, keeping the temperature for 90min, and cooling to 980 ℃ within 30min to complete the temperature gradient annealing of the substrate.
(3) And after the annealing is finished, introducing mixed gas of 15sccm methane and argon, keeping the volume ratio of methane at 0.1 percent and hydrogen unchanged, and heating to 1050 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 40sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Placing the substrate after graphene growth in a high-temperature area of a dual-temperature-area CVD tube furnace, placing elemental sulfur in a quartz boat in the low-temperature area, and using the amount of elemental sulfur powder: per cm 2 The surface area of the metal substrate was 5.5 mg. And introducing 300sccm argon to keep the air pressure at-0.5 MPa, heating the high-temperature region to 700 ℃ within 20min, simultaneously heating the low-temperature region to 250 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and preserving heat for 4min to form an interface stable sulfide.
(5) And finally, turning off argon, and naturally cooling to obtain the graphene crystal domain with the size of 400 mu m in a free state.
Examples 5,
A method for preparing easy-to-strip near-free state graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (4) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 mbar, introducing argon with high-purity flow of 500sccm, and controlling pressureHeating to-0.5 MPa, raising the temperature to 1000 ℃, wherein the heating rate is 10 ℃/min, introducing 10sccm hydrogen, raising the temperature to 1070 ℃ within 30min, preserving the temperature for 30min, and then reducing the temperature to 1000 ℃ within 30min to complete the temperature gradient annealing of the substrate.
(3) And after the annealing is finished, introducing mixed gas of 15sccm methane and argon, keeping the volume ratio of methane at 0.1 percent and hydrogen unchanged, and heating to 1050 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 40sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Placing the substrate after graphene growth in a high-temperature area of a dual-temperature-area CVD tube furnace, placing elemental sulfur in a quartz boat in the low-temperature area, and using the amount of elemental sulfur powder: per cm of 2 The surface area of the metal substrate was 6.5 mg. And introducing 300sccm argon gas to keep the air pressure at-0.5 MPa, heating the high-temperature region to 600 ℃ within 20min, simultaneously heating the low-temperature region to 200 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and preserving the heat for 10min to form interface stable sulfides.
(5) And finally, turning off argon, and naturally cooling to obtain a free-state graphene crystal domain with the size of 400 mu m.
Examples 6,
A method for preparing easily stripped near-free graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (3) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 Introducing argon with high purity of 500sccm at a pressure of-0.5 MPa, heating to 980 deg.C at a heating rate of 10 deg.C/min, introducing 10sccm hydrogen, heating to 1050 deg.C within 30min, maintaining for 30min, and cooling to 980 deg.C within 30min to complete temperature gradient annealing of the substrate.
(3) And after the annealing is finished, introducing mixed gas of 5sccm methane and argon, keeping the volume ratio of methane at 0.1 percent and hydrogen unchanged, and heating to 1035 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 30sccm within 5min, ending the nucleation growth process of the graphene after 30min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Placing the substrate after graphene growth in a high-temperature area of a dual-temperature-area CVD tube furnace, placing elemental sulfur in a quartz boat in the low-temperature area, and using the amount of elemental sulfur powder: per cm of 2 The surface area of the metal substrate was 10.0 mg. And introducing argon of 300sccm to keep the air pressure at-0.5 MPa, heating the high-temperature region to 700 ℃ within 20min, simultaneously heating the low-temperature region to 250 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and preserving the heat for 4min to form an interface stable sulfide.
(5) And finally, turning off argon, and naturally cooling to obtain a free-state graphene crystal domain with the size of 200 mu m.
Example 7,
A method for preparing easy-to-strip near-free state graphene by utilizing a sulfur beam decoupling technology takes a copper substrate as an example and comprises the following steps:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) And (4) placing the pretreated copper foil in a quartz boat in a high-temperature area of the CVD tube furnace. Vacuum-pumping CVD furnace chamber with vacuum degree of 3.4 × 10 -5 Introducing argon with high purity of 500sccm at a pressure of-0.5 MPa, heating to 980 deg.C at a heating rate of 10 deg.C/min, introducing 10sccm hydrogen, heating to 1050 deg.C within 30min, maintaining for 60min, and cooling to 980 deg.C within 30min to complete temperature gradient annealing of the substrate.
(3) And after the annealing is finished, introducing mixed gas of 15sccm methane and argon, keeping the volume ratio of methane at 0.1 percent and hydrogen unchanged, and heating to 1050 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of the mixed gas to 40sccm within 5min, finishing the nucleation growth process of the graphene after 60min, closing the hydrogen and the mixed gas, and pushing away the furnace chamber to reduce the temperature of the quartz tube at the position of the quartz boat in the air.
(4) Lining after growing grapheneThe bottom is arranged in a high-temperature area of the double-temperature-area CVD tubular furnace, and elemental sulfur is placed in a quartz boat in the low-temperature area, wherein the elemental sulfur powder comprises the following components in percentage by weight: per cm 2 The surface area of the metal substrate was 20.0 mg. And introducing 300sccm argon gas to keep the air pressure at-0.5 MPa, heating the high-temperature region to 500 ℃ within 20min, simultaneously heating the low-temperature region to 150 ℃ to evaporate S to generate a beam, introducing the beam into the high-temperature region, vulcanizing the interface of the graphene substrate, and preserving the heat for 10min to form an interface stable sulfide.
(5) And finally, turning off argon, and naturally cooling to obtain a graphene crystal domain with the size of 600 mu m in a free state.
Comparative example
As described in example 1, except that elemental sulfur powder is not placed in the low temperature region of the CVD furnace, graphene spontaneous nucleation growth is directly performed on the copper substrate in the high temperature region, and the steps are as follows:
(1) the copper foil with a thickness of 25 μm was polished and cleaned.
(2) putting the processed copper foil in the step (1) in a quartz boat in a high-temperature area of a CVD tubular furnace, wherein the vacuum degree of the chamber of the CVD furnace is 3.4 multiplied by 10 -5 Introducing argon with high purity of 500sccm at a pressure of-0.5 MPa, heating to 980 deg.C at a heating rate of 10 deg.C/min, introducing 10sccm hydrogen, heating to 1050 deg.C within 30min, maintaining for 30min, and cooling to 980 deg.C within 30min to complete temperature gradient annealing of the substrate.
(3) After the annealing is finished, 0.1 percent CH of 15sccm is introduced 4 Keeping the gas and hydrogen unchanged, and heating to 1050 ℃ within 30 min. And then, keeping the temperature unchanged, increasing the flow of methane to 40sccm within 5min, finishing the nucleation growth process of the graphene after 30min, closing hydrogen and methane, pushing away the furnace chamber to cool the quartz tube at the position of the quartz boat in the air, and thus obtaining the graphene crystal domain with the size of 450 microns on the Cu substrate.
In this comparative example, an optical microscope image of graphene grown on a copper foil substrate is shown in fig. 7.
As can be seen from comparison of fig. 6 and 7, the near-free-state graphene can be prepared on the Cu substrate by using the sulfur beam decoupling technology, and the obtained graphene has good quality, can maintain the structure and electronic characteristics of the near-free state, and can be directly peeled off to be used for manufacturing microelectronic devices.

Claims (6)

1. A method for preparing easy-to-strip near-free state graphene by using a sulfur beam decoupling technology comprises the following steps:
(1) providing a metal substrate;
(2) placing the substrate in a high-temperature area of a dual-temperature-area CVD tube furnace, vacuumizing the tube furnace, and carrying out temperature gradient annealing on the substrate in the atmosphere of high-purity argon and high-purity hydrogen;
(3) keeping the flow rate of hydrogen and argon unchanged, introducing carbon source gas, heating to the growth temperature, keeping the temperature for 30-240 min for graphene growth, and quickly cooling to room temperature after the growth is finished; the growth temperature is 980-1070 ℃, and the heating rate is 1-5 ℃/min;
(4) placing a substrate for growing graphene in a high-temperature area of a dual-temperature-area CVD tubular furnace, placing a sulfur source in a quartz boat in a low-temperature area, heating the high-temperature area to 400-800 ℃, heating the low-temperature area to 100-400 ℃ to evaporate the sulfur source to generate sulfur beams, introducing the sulfur beams into the high-temperature area, vulcanizing the interface of the graphene substrate, and preserving heat for 1-30 min to form stable sulfides on the interface of the graphene and the substrate; the sulfur source is elemental sulfur powder, and the dosage of the elemental sulfur powder is as follows: 1.5mg is less than or equal to each cm 2 The surface area of the metal substrate is less than or equal to 20.0 mg; the heating rate of the high-temperature area is 5-30 ℃/min, and the heating rate of the low-temperature area is 5-30 ℃/min;
(5) and turning off all gases, pumping out, and naturally cooling in an inert atmosphere to obtain the easily-stripped near-free graphene on the surface of the substrate.
2. The method of claim 1, wherein the metal substrate is a single crystal substrate or a polycrystalline substrate selected from a copper foil substrate, a platinum substrate, or a nickel substrate; the metal substrate is in the shape of foil, plate, block, tube or bag; before the substrate is used, polishing and cleaning are carried out, wherein the polishing is carried out in an electrochemical polishing or chemical mechanical polishing mode, and the cleaning is carried out by wet-process chemistry; finally obtaining the substrate with clean surface and roughness less than or equal to 10 nm.
3. The method according to claim 1, wherein in the step (2), the vacuum degree of the tube furnace chamber after vacuumizing is 1 mbar-4 x 10 -5 mbar; the temperature gradient annealing of the substrate specifically comprises the following steps: introducing high-purity argon, heating to 950-1000 ℃, then introducing high-purity hydrogen, slowly heating to 1030-1070 ℃, preserving heat for 30-90 min, and then slowly cooling to finish annealing of the substrate; heating to 950-1000 ℃ at a heating rate of 5-20 ℃/min, and introducing high-purity argon at a flow rate of 300-500 sccm; heating to 1030-1070 ℃, wherein the heating rate is 1-5 ℃/min, and the flow of high-purity hydrogen is 10-50 sccm; the high-purity argon and the high-purity hydrogen are argon and hydrogen with the purity of more than 5N; the slow cooling rate is 1-5 ℃/min, and the temperature is reduced to 900-980 ℃.
4. The method of claim 1, wherein in the step (3), the carbon source gas is a mixed gas of methane and argon, and the volume ratio of methane is 0.1-0.3%.
5. The method of claim 4, wherein the carbon source gas is introduced in a manner that: firstly, introducing a carbon source gas at a flow rate of 5-10 sccm, keeping the temperature constant for 15-30 min, and then increasing the flow rate of methane to 15-50 sccm within 5 min.
6. The method of claim 1, wherein in the step (5), the inert atmosphere is argon, the pressure is controlled to be-0.1 MPa to-0.05 MPa, and the temperature is naturally reduced along with the furnace.
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