CN108396377B - Preparation method of high-quality single-layer polycrystalline graphene film - Google Patents

Preparation method of high-quality single-layer polycrystalline graphene film Download PDF

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CN108396377B
CN108396377B CN201710066047.1A CN201710066047A CN108396377B CN 108396377 B CN108396377 B CN 108396377B CN 201710066047 A CN201710066047 A CN 201710066047A CN 108396377 B CN108396377 B CN 108396377B
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CN108396377A (en
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任文才
马腾
成会明
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Institute of Metal Research of CAS
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B28/00—Production of homogeneous polycrystalline material with defined structure
    • C30B28/12—Production of homogeneous polycrystalline material with defined structure directly from the gas state
    • C30B28/14—Production of homogeneous polycrystalline material with defined structure directly from the gas state by chemical reaction of reactive gases

Abstract

The invention relates to a novel graphene material and a Chemical Vapor Deposition (CVD) preparation technology thereof, in particular to a preparation method of high-quality single-layer polycrystalline graphene, which is suitable for preparing a high-quality single-layer polycrystalline graphene film. By adopting a CVD technology, metal with medium carbon dissolving amount is taken as a growth matrix, a graphene crystal nucleus with controllable density is formed by infiltration and precipitation, and then the polycrystalline graphene film with uniform and adjustable grain size is obtained by surface growth. The invention can obtain the high-quality single-layer polycrystalline graphene film with small grain size, uniformity and controllability and perfect crystal boundary splicing, and lays a foundation for the application of the high-quality single-layer polycrystalline graphene film in the electronic, photoelectric and thermoelectric fields of nano electronic devices, photoelectric devices, photonic devices, gas sensors, thin-film electronic devices and the like.

Description

Preparation method of high-quality single-layer polycrystalline graphene film
The technical field is as follows:
the invention relates to a novel graphene material and a Chemical Vapor Deposition (CVD) preparation technology thereof, in particular to a preparation method of high-quality single-layer polycrystalline graphene, which is suitable for preparing a high-quality single-layer polycrystalline graphene film.
Background art:
graphene is a monolayer carbon atom crystal which is tightly packed into a two-dimensional honeycomb crystal structure, and is a basic unit for constructing carbon materials with other dimensions. The strict two-dimensional crystal material has excellent electrical, thermal, mechanical and optical properties, such as: the electron mobility of the material at room temperature is as high as 200,000cm2V.s, thermal conductivity up to 5000 W.m-1·K-1The Young's modulus is as high as 1TPa, and the visible light absorptivity is only 2.3%. Due to the excellent performances of the graphene, the graphene is expected to be widely applied to the fields of multifunctional nano-electronic devices, transparent conducting films, composite materials, energy storage materials, gas sensors and the like. Therefore, since the discovery in 2004, it has rapidly become the leading edge of the most active research in the fields of material science, condensed state physics, chemistry, and the like.
At present, there are many methods for preparing graphene, mainly including a micro-mechanical lift-off method, a chemical oxidation-reduction method, a silicon carbide epitaxial growth method, and a Chemical Vapor Deposition (CVD) method. The CVD method has the advantages of simplicity, feasibility, high quality of the obtained graphene, realization of large-scale growth, easiness in transfer and the like, so that the CVD method is widely used for preparing graphene field effect transistors and transparent conductive films and is gradually the main method for preparing high-quality graphene films at present. The grain boundary is an important structural feature of graphene prepared by a CVD method and can affect various properties of the graphene. Therefore, the preparation of the high-quality single-layer polycrystalline graphene film with uniform and adjustable grain size has important significance for adjusting the electrical, photoelectric and thermoelectric properties of graphene and the like.
However, under the condition of ensuring single-layer graphene, it is difficult to realize the preparation of large-size single-crystal or nano-crystal graphene films simply by reducing or increasing nucleation density. For example, for a copper matrix with a low carbon concentration, graphene growth follows a surface adsorption mechanism, and a high carbon source increases the nucleation density of graphene, but also brings about a multi-layer region. In contrast, for a nickel matrix with a high carbon concentration, graphene growth follows an infiltration precipitation mechanism, and it is difficult to obtain single-layer graphene. Therefore, the grain size of graphene thin films is mostly distributed between 1 μm and 1 mm. How to prepare high-quality single-layer polycrystalline graphene with uniform and controllable grain size by using a CVD method is a difficulty in the field of graphene research.
The invention content is as follows:
the invention aims to provide a preparation method of high-quality single-layer polycrystalline graphene, which has the advantages of low cost, simplicity in operation, good controllability and the like, and therefore can be used as an ideal method suitable for preparing high-quality single-layer polycrystalline graphene.
The technical scheme of the invention is as follows:
the invention provides a preparation method of high-quality single-layer polycrystalline graphene, which comprises the steps of firstly, adopting a chemical vapor deposition technology, carrying out annealing treatment on a metal matrix in the presence of hydrogen, and utilizing carbon source gas with larger flow rate to carry out catalytic cracking on the surface of the metal matrix at high temperature to grow a graphene film; secondly, etching the graphene on the surface layer of the substrate by changing the growth atmosphere into inert gas, and then separating out carbon atoms dissolved in the substrate to the surface of the substrate by utilizing trace hydrogen to form a graphene crystal nucleus with adjustable density; and thirdly, introducing a small amount of carbon source gas to regrow the surface of the graphene crystal nucleus, wherein the flow rate of the carbon source gas is not more than 0.5sccm, and finally obtaining the high-quality single-layer polycrystalline graphene film with uniform and controllable crystal grain size.
In the invention, the metal substrate is a thin sheet or film of platinum, ruthenium or iridium metal with a flat surface, the purity is more than 98 wt%, the thickness is not less than 300nm, and the thickness is preferably 50-200 μm.
In the invention, the metal matrix is respectively cleaned by ultrasonic in one or more than two of acetone, ethyl lactate, water, isopropanol and ethanol for not less than 10 minutes, preferably 1-2 hours.
In the invention, the metal matrix is annealed at 800-1600 deg.C, preferably 1000-1100 deg.C; the atmosphere is hydrogen (or the mixed gas of hydrogen and nitrogen or argon and the like), wherein the molar ratio of the hydrogen is not less than 1%, the gas flow rate is not less than 20sccm, and the annealing time is not less than 10 minutes. Preferably, the molar ratio of the hydrogen is 90-100%, the gas flow rate is 500-700 sccm, and the annealing time is 8-10 hours.
In the invention, a chemical vapor deposition method is adopted to prepare high-quality single-layer polycrystalline graphene, the used carbon source is one or more than two of hydrocarbons such as methane, ethane, acetylene, ethylene, ethanol and the like, the carrier is hydrogen (or mixed gas of hydrogen and nitrogen or argon and the like), and the purity of the carbon source and the carrier gas is more than 98 percent (volume).
In the invention, the molar ratio of the carbon source to the hydrogen in the first growth step is 0.004-1, preferably 0.01-0.1. The growth temperature is 500-1300 ℃, preferably 600-1050 ℃. The growth time is not less than 10 minutes, preferably 30 minutes to 1 hour.
In the invention, the etching method used in the second step has the etching temperature of 500-1300 ℃, preferably 600-1050 ℃, the etching time is not less than 10 minutes, preferably 20 minutes-2 hours, and the atmosphere is inert gas and dispersed impurities thereof.
In the method for preparing the high-density graphene crystal grains used in the second step, the precipitation temperature is 500-1300 ℃, and preferably 600-1050 ℃. The precipitation time is not less than 10 minutes, preferably 30 minutes to 3 hours. The molar ratio of the hydrogen to the inert gas is 0.005-0.1, preferably 0.007-0.05.
In the third step of the present invention, the regrowth temperature is 500 ℃ to 1300 ℃, preferably 600 ℃ to 1050 ℃, and the regrowth time is not less than 20 minutes, preferably 1 hour to 6 hours. The regrowth atmosphere is a mixed gas of a carbon source and hydrogen, and the carbon source is one or more than two of methane, ethane, acetylene, ethylene and ethanol hydrocarbon. The molar ratio of the carbon source to the hydrogen gas is 0.005 to 0.1, preferably 0.01 to 0.05.
In the invention, after the growth is finished, the metal matrix is rapidly cooled to below 200 ℃ and preferably 100-150 ℃ under the protection of a carrier containing hydrogen; the carrier gas is a mixed gas of hydrogen and nitrogen or argon, the hydrogen molar ratio is not less than 1%, and the preferable ratio is 50-80%; the rapid cooling rate is not less than 50 ℃/second, preferably 80-100 ℃/second.
In the invention, the grain size of the single-layer polycrystalline graphene film prepared by the method is continuously adjustable from 10 nanometers to 1 micrometer (generally ranging from 50 nanometers to 1 micrometer).
The invention has the characteristics and beneficial effects that:
1. the method adopts a chemical vapor deposition technology, uses metals with medium carbon-soluble amount such as platinum, iridium and the like as a growth substrate, uses hydrocarbon as a carbon source, firstly carries out annealing treatment on the metal substrate in the presence of hydrogen, and utilizes carbon source gas with larger flow rate to carry out catalytic cracking on the surface of the metal substrate at high temperature to grow the graphene film; then, etching the graphene on the surface layer of the substrate by changing the growth atmosphere into inert gas, then separating out carbon atoms dissolved in the substrate to the surface of the substrate by utilizing trace hydrogen, and forming a high-density graphene crystal nucleus with adjustable density through infiltration and separation; and then introducing a small amount of carbon source gas again to regrow the surface of the film, and finally obtaining the high-quality single-layer polycrystalline graphene film with uniform and controllable grain size and perfect crystal boundary splicing.
2. The invention has simple process flow, easy operation and low cost, and is expected to be produced in large scale.
3. The method can be used for obtaining the high-quality small-grain-size graphene film, the grain size can be adjusted within 10 nanometers to 1 micrometer, and the grain boundaries are perfectly spliced, so that a foundation is laid for the application of the graphene in the electronic, photoelectric and thermoelectric fields such as nano-photonic devices, photoelectric devices, nano-light sources, transparent conductive films, gas sensors, thin-film electronic devices and the like.
Description of the drawings:
fig. 1 is a schematic diagram of an experimental device for growing polycrystalline graphene by a CVD method. In the figure, 1 gas inlet; 2 a metal substrate; 3, a thermocouple; 4, a gas outlet; 5 mass flow meter.
Fig. 2 is a schematic growth diagram of the polycrystalline graphene film after growth, etching, precipitation and regrowth, and a scanning electron microscope photograph of the polycrystalline graphene film at a corresponding stage. Wherein, FIG. 2(A) is a schematic view of a growth process; fig. 2(B) is a graphene film prepared by first growth; FIG. 2(C) shows the surface of the platinum substrate after etching in FIG. 2 (B); fig. 2(D) shows the high-density graphene crystal grains precipitated in fig. 2 (C); fig. 2(E) shows the single-layer polycrystalline graphene thin film after regrowth in fig. 2(D), see example 1.
Fig. 3(a) and 3(B) are raman spectra of high-density graphene crystal grains and corresponding polycrystalline graphene, respectively.
Fig. 4 characterization of different grain size nuclei and corresponding polycrystalline graphene thin films. FIG. 4(A), FIG. 4(B), FIG. 4(C) and FIG. 4(D) are high density graphene nuclei at precipitation temperatures of 900 deg.C, 950 deg.C, 1000 deg.C and 1040 deg.C, respectively; fig. 4(E), 4(F), 4(G) and 4(H) are transmission electron microscope dark field images of polycrystalline graphene thin films having grain sizes of about 200 nm, 500 nm, 700 nm and 1 μm, respectively, with a scale of 500 nm. FIGS. 4(I) and 4(J) are high-resolution TEM photographs of polycrystalline graphene films with grain sizes of about 200 nm and 700 nm, respectively, with a scale of 1 nm; fig. 4(K), fig. 4(L), fig. 4(M) and fig. 4(N) are the corresponding grain size statistics.
Fig. 5 is a graph of the thermal and electrical properties of polycrystalline graphene as a function of grain size. Fig. 5(a) and 5(B) are graphs showing the relationship between the thermal conductivity and the reciprocal of the polycrystalline graphene thin film and the change in the crystal grain size and the reciprocal thereof, respectively. Fig. 5(C) and 5(D) are the square resistance and conductivity of the polycrystalline graphene thin film as a function of the grain size, respectively.
The specific implementation mode is as follows:
in the specific implementation process, the chemical vapor deposition technology is adopted, metals such as platinum, iridium and the like are used as a growth substrate, hydrocarbon is used as a carbon source, the metal substrate is annealed in the presence of a carrier gas containing hydrogen, and the carbon source gas is utilized to perform catalytic cracking on the surface of the metal substrate at a high temperature to grow the graphene film; then changing the growth atmosphere into inert gas, etching the graphene on the surface layer of the substrate by using impurities in the atmosphere, separating out carbon atoms dissolved in the substrate to the surface of the substrate by using trace hydrogen to form high-density graphene crystal nuclei with uniform and adjustable size, and introducing carbon source gas again to regrow the carbon atoms to finally obtain the polycrystalline graphene film. The high-quality single-layer polycrystalline graphene film with uniform and controllable grain size not only provides a material foundation for deeply understanding the influence of the grain size on the electrical and thermal properties of a macroscopic graphene film, but also has important technical prospects in the aspects of adjusting the electrical, photoelectric and thermoelectric properties of the graphene, and lays a foundation for the application of the graphene in the photoelectric and thermoelectric fields of nano-photonic devices, photoelectric devices, nano-light sources, transparent conductive films, gas sensors and the like.
The invention is further described in detail below by way of examples and figures.
Example 1
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 900 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 7 ml/min for methane and 700 ml/min for hydrogen) after the heat treatment is finished, starting to grow the graphene for 10 minutes, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 20 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to be 5 ml/minute, separating out small graphene crystal grains to the surface of the platinum substrate, wherein the separation time is 20 minutes, finally introducing methane gas, adjusting the flow to be 0.1 ml/minute, regrowing the graphene, and prolonging the regeneration time to 1 hour. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 100 ℃/second to obtain the high-quality single-layer polycrystalline graphene (see figure 2).
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 200 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer. The thermal conductivity of the polycrystalline graphene film is only 600 W.m-1K-1The conductivity can reach 1.2 multiplied by 106S·m-1。
Example 2
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 950 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 7 ml/min for methane and 700 ml/min for hydrogen) after the heat treatment is finished, starting to grow the graphene for 8 minutes, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 20 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to 10 ml/minute to separate out small graphene crystal grains to the surface of the platinum substrate, wherein the separation time is 20 minutes, and finally introducing methane gas, wherein the flow is adjusted to 0.1 ml/minute, the graphene grows again, and the regeneration time is 1 hour. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 100 ℃/second to obtain the high-quality single-layer polycrystalline graphene (see figure 4).
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 500 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer. The thermal conductivity of the polycrystalline graphene film is only 1500 W.m-1K-1The conductivity can reach 1.6 multiplied by 106S·m-1。
Example 3
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 1000 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 7 ml/min for methane and 700 ml/min for hydrogen) after the heat treatment is finished, starting to grow the graphene for 5 minutes, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 20 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to be 15 ml/minute, separating out small graphene crystal grains to the surface of the platinum substrate, wherein the separation time is 20 minutes, finally introducing methane gas, adjusting the flow to be 0.1 ml/minute, regrowing the graphene, and prolonging the regeneration time to be 50 minutes. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 100 ℃/second to obtain the high-quality single-layer polycrystalline graphene (see figure 4).
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 700 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality and is a single layer. The thermal conductivity of the polycrystalline graphene film is only 2000 W.m-1K-1The conductivity can reach 2.1 multiplied by 106S·m-1。
Example 4
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 1040 deg.C in hydrogen atmosphere (hydrogen flow rate is 700 ml/min, heating rate is 50 deg.C/min), and heat treating for 30 min; and introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 7 ml/min for methane and 700 ml/min for hydrogen) after the heat treatment is finished, starting to grow the graphene for 3 minutes, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 20 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to be 20 ml/minute, separating out small graphene crystal grains to the surface of the platinum substrate, wherein the separation time is 20 minutes, finally introducing methane gas, adjusting the flow to be 0.1 ml/minute, regrowing the graphene, and prolonging the regeneration time to be 30 minutes. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 100 ℃/second to obtain the high-quality single-layer polycrystalline graphene (see figure 4).
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 1 micron, the graphene crystal structure is continuous, complete and unbroken, has high quality and is a single layer. The thermal conductivity of the polycrystalline graphene film is only 2500 W.m-1K-1The conductivity can reach 2.5 multiplied by 106S·m-1。
Example 5
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 800 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and after the heat treatment is finished, introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 10 ml/min for methane and 700 ml/min for hydrogen), starting to grow the graphene for 10 min, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 50 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to be 3 ml/minute, separating out small graphene crystal grains to the surface of the platinum substrate, wherein the separation time is 1 hour, finally introducing methane gas, adjusting the flow to be 0.1 ml/minute, regrowing the graphene, and prolonging the regeneration time to be 3 hours. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 200 ℃/s to obtain the high-quality single-layer polycrystalline graphene.
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 50 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer.
Example 6
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (platinum in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is placed in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, a polycrystalline platinum sheet (thickness 180 μm, length × width 20mm × 20mm) was ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes. After the completion of the cleaning, the platinum sheet was placed in a high temperature furnace and annealed at 1100 ℃ for 10 hours to sufficiently remove carbon atoms dissolved into the inside of the platinum substrate. Then, placing the annealed platinum sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the temperature of the furnace in real time by a thermocouple at the position; heating to 700 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and after the heat treatment is finished, introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 20 ml/min for methane and 700 ml/min for hydrogen), starting to grow the graphene, wherein the growth time is 15 min, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. The graphene is etched for 1 hour, hydrogen gas is introduced after etching is finished, the flow is adjusted to be 1 ml/min, small graphene crystal grains are separated out to the surface of the platinum substrate, the separation time is 2 hours, finally, methane gas is introduced, the flow is adjusted to be 0.1 ml/min, the graphene grows again, and the regrowth time is 5 hours. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 200 ℃/second to obtain the high-quality single-layer polycrystalline graphene (see figure 2).
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 10 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer.
Example 7
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (iridium in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is located in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, polycrystalline iridium chips (thickness 180 μm, length × width 20mm × 20mm) were ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes, respectively. After the cleaning, the iridium sheet is placed in a high temperature furnace and annealed at 1200 ℃ for 10 hours to sufficiently remove carbon atoms dissolved in the iridium matrix. Then, placing the annealed iridium sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the furnace temperature in real time by a thermocouple at the position; heating to 900 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 7 ml/min for methane and 700 ml/min for hydrogen) after the heat treatment is finished, starting to grow the graphene for 10 minutes, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 20 minutes, introducing hydrogen gas after the etching is finished, regulating the flow to be 5 ml/minute, separating out small graphene crystal grains to the surface of the iridium matrix, wherein the separation time is 20 minutes, and finally introducing methane gas, wherein the flow is regulated to be 0.1 ml/minute, the graphene grows again, and the regeneration time is 1 hour. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 100 ℃/s to obtain the high-quality single-layer polycrystalline graphene.
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 100 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer.
Example 8
As shown in FIG. 1, the present invention adopts a horizontal reactor to grow graphene, both ends of the horizontal reactor are respectively provided with a gas inlet 1 and a gas outlet 4, a metal substrate 2 (iridium in this embodiment) is placed in a high temperature zone of the horizontal reactor, and a thermocouple 3 is located in the high temperature zone of the horizontal reactor to monitor the reaction temperature in real time. First, polycrystalline iridium chips (thickness 180 μm, length × width 20mm × 20mm) were ultrasonically cleaned in acetone, water, and isopropyl alcohol for 40 minutes, respectively. After the cleaning, the iridium sheet is placed in a high temperature furnace and annealed at 1200 ℃ for 10 hours to sufficiently remove carbon atoms dissolved in the iridium matrix. Then, placing the annealed iridium sheet in the central area (reaction area) of a horizontal reaction furnace (the diameter of the furnace tube is 22 mm, and the length of the reaction area is 40 mm) and monitoring the furnace temperature in real time by a thermocouple at the position; heating to 800 ℃ in hydrogen atmosphere (the hydrogen flow rate is 700 ml/min in the heating process, the heating rate is 50 ℃/min), and carrying out heat treatment for 30 min; and after the heat treatment is finished, introducing mixed gas of methane and hydrogen (the gas flow rates are respectively 10 ml/min for methane and 700 ml/min for hydrogen), starting to grow the graphene for 10 min, rapidly introducing argon (the gas flow rate is 700 ml/min) after the growth is finished, and simultaneously turning off the methane and hydrogen. And etching the graphene, wherein the etching time is 50 minutes, introducing hydrogen gas after the etching is finished, adjusting the flow to be 3 ml/minute, separating out small graphene crystal grains to the surface of the iridium matrix, wherein the separation time is 1 hour, and finally introducing methane gas, wherein the flow is adjusted to be 0.1 ml/minute, the graphene grows again, and the regrowth time is 5 hours. And after the growth is finished, rapidly cooling to below 200 ℃ at the speed of 200 ℃/s to obtain the high-quality single-layer polycrystalline graphene.
The observation of a scanning electron microscope, a resonance laser Raman spectrum and a transmission electron microscope shows that the obtained graphene is of a high-quality polycrystalline structure. The size of the graphene crystal grain is about 20 nanometers, the graphene crystal structure is continuous, complete and unbroken, has high quality, and is a single layer.
As shown in fig. 1, one end of the gas inlet 1 is provided with a plurality of mass flowmeters 5, which can selectively control the introduction of gases such as hydrogen, methane, ethylene, acetylene or argon. A liquid carbon source (e.g., ethanol, methanol, benzene, toluene, cyclohexane, etc.) is placed in a Menten wash bottle and introduced by bubbling argon or a mixture of argon and nitrogen, etc.
As shown in fig. 2, after growth-etch-precipitation, the graphene shows a large number of high-density crystal nuclei, and the grain size is only about 50 nm. The regrown graphene film is complete and is a single layer, and the method can be proved to be capable of preparing a single-layer polycrystalline graphene film.
As shown in FIG. 3, it can be seen from the Raman spectrum of graphene that the graphene prepared by the method has extremely high grain density, which is represented by 1340cm in the Raman spectrum-1The strength of the position of the (D mold) is high, but after the graphene crystal grains are spliced into the film, the D mold nearly disappears, which shows that the single-layer polycrystalline graphene film prepared by the method has high quality.
As shown in fig. 4, the crystal nucleus density of graphene can be precisely adjusted by the precipitation temperature. As can be seen from the transmission electron microscope photo of graphene on platinum, the polycrystalline graphene film is formed by splicing graphene crystal grains with different orientations, and the splicing positions are all five-seven rings, which further shows that the graphene film has high quality.
As shown in FIG. 5, the polycrystalline graphene grown by the methodHas a thermal conductivity of only 600 W.m-1K-1The conductivity can reach 1.2 multiplied by 106S·m-1The method proves that the crystal boundary can greatly reduce the thermal property but has little influence on the electrical property, and lays a foundation for the application of the graphene in the photoelectric and thermoelectric fields of nano-electronic devices, photonic devices, gas sensors, thin-film electronic devices and the like.
The embodiment result shows that the graphene is grown, etched and precipitated by comprehensively regulating and controlling the concentrations of hydrogen, argon and a carbon source, the distribution density of graphene crystal nuclei is regulated and controlled by changing the precipitation temperature, and then the reaction atmosphere is regulated again to regrow the graphene crystal nuclei, so that the high-quality single-layer polycrystalline graphene film with adjustable grain size is finally obtained. The breakthrough in the direction lays a foundation for promoting the application of graphene, particularly the application in the photoelectric and thermoelectric fields of nano-electronic devices, photonic devices, gas sensors, thin-film electronic devices and the like.

Claims (5)

1. A preparation method of a high-quality single-layer polycrystalline graphene film is characterized in that a chemical vapor deposition technology is adopted, in the presence of hydrogen, annealing treatment is carried out on a metal substrate in the first step, carbon source gas with large gas flow is utilized to carry out catalytic cracking on the surface of the metal substrate at high temperature, the gas flow rate is not less than 20sccm, and the graphene film grows; secondly, etching the graphene on the surface layer of the substrate by changing the growth atmosphere into inert gas, and separating out carbon atoms dissolved in the substrate to the surface of the substrate by using trace hydrogen to form a graphene crystal nucleus with adjustable density; thirdly, introducing carbon source gas to regrow the surface of the graphene crystal nucleus to finally obtain a polycrystalline graphene film; the method is used for effectively adjusting the grain size of the graphene film, so that the high-quality single-layer polycrystalline graphene film with uniform and controllable grain size and perfect crystal boundary splicing is obtained;
the metal matrix is a thin sheet or film of platinum, ruthenium or iridium metal with a smooth surface, the purity is more than 98 wt%, the thickness is not less than 300nm, and the carbon dissolving amount of the matrix is between 0.01wt% and 0.2 wt%;
the annealing treatment temperature of the metal matrix is 800-1600 ℃, and the atmosphere is hydrogen; or the atmosphere is a mixed gas of hydrogen and nitrogen or inert gas, wherein the molar ratio of the hydrogen is not less than 1%, and the annealing time is not less than 10 minutes;
the growth temperature in the first step is 500-1300 ℃, the molar ratio of the carbon source to the hydrogen is 0.004-1, and the growth time is not less than 10 minutes;
in the second step, the etching temperature is 500-1300 ℃, the etching time is not less than 10 minutes, and the atmosphere is inert gas and dispersed impurities thereof; in the second step, the precipitation temperature of the graphene is 500-1300 ℃, the precipitation time is not less than 10 minutes, and the molar ratio of hydrogen to inert gas is 0.005-0.1;
in the third step, the regrowth temperature is 500-1300 ℃, the regrowth time is not less than 20 minutes, and the molar ratio of the carbon source to the hydrogen is 0.005-0.1.
2. The method for preparing a high-quality single-layer polycrystalline graphene thin film according to claim 1, wherein: the metal matrix is ultrasonically cleaned in one or more of acetone, ethyl lactate, water, isopropanol and ethanol for at least 10 min.
3. The method for preparing a high-quality single-layer polycrystalline graphene thin film according to claim 1, wherein: the carbon source is one or more than two of methane, ethane, acetylene, ethylene and ethanol hydrocarbon, the carrier is hydrogen, or the carrier is mixed gas of hydrogen and nitrogen or inert gas, and the volume purities of the carbon source and the carrier gas are both more than 98%.
4. The method for preparing a high-quality single-layer polycrystalline graphene thin film according to claim 1, wherein: after the growth is finished, the metal matrix is rapidly cooled to below 200 ℃ under the protection of a carrier containing hydrogen, the molar ratio of the hydrogen in the carrier gas is not less than 1%, and the rapid cooling rate is not less than 50 ℃/s.
5. The method for preparing a high-quality single-layer polycrystalline graphene thin film according to claim 1, wherein: the grain size of the prepared graphene film can be continuously adjusted in a large range, and the grain size is distributed between 10 nanometers and 1 micrometer.
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