TWI537210B - Method of preparing graphene - Google Patents

Description

Method for preparing graphene

This invention relates to a process for the preparation of graphene, and more particularly to a process for the preparation of graphene in a multi-stage heating zone.

Graphene is a monoatomic layer of graphite, each of which is sp ² mixed with adjacent three atoms to form a bond and extends into a honeycomb two-dimensional structure. Graphene has always been considered a hypothetical structure and cannot be stably existed in nature until it was successfully separated from graphite in 2004. Current studies have shown that graphene has a carrier mobility of up to 200,000 cm ² /Vs, and graphene has a resistivity of about 1.0 μΩ-cm at room temperature. It is the lowest known resistivity at room temperature and also has good properties. The properties of heat conduction and high transmittance are also the thinnest and hardest nanomaterials known in the world. Therefore, it has been widely used in fields such as nanoelectronic components, touch panels, capacitors, lithium batteries, semiconductors, solar cell composite materials, and hydrogen storage materials.

Conventional techniques for preparing graphene mainly include mechanical exfoliation, SiC epitaxial growth, reduction from graphene oxides, and chemical vapor deposition. Deposition, CVD) and other methods. Among them, chemical vapor deposition is the most common method at present, because it is most suitable for mass production, and it is easy to operate and the equipment is simple in construction, but the process temperature required for cracking the raw material gas is very high. High (900~1000°C), so it is not suitable for deposition on substrates with lower melting points. It is often necessary to transfer to other substrates such as ITO glass substrates. Transfer refers to the graphene layer originally grown on metal substrates. Transfer to the desired substrate. For example, a conventional technique is to grab a graphene layer grown on a copper substrate with a polymer support layer (for example, PMMA), then etch the copper substrate, transfer it to a desired substrate, and dissolve it high. The molecular support layer transfers the graphene layer to the desired substrate. Such transfer easily causes cracking or irregular wrinkles of the graphene layer, and polymer residue remains on the surface of the graphene layer, so that the material properties excellent in the graphene layer are seriously affected. Moreover, such transfer cannot be compatible with current semiconductor processes (eg, tantalum process) technology, limiting the prospect of wafer-scale large-scale production of integrated circuit components, thereby increasing process cost, time consuming, and chemical residues. problem. Therefore, how to directly grow high-quality, large-area single-layer graphene on a common insulating dielectric (for example, a ceria substrate) is an important issue for the development of graphene electronic components.

In view of the above problems of the prior art, the object of the present invention is to provide a method for preparing graphene in a multi-stage heating zone, so as to solve the problem that the types of substrates suitable for the prior art are not many and cannot be directly deposited on a glass substrate. .

According to an object of the present invention, a method for preparing graphene is provided. A reaction furnace can be used. The reaction furnace is divided into a first heating zone and a second heating zone, wherein the first heating zone is located in the front section of the reactor and the second heating zone is in the reaction. In the furnace section, the method may comprise the steps of: placing the catalyst in the first heating zone and placing the substrate in the second heating zone; heating the first heating zone to between about 900 ° C and about 1000 ° C, and heating the second heating From about 500 ° C to about 600 ° C; and a methane having a flow rate of from about 10 sccm to about 50 sccm Into the reaction furnace, methane is cracked by the above temperature and catalyst catalysis, and deposited on a substrate to form graphene.

Preferably, the pressure in the furnace of the reactor is about 5 x 10 ^-3 torr.

Preferably, the catalyst comprises a copper foil.

Preferably, the substrate comprises a copper substrate or a ceria substrate.

Preferably, a hydrogen gas having a flow rate of from about 20 sccm to about 100 sccm is simultaneously introduced into the methane.

According to another object of the present invention, a method for preparing graphene using a three-stage reactor is provided. The three-stage reactor can be divided into a first heating zone, a second heating zone and a third heating zone, wherein the first heating zone Located in the front section of the reactor, the second heating zone is located in the middle section of the reactor, and the third heating zone is located in the end section of the reactor. The method can include the steps of: placing a catalyst in a second heating zone and placing the substrate in a third heating zone; heating the first heating zone and the second heating zone to between about 900 ° C and about 1000 ° C, and heating the third The heating zone is heated to a temperature of from about 500 ° C to about 600 ° C; and methane having a flow rate of from about 10 sccm to about 50 sccm is introduced into the reaction furnace, methane is cracked by the above temperature and catalyst catalysis, and deposited on the substrate to form graphene.

Preferably, the pressure in the furnace of the reactor is about 5 x 10 ^-3 torr.

Preferably, the catalyst comprises a copper foil.

Preferably, the substrate comprises a copper substrate or a ceria substrate.

Preferably, a hydrogen gas having a flow rate of from about 20 sccm to about 100 sccm is simultaneously introduced into the methane.

As described above, the method for preparing graphene disclosed in the present invention may have one or more of the following advantages:

(1) The method for preparing graphene can be carried out on a substrate by using a multi-stage heating zone reaction furnace, whereby graphene can be deposited on a substrate at a temperature lower than 600 ° C, and thus can be applied to a substrate having a lower melting point. The number of substrates that can be selected is increased.

(2) The method for preparing graphene can be directly deposited on a glass substrate by using a multi-stage heating zone reaction furnace, without being transferred to other substrates, thereby reducing cost and process time.

(3) The method for preparing graphene can be carried out by using a multi-stage heating zone reactor, whereby graphene deposited on a substrate in an environment lower than 600 ° C can be compared with an environment higher than 900 ° C. The graphene deposited on the substrate has fewer layers and fewer defects.

S11~S13‧‧‧Steps

1‧‧‧Three-stage reactor

10‧‧‧First heating zone

20‧‧‧second heating zone

30‧‧‧ third heating zone

40‧‧‧ Catalyst

50‧‧‧Substrate

60‧‧‧Quartz boat

70‧‧‧heating coil

80‧‧‧ gas inlet end

90‧‧‧ gas outlet

Fig. 1 is a flow chart showing a method of producing graphene according to a first embodiment of the present invention.

Fig. 2 is a structural view of a three-stage reactor used in the method for producing graphene of the present invention.

Fig. 3 is a graph showing the relationship between the temperature rise and the time of the method for producing graphene of the present invention.

Figure 4a is a graphene Raman produced by the second to sixth embodiments of the present invention having a fixed methane flow rate of 20 sccm but varying hydrogen flow rates of 20, 40, 60, 80, 100 sccm, respectively, at a heating temperature of 950 °C. Spectrum.

Figure 4b is a graphene Raman produced by the second to sixth embodiments of the present invention having a fixed methane flow rate of 20 sccm but varying hydrogen flow rates of 20, 40, 60, 80, 100 sccm, respectively, at a heating temperature of 550 °C. Spectrum.

Figure 5a is a graphene Raman produced by the sixth to tenth embodiments of the present invention having a fixed hydrogen flow rate of 100 sccm but varying methane flows of 20, 10, 30, 40, 50 sccm, respectively, at a heating temperature of 950 °C. Spectrum.

Figure 5b is a graphene Raman produced by the sixth to tenth embodiments of the present invention having a fixed hydrogen flow rate of 100 sccm but varying methane flows of 20, 10, 30, 40, 50 sccm, respectively, at a heating temperature of 550 °C. Spectrum.

Figure 6a is a heating temperature of the eleventh to twelfth embodiments of the eleventh to twelfth embodiments in which the fixed methane flow rate of the present invention is 20 sccm and the hydrogen flow rate of the fixed reaction stage is 100 sccm, respectively, and the temperature of the annealing and the annealing stage is 100, 50 sccm. A Raman spectrum of the graphene produced.

Figure 6b is the heating temperature of the thirteenth to fourteenth embodiments of the thirteenth to fourteenth embodiments in which the fixed methane flow rate of the present invention is 10 sccm and the hydrogen flow rate of the fixed reaction stage is 100 sccm, respectively, and the temperature of the annealing and the annealing stage is 100, 50 sccm. A Raman spectrum of the graphene produced.

Figure 7a shows the fixed methane flow rate of the present invention is 20 sccm, but the hydrogen flow rate of the first, second and third reactions is changed to 100, 0~100, 0~100 sccm to grow double-layer and three-layer graphene, respectively. The fifteenth and sixteenth embodiments of the present invention produce a Raman spectrum of graphene at a heating temperature of 950 °C.

Figure 7b is the fixed methane flow rate of the present invention is 20sccm, but the hydrogen flow rate of the first, second and third reactions is changed to 100, 0~100, 0~100sccm to grow single layer, double layer and three respectively. The seventeenth to nineteenth embodiments of the layer graphene were prepared at a heating temperature of 550 ° C to obtain a Raman spectrum of graphene.

Fig. 8a is a HRTEM image of graphene prepared by heating at a temperature of 950 °C in the fifteenth embodiment of the invention.

Fig. 8b is a HRTEM image of graphene prepared by heating at a temperature of 950 °C in the sixteenth embodiment of the invention.

Fig. 9a is a HRTEM image of graphene obtained by heating at a heating temperature of 550 °C in the seventeenth embodiment of the invention.

Fig. 9b is a HRTEM image of graphene obtained by heating at a heating temperature of 550 °C in the eighteenth embodiment of the invention.

Fig. 9c is a HRTEM chart of graphene obtained by heating at a heating temperature of 550 °C in the nineteenth embodiment of the invention.

Fig. 10 is a Raman spectrum diagram of graphene obtained by heating at 950 ° C in the twentieth embodiment of the present invention.

Fig. 11 is a Raman spectrum diagram of graphene obtained by heating at 950 ° C and 550 ° C for the twenty-first embodiment of the present invention.

Fig. 12a is an SEM image of the surface of the copper substrate before heating at a heating temperature of 550 ° C in the sixth embodiment of the invention.

Fig. 12b is an SEM image of the surface of a copper substrate obtained by heating a heating temperature of 550 ° C in the sixth embodiment of the present invention.

Fig. 12c is a high-magnification SEM image of the surface of the copper substrate on which graphene is obtained after heating at a heating temperature of 550 °C in the sixth embodiment of the present invention.

Figure 13a is an optical micrograph of the size of a copper substrate on which graphene has not grown.

Figure 13b is an optical micrograph of the surface of a copper substrate on which graphene has not grown.

Figure 13c is an optical micrograph of the surface of a copper substrate on which graphene has grown.

Figure 14a is an optical micrograph of the size of the ceria substrate to which graphene has not been transferred.

Figure 14b is an optical micrograph of the surface of a ceria substrate on which graphene has not been transferred.

Figure 14c is an optical micrograph of the surface of the ceria on which graphene is transferred.

Figure 15a is an optical micrograph of the size of the soda glass substrate to which the graphene has not been transferred.

Figure 15b is an optical micrograph of the surface of a soda glass substrate on which graphene has not been transferred.

Figure 15c is an optical micrograph of the surface of the soda glass onto which graphene is transferred.

Fig. 16 is a graph showing the relationship between the resistivity and the number of layers of graphene obtained by heating at 550 ° C in the sixth embodiment of the present invention.

Fig. 17 is a view showing the ultraviolet/visible spectrum of the glass substrate on which the graphene is transferred at the heating temperature of 550 ° C in the sixth embodiment of the present invention.

The invention will be further described in detail by the following preferred embodiments and the accompanying drawings. It should be noted that the experimental data disclosed in the following embodiments are for explaining the technical features of the present invention, and are not intended to limit the manner in which they can be implemented.

Please refer to FIG. 1, which is a flow chart of a method for preparing graphene according to a first embodiment of the present invention. The reaction furnace used in the method can be divided into a first heating zone and a second heating zone, wherein the first heating zone is located in the front section of the reactor and the second heating zone is located in the end section of the reaction furnace. The method may comprise the steps of: placing a catalyst in a first heating zone, placing the substrate in a second heating zone (step S11), heating the first heating zone to between about 900 ° C and about 1000 ° C, and heating the second heating The zone is from about 500 ° C to about 600 ° C (step S12), and the flow rate is about 10 standard cubic centimeters per minute (standard cubic centimeter per Minute, sccm) to about 50 sccm of methane to the reaction furnace, methane is cleaved by catalyst catalysis, and deposited on a substrate to form graphene (step S13).

Please refer to Fig. 2, which is a structural view of a three-stage reactor used in the method for producing graphene of the present invention. In the second embodiment, the structure of the three-stage reactor 1 used is similar to that of the two-stage reactor used in the first embodiment, except that the third-stage reactor 1 has a third heating zone 30. In this embodiment, the manufacturing step is to first place the copper foil as the catalyst 40 on the quartz boat 60 and place it in the second heating zone 20; then cut the copper foil (99.8%, 25 μm ) into 1 cm x 1 cm. The size is taken as the substrate 50, and is placed in the third heating zone 30; the mechanical pump is started to evacuate the three-stage reactor 1 to a pressure of about 5×10 ⁻³ torr; the temperature of the first heating zone 10 and the second heating zone 20 are set. At about 950 ° C and the temperature of the third heating zone 30 is about 550 ° C, hydrogen gas (H ₂ ) having a flow rate of about 20 sccm and argon gas (Ar) having a flow rate of about 20 sccm are introduced from the gas inlet end 80, and the gas outlet end is used. 90 is discharged, wherein hydrogen acts as an etching gas, which can interrupt the bonding of oxygen and copper to avoid the formation of copper oxide, to maintain the catalytic properties of copper and to reduce the defects of the formed graphene, and argon gas only acts as a carrier gas. Then, the heating coil 70 is activated, and the first heating zone 10, the second heating zone 20, and the third heating zone 30 are heated for about 100 minutes to the respective set temperatures, and then annealed for 25 minutes at the same temperature to close the argon gas. Then, methane (CH ₄ ) having a flow rate of about 20 sccm was introduced into the three-stage reactor 1 for about 10 minutes, and methane was cracked by the above temperature and catalyst catalysis, and deposited on the substrate 50 to form graphene. Finally, the methane was introduced and argon gas was introduced, and the graphene deposited on the substrate was taken out after the temperature was lowered to room temperature. The relationship between temperature rise and time is shown in Figure 3.

The third, fourth, fifth and sixth embodiments of the present invention are similar to the second embodiment in that the hydrogen flow rates are about 40 sccm, 60 sccm, 80 sccm, and 100 sccm, respectively.

The seventh, eighth, ninth and tenth embodiments of the present invention are similar to the preparation of the sixth embodiment except that the methane flow rates are approximately 10 sccm, 30 sccm, 40 sccm and 50 sccm, respectively.

For the sake of easy understanding, the parameter conditions of the second to tenth embodiments of the present invention are as detailed in Table 1.

Please refer to FIGS. 4a to 5b, which are Raman spectra of graphene prepared in the second heating zone and the third heating zone according to the second to tenth embodiments of the present invention. 4A, 4b, 5a, and 5b are second to sixth embodiments of the present invention, wherein the fixed methane flow rate is 20 sccm, but the hydrogen flow rate is changed to 20, 40, 60, 80, 100 sccm, respectively. A Raman spectrum of graphene prepared at a heating temperature of 950 ° C, and a second to sixth embodiment of the present invention in which the fixed methane flow rate is 20 sccm but the hydrogen flow rate is changed to 20, 40, 60, 80, 100 sccm, respectively. The Raman spectrum of graphene obtained by heating at °C, the sixth to tenth embodiment of the present invention having a fixed hydrogen flow rate of 100 sccm but varying methane flow rates of 20, 10, 30, 40, 50 sccm respectively at 950 ° C Raman spectrum of graphene obtained by heating temperature and heating temperature of 550 ° C of the sixth to tenth embodiments of the present invention in which the fixed hydrogen flow rate is 100 sccm but the methane flow rate is changed to 20, 10, 30, 40, 50 sccm, respectively. A Raman spectrum of the graphene produced. As shown in the above four figures, the graphene quality (that is, the defect condition) and the number of generated layers are identified by Raman spectroscopy, and the D characteristic peak (1350 cm ^-1 ), the G characteristic peak (1580 cm ^-1 ), and the 2D characteristic peak can be obtained. (2680~2700cm ^-1 ) to judge. The intensity ratio of the D characteristic peak to the G characteristic peak I _D /I _G can determine the quality, and the intensity ratio of the intensity of the 2D characteristic peak to the G characteristic peak I _2D /I _G can determine the number of layers. When the I _D /I _{G is} smaller, the defect is less. When I _2D /I _{G is} less than 1 is a multilayer, I _2D /I _{G is} greater than or equal to 1 and less than 2 is an oligo layer of two to three layers, and I _2D /I _{G is} larger than 2 is a single layer. The comparison results are shown in Table 2.

It can be seen from Table 2 that in the second embodiment to the sixth embodiment, the fixed methane flow rate is gradually increased as the hydrogen flow rate is increased, regardless of the second heating zone and the lower temperature at a higher temperature (950 ° C). In the third heating zone (550 ° C), the I _2D /I _G tendency gradually becomes larger, which means that the number of graphene layers is less, and all are oligo-layer graphene. At the same time, the number of graphene layers in the third heating zone is mostly less than that in the second heating zone, which means that the lower temperature zone is relatively easy to obtain the desired single layer graphene. In the second embodiment to the sixth embodiment, the fixed methane flow rate is gradually increased as the hydrogen flow rate is increased, and the second heating zone of I _D /I _G at a higher temperature (950 ° C) tends to be When it becomes larger, it means that the defect becomes more, and the trend of the third heating zone of I _D /I _G at a lower temperature (550 ° C) becomes smaller, indicating that the defect is less. The sixth embodiment produces fewer graphene defects in the higher temperature zone and the lower temperature zone, and the number of layers is a single layer, which is a preferred embodiment.

In the sixth embodiment to the tenth embodiment, the fixed hydrogen flow rate is gradually increased as the methane flow rate is increased, regardless of the second heating zone at a higher temperature (950 ° C) and the lower temperature (550 ° C). In the third heating zone, the I _2D /I _G trend gradually becomes smaller, which means that the number of graphene layers is increased, but it is still oligo-layer graphene. There is no significant difference in the number of graphene layers between the second heating zone and the third heating zone. In the second embodiment to the sixth embodiment Sixth embodiment, the hydrogen flow rate into fixed, as the flow rate through the methane is gradually increased, I _D / I _G at relatively high temperature (950 deg.] C) of the second heating zone trends It is getting bigger and bigger, representing more defects. However, the trend of I _D /I _G in the third heating zone at lower temperature (550 °C) is irregular, indicating that there is no regularity in the defect status and the amount of methane flow.

The eleventh to fourteenth embodiments of the present invention are similar to the sixth embodiment except that the flow rate of the hydrogen gas is fixed in the reaction stage, and is different in the temperature rising annealing stage, and the methane flow rate is also different to determine the hydrogen gas. Whether the difference in flow rate during the annealing process affects the growth quality of graphene, the relevant parameters are shown in Table 3.

Please refer to FIG. 6a, which is an eleventh to twelfth embodiment in which the fixed methane flow rate of the present invention is 20 sccm and the hydrogen flow rate in the fixed reaction stage is 100 sccm, respectively, and the hydrogen flow rate in the annealing stage is changed to 100, 50 sccm. A Raman spectrum of graphene was prepared at a heating temperature of °C. As shown in the figure, when the fixed methane flow rate is 20 sccm, the hydrogen gas is 100 sccm in the reaction stage, and the hydrogen peak in the heating and annealing phase is 50 sccm, and the D peak is higher than the 100 sccm D peak, resulting in a higher I _D /I _G value. It is shown that the hydrogen flow rate in the heating and annealing stages is reduced from 100 sccm to 50 sccm, and the graphene defects are increased, so that a sufficient hydrogen flow rate in the temperature rising and annealing stages can effectively reduce the graphene defects. Next, please refer to FIG. 6b, which is a thirteenth to fourteenth embodiment in which the fixed methane flow rate is 10 sccm and the fixed reaction phase hydrogen flow rate is 100 sccm, but the temperature rise and the annealing stage hydrogen flow rate are 100, 50 sccm, respectively. The Raman spectrum of graphene was obtained at a heating temperature of 550 ° C. As shown in the figure, when the fixed methane flow rate was 10 sccm, the hydrogen gas was 100 sccm in the reaction stage, and the hydrogen gas was 50 sccm D peak and 100 sccm in the heating and annealing stages. There was no significant difference in the D peak.

Therefore, in comparison with the above-described second to fourteenth embodiments, the graphene having the lowest temperature growth in the hydrogen gas flow rate of 100 sccm in the temperature rising annealing stage or the reaction stage and the methane flow rate of 20 sccm is obtained. That is, the lower temperature growth condition of the sixth embodiment is an optimized parameter.

The fifteenth to nineteenth embodiments of the present invention are similar to the sixth embodiment, except that the step of growing the graphite thinning is performed three times in succession, wherein the methane flow rate is fixed to 20 sccm three times, and the hydrogen flow rate is the first time, The second and third reactions were 100, 0 to 100, and 0 to 100 sccm, respectively. A single layer of graphite is formed by the first reaction, and a second layer of graphite is thinned on the single layer of graphite to form a double layer of graphite. The third reaction is further stacked with a layer of graphite diluted on the double layer of graphite to form a thin layer. The three layers of graphite are diluted and thus controlled to obtain oligo-layer graphene. The relevant experimental manipulation parameters and the number and defects of the graphene layers produced are shown in Table 4.

Please refer to Figures 7a and 7b, respectively. The fixed methane flow rate of the present invention is 20 sccm, but the hydrogen flow rates of the first, second and third reactions are changed to 100, 0 to 100, 0 to 100 sccm, respectively. The fifteenth and sixteenth embodiments of the two-layer and three-layer graphene are grown at a heating temperature of 950 ° C to obtain a Raman spectrum of graphene, and the fixed methane flow rate of the present invention is 20 sccm but the change is the first time, The hydrogen flow rate of the second and third reactions is 100, 0-100, 0-100 sccm to grow the heating temperature of the seventeenth to nineteenth embodiments of the single-layer, double-layer and three-layer graphene at 550 ° C, respectively. A Raman spectrum of the graphene produced. The I _2D /I _G and I _D /I _G values obtained from the two figures are as shown in the above table. It can be seen that the three layers of the oligo layer in the higher temperature region have significantly lower defects than the double layer, and it is presumed to be stacked again. When a layer of graphene is used, it causes recrystallization to grow before it is completely crystallized. From the 7th and 7th diagrams, it is known that the number of layers is in the range of the oligo layer. The double layer or the third layer is actually identified by high-resolution transmission electron microscope (HRTEM) analysis.

Next, please refer to FIGS. 8a and 8b, which are HRTEM images of graphene prepared at a heating temperature of 950 ° C in the fifteenth embodiment of the present invention, and heating at 950 ° C in the sixteenth embodiment of the present invention. HRTEM image of graphene prepared by temperature. The graphene in Fig. 8a has a thickness of 1 nm and is a two-layer structure, and the graphene in Fig. 8b has a thickness of 1 nm and has a three-layer structure. Therefore, the HRTEM and Raman diagrams show that the number of graphene growth layers in the higher temperature region is difficult to control.

Next, please refer to Figures 9a, 9b and 9c, which are HRTEM images of graphene obtained at a heating temperature of 550 ° C for the seventeenth embodiment of the present invention, and an eighteenth embodiment of the present invention at 550 The HRTEM image of graphene obtained by heating at °C and the HRTEM image of graphene prepared at a heating temperature of 550 ° C in the nineteenth embodiment of the present invention. The graphene of Fig. 9a has a thickness of 0.335 nm and is a single layer. The upper right is the Selected Area Diffraction (SAD), which shows that the crystal phases in the figure are irregularly arranged. The thickness of graphene in Fig. 9b is 0.67 nm, which is obviously double layer. The graphene of Fig. 9c has a thickness of 1 nm and is three layers. Therefore, by the HRTEM image and the Raman spectrum, the method for preparing graphene by the segmented heating zone of the present invention can smoothly grow single-layer graphene in the lower temperature region at 550 ° C, or double-layer and three-layer graphite in the oligo layer. Aene, and the defects are low in quality.

The twentieth and twenty-first embodiments of the present invention are similar to the second embodiment, except that the substrate is a ceria substrate (glass substrate), and the hydrogen flow rate of the twentieth embodiment is about 100 sccm and is introduced. The methane flow rate is about 5 sccm, the hydrogen flow rate of the twenty-first embodiment is about 24 sccm, and the methane flow rate is about 35 sccm, and the reaction time of both examples is longer than the second embodiment, about 30 minutes. . Please refer to FIG. 10 and FIG. 11 , which are respectively a Raman spectrum of graphene prepared at a heating temperature of 950 ° C according to a twentieth embodiment of the present invention, and a twenty-first embodiment of the present invention respectively A Raman spectrum of graphene was prepared at a heating temperature of 950 ° C and 550 ° C. The comparison results of I _2D /I _G and I _D /I _G measured by the graph are shown in Table 5.

It can be seen from Fig. 10 and Table 5 that in the twentieth embodiment, graphene cannot be produced in the second heating zone of higher temperature, which is lower in the lower temperature zone. As can be seen from Fig. 11, the conditions of the twenty-first embodiment can produce graphene at 950 ° C and 550 ° C, regardless of the second heating zone of higher temperature or the third heating zone of lower temperature, I _2D /I _G Both are less than 1 and I _D /I _G are 1.93, indicating that although graphene is formed in the higher temperature zone or the lower temperature zone, the number of layers is multi-layer and many defects. It can be seen from the twenty-first embodiment that graphene can form graphene directly on the glass substrate at a temperature of about 550 ° C under the above-mentioned hydrogen and methane flow conditions, so that the process of transferring to other substrates is not required. The second to nineteenth embodiments using the copper substrate can reduce the transfer cost and the process time.

Next, the morphology analysis of graphene growth on the substrate was carried out under the conditions of the sixth embodiment of the present invention. Referring to Figures 12a to 12c, which are respectively an SEM image of the surface of the copper substrate before heating at a heating temperature of 550 ° C according to the sixth embodiment of the present invention, and the sixth embodiment of the present invention is heated at a heating temperature of 550 ° C. The SEM image of the surface of the copper substrate obtained by graphene, and the sixth embodiment of the present invention were heated at a heating temperature of 550 ° C to obtain a high-magnification SEM image of the surface of the copper substrate of graphene. It can be seen from Fig. 12a that before the heating, it can be clearly seen that the surface of the copper substrate has a strip shape. From Fig. 12b, it can be seen that the copper substrate after the growth of graphene has some slight wrinkles on the surface. Because the copper substrate is in thermal expansion and contraction, graphene is caused by cold expansion and contraction, and the wrinkles cause the graphene to stably exist. From Fig. 12c, it can be clearly seen under high-magnification SEM that graphene has a honeycomb shape in which a plurality of hexagons are combined.

Next, a comparison of the surface topography of the graphene formed on the copper substrate to another substrate was observed, and it was observed by an optical microscope (Optical Microscope). Please refer to Figures 13a to 13c, which are optical micrograph images of the size of the copper substrate on which graphene has not grown, optical micrographs of the surface of the copper substrate on which graphene has not grown, graphene An optical micrograph of the surface of a copper substrate that has grown thereon. From Fig. 13b, it can be clearly seen that the surface of the copper substrate has a stripe pattern, and from Fig. 13c, the graphene growth trace of the white block on the surface of the copper substrate can be seen.

Next, please refer to the figures 14a to 14c, which are optical micrograph images of the size of the ceria substrate on which the graphene is not transferred, and the optics of the surface of the ceria substrate on which the graphene is not transferred. A microscopic image, an optical micrograph of the surface of the ceria on which graphene is transferred. by As shown in Fig. 14c, since the refractive index of cerium oxide is extremely low and the transmittance of graphene in the visible light region is high, only the uncleaned PMMA can be seen.

Next, please refer to Figures 15a to 15c, which are optical micrograph images of the size of the soda glass substrate on which graphene is transferred, and optical microscopy images of the surface of the soda glass substrate on which graphene is not transferred. Figure. Optical micrograph of the surface of the soda glass onto which graphene is transferred. From the comparison of Fig. 15b and Fig. 15c, it is known that after the graphene is covered, the surface of the soda glass becomes darker in color.

Next, the electrical analysis of the graphene produced in the lower temperature region of the present invention was tested, and the values thereof are shown in Table 6 below.

It can be seen from Table 6 that the graphene produced at a lower temperature has a lower resistivity and better carrier mobility than the graphene produced at a higher temperature, and the resistivity is smaller than that of the double layer and the third layer formed in the low temperature region. . Therefore, the single-layer graphene produced in the lower temperature region has higher electrical properties and better quality. Next, please refer to Fig. 16, which is a graph showing the relationship between the resistivity and the number of layers of graphene prepared at a heating temperature of 550 ° C in the sixth embodiment of the present invention. As shown in the figure, as the number of layers increases, the resistivity also increases, which also causes the conductivity to decrease.

Next, the transmittance analysis of the graphene prepared in the lower temperature region of the present invention was tested. Referring to Fig. 17, which is a UV/Vis spectrum of a glass substrate on which graphene is transferred at a heating temperature of 550 ° C according to a sixth embodiment of the present invention. As shown in the figure, the glass substrate transmittance is 91.11%, and the graphene/glass transmittance is 87.22%. Assuming graphene transmittance is 100%, graphene/glass should be 91.11%, so graphene is estimated. The penetration rate was 95.73%, which was slightly lower than the graphene penetration rate of 97.7% obtained by mechanical peeling in the literature. It is speculated that during the transfer process, the PMMA is not cleaned and remains on the surface of the graphene, resulting in a decrease in the transmittance.

In summary, the method for preparing graphene of the present invention can deposit graphene on a substrate at a temperature lower than 600 ° C due to a multi-stage heating zone reaction furnace, so that it can be applied to a substrate having a lower melting point. The number of substrates selected has increased. In particular, it can be applied to commonly used glass substrates without additional transfer processes, which can reduce cost and process time. At the same time, the graphene formed in the lower temperature heating zone of about 500 ° C to about 600 ° C has a lower number of layers than the graphene produced in the higher temperature heating zone of about 900 ° C to about 1000 ° C, with fewer defects and high conductivity. Good penetration rate.

The above is intended to be illustrative only and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

S11~S13‧‧‧Steps

Claims (8)

A method for preparing graphene is to use a reaction furnace which is divided into a first heating zone and a second heating zone, wherein the first heating zone is located in front of the reactor and the second heating zone is located At the end of the reactor, the method comprises the steps of: placing a catalyst in the first heating zone, and placing a cerium oxide substrate in the second heating zone; heating the first heating zone to about 900 ° C to About 1000 ° C, and heating the second heating zone to about 500 ° C to about 600 ° C; and introducing a flow of methane from about 10 sccm to about 50 sccm into the reactor, passing methane through the first heating zone to about 900 ° C to The catalyst is catalytically cracked at a temperature of about 1000 ° C and deposited on the ceria substrate at a temperature of from about 500 ° C to about 600 ° C in the second heating zone to form graphene. The method of claim 1, wherein the furnace pressure in the furnace is about 5 x 10 ^-3 torr. The method of claim 1, wherein the catalyst comprises a copper foil. The method of claim 3, wherein the introduction of methane simultaneously introduces a hydrogen gas having a flow rate of from about 20 sccm to about 100 sccm. A method for preparing graphene by using a three-stage reactor, the three-stage reactor is divided into a first heating zone, a second heating zone and a third heating zone, wherein the first heating zone is located in the reactor In the preceding stage, the second heating zone is located in the middle of the reaction furnace, and the third heating zone is located at the end of the reaction furnace. The method comprises the steps of: placing a catalyst in the second heating zone and a second oxidation zone矽 substrate placed in the first a third heating zone; heating the first heating zone and the second heating zone to about 900 ° C to about 1000 ° C, and heating the third heating zone to about 500 ° C to about 600 ° C; and the flow rate of about 10 sccm to about 50 sccm of methane is introduced into the reaction furnace, methane is cleaved by the catalyst at a temperature of about 900 ° C to about 1000 ° C in the second heating zone, and is deposited at a temperature of about 500 ° C to about 600 ° C in the third heating zone. On the ceria substrate, graphene is formed. The method of claim 5, wherein the furnace pressure in the furnace is about 5 x 10 ^-3 torr. The method of claim 5, wherein the catalyst comprises a copper foil. The method of claim 7, wherein the introduction of methane simultaneously introduces a hydrogen gas having a flow rate of from about 20 sccm to about 100 sccm.