CN103172061A - Method for growing large-area graphene on insulating substrate - Google Patents

Abstract

The invention discloses a method for growing large-area graphene on an insulating substrate. The method uses insulating material as the growth substrate, copper foil as the catalyst, carbon source, hydrogen and protective gas as the gas source, and adopts a two-step chemical vapor deposition method (low-pressure growth and high-pressure growth). Foil face-to-face contact, using the short-range catalytic effect of copper foil to grow large-area graphene on an insulating substrate. The whole process of the method of the invention is simple to operate, low in cost, high in repeatability of sample preparation and less affected by external interference. The prepared single-layer graphene can be made into large-scale circuit devices by exposure method without cumbersome transfer process.

Description

A method for growing large-area graphene on an insulating substrate

technical field

The invention relates to a method for growing large-area graphene on an insulating substrate.

Background technique

Professors Konstantin Novoselov and Andre Geim of the University of Manchester won the 2010 Nobel Prize in Physics for their discovery of graphene's special Dirac electronic band structure and the singular fractional quantum Hall effect. At room temperature, the high carrier mobility and saturation velocity in graphene make graphene expected to replace silicon as the basic material for the next generation of large-scale integrated circuits. At present, the large-scale industrial application of graphene is mainly limited to the growth of graphene. In recent years, the research on graphene growth, especially the low-cost large-area growth, has attracted more and more attention from domestic and foreign companies, research institutes and university researchers.

Although the graphene obtained by the mechanical exfoliation method for preparing graphene proposed in 2005 has the highest quality of graphene reported now, the size of graphene obtained by this method is severely limited, generally only tens of microns size, and the cost and technical proficiency requirements of graphene prepared by this method are very high, which is only suitable for laboratory research and is not conducive to large-scale industrial growth (K.S.Novoselov et al., Nature438, 197.2005). In 2006, Professor Walter de Heer of Georgia Institute of Technology in the United States proposed a method of epitaxially growing graphene by thermally decomposing silicon carbide in ultra-high vacuum (C.Berger et al., Science312, 1191.2006). However, the expensive price of the substrate material silicon carbide, the expensive ultra-high vacuum equipment required for growth conditions, and the high temperature, stable, and uniform heating system have greatly increased the cost of mass production, which has greatly hindered large-scale industrialization. obstacles. In 2009, Professor Rodney S.Ruoff of the University of Texas at Austin adopted a large-scale industrial growth method-chemical vapor deposition method, using methane and hydrogen as gas sources, and using the catalytic effect of copper foil to deposit on copper foil. A large area of graphene monolayer (X.Li et al., Science324, 1312.2009) has grown on it. However, due to the conductivity of the substrate, if it is to be made into an integrated circuit, the grown graphene needs to be transferred. And the technology of this transfer step is quite loaded down with trivial details and requires very high to the technique and proficiency of transfer personnel. At the same time, the pollution that may be introduced during the transfer process and the large amount of metal ions and organic macromolecules at the interface make the quality of graphene degrade significantly in actual devices. In view of the complexity and uncontrollability of the above factors, graphene grown by chemical vapor deposition based on metal catalysis is still a long way from large-scale industrial application.

Therefore, large-scale growth of graphene on an insulating substrate by chemical vapor deposition is of great significance for the application of graphene in the large-scale integrated circuit industry and the research of ultrafast electronics.

Contents of the invention

The object of the invention is to provide a method for growing large-area graphene on an insulating substrate.

The present invention uses insulating material as growth substrate, copper foil as catalyst, carbon source (such as methane), hydrogen and protective gas (such as inert gas) as gas source, and adopts two-step chemical vapor phase method (low pressure growth and high pressure growth) The deposition method, through the face-to-face contact between the insulating substrate and the copper foil, uses the short-range catalytic effect of the copper foil to grow large-area graphene on the insulating substrate.

The specific method includes the following steps:

1) Sample preparation: cleaning the insulating substrate and copper foil to remove organic matter and metal ion impurities; making the cleaned insulating substrate surface-to-surface contact with the copper foil to obtain a sample;

2) Heating stage: Continuously feed the mixed gas of protective gas and hydrogen into the reactor, and at the same time place the sample in the reactor, heat up to 1005-1030°C (preferably 1020°C), and keep warm for 10- 30 minutes (preferably 10 minutes);

3) Low-pressure growth stage: maintain the temperature of the reactor, and adjust the pressure in the reactor to be 100-120Pa (preferably 100Pa), then feed carbon source, protective gas and hydrogen into the reactor simultaneously, Grow graphene 20-40 minutes (preferably 30 minutes) under this condition;

4) High-pressure growth stage: maintain the temperature of the reactor, keep the flow of each gas in step 3) constant, adjust the pressure in the reactor to 400-500Pa (preferably 400Pa), grow graphene under this condition 50-70 minutes (preferably 60 minutes);

5) Cooling process: After the growth is over, reduce the temperature of the reactor to room temperature, take out the sample, and obtain a large area of graphene deposited on the insulating substrate; keep the pressure, carbon source, and the flow rate of the protective gas constant in this process. Change, increase the flow rate of hydrogen.

Wherein, the insulating substrate in step 1) may specifically be a substrate made of any of the following materials: sapphire, quartz, and the like. The copper foil is a commercial product with a purity of over 99.999% and a thickness of 0.02 μm-0.04 μm.

The protective gas in step 2) can be an inert gas (such as argon, etc.), and its flow rate is 90-110 sccm, specifically 100 sccm; the hydrogen flow rate is 15-20 sccm, specifically 20 sccm. During the heating and heat preservation process, the pressure in the reactor was 400Pa.

The carbon source described in step 3) can specifically be methane, ethylene, etc., and its flow rate is 1-5 sccm, preferably 4-5 sccm; the hydrogen flow rate is 0.4-0.8 sccm, specifically 0.8 sccm; the protective gas can be an inert gas (such as argon etc.), its flow rate is 90-110 sccm, specifically can be 100 sccm.

The reactor described in the present invention can specifically be a high-temperature tube furnace.

The invention combines the catalytic effect of the copper foil with the base advantage of the insulating substrate, and grows a large-area single-layer graphene on the insulating substrate through a chemical vapor deposition method.

The present invention has following beneficial effects:

1) The method of the present invention can really realize the rapid growth of a single layer of graphene in a large area on an insulating substrate, instead of growing into nanoscale granular graphene like the reported method;

2) The single-layer graphene grown by the method of the present invention can be made into a large-scale circuit device by exposure without a cumbersome transfer process;

3) The whole process of the method of the present invention is simple to operate, low in cost, highly repeatable in sample preparation, and less affected by external interference.

4) The copper foil as a catalyst can be used repeatedly hundreds of times, which reduces the production cost.

Description of drawings

Fig. 1 is a schematic diagram of the experimental principle of the graphene growth method provided by the present invention, wherein, (a) a low-pressure growth stage, (b) a high-pressure growth stage.

Fig. 2 is the atomic force microscope appearance of the graphene grown on (0001) plane sapphire utilizing the method of the present invention; Wherein, (a) methane flow rate is 1 sccm, (b) methane flow rate is 3 sccm, (c) methane flow rate is 4 sccm .

Figure 3 is the atomic force microscope Tapping mode characterization (a, b), Raman spectrum characterization (c) and X-ray photoelectron spectrum characterization (d) of graphene grown on the (0001) plane sapphire substrate in the case of a methane flow rate of 5 sccm .

Figure 4 is an electrical test of a 1 μm × 2 μm graphene ribbon grown on a sapphire substrate.

Detailed ways

The method of the present invention will be described below through specific examples, but the present invention is not limited to the growth of graphene on a sapphire insulating substrate.

The experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial sources.

Embodiment 1, grow large-scale monolayer graphene on (0001) plane sapphire substrate

1) Ultrasonic cleaning of sapphire (Kyocera, Japan) and copper foil (Alfa Aesar, UK) with acetone to remove organic residues, and then ultrasonically clean them with deionized water to remove impurities such as metal ions, and then quickly dry them with a nitrogen gun sample.

2) Cover the (0001) surface sapphire on the copper foil, and make the two closely contact. The entire sample is then pushed into the center of a horizontal quartz tube furnace.

3) Clean the quartz tube of the whole tube furnace three times with argon gas so as to remove the residual impurity gas in the quartz tube.

4) Before the temperature rise starts, 100 sccm of argon gas and 20 sccm of hydrogen gas are introduced, and the pressure is stabilized at 400 Pa by controlling the valve of the mechanical pump. Then the tube furnace was raised to 1020° C. within 50 minutes, and kept at this growth temperature for 10 minutes to ensure the stability of the temperature distribution in the temperature zone of the quartz tube.

5) Before the growth starts, open the valve of the mechanical pump so that the pressure in the tube furnace drops to 100 Pa, then feed 1-5 sccm of methane, and adjust the flow of hydrogen from 20 sccm to 0.8 sccm. In this first low-pressure growth stage, the time is maintained for 30 minutes.

6) After the above process is completed, close the valve of the mechanical pump to make the pressure rise to about 400Pa. This is the second high-pressure growth stage, and the time is maintained for 60 minutes. Keep the flow of methane, argon and hydrogen in this step with step 5).

7) After the growth process is over, turn off the power supply of the tube furnace, adjust the hydrogen flow back to 20 sccm, and keep other conditions in 6) unchanged. After naturally cooling to room temperature, the sample was taken out to obtain a large-area single-layer graphene deposited on the (0001) plane sapphire. The thickness value of the graphene obtained by the atomic force microscope is 0.456 nm, which shows that it is a single-layer graphene.

Figure 2 by changing the flow of methane (from 1 sccm to 4 sccm) while keeping other growth parameters unchanged. When the flow rate of methane was 1 sccm, very low-density small graphene islands appeared on the surface of sapphire. As the flux of methane increased, both the density of the graphene islands and their size increased. The height of these circular graphene islands is about 0.45 nm.

In Fig. 3, the flow rate of methane is set at 5 sccm, and the growth temperature is set at 1020 degrees, and graphene is grown under this specific condition. Figure 3(a) is the topography diagram of the tapping mode of the atomic force microscope, and (b) is the phase diagram of the tapping mode of the atomic force microscope. From the phase diagram, it can be seen that the sapphire surface is covered with about 92% graphene, and the size of each island is close to one micron. (c) is the Raman spectrum curve of graphene. Three characteristic peaks of graphene can be clearly seen from the Raman spectrum, the D peak at 1355cm ^-1 , the G peak at 1612cm ^-1 and the 2D peak at 2692cm ^-1 . (d) is the X-ray photoelectron spectrum of graphene, the three peaks centered at 284.8eV, 285.8eV and 289.2eV respectively correspond to the three chemical bonds of CC sp ² , CH and COOH.

Figure 4 is the electrical measurement data of graphene. As the temperature decreases, the resistivity continues to increase, but it can always maintain a limited resistance value at low temperatures. We also studied the IV characteristics of graphene at different temperatures, the linearity of the IV curves was maintained down to the lowest temperature, good ohmic characteristics and limited resistance at low temperatures indicated fewer defects and higher quality in the grown graphene .

Claims (5)

1. a method for preparing large-area graphene on an insulating substrate, adopts chemical vapor deposition to prepare, comprising the steps of: 1) cleaning the insulating substrate and the copper foil, making the cleaned insulating substrate contact with the copper foil surface to obtain a sample; 2) Continuously feed the mixed gas of protective gas and hydrogen into the reactor, place the sample in the reactor at the same time, heat up to 1005-1030° C., and keep it warm for 10-30 minutes; 3) maintain the temperature of the reactor, and adjust the pressure in the reactor to be 100-120Pa, then feed carbon source, protective gas and hydrogen into the reactor simultaneously, grow graphene 20 under this condition -40 minutes; 4) maintain the temperature of the reactor, keep the flow of carbon source, protective gas and hydrogen described in step 3) constant, adjust the pressure in the reactor to 400-500Pa, grow graphene 50 under this condition -70 minutes; 5) After the growth is finished, reduce the temperature of the reactor to room temperature, take out the sample, and obtain large-area graphene deposited on the insulating substrate. 2. The method according to claim 1, characterized in that: the insulating substrate in step 1) is made of any one of the following materials: sapphire and quartz; the thickness of the copper foil is 0.02 μm -0.04 μm. 3. The method according to claim 1 or 2, characterized in that: the shielding gas described in step 2) is an inert gas, and its flow rate is 90-110 sccm; the hydrogen flow rate is 15-20 sccm; During the heating and heat preservation process, the pressure in the reactor was 400Pa. 4. The method according to any one of claims 1-3, characterized in that: the carbon source described in step 3) is methane or ethylene, and its flow rate is 1 to 5 sccm, preferably 4 to 5 sccm; the hydrogen flow rate is 0.4 -0.8 sccm; the protective gas is an inert gas, and its flow rate is 90-110 sccm. 5. The method according to any one of claims 1-4, characterized in that: the graphene is single-layer graphene.

Images