A method for preparing graphene using cyclic heating

Abstract

The present application relates to the technical field of semiconductor thin film, and provides a method for preparing graphene by cyclic heating, which comprises cyclic heating a silicon carbide substrate in a vacuum or an environment with a protective atmosphere, wherein each heating process comprises: first heating at a first temperature for a first predetermined time to make silicon atoms on the surface of the silicon carbide substrate sublimate and the remaining carbon atoms migrate and gather on the surface of the silicon carbide; second heating at a second temperature for a second predetermined time to make the carbon atoms that migrate and gather on the surface of the silicon carbide further react to form graphene; and finally making the silicon atoms on the surface of the silicon carbide substrate sublimate sufficiently and the carbon atoms react sufficiently to form graphene, so that large-area and high-quality graphene is obtained.

Description

Technical Field

[0001] This invention relates to the field of semiconductor thin film technology, specifically a method for preparing graphene using cyclic heating. Background Technology

[0002] Graphene, as a two-dimensional material with a single layer of carbon atoms, has many excellent properties, such as the presence of Lach fermions, the quantum Hall effect at room temperature, high carrier mobility and aggregation rate, and long spin relaxation length (up to the micrometer scale at room temperature). Among these, single-layer or multi-layer graphene can be obtained by mechanical exfoliation, chemical exfoliation, and chemical vapor deposition on metal surfaces.

[0003] However, in practical applications, the above methods all involve the process of transferring graphene back to the surface of the desired substrate, and this process can easily damage the unique properties of graphene itself. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of existing graphene preparation methods requiring transfer, and to provide a method for preparing graphene on the surface of silicon carbide using a cyclic heating method.

[0005] To achieve the above objectives, the present invention provides a method for preparing graphene using cyclic heating, comprising the following steps:

[0006] Provide silicon carbide substrates;

[0007] The silicon carbide substrate is heated in a vacuum or protective atmosphere. The heating process is as follows: first, the substrate is heated at a first temperature for a first predetermined time, causing silicon atoms on the surface of the silicon carbide substrate to sublimate, while the remaining carbon atoms migrate and aggregate on the surface of the silicon carbide; then, the substrate is heated at a second temperature for a second predetermined time, causing the carbon atoms that have migrated and aggregated on the surface of the silicon carbide to further react and form graphene.

[0008] The heating process is repeated multiple times to cycle the heating of the silicon carbide substrate, so that the silicon atoms on the surface of the silicon carbide substrate are fully sublimated and the carbon atoms are fully reacted to form graphene.

[0009] As one possible implementation, the step of providing a silicon carbide substrate specifically includes:

[0010] A silicon carbide substrate is provided, and the silicon carbide substrate is pretreated to remove the oxide layer and impurities on the surface of the silicon carbide substrate.

[0011] As one possible implementation method, the pretreatment includes degassing under low-temperature annealing conditions, with the temperature range of low-temperature annealing being 600℃-650℃ and the degassing time range being 6h-10h.

[0012] As one possible implementation, during the heating process, the silicon carbide substrate is placed in the vacuum preparation chamber of a scanning probe microscope.

[0013] In one possible implementation, the first temperature is higher than the sublimation temperature of silicon atoms on the silicon carbide surface and lower than the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene, and the second temperature is the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene.

[0014] In one possible implementation, the second temperature is higher than the first temperature, and both the first temperature and the second temperature are higher than 900°C and lower than 1500°C.

[0015] As one possible implementation, the first temperature range is 900℃-1000℃, and the second temperature range is 1400℃-1500℃.

[0016] As one possible implementation, both the first predetermined time range and the second predetermined time range are 10 min to 15 min.

[0017] As one possible implementation, the heating process is repeated at least four times.

[0018] As one possible implementation method, the vacuum level of the vacuum environment is no higher than 1×10⁻⁶ before the heating process is carried out in a vacuum environment. -10 When the heating process is carried out in a vacuum environment, the vacuum level of the vacuum environment shall not exceed 5 × 10⁻⁶. -8 torr.

[0019] The beneficial effects of this invention are as follows: This invention provides a method for preparing graphene using cyclic heating. A silicon carbide substrate is subjected to multiple cyclic heating cycles in a vacuum or protective atmosphere. Each heating process involves: first, heating at a first temperature for a first predetermined time, causing silicon atoms on the surface of the silicon carbide substrate to sublimate, while the remaining carbon atoms migrate and aggregate on the silicon carbide surface; then heating at a second temperature for a second predetermined time, causing the migrated and aggregated carbon atoms on the silicon carbide surface to further react and form graphene; ultimately, the silicon atoms on the surface of the silicon carbide substrate are fully sublimated, and the carbon atoms are fully reacted to form graphene, thereby obtaining large-area and high-quality graphene. Furthermore, this invention eliminates the need for separate graphene transfer during the graphene preparation process, allowing direct application in semiconductor technology. This avoids the damage to graphene properties caused by transfer. Additionally, the ultrathin epitaxial graphene film grown on the silicon carbide substrate surface can be patterned using standard nano-etching methods, ensuring compatibility with current semiconductor technology. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the steps involved in preparing graphene using cyclic heating, as described in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram illustrating the effect of one embodiment of the method for preparing graphene using cyclic heating according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] See Figure 1 This embodiment provides a technical solution: a method for preparing graphene using cyclic heating, comprising the following steps:

[0024] Step S100: Provide a silicon carbide substrate;

[0025] Step S200: In a vacuum or protective atmosphere environment, the silicon carbide substrate is heated, wherein the heating process is as follows: first, the substrate is heated at a first temperature for a first predetermined time, causing silicon atoms on the surface of the silicon carbide substrate to sublimate, while the remaining carbon atoms migrate and aggregate on the surface of the silicon carbide; then, the substrate is heated at a second temperature for a second predetermined time, causing the carbon atoms that have migrated and aggregated on the surface of the silicon carbide to further react and form graphene.

[0026] Step S300: Repeat the heating process multiple times to cycle-heat the silicon carbide substrate, so that the silicon atoms on the surface of the silicon carbide substrate are fully sublimated and the carbon atoms are fully reacted to form graphene.

[0027] Before preparing graphene on the surface of a silicon carbide substrate, step S100 requires pretreatment of the silicon carbide substrate, namely, removing the oxide layer and impurities on the surface of the silicon carbide substrate to prevent the oxide layer and impurities from affecting the preparation of graphene.

[0028] Therefore, in this embodiment, the specific steps for providing the pretreated silicon carbide substrate include:

[0029] A silicon carbide substrate is provided, and the silicon carbide substrate is pretreated to remove the oxide layer and impurities on the surface of the silicon carbide substrate.

[0030] In some embodiments, the silicon carbide substrate can be degassed by low-temperature annealing in a vacuum environment, thereby removing the oxide layer and impurities on the surface of the silicon carbide substrate, which is beneficial for the subsequent evaporation of silicon atoms to generate high-quality graphene.

[0031] Specifically, the pretreatment process can be carried out in the vacuum preparation chamber of a scanning probe microscope (STM). This involves thermal annealing in the ultra-high vacuum preparation chamber of a STM to degas the silicon carbide substrate for a period of time at a low temperature. The purpose of degassing is firstly to remove surface impurities and make the surface cleaner, and secondly to remove the oxide layer on the silicon carbide surface so that it can be characterized using STM. Because STM requires the sample to be conductive, if there is too much oxide on the surface, electrons cannot penetrate, making characterization impossible using STM.

[0032] The temperature range for low-temperature annealing can be 600℃-650℃, and the degassing time range can be 6h-10h, so as to effectively remove the oxide layer and impurities on the surface of the silicon carbide substrate.

[0033] Moreover, during the low-temperature annealing process, since the sublimation temperature of silicon atoms is relatively low, the silicon atoms on the surface of the silicon carbide substrate will also be partially sublimated, and carbon atoms that can generate graphene will be formed or left on the surface of the silicon carbide substrate. Then, when heated at the first temperature, the carbon atoms can directly migrate and aggregate, preparing for the subsequent generation of graphene.

[0034] In step S200, the heating process can be performed in a vacuum or a protective atmosphere. This embodiment prefers a vacuum environment because it eliminates the need for additional protective gas, saving resources; direct cyclic annealing suffices, simplifying the operation. Furthermore, the ultra-high vacuum environment results in a cleaner graphene surface, further ensuring the quality of the graphene subsequently prepared on the silicon carbide surface. In some embodiments, graphene can also be prepared on the silicon surface of a silicon carbide substrate, resulting in even better quality graphene.

[0035] In addition, after the graphene is prepared, the silicon carbide substrate needs to be transferred to the scanning cavity of the scanning tunneling microscope for scanning characterization. Since the scanning cavity is an ultra-high vacuum and the preparation cavity and the scanning cavity of the scanning tunneling microscope are connected, in this embodiment, after the graphene is prepared in the preparation cavity, it can be directly sent into the scanning cavity for characterization through the vacuum channel, which is more convenient.

[0036] To achieve better results, this embodiment sets the vacuum level of the vacuum environment to no higher than 1×10⁻⁶ before the heating process begins. -10torr, when the heating process is carried out in a vacuum environment, the vacuum level of the vacuum environment shall not exceed 5×10 -8 Torr occurs because when an ultra-high vacuum scanning chamber is connected to a preparation chamber requiring pretreatment, the vacuum level is already poor without heating. This means that after the cyclic heating process, it takes a very long time to reduce the vacuum level, leading to contamination of the graphene on the silicon carbide surface, resulting in numerous impurities. Furthermore, when the graphene is transferred to the scanning chamber for characterization after preparation, it is prone to contamination. However, if the vacuum level is relatively good before heating, only increasing during heating, and then quickly decreasing after heating stops, while ensuring that the vacuum level during heating does not exceed 5 × 10⁻⁶, then the vacuum level is suitable for the process. -8 Torr can prevent contamination by impurities. Therefore, in this embodiment, the vacuum level of the vacuum environment before the heating process in a vacuum environment is set not higher than 1×10⁻⁶. -10 torr is used to achieve this effect.

[0037] In this embodiment, the silicon atoms on the surface of the silicon carbide substrate are first heated at a first temperature for a first predetermined time, causing them to sublimate. The remaining carbon atoms migrate and aggregate on the silicon carbide surface, making the distance between the carbon atoms on the silicon carbide surface short enough to allow for a subsequent chemical reaction to form graphene. Then, the substrate is heated at a second temperature for a second predetermined time, causing the carbon atoms that have migrated and aggregated on the silicon carbide surface to further react and form graphene. That is, the first temperature is higher than the sublimation temperature of the silicon atoms on the silicon carbide surface and lower than the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene, and the second temperature is the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene.

[0038] When the silicon carbide substrate is heated at a first temperature, since the first temperature is higher than the sublimation temperature of silicon atoms on the silicon carbide surface, the silicon atoms on the silicon carbide substrate surface can be further sublimated, leaving carbon atoms on the silicon carbide substrate surface. Furthermore, since the first temperature is lower than the temperature at which the remaining carbon atoms on the silicon carbide surface can generate graphene, the carbon atoms migrate and aggregate on the silicon carbide surface, but the migration and aggregation speed is slow and insufficient to generate graphene. This prepares for the subsequent generation of large-area graphene, avoiding the situation where carbon atoms, before fully reaching the temperature for graphene generation, can only generate blocky graphene, which signifies poor quality. Then, the silicon carbide substrate is directly heated at a second temperature for a second predetermined time, so that, with the support of the preliminary preparation process, the carbon atoms on the silicon carbide substrate surface can directly generate large-area, high-quality graphene at a suitable temperature.

[0039] Meanwhile, this embodiment sets a first predetermined time to allow the remaining carbon atoms on the surface of the silicon carbide substrate sufficient time to migrate and aggregate on the surface, preparing for the subsequent high-temperature generation of large-area graphene. This prevents the silicon atoms on the surface from failing to sublimate effectively in a single heating process due to insufficient heating time, and also prevents the remaining carbon atoms on the surface of the silicon carbide substrate from failing to have sufficient time to migrate and aggregate on the surface. It also prevents the temperature of the silicon carbide substrate surface from becoming too high due to excessive heating time, which would prevent the carbon atoms on the surface of the silicon carbide substrate from generating graphene at a more suitable temperature, and instead cause them to directly graphitize, resulting in only small-area blocky graphene or other low-quality graphene.

[0040] After heating the silicon carbide substrate at the first temperature, this embodiment heats it at the second temperature by directly raising the temperature, so that carbon atoms form graphene at a suitable temperature; and by setting a second predetermined time to heat at the second temperature, the remaining carbon atoms on the surface of the silicon carbide substrate have enough time to react and generate graphene.

[0041] In this embodiment, the second temperature is higher than the first temperature. In some embodiments, the first temperature and the second temperature can be set to be both higher than 900°C and lower than 1500°C.

[0042] In some embodiments, the first temperature range can be set to 900℃-1000℃, and the second temperature range can be set to 1400℃-1500℃; both the first predetermined time range and the second predetermined time range are 10min-15min.

[0043] Specifically, to ensure complete sublimation of silicon atoms on the surface and prevent issues such as insufficient sublimation due to low temperature or short heating time, which would hinder subsequent graphene growth, and to prevent direct graphitization of the silicon carbide substrate surface due to excessively high temperature or long heating time, resulting in only small-area blocky graphene and poor quality, the first temperature range can be set to 900℃-1000℃ and the first predetermined time range to 10min-15min. This allows silicon atoms on the silicon carbide substrate surface to sublimate, and the carbon atoms have sufficient time to migrate and aggregate on the silicon carbide substrate surface at a slow rate, preventing direct graphene formation and preparing for the subsequent high-temperature generation of large-area graphene.

[0044] To enable the carbon atoms on the silicon carbide substrate surface to react and form large-area, uniform, and defect-free graphene, the second temperature range can be set to 1400℃-1500℃ and the first predetermined time range to 10min-15min. This allows the carbon atoms that have migrated and aggregated on the silicon carbide surface to further react and form large-area graphene. The setting of the second temperature prevents the carbon atoms on the surface from not reacting sufficiently due to the low temperature, resulting in poor graphene quality. It also prevents the carbon atoms from undergoing a rapid chemical reaction due to the high surface temperature, forming blocky graphene or protrusions on the graphene surface, which would also result in poor quality.

[0045] In step S300, in some embodiments, after repeatedly heating the silicon carbide substrate, several layers of carbon atoms on the silicon carbide surface will form corresponding multilayer graphene. However, it should be noted that a single heating process does not necessarily produce a single layer of graphene. In some embodiments, when the first temperature range is set to 900℃-1000℃, the second temperature range is set to 1400℃-1500℃, and both the first and second predetermined time ranges are 10min-15min, the number of cyclic heating cycles can be greater than or equal to 4.

[0046] Specifically, it is possible to form a large area of ​​high-quality graphene on the surface of a silicon carbide substrate in 4-5 cycles. This is because when the number of cycles is less than this, the silicon atoms on the surface of the silicon carbide substrate cannot be completely evaporated, and the carbon atoms cannot react fully, resulting in poor quality. If the number of cycles is more than this, it will take longer. In addition, it can also prevent wrinkles that may occur.

[0047] In some embodiments, when graphene is prepared in a vacuum environment, the pretreatment and heating process of the silicon carbide substrate can be carried out in the vacuum preparation chamber of the scanning probe microscope. That is, firstly, the silicon carbide is degassed at low temperature for a long time in the preparation chamber of the scanning tunneling microscope by thermal annealing, then the heating power is cut off after several cycles of heating in the preparation chamber of the scanning tunneling microscope, and finally the silicon carbide substrate is transferred into the scanning chamber of the scanning tunneling microscope, and the graphene preparation on the silicon carbide surface is directly characterized by the scanning tunneling microscope.

[0048] Specifically, as an example, a silicon carbide substrate is first placed into the ultra-high vacuum preparation chamber of a scanning tunneling microscope (STM). In the preparation chamber, the silicon carbide is degassed at 650°C for 6 hours using a thermal annealing method to remove the surface oxide layer. Then, the temperature is directly increased, and the silicon carbide substrate is heated sequentially at 900°C and 1400°C for 15 minutes each. The heating temperature is then lowered back to 900°C, and then directly increased again for heating, until this cycle is repeated 5 times. The heating power is then disconnected. The sample is then transferred from the ultra-high vacuum preparation chamber of the STM to the vacuum scanning chamber of the STM. The silicon surface can be positioned upwards, and the quality of the graphene on the silicon surface can be directly characterized using the STM. Figure 2 The image shown is a 500nm×500nm scanning tunneling microscope image on a silicon carbide substrate, which means that a large area of ​​high-quality graphene 10 was obtained on the silicon carbide surface. At the same time, it can be seen that there are no obvious defects and impurities on the surface, indicating that the quality is very good.

[0049] As other examples, experiments conducted within the parameter range disclosed in this embodiment can also demonstrate that high-quality graphene can be obtained. For instance, silicon carbide can be degassed at 650°C for 6 hours in the preparation chamber of a scanning tunneling microscope by thermal annealing to remove the surface oxide layer. Then, the temperature is directly increased, and the above sample is heated at 900°C and 1500°C for 10 minutes each. After that, the heating temperature is directly reduced to 900°C again, and the cycle is repeated until the cycle is completed 4 times. The heating power is then disconnected. The silicon carbide substrate with graphene formed on its surface is then sent into the scanning chamber of the scanning tunneling microscope with the silicon side facing up, and the quality of the graphene on the silicon side is directly characterized using the scanning tunneling microscope.

[0050] This embodiment obtains large-area, high-quality graphene by directly thermally decomposing it on the surface of a silicon carbide substrate. The obtained graphene does not require transfer and can be directly applied to semiconductor technology, avoiding the damage to graphene performance caused by transfer. Furthermore, the ultrathin epitaxial graphene film grown on the surface of the silicon carbide substrate can be patterned using standard nano-etching methods, making it compatible with current semiconductor technology.

[0051] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing graphene using cyclic heating, characterized in that, Includes the following steps: Provide silicon carbide substrates; The silicon carbide substrate is heated in a vacuum or protective atmosphere. The heating process is as follows: first, the substrate is heated at a first temperature for a first predetermined time, causing silicon atoms on the surface of the silicon carbide substrate to sublimate, while the remaining carbon atoms migrate and aggregate on the surface of the silicon carbide; then, the substrate is heated at a second temperature for a second predetermined time, causing the carbon atoms that have migrated and aggregated on the surface of the silicon carbide to further react and form graphene. The heating process is repeated multiple times to cycle the heating of the silicon carbide substrate, so that the silicon atoms on the surface of the silicon carbide substrate are fully sublimated and the carbon atoms are fully reacted to form graphene. The first temperature range is 900℃-1000℃, and the second temperature range is 1400℃-1500℃; The first and second predetermined time ranges are both 10 min to 15 min.

2. The method for preparing graphene using cyclic heating according to claim 1, characterized in that, The steps for providing a silicon carbide substrate specifically include: A silicon carbide substrate is provided, and the silicon carbide substrate is pretreated to remove the oxide layer and impurities on the surface of the silicon carbide substrate.

3. The method for preparing graphene using cyclic heating according to claim 2, characterized in that, The pretreatment includes degassing under low-temperature annealing conditions, with the temperature range of 600℃-650℃ and the degassing time range of 6h-10h.

4. The method for preparing graphene using cyclic heating according to claim 1, characterized in that, During the heating process, the silicon carbide substrate is placed in the vacuum preparation chamber of a scanning probe microscope.

5. The method for preparing graphene using cyclic heating according to claim 1, characterized in that, The first temperature is higher than the sublimation temperature of silicon atoms on the silicon carbide surface and lower than the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene, and the second temperature is the temperature at which the remaining carbon atoms on the silicon carbide surface form graphene.

6. The method for preparing graphene using cyclic heating according to claim 1, characterized in that, The heating process is repeated at least four times.

7. The method for preparing graphene using cyclic heating according to claim 1, characterized in that, Before the heating process is carried out in a vacuum environment, the vacuum level of the vacuum environment shall not exceed 1×10⁻⁶. -10 When the heating process is carried out in a vacuum environment, the vacuum level of the vacuum environment shall not exceed 5 × 10⁻⁶. -8 torr.

Images