Method for synthesizing porous graphene on surface of semiconductor substrate and porous graphene based on surface of semiconductor substrate

Abstract

The invention provides a method for synthesizing porous graphene on the surface of a semiconductor substrate and porous graphene based on the surface of the semiconductor substrate, and the method comprises the following steps: S1, preparing a few-layer FeO material on a clean Au (111) substrate to obtain a few-layer FeO substrate; s2, precursor molecules are deposited on the few-layer FeO substrate, and the precursor molecules are 1, 3, 5-tri (4-iodophenyl) benzene; s3, heating the precursor molecules to enable the precursor molecules to be subjected to Ullmann coupling reaction, and performing epitaxial growth and deposition along the surface of the substrate to obtain single-layer two-dimensional porous graphene; and S4, annealing treatment is carried out, and FeIX is removed. According to the technical scheme, the single-layer porous graphene is obtained, a semiconductor / organic matter heterostructure is constructed, the method is simple, and the graphene is expected to be applied to sensing chips such as gas sensing chips, biomolecular detection chips and photoelectric detectors.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular, to a method for synthesizing porous graphene on the surface of a semiconductor substrate and porous graphene based on the surface of a semiconductor substrate. Background Art

[0002] Graphene materials have high carrier mobility and zero bandgap characteristics. For device applications, it is usually desired to have a relatively wide bandgap while having high carrier mobility, so that high-sensitivity sensing characteristics can be obtained while having a high on-off ratio. Considering this, it is necessary to prepare a graphene-like material to meet the requirements, and two-dimensional porous graphene is expected to solve this problem. First, two-dimensional porous graphene is structurally similar to graphene materials, but nanopores are introduced into the structure by the selection and design of precursor molecules. The role of nanopores has been shown to open the bandgap of two-dimensional materials in past studies. And the bandgap of the material can be changed by changing the size of the nanopores. Second, it has been found that the presence of nanopores can adsorb gas molecules, which lays the foundation for the preparation of gas molecule sensors. However, it is difficult to prepare two-dimensional porous graphene on non-metal substrates such as semiconductors. Most past studies have been limited to synthesis on metal substrates, which brings a problem: it is necessary to transfer from the metal substrate to the semiconductor substrate to fabricate devices. And the transfer process often brings impurity contamination and affects the performance of the devices.

[0003] In addition, metal-organic coordination allows organic two-dimensional materials to adsorb well on the surface. Most importantly, these metal substrates can serve as ideal surface-assisted catalysts to promote Ullmann coupling at high temperatures. This reaction involves the dehalogenation of various halogenated aromatic compounds and subsequent polymerization to form stable C-C bonds and construct a porous organic framework. And in past studies, a method of auxiliary synthesis by loading metal catalysts on non-metal substrates has also been proposed. This method involves a two-step deposition process of molecules and metals, which increases the process complexity. Secondly, the metal coverage is an important factor affecting the synthesis of covalent structures, which requires a certain amount of time to explore. Summary of the Invention

[0004] In view of the above technical problems, the present invention discloses a method for synthesizing porous graphene on the surface of a semiconductor substrate and porous graphene based on the surface of a semiconductor substrate.

[0005] For this, the technical solution adopted by the present invention is as follows: A method for synthesizing porous graphene on the surface of a semiconductor substrate, comprising the following steps: Step S1, preparing a few-layer FeO material on a clean Au(111) substrate to obtain a few-layer FeO substrate; wherein the few-layer has a thickness not greater than 5 layers, and further preferably 3-4 layers.

[0006] Step S2, deposit precursor molecules on the few-layer FeO substrate, where the precursor molecules are 1,3,5-tris(4-iodophenyl)benzene; Step S3, heat the precursor molecules to cause Ullmann coupling reaction, and grow epitaxially along the substrate surface to deposit, obtaining monolayer two-dimensional porous graphene; Step S4, perform annealing treatment to remove FeI X 。

[0007] With this technical solution, the steps are few and the method is simple; this reaction synthesis work can be directly completed on a semiconductor substrate without additional deposition of metal assistance, and devices can be directly fabricated on the prepared samples without transfer, which will facilitate the subsequent device fabrication process. In addition, there is a high-density delocalized free electron gas on the surface of the metal substrate, which will cause the sample to be preferentially affected by the external electric field during the characterization of the electronic state of the sample, that is, the metal shields the electronic state. This strong organic-metal coupling can lead to the reconstruction of the electronic energy band of the sample and cause the metallization of porous graphene, affecting the conductivity, band gap and even optical response of the porous graphene sample. However, as a semiconductor FeO substrate, this problem does not exist, and as a semiconductor substrate, the band gap of FeO is about 0.5 eV. For the porous graphene sample prepared by the technical solution of the present invention, its unoccupied state is lower than the Fermi level of FeO. At this time, due to the interfacial interaction between the two, electrons will flow from the FeO substrate to the porous graphene sample, which can be regarded as n-type doping of the sample. Moreover, for the porous graphene sample prepared by the technical solution of the present invention, the occupied state is higher than the Fermi level of FeO. At this time, electrons will flow from the porous graphene sample to the substrate, which is equivalent to P-type doping of the porous graphene sample. In addition, since both the substrate and the sample are semiconductor properties, the prepared sample can be regarded as a heterojunction, which will bring completely different optoelectronic properties. In addition, the synthesis method of the technical solution of the present invention has guiding significance for the synthesis of semiconductor substrates, and different substrate types can be changed to obtain different heterostructures.

[0008] As a further improvement of the present invention, in step S1, the few-layer FeO material is synthesized on the Au(111) surface by the principle of thermal oxidation of Fe in a carbon monoxide gas atmosphere.

[0009] As a further improvement of the present invention, for the synthesis of FeO, first deposit Fe on the Au(111) surface by thermal evaporation method and then perform thermal oxidation in a carbon monoxide gas atmosphere.

[0010] As a further improvement, during the thermal evaporation, the temperature of the Au(111) substrate is 100~150 °C and the deposition time is 5~30 mins.

[0011] As a further improvement, when depositing Fe, the environmental vacuum degree is not greater than 1×10-8 mbar.

[0012] As a further improvement of the present invention, after depositing the few-layer FeO substrate in step S1, an annealing treatment is further included, the annealing temperature is 100 - 150 °C, and the time is 10 - 30 mins.

[0013] As a further improvement of the present invention, in step S2, precursor molecules are deposited by molecular beam epitaxy; when heating the molecular source to deposit molecules, the temperature of the few-layer FeO substrate is 100 - 150 °C, and the heating time is 5 - 10 mins.

[0014] As a further improvement of the present invention, in step S3, the temperature of the substrate during deposition is 180 - 320 °C, and the treatment time is 5 - 120 mins.

[0015] As a further improvement of the present invention, in step S2, an annealing treatment is further included, the annealing temperature is 100 - 150 °C, and the annealing time is 5 - 10 mins. Among them, the annealing treatment is an in-situ vacuum annealing treatment.

[0016] As a further improvement of the present invention, in step S3, an annealing treatment is further included after deposition. When performing the annealing treatment, the temperature of the substrate is 180 - 320 °C, and the duration is 5 - 120 mins. Among them, the annealing treatment is an in-situ vacuum annealing treatment.

[0017] Whether the precursor molecules can form a large-area porous graphene structure is mainly related to the annealing temperature, the crystal phase of the substrate, and the number of surface defects.

[0018] As a further improvement of the present invention, in step S4, when annealing, the temperature of the substrate is 350 - 400 °C, and the duration is 5 - 120 mins.

[0019] The present invention also discloses porous graphene based on the surface of a semiconductor substrate, which is prepared by using the method for synthesizing porous graphene on the surface of a semiconductor substrate described in any one of the above.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The technical solution of the present invention selects TIB as the precursor molecule, deposits it on the surface of the FeO substrate, and through heating, promotes the coupling reaction of the precursor molecules to grow epitaxially along the surface of the substrate, and finally obtains monolayer porous graphene, constructing a semiconductor / organic heterogeneous structure. The method is simple and is expected to be applied to sensing chips such as gas sensing, biomolecule detection, and photodetectors. The method of the technical solution of the present invention can be extended to the synthesis of two-dimensional materials on other semiconductor substrates, and can provide guidance for the synthesis on other semiconductor substrates. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the structural change of TIB during the preparation process of the embodiment of the present invention.

[0022] Figure 2 It is a picture of the clean FeO surface without deposited molecules in step S1 of the embodiment of the present invention.

[0023] Figure 3 It is the result of self-assembly with high coverage on the FeO surface after depositing precursor molecules in step S2 of the embodiment of the present invention and undergoing high-temperature heating annealing.

[0024] Figure 4 It is the LT-STM picture of the sample after depositing molecules in step S3 of the embodiment of the present invention; among them, (a) and (b) are pictures of different positions.

[0025] Figure 5 It is the LT-STM picture of the electronic states of different lattice structures of the porous graphene structure in step S4 of the embodiment of the present invention. Detailed implementation manners

[0026] The following further elaborates on the preferred embodiments of the present invention.

[0027] A synthesis method of porous graphene based on the surface of a semiconductor substrate, that is, a method for synthesizing porous graphene from precursor molecules on an FeO semiconductor substrate, includes the following steps: S1. Prepare few-layer FeO material by thermal oxidation on a clean Au(111) substrate.

[0028] S2. Deposit precursor molecules on the few-layer FeO substrate.

[0029] S3. Through heating, the Ullmann coupling reaction occurs for the precursor molecules, and epitaxial growth occurs along the substrate surface, finally obtaining a large-area single-layer two-dimensional porous graphene.

[0030] S4. Anneal the prepared sample to remove FeI X .

[0031] Optionally, in step S1: The condition for depositing the metal is an ultra-high vacuum condition.

[0032] Optionally, in step S1: The vacuum degree of deposition is less than or equal to 1×10 -8 mbar.

[0033] Optionally, in step S1: The temperature of the substrate during deposition is 100~150 °C.

[0034] Optionally, in step S1: The deposition time is 5~30 mins.

[0035] Optionally, in step S2: the substrate temperature is 100 - 150 °C when depositing molecules.

[0036] Optionally, in step S2: the annealing time is 5 - 10 mins.

[0037] Optionally, in step S3: the deposition vacuum degree is less than or equal to 1×10 -8 mbar.

[0038] Optionally, in step S3: the substrate temperature is 100 - 150 °C when depositing molecules.

[0039] Optionally, in step S3: the substrate temperature is 180 - 320 °C during annealing.

[0040] Optionally, in step S3: the deposition time is 5 - 120 mins.

[0041] Optionally, in step S4: the substrate temperature is 350 - 400 °C during annealing.

[0042] Optionally, in step S4: the annealing time is 5 - 120 mins.

[0043] Traditionally, graphene materials have high carrier mobility and zero bandgap characteristics. For device applications, we usually hope to have a relatively wide bandgap while maintaining high carrier mobility, so as to obtain high-sensitivity sensing characteristics and a high on-off ratio at the same time. Considering this, a graphene-like material is prepared as needed to meet the requirements, and two-dimensional porous graphene is expected to solve this problem.

[0044] First, two-dimensional porous graphene is structurally similar to graphene materials. By selecting and designing precursor molecules, nanopores are introduced into the structure. The role of nanopores in past studies has been to open the bandgap of two-dimensional materials. And the bandgap of the material can be changed by altering the nanopore size.

[0045] Secondly, it is found in experiments that the presence of nanopores can adsorb gas molecules, which lays a foundation for the preparation of gas molecule sensors. However, it is difficult to prepare two-dimensional porous graphene on non-metal substrates such as semiconductors. Most past studies have been limited to synthesis on metal substrates, which brings a problem: it is necessary to transfer from the metal substrate to the semiconductor substrate to fabricate devices. And the transfer process often brings impurity contamination and affects the performance of the devices. For example, gold (Au) is often used because of its excellent supporting performance, high chemical inertness and ordered atomic arrangement, which can promote efficient molecular organization.

[0046] In addition, metal-organic coordination allows organic two-dimensional materials to adsorb well on the surface. Most importantly, these metal substrates can serve as ideal surface-assisted catalysts to promote Ullmann coupling at high temperatures. This reaction involves the dehalogenation of various halogenated aromatic compounds and subsequent polymerization, thereby forming stable C-C bonds and constructing porous organic frameworks. In previous studies, a method of assisting synthesis by loading metal catalysts on non-metal substrates was also proposed. This method involves a two-step deposition process of molecules and metals, which increases the process complexity. Secondly, the metal coverage is an important factor affecting the synthesis of covalent structures, which requires some time to explore. Therefore, we need a process with fewer steps and a simple method to synthesize. Thus, through the preparation method of the present invention, this reaction synthesis work can be directly completed on a semiconductor substrate without additional deposition of metal assistance. Finally, we can directly fabricate devices on the prepared samples without transfer. This will facilitate the subsequent process of fabricating devices. In addition, there is a high-density delocalized free electron gas on the surface of the metal substrate, which will cause us to prioritize the sample under the action of an external electric field when characterizing the electronic state of the sample, that is, the metal shields the electronic state. This strong organic-metal coupling can lead to the reconstruction of the electronic energy band of the sample and cause the metallization of porous graphene, affecting the conductivity, band gap, and even optical response of the porous graphene sample. However, the FeO substrate as a semiconductor does not have this problem. And as a semiconductor substrate, the band gap of FeO is about 0.5 eV. If the unoccupied state of the prepared porous graphene sample is lower than the Fermi level of FeO, at this time, due to the interfacial interaction between the two, electrons will flow from the FeO substrate to the porous graphene sample, which can be regarded as n-type doping of the sample. If the occupied state of the prepared porous graphene sample is higher than the Fermi level of FeO, at this time, electrons will flow from the porous graphene sample to the substrate, which is equivalent to P-type doping of the porous graphene sample. In addition, since both the substrate and the sample are semiconductor properties, the prepared sample can be regarded as a heterojunction, which will bring completely different optoelectronic properties. Finally, the synthesis method of the technical solution of the present invention has a guiding effect on the synthesis of semiconductor substrates, can change the type of substrate, and obtain different heterostructures. Moreover, while ensuring a certain chemical activity on the surface of the FeO substrate, it will not form a strong coupling with the organic structure on the surface, which can provide guidance for the synthesis on other semiconductor substrates.

[0047] The following is an illustration with specific examples.

[0048] A method for synthesizing a covalent organic framework from a precursor molecule on an FeO substrate, comprising the following steps: S1. Prepare few-layer FeO material on a clean Au(111) substrate by thermal oxidation to obtain a few-layer FeO substrate. Specifically, first deposit Fe on the Au(111) surface by thermal evaporation. During thermal evaporation, the temperature of the Au(111) substrate is 100 - 150 °C, the deposition time is 5 - 30 mins, and the environmental vacuum degree is not greater than 1×10 -8 mbar. Then synthesize FeO on the Au(111) surface based on the principle of thermal oxidation of Fe in a carbon monoxide gas atmosphere. Further, after depositing the few-layer FeO substrate, annealing treatment is also included. The annealing temperature is 100 - 150 °C and the time is 10 - 30 mins.

[0049] S2. Deposit precursor molecules on the few-layer FeO substrate again; in this embodiment, 1,3,5-tris(4-iodophenyl)benzene (TIB) is selected as the precursor molecule, and the precursor molecules are deposited by molecular beam epitaxy; when heating the molecular source to deposit molecules, the temperature of the few-layer FeO substrate is 100 - 150 °C and the heating time is 5 - 10 mins. Then in-situ vacuum annealing treatment is carried out. The annealing temperature is 100 - 150 °C and the annealing time is 5 - 10 mins.

[0050] S3. Through heating the precursor molecules, Ullmann coupling reaction occurs, and epitaxial growth is carried out along the substrate surface, and finally a large-area single-layer porous graphene is obtained. In this step, the temperature of the substrate is 180 - 320 °C and the treatment time is 5 - 120 minss. After depositing the single-layer porous graphene, in-situ annealing treatment is also included. During the annealing treatment, the substrate temperature is 180 - 320 °C and the duration is 5 - 120 mins.

[0051] S4. Anneal the prepared sample to remove FeI X . In this step, the temperature of the substrate is 350 - 400 °C and the duration is 5 - 120 mins.

[0052] In steps S3 and S4, at this temperature, the adsorbed precursor molecules can undergo Ullmann dehalogenation polymerization reaction to form covalent bonds.

[0053] The technical solution of the present invention selects TIB as the precursor molecule, deposits it on the surface of the FeO substrate, and promotes the coupling reaction of the precursor molecules by heating, and epitaxial growth is carried out along the substrate surface, and finally single-layer porous graphene is obtained. Finally, annealing is carried out to remove FeI X .

[0054] Further, select the TIB molecular source as the precursor evaporation source. Before the evaporation source deposition, impurity removal treatment can be carried out. By heating, small molecule impurities with low evaporation temperature are slowly evaporated for 1-2 days until a pure precursor molecular evaporation source is obtained. The FeO substrate can be subjected to surface cleaning treatment to make it clean and increase its adsorption capacity through thermal annealing treatment.

[0055] Further, in step S1, by using the above-mentioned FeO, while playing a good supporting role for two-dimensional porous graphene, it can meet the requirement that the substrate for LT-STM testing needs to be conductive, and it will not produce strong coupling with the material to affect the electronic state research of monolayer porous graphene.

[0056] Optionally, in step S1, the FeO is FeO(111). Using the above substrate can ensure its semiconductor properties.

[0057] Optionally, in steps S1 and S2: the substrate temperature during deposition is 100-150 °C. At this temperature, the molecular source can be successfully evaporated.

[0058] Optionally, in steps S1 and S3: the deposition condition is an ultra-high vacuum condition, and the vacuum degree is less than 1×10 -8 mbar. Depositing under vacuum conditions greatly improves the quality of monolayer materials.

[0059] Optionally, in step S1: the deposition time is 5-30 mins; in step S2, the deposition time is 5-10 mins. At this time, monolayer molecules or few-layer molecule coverage can be obtained.

[0060] Select TIB as the precursor molecule, and the structure of TIB Figure 1 is shown. Heat the TIB molecular source to 130 °C for about two days (40-48 h) to remove impurities and purify the precursor molecules, and obtain a stable molecular evaporation rate; anneal the FeO substrate to 500 °C to obtain an atomically flat substrate; deposit the precursor molecules on the FeO substrate by thermal evaporation, the required temperature is 140 °C, the deposition time of the molecules is 5 mins, and the air pressure during deposition is 1×10 -8 mbar; at this time, transfer the sample to the low-temperature high-resolution scanning tunneling microscope (LT-STM) cavity for in-situ imaging characterization, and the self-assembly behavior of the precursor molecules can be observed, proving that the precursor molecules have been successfully evaporated on the FeO surface. The FeO substrate synthesized on the metal substrate is as Figure 2 shown. Heat the TIB molecular source to deposit it on the substrate, and then anneal it to observe the self-assembly. The temperature is 120 °C and the duration is 5 mins. The result is as Figure 3As shown. Then, the substrate is heated to 400 °C to promote the Ullmann coupling reaction. The precursor molecules deiodinate to form carbon-carbon covalent bonds, thereby epitaxially growing a two-dimensional porous graphene film on the FeO substrate surface as the main structure. At this time, the sample is transferred to a low-temperature high-resolution scanning tunneling microscope (LT-STM) chamber for in-situ imaging characterization, and a monolayer of two-dimensional porous graphene on the FeO surface can be observed. The results are as Figure 4 shown. The results show the presence of lattice units with different pore sizes in the two-dimensional porous graphene. After the deposition and treatment in step S4, the sample is transferred to a low-temperature high-resolution scanning tunneling microscope (LT-STM) chamber for in-situ imaging characterization. The results show the electronic states of different lattice structures of the porous graphene on FeO. The results are as Figure 5 shown.

[0061] The specific reasons or mechanisms of the above method may be as follows: (1) Through the principle of thermal evaporation, TIB molecules can be evaporated from the molecular source onto the FeO substrate. Middle- and high-temperature heating and annealing treatment of the substrate is to ensure that the precursor molecules can stably adsorb on the surface in a monolayer two-dimensional structure, so as to facilitate subsequent covalent bonding ( Figure 3 shown); (2) Through high-temperature annealing, the precursor molecules deiodinate and polymerize to form a two-dimensional porous graphene film with a lattice structure of different pore sizes ( Figure 4 shown); (3) The present invention reveals the synthesis mechanism of two-dimensional porous graphene on a semiconductor substrate and constructs a semiconductor / organic heterostructure (as Figure 4 shown); (4) The present invention reveals the electronic states of the two-dimensional porous graphene film synthesized on the FeO substrate (as Figure 5 shown).

[0062] The technical solution of the present invention can be extended to the synthesis of two-dimensional materials on other semiconductor substrates. For example, the synthesis of some other two-dimensional materials on MoS2 and h-BN, including semiconductor substrates with strong surface activity such as TiO2. For those skilled in the art, the present invention can have various changes and modifications.

[0063] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for synthesizing porous graphene on the surface of a semiconductor substrate, characterized in that, It includes the following steps: Step S1: Prepare few-layer FeO material on a clean Au(111) substrate to obtain a few-layer FeO substrate; Step S2: Deposit precursor molecules on the few-layer FeO substrate, and the precursor molecules are 1,3,5-tris(4-iodophenyl)benzene; Step S3: Heat the precursor molecules to cause Ullmann coupling reaction, and grow and deposit epitaxially along the substrate surface to obtain monolayer two-dimensional porous graphene; Step S4, annealing treatment to remove FeI X .

2. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 1, characterized in that, In Step S1, the few-layer FeO material is synthesized by thermally oxidizing Fe in a carbon monoxide gas atmosphere on the Au(111) surface.

3. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 2, wherein: For the synthesis of FeO, Fe is first deposited on the Au(111) surface by thermal evaporation method, and then thermally oxidized in a carbon monoxide gas atmosphere.

4. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 3, characterized in that: During thermal evaporation, the temperature of the Au(111) substrate is 100~150 °C, the deposition time is 5~30 mins, and the environmental vacuum is not more than 1×10 - 8 mbar.

5. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 4, characterized in that: In Step S1, after depositing the few-layer FeO substrate, annealing treatment is also included. The annealing temperature is 100 - 150 °C and the time is 10 - 30 mins.

6. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 1, characterized in that: In Step S2, molecular beam epitaxy method is used to deposit precursor molecules; when heating the molecular source to deposit molecules, the temperature of the few-layer FeO substrate is 100 - 150 °C and the heating time is 5 - 10 mins.

7. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 1, wherein: In Step S3, the temperature of the substrate during deposition is 180 - 320 °C and the treatment time is 5 - 120 mins.

8. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 7, wherein: In Step S2, in-situ vacuum annealing treatment is also included. The annealing temperature is 100 - 150 °C and the annealing time is 5 - 10 mins; In Step S3, annealing treatment is also included after deposition. The temperature of the substrate during the annealing treatment is 180 - 320 °C and the duration is 5 - 120 mins.

9. The method for synthesizing porous graphene on the surface of a semiconductor substrate according to claim 3, wherein: In Step S4, during the annealing, the temperature of the substrate is 350 - 400 °C and the duration is 5 - 120 mins.

10. Porous graphene based on the surface of a semiconductor substrate, characterized in that: It is prepared by using the method for synthesizing porous graphene on the surface of a semiconductor substrate according to any one of claims 1 - 9.

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