Method for preparing nanotube array, nanotube array and device

Abstract

The present invention provides a method for preparing a nanotube array, a nanotube array and a device. The method includes: preparing a bilayer two-dimensional material with a relative angle between lattice orientations on a substrate, and using the bilayer two-dimensional material as a template; determining the chiral parameters of the nanotubes to be prepared corresponding to the relative angle between the lattice orientations of the bilayer two-dimensional material, determining the nanotape orientation and nanotape width based on the determined chiral parameters, determining the spacing between nanotapes based on the density of the nanotubes to be prepared and the nanotape width, and etching the bilayer two-dimensional material based on the determined nanotape orientation, nanotape width and spacing between nanotapes to obtain a nanotape array of the bilayer two-dimensional material; and performing a thermal excitation treatment on the obtained nanotape array of the bilayer two-dimensional material to obtain a nanotube array. The present invention can prepare a nanotube array with controllable density, orientation and chirality.

Description

Technical Field

[0001] The present invention relates to the technical fields of nanomaterial preparation and semiconductor technology, and in particular to a method for preparing a nanotube array, a nanotube array, and a device. Background Art

[0002] Single-walled carbon nanotubes (hereinafter referred to as carbon nanotubes) can be regarded as quasi-one-dimensional structures formed by curling graphene. Depending on the curling method (chirality), single-walled carbon nanotubes can exhibit metallic or semiconducting properties. An all-semiconducting, high-density (more than 125 per micrometer) parallel-aligned semiconducting single-walled carbon nanotube array is the core material for constructing high-performance carbon-based transistors and integrated circuits.

[0003] Currently, the preparation methods of single-walled carbon nanotubes are mainly divided into two categories: The first category is the catalyst-assisted chemical vapor deposition method (for example, see the following references: Reference 1: Zhang S et al., Nature, 2017, 543: 234-238; Reference 2: Wang J et al., Nature Catalysis, 2018, 1: 326-331.). This method can directly grow an all-semiconducting, even single-chirality single-walled carbon nanotube array. However, the disadvantages of this method are high synthesis temperature, incompatibility with integrated circuit processes, and low array density. The second category is the solution separation + assembly arrangement method. A typical scheme is to use polymers to disperse to obtain a single-walled carbon nanotube solution, and combine density gradient centrifugation and other methods to achieve the separation of metallic-semiconducting single-walled carbon nanotubes, and then self-assemble to form a carbon nanotube array wafer (for example, see the following references: Reference 3: Liu L et al., Science, 2020, 368: 850-856; Reference 4: Jinkins KR et al., Science advances, 2021, 7(37): eabh0640.). This type of method can meet the performance index requirements of advanced technology nodes in terms of the purity and density of semiconductor carbon nanotubes, etc., but it will introduce polymer residues that are difficult to control, and there will also be non-uniformities such as local agglomeration and stacking in the arrangement of carbon nanotubes. At the same time, this type of method still lacks effective control over the chirality of carbon nanotubes, that is, the chirality of carbon nanotubes is randomly distributed.

[0004] Generally speaking, there are still many problems and challenges in the current carbon nanotube array preparation technology. It is difficult to simultaneously ensure the carbon nanotube array density, orientation, chirality control, and cleanliness, so that the high orientation, high density, all-semiconducting property, and high cleanliness requirements when the carbon nanotube array is used to construct high-performance carbon-based transistors and integrated circuits cannot be met at the same time, thus affecting the realization of high-performance carbon-based transistors and integrated circuits. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a method for preparing a nanotube array, a nanotube array and a device to eliminate or improve one or more defects existing in the prior art.

[0006] In one aspect of the present invention, a method for preparing a nanotube array is provided, the method comprising the following steps:

[0007] A template preparation step of preparing a bilayer two-dimensional material with a relative angle in the lattice orientation on a substrate, and the bilayer two-dimensional material serves as a template;

[0008] A nanoribbon array etching step of determining the chiral parameters of the nanotubes to be prepared corresponding to the relative angle of the lattice orientation of the bilayer two-dimensional material, determining the nanoribbon orientation and nanoribbon width based on the determined chiral parameters, determining the spacing between nanoribbons based on the density of the nanotubes to be prepared and the nanoribbon width, and etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons to obtain a nanoribbon array of the bilayer two-dimensional material;

[0009] A nanotube array generation step of performing a thermal excitation treatment on the obtained nanoribbon array of the bilayer two-dimensional material to obtain a nanotube array.

[0010] In some embodiments of the present invention, the preparing a bilayer two-dimensional material with a relative angle in the lattice orientation on the substrate includes: preparing a bilayer two-dimensional material with a relative angle in the lattice orientation on the substrate by using mechanical exfoliation combined with a controllable angle transfer method or by using liquid-phase transfer combined with a controllable angle transfer method; or obtaining a single-layer two-dimensional material by mechanical exfoliation or liquid-phase transfer, folding the obtained single-layer two-dimensional material according to a set orientation to obtain a bilayer two-dimensional material with a relative angle in the lattice orientation; or directly growing a bilayer two-dimensional material with a relative angle in the lattice orientation by a growth method, and the growth method includes one of the following: chemical vapor deposition, molecular beam epitaxy or physical vapor deposition method.

[0011] In some embodiments of the present invention, the etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons includes: etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons by using the following etching techniques: laser lithography, electron beam lithography, focused ion beam, high-energy electron beam, mask method or chemical etching.

[0012] In some embodiments of the present invention, the thermal excitation treatment includes one or more of the following treatments: annealing, laser excitation, Joule heating and high-energy ray irradiation.

[0013] In some embodiments of the present invention, at least one two-dimensional material in the bilayer two-dimensional material is a p-type doped or n-type doped two-dimensional material.

[0014] In some embodiments of the present invention, at least one two-dimensional material in the double-layer two-dimensional material is a two-dimensional material with grain boundaries; the lattice orientations of different regions of the same double-layer two-dimensional material prepared in the template preparation step have different relative angles, and / or different sections in the length direction of the nanobelts of the same double-layer two-dimensional material in the nanobelt array etching step correspond to different nanobelt widths; the nanotube array obtained in the nanotube array generation step is an array of nanotubes with different chiral splices.

[0015] In some embodiments of the present invention, the nanobelt array etching step further includes: determining the length of the nanobelt based on the length of the nanotube to be prepared; the etching of the double-layer two-dimensional material based on the determined nanobelt orientation, nanobelt width, and spacing between nanobelts includes: etching the double-layer two-dimensional material based on the determined nanobelt orientation, nanobelt width, spacing between nanobelts, and length of the nanobelt.

[0016] In some embodiments of the present invention, the double-layer two-dimensional material is double-layer graphene, and the obtained nanotube array is a carbon nanotube array.

[0017] In some embodiments of the present invention, the double-layer two-dimensional material is a double-layer boron nitride two-dimensional material, a double-layer molybdenum disulfide two-dimensional material, a double-layer molybdenum selenide two-dimensional material, or a double-layer tungsten disulfide two-dimensional material; the obtained nanotube array is a boron nitride nanotube array, a molybdenum disulfide nanotube array, a molybdenum selenide nanotube array, or a tungsten disulfide nanotube array.

[0018] In some embodiments of the present invention, the nanobelt orientation is obtained based on the following orientation formula:

[0019]

[0020] The nanobelt width is obtained based on the following width formula:

[0021] where ψ0 represents the nanobelt orientation, w represents the nanobelt width, a is the lattice constant of the two-dimensional material, and n and m are the chiral indices of the nanotube; or

[0022] The nanobelt orientation and the nanobelt width are respectively obtained by introducing deviations to the orientation formula and the width formula.

[0023] On the other hand, the present invention also provides a nanotube array prepared by using the foregoing method.

[0024] On the other hand, the present invention also provides a semiconductor device (such as a carbon nanotube transistor) prepared by using the foregoing nanotube array.

[0025] The method for preparing a nanotube array provided by the present invention can prepare a nanotube array with controllable density, orientation, and chirality.

[0026] Furthermore, in some embodiments, a chiral-controllable single-walled carbon nanotube array with high density, high orientation, and all-semiconducting properties can be prepared. Due to the controllable density, the carbon nanotubes are evenly distributed without aggregation and stacking.

[0027] The additional advantages, objectives, and features of the present invention will be partially elaborated in the following description, and will become partially apparent to those of ordinary skill in the art after studying the following text, or can be learned from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the specification and the drawings.

[0028] Those skilled in the art will understand that the objectives and advantages that can be achieved by the present invention are not limited to the above specific descriptions, and the above and other objectives that the present invention can achieve will be more clearly understood according to the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not limit the present invention. In the drawings:

[0030] Figure 1 It is a schematic diagram of the chirality of carbon nanotubes.

[0031] Figures 2A to 2C It is a schematic diagram of the geometric relationship between a bilayer graphene nanoribbon and the chirality of a carbon tube in an embodiment of the present invention.

[0032] Figure 3 It is a schematic flowchart of the method for preparing a nanotube array in an embodiment of the present invention.

[0033] Figure 4 It is a schematic diagram of the preparation process of a carbon nanotube array in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but do not limit the present invention.

[0035] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, and other details less related to the present invention are omitted.

[0036] It should be emphasized that when the term "comprising / including" is used herein, it refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0037] Here, it should also be noted that if not otherwise specified, the term "connection" herein can not only refer to a direct connection, but also represent an indirect connection with an intermediate.

[0038] In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0039] It should be emphasized here that the step marks mentioned hereinafter are not intended to limit the order of the steps. Instead, it should be understood that the steps can be executed in the order mentioned in the embodiments, or different from the order in the embodiments, or several steps can be executed simultaneously.

[0040] Aiming at the problems of the existing carbon nanotube array density, orientation and chirality being difficult to control simultaneously, resulting in uneven array orientation, local agglomeration, uneven stacking and other distribution unevenness or chirality inconsistency, the present invention proposes a new method for preparing a chirality-controllable single-walled carbon nanotube array based on bilayer graphene. The method provided by the present invention is a new top-down means for selecting and controlling the chirality of carbon nanotubes (or simply referred to as carbon tubes), which can realize the adjustment of the single-walled carbon nanotube array density ρ within the following range: 0 < ρ ≤ 350 tubes / μm. At the same time, it can keep the orientation of the single-walled carbon nanotubes in the array highly consistent. In addition, it can also realize the control of the chirality of carbon nanotubes, that is, it can manufacture single-walled carbon nanotubes with specific chirality. Further, a gold-semiconductor junction or a chiral junction with different bandgaps can be introduced as needed to meet the requirements of high-performance carbon nanotube transistors and integrated circuits for channel materials.

[0041] First, the principle of the nanotube array preparation method of the present invention will be described by taking the preparation of single-walled carbon tubes using bilayer graphene as an example, and then the nanotube array preparation method of the present invention will be described in detail.

[0042] As Figure 1 shown, the geometric structure of a single-walled carbon nanotube can be regarded as being curled from a layer of graphene along the chiral vector Ch. Depending on the direction and magnitude of the chiral vector Ch, the curled carbon nanotubes have different chiralities, which can also be represented by Ch. Figure 1 The vectors a1 and a2 indicated by the arrows in [figure] represent the basis vectors of the single-layer graphene lattice. In the present invention, the geometric relationships involved in the present invention are described by taking the two zigzag edges of graphene as the basis vectors, including but not limited to angular relationships and length relationships. The principle derivations with different geometric descriptions but equivalent structures due to different basis vector selection methods are also covered within the protection scope of the present invention.

[0043] The chiral vector Ch of a carbon nanotube can be represented by the basis vectors a1 and a2. When Ch = na1 + ma2, the chirality of the carbon nanotube is (n,m). The electronic structure of a carbon nanotube is related to its chirality index. When n - m is divisible by 3, the carbon nanotube exhibits metallicity; when n - m is not divisible by 3, the carbon nanotube is semiconducting. At the same time, the bandgap of the carbon nanotube is also affected by the magnitude of Ch. The larger Ch is, the smaller the bandgap is. Therefore, controlling the chirality of a carbon nanotube can control its electronic structure. Figure 1 In it, θ represents the angle between the chiral vector and the graphene basis vector, and T represents the radial direction of the carbon nanotube.

[0044] As Figure 2A shown, when a single-layer graphene is folded in half at 1 / 2Ch, a bilayer graphene nanoribbon as shown in Figure 2B can be obtained. At this time, the geometric topology between the bilayer graphene nanoribbon and the single-layer graphene before folding has not changed. If the carbon atoms in the upper and lower layers at both edges of the bilayer graphene nanoribbon are connected and the entire planar bilayer structure is bulged into a cylindrical shape, a carbon nanotube with a chiral vector of Ch is obtained. The inventors found that the edges of the bilayer graphene will form a bulged closed structure under annealing conditions. Based on this phenomenon, the inventors of the present application innovatively used bilayer graphene as a template for preparing a parallel array of carbon nanotubes, and then etched the bilayer graphene into a bilayer graphene nanoribbon array with an orientation and width matching the chiral parameters of the carbon nanotubes, and used thermal excitation treatments such as annealing to convert the bilayer graphene nanoribbon array into a single-walled carbon nanotube array. Therefore, the present invention proposes a method for obtaining a carbon nanotube with a determined target chirality by preparing bilayer graphene nanoribbons with a specific relative angle and a specific width, and then performing a thermal excitation treatment (such as annealing).

[0045] The chirality of a carbon nanotube is determined by the relative angle θ0 between the lattice orientations of the bilayer graphene and the width w of the nanoribbon. Refer to Figures 2A to 2C , for a carbon nanotube with a target chiral vector of C h , with a direction of θ and a magnitude of |C h |, according to geometric relationship derivation, the relationship between the target chirality (n,m) of the carbon nanotube, the width w of the bilayer graphene nanoribbon, and the relative angle θ0 between the lattice orientations of the bilayer graphene (i.e., the angle between the basis vectors of the two layers of graphene) is as follows (Equation Group 1):

[0046] θ0 = 60 - 2*θ;

[0047] w = 0.5*|C h |;

[0048] Among them, the relative included angle θ0 between the lattice orientations of the bilayer graphene determines the direction of the chiral vector Ch of the carbon nanotube (i.e., the included angle θ between the chiral vector and the graphene basis vector), and the width w of the bilayer nanoribbon determines the magnitude |C h |. The relationship between the chiral indices (n, m) and the direction and magnitude of the chiral vector is as follows (Equation Group 2):

[0049]

[0050] where a is the lattice constant of graphene, and d t is the diameter of the target carbon nanotube. Substituting θ and |C h | into Equation Group 1, the relationship between the width w of the bilayer graphene nanoribbon, the relative included angle θ0 between the interlayer lattice orientations, and the chiral indices (n, m) of the target carbon nanotube can be obtained (Equation Group 3):

[0051]

[0052] According to the relationship in the above formula, in the present invention, by designing a bilayer graphene nanoribbon with a specific relative included angle θ0 and a specific width w, and performing heat treatment such as annealing on the bilayer graphene nanoribbon, carbon nanotubes with corresponding chirality can be obtained.

[0053] The method of the present invention is not limited to the preparation of single-walled carbon nanotube arrays. Since the phenomenon of closing after annealing generally exists at the edges of bilayer two-dimensional material nanoribbons, by replacing the bilayer graphene with other two-dimensional material templates, the method designed in the present invention can also be applied to the production and processing of other one-dimensional nanotubes and their arrays. For example, boron nitride nanotube arrays, molybdenum sulfide nanotube arrays, molybdenum selenide nanotube arrays, tungsten sulfide nanotube arrays and other nanotube arrays can be respectively prepared based on bilayer boron nitride two-dimensional materials, molybdenum sulfide two-dimensional materials, molybdenum selenide two-dimensional materials, and tungsten sulfide two-dimensional materials. When calculating the orientation and width of the nanoribbon to be etched, the lattice constant a of graphene in the previous formula needs to be replaced with the lattice constant of the corresponding crystal. These novel one-dimensional nanotube arrays also have the advantages of precise control of array density, orientation, and chirality. The nanotube arrays listed here are only examples, and the present invention is not limited thereto.

[0054] Figure 3 The following shows a schematic flowchart of the method for preparing a nanotube array in an embodiment of the present invention. As Figure 3 shown, the method includes the following steps S110 to S130:

[0055] Template preparation step S110, preparing a bilayer two-dimensional material with a relative included angle in the lattice orientation on a substrate, and this bilayer two-dimensional material serves as a template.

[0056] When the two-dimensional material is graphene, this method corresponds to the preparation of single-walled carbon nanotubes. In the embodiments of the present invention, there are no special requirements for the selection of the substrate. In principle, it can withstand the annealing temperature. However, since the nanotubes prepared by the method of the present invention have a very high cleanliness and can be used for the preparation of high-performance semiconductor devices, from the perspective of facilitating the subsequent direct preparation of semiconductor devices, the substrate can be a surface-insulated substrate, such as a surface-insulated silicon substrate. More specifically, it can be a silicon wafer covered with silicon dioxide, but the present invention is not limited thereto.

[0057] In the nanoribbon array etching step S120, determine the chiral parameters of the nanotubes to be prepared corresponding to the relative angle of the lattice orientations of the bilayer two-dimensional material, determine the nanoribbon orientation and nanoribbon width based on the determined chiral parameters, determine the spacing between nanoribbons based on the density of the nanotubes to be prepared and the nanoribbon width, and etch the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons to obtain a nanoribbon array of the bilayer two-dimensional material.

[0058] In the nanotube array generation step S130, perform a thermal excitation treatment on the obtained nanoribbon array of the bilayer two-dimensional material to obtain a nanotube array.

[0059] Based on the above steps, a nanotube array with determined chirality can be obtained.

[0060] In step S110, a two-layer two-dimensional material with a relative angle of lattice orientation is prepared on the substrate as a template. In the case where this preparation method is used to prepare single-walled carbon nanotubes, the two-layer two-dimensional material used as the template is bilayer graphene.

[0061] For a carbon nanotube array with a specified chirality (n,m), according to the relationship between the relative angle θ0 of bilayer graphene in the formula group 3 and the chiral index (n,m), it is first necessary to prepare bilayer graphene with an interlayer relative rotation angle of θ0. There are many preparation methods for bilayer graphene with an interlayer relative rotation angle of θ0, for example, including: (1) mechanical exfoliation combined with a controllable angle transfer method (mechanical exfoliation + controllable angle transfer method); (2) liquid-phase transfer combined with a controllable angle transfer method (liquid-phase transfer + controllable angle transfer method); or (3) single-layer graphene folding method.

[0062] (1) Mechanical exfoliation + controllable angle transfer method

[0063] The preparation of bilayer graphene by the mechanical exfoliation + controllable angle transfer method means that first, the mechanical exfoliation method is used to obtain two single-layer graphene sheets through two mechanical exfoliations respectively, and then the controllable angle transfer technology is used to transfer the two single-layer graphene sheets obtained by the two mechanical exfoliations to the substrate to obtain bilayer graphene.

[0064] Among them, the mechanical exfoliation method is used to obtain single-layer graphene, that is, by applying mechanical forces (such as frictional force and / or tensile force, etc.) to the graphite crystal, the graphene sheets are separated from the graphite crystal. Since the mechanical exfoliation method to obtain single-layer graphene is an existing mature technology, it will not be elaborated here.

[0065] The process of obtaining bilayer graphene by using the controllable angle transfer technology specifically includes:

[0066] After mechanically exfoliating to obtain two single-layer graphene respectively, they can be maintained on transparent substrates such as PDMS (polydimethylsiloxane), PMMA (polymethyl methacrylate), etc., for subsequent controlling the relative stacking angle of the two single-layer graphene by using an optical rotation console; here, the materials used for the transparent substrate are only examples, and the present invention is not limited thereto.

[0067] In the process of controlling the relative stacking angle of the two single-layer graphene by using the optical rotation console, means such as angle-resolved Raman, crystallographic structure (such as edge angle, etc.) determination or low-energy electron beam diffraction are used to determine and mark the lattice orientations of the two single-layer graphene, and the two single-layer graphene with determined crystallographic orientations are attached together at a specific relative angle by using the controllable angle with the optical rotation console, so as to prepare bilayer graphene with a relative angle of a specific lattice orientation;

[0068] Subsequently, the obtained bilayer graphene with a relative angle of a specific lattice orientation can be transferred to the substrate by using transfer technologies such as dry method or wet method.

[0069] (2) Liquid-phase transfer + controllable angle transfer method

[0070] Preparing bilayer graphene by using the liquid-phase transfer + controllable angle transfer method means using two liquid-phase transfers to obtain two single-layer graphene, and using the controllable angle transfer technology to transfer the two single-layer graphene obtained by the two liquid-phase transfers to the substrate to obtain bilayer graphene.

[0071] Obtaining single-layer graphene by using liquid-phase transfer includes:

[0072] On two substrates with single-layer graphene grown by methods such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), chemical vapor transport method (CVT), etc., liquid-phase transfer is used to obtain two single-layer graphene respectively. Then, the two obtained single-layer graphene are maintained on transparent substrates such as PDMS, PMMA, etc., for subsequent controlling the relative stacking angle by the rotation console.

[0073] In the process of controlling the relative stacking angle of two single-layer graphene sheets using an optical rotation control platform, methods such as angle-resolved Raman spectroscopy, crystallographic structure determination (such as edge angle measurement), or low-energy electron diffraction are used to determine and mark the lattice orientations of the two single-layer graphene sheets. Then, with the optical rotation control platform, the two single-layer graphene sheets with determined crystallographic orientations are brought together at a specific relative angle to form bilayer graphene with a specific relative angle of lattice orientation.

[0074] Subsequently, transfer techniques such as dry or wet transfer can be used to transfer the obtained bilayer graphene with a specific relative angle of lattice orientation onto a substrate.

[0075] (3) Single-layer graphene folding method

[0076] Single-layer graphene can be obtained by mechanical exfoliation or liquid-phase transfer. Then, the obtained single-layer graphene is folded according to a set orientation to obtain a bilayer two-dimensional material with a relative angle of lattice orientation.

[0077] Alternatively, growth methods such as chemical vapor deposition, molecular beam epitaxy, or physical vapor deposition can be used to directly grow bilayer two-dimensional materials with a relative angle of lattice orientation. Using the above methods, graphene can be replaced with other two-dimensional materials, and bilayer two-dimensional materials with a relative angle of lattice orientation can also be prepared on a substrate. Therefore, in a similar manner, bilayer two-dimensional materials such as boron nitride, molybdenum sulfide, molybdenum selenide, and tungsten sulfide can also be obtained on a substrate in step S110, with the relative angle between layers being controllable.

[0078] In addition, in the embodiments of the present invention, for bilayer graphene with an arbitrary interlayer relative rotation angle θ0, such as bilayer graphene obtained by direct growth, the chiral index (n,m) that can be processed to meet the electron structure requirements at an interlayer rotation angle of θ0 can also be deduced based on the required carbon nanotube electron structure, such as semiconductivity.

[0079] In step S120, before etching the nanoribbon array, the chiral parameters of the nanotubes to be prepared, such as the chiral index (n,m), need to be determined first. Then, based on the determined chiral parameters of the nanotubes, the orientation of the nanoribbon array to be etched is determined, that is, the angle ψ0 between the nanoribbon array to be etched and the lattice orientation of the bilayer two-dimensional material. Furthermore, the nanoribbon width and the spacing between nanoribbons are determined.

[0080] Taking the etching of a bilayer graphene nanoribbon array as an example, before etching the bilayer graphene nanoribbon array, the angle ψ0 between the nanoribbon array to be etched and the bilayer graphene lattice needs to be determined first. Due to structural symmetry, the orientation of the nanoribbons should satisfy the angle with the basis vector directions of both layers of graphene being ψ0. Based on Figures 2A - 2CAs for the geometric relationship shown, when the angle between the chiral vector Ch and the graphene base vector a1 is θ, there is:

[0081]

[0082] There are various ways to determine the crystallographic orientation of bilayer graphene, including but not limited to the combination of one or several of the following methods: optical microscopy, scanning electron microscopy, low-energy electron diffraction, electron diffraction, angle-resolved photoemission spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, etc. Based on the determined crystallographic orientation of bilayer graphene, the angle ψ between the orientation of the nanoribbon array to be etched and the bilayer graphene lattice can be determined, that is, the orientation of the bilayer graphene nanoribbon array can be determined.

[0083] After determining the orientation of the bilayer graphene nanoribbon array, the width of a single nanoribbon is determined by w in Equation Group 3, and the spacing Δx between nanoribbons is determined by the required carbon nanotube density ρ (the number of carbon nanotubes per unit length), which can be expressed as:

[0084] Δx = 1 / ρ – w;

[0085] As can be seen from the above formula, the carbon nanotube array density ρ can be controlled by adjusting the gap (the width of the gap between nanoribbons) Δx between bilayer graphene nanoribbons. In addition, when Δx is 0, the carbon nanotube density ρ reaches the maximum value ρ max , the maximum density ρ max is also related to the tube diameter d t of the target chiral carbon nanotube, so it can be expressed as:

[0086] ρ max = 1 / w = 1 / (0.5 * d t * π);

[0087] In the present invention, the control range of the carbon nanotube density in the carbon nanotube array is 0 < ρ < ρ max . In addition, the length L of the graphene nanoribbon determines the length of the carbon nanotube formed after annealing, and the length L of the nanoribbon can be selected according to actual experimental requirements.

[0088] After determining the nanoribbon orientation, nanoribbon width, spacing between nanoribbons, and nanoribbon length, the nanoribbon array can be etched based on these determined parameters. There are various etching methods for the bilayer graphene nanoribbon array, including but not limited to: laser lithography, electron beam lithography, focused ion beam, high-energy electron beam, mask method, chemical etching, etc. One etching method can be selected from them for etching the nanoribbons.

[0089] In a manner similar to the etching of graphene nanoribbon arrays, nanoribbon arrays of two-dimensional materials such as bilayer boron nitride nanoribbon arrays, bilayer molybdenum disulfide nanoribbon arrays, bilayer molybdenum selenide nanoribbon arrays, or bilayer tungsten disulfide nanoribbon arrays can be prepared. These materials are only examples, and the present invention is not limited thereto.

[0090] Similarly, taking the thermal excitation treatment of the bilayer graphene nanoribbon array as an example to describe step S130. There are many methods for the thermal excitation treatment in this step, as long as sufficient external excitation can be provided to cause edge closure reconstruction of the bilayer graphene nanoribbons. As an example, the thermal excitation treatment may include one or more of the following treatments: annealing, laser excitation, Joule heating, and high-energy ray irradiation, but the present invention is not limited thereto.

[0091] Taking annealing as an example, in some embodiments of the present invention, the temperature of the annealing treatment of the bilayer graphene nanoribbon array can be, for example, between 250°C and 1300°C, and the range of the annealing time can be, for example, between 0.1 s and 600 s depending on the heating temperature, or annealing can be carried out at different temperatures in different time periods, but the present invention is not limited thereto. The annealing treatment of the bilayer graphene nanoribbon array can be carried out under vacuum conditions or in an inert gas environment.

[0092] When other thermal excitation treatment methods such as laser excitation, Joule heating, or high-energy ray irradiation are used to replace the annealing of the bilayer graphene nanoribbon array, the heating temperature range of these other thermal excitation treatment methods can also be between 250°C and 1300°C, and the heating time range can be, for example, between 0.1 s and 600 s depending on the heating temperature.

[0093] After the etching is completed, the bilayer graphene nanoribbons have the same orientation ψ, nanoribbon spacing Δx, relative interlayer rotation angle θ0, and nanoribbon width w. The process of generating single-walled carbon nanotubes by thermal excitation only involves the reconstruction and connection of unsaturated carbon atoms on both sides of the bilayer graphene nanoribbons through thermal excitation. Therefore, the carbon nanotubes after thermal excitation have the same orientation ψ as the graphene nanoribbons, and the inter-tube spacing Δx tube Since the planar structure changes to a tubular structure after tube formation, it becomes Δx tube = Δx + w - d t . Since each carbon tube is transformed from bilayer graphene with the same width w and the same relative angle θ0, each single-walled carbon nanotube in the array has the same chirality (n, m). Therefore, after the bilayer graphene nanoribbon array is thermally excited in the present invention, a single-walled carbon nanotube array with the same orientation ψ (high orientation), the same spacing Δx tube (high uniformity), consistent chirality, all (n, m) (chirality controllable), and adjustable density in the range of 0 < ρ < ρ max can be obtained (that is, high density and adjustable spacing can be achieved).

[0094] Meanwhile, since the method of the present invention does not require means such as catalyst growth and polymer centrifugal lifting for growing, selecting, and arranging carbon nanotubes, the impurity level only depends on the cleanliness of graphene and the residues in the conventional semiconductor process flow. Therefore, the fabricated carbon nanotube array has a cleanliness level that can be directly used for the preparation of high-performance devices.

[0095] Similar to the treatment of the bilayer graphene nanoribbon array, for the nanoribbon array of other two-dimensional materials in bilayer obtained in step S120 (such as boron nitride nanoribbon array, molybdenum sulfide nanoribbon array, molybdenum selenide nanoribbon array, or tungsten sulfide nanoribbon array), thermal excitation treatment is also carried out in the temperature range of 250 °C to 1300 °C. Since the tube-forming temperatures of different materials are different, the thermal excitation treatment temperature can be adjusted adaptively, and nanotube arrays can also be obtained, such as boron nitride nanotube array, molybdenum sulfide nanotube array, molybdenum selenide nanotube array, or tungsten sulfide nanotube array.

[0096] As can be seen from the above, the method of the present invention can prepare a carbon nanotube array with high orientation, high density, chiral controllability, adjustable spacing, uniform distribution, and high cleanliness using bilayer graphene as a template. In addition, nanotube arrays of other materials can also be prepared in the same way.

[0097] In some embodiments of the present invention, one or both layers of the bilayer graphene used for preparing single-walled carbon nanotubes can be replaced by p-type doped graphene or n-type doped graphene. When both layers are doped, the two layers of graphene can be of the same or different doping types. If the doping types of the two layers are the same, the carbon nanotubes that can be prepared using this as a template are p-type carbon nanotube arrays or n-type carbon nanotube arrays. If one layer is replaced by p-type doped graphene and the other layer is replaced by n-type doped graphene, the carbon nanotube array prepared using this as a template is a carbon nanotube array with a radial pn junction.

[0098] In some embodiments of the present invention, since the chirality (n, m) of the prepared carbon nanotubes is regulated by the relative angle θ0 between the layers and the width w of the graphene nanoribbons in the bilayer, different relative angles θ0 and / or widths w can be introduced in the same bilayer graphene nanoribbon. In this way, carbon nanotubes formed by splicing different chiralities can be formed, and the different chiral carbon nanotubes are connected by chiral junctions. The change in the interlayer rotation angle θ0 can be generated by introducing grain boundaries. In comparison, the width w of the nanoribbon is easier to regulate and can be regulated by changing the etching template. More specifically, by converting one or both layers of graphene in the bilayer graphene into polycrystalline graphene, the graphene nanoribbons on both sides of the grain boundary can have different included angles θ0. For the realization of different widths w, during the etching process, the width of the nanoribbon to be retained can be controlled so that different sections in the length direction of the same bilayer graphene nanoribbon correspond to different nanoribbon widths w.

[0099] For a two-dimensional material extended to a bilayer, when at least one layer of the two-dimensional material in the bilayer is a two-dimensional material with grain boundaries, the lattice orientations of different regions of the same bilayer two-dimensional material prepared in the template preparation step will have different relative angles; correspondingly, the nanotube array obtained in the nanotube array generation step is an array of nanotubes with different chiral splices.

[0100] Similar treatments are also applicable to two-dimensional materials such as bilayer boron nitride, molybdenum sulfide, molybdenum selenide, tungsten sulfide, etc.

[0101] Figure 4 The schematic process of preparing a single-walled carbon nanotube array on a substrate is shown.

[0102] As Figure 4 shown in (a) of [], bilayer graphene 20 and 30 with a relative angle θ0 in lattice orientation are prepared on a surface-insulated substrate (such as a silicon wafer covered with silicon dioxide) 10. For example, single-layer graphene 20 is exfoliated from the surface of a graphite crystal by mechanical exfoliation method, and the exfoliated single-layer graphene 20 is transferred to the substrate 10 with a predetermined orientation, and then the steps of mechanical exfoliation and transfer are performed again to place the single-layer graphene 30 exfoliated again on the single-layer graphene 20 exfoliated for the first time, forming a stacked bilayer graphene as a template and the relative angle between the lattice orientations of the bilayer graphene is controlled to be θ0 during the transfer operation. In some embodiments of the present invention, θ0 can be any value between 0° and 360°. In an alternative embodiment of the present invention, during the transfer step, the bilayer graphene can also be placed on the substrate 10 at any angle, and the relative crystallographic angle can be determined by means such as scanning electron microscopy and transmission electron microscopy after the bilayer graphene is formed.

[0103] Figure 4 Shown in (b) of [] is the etching of the bilayer graphene obtained in (a) using a mask 40 to obtain a bilayer graphene nanoribbon array. First, the nanoribbon orientation (such as the angle ψ0 between the nanoribbon orientation and the graphene lattice orientation) and the nanoribbon width are determined based on the chiral parameters corresponding to the relative angle θ0, the spacing between the nanoribbons is determined based on the carbon nanotube density to be prepared and the nanoribbon width, and the bilayer graphene is etched based on the determined nanoribbon orientation, nanoribbon width and the spacing between the nanoribbons to obtain a bilayer graphene nanoribbon array 50, as Figure 4 shown in (c) of []. The bilayer graphene nanoribbon array is annealed, the annealing temperature is between 250°C and 1300°C, and the annealing time is between 0.1 s and 600 s, depending on the annealing temperature, to obtain Figure 4 the carbon nanotube array 60 shown in (d) of [].

[0104] In the process of preparing the carbon nanotube array of the present invention, when there are errors in processing graphene nanoribbons, such as width Δw, orientation Δψ error, and relative angle error Δθ0 between layers in the nanoribbons, due to the inability to maintain perfect geometric connection at this time, topological defects such as 5-8 rings and 5-7-7-5 rings will exist in the formed carbon nanotubes. As the error increases, the mismatch density at the edges of the bilayer graphene nanoribbons will increase accordingly, and the defect density in the formed carbon nanotubes will also increase. However, due to the tendency of the edges of bilayer graphene nanoribbons to form closed structures to reduce energy under high-temperature conditions, carbon nanotube structures can always be formed. In the case of extreme deterioration, if w, ψ0, and θ0 are not determined strictly in accordance with the geometric relationships described above, a carbon nanotube array can also be formed, which also has the characteristics of uniformity, high density, high cleanliness, and adjustable spacing, but loses chiral controllability and introduces a large number of topological defects in the carbon nanotubes. However, this method of preparing a carbon nanotube array by the deterioration technology should also be included in the protection scope of the present invention.

[0105] Using the geometric relationships of w, ψ0, and θ0 in the foregoing formula, the present invention can also construct carbon nanotubes with metal-semiconductor junctions and chiral junctions. At this time, the bilayer graphene is at least one bilayer graphene with grain boundaries, and different regions between the bilayer graphene have different relative included angles. In addition, in the step of etching the nanoribbon array, in the step of etching the nanoribbon array, different chiral parameters of the carbon nanotubes to be prepared from the bilayer graphene with different relative included angles are determined, and the nanoribbon orientation and different nanoribbon widths corresponding to different chiral parameters in different sections in the length direction of the nanoribbon can be further determined based on the determined different chiral parameters. The following is an example: Different relative angles θ 0A , θ 0B and width w A and w B are introduced in the same bilayer graphene nanoribbon, where the different relative angles are generated by the grain boundaries during graphene growth, and the different widths can be set by the etching parameters during exposure etching. After annealing such bilayer graphene nanoribbons to form carbon nanotubes, the chiral indices (n 0A , m A ) of the θ A , m A section and the chiral indices (n 0B , m B ) of the θ B , n B section can be obtained from the foregoing formula, and at this time, chiral junction carbon nanotubes with chiral differences are formed. Conversely, the present invention can derive the processing parameters θ A , θ A and w B using the formula based on the pre-designed chiral indices (n B ) and (n 0A , m 0B ).A , w B . Since the chirality index determines the metallicity and semiconductivity of carbon nanotubes, when one side has a metallic carbon nanotube chirality and the other side has a semiconducting carbon nanotube chirality, a carbon nanotube with a metal-semiconductor junction is formed. The number of chiral junctions and metal-semiconductor junctions depends on how many different combinations of processing parameters w, ψ0, and θ0 are introduced in the same bilayer graphene strip.

[0106] The prior art cannot simultaneously meet requirements such as high orientation, high density, all-semiconducting, adjustable spacing, and uniform distribution (referring to uniform carbon nanotube spacing, no agglomeration, and no stacking). On this basis, there is also a lack of effective means for chiral control of carbon nanotubes. In the existing methods for growing carbon nanotube arrays by CVD, the prepared carbon nanotubes have a low and uncontrollable density, a wide and non-uniform chiral distribution (i.e., uncontrollable chirality), and catalyst residues. In the existing liquid-phase lifting method for preparing carbon nanotube arrays, the density is too high and uncontrollable, and only semiconducting chirality (incompletely controllable chirality) can be obtained. The orientation of the nanotubes is complex and there is a stacking phenomenon, and the prepared carbon nanotubes have polymer contamination. In contrast, the carbon nanotubes prepared by the method for preparing carbon nanotubes of the present application have controllable density and chirality. They can be used to prepare both semiconducting carbon nanotubes and metallic carbon nanotubes. In addition, the spacing between carbon nanotubes is uniform and the surface is clean. Therefore, the method of the present invention can provide a single-walled carbon nanotube array that meets the needs of controllable density, orientation, and chirality, and the cleanliness of the prepared single-walled carbon nanotube array meets the requirements of carbon nanotube (CNT) transistors and their integrated circuits for carbon nanotube materials.

[0107] Using the carbon nanotube array with better performance prepared by the above method to construct a carbon nanotube transistor can avoid the loss of device performance caused by carbon nanotube stacking, surface contamination, and diameter distribution, and obtain a carbon nanotube transistor with better performance.

[0108] It should be clear that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, the detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order between steps after understanding the spirit of the present invention.

[0109] In the present invention, the features described and / or illustrated for one embodiment can be used in the same way or in a similar way in one or more other embodiments, and / or combined with the features of other embodiments or replace the features of other embodiments.

[0110] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a nanotube array, characterized in that The method includes the following steps: A template preparation step of preparing a bilayer two-dimensional material with a relative angle between lattice orientations on a substrate, and the bilayer two-dimensional material serves as a template; A nanoribbon array etching step of determining the chiral parameters of the nanotubes to be prepared corresponding to the relative angle between the lattice orientations of the bilayer two-dimensional material, determining the nanoribbon orientation and nanoribbon width based on the determined chiral parameters, determining the spacing between nanoribbons based on the density of the nanotubes to be prepared and the nanoribbon width, and etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons to obtain a nanoribbon array of the bilayer two-dimensional material; A nanotube array generation step of performing a thermal excitation treatment on the obtained nanoribbon array of the bilayer two-dimensional material to obtain a nanotube array.

2. The method according to claim 1, characterized in that, The preparation of the bilayer two-dimensional material with a relative angle between lattice orientations on the substrate includes: Preparing a bilayer two-dimensional material with a relative angle between lattice orientations on the substrate by using mechanical exfoliation combined with a controllable angle transfer method or by using liquid-phase transfer combined with a controllable angle transfer method; or Obtaining a single-layer two-dimensional material by using mechanical exfoliation or liquid-phase transfer, folding the obtained single-layer two-dimensional material according to a set orientation to obtain a bilayer two-dimensional material with a relative angle between lattice orientations; or Directly growing a bilayer two-dimensional material with a relative angle between lattice orientations by using a growth method, and the growth method includes one of the following: chemical vapor deposition, molecular beam epitaxy, or physical vapor deposition method.

3. The method according to claim 1, wherein The etching of the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons includes: Etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons by using the following etching techniques: laser lithography, electron beam lithography, focused ion beam, high-energy electron beam, mask method, or chemical etching.

4. The method according to claim 1, characterized in that, The thermal excitation treatment includes one or more of the following treatments: annealing, laser excitation, Joule heating, and high-energy ray irradiation.

5. The method according to claim 1, wherein At least one two-dimensional material in the bilayer two-dimensional material is a p-type doped or n-type doped two-dimensional material.

6. The method according to claim 1, characterized in that, At least one two-dimensional material in the bilayer two-dimensional material is a two-dimensional material with grain boundaries; The lattice orientations of different regions of the same bilayer two-dimensional material prepared in the template preparation step have different relative angles, and / or different sections in the length direction of the nanoribbons of the same bilayer two-dimensional material in the nanoribbon array etching step correspond to different nanoribbon widths; The nanotube array obtained in the nanotube array generation step is an array of nanotubes with different chiral splices.

7. The method according to claim 1, characterized in that The nanoribbon array etching step further includes: determining the length of the nanoribbons based on the length of the nanotubes to be prepared; The etching of the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons includes: etching the bilayer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, spacing between nanoribbons, and length of the nanoribbons.

8. The method according to any one of claims 1-7, characterized in that, The bilayer two-dimensional material is bilayer graphene, and the obtained nanotube array is a carbon nanotube array.

9. According to the method described in claim 8, wherein, The bilayer two-dimensional material with a relative included angle in the lattice orientation is at least one bilayer graphene with grain boundaries, and different regions between the bilayer graphene have different relative included angles; In the step of etching the nanoribbon array, different chiral parameters of the carbon nanotubes to be prepared from the bilayer graphene with different relative included angles are determined, and based on the determined different chiral parameters, the nanoribbon orientation and different nanoribbon widths corresponding to the different chiral parameters in different sections in the nanoribbon length direction are determined.

10. The method according to any one of claims 1-7, characterized in that, The bilayer two-dimensional material is a bilayer boron nitride two-dimensional material, a bilayer molybdenum disulfide two-dimensional material, a bilayer molybdenum selenide two-dimensional material or a bilayer tungsten disulfide two-dimensional material; The obtained nanotube array is a boron nitride nanotube array, a molybdenum disulfide nanotube array, a molybdenum selenide nanotube array or a tungsten disulfide nanotube array.

11. The method according to claim 8, wherein: The nanoribbon orientation is obtained based on the following orientation formula: The width of the nanobelt is obtained based on the following width formula: where ψ0 represents the nanoribbon orientation, w represents the nanoribbon width, a is the lattice constant of the two-dimensional material, and n and m are the chiral indices of the nanotube; or The nanoribbon orientation and the nanoribbon width are respectively obtained by introducing deviations into the orientation formula and the width formula.

12. A nanotube array, characterized in that, The nanotube array is prepared by the nanotube array preparation method according to any one of claims 1-11.

13. A carbon nanotube transistor prepared by using a carbon nanotube array, characterized in that, The carbon nanotube array is prepared by the method according to claim 8 or 9.

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