Nanotube array preparation method, nanotube array, and device

Abstract

A nanotube array preparation method, a nanotube array, and a device. The method comprises: on a substrate (10), preparing a double-layer two-dimensional material with lattice orientations having a relative included angle formed therebetween, and using the double-layer two-dimensional material as a template; determining a chiral parameter of a nanotube to be prepared corresponding to the relative included angle between the lattice orientations of the double-layer two-dimensional material, determining a nanoribbon orientation and a nanoribbon width on the basis of the determined chiral parameter, determining the spacing between nanoribbons on the basis of the density of the nanotube to be prepared and the nanoribbon width, and etching the double-layer two-dimensional material on the basis of the determined nanoribbon orientation, nanoribbon width, and spacing between the nanoribbons to obtain a nanoribbon array of the double-layer two-dimensional material; and performing thermal excitation treatment on the obtained nanoribbon array of the double-layer two-dimensional material to obtain a nanotube array. In this way, the nanotube array having controllable density, orientation and chirality can be prepared.

Description

Nanotube array preparation method, nanotube array and device Technical Field

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

[0002] Single-walled carbon nanotubes (CNTs) can be viewed as quasi-one-dimensional structures formed by curling graphene. Depending on the curling pattern (chirality), SWNTs can exhibit either metallic or semiconducting properties. High-density (over 125 per micron) arrays of fully semiconducting, parallel-packed SWNTs are the core material for building high-performance carbon-based transistors and integrated circuits.

[0003] Currently, the methods used to produce single-walled carbon nanotubes (SWNTs) fall into two main categories: the first is catalyst-assisted chemical vapor deposition (CATCVD) (e.g., 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 produce fully semiconducting, or even single-chirality, SWNT arrays. However, this method has the disadvantages of high synthesis temperatures, incompatibility with integrated circuit processes, and low array density. The second type is the solution separation + assembly arrangement method. The typical scheme is to use polymer dispersion to obtain a single-walled carbon tube solution, combine density gradient centrifugation and other methods to achieve metal-semiconductor single-walled carbon tube separation, and then self-assemble into carbon nanotube array wafers (for example, see the following documents, document 3: Liu L et al., Science, 2020, 368: 850-856; Document 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 semiconductor carbon tube purity and density, but it will introduce difficult-to-control polymer residues, and the arrangement of carbon tubes will also have local agglomeration, stacking and other heterogeneities. At the same time, this type of method currently lacks effective control of carbon tube chirality, that is, carbon tube chirality is randomly distributed.

[0004] In summary, the current carbon tube array preparation technology still has many difficulties and challenges. It is difficult to simultaneously ensure the density, orientation, chirality control and cleanliness of the carbon tube array, and thus it is impossible to simultaneously meet the high orientation, high density, full semiconductor and high cleanliness requirements of carbon nanotube arrays when used to construct high-performance carbon-based transistors and integrated circuits, thus affecting the realization of high-performance carbon-based transistors and integrated circuits.

[0005] Summary of the Invention

[0006] 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 in the prior art.

[0007] In one aspect of the present invention, a method for preparing a nanotube array is provided, the method comprising the following steps:

[0008] a template preparation step of preparing a double-layer two-dimensional material having a relative angle of lattice orientation on a substrate, wherein the double-layer two-dimensional material serves as a template;

[0009] a nanoribbon array etching step, determining chiral parameters of the nanotubes to be prepared corresponding to the relative angle of the lattice orientation of the double-layer two-dimensional material, determining the nanoribbon orientation and nanoribbon width based on the determined chiral parameters, determining the spacing between the nanoribbons based on the density of the nanotubes to be prepared and the nanoribbon width, and etching the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, and spacing between the nanoribbons to obtain a nanoribbon array of the double-layer two-dimensional material;

[0010] The nanotube array generation step is to subject the obtained double-layer two-dimensional material nanotube array to thermal excitation treatment to obtain a nanotube array.

[0011] In some embodiments of the present invention, the preparation of a double-layer two-dimensional material with a relative angle of lattice orientation on a substrate includes: preparing a double-layer two-dimensional material with a relative angle of lattice orientation on the substrate by using mechanical exfoliation combined with a controllable angle transfer method or using liquid phase transfer combined with a controllable angle transfer method; or using mechanical exfoliation or liquid phase transfer to obtain a single-layer two-dimensional material, and folding the obtained single-layer two-dimensional material according to a set orientation to obtain a double-layer two-dimensional material with a relative angle of lattice orientation; or directly growing a double-layer two-dimensional material with a relative angle of 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.

[0012] In some embodiments of the present invention, the etching of a double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons includes: etching the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons using the following etching techniques: laser lithography, electron beam lithography, focused ion beam, high-energy electron beam, mask method or chemical etching.

[0013] 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.

[0014] In some embodiments of the present invention, at least one layer of the two-dimensional material in the double-layer two-dimensional material is a p-type doped or n-type doped two-dimensional material.

[0015] In some embodiments of the present invention, at least one layer of the two-dimensional material in the double-layer two-dimensional material is a two-dimensional material with grain boundaries; different regions of the same double-layer two-dimensional material prepared in the template preparation step have relative angles of different lattice orientations, and / or different sections in the length direction of the nanoribbon of the same double-layer 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 spliced ​​with different chirality.

[0016] In some embodiments of the present invention, the nanoribbon array generation step also includes: determining the length of the nanoribbon based on the length of the nanotube to be prepared; etching the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons includes: etching the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width, spacing between nanoribbons and length of the nanoribbon.

[0017] In some embodiments of the present invention, the double-layer two-dimensional material is a double-layer graphene, and the obtained nanotube array is a carbon nanotube array.

[0018] 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 sulfide two-dimensional material, a double-layer molybdenum selenide two-dimensional material or a double-layer tungsten sulfide two-dimensional material; the obtained nanotube array is a boron nitride nanotube array, a molybdenum sulfide nanotube array, a molybdenum selenide nanotube array or a tungsten sulfide nanotube array.

[0019] In some embodiments of the present invention, the nanoribbon orientation is obtained based on the following orientation formula:

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

[0021] 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

[0022] The nanoribbon orientation and the nanoribbon width are obtained by introducing deviations into the orientation formula and the width formula, respectively.

[0023] Another aspect of the present invention provides a nanotube array prepared by the above method.

[0024] Another aspect of the present invention provides a semiconductor device (such as a carbon nanotube transistor) manufactured using the aforementioned nanotube array.

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

[0026] Furthermore, in some embodiments, high-density, highly oriented, fully semiconducting single-walled carbon nanotube arrays with controllable chirality can be produced. Due to the controllable density, the carbon nanotubes are evenly distributed without aggregation or stacking.

[0027] Additional advantages, objects, and features of the present invention will be set forth in part in the following description and will become apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the structures particularly pointed out in the description and drawings.

[0028] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present invention are not limited to the above specific descriptions, and the above and other purposes that can be achieved by the present invention will be more clearly understood based on 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, constitute a part of this application, and do not constitute a limitation of the present invention. In the drawings:

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

[0031] 2A to 2C are schematic diagrams showing the geometric relationship between the chirality of double-layer graphene nanoribbons and carbon tubes according to an embodiment of the present invention.

[0032] FIG3 is a schematic flow chart of a method for preparing a nanotube array according to an embodiment of the present invention.

[0033] FIG4 is a schematic diagram of a carbon nanotube array preparation process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0035] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

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

[0037] It should also be noted that, unless otherwise specified, the term "connection" herein may refer not only to a direct connection but also to an indirect connection involving an intermediate.

[0038] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying 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 below do not limit the order of the steps, but it should be understood that the steps can be executed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be executed simultaneously.

[0040] To address the difficulty in simultaneously controlling the density, orientation, and chirality of existing carbon nanotube arrays, resulting in uneven array orientation, localized agglomeration, stacking, and other uneven distributions or inconsistent chirality, this present invention proposes a novel method for preparing single-walled carbon nanotube arrays with controllable chirality based on double-layer graphene. The method provides a novel top-down approach for selecting and controlling the chirality of carbon nanotubes (CNTs), enabling the adjustment of the density ρ of the CNT array within the following range: 0 < ρ ≤ 350 tubes / μm, while maintaining highly consistent orientation of the CNTs within the array. Furthermore, the chirality of the CNTs can be controlled, enabling the production of single-walled carbon nanotubes with specific chirality. Furthermore, gold half-junctions or chiral junctions with varying band gaps can be introduced as needed to meet the channel material requirements of high-performance CNT transistors and integrated circuits.

[0041] The principle of the method for preparing a nanotube array of the present invention will be described below by taking the preparation of single-walled carbon tubes using double-layer graphene as an example, and then the method for preparing a nanotube array of the present invention will be described in detail.

[0042] As shown in Figure 1, the geometric structure of a single-walled carbon nanotube can be regarded as a layer of graphene curled along the chiral vector Ch. Depending on the direction and size of the chiral vector Ch, the curled carbon nanotube has different chirality, which can also be represented by Ch. The vectors a1 and a2 indicated by the arrows in Figure 1 represent the basis vectors of the single-layer graphene lattice. In the present invention, the two zigzag edges of graphene are used as basis vectors to describe the geometric relationships involved in the present invention, including but not limited to angle relationships and length relationships. The derivation of the principle that the geometric descriptions are different but the structures are equivalent due to different selection methods of the basis vectors is also covered within the scope of protection of the present invention.

[0043] The chirality 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 nm is divisible by 3, the carbon nanotube exhibits metallic properties; when nm is not divisible by 3, the carbon nanotube becomes semiconducting. The band gap of the carbon nanotube is also affected by the value of Ch: a larger Ch means a smaller band gap. Therefore, controlling the chirality of the carbon nanotube can control its electronic structure. In Figure 1, θ represents the angle between the chirality vector and the graphene basis vector, and T represents the radial direction of the carbon nanotube.

[0044] As shown in Figure 2A, when a single-layer graphene is folded in half along 1 / 2Ch, a double-layer graphene nanoribbon as shown in Figure 2B is obtained. The geometric topology of the double-layer graphene nanoribbon at this point remains unchanged from that of the single-layer graphene before folding. If the carbon atoms at the upper and lower edges of the double-layer graphene nanoribbon are connected and the entire planar double-layer structure is bulged into a cylindrical shape, a carbon nanotube with a chiral vector of Ch is obtained. The inventors discovered that the edges of double-layer graphene form a bulged closed structure under annealing conditions. Based on this phenomenon, the inventors of this application innovatively used double-layer graphene as a template for preparing parallel arrays of carbon nanotubes. They then etched the double-layer graphene into a double-layer graphene nanoribbon array whose orientation and width matched the chiral parameters of the carbon nanotubes. They then used thermal stimulation treatments such as annealing to convert the double-layer graphene nanoribbon array into a single-walled carbon nanotube array. Therefore, the present invention proposes a method for obtaining carbon nanotubes of a specific target chirality by preparing double-layer 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 carbon nanotubes is determined by the relative angle θ0 between the lattice orientations of the two layers of graphene and the width w of the nanoribbon. h , direction is θ, size is |C h | carbon nanotubes, according to the geometric relationship, the relationship between the target chirality (n, m) of the carbon nanotubes and the width w of the double-layer graphene nanoribbon and the relative angle θ0 of the lattice orientation between the double-layer graphene (i.e., the angle between the basis vectors of the two layers of graphene) is as follows (Formula Group 1): θ0 = 60-2*θ; w = 0.5*|C h |;

[0046] The relative angle θ0 of the lattice orientation between the double-layer graphene determines the direction of the carbon nanotube chiral vector Ch (i.e., the angle θ between the chiral vector and the graphene basis vector), and the width w of the double-layer nanoribbon determines the size of the carbon nanotube chiral vector Ch. h The relationship between the chiral index (n, m) and the direction and magnitude of the chiral vector is (Formula Group 2):

[0047] Where a is the lattice constant of graphene, d t is the diameter of the target carbon tube, and θ is related to |C h Substituting into Formula Group 1, we can obtain the relationship between the width w of the double-layer graphene nanoribbon, the relative angle θ0 between the interlayer lattice orientations, and the target carbon nanotube chirality index (n, m) (Formula Group 3):

[0048] According to the relationship in the above formula, the present invention designs a double-layer graphene nanoribbon with a specific relative angle θ0 and a specific width w, and performs heat treatment such as annealing on the double-layer graphene nanoribbon to obtain carbon nanotubes with corresponding chirality.

[0049] The method of the present invention is not limited to the preparation of single-walled carbon nanotube arrays. Since the edges of double-layer two-dimensional material nanoribbons generally close after annealing, the method designed in the present invention can also be applied to the production and processing of other one-dimensional nanotubes and their arrays by replacing the double-layer graphene with other two-dimensional material templates. For example, other nanotube arrays such as boron nitride nanotube arrays, molybdenum sulfide nanotube arrays, molybdenum selenide nanotube arrays, and tungsten sulfide nanotube arrays can be prepared based on double-layer 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 nanoribbons to be etched, it is necessary to replace the lattice constant a of the graphene in the previous formula with the lattice constant of the corresponding crystal. These new one-dimensional nanotube arrays also have the advantage of precise control of array density, orientation, and chirality. The nanotube arrays listed here are only examples, and the present invention is not limited to them.

[0050] FIG3 is a schematic diagram of a process for preparing a nanotube array according to an embodiment of the present invention. As shown in FIG3 , the method includes the following steps S110 to S130:

[0051] In the template preparation step S110 , a double-layer two-dimensional material with lattice orientations having a relative angle is prepared on a substrate, and the double-layer two-dimensional material serves as a template.

[0052] 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 substrate rotation; in principle, it only needs to be able to withstand the annealing temperature. However, since the nanotubes prepared using the method of the present invention are highly clean and can be used in the preparation of high-performance semiconductor devices, the substrate can be a surface-insulating substrate, such as a surface-insulating silicon substrate, more specifically, a silicon wafer covered with silicon dioxide, to facilitate the subsequent direct preparation of semiconductor devices. However, the present invention is not limited to this.

[0053] Nanoribbon array etching step S120, determining the chiral parameters of the nanotubes to be prepared corresponding to the relative angle of the lattice orientation of the double-layer 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 double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons to obtain a nanoribbon array of the double-layer two-dimensional material.

[0054] In the nanotube array forming step S130 , the obtained nanotube array of the double-layer two-dimensional material is subjected to a thermal excitation process to obtain a nanotube array.

[0055] Based on the above steps, a nanotube array with determined chirality can be obtained.

[0056] In step S110, two layers of two-dimensional material with lattice orientations having a relative angle are prepared on a substrate as a template. When this preparation method is used to prepare single-walled carbon nanotubes, the two layers of two-dimensional material used as the template are double-layer graphene.

[0057] For a carbon nanotube array of a given chirality (n, m), based on the relationship between the relative angle θ0 of bilayer graphene and the chiral index (n, m) in Formula Group 3, it is first necessary to prepare bilayer graphene with an interlayer relative rotation angle of θ0. There are many methods for preparing bilayer graphene with an interlayer relative rotation angle of θ0, 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) a single-layer graphene folding method.

[0058] (1) Mechanical peeling + controlled angle transfer method

[0059] The preparation of double-layer graphene by mechanical exfoliation + controlled angle transfer method means first using mechanical exfoliation to obtain two single-layer graphenes through two mechanical exfoliations respectively, and then using controlled angle transfer technology to obtain double-layer graphene by transferring the two single-layer graphenes obtained by the two mechanical exfoliations to a substrate.

[0060] Among them, the mechanical exfoliation method is used to obtain single-layer graphene, which is to separate the graphene sheets from the graphite crystal by applying mechanical force (such as friction and / or tension, etc.) to the graphite crystal. Since the mechanical exfoliation method for obtaining single-layer graphene is an existing mature technology, it will not be described in detail here.

[0061] The process of obtaining double-layer graphene using controlled angle transfer technology specifically includes:

[0062] After mechanical exfoliation is used to obtain two monolayer graphene layers, they can be maintained on a transparent substrate such as PDMS (polydimethylsiloxane) or PMMA (polymethyl methacrylate) so that the relative superposition angle of the two monolayer graphene layers can be controlled using an optical angle control console. Here, the material used for the transparent substrate is only an example and the present invention is not limited to this.

[0063] In the process of controlling the relative superposition angle of two single-layer graphenes using an optical angle control console, the lattice orientations of the two single-layer graphenes are determined and marked using angle-resolved Raman, crystallographic structure (such as edge angle, etc.) measurement, or low-energy electron beam diffraction, and the two single-layer graphenes with determined crystallographic orientations are bonded together at a specific relative angle using the optical angle control console at a controllable angle, thereby preparing a double-layer graphene having a specific lattice orientation relative angle;

[0064] Subsequently, the obtained double-layer graphene with a relative angle of specific lattice orientation can be transferred to a substrate using a transfer technique such as a dry method or a wet method.

[0065] (2) Liquid phase transfer + controlled angle transfer method

[0066] The preparation of double-layer graphene by liquid phase transfer + controlled angle transfer method refers to using two liquid phase transfers to obtain two single-layer graphenes, and using controlled angle transfer technology to transfer the two single-layer graphenes obtained by the two liquid phase transfers to a substrate to obtain double-layer graphene.

[0067] The methods of obtaining single-layer graphene by liquid phase transfer include:

[0068] Liquid phase transfer is used to deposit two separate graphene monolayers onto two substrates grown using methods such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), and chemical vapor transport (CVT). The two monolayers are then placed on a transparent substrate such as PDMS or PMMA, allowing the angle control console to control the relative stacking angle.

[0069] In the process of controlling the relative superposition angle of two single-layer graphenes using an optical angle control console, the lattice orientations of the two single-layer graphenes are determined and marked using angle-resolved Raman, crystallographic structure (such as edge angle, etc.) measurement, or low-energy electron beam diffraction, and the two single-layer graphenes with determined crystallographic orientations are bonded together at a specific relative angle using the optical angle control console at a controllable angle, thereby preparing a double-layer graphene having a specific lattice orientation relative angle;

[0070] Subsequently, the obtained double-layer graphene with a relative angle of specific lattice orientation can be transferred to a substrate using a transfer technique such as a dry method or a wet method.

[0071] (3) Single-layer graphene folding method

[0072] Single-layer graphene can be obtained by mechanical exfoliation or liquid phase transfer, and then the obtained single-layer graphene is folded according to a set orientation to obtain a double-layer two-dimensional material with a relative angle of lattice orientation.

[0073] Alternatively, a bilayer of two-dimensional materials with a controlled relative angle of lattice orientation can be directly grown using growth methods such as chemical vapor deposition, molecular beam epitaxy, or physical vapor deposition. Using these methods, graphene can be replaced with other two-dimensional materials to similarly produce bilayer two-dimensional materials with a controlled relative angle of lattice orientation on a substrate. Therefore, using a similar approach, in step S110, a bilayer of two-dimensional materials such as boron nitride, molybdenum sulfide, molybdenum selenide, or tungsten sulfide can also be obtained on a substrate, with the relative angle between the layers being controllable.

[0074] In addition, in an embodiment of the present invention, for double-layer graphene with an arbitrary interlayer relative rotation angle θ0, such as double-layer graphene obtained by a direct growth method, the chiral index (n, m) that can be processed to meet the electronic structure requirements when the interlayer rotation angle is θ0 can also be inferred based on the actual required carbon nanotube electronic structure, such as semiconductor properties.

[0075] In step S120, before etching the nanoribbon array, it is first necessary to determine the chiral parameters of the nanotubes to be prepared, such as the chiral index (n, m). 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 of the nanoribbon array to be etched relative to the lattice orientation of the double-layer two-dimensional material, and the nanoribbon width and the spacing between the nanoribbons are further determined.

[0076] Taking the etching of a double-layer graphene nanoribbon array as an example, before etching the double-layer graphene nanoribbon array, it is necessary to first determine the angle ψ0 of the nanoribbon array to be etched relative to the double-layer graphene lattice. Due to structural symmetry, the orientation of the nanoribbons should simultaneously satisfy the angle ψ with the basis vector directions of both layers of graphene. Based on the geometric relationships shown in Figures 2A-2C, when the angle between the chiral vector Ch and the graphene basis vector a1 is θ, we have:

[0077] The crystallographic orientation of bilayer graphene can be determined using a variety of methods, including but not limited to one or a combination of the following: optical microscopy, scanning electron microscopy, low-energy electron diffraction, electron diffraction, angle-resolved photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy. Based on the determined crystallographic orientation of the bilayer graphene, the angle ψ between the orientation of the nanoribbon array to be etched and the bilayer graphene lattice can be determined, thereby determining the orientation of the bilayer graphene nanoribbon array.

[0078] After determining the orientation of the double-layer graphene nanoribbon array, the width of a single nanoribbon is determined by w in Formula 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: Δx = 1 / ρ – w;

[0079] From the above formula, we can see that the carbon nanotube array density ρ can be controlled by adjusting the gap between the double-layer graphene nanoribbons (the width of the gap between the nanoribbons) Δx. In addition, when Δx is 0, the carbon nanotube density ρ reaches the maximum value ρ max , maximum density ρ max The diameter d of the target chiral carbon nanotubes t is related, so it can be expressed as: ρ max =1 / w=1 / (0.5*d t *π);

[0080] The control range of the carbon nanotube density in the carbon tube array in the present invention 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.

[0081] After determining the nanoribbon orientation, nanoribbon width, inter-ribbon spacing, and nanoribbon length, the nanoribbon array can be etched based on these parameters. Etching of the bilayer graphene nanoribbon array can be performed using a variety of methods, including but not limited to laser lithography, electron beam lithography, focused ion beam lithography, high-energy electron beam lithography, mask etching, and chemical etching. One of these etching methods can be selected for nanoribbon etching.

[0082] In a manner similar to etching graphene nanoribbon arrays, nanoribbon arrays of two-dimensional materials such as two-layer boron nitride nanoribbon arrays, two-layer molybdenum sulfide nanoribbon arrays, two-layer molybdenum selenide nanoribbon arrays, or two-layer tungsten sulfide nanoribbon arrays can be prepared. These materials are only examples and the present invention is not limited to them.

[0083] Step S130 is also described using the thermal excitation treatment of a bilayer graphene nanoribbon array as an example. The thermal excitation treatment in this step can be performed in a variety of ways, as long as sufficient external excitation is provided to cause edge closure reconstruction of the bilayer graphene nanoribbons. For example, the thermal excitation treatment may include one or more of the following: annealing, laser excitation, Joule heating, and high-energy ray irradiation, but the present invention is not limited thereto.

[0084] Taking annealing as an example, in some embodiments of the present invention, the annealing temperature of the bilayer graphene nanoribbon array can be between 250°C and 1300°C, and the annealing time can range from 0.1s to 600s, depending on the heating temperature. Annealing can also be performed at different temperatures over different time periods, but the present invention is not limited thereto. The annealing of the bilayer graphene nanoribbon array can be performed under vacuum conditions or in an inert gas atmosphere.

[0085] When other thermal excitation treatment methods such as laser excitation, Joule heating or high-energy ray irradiation are used to replace annealing of the double-layer 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 0.1s and 600s depending on the heating temperature.

[0086] After etching, the double-layer graphene nanoribbons have the same orientation ψ, nanoribbon spacing Δx, interlayer relative rotation angle θ0 and nanoribbon width w. The process of generating single-walled carbon nanotubes by thermal excitation only involves reconstructing the unsaturated carbon atoms on both sides of the double-layer graphene nanoribbons through thermal excitation. Therefore, the carbon nanotubes after thermal excitation have the same orientation ψ and intertube spacing Δx as the graphene nanoribbons. tube Since the planar structure changes to a tubular structure after forming the tube, it becomes Δx tube =Δx+wd t Since each carbon tube is transformed from double-layer 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 double-layer graphene nanoribbon array is thermally excited, the present invention can obtain single-walled carbon nanotubes with the same orientation ψ (high orientation) and the same spacing Δx. tube (High uniformity), consistent chirality, all (n, m) (chirality controllable), density 0<ρ<ρ max Single-walled carbon nanotube arrays with adjustable spacing (i.e., high density and adjustable spacing).

[0087] Furthermore, because the method of the present invention does not require catalyst growth or polymer centrifugal pulling to grow, select, and align carbon nanotubes, impurity levels are determined solely by the graphene's cleanliness and residuals from conventional semiconductor processes. Consequently, the resulting carbon nanotube arrays are clean enough for direct use in the fabrication of high-performance devices.

[0088] Similar to the treatment of a double-layer graphene nanoribbon array, the double-layer nanoribbon array of other two-dimensional materials (such as a boron nitride nanoribbon array, a molybdenum sulfide nanoribbon array, a molybdenum selenide nanoribbon array or a tungsten sulfide nanoribbon array) obtained in step S120 is also thermally stimulated in the temperature range of 250°C to 1300°C. Since the tube-forming temperatures of different materials are different, the thermal stimulation treatment temperature can be adaptively adjusted, and a nanotube array can also be obtained, such as a boron nitride nanotube array, a molybdenum sulfide nanotube array, a molybdenum selenide nanotube array or a tungsten sulfide nanotube array.

[0089] As can be seen from the above, the method of the present invention can produce carbon nanotube arrays with high orientation, high density, controllable chirality, adjustable spacing, uniform distribution, and high cleanliness using double-layer graphene as a template. In addition, nanotube arrays of other materials can also be produced in the same manner.

[0090] In some embodiments of the present invention, one or both layers of the double-layer graphene used to prepare single-walled carbon nanotubes can be replaced with p-type doped graphene or n-type doped graphene. When both layers are doped, the two graphene layers can have the same or different doping types. If the two layers have the same doping type, the carbon nanotubes produced using this template are either p-type or n-type carbon nanotube arrays. If one layer is replaced with p-type doped graphene and the other with n-type doped graphene, the carbon nanotube array produced using this template is a carbon nanotube array with radial pn junctions.

[0091] In some embodiments of the present invention, since the chirality (n, m) of the prepared carbon nanotubes is controlled by the interlayer relative angle θ0 and the nanoribbon width w of the double-layer graphene nanoribbon, different relative angles θ0 and / or widths w can be introduced into the same double-layer graphene nanoribbon, so that carbon nanotubes composed of different chiralities can be formed, and the carbon nanotubes of different chiralities are connected by chiral junctions. The change in the interlayer angle θ0 can be caused by the introduction of grain boundaries. In comparison, the width w of the nanoribbon is easier to control and can be controlled by changing the etching template. More specifically, by converting one or two layers of graphene in the double-layer graphene into polycrystalline graphene, the graphene nanoribbons on both sides of the grain boundary can have different angles θ0. To achieve different widths w, the retained nanoribbon width can be controlled during the etching process so that different sections along the length of the same double-layer graphene nanoribbon correspond to different nanoribbon widths w.

[0092] Extending to double-layer two-dimensional materials, when at least one layer of the two-dimensional material in the double-layer two-dimensional material can be a two-dimensional material with grain boundaries, different regions of the same double-layer two-dimensional material prepared in the template preparation step will have relative angles of different lattice orientations; correspondingly, the nanotube array obtained in the nanotube array generation step is an array of nanotubes with different chiralities spliced ​​together.

[0093] Similar treatments are also applicable to double-layer two-dimensional materials such as boron nitride, molybdenum sulfide, molybdenum selenide, and tungsten sulfide.

[0094] FIG4 shows a schematic process for preparing a single-walled carbon nanotube array on a substrate.

[0095] As shown in FIG4 (a), double-layer graphene 20 and 30 having a lattice orientation with a relative angle θ0 is prepared on a surface-insulating substrate (such as a silicon wafer covered with silicon dioxide) 10. For example, a single-layer graphene 20 is peeled off from the surface of a graphite crystal by mechanical exfoliation, and the peeled single-layer graphene 20 is transferred to the substrate 10 in a predetermined orientation. Then, the mechanical exfoliation and transfer steps are performed again to place the single-layer graphene 30 peeled off again on the single-layer graphene 20 peeled off for the first time, forming a stacked double-layer graphene as a template and the relative angle of the lattice orientation between the double-layer 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, in the step of transferring, double-layer graphene can also be placed on the substrate 10 at any angle, and after the double-layer graphene is formed, the crystallographic relative angle is determined by scanning electron microscopy, transmission electron microscopy, and the like.

[0096] Figure 4(b) shows the double-layer graphene obtained in (a) being etched using mask 40 to produce a double-layer graphene nanoribbon array. First, the nanoribbon orientation (e.g., the angle ψ0 between the nanoribbon orientation and the graphene lattice orientation) and 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 desired carbon nanotube density and nanoribbon width. Based on the determined nanoribbon orientation, nanoribbon width, and spacing between nanoribbons, the double-layer graphene is etched to produce a double-layer graphene nanoribbon array 50, as shown in Figure 4(c). The double-layer graphene nanoribbon array is then annealed at a temperature between 250°C and 1300°C for a time between 0.1s and 600s, depending on the annealing temperature, to produce the carbon nanotube array 60 shown in Figure 4(d).

[0097] During the preparation process of the carbon nanotube array of the present invention, when errors occur in the processing of graphene nanoribbons, such as errors in width Δw, orientation Δψ, and relative angle error Δθ0 between layers of the nanoribbons, topological defects such as 5-8 rings and 5-7-7-5 rings will be present in the formed carbon nanotubes due to the inability to maintain perfect geometry. As the error increases, the mismatch density at the edge of the double-layer graphene nanoribbons will increase, and the defect density in the formed carbon tubes will also increase. However, since the edges of the double-layer graphene nanoribbons tend to form closed structures to reduce energy under high temperature conditions, a carbon tube structure can always be formed. In extreme degradation conditions, if w, ψ0, and θ0 are not determined strictly in accordance with the geometric relationship 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 chirality controllability and introduces a large number of topological defects in the carbon nanotubes. However, this degradation technology for preparing carbon nanotube arrays should also be included in the scope of protection of the present invention.

[0098] By utilizing the geometric relationship between w, ψ0 and θ0 in the aforementioned formula, the present invention can also construct carbon nanotubes with gold half junctions and chiral junctions. In this case, the double-layer graphene is a double-layer graphene with at least one layer having a grain boundary, and different regions between the double-layer graphene have different relative angles. In addition, in the nanoribbon array etching step, in the nanoribbon array etching step, the different chiral parameters of the carbon nanotubes to be prepared from the double-layer graphene with different relative angles are determined, and the different nanoribbon widths corresponding to the different chiral parameters in the nanoribbon orientation and 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 are introduced into the same double-layer graphene nanoribbon. 0A ,θ 0B With width w A With w B , where different relative angles are generated by the grain boundaries during graphene growth, and different widths can be set by the etching parameters during exposure and etching. After annealing such double-layer graphene nanoribbons to form carbon nanotubes, θ 0A ,w A The chiral index of the segment (n A ,m A ) and θ 0B ,w B The chiral index of the segment (n B ,m B ) can be obtained from the above formula, and then a chiral carbon nanotube with a chirality difference is formed. On the contrary, the present invention can be based on the pre-designed chiral index (n A ,m A ) and (n B ,m B ) Use the formula to derive the processing parameters θ 0A ,θ 0B With wA ,w B Because the chiral index determines the metallic and semiconducting properties of a carbon nanotube, a carbon nanotube with gold half-junctions is formed when one side of the carbon nanotube is metallic and the other side is semiconducting. The number of chiral junctions and gold half-junctions depends on how many different processing parameter combinations (w, ψ0, and θ0) are introduced into the same bilayer graphene ribbon.

[0099] The existing technology cannot simultaneously meet the requirements of high orientation, high density, full semiconductor properties, adjustable spacing, and uniform distribution (referring to uniform spacing between carbon tubes, no agglomeration or stacking). On this basis, there is also a lack of effective means for controlling the chirality of carbon tubes. The existing CVD method for growing carbon nanotube arrays produces carbon nanotubes with low and uncontrollable density, a wide and non-uniform chirality distribution (i.e., uncontrollable chirality), and catalyst residues. The existing liquid phase pulling method for preparing carbon nanotube arrays has too high a density and is uncontrollable, and can only obtain semiconductor chirality (chirality is not fully controllable). The nanotube orientation is complex and there is a stacking phenomenon, and the prepared carbon nanotubes are contaminated by polymers. In contrast, the carbon nanotubes prepared by the method for preparing carbon nanotubes of the present application have controllable density and chirality, and can prepare both semiconducting 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 single-walled carbon nanotube arrays that meet the requirements of controllable density, orientation and chirality, and the cleanliness of the prepared single-walled carbon nanotube arrays meets the requirements of carbon nanotube (CNT) transistors and their integrated circuits for carbon nanotube materials.

[0100] By using the carbon nanotube array with better performance prepared by the above method to construct a carbon nanotube transistor, device performance loss caused by carbon nanotube stacking, surface contamination, and tube diameter distribution can be avoided, and a carbon nanotube transistor with better performance can be obtained.

[0101] It should be understood that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted. In the above embodiments, several specific steps are described and illustrated as examples. However, the method of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art may make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present invention.

[0102] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or replace features of other embodiments.

[0103] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations to the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. [Corrected 22.05.2024 in accordance with Rule 91] A method for preparing a nanotube array, characterized in that: The method comprises the following steps: a template preparation step, preparing a double-layer two-dimensional material having a relative angle of lattice orientation on a substrate, wherein the double-layer two-dimensional material is used as a template; a nanoribbon array etching step, determining the chiral parameters of the nanotubes to be prepared corresponding to the relative angle of the lattice orientation of the double-layer two-dimensional material, determining the nanoribbon orientation and the nanoribbon width based on the determined chiral parameters, determining the spacing between the nanoribbons based on the density of the nanotubes to be prepared and the nanoribbon width, and etching the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between the nanoribbons to obtain a nanoribbon array of the double-layer two-dimensional material; The nanotube array generation step is to subject the obtained double-layer two-dimensional material nanobelt array to thermal excitation treatment to obtain a nanotube array.

2. The method according to claim 1, characterized in that The method of preparing a double-layer two-dimensional material having a relative angle of lattice orientation on a substrate comprises: Using mechanical exfoliation combined with a controlled angle transfer method or using liquid phase transfer combined with a controlled angle transfer method to prepare a double-layer two-dimensional material with a relative angle of lattice orientation on the substrate; or Mechanical exfoliation or liquid phase transfer is used to obtain a single-layer two-dimensional material, and the obtained single-layer two-dimensional material is folded according to a set orientation to obtain a double-layer two-dimensional material with a relative angle of lattice orientation; or A double-layer two-dimensional material with a relative angle of lattice orientation is directly grown by a growth method, wherein the growth method includes one of the following: chemical vapor deposition, molecular beam epitaxy or physical vapor deposition.

3. The method according to claim 1, characterized in that The etching of the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons comprises: The double-layer two-dimensional material is etched based on the determined nanobelt orientation, nanobelt width and spacing between nanobelts 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, characterized in that At least one layer of the two-dimensional material in the double-layer 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 layer of the two-dimensional material in the double-layer two-dimensional material is a two-dimensional material having a grain boundary; Different regions of the same double-layer two-dimensional material prepared in the template preparation step have different relative angles of lattice orientation, and / or different sections of the same double-layer two-dimensional material nanoribbon 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 spliced ​​with different chirality.

7. The method according to claim 1, characterized in that The nanoribbon array generation step further includes: determining the length of the nanoribbon based on the length of the nanotube to be prepared; The etching of the double-layer two-dimensional material based on the determined nanoribbon orientation, nanoribbon width and spacing between nanoribbons includes: etching the double-layer 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 to 7, characterized in that: The double-layer two-dimensional material is a double-layer graphene, and the obtained nanotube array is a carbon nanotube array.

9. The method according to claim 8, characterized in that The double-layer two-dimensional material having a relative angle of lattice orientation is at least one layer of double-layer graphene having a grain boundary, and different regions between the double-layer graphene have different relative angles; In the nanoribbon array etching step, different chiral parameters of carbon nanotubes to be prepared from double-layer graphene with different relative angles are determined, and different nanoribbon widths corresponding to different chiral parameters in different sections along the nanoribbon orientation and the nanoribbon length direction are determined based on the determined different chiral parameters.

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

11. The method according to claim 8, characterized in that: The nanoribbon orientation is obtained based on the following orientation formula: The nanoribbon width 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 obtained by introducing deviations into the orientation formula and the width formula, respectively.

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 to 11.

13. A carbon nanotube transistor prepared 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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