A method for controlled growth of single-conductivity-property single-wall carbon nanotubes by substrate-lattice oxygen release

Abstract

The present application relates to the field of controlling the growth of single-walled carbon nanotubes with conductive properties, and particularly relates to a method for controlling the lattice oxygen vacancy concentration of specific crystal planes of a substrate and growing high-purity single-walled carbon nanotubes with single conductive properties. The method selects a face-centered cubic oxide single crystal substrate, exposes the (110) and (100) planes, uses the normal pressure chemical vapor deposition method, uses the oxygen-poor (110) plane to prepare single-walled carbon nanotubes with metallic properties, and uses the oxygen-rich (100) plane to prepare single-walled carbon nanotubes with semiconductive properties. The present application realizes the controllable preparation of single-walled carbon nanotubes with single conductive properties by selecting substrate crystal planes with different oxygen contents and regulating the release of lattice oxygen, and lays a material foundation for the development of carbon nanotube-based nanoelectronic devices.

Description

Technical Field

[0001] This invention relates to the field of controlled growth of single-walled carbon nanotubes with conductivity properties, specifically a method for growing single-walled carbon nanotubes with a single conductivity property by releasing oxygen from the substrate lattice. By utilizing the concentration of oxygen vacancies in the lattice of a single-crystal substrate, single-walled carbon nanotubes enriched with metallic or semiconductor properties can be grown in a controlled manner. Background Technology

[0002] Semiconducting single-walled carbon nanotubes can be used as channel materials for field-effect transistors, and are expected to be used to construct integrated circuits with advanced processes of 5 nm and below. They are considered one of the most competitive low-dimensional nanomaterials in the post-Moore's Law era. Metallic single-walled carbon nanotubes have high electrical conductivity and current carrying capacity, and can be used as high-performance interconnect wires and electrode materials.

[0003] The application of single-walled carbon nanotubes (SUVs) in nanoelectronic devices is mainly limited by the fact that the directly prepared samples are mixtures of metallic (~1 / 3) and semiconducting (~2 / 3) SUVs. This is because the differences in structure and formation energy between metallic and semiconducting SUVs are very small. Therefore, it is very difficult to controllably prepare SUVs with a single conductive property. Currently, representative works on the selective preparation of high-purity, single-walled carbon nanotubes with superior conductivity mainly include: the preparation of single-walled carbon nanotubes with predominantly metallic / semiconductor properties through catalyst design combined with in-situ selective etching (Reference 1, Liu Z., Qian L., Zhang J., Journal of the American Chemical Society, 2025, 147, 32752; Reference 2, Li X.; Zhang F.; Liu C. et al.; ACS Nano, 2022, 16, 232; Reference 3, Zhang F.; Hou P.X.; Liu C. et al.; Journal of Materials Science & Technology, 2020, 54, 105; Reference 4, Zhang, LL; Sun, DM; Liu, C. et al.; Advanced Materials, 2017, 29, 32; Reference 5, Zhang F.; Hou PX; Liu C. et al.; Nature Communication, 2016, 7, 11160).

[0004] Significant progress has been made in the controllable fabrication of single-walled carbon nanotubes with a single conductive property, particularly semiconducting ones. However, the following problems and challenges still exist in the controlled fabrication of single-walled carbon nanotubes with a single conductive property: (1) The generation energy and reactivity of metallic and semiconducting single-walled carbon nanotubes are very similar, and the dosage of vapor phase etchants such as hydrogen, oxygen, water, alcohol or ketones carrying hydrogen, oxygen or hydroxyl radicals is relatively high in the traditional chemical vapor deposition process (1 sccm H2 = 2.46 × 10⁻⁶). 20 (atoms / min), with poor etching selectivity for metallic / semiconductor single-walled carbon nanotubes; (2) Even slight changes in the size, composition, structure and density of oxygen-containing catalysts and powder supports carrying O can cause significant changes in the O content in the growth environment, affecting the purity of single-walled carbon nanotube products with single conductive properties. (3) It has been found that the diameter of single-walled carbon nanotubes in hexagonal single-crystal substrates is mainly controlled by the size of the catalyst, and an etchant is still required to control the conductivity. However, the effect of the lattice oxygen vacancy concentration of single-crystal planar substrates on the control of conductivity has not been reported.

[0005] Therefore, there is an urgent need to develop a simple, efficient, stable and reproducible technique for growing single-walled carbon nanotubes with a single conductive property in order to promote their application in the field of nanoelectronic devices. Summary of the Invention

[0006] The purpose of this invention is to provide a method for growing single-walled carbon nanotubes with a single conductive property by releasing oxygen from the substrate lattice. This method controls the conductivity of single-walled carbon nanotubes by selecting the crystal plane index and oxygen content of the same oxide single-crystal substrate and utilizing the difference in lattice oxygen vacancy concentration.

[0007] This invention relates to the field of controlled growth of single-walled carbon nanotubes (SHUs) with controlled conductivity properties, specifically a method for growing high-purity SHUs with a single conductive property by controlling the lattice oxygen vacancy concentration on a specific crystal plane of a substrate. The method selects a face-centered cubic (FCC) single-crystal substrate with exposed crystal planes of (110) or (100). Using atmospheric pressure chemical vapor deposition (CVD), SHUs with metallic dominance are prepared on the oxygen-depleted (110) plane, while those with semiconductor dominance are prepared on the oxygen-rich (100) plane. This invention achieves controllable preparation of SHUs with a single conductive property by selecting substrate crystal planes with different lattice oxygen contents and controlling their lattice oxygen release, laying a material foundation for the development of carbon nanotube-based nanoelectronic devices.

[0008] The technical solution of this invention is: A method for growing single-walled carbon nanotubes with a single conductive property by controlling the oxygen release of the substrate lattice is characterized by: screening a face-centered cubic oxide single-crystal substrate with an exposed surface that is an oxygen-depleted crystal plane (110) and / or an oxygen-rich crystal plane (100); controlling the crystal plane of the single-crystal substrate by heat treatment; then preparing a Co thin film on its surface; and growing single-walled carbon nanotubes on its surface by atmospheric pressure chemical vapor deposition.

[0009] (1) Substrate pretreatment: A face-centered cubic oxide single-crystal substrate with exposed (100) and / or (110) crystal planes, measuring 5~10 mm × 5~10 mm × 0.5~1 mm, is ultrasonically cleaned in water, acetone, and ethanol for 10~15 min respectively, and then dried. The substrate is then heat-treated at 880~930 ℃ (preferably 900-930 ℃, more preferably 910-930 ℃) for 2~5 h (preferably 2-4 h, more preferably 2-2.5 h) to obtain a two-dimensional planar single-crystal substrate suitable for the growth of single-walled carbon nanotubes. (2) Preparation of catalyst A Co metal thin film with a thickness of 0.1~0.2 nm was sputtered on the crystal surface of a substrate using an Ar ion beam coating instrument. The film was then oxidized in air for 30~40 min (preferably 30-38 min, more preferably 30-35 min) by heating the film in a furnace to 770~825 °C (preferably 770-810 °C, more preferably 770-800 °C), and then reduced with H2 for 1-5 min (preferably 1-3 min, more preferably 1-2 min) at 770~825 °C (preferably 770-810 °C, more preferably 770-800 °C) to obtain catalyst particles. (3) Growth of single-walled carbon nanotubes by chemical vapor deposition Single-walled carbon nanotubes were grown at 765-785 °C (preferably 770-810 °C, more preferably 770-800 °C) using 5-15 sccm (preferably 5-12 sccm, more preferably 5-10 sccm) of argon gas loaded into ethanol (in an ice-water bath at 0 °C-4 °C) as a carbon source, while 0.05-0.5 sccm of H2 (preferably 0.05-0.2 sccm, more preferably 0.05-0.1 sccm) and 25-50 sccm of argon gas (preferably 25-40 sccm, more preferably 25-30 sccm) were introduced for 5-10 min.

[0010] The oxide single crystal is spinel MgAl2O4.

[0011] The diameter of metallic single-walled carbon nanotubes ranges from 1.1 ± 0.3 nm, and the length ranges from 5 to 7 μm; the diameter of semiconducting single-walled carbon nanotubes ranges from 1.7 ± 0.3 nm, and the length ranges from 10 to 15 μm.

[0012] Choose the oxygen-depleted (110) and / or oxygen-enriched (100) sides of the face-centered cubic matrix as the growth substrate; Controlled growth can be achieved by selectively inhibiting or promoting the growth kinetics of metallic / semiconductor single-walled carbon nanotubes.

[0013] Metallic single-walled carbon nanotubes with a purity higher than 92.5% are preferentially grown on the oxygen-deficient (110) facet; semiconducting single-walled carbon nanotubes with a purity higher than 91.5% are preferentially grown on the oxygen-rich (100) facet.

[0014] The design concept of this invention is: By taking advantage of the difference in chemical interaction between metallic and semiconductor single-walled carbon nanotubes and oxygen, different lattice oxygen vacancies, such as (100) and (110) crystal planes, are provided on the crystal planes of FCC oxide single crystal substrates with fixed geometric dimensions. The release of lattice O differs under high-temperature heat treatment in a reducing atmosphere, thereby selectively controlling the growth of single-walled carbon nanotubes with a single conductive property.

[0015] This method screens face-centered cubic oxide single-crystal substrates, exposing the (110) and (100) planes. Using atmospheric pressure chemical vapor deposition, metallic-dominant single-walled carbon nanotubes are prepared using the oxygen-depleted (110) plane, while semiconductor-dominant single-walled carbon nanotubes are prepared using the oxygen-rich (100) plane. This invention achieves controllable fabrication of single-walled carbon nanotubes with a single conductive property by selecting substrate crystal planes with different oxygen contents and controlling the release of oxygen from their lattice, laying a material foundation for the development of carbon nanotube-based nanoelectronic devices.

[0016] The advantages and beneficial effects of this invention are: (1) The present invention selects a single crystal substrate with a high melting point, face-centered cubic structure, and exposed (100) and (110) crystal planes. The crystallinity and atomic order of the substrate are controlled by air heat treatment (880~930 ℃, 2~5 h). Then, the single-walled carbon nanotubes enriched with metallicity and semiconductority are directly grown on the single crystal substrate by atmospheric pressure chemical vapor deposition, laying the material foundation for the application of carbon nanotubes in carbon-based chips.

[0017] (2) The present invention mainly utilizes the single crystal substrate, which has high repeatability and reliability, and avoids the inhomogeneity of conductivity properties caused by the slight differences in size, composition, structure and density of nano-sized catalysts and powder supports.

[0018] (3) This invention achieves selective etching or inhibition of the growth of single-walled carbon nanotubes with certain conductive properties by quantitatively or tracely releasing lattice oxygen on the substrate crystal plane, which has high selectivity. This method maintains the integrity of the intrinsic structure of carbon nanotubes and avoids the low selectivity and damage to the tube wall structure caused by introducing a high concentration of etchant during chemical vapor deposition growth, providing a new idea for controlling the conductive properties of single-walled carbon nanotubes. Attached Figure Description

[0019] Figure 1Schematic diagram of the surface atomic structure of the substrate: (a) (100) and (b) (110) crystal planes.

[0020] Figure 2 Atomic force microscopy, backscattered electron imaging, and X-ray diffraction of the substrate after air heat treatment at 930℃ for 2 h: (ac) (100) plane; (df) (110) plane.

[0021] Figure 3 Characterization of lattice oxygen content before and after substrate growth: (a) Fine photoelectron spectroscopy of O 1s on the depth-sputtered (100) plane; (b) and (c) fine photoelectron spectroscopy peak division of O 1s on the (100) and (110) planes; (de) O content before and after growth on the (100) and (110) planes. n- SIMS anion characterization and its integrated area; (f) XPS and SIMS characterization of the decrease in O content before and after growth of (100) and (110) surfaces.

[0022] Figure 4 (100) Single-walled carbon nanotubes grown on a spinel substrate: (a) typical scanning electron microscope image; (b) atomic force microscope image; breathing modes of multi-wavelength Raman spectra: excitation wavelengths of (c) 633 nm, (d) 532 nm and (e) 785 nm; (f) D and G modes of Raman spectra excited by a 633 nm laser, with the abscissa being the Raman shift (cm). -1 The vertical axis represents relative intensity (au).

[0023] Figure 5 (110) Single-walled carbon nanotubes grown on a spinel substrate: (a) typical scanning electron microscope image; (b) atomic force microscope image; multi-wavelength Raman spectral breathing modes: excitation wavelengths of (c) 633 nm, (d) 532 nm and (e) 785 nm; (f) D and G modes of Raman spectrum excited by 633 nm laser, with the abscissa being Raman shift (cm-1) and the ordinate being relative intensity (au).

[0024] Figure 6 (111) Schematic diagram of the atomic structure of the substrate crystal plane (a); atomic force microscopy image (b), backscattered electron imaging and (d) X-ray diffraction of the substrate after air heat treatment at 930℃ for 2 h.

[0025] Figure 7 (111) Characterization of lattice oxygen content before and after surface growth: (a) Fine peak division of photoelectron energy spectrum of O 1s; (b) O n- (c) SIMS anion characterization and its integral area; (d) Decrease in O content characterized by XPS and SIMS.

[0026] Figure 8 (111) Single-walled carbon nanotubes grown on a spinel substrate: (a) Scanning electron microscope image; (b) Atomic force microscope image; Multi-wavelength Raman spectroscopy: breathing modes with excitation wavelengths of (c) 633 nm and (d) 532 nm.

[0027] Figure 9 (a) Statistical diagram of electrical conductivity of single-walled carbon nanotubes grown on face-centered cubic low-index crystal planes; (b) Statistical diagram of chirality of single-walled carbon nanotubes grown on (100) and (110) planes; (c) Statistical diagram of chirality angle of single-walled carbon nanotubes grown on (100) and (110) planes; (d) Binding energy of O in single-walled carbon nanotubes with different chirality grown on (100) and (110) planes. Detailed Implementation

[0028] In the specific implementation process, the present invention uses a single crystal with exposed face-centered cubic (100) and (110) crystal planes as the substrate, and the surface atomic structure schematic diagram is shown below. Figure 1 As shown, atomically ordered crystal planes were obtained by heat treatment at 880–930 °C for 2–5 h under a specific atmosphere. Catalyst nanoparticles were then prepared on their surfaces, and single-walled carbon nanotubes with single conductive properties were grown by controlling the lattice oxygen vacancy concentration on different substrate crystal planes using chemical vapor deposition.

[0029] The method for growing single-walled carbon nanotubes with a single conductive property through substrate lattice oxygen release according to the present invention comprises the following steps: (1) Pretreatment of spinel substrate: Using the (100) and (110) crystal planes of face-centered cubic oxide single crystal MgAl2O4 with exposed (100) and (110) crystal planes as a substrate, with dimensions of ~5 mm × ~5 mm × ~0.5 mm, one side was polished and ultrasonically cleaned in deionized water, acetone, and ethanol for 10-15 min respectively, and then dried with a nitrogen gun. The substrate was placed in a quartz boat and pushed into a tube furnace, and heat-treated at 880-930 ℃ for 2-5 h to obtain a two-dimensional planar single crystal substrate suitable for the growth of single-walled carbon nanotubes.

[0030] (2) Preparation of catalyst Catalyst nanoparticles were prepared by sputtering a Co metal thin film with a thickness of 0.1~0.2 nm onto the substrate crystal surface using an Ar ion beam deposition apparatus, followed by oxidation at 770~825 ℃ for 30~40 min and reduction with H2 at 770~825 ℃ for 1~5 min.

[0031] (3) Growth of single-walled carbon nanotubes by chemical vapor deposition Single-walled carbon nanotubes were grown at 765–785 °C, using 5–15 sccm of argon gas (by bubbling) loaded with ethanol (in a 0 °C ice-water bath) as the carbon source, while simultaneously introducing 0.05–0.5 sccm of H2 and 25–50 sccm of argon gas, with the total gas flow rate maintained at 30.1–65.5 sccm. The growth time was 5–10 min.

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention is described in detail below with reference to embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0033] Example 1 In this embodiment, a method for growing single-walled carbon nanotubes with a single conductive property through substrate lattice oxygen release includes the following specific steps: (1) The (100) and (110) crystal planes of face-centered cubic oxide single crystal MgAl2O4 were selected as the substrate, with a size of ~5mm×~5mm×~0.5mm. The substrate was polished on one side and cut with

[110] as one of the positioning edges. The single crystal was produced by Hefei Kejing Materials Technology Co., Ltd. and the single crystal preparation method was CZ Czochralski method. The substrate was ultrasonically cleaned in 8 ml of deionized water, acetone and ethanol for 12 min respectively, and dried with nitrogen gun. The substrate was placed in a quartz boat and pushed into a tube furnace for pretreatment. The heat treatment temperature was 930 ℃ and the heat treatment time was 2 h. The heat treatment atmosphere was air. The substrate was cooled to room temperature and taken out. The atomic force microscope image, backscattered electron image and X-ray electron diffraction pattern of the substrate after heat treatment are as follows. Figure 2 As shown, its surface has a uniform, long-range ordered periodic structure, making it a suitable two-dimensional single-crystal substrate surface for the growth of single-walled carbon nanotubes.

[0034] (2) A 0.1 nm Co metal thin film was sputtered on the crystal surface of the substrate using an Ar ion beam coating instrument. The catalyst nanoparticles were prepared by sequentially heating the furnace to 770 °C and oxidizing in air for 30 min, followed by H2 reduction at 770 °C for 1 min. The particle size range was 2.1~3.0 nm.

[0035] (3) At 770 °C, ethanol was loaded with 5 sccm of argon gas (in a 0 °C ice-water bath, argon gas was introduced below the surface of the ethanol liquid in the container containing ethanol, and ethanol was carried by bubbling) as a carbon source, and 0.1 sccm of H2 and 25 sccm of argon gas were introduced simultaneously for single-walled carbon nanotube growth. The growth time was 5 min. XPS characterization was performed on the (100) facet before and after growth by depth sputtering. Figure 3a) It can be seen that before growth (the substrate obtained by heat treatment in step (1)), the peak position of O1s remains consistent at different sputtering depths, representing lattice O; while after growth (the product obtained in step (3)), the peak position of O clearly shifts towards higher binding energy, i.e., surface adsorbed O in the reduced state, and with the increase of sputtering depth, the peak position gradually tends towards the peak position of lattice O before growth; indicating that there is lattice O release on the substrate surface during growth, generating O vacancies. The fine spectrum of O1s at a depth of ~10 nm before and after growth of the low index crystal plane is peaked, with ~530 eV representing lattice O and ~532 eV representing surface adsorbed O. From Figure 3 As can be seen from bc, the lattice O of different crystal planes decreases to varying degrees after carbon nanotube growth, with the decrease being (100)(29%) > (110)(3%). Figure 3 bc and Figure 3 f). SIMS was used to characterize the surface atoms of a low-index crystal plane at a depth of 1 nm. n- Calculate O by integrating the area n- This indicates that O n- The decrease was (100)(57%) > (110)(10%). Figure 3 This result qualitatively reflects that the ability of the (100) surface atoms to release lattice O is greater than that of (110).

[0036] Scanning electron microscope (SEM) and atomic force microscope (AFM) images of single-walled carbon nanotubes grown on the (100) surface are shown below. Figure 4 As shown in Figure ab, the length is 10–15 μm and the diameter is 1.7 ± 0.3 nm. The electrical conductivity of the grown single-walled carbon nanotubes was characterized using multi-wavelength Raman spectroscopy. Figure 4 Ce yielded respiratory mode peaks excited at wavelengths of 633 nm, 532 nm, and 785 nm. The respiratory mode peak at 633 nm was concentrated in the range of 121–164 cm⁻¹. -1 The 532 nm respiratory peak is mainly concentrated in the 142~174 cm⁻¹ range. -1 The peak intensity is relatively high; there is no excitation signal in the breathing mode at 785 nm; it can be seen that most of the excited breathing modes are located in the semiconductor region. Using the Kataura diagram to classify their conductivity properties, the number of breathing mode peaks of semiconducting single-walled carbon nanotubes was counted, and ~90% were located in the semiconducting region. Further analysis of the conductivity properties of single-walled carbon nanotubes in the 1200~1800 cm⁻¹ range... -1 Raman spectra within the range ( Figure 4 f) Analysis showed that the G-mode is a typical Lorentz linear form of high-purity semiconducting single-walled carbon nanotubes; and I G / I D =20, which reflects the high crystallinity of single-walled carbon nanotubes.

[0037] (110) Scanning electron microscope and atomic force microscope images of single-walled carbon nanotubes grown on the surface are shown in Figure 110. Figure 5 As shown in Figure ab, the length of the single-walled carbon nanotubes is 5–7 μm, and the diameter is 1.1 ± 0.3 nm. The electrical conductivity of the grown single-walled carbon nanotubes was characterized using multi-wavelength Raman spectroscopy. Figure 5 The ce spectrum is a typical three-wavelength respiratory mode spectrum, where no respiratory mode signal was excited at 633 nm and 785 nm; the respiratory mode peak at 532 nm is mainly concentrated in the 225-240 cm⁻¹ range. -1 Furthermore, the peak intensity is high, indicating that most of the breathing mode peaks of the excited carbon nanotubes are located in the metallic region. Using the Kataura diagram to classify its conductivity, approximately 94% of the breathing mode peaks of the three-wavelength Raman spectroscopy are located in the metallic region, indicating that the sample is enriched with metallic carbon nanotubes. In addition, the conductivity of the sample can also be determined using the shape of the Raman G peak, such as... Figure 5 f represents the carbon nanotube density in the 1200-1800 cm⁻¹ range. -1 Typical Raman spectra within the range. The visible G-mode splits at 1601 cm⁻¹. -1 G + Peak and 1556 cm -1 G - The peak is a typical BWF-type peak of metallic carbon nanotubes, which further verifies the high content of metallic carbon nanotubes in the sample.

[0038] In summary, semiconducting single-walled carbon nanotubes with a purity of ~92.5% were prepared on the FCC (1 0 0) oxygen-rich crystal plane, and metallic single-walled carbon nanotubes with a purity of ~93.5% were prepared on the (110) oxygen-poor crystal plane.

[0039] Example 2: Growth of semiconducting / metallic single-walled carbon nanotubes in LaAlO3 (100) and (110) 1) The (100) and (110) crystal planes of face-centered cubic oxide single crystal LaAlO3 were selected as the substrate, with a size of ~5mm × ~5mm × ~0.5mm. The substrate was polished on one side and cut with

[110] as one of the positioning edges. The single crystal was produced by Hefei Kejing Materials Technology Co., Ltd. and the single crystal preparation method was Czochralski method. The substrate was ultrasonically cleaned in 10 ml of deionized water, acetone and ethanol for 12 min respectively, and dried with nitrogen gun. The substrate was placed in a quartz boat and pushed into a tube furnace for pretreatment. The heat treatment temperature was 930 ℃ and the heat treatment time was 2 h. The heat treatment atmosphere was air.

[0040] The process and conditions are the same as steps (2) and (3) of Example 1, except that: single-walled carbon nanotubes are oxidized, reduced, and grown under the same CVD conditions at 775 °C. The single-walled carbon nanotubes grown on the (100) surface are semiconductor single-walled carbon nanotubes with a length of 11~16 μm, a diameter of 1.7±0.4 nm, and a purity of ~92%. The single-walled carbon nanotubes grown on the (110) surface are metallic single-walled carbon nanotubes with a length of 6~8 μm, a diameter of 1.1±0.4 nm, and a purity of ~93%.

[0041] Comparative Example 1: (1 1 1) Faceted growth of metallic / semiconductor hybrid single-walled carbon nanotubes The process and conditions are the same as in Example 1, except that: (1) Using face-centered cubic oxide single crystal MgAl2O4 (111) as the substrate, its surface atomic structure is shown in the schematic diagram below. Figure 6 As shown in a. The dimensions are ~5 mm × ~5 mm × ~0.5 mm, single-sided polished, and cut with

[110] as one of the positioning edges. The single crystal is produced by Hefei Kejing Materials Technology Co., Ltd., and the single crystal preparation method is CZ Czochralski method. It is ultrasonically cleaned in deionized water, acetone and ethanol for 12 min respectively, and dried with nitrogen gun. The substrate is placed in a quartz boat and pushed into a tube furnace. It is pretreated by the above specific preparation steps (1). The heat treatment temperature is 930 ℃, the heat treatment time is 2 h, the heat treatment atmosphere is air, and it is cooled to room temperature and taken out. The atomic force microscope image, backscattered electron image and X-ray electron diffraction pattern of the substrate after heat treatment are shown in the figure. Figure 6 As shown in bd, its surface has a uniform, long-range ordered periodic structure, which is a two-dimensional single-crystal substrate surface suitable for the growth of single-walled carbon nanotubes.

[0042] The O1s fine spectrum at a depth of ~10 nm before and after growth of the (111) crystal plane was peaked, with ~530 eV representing lattice O and ~532 eV representing surface adsorbed O. From Figure 7 As can be seen from a, the O lattice size decreases by 10% after carbon nanotube growth, falling between (100) and (110). SIMS was used to characterize the O atoms of the surface atoms at a depth of 1 nm on low-index crystal planes. n- ( Figure 7 b) Calculate O by integrating the area n- ( Figure 7 c), indicating O n- The decrease was 35%. Figure 7 d), which is between (100) and (110). This result can qualitatively reflect that the ability of the lattice O of the surface atoms of (111) is greater than that of (110) but less than that of (100).

[0043] The process and conditions are the same as steps (2) and (3) of Example 1, except that: single-walled carbon nanotubes are oxidized, reduced, and grown under the same CVD conditions at 775 °C, and the single-walled carbon nanotubes grown on the (111) surface form a near-disordered network. Figure 8 (ab) The length is 15~20 μm and the diameter is 1.0~2.4 nm. Unlike the narrow respiratory peak distribution of single-walled carbon nanotubes grown on (100) and (110), the respiratory peak distribution of single-walled carbon nanotubes grown on (111) facet is wider; the respiratory peak at 633 nm is located in the range of 105~220 cm. -1 ( Figure 8 c), the 532 nm respiratory peak is located in the 105–215 cm⁻¹ range. -1 ( Figure 8 d). The above results indicate that the lattice oxygen vacancies released on the (111) face have little effect on the growth of single-walled carbon nanotubes, and the prepared single-walled carbon nanotubes do not exhibit selectivity in conductivity properties.

[0044] Comparative Example 2: SiO x Hybrid metallic / semiconductor carbon nanotubes grown on Si substrates (1) Select amorphous SiO2 with a surface thickness of ~300 nm. x The substrate is silicon-on-insulator (SOI), produced by Hefei Kejing Materials Technology Co., Ltd. The substrate is prepared by depositing a layer of SiO2 on the Si(100) crystal plane. x The film dimensions were ~5 mm × ~5 mm × ~0.5 mm, and it was polished on one side. It was ultrasonically cleaned sequentially in deionized water, acetone, and ethanol for 12 min each, and then dried with a nitrogen gun. The substrate was placed in a quartz boat and pushed into a tube furnace for pretreatment. The heat treatment temperature was 930 ℃, the heat treatment time was 2 h, and the heat treatment atmosphere was air. After cooling to room temperature, it was removed.

[0045] The process and conditions are the same as steps (2) and (3) in Example 1, except that: single-walled carbon nanotubes are oxidized, reduced, and grown under the same CVD conditions at 775 °C, with a length of 30~50 μm and a diameter of 0.8~3 nm. The prepared single-walled carbon nanotubes have 1 / 3 metallic properties and 2 / 3 semiconductor properties. Unlike single crystals (100) and (110), since the substrate surface is not single crystal, the concentration and rate of oxygen vacancy release are uncontrollable, which will have a non-selective effect on the metallic / semiconductor single-walled carbon nanotubes and cannot regulate the conductivity properties.

[0046] The examples and comparative examples illustrate that, in this invention, the (100) and (110) exposed surfaces of a face-centered cubic structure are selected as substrates. By controlling the release of lattice oxygen vacancy concentration, semiconducting single-walled carbon nanotubes with a purity of 91% are prepared on the oxygen-rich (100) surface, and metallic single-walled carbon nanotubes with a purity of 91% are prepared on the oxygen-depleted (110) surface. Figure 9 a). According to the Kataura diagram, the chirality angle of the (100) plane semiconducting single-walled carbon nanotube is greater than that of the (110) plane metallic single-walled carbon nanotube. Figure 9 bc).

[0047] First-principles calculations revealed that the binding energy between the edge of chiral angular metallic carbon nanotubes and O is significantly higher than that of semiconducting carbon nanotubes. Figure 9 d). This indicates that, under kinetic conditions, the growth of metallic single-walled carbon nanotubes is inhibited on the oxygen-rich (100) surface, where O is more readily adsorbed than C at its edges, hindering the assembly and elongation of C1 and C2 on the metallic single-walled carbon nanotubes, thus resulting in the growth of high-purity semiconducting single-walled carbon nanotubes; while on the oxygen-depleted (110) surface, C is more readily assembled and grown on the metallic single-walled carbon nanotubes, leading to the growth of high-purity metallic single-walled carbon nanotubes on the oxygen-depleted surface. The conductivity properties of single-walled carbon nanotubes are thus regulated through trace oxygen release from the substrate.

[0048] This invention is the first to achieve direct control of the conductivity of single-walled carbon nanotubes by the concentration of oxygen vacancies in the substrate lattice, elucidating the control mechanism and laying the material foundation for the application of single-walled carbon nanotubes in integrated circuit channel materials.

Claims

1. A method for controlling the growth of single-walled carbon nanotubes with a single conductive property under substrate lattice oxygen release control, characterized in that: A face-centered cubic oxide single-crystal substrate was selected, with the exposed surface being an oxygen-depleted crystal plane (110) and / or an oxygen-rich crystal plane (100). The crystal plane of the single-crystal substrate was controlled by heat treatment, and then a Co thin film was prepared on its surface. Single-walled carbon nanotubes were grown on its surface by atmospheric pressure chemical vapor deposition.

2. The method according to claim 1, characterized in that: (1) Substrate pretreatment: A face-centered cubic oxide single-crystal substrate with exposed (100) and / or (110) crystal planes, measuring 5~10 mm × 5~10 mm × 0.5~1 mm, is ultrasonically cleaned in water, acetone, and ethanol for 10~15 min respectively, and then dried. The substrate is then heat-treated at 880~930℃ (preferably 900-930℃, more preferably 910-930℃) for 2~5 h (preferably 2-4 h, more preferably 2-2.5 h) to obtain a two-dimensional planar single-crystal substrate suitable for the growth of single-walled carbon nanotubes. (2) Preparation of catalyst A Co metal thin film with a thickness of 0.1~0.2 nm was sputtered on the crystal surface of a substrate using an Ar ion beam coating instrument. The film was then oxidized in air for 30~40 min (preferably 30-38 min, more preferably 30-35 min) by heating the film in a furnace to 770~825 °C (preferably 770-810 °C, more preferably 770-800 °C), and then reduced with H2 for 1-5 min (preferably 1-3 min, more preferably 1-2 min) at 770~825 °C (preferably 770-810 °C, more preferably 770-800 °C) to obtain catalyst particles. (3) Growth of single-walled carbon nanotubes by chemical vapor deposition Single-walled carbon nanotubes were grown at 765-785 °C (preferably 770-810 °C, more preferably 770-800 °C) using 5-15 sccm (preferably 5-12 sccm, more preferably 5-10 sccm) of argon gas loaded into ethanol (in an ice-water bath at 0 °C-4 °C) as a carbon source, while 0.05-0.5 sccm of H2 (preferably 0.05-0.2 sccm, more preferably 0.05-0.1 sccm) and 25-50 sccm of argon gas (preferably 25-40 sccm, more preferably 25-30 sccm) were introduced for 5-10 min.

3. The method according to claim 1 or 2, characterized in that: The oxide single crystal is spinel MgAl2O4.

4. The method according to claim 1 or 2, characterized in that: The diameter of metallic single-walled carbon nanotubes ranges from 1.1 ± 0.3 nm, and the length ranges from 5 to 7 μm; the diameter of semiconducting single-walled carbon nanotubes ranges from 1.7 ± 0.3 nm, and the length ranges from 10 to 15 μm.

5. The method according to claim 1 or 2, characterized in that: Choose the oxygen-depleted (110) and / or oxygen-enriched (100) sides of the face-centered cubic matrix as the growth substrate; Controlled growth can be achieved by selectively inhibiting or promoting the growth kinetics of metallic / semiconductor single-walled carbon nanotubes.

6. The method according to claim 1 or 2, characterized in that: Metallic single-walled carbon nanotubes with a purity higher than 92.5% are preferentially grown on the oxygen-deficient (110) facet; semiconducting single-walled carbon nanotubes with a purity higher than 91.5% are preferentially grown on the oxygen-rich (100) facet.

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