Method for preparing and transferring inclined chromic oxide single-crystal nanosheet
By growing tilted chromium oxide single-crystal nanosheets on SiO2/Si substrates and using a mechanical pressing transfer method, the performance damage caused by chemical solvents during nanosheet transfer was solved, achieving the preparation of high-quality nanosheets and pollution-free transfer, applicable to a variety of substrates.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF POSTS & TELECOMM
- Filing Date
- 2026-04-02
- Publication Date
- 2026-05-26
AI Technical Summary
The nanosheets prepared by existing vapor deposition methods require chemical solvents or polymers during the transfer process, which can damage the surface of the nanosheets and affect their performance.
A mixture of potassium chromate and chromium chloride was used as a precursor. Combined with molecular sieves and SiO2/Si substrates, tilted chromium oxide single-crystal nanosheets were grown in a vacuum tube furnace and transferred to other substrates by mechanical pressing, avoiding the use of chemical solvents.
The preparation and contamination-free transfer of high-quality chromium oxide single-crystal nanosheets were achieved, ensuring that the performance of the nanosheets was not compromised. The process was also low-cost, applicable to various substrates, and exhibited good controllability and repeatability.
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Figure CN122082115A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nanomaterials technology, specifically relating to a method for preparing and transferring tilted chromium oxide single-crystal nanosheets. Background Technology
[0002] Since the successful preparation of two-dimensional graphene via mechanical exfoliation, two-dimensional materials have rapidly become a hot topic in academic research. In recent years, many methods for preparing two-dimensional materials have been reported, including mechanical exfoliation, chemical vapor deposition, liquid-phase methods, and atomic layer deposition. Among two-dimensional materials, metal oxides have been extensively explored in the fields of electronics and optoelectronics due to their diverse crystal structures, wide band gaps, high environmental stability, and intrinsic p-type conductivity.
[0003] Among various oxide materials, vapor deposition, as a common method for growing single-crystal nanomaterials, has been used to grow a variety of metal oxides, such as Cr₂O₃, Mn₃O₄, ZrO₂, WO₂, MoO₃, and Bi₂O₃. Chromium oxide, as the main oxide of chromium, naturally exists in minerals and possesses excellent environmental stability, including high hardness, excellent thermal conductivity, thermal stability, chemical stability, high melting point, and corrosion resistance. Furthermore, chromium oxide has a high dielectric constant, which is crucial for the study of insulating layers. A high dielectric constant helps enhance the capacitance effect of field-effect transistors while reducing the electric field between the gate and the channel. The conductivity of chromium oxide can be tuned through doping, adapting it to various applications and achieving improved electron transport properties. Therefore, developing a method for preparing high-quality chromium oxide single-crystal nanosheets is particularly important for studying the potential properties of chromium oxide.
[0004] Currently, nanosheets deposited by vapor deposition on target substrates require chemical solvents or other polymers for transfer due to van der Waals epitaxy, which inevitably damages the surface of the nanosheets.
[0005] Therefore, it is essential to develop a transfer method that is free from the influence of chemical solvents and other factors, so as to ensure that the performance of such nanosheets is not affected. Summary of the Invention
[0006] The technical problem this invention aims to solve is to address the shortcomings of existing technologies. Based on the influence of the precursor chromium source during nanosheet preparation, differences in growth temperature, different substrates, the role of molecular sieves in the reaction process, and considering the feasibility of transfer to different substrates, this invention provides a method for preparing tilted chromium oxide single-crystal nanosheets and a corresponding polymer-free mechanical pressing and transfer method. This preparation method is low-cost, produces high-quality crystals, and the grown chromium oxide can be transferred to any substrate through simple mechanical pressing, providing a new approach for preparing nanosheets using vapor deposition.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] The first aspect of this invention provides a method for preparing and transferring tilted chromium oxide single-crystal nanosheets, comprising the following steps:
[0009] S1. Mix potassium chromate and chromium chloride evenly to obtain precursor powder;
[0010] S2. Transfer the precursor powder into a ceramic boat and simultaneously cover the surface of the precursor powder with molecular sieves;
[0011] S3. The SiO2 / Si substrate is tilted and covered on the molecular sieve with the oxide layer facing down; the ceramic boat is transferred to a vacuum tube furnace, heated and reacted, and after cooling, tilted chromium oxide single crystal nanosheets are prepared on the surface of the SiO2 / Si substrate.
[0012] S4. Place the tilted chromium oxide single crystal nanosheets prepared in S3 onto other clean substrates, and complete the transfer of chromium oxide single crystal nanosheets to other clean substrates by mechanical pressing.
[0013] In some embodiments of the present invention, in S1, the mass ratio of potassium chromate to chromium chloride is 3:1; both potassium chromate and chromium chloride are powders.
[0014] In some embodiments of the present invention, in S1, the potassium chromate and chromium chloride are mixed by grinding them in a mortar for 5 minutes.
[0015] In some embodiments of the present invention, in S2, the molecular sieve is a 4A type molecular sieve; the molecular sieve ensures that it can completely cover the surface of the precursor powder.
[0016] In some embodiments of the present invention, in S3, the size of the SiO2 / Si substrate is (2~4) cm × 1 cm.
[0017] In some embodiments of the present invention, in S3, the size of the SiO2 / Si substrate is 3 cm × 1 cm.
[0018] In some embodiments of the present invention, in S3, the heating reaction is carried out under the following process conditions: under an inert atmosphere, the heating rate is 25 °C / min, the temperature is raised to 730~760 °C, and held at the temperature for 15 min.
[0019] In some embodiments of the present invention, in S3, the heating reaction is carried out under the following process conditions: under an inert atmosphere, the heating rate is 25 °C / min, the temperature is raised to 760 °C, and held at the temperature for 15 min.
[0020] In some embodiments of the present invention, in S3, the inert atmosphere is provided by argon gas at a flow rate of 100 sccm.
[0021] In some embodiments of the present invention, in S3, air needs to be introduced into the furnace before the heating reaction, and the specific process conditions are: argon flow rate 600 sccm, and introduction time 5 min.
[0022] In some embodiments of the present invention, in S4, the clean substrate includes any one of SiO2 / Si substrate, sapphire substrate, quartz glass substrate and PDMS substrate.
[0023] A second aspect of the present invention provides a chromium oxide single-crystal nanosheet, which is prepared or transferred by the method provided in the first aspect of the present invention.
[0024] In some embodiments of the present invention, the chromium oxide single-crystal nanosheets are grown obliquely on the substrate surface or flattened and covered on the substrate surface by a mechanical transfer method of pressing.
[0025] In some embodiments of the present invention, tilted single-crystal chromium oxide nanosheets were successfully prepared on the surface of a SiO2 / Si substrate by the preparation method provided in the first aspect of the present invention. By characterizing their microstructure, it was demonstrated that the single-crystal chromium oxide nanosheets exhibit a tilted state on the surface of the SiO2 / Si substrate.
[0026] In some embodiments of the present invention, the preparation method provided in the first aspect of the present invention further transfers the single-crystal chromium oxide nanosheets with an inclined state on the surface of the SiO2 / Si substrate to other clean substrates by mechanical pressing. By characterizing their microstructure, it is demonstrated that flat chromium oxide nanosheets were successfully prepared on different clean substrates.
[0027] Beneficial effects:
[0028] This invention discloses a method for preparing and transferring tilted chromium oxide single-crystal nanosheets. By controlling the influence of the precursor chromium source, differences in growth temperature, different substrates, the role of molecular sieves in the reaction process, and considering the feasibility of transfer to different substrates, a method for preparing tilted chromium oxide single-crystal nanosheets is proposed. This method is low-cost, produces high-quality crystals, and the grown chromium oxide can be transferred to any substrate by simple mechanical pressing. This invention can prepare ultrathin, large-size tilted chromium oxide nanosheets with dimensions of 3-36 μm and thicknesses of 4.9-40 nm. Furthermore, it allows for easy, contamination-free transfer to various substrates via polymer-free mechanical pressing, ensuring that the transferred samples have atomically flat planes. The provided method offers advantages such as good controllability, high repeatability, high yield, low cost, and contamination-free transfer. Attached Figure Description
[0029] The present invention will be further described in detail below with reference to the accompanying drawings, and the advantages of the present invention in the above and / or other aspects will become clearer.
[0030] Figure 1 This is a schematic diagram of the preparation process of tilted chromium oxide single-crystal nanosheets provided in Example 1 of the present invention.
[0031] Figure 2 These are optical microscope images and scanning electron microscope images of the tilted-grown single-crystal chromium oxide nanosheets in Example 1 of the present invention.
[0032] Figure 3 The images show transmission electron microscopy (TEM) images and elemental mapping diagrams of the tilted-grown single-crystal chromium oxide nanosheets in Example 1 of this invention.
[0033] Figure 4 This is the elemental energy spectrum of the tilted-grown single-crystal chromium oxide nanosheets in Example 1 of the present invention.
[0034] Figure 5 The images show a high-magnification transmission electron microscope image and a selected area electron diffraction pattern of the tilted-grown single-crystal chromium oxide nanosheets in Example 1 of this invention.
[0035] Figure 6 This is a schematic diagram of the transfer process of tilted chromium oxide single-crystal nanosheets provided in Embodiment 2 of the present invention.
[0036] Figure 7 These are optical microscope images and scanning electron microscope images of chromium oxide nanosheets on different clean substrates in Example 2 of the present invention.
[0037] Figure 8 These are optical microscope images of chromium oxide nanosheets grown at different temperatures on the same clean substrate in Example 3 of the present invention.
[0038] Figure 9 These are optical microscope images and atomic force microscope images of chromium oxide nanosheets of different thicknesses on the same clean substrate in Example 3 of the present invention.
[0039] Figure 10 These are optical microscope images of tilted-grown single-crystal chromium oxide nanosheets constructed with and without molecular sieves in Comparative Example 1 of this invention.
[0040] Figure 11 This is an optical microscope image of the tilted-grown single-crystal chromium oxide nanosheets constructed at a growth temperature of 780 °C in Comparative Example 2 of this invention. Detailed Implementation
[0041] The present invention will be further described in detail below with reference to specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.
[0042] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.
[0043] Example 1:
[0044] This embodiment provides a method for preparing tilted chromium oxide single-crystal nanosheets. Figure 1 This is a schematic diagram of the preparation process of the tilted chromium oxide single-crystal nanosheets provided in this embodiment. The specific preparation steps are as follows:
[0045] 90 mg of potassium chromate powder and 30 mg of chromium chloride powder were mixed and ground in a mortar for 5 min to obtain a uniformly mixed precursor powder. The precursor powder was placed in a ceramic boat, and a type 4A molecular sieve was used to cover the surface of the precursor powder. The SiO2 / Si substrate was cut into 3 cm × 1 cm pieces, with the oxide layer of the cut SiO2 / Si substrate facing down, and supported on the molecular sieve at an angle to the bottom of the molecular sieve / ceramic boat. The ceramic boat was then placed in the central temperature zone of a tube furnace and purged with argon gas at a flow rate of 600 sccm for 5 min to remove residual air from the tube. Subsequently, 100 sccm of argon gas was introduced, and the temperature was raised to 750 °C at a heating rate of 25 °C / min and held at that temperature for 15 min. After heating, the sample was allowed to cool naturally to room temperature, and the grown sample was removed. At this point, a tilted-grown single-crystal chromium oxide nanosheet was prepared on the surface of the SiO2 / Si substrate.
[0046] The microstructure of single-crystal chromium oxide nanosheets grown at an angle on a SiO2 / Si substrate was characterized. Figure 2 Optical microscope images and cross-sectional scanning electron microscope images of tilted-grown single-crystal chromium oxide nanosheets, by Figure 2As can be seen, this embodiment successfully generated tilted-grown chromium oxide single-crystal nanosheets on a SiO2 / Si substrate. Dispersed sheet-like / polygonal nanosheets formed on the SiO2 / Si substrate surface, with relatively clear edges and micrometer-scale dimensions. Scanning electron microscopy further showed that there was a significant angle between the sheets and the substrate, indicating that the obtained product was tilted-grown chromium oxide nanosheets.
[0047] Figure 3 Transmission electron microscope images and elemental mapping diagrams of tilted-grown single-crystal chromium oxide nanosheets. Figure 4 The elemental energy spectrum of tilted-grown single-crystal chromium oxide nanosheets is shown by [the following]. Figure 3 and Figure 4 As can be seen, the nanosheets have straight edges and uniform contrast in the transmission electron microscope image; the Cr and O element mapping is uniformly distributed throughout the entire sheet, and the characteristic peaks of Cr and O can be seen in the elemental energy spectrum, indicating that the obtained nanosheets are mainly composed of Cr and O elements, and no obvious elemental segregation is observed.
[0048] Figure 5 High-magnification transmission electron microscope (TEM) image and selected area electron diffraction (SAD) pattern of tilted-grown single-crystal chromium oxide nanosheets, by Figure 5 As can be seen, clear and continuous lattice fringes can be observed in the high-resolution transmission electron microscope, with a crystal plane spacing of about 0.25 nm, corresponding to the (110) crystal plane; selected area electron diffraction shows regular dot-shaped diffraction spots, indicating that the obtained chromium oxide nanosheets have a good single crystal structure.
[0049] Example 2:
[0050] Building upon the successful fabrication of tilted-grown single-crystal chromium oxide nanosheets on a SiO2 / Si substrate in Example 1, this example further provides a method for transferring single-crystal chromium oxide nanosheets. Figure 6 This is a schematic diagram of the transfer process for the tilted chromium oxide single-crystal nanosheets provided in this embodiment. The specific transfer steps are as follows:
[0051] SiO2 / Si substrate, sapphire substrate, quartz glass substrate, and PDMS substrate were taken separately. The SiO2 / Si substrate, sapphire substrate, and quartz glass substrate were ultrasonically cleaned in acetone solution for 10 minutes, followed by ultrasonic cleaning in alcohol solution for 10 minutes, and finally dried with a nitrogen gun to obtain clean substrates. The PDMS substrate was directly selected from freshly cut substrates, which were also considered clean substrates at this stage.
[0052] The substrate with tilted nanosheets obtained in Example 1 was placed on a prepared clean substrate, and the back side of the substrate with tilted nanosheets was pressed firmly with a cotton swab for 5-10 seconds. Finally, chromium oxide nanosheets with smooth surfaces were obtained on different clean substrates.
[0053] The chromium oxide nanosheets transferred onto different clean substrates were characterized. Figure 7 Optical microscope and scanning electron microscope images of chromium oxide nanosheets on different clean substrates, by Figure 7 As can be seen, this embodiment successfully prepared flat chromium oxide nanosheets on different clean substrates.
[0054] Example 3:
[0055] This embodiment provides a method for preparing and transferring tilted chromium oxide single-crystal nanosheets, the specific steps of which are as follows:
[0056] 90 mg of potassium chromate powder and 30 mg of chromium chloride powder were mixed and ground in a mortar for 5 min to obtain a uniformly mixed precursor powder. The precursor powder was placed in a ceramic boat and covered with a type 4A molecular sieve. The SiO2 / Si substrate was cut into 3 cm × 1 cm pieces, with the oxide layer of the cut SiO2 / Si substrate facing down, and tilted over the molecular sieve. The ceramic boat was then placed in the central temperature zone of a tube furnace and purged with argon gas at a flow rate of 600 sccm for 5 min to remove residual air from the tube. Subsequently, 100 sccm of argon gas was introduced, and the temperature was raised to 730 ℃, 740 ℃, 750 ℃, and 760 ℃ at a heating rate of 25 ℃ / min, respectively, and held at the temperature for 15 min. After heating, the samples were allowed to cool naturally to room temperature, and the grown samples were removed. At this point, single-crystal chromium oxide nanosheets grown at different growth temperatures were obtained on the surface of the SiO2 / Si substrate.
[0057] The substrate with the tilted nanosheets was placed on the prepared SiO2 / Si substrate, and the back side of the substrate with the tilted nanosheets was pressed firmly with a cotton swab for 5-10 seconds. Finally, chromium oxide nanosheets with a smooth surface were obtained on the clean substrate.
[0058] Chromium oxide nanosheets grown at different temperatures on clean substrates were characterized. Figure 8 Optical microscope images and scanning electron microscope images of chromium oxide nanosheets grown at different temperatures on the same clean substrate, by Figure 8 It can be seen that the transverse dimensions show a significant changing trend with increasing growth temperature. Figure 8 In the image, a and e are optical microscope images and scanning electron microscope images of chromium oxide nanosheets grown at 730 °C, respectively. When the temperature is maintained at about 730 °C, nanosheets with smaller lateral dimensions (about 3~7 μm) can be obtained. Figure 8b and f in the image are optical microscope and scanning electron microscope images of chromium oxide nanosheets grown at 740 °C, respectively. When the growth temperature is increased to 740 °C, the lateral size increases from about 5 μm to 13 μm. Figure 8 c and g in the image are optical microscope and scanning electron microscope images of chromium oxide nanosheets grown at 750 °C, respectively. When the growth temperature is further increased to about 750 °C, the nanosheets mainly exhibit larger lateral dimensions (about 8~20 μm). Figure 8 In the image, d and h are optical microscope and scanning electron microscope images of chromium oxide nanosheets grown at 760 °C, respectively. When the growth temperature is further increased to 760 °C, the lateral size increases from about 16 μm to 36 μm. Figure 9 These are optical microscope images and atomic force microscope images of chromium oxide nanosheets of different thicknesses on SiO2 / Si substrates, ranging from approximately 4.9 nm to 40 nm.
[0059] Comparative Example 1:
[0060] This comparative example follows the preparation method of Example 1, preparing tilted-grown single-crystal chromium oxide nanosheets on the surface of a SiO2 / Si substrate. The difference is that this comparative example does not use a 4A molecular sieve, but directly tilts the oxide layer of the SiO2 / Si substrate downwards onto the precursor powder, while the other preparation steps remain unchanged.
[0061] The tilted-grown single-crystal chromium oxide nanosheets constructed in this comparative example were characterized. Figure 10 Optical microscope images of tilted-grown single-crystal chromium oxide nanosheets with and without molecular sieves, wherein... Figure 10 In this context, 'a' represents the SiO2 / Si substrate obtained without the addition of molecular sieves. Figure 10 In the figure, b represents the SiO2 / Si substrate obtained by adding molecular sieves. As can be seen from the comparison, without the addition of molecular sieves, a large number of fine particles and irregular blocky deposits can be observed in the substrate background, and the background uniformity is poor, indicating that there are more by-products. After adding molecular sieves, the substrate background is significantly cleaner, and the morphology of the target sheet nanosheets is clearer and the distribution is more uniform, indicating that molecular sieves help to suppress the generation of by-products and improve the controllable growth of the target nanosheets.
[0062] Comparative Example 2:
[0063] This comparative example follows the preparation method of Example 1, preparing tilted single-crystal chromium oxide nanosheets on the surface of a SiO2 / Si substrate. The difference is that the growth temperature is controlled at 780 °C in this comparative example, while the other preparation steps remain unchanged.
[0064] The tilted-grown single-crystal chromium oxide nanosheets constructed in this comparative example were characterized. Figure 11Optical microscope images of tilted-grown single-crystal chromium oxide nanosheets constructed at a growth temperature of 780 °C, by [Author Name / Organization Name]. Figure 11 As can be seen, at 780 °C, a large number of fine particles, colored spots, and irregular strip / dendritic deposits appeared in the substrate background, similar to the situation without the addition of molecular sieves. This indicates a significant increase in byproducts, a decrease in substrate cleanliness, and an impact on the formation of regular sheet-like nanostructures. It is speculated that the precursor evaporates too quickly at 780 °C, weakening the controllability of the molecular sieves and thus leading to an increase in uncontrolled deposition.
[0065] This invention provides a method for preparing and transferring tilted chromium oxide single-crystal nanosheets. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.
Claims
1. A method for preparing and transferring tilted chromium oxide single-crystal nanosheets, characterized in that, Includes the following steps: S1. Mix potassium chromate and chromium chloride evenly to obtain precursor powder; S2. Transfer the precursor powder into a ceramic boat and simultaneously cover the surface of the precursor powder with molecular sieves; S3. The SiO2 / Si substrate is tilted and covered on the molecular sieve with the oxide layer facing down; the ceramic boat is transferred to a vacuum tube furnace, heated and reacted, and after cooling, tilted chromium oxide single crystal nanosheets are prepared on the surface of the SiO2 / Si substrate. S4. Place the tilted chromium oxide single crystal nanosheets prepared in S3 onto other clean substrates, and complete the transfer of chromium oxide single crystal nanosheets to other clean substrates by mechanical pressing.
2. The method according to claim 1, characterized in that, In S1, the mass ratio of potassium chromate to chromium chloride is 3:1; both potassium chromate and chromium chloride are powders.
3. The method according to claim 1, characterized in that, In S2, the molecular sieve is a 4A type molecular sieve, ensuring that the molecular sieve can completely cover the precursor powder.
4. The method according to claim 1, characterized in that, In S3, the size of the SiO2 / Si substrate is 3 cm × 1 cm.
5. The method according to claim 1, characterized in that, In S3, the heating reaction is carried out under the following process conditions: under an inert atmosphere, the heating rate is 25 °C / min, the temperature is raised to 730~760 °C, and held at the temperature for 15 min.
6. The method according to claim 5, characterized in that, In S3, the inert atmosphere is provided by argon gas at a flow rate of 100 sccm.
7. The method according to claim 1, characterized in that, In S4, the clean substrate includes any one of SiO2 / Si substrate, sapphire substrate, quartz glass substrate and PDMS substrate.
8. Chromium oxide single-crystal nanosheets prepared by the method according to any one of claims 1 to 7.
9. The chromium oxide single-crystal nanosheets according to claim 8, characterized in that, The chromium oxide single-crystal nanosheets are either tilted or flat on the substrate surface.