Ionogenic compound thin film, method for preparing the same, and use thereof

Abstract

The application discloses an ionic compound film and a preparation method and application thereof. 4,4'-dipyridine is used as a molecular main body, different halogenated hydrocarbons are used as reaction raw materials, methyl, ethyl or benzyl groups are respectively introduced at the ends of the molecules, and sodium tetrafluoroborate or ammonium tetrafluoroborate is used as a reactant to perform an anion exchange reaction on the molecules, so that ionic compounds with different structures are obtained. Then, the ionic compounds are dissolved in a solvent, and are deposited on the surface of a conductive substrate by electrophoresis to form a film. Finally, the three ionic compounds are prepared into a memory device with a sandwich structure, and the application of the ionic compound film as multi-radix information storage is provided. The spatial steric hindrance of the end groups is simply adjusted, and different information storage performances can be realized, which is simpler and faster than a complex and tedious structure design idea.

Description

Technical Field

[0001] This invention belongs to the fields of functional semiconductor materials and electronic information, and relates to an ionic compound thin film, its preparation method and application. Background Technology

[0002] In the context of the intelligent era, digital life has brought numerous conveniences to people; however, the explosive growth of massive amounts of data poses a severe challenge to current information storage technologies. Therefore, there is an urgent need to develop a new type of electrical storage medium that simultaneously meets the requirements of ultra-high storage density, fast response time, and ultra-large storage capacity. Compared to traditional silicon-based memories, which face the challenges of physical size limitations and ever-increasing manufacturing costs, organic semiconductor memory devices possess unique advantages such as excellent flexibility, solution processing feasibility, low cost-effectiveness, and tunable molecular structure, thus showing tremendous research and application prospects in recent decades. Currently, the main strategies for controlling organic semiconductor materials include the introduction of groups unaffected by molecular stacking defects, the introduction of large π-conjugated planar groups, the introduction of hydrogen-bonding groups, and the introduction of halogen-bonding groups. While some progress has been made in the development of organic materials in the field of electrical storage, these devices still generally suffer from problems such as poor device stability, low repeatability, and unclear storage mechanisms. These significantly limit the future practical application of organic multi-level electrical storage. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to solve the problems of poor ordered molecular stacking and poor device stability in existing memory devices, and to provide an ionic compound thin film and its preparation method.

[0004] Another objective of this invention is to provide an application of ionic compound thin films as ultra-high density information storage.

[0005] Technical solution: A method for preparing an ionic compound thin film according to the present invention includes the following steps:

[0006] (1) Using 4,4'-bipyridine as the main molecule, it is dissolved in a first organic solvent to obtain a first solution. Using a haloalkane as the reactant, the haloalkane is added dropwise to the first solution and the temperature is raised to react, thus obtaining an ionic compound containing halo ions.

[0007] (2) Sodium tetrafluoroborate or ammonium tetrafluoroborate is used as reactant to carry out anion exchange reaction on the ionic compound containing halide ions obtained in step (1) to obtain the target ionic compound;

[0008] (3) Dissolve the ionic compound obtained in step (2) in the second organic solvent, sonicate and heat to obtain the second solution, then place the cleaned conductive substrate in the electrophoresis tank containing the second solution, and form a thin film by electrophoretic deposition on the surface of the conductive substrate. Place the conductive substrate with the deposited film in a vacuum oven and wait for the solvent to evaporate until it is completely dry to obtain the target ionic compound film.

[0009] In step (2), the structural formula of the target ionic compound is shown in Formula 1. The molecular three synthesis process can be referred to the published patent CN114967264A.

[0010]

[0011] Formula 1.

[0012] Furthermore, the haloalkane is selected from iodomethane, bromoethane, or benzyl chloride, and is used to introduce methyl, ethyl, or benzyl groups at the molecular end of 4,4'-bipyridine, respectively; the molar ratio of the haloalkane to 4,4'-bipyridine is (2~12):1; the dropping rate of the haloalkane is 3-6 drops / minute.

[0013] Further, in step (1), the first organic solvent is selected from N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile.

[0014] Furthermore, in step (1), the temperature is raised to 70~80 °C; the reaction time is 4~48 h.

[0015] Further, in step (1), the reaction solvent for the anion exchange reaction is one of deionized water, methanol, or ethanol, and the reaction time is 48 to 120 h.

[0016] Further, in step (3), the second organic solvent is selected from one of propylene carbonate (PC), dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), and the concentration of the second solution is 0.01~0.05 mg / mL.

[0017] Further, in step (3), the voltage of the electrophoretic deposition is 10~20 volts, and the electrophoretic deposition time is 2~5 minutes.

[0018] Furthermore, in step (3), the temperature of the vacuum oven is set to 100~120 ℃.

[0019] Another object of the present invention is to provide an ionic compound thin film prepared by the above-described preparation method.

[0020] Another object of the present invention is to provide an application of the above-mentioned ionic compound thin film in the preparation of multi-level memory devices.

[0021] Reaction Mechanism: This invention uses 4,4'-bipyridine as the molecular host and haloalkanes as reactants. Methyl, ethyl, or benzyl groups are introduced at the molecular ends to obtain ionic compounds with different structures. Then, anion exchange is performed to replace the halide anion with BF4. - On the one hand, it can further improve the solubility of ionic compounds in organic solvents, and formulate clear and transparent electrophoretic solutions, thereby achieving uniform and controllable thin film deposition under the action of an electric field; on the other hand, BF4 - Compared to the larger volume of halide anions, the exchange significantly weakens the electrostatic locking between cations and anions, allowing the steric hindrance differences of different terminal groups to be fully manifested. Finally, electrophoretic deposition transforms these microstructural differences into completely different packing states within the film. Although these three ionic compounds exhibit a consistent molecular framework and energy level orbitals, their different terminal groups endow the molecules with different steric hindrances and packing properties, resulting in completely different packing states in the film. Electrical tests further demonstrate that these three ionic compounds exhibit different storage properties due to their different packing states. This invention achieves different information storage performance simply by adjusting the steric hindrance of the terminal groups, which is much simpler and faster than complex and cumbersome structural design approaches.

[0022] Beneficial effects: (1) The pyridine group at the end of the 4,4'-bipyridine skeleton selected in this invention has a weak electron-withdrawing ability, so it generally cannot be used directly as an effective active layer in the semiconductor field; after the ionization treatment of haloalkanes, the electron-withdrawing ability of pyridine salts is greatly increased, and pyridine cations can act as "charge traps" to hinder the effective transmission of electrons in the thin film, thereby realizing the information storage function under the action of electric field.

[0023] (2) The 4,4'-bipyridine host in the ionic compound of the present invention has a large conjugated plane, which is conducive to enhancing the π-π stacking effect between molecules, and thus to enhancing the close stacking state between molecules; at the same time, the pyridine cation in the ionic compound can also effectively improve the ordered stacking mode between molecules through Coulomb interaction, further enhancing the regular and consistent stacking state between molecules in the film, which is conducive to the effective transport of charge carriers between films, and finally achieving stable information storage performance.

[0024] (3) The ionic compounds of this invention are deposited into films using electrophoretic deposition. Due to the distinct steric hindrance of the terminal groups, their packing state in the film also changes accordingly. Electrical performance analysis shows that the packing state between molecules in the film significantly affects the storage performance of the device. This invention can further establish the relationship between "molecular structure-packing state-storage performance" based on the previous single "structure-performance" multi-level material design, providing a new approach for the preparation of high-performance electrical storage materials. Compared to simple molecular structure control, this is simpler and easier, providing a simple and efficient strategy for the subsequent manufacturing of low-cost, well-packed, and high-density storage devices. Attached Figure Description

[0025] Figure 1 The synthetic route for molecule one in Example 1 is shown below;

[0026] Figure 2 The synthetic route for molecule two in Example 2 is shown below;

[0027] Figure 3 The hydrogen NMR spectrum of molecule one in Example 1;

[0028] Figure 4 The 1H NMR spectrum of molecule 2 in Example 2;

[0029] Figure 5 This is a schematic diagram of the quartz electrophoresis tank and subsequent electrophoretic deposition in Examples 3-5;

[0030] Figure 6 The microstructure of the films obtained in Examples 3-5 is shown below; where (a) is the stacking mode corresponding to molecule one; (b) is the stacking mode corresponding to molecule two; and (c) is the stacking mode corresponding to molecule three.

[0031] Figure 7 The images show the device with a "sandwich" structure fabricated based on the thin film of the test example, where (a) is a schematic diagram and (b) is a physical image. Figure 8 for Figure 7 Scanning electron microscope (SEM) image of the actual object;

[0032] Figure 9 This is a graph showing the electrical storage performance of the storage device prepared based on Example 3;

[0033] Figure 10 This is a graph showing the electrical storage performance of the storage device prepared based on Example 4;

[0034] Figure 11 This is a graph showing the electrical storage performance of the storage device prepared based on Example 5. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0036] Example 1:

[0037] The synthesis of molecule one, such as Figure 1 The specific steps are as follows:

[0038] 4,4'-Bipyridine (5 g, 0.03 mol) was dissolved in 100 mL of acetonitrile and placed in a 250 mL three-necked flask. Iodomethane (5 mL, 0.08 mol) was slowly added at a rate of 3 drops / min through a constant-pressure dropping funnel in a fume hood at room temperature. After the addition was complete, the temperature was slowly raised to 70 °C and the reaction was continued at this temperature for 12 h. During the reaction, the solution was observed to gradually change from colorless and transparent to pink, eventually forming an orange-red solid. After the reaction was complete, the solution was allowed to cool naturally for 30 min to ensure complete evaporation of residual iodomethane. The product was separated by vacuum filtration (0.08 MPa), washed with acetonitrile (3 × 20 mL) to remove soluble impurities, and then washed with diethyl ether (3 × 20 mL) to remove residual acetonitrile. After drying, a red solid (13.2 g, yield 93.8%) was obtained.

[0039] NaBF4 (5 g) was added to 500 mL of methanol and magnetically stirred until completely dissolved. The 4,4'-dimethyl-4,4'-bipyridine salt obtained from the above reaction was slowly added to the above solution in portions (≤0.2 g each time, 2 min intervals), and the reaction was continuously stirred at room temperature for 48 h. During the reaction, the solution color gradually changed from transparent orange-red to orange-yellow, and orange-yellow particles precipitated, indicating that the ion exchange reaction was underway. After the reaction was complete, the precipitate was collected by vacuum filtration (0.08 MPa) and washed three times with methanol (100 mL each time) to remove residual NaBF4. Finally, the solid product was dried in a vacuum drying oven (60 ℃, 10 Pa) for 6 h, yielding an orange-yellow solid (10.5 g, yield 97.1%). 1 H NMR (400 MHz, CD3CN) δ 8.84 (d, J = 6.8 Hz, 4H), 8.37 (d, J = 6.5Hz, 4H), 4.38 (s, 6H).

[0040] Example 2:

[0041] Synthesis of molecule II, such as Figure 2 The specific steps are as follows:

[0042] 4,4'-Bipyridine (5 g, 0.03 mol) was dissolved in 100 mL of acetonitrile and placed in a 250 mL three-necked flask. In a fume hood, bromoethane (8 mL, 0.10 mol) was slowly added at a rate of 5 drops / min through a constant-pressure dropping funnel at room temperature. After the addition was complete, the temperature was slowly raised to 75 °C and the reaction was continued at this temperature for 48 h. During the reaction, a color change was observed in the solution (clear solution → yellow solution → yellow solid), eventually forming a pale yellow solid. After the reaction was complete, the solution was allowed to cool naturally for 30 min to ensure complete volatilization of residual bromoethane. The product was separated by vacuum filtration (0.08 MPa), washed with acetonitrile (3 × 50 mL) to remove soluble impurities, and then washed with diethyl ether (3 × 20 mL) to remove residual acetonitrile. After drying, a pale yellow solid (7.4 g, yield 61.5%) was obtained.

[0043] NaBF4 (5 g) was added to 500 mL of methanol and magnetically stirred until completely dissolved. The 4,4'-diethyl-4,4'-bipyridine salt obtained from the above reaction was slowly added to the above solution in portions (≤0.2 g each time, 2 min intervals), and the reaction was continuously stirred at room temperature for 72 h. During the reaction, the solution color gradually changed from an initial yellow solution to a transparent white solution, eventually precipitating a white precipitate, indicating that the ion exchange reaction was underway. After the reaction was complete, the precipitate was collected by vacuum filtration (0.08 MPa) and washed three times with methanol (100 mL each time) to remove residual NaBF4. Finally, the solid product was dried in a vacuum drying oven (60 ℃, 10 Pa) for 6 h to obtain a white solid (6.0 g, yield 78.1%). 1 H NMR (400 MHz, D2O) δ 9.02 (d, J = 6.1 Hz, 4H), 8.42 (d, J = 5.1 Hz, 4H), 4.67 (q, 4H), 1.59 (t, J = 7.3 Hz, 6H).

[0044] Example 3:

[0045] The specific steps for preparing ionic compound thin films are as follows:

[0046] Clean the surface of a 2×2 cm ITO conductive glass piece using laundry detergent or dish soap to remove fine particles. After cleaning, immerse the ITO conductive glass piece sequentially in deionized water, acetone, and isopropanol, then ultrasonically clean each for 20 minutes. After ultrasonic cleaning, use a hairdryer to vertically dry the ITO conductive glass. Set a multimeter to the ohm range and touch the two test pens to the glass surface; if a reading is obtained, it is the conductive side. Place the conductive side of the glass piece face up in a clean container for later use. Dissolve the synthesized target ionic compound (molecule one) in propylene carbonate (PC), maintaining a solution concentration of 0.02 mg / mL.

[0047] The prepared solution is placed in a quartz electrophoresis tank of a specific size, such as... Figure 5 As shown, the length, width, and height of the electrophoresis tank are 30 mm, 12 mm, and 45 mm, respectively. Two ITO conductive glasses are then slowly placed on either side of the quartz electrophoresis tank to charge the working and counter electrodes, with the conductive sides of the ITO conductive glasses facing each other, spaced approximately 10 mm apart. Next, a 20 V DC voltage is applied to the two ITO conductive glasses. Under the influence of the electric field, the synthesized target cation-type ionic compound will be directionally migrated to the cathode ITO conductive glass. After electrophoretic deposition for 2 minutes, the target product will form an organic semiconductor thin film of a certain thickness on the cathode ITO conductive glass. Finally, the electric field is removed, and the cathode ITO conductive glass is slowly raised until its bottom edge leaves the liquid surface. The pulled-out ITO glass is then placed horizontally in a vacuum oven at a temperature of 120 °C. This temperature ensures the slow evaporation of propylene carbonate (PC) solvent. After approximately 24 hours, the target ionic thin film system is obtained.

[0048] Example 4:

[0049] The specific steps for preparing ionic compound thin films are as follows:

[0050] Clean the surface of a 2×2 cm ITO conductive glass piece using laundry detergent or dish soap to remove fine particles. After cleaning, immerse the ITO conductive glass piece sequentially in deionized water, acetone, and isopropanol, then ultrasonically clean each for 20 minutes. After ultrasonic cleaning, use a hairdryer to vertically dry the ITO conductive glass. Set a multimeter to the ohm range and touch the two test pens to the glass surface; a reading indicates the conductive side. Place the conductive side of the glass piece face up in a clean container for later use. Dissolve the synthesized target ionic compound (molecule II) in dimethyl sulfoxide (DMSO), maintaining a solution concentration of 0.03 mg / mL.

[0051] The prepared solution is placed in a quartz electrophoresis tank of a specific size, such as... Figure 5As shown, the length, width, and height of the electrophoresis tank are 30 mm, 12 mm, and 45 mm, respectively. Two ITO conductive glass plates are then slowly placed on either side of the quartz electrophoresis tank to charge the working and counter electrodes, with the conductive sides of the ITO conductive glass plates facing each other, spaced approximately 10 mm apart. Next, a 15 V DC voltage is applied to the two ITO conductive glass plates. Under the influence of the electric field, the synthesized target cation-type ionic compound will be directionally migrated to the cathode ITO conductive glass. After electrophoretic deposition for 3 minutes, the target product will form an organic semiconductor thin film of a certain thickness on the cathode ITO conductive glass. Finally, the electric field is removed, and the cathode ITO conductive glass is slowly raised until its bottom edge leaves the liquid surface. The pulled-out ITO glass is then placed horizontally in a vacuum oven at a temperature of 120 °C. At this temperature, the dimethyl sulfoxide (DMSO) solvent can be slowly evaporated. After approximately 24 hours, the target ionic thin film system is obtained.

[0052] Example 5:

[0053] The specific steps for preparing ionic compound thin films are as follows:

[0054] Clean the surface of a 2×2 cm ITO conductive glass piece using laundry detergent or dish soap to remove fine particles. After cleaning, immerse the ITO conductive glass piece sequentially in deionized water, acetone, and isopropanol, then ultrasonically clean each for 20 minutes. After ultrasonic cleaning, use a hairdryer to vertically dry the ITO conductive glass. Set a multimeter to the ohm range and touch the two test pens to the glass surface; a reading indicates the conductive side. Place the conductive side of the glass piece face up in a clean container for later use. Dissolve the synthesized target ionic compound (molecule tri) in N,N-dimethylformamide (DMF), maintaining a solution concentration of 0.04 mg / mL.

[0055] The prepared solution is placed in a quartz electrophoresis tank of a specific size, such as... Figure 5As shown, the length, width, and height of the electrophoresis tank are 30 mm, 12 mm, and 45 mm, respectively. Two ITO conductive glasses are then slowly placed on either side of the quartz electrophoresis tank to charge the working and counter electrodes, with the conductive sides of the ITO conductive glasses facing each other, spaced approximately 10 mm apart. Next, a 10 V DC voltage is applied to the two ITO conductive glasses. Under the influence of the electric field, the synthesized target cation-type ionic compound will be directionally migrated to the cathode ITO conductive glass. After electrophoretic deposition for 5 minutes, the target product will form an organic semiconductor thin film of a certain thickness on the cathode ITO conductive glass. Finally, the electric field is removed, and the cathode ITO conductive glass is slowly raised until its bottom edge leaves the liquid surface. The pulled-out ITO glass is then placed horizontally in a vacuum oven at a temperature of 100°C. This temperature ensures the slow evaporation of the N,N-dimethylformamide (DMF) solvent. The target ionic thin film system is obtained after approximately 24 hours.

[0056] Test example:

[0057] Figure 6 The figures show the intermolecular packing patterns simulated by X-ray diffraction (XRD) patterns of the films prepared according to Examples 3-5. In the figures, (a) is the packing pattern corresponding to molecule one, (b) is the packing pattern corresponding to molecule two, and (c) is the packing pattern corresponding to molecule three. As can be seen from the figures, although the three ionic compounds synthesized have consistent electronic properties, the films they produce exhibit completely different packing patterns. This indicates that the end ionization treatment has a qualitative impact on the intermolecular packing state within the film, thereby affecting the effective transport of charge carriers within the film and the final storage performance.

[0058] The specific steps for fabricating devices and testing the electrical performance of ionic thin film systems are as follows:

[0059] The prepared ionic compound film was placed in a vacuum evaporation apparatus, and an aluminum electrode with a thickness of 100 nanometers and a diameter of 120 micrometers was deposited on its surface to obtain the following result: Figure 7 and Figure 8 The memory device shown has a "sandwich" structure, including a glass substrate 1, an ITO conductive glass 2, an ionic compound thin film 3 deposited on the ITO conductive glass 2, and an aluminum electrode 4. The device was then placed on a semiconductor parameter analyzer, and scan voltages of 0 to -5 V and 0 to 5 V were applied to record its electrical performance.

[0060] like Figure 9 , 10 As shown in Figure 11: Figure 9 The graph shows the electrical performance of the device prepared based on ionic compound one (molecule one) in Example 3. Figure 10 The graph shows the electrical performance of the device fabricated based on ionic compound II (molecule II) in Example 4. As can be seen from the graph, the memory devices fabricated based on both molecule I and molecule II exhibit conventional binary memory performance. Figure 11 The figure shows the electrical performance of the device prepared based on the ionic compound tri(molecular tri) in Example 5. As can be seen from the figure, the device exhibits typical ternary storage performance, which greatly improves the storage density of the device. This invention can achieve different information storage performances simply by adjusting the steric hindrance of the terminal groups, which is much simpler and faster than through complex and cumbersome structural design.

[0061] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing an ionic compound thin film, characterized in that, Includes the following steps: (1) Using 4,4'-bipyridine as the main molecule, it is dissolved in a first organic solvent to obtain a first solution. Using a haloalkane as the reactant, the haloalkane is added dropwise to the first solution and the temperature is raised to react, thus obtaining an ionic compound containing halo ions. (2) Sodium tetrafluoroborate or ammonium tetrafluoroborate is used as reactant to carry out anion exchange reaction on the ionic compound containing halide ions obtained in step (1) to obtain the target ionic compound; (3) Dissolve the ionic compound obtained in step (2) in a second organic solvent, sonicate and heat to obtain a second solution, then place the cleaned conductive substrate in an electrophoresis tank containing the second solution, and form a thin film by electrophoretic deposition on the surface of the conductive substrate. Place the conductive substrate with the deposited film in a vacuum oven and wait for the solvent to evaporate until it is completely dry to obtain the target ionic compound film. In step (1), the haloalkane is selected from iodomethane, bromoethane or benzyl chloride, and is used to introduce methyl, ethyl or benzyl groups at the molecular end of 4,4'-bipyridine; the molar ratio of the haloalkane to 4,4'-bipyridine is (2~12):1; the dropping rate of the haloalkane is 3-6 drops / minute; In step (3), the voltage of the electrophoretic deposition is 10 to 20 volts, and the electrophoretic deposition time is 2 to 5 minutes.

2. The method for preparing ionic compound thin films according to claim 1, characterized in that, In step (1), the first organic solvent is selected from N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile.

3. The method for preparing ionic compound thin films according to claim 1, characterized in that, In step (1), the temperature is raised to 70~80 ℃; the reaction time is 4~48 h.

4. The method for preparing ionic compound thin films according to claim 1, characterized in that, In step (1), the reaction solvent for the anion exchange reaction is one of deionized water, methanol, or ethanol, and the reaction time is 48 to 120 h.

5. The method for preparing ionic compound thin films according to claim 1, characterized in that, In step (3), the second organic solvent is selected from propylene carbonate, dimethyl sulfoxide and N,N-dimethylformamide, and the concentration of the second solution is 0.01~0.05 mg / mL.

6. The method for preparing ionic compound thin films according to claim 1, characterized in that, In step (3), the temperature of the vacuum oven is set to 100~120 ℃.

7. An ionic compound thin film, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The use of the ionic compound thin film of claim 7 in the preparation of multi-level memory devices.

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