Preparation method of PbS quantum dots for resistive random access memory and reaction device thereof

Abstract

This invention relates to the field of semiconductor nanomaterials technology, specifically to a method and reaction apparatus for preparing PbS quantum dots for resistive switching memory. The technical solution adopted in this invention is as follows: Lead oxide and oleic acid are weighed and mixed, octadecene is added, and the mixture is heated to 120°C at a rate of 1.5°C / min under nitrogen protection. The mixture is stirred at this constant temperature until the solution becomes transparent, obtaining a lead precursor solution. Hexamethyldisilazane is measured and mixed with octadecene, and the mixture is magnetically stirred for 15 minutes to obtain a hot-injection solution. The lead precursor undergoes three vacuum-Ar cycles, resulting in an oxygen residue of <50 ppm. The temperature is controlled at 120°C ± 0.5°C, and the hot-injection solution is injected at a rate of 1.0 mL / min. The reaction is stirred at 800 rpm for 2 minutes, quenched in an ice bath, and the reaction solution is mixed with acetone and isopropanol and centrifuged. The precipitate is washed three times with n-hexane and dried under vacuum at 60°C to obtain PbS quantum dots. The prepared PbS quantum dots have advantages such as high surface density, uniform size, low cost, and fast synthesis cycle.

Description

Technical Field

[0001] This invention relates to the field of semiconductor nanomaterials technology, specifically to a method for preparing PbS quantum dots for resistive switching memory and its reaction apparatus. Background Technology

[0002] Resistive random access memory (RRAM), as a novel in-memory computing device, has the advantages of low power consumption, high speed, and compatibility with complementary metal-oxide-semiconductor (CMOS) processes. Although the solution-based preparation of PbS quantum dots has made some progress in the existing technology, there are still some defects that restrict its application in RRAM.

[0003] For example, the patent application number "CN201611050553.3" entitled "A Method for Preparing PbS Quantum Dots" discloses a method for preparing PbS quantum dots based on a solution method. Its problem is as follows:

[0004] 1) Due to residual oxygen impurities during the reaction process, the surface defects of the quantum dots increase, leading to unstable performance of the resistive switching memory.

[0005] 2) Traditional single-hole reaction devices cannot achieve precise Ar gas circulation and micro-dosing of reagents, resulting in uneven quantum dot size distribution.

[0006] 3) The size deviation of the prepared PbS quantum dots is >15%, which seriously affects their photoelectric properties.

[0007] 4) Lack of integrated temperature control and air pressure monitoring system, resulting in poor reaction repeatability.

[0008] 5) Byproducts are easily generated during high-temperature reactions, and the surface modification of quantum dots is insufficient, which limits their application in resistive switching memory.

[0009] In summary, existing methods for preparing PbS quantum dots have significant shortcomings in terms of reaction condition control, size uniformity, and surface defects. These shortcomings result in high surface defect density, poor size uniformity, and low batch repeatability of PbS quantum dots. A new preparation method is urgently needed to solve these problems and improve their performance in resistive switching memory applications. Summary of the Invention

[0010] In view of this, the present invention provides a method for preparing PbS quantum dots for resistive switching memory and a reaction apparatus thereof, which provides PbS quantum dots with advantages such as high surface density, uniform size, low cost, and fast synthesis cycle.

[0011] To solve the above problems, the technical solution adopted by the present invention is: a method for preparing PbS quantum dots for resistive switching memory, characterized by the following steps:

[0012] Step 1): Mix lead oxide (PbO) and oleic acid (OA) in a mass ratio of 1:2.5-1:3, add octadecene (ODE) in volume 8-12 times that of oleic acid as a solvent, heat to 110-130℃ under nitrogen protection and stir until completely dissolved to form a lead precursor solution.

[0013] Step 2): Place the lead precursor solution obtained in Step 1 into the reaction apparatus for reaction, and monitor the pressure inside the reaction flask in real time.

[0014] Step 3): Mix hexamethyldisilazane (TMS) and octadecene (ODE) at a volume ratio of 1:25-1:35 and stir for 10-20 minutes to obtain a hot-injection solution. Transfer the lead precursor solution to a three-necked flask, heat to 110-130℃, and deoxygenate through three vacuum-Ar gas circulation cycles. Then, rapidly inject the hot-injection solution at a rate of 0.8-1.2 mL / min, with a magnetic stirring speed of 500-800 rpm, and control the reaction time to 1-5 minutes. Quench the reaction in an ice bath.

[0015] Step 4): Centrifuge the product from step 3) in a mixture of acetone and isopropanol at 7000-9000 rpm for 5-10 minutes. Redissolve the precipitate in n-hexane and wash it 3-4 times to obtain PbS quantum dot colloids coated with oleic acid. Then, dry it in a vacuum drying oven at 60℃ for 12 hours to completely evaporate the solvent in the quantum dots and obtain PbS quantum dots.

[0016] Furthermore, in step 3), the vacuum degree of the vacuum-Ar gas circulation deoxygenation is 10. -3 Up to 10 -2 Pa, oxygen residue <100ppm.

[0017] Furthermore, in step 4), the volume ratio of the acetone to isopropanol mixture is 2-3:1.

[0018] A reaction apparatus used in a method for preparing PbS quantum dots for resistive switching memory is characterized by comprising a three-necked flask, a pressure-resistant venting hose, a vacuum pump, and an Ar gas cylinder. The three-necked flask is fixed in a silicone oil thermostat by a metal bracket. A micro-injector is connected to the left neck, a condenser is connected to the center neck, and a thermometer is installed at the right neck. One end of the pressure-resistant venting hose is connected to the upper end of the condenser, and the other end is split into two paths, which are connected to the vacuum pump and the Ar gas cylinder, respectively. A pressure gauge is connected to the main gas path of the pressure-resistant venting hose to monitor the pressure inside the reaction flask in real time.

[0019] Furthermore, dual-passage air valves are installed on the main air line and the two branch air lines of the ventilation hose.

[0020] Compared with the prior art, the beneficial effects of this invention patent are as follows:

[0021] 1) This invention uses a three-necked flask to integrate temperature monitoring (right hole), Ar gas / vacuum dual passage (center hole) and micro-injector (left hole), combined with real-time monitoring and feedback from a pressure gauge, to achieve dynamic deoxygenation and inert atmosphere protection, significantly improving the uniformity of quantum dot size.

[0022] 2) This invention places a three-necked flask in a silicone oil thermostat (temperature control accuracy ±0.5℃) and combines it with a low-temperature reaction at 120℃. The hot-injected solution is injected at a rate of 1.0 mL / min, shortening the reaction time to 2 minutes. The quantum dot synthesis cycle is 50% more efficient than the traditional process (4-6 minutes).

[0023] 3) This invention uses a modular device, and the pressure gauge and syringe can be disassembled and reused. It also uses a solution method for low-temperature synthesis, which avoids the high cost of traditional MBE epitaxy. Furthermore, it is suitable for large-area deposition on flexible substrates (PET, PI), providing a technical foundation for the industrialization of resistive switching memory. Attached Figure Description

[0024] Figure 1 This is a diagram of the reaction apparatus of the present invention.

[0025] Figure 2 These are TEM images of PbS quantum dots from Embodiments 1 and 2 of the present invention.

[0026] Labeling instructions: 1. Three-necked flask; 2. Metal holder; 3. Microsyringe; 4. Condenser; 5. Thermometer; 6. Pressure-resistant venting hose; 7. Pressure gauge; 8. Two-way valve; 9. Vacuum pump; 10. Ar gas cylinder. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention patent based on the specific circumstances.

[0029] Example 1

[0030] The steps involved in the fabrication of PbS quantum dots for resistive switching memory are as follows:

[0031] Step 1: Preparation of precursor solution. Weigh 1.15g lead oxide (PbO, 5.2mmol) and mix with 3.5mL oleic acid (OA, 11mmol). Add 45mL octadecene (ODE) as solvent. Under nitrogen protection, heat to 120℃ at 1.5℃ / min and stir at a constant temperature until the solution is clear (about 25 minutes) to obtain lead precursor solution (PbO concentration 0.31mol / L).

[0032] Step 2: Setting up the reaction apparatus, such as... Figure 1 As shown, the device includes a three-necked flask 1, a metal bracket 2, a micro-injector 3, a condenser 4, a thermometer 5, a pressure-resistant venting hose 6, a pressure gauge 7, a dual-channel gas valve 8, a vacuum pump 9, and an Ar gas cylinder 10. The three-necked flask 1 is fixed in a silicone oil thermostatic bath by the metal bracket 2. The micro-injector 3 is connected to the left neck, the condenser 4 is connected to the center neck, and the thermometer 5 is installed at the right neck. One end of the pressure-resistant venting hose 6 is connected to the upper end of the condenser 4, and the other end is split into two paths, which are connected to the vacuum pump 9 and the Ar gas cylinder 10 respectively. The pressure gauge 7 is connected to the main gas path of the pressure-resistant venting hose 6 to monitor the pressure inside the reaction flask in real time (the pressure gauge 7 has a range of 0-1 MPa and an accuracy of ±0.01 MPa). Dual-channel gas valves 8 are respectively installed on the main gas path and the two branch gas paths of the venting hose 6.

[0033] Step 3: Preparation of lead sulfide quantum dots. 0.48 mL of hexamethyldisilazane (TMS, 2.0 mmol) was mixed with 28.8 mL of octadecene ODE and magnetically stirred for 15 minutes to obtain a hot-injection solution (concentration 0.069 mol / L). The lead precursor solution was transferred to a three-dimensional flask, heated to 120 °C, and then deoxygenated through three vacuum-Ar gas circulation cycles at a vacuum degree of 10. -2 Pa, residual oxygen 85ppm, temperature controlled at 100℃±2℃, hot injection solution injected at a rate of 0.8mL / min, magnetically stirred at a rate of 600rpm for 5 minutes, and then quenched in an ice bath.

[0034] Step 4: Product processing and centrifugation. The reaction solution and a mixture of acetone and isopropanol at a volume ratio of 2:1 were centrifuged at 8000 rpm for 10 min. The precipitate was reconstituted with n-hexane and washed three times to obtain PbS quantum dot colloids coated with oleic acid. Finally, the colloid was placed in a vacuum drying oven at 60℃ and dried for 12 hours to completely evaporate the solvent in the quantum dots, thus obtaining PbS quantum dots.

[0035] The TEM analysis image of the PbS quantum dots obtained in this embodiment is as follows: Figure 2 As shown on the left, the quantum dot particle size is 3.5 ± 0.3 nm (relative standard deviation 8.6%), and local aggregation exists.

[0036] Example 2

[0037] The steps involved in the fabrication of PbS quantum dots for resistive switching memory are as follows:

[0038] Step 1: Preparation of precursor solution. Weigh 1.15g of lead oxide (PbO, 5.2mmol) and mix with 3.5mL of oleic acid (OA, 11mmol). Add 40mL of octadecene (ODE) as solvent. Under nitrogen protection, heat to 120℃ at 1.5℃ / min and stir at a constant temperature until the solution becomes clear (about 25 minutes) to obtain lead precursor solution (PbO concentration 0.31mol / L).

[0039] Step 2: The reaction apparatus is set up in the same way as in Example 1.

[0040] Step 3: Preparation of lead sulfide quantum dots. 0.52 mL of hexamethyldisilazane (TMS, 2.1 mmol) was mixed with 31.2 mL of octadecene ODE and magnetically stirred for 15 minutes to obtain a hot-injection solution (concentration 0.067 mol / L). The lead precursor solution was injected into a three-necked flask, heated to 110 °C, and then deoxygenated through three vacuum-Ar gas circulation cycles at a vacuum degree of 10. -2 Pa, oxygen residue <50ppm, temperature controlled at 120℃±0.5℃, hot injection solution is injected at a rate of 1.0mL / min, magnetic stirring is performed at 800rpm for 2 minutes, and then quenched in an ice bath.

[0041] Step 4: Product processing and centrifugation. The reaction solution and a mixture of acetone and isopropanol at a volume ratio of 2:1 were centrifuged at 8000 rpm for 10 min. The precipitate was reconstituted with n-hexane and washed three times to obtain PbS quantum dot colloids coated with oleic acid. Finally, the colloid was placed in a vacuum drying oven at 60℃ and dried for 12 hours to completely evaporate the solvent in the quantum dots, thus obtaining PbS quantum dots.

[0042] The TEM analysis of the PbS quantum dots obtained in Example 1 is as follows: Figure 2 As shown on the right: the quantum dots are monodisperse spherical, densely arranged and without obvious aggregation, with a size of 4.2 ± 0.8 nm (relative standard deviation 19.0%).

[0043] Comparing Example 1 and Example 2, Example 2 (120℃±0.5℃, hot-injected solution 1.0mL / min) showed a larger average particle size and more uniform particle size compared to Example 1 (100℃±2℃, 0.7mL / min). Considering size uniformity, crystal quality, and process stability, Example 2 is the best example.

[0044] Example 3:

[0045] The steps involved in the fabrication of PbS quantum dots for resistive switching memory are as follows:

[0046] Step 1: Preparation of precursor solution. Weigh 1.18g of lead oxide (PbO, 5.3mmol) and mix with 3.5mL of oleic acid (OA, 11mmol). Add 50mL of octadecene (ODE) as solvent. Under nitrogen protection, heat to 110℃ at 1.5℃ / min and stir at a constant temperature until the solution is clear (about 25 minutes) to obtain lead precursor solution (PbO concentration 0.32mol / L).

[0047] Step 2: The reaction apparatus is set up in the same way as in Example 1.

[0048] Step 3: Preparation of lead sulfide quantum dots. 0.56 mL of hexamethyldisilazane (TMS, 2.2 mmol) was mixed with 32 mL of octadecene ODE and magnetically stirred for 18 minutes to obtain a hot-injection solution (concentration 0.068 mol / L). The lead precursor solution was transferred to a three-dimensional flask, heated to 120 °C, and then deoxygenated under vacuum-Ar gas circulation three times at a vacuum degree of 10. -3 Pa, oxygen residue 60ppm, temperature controlled at 110℃±1℃, hot injection solution injected at a rate of 1.1mL / min, magnetically stirred at 600rpm for 3 minutes, and then quenched in an ice bath.

[0049] Step 4: Product processing and centrifugation. The reaction solution and a mixture of acetone and isopropanol at a volume ratio of 2:1 were centrifuged at 8000 rpm for 10 min. The precipitate was reconstituted with n-hexane and washed three times to obtain PbS quantum dot colloids coated with oleic acid. Finally, the colloid was placed in a vacuum drying oven at 60℃ and dried for 12 hours to completely evaporate the solvent in the quantum dots, thus obtaining PbS quantum dots.

[0050] Example 4

[0051] The steps involved in the fabrication of PbS quantum dots for resistive switching memory are as follows:

[0052] Step 1: Preparation of precursor solution. Weigh 1.2g of lead oxide (PbO, 5.4mmol) and mix with 3.5mL of oleic acid (OA, 11mmol). Add 45mL of octadecene (ODE) as solvent. Under nitrogen protection, heat to 130℃ at 1.5℃ / min and stir at a constant temperature until the solution is clear (about 25 minutes) to obtain lead precursor solution (PbO concentration 0.35mol / L).

[0053] Step 2: The reaction apparatus is set up in the same way as in Example 1.

[0054] Step 3: Preparation of lead sulfide quantum dots. 0.60 mL of hexamethyldisilazane (TMS, 2.3 mmol) was mixed with 32.8 mL of octadecene ODE and magnetically stirred for 20 minutes to obtain a hot-injection solution (concentration 0.070 mol / L). The lead precursor solution was transferred to a three-dimensional flask, heated to 125 °C, and then deoxygenated through three vacuum-Ar gas circulation cycles at a vacuum degree of 10. -3 Pa, oxygen residue 40ppm, temperature controlled at 115℃±2℃, hot injection solution injected at a rate of 1.2mL / min, magnetically stirred at 800rpm for 3 minutes, and then quenched in an ice bath.

[0055] Step 4: Product processing and centrifugation. The reaction solution and a mixture of acetone and isopropanol at a volume ratio of 2:1 were centrifuged at 8000 rpm for 10 min. The precipitate was reconstituted with n-hexane and washed three times to obtain PbS quantum dot colloids coated with oleic acid. Finally, the colloid was placed in a vacuum drying oven at 60℃ and dried for 12 hours to completely evaporate the solvent in the quantum dots, thus obtaining PbS quantum dots.

[0056] Many specific details have been set forth in the foregoing description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating PbS quantum dots for resistive switching memory, characterized in that, The steps are as follows: Step 1): Mix lead oxide (PbO) and oleic acid (OA) in a mass ratio of 1:2.5-1:3, add octadecene (ODE) in volume 8-12 times that of oleic acid as a solvent, heat to 110-130℃ under nitrogen protection and stir until completely dissolved to form a lead precursor solution. Step 2): Place the lead precursor solution obtained in Step 1 into the reaction apparatus for reaction, and monitor the pressure inside the reaction flask in real time. Step 3): Mix hexamethyldisilazane (TMS) and octadecene (ODE) at a volume ratio of 1:25-1:35 and stir for 10-20 minutes to obtain a hot-injection solution. Transfer the lead precursor solution to a three-necked flask, heat to 110-130℃, and deoxygenate through three vacuum-Ar gas circulation cycles. Then, rapidly inject the hot-injection solution at a rate of 0.8-1.2 mL / min, with a magnetic stirring speed of 500-800 rpm, and control the reaction time to 1-5 minutes. Quench the reaction in an ice bath. Step 4): Centrifuge the product from step 3) in a mixture of acetone and isopropanol at 7000-9000 rpm for 5-10 minutes. Redissolve the precipitate in n-hexane and wash it 3-4 times to obtain PbS quantum dot colloids coated with oleic acid. Then, dry it in a vacuum drying oven at 60℃ for 12 hours to completely evaporate the solvent in the quantum dots and obtain PbS quantum dots.

2. The method for fabricating PbS quantum dots for resistive switching memory according to claim 1, characterized in that, In step 3), the vacuum degree of the vacuum-Ar gas circulation deoxygenation is 10. -3 Up to 10 -2 Pa, oxygen residue <100ppm.

3. A method for fabricating PbS quantum dots for resistive switching memory according to claim 1 or 2, characterized in that, In step 4), the volume ratio of the acetone to isopropanol mixture is 2-3:

1.

4. The reaction apparatus used in the method for preparing PbS quantum dots for resistive switching memory according to claim 1, characterized in that, The reaction vessel includes a three-necked flask (1), a pressure-resistant venting hose (6), a vacuum pump (9), and an Ar gas cylinder (10). The three-necked flask (1) is fixed in a silicone oil thermostat by a metal bracket (2). A micro-injector (3) is connected to the left neck, a condenser (4) is connected to the center neck, and a thermometer (5) is installed at the right neck. One end of the pressure-resistant venting hose (6) is connected to the upper end of the condenser (4), and the other end is split into two paths, which are connected to the vacuum pump (9) and the Ar gas cylinder (10) respectively. A pressure gauge (7) is connected to the main gas path of the pressure-resistant venting hose (6) to monitor the pressure inside the reaction vessel in real time.

5. The reaction apparatus according to claim 4, characterized in that, The ventilation hose (6) is equipped with dual-passage air valves (8) on the main air line and the two branch air lines respectively.

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