CN109932373B - Method for measuring coverage rate of ligand on surface of quantum dot - Google Patents
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Abstract
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot, which can be used for quality evaluation of the quantum dot. If KiLess than 2 x 10‑10mol/cm2If the quantum dot quality is not good enough, K should be addediValue is carriedAnd then the solution or ink is prepared and the like. The method for determining the coverage rate of the ligand on the surface of the quantum dot has the advantages of accurate result and simple operation, and further can ensure the stability of the content of the ligand on the surface of the quantum dot, ensure the solubility of the quantum dots in different batches, avoid the coffee ring effect caused by different drying rates when the quantum dot solution is prepared into a film, and improve the pixel resolution, the starting voltage and the uniformity of the photoelectric efficiency of the quantum dot display panel.
Description
Technical Field
The invention relates to the technical field of quantum dots, in particular to a method for measuring the coverage rate of a ligand on the surface of a quantum dot.
Background
Quantum dots, refers to semiconductor nanocrystals whose geometric dimensions are smaller than the exciton bohr radius. The quantum dots have excellent optical properties such as wide absorption band, narrow fluorescence emission band, high quantum efficiency, good light stability and the like, and have great potential application in the fields of biomedicine, environmental energy, illumination display and the like. In recent years, the display technology based on quantum dot light emission receives high attention from the display industry, and compared with liquid crystal display and organic light emitting display, quantum dot light emission has the advantages of wider color gamut, higher color purity, simpler structure and higher stability, and is considered as a new generation display technology.
The preparation technology of the quantum dot display device comprises spin coating, ink jet printing and the like. The specific process of the two methods is to spray the quantum dot solution on the substrate material, and form a quantum dot film at a specific position after drying. The viscosity, surface tension and charge transport capacity of the quantum dot solution determine the wetting capacity, drying rate, coffee ring effect and photoelectric properties of the film of the quantum dot liquid drop in the preparation process of the device, so that the quality of the quantum dot solution plays an important role in the preparation of the device. In the preparation process of the quantum dot solution, the surface ligand of the quantum dot has an important influence on the quantum dot solution, and the surface ligand not only influences the photoelectric property of the quantum dot, but also influences the solubility and stability of the quantum dot solution. Common quantum dot surface ligands are carboxylic acids, amines, alkyl phosphorus, alkyl phosphine oxides, alkyl phosphoric acids, thiols, and the like. The influence of the surface ligand on the optical performance of the quantum dot per se is shown as follows: the average particle diameter of the quantum dots is smaller than the bohr radius of excitons, excitons are exposed on the surface to a certain extent, and the surface is easily influenced to reduce the optical performance of the excitons; when the surface atomic number of the quantum dot is increased, the surface dangling bonds are also increased rapidly, the atomic coordination is insufficient, so that a plurality of defects exist on the surface of the quantum dot, the probability of non-radiative recombination is increased due to the existence of the defects such as electrons or holes, and the recombination efficiency of normal radiative recombination is greatly reduced. When a proper surface ligand is added, the surface dangling bonds of the quantum dots can be effectively reduced, excitons are not exposed on the surface any more, and the optical performance of the quantum dots is improved. The influence of the surface ligand on the solubility and stability of the quantum dot is shown as follows: the increase of dangling bonds on the surface of the quantum dot leads the surface free energy to be very large, the surface becomes abnormally active, the system is unstable, the quantum dot tends to aggregate to reduce the surface area, and the solubility of the quantum dot solution is reduced. After the surface ligand is introduced, one end of the ligand is connected to the surface atoms of the quantum dots, and the other end of the ligand is dissolved in the solution, so that the surface energy of the quantum dots can be reduced, the solubility of the quantum dots can be improved, and the generation of precipitation in the quantum dot solution can be effectively inhibited.
Therefore, the solubility of the quantum dots greatly affects the preparation and performance of the device. Besides the solubility of the quantum dots and the types of the quantum dots, another important influence factor is the coverage rate of the ligands on the surfaces of the quantum dots. If the coverage rate of the surface of the quantum dot is low, the solubility of the quantum dot is poor, the uniformity of the quantum dot solution is poor, and the drying rate of the quantum dot solution and the coffee ring effect affect the quality of the luminescent layer film, which directly causes the problems of uneven quality of the printed panel, low pixel resolution, uneven lighting voltage, uneven photoelectric efficiency, and the like.
Disclosure of Invention
In view of the defects of the prior art, the invention firstly provides a method for measuring the coverage rate of the ligand on the surface of the quantum dot in order to ensure the quality stability of the quantum dot ink.
A method for measuring the coverage rate of a ligand on the surface of a quantum dot comprises the following steps:
providing sample particles, wherein each particle in the sample particles comprises a quantum dot and an organic ligand bound on the surface of the quantum dot, wherein the organic ligand is selected from aliphatic carboxylic acid ligand, nitrogen-containing organic ligand, phosphorus-containing organic ligand or sulfur-containing organic ligand;
when the organic ligand on the surface of the quantum dot is an aliphatic carboxylic acid ligand, the quantum dot does not contain oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the quantum dot does not contain phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the quantum dot does not contain sulfur element;
determining the average particle size of particles in the sample particles;
placing the sample particles to be detected in an energy spectrum analyzer, and collecting data of the content of each element in the sample particles to be detected to obtain a content curve of each element in the sample particles;
and calibrating the element types in the content curve, and calculating to obtain the coverage rate of the quantum dot surface ligand.
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot. Determining the surface ligand coverage rate K by measuring the size of the quantum dot and the relative content of the surface ligand in the quantum dotiFor the coverage of the quantum dot surface ligand KiIf K isiLess than 2 x 10-10mol/cm2If the solubility of the quantum dot is not good enough, K should be addediAfter the value is increased, the application such as solution or ink preparation is carried out. The method for determining the coverage rate of the ligand on the surface of the quantum dot can ensure the stability of the content of the ligand on the surface of the quantum dot, the solubility of the quantum dots in different batches, the drying rate of a quantum dot solution and the stability of a coffee ring effect, and can improve the pixel resolution, the lighting voltage and the uniformity of the photoelectric efficiency of the quantum dot display panel.
Drawings
FIG. 1 is a graph of the spectral analysis selected region of the CdZnSe/CdZnSe/ZnSe quantum dots in example 1.
Detailed Description
The invention provides a method for measuring the coverage rate of a ligand on the surface of a quantum dot, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A method for measuring the coverage rate of a ligand on the surface of a quantum dot comprises the following steps:
s10 providing sample particles, wherein individual particles of the sample particles comprise quantum dots and organic ligands bound to the surfaces of the quantum dots, the organic ligands being selected from aliphatic carboxylic acid ligands, nitrogen-containing organic ligands, phosphorus-containing organic ligands, or sulfur-containing organic ligands;
when the organic ligand on the surface of the quantum dot is an aliphatic carboxylic acid ligand, the quantum dot does not contain oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the quantum dot does not contain phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the quantum dot does not contain sulfur element;
s20 determining the average particle size of the particles in the sample particles;
s30, placing the sample particles in a scanning electron microscope, and selecting the sample particles to be detected;
s40, placing the sample particles to be detected in an energy spectrum analyzer, and collecting data of the content of each element in the sample particles to be detected to obtain a content curve of each element in the sample particles;
s50, calibrating the element types in the content curve, and calculating to obtain the coverage rate of the quantum dot surface ligand.
The invention provides a method for determining the coverage rate of a ligand on the surface of a quantum dot by using an energy spectrum analysis method. By measuring the coverage rate K of the organic ligand on the surface of the quantum dotiCan be used forAnd (5) evaluating the quality of the quantum dots. If KiLess than 2 x 10-10mol/cm2If the quantum dot quality is not good enough, K is requirediAfter the value is increased, the application such as solution or ink preparation is carried out. The method for determining the coverage rate of the ligand on the surface of the quantum dot has the advantages of accurate result and simple operation, and further can ensure the stability of the content of the ligand on the surface of the quantum dot, ensure the solubility of the quantum dots in different batches, avoid the coffee ring effect caused by different drying rates when the quantum dot solution is prepared into a film, and improve the pixel resolution, the starting voltage and the uniformity of the photoelectric efficiency of the quantum dot display panel.
The quantum dot surface ligand coverage rate test and calculation principle is as follows:
the sample particle is a collection of several individual particles, which comprise quantum dots and ligands bound to the surface of the quantum dots. Surface ligand coverage K in the present inventioniThe surface ligand coverage rate K can be calculated and obtained through the quantity of substances of characteristic elements in special groups combined with the quantum dotsi. Surface ligand coverage KiThe passing surface can be obtained by the following formula:
Ki＝ml/(0.74MlmQSq/ρQVq) (formula 1)
Specifying the mass m of the characteristic element in the specific functional group in the surface ligand of the quantum dot in the sample particlelMolar mass MlTotal mass of sample particles is mQDensity is rhoQSurface area S of individual particles in sample particlesqVolume is VqThe sample particles were densely packed with a space utilization of 0.74, assuming spherical particles with an average particle size of d.
Wherein the volume of the single particle is
Surface area of individual particles
Substituting into a formula and calculating to obtain Ki＝mlρQd/4.44MlmQ(formula 2), wherein, when the organic ligand is the aliphatic carboxylic acid ligand, the organic ligand is divided by 2; when the organic ligand is a multidentate ligand, it is desirable to remove the ligand denticity, for example, 2 when the ligand is a dithiol.
In the above formula 2,. rhoQThe method can be obtained by searching the density of related substances or testing by using an Archimedes principle, and the d can be obtained by testing the size of the quantum dot according to a TEM. Therefore, m is required to be tested by adopting a proper methodl/mQThus obtaining the ligand coverage rate on the surface of the quantum dot.
The invention adopts a method of energy spectrum analysis to obtain a content curve of each element in sample particles, calibrates each element type of the sample particles to be detected, obtains the relative content of each element in the sample particles to be detected according to the integral area of each element curve in the content curve, takes the relative content of the characteristic element in the organic ligand, and calculates the mass ratio m of the characteristic element in the organic ligand to the particles of the samplel/mQ. When the organic ligand on the surface of the equivalent quantum dot is an aliphatic carboxylic acid ligand, the characteristic element in the organic ligand is oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the characteristic element in the organic ligand is a nitrogen element; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the characteristic element in the organic ligand is a phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the characteristic element in the organic ligand is a sulfur-containing element. When the organic ligand on the surface of the quantum dot is an aliphatic carboxylic acid ligand, the quantum dot does not contain oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen elements; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the quantum dot does not contain phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the quantum dot does not contain sulfur element. For example, when the equivalent quantum point is CdZnSeS, the surface ligand cannotIs a thiol-containing ligand; when the quantum dots are InP/ZnS, the surface ligands cannot be thiol-and phosphine-containing ligands.
The quantum dot comprises a known quantum dot A, wherein the quantum dot A comprises a unary, binary, ternary and quaternary quantum dot.
Specifically, in step S10, the quantum dots may be selected from unary quantum dots, binary quantum dots, ternary quantum dots, or quaternary quantum dots. For example: the unitary quantum dots are selected from Au, Ag, Cu, Pt or C quantum dots; the binary quantum dots are selected from CdSe, ZnSe, PbSe, CdTe, ZnO, MgO and CeO2、NiO、TiO2InP or CaF2Quantum dots; the ternary quantum dots are selected from CdZnS, CdZnSe, CdSeS, PbSeS, ZnCdTe, CdS/ZnS, CdZnS/ZnS, CdZnSe/ZnSe, CdSeS/CdSeS/CdS, CdSe/CdZnSe/CdZnSe/ZnSe, CdS/CdZnS/CdZnS/ZnS, NaYF4Or NaCdF4Quantum dots; the quaternary quantum dots comprise CdSZnSeyS, CdSe/ZnS, CdSe/CdS/ZnS, CdSe/ZnSe/ZnS, CdSZnSe/CdS/ZnS or InP/ZnS quantum dots.
Specifically, in step S10, the sulfur-containing organic ligand is selected from mono-thiol, di-thiol, mercapto alcohol, mercaptoamine, or mercaptoacid; preferably, the monothiol is selected from the group consisting of hexanethiol, octanethiol, nonanethiol, decanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, hexadecanethiol, and octadecanethiol, but is not limited thereto; preferably, the dithiol is selected from but not limited to 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 4-butanedithiol, 1, 5-pentanethiol, 1, 6-hexanedithiol, 1, 8-octanethiol or 1, 10-decanedithiol; preferably, the mercaptoalcohol is selected from the group consisting of but not limited to 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol, 5-mercapto-1-pentanol or 6-mercapto-1-hexanol, 8-mercapto-1-octanol; preferably, the mercapto acid is selected from the group consisting of 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid, 4-mercaptobenzoic acid, and cysteine, but is not limited thereto; preferably, the mercaptoamine is selected from the group consisting of 2-mercaptoethylamine, 3-mercaptopropylamine, 4-mercaptobutylamine, 5-mercaptopentylamine, 6-mercaptohexylamine, 2-amino-3-mercaptopropionic acid, 2-aminothiophenol, and mercaptoundecanamine, but is not limited thereto.
The fatty carboxylic acid ligand is a fatty acid having 8 to 18 carbon atoms, and preferably, for example, the fatty carboxylic acid ligand may be selected from stearic acid, octadecenoic acid, heptadecanoic acid, heptadecenoic acid, hexadecanoic acid, hexadecenoic acid, tetradecanoic acid, dodecenoic acid, or decenoic acid, but not limited thereto.
The phosphorus-containing organic ligand is selected from alkyl phosphorus, alkyl phosphine oxide or alkyl phosphoric acid. Preferably, the alkyl phosphine is selected from the group consisting of tributylphosphine, tripentylphosphine, trihexylphosphine, trimore-ylphosphine, trioctylphosphine, trinonyl phosphine, and tridecyl phosphine, but is not limited thereto; preferably, the alkyl phosphine oxide is selected from the group consisting of tributyl phosphine oxide, tripentyl phosphine oxide, trihexyl phosphine oxide, triheptyl phosphine oxide, trioctyl phosphine oxide, trinonyl phosphine oxide and tridecyl phosphine oxide, but not limited thereto; preferably, the alkyl phosphoric acid is selected from alkyl phosphoric acids having more than 8 carbon atoms, such as, but not limited to, dodecyl phosphoric acid, undecyl phosphoric acid, dodecyl phosphoric acid, tridecyl phosphoric acid, tetradecyl phosphoric acid, pentadecyl phosphoric acid, hexadecyl phosphoric acid, or octadecyl phosphoric acid. The fatty carboxylic acid ligand is selected from fatty acids with 8-18C atoms, such as stearic acid, octadecenoic acid, heptadecanoic acid, heptadecenoic acid, hexadecanoic acid, hexadecenoic acid, tetradecanoic acid, dodecenoic acid, or decenoic acid, but not limited thereto.
In one embodiment, in step S20 of the present invention, the transmission electron microscope analyzer may be used to determine the average particle size of the particles in the sample particles.
Specifically, the test conditions for determining the average particle size of particles in the sample particles by using a transmission electron microscope analyzer are as follows: the accelerating voltage is 200-300kV, the emission current is 7-20 muA, the working distance is 10-20mm, and the dead time is 20-40%.
The step of determining the average particle size of the particles in the sample particles using a transmission electron microscope analyzer comprises: and (3) dissolving sample particles in a nonpolar solvent to prepare a sample particle solution with the concentration of 1-5mg/mL, after the solution is completely dissolved, dripping 5-10 drops of a small amount of sample particle solution on a copper net, and placing the copper net in a transmission electron microscope analyzer for test analysis d. Specifically, a sample is amplified and analyzed by the magnification factor of 70000-150000 times, a TEM picture is obtained by focusing a region with concentrated and uniformly dispersed quantum dots, then the TEM picture is analyzed by software, the length of a ruler is set, then 30-80 quantum dots are calibrated, and finally the average particle size d of particles is obtained by calculation.
Specifically, in step S30, sampling sample particles, adhering a conductive adhesive or a double-sided adhesive paper on a sample holder, uniformly scattering the sample particles on the sample holder, and plating a conductive film, preferably an Au conductive film, an Ag conductive film or a Pt conductive film, for 1-10 min; observing the sample particles in a scanning electron microscope, setting the magnification of 200-1500 times, selecting a sample particle concentrated region as an analysis region, wherein the size of the analysis region is 5 x 5-20 x 20um2And the sample particles in the analysis area are sample particles to be detected.
Specifically, in step S40, the sample particles to be measured are placed in an energy spectrum analyzer to collect content data of each element contained in the sample particles to be measured, so as to obtain a content curve of the element in the quantum dot.
Specifically, in the step S50, the element types in the element content curve obtained in the step S30 are calibrated, the relative content of the characteristic element in the organic ligand is obtained by taking the relative content of each element according to the integral area of each element peak, and the mass ratio m of the characteristic element in the organic ligand to the particles of the sample is calculatedl/mQ. Preferably, 5-10 analysis areas can be selected from the same sample particle to be used as 5-10 groups of sample particles to be detected for analysis, and the mass ratio m of the characteristic elements in 5-10 organic ligands to the particles of the sample is calculatedl/mQAfter the average value is taken, the surface coverage rate K of the quantum dots is obtained through calculationi。
The research shows that the coverage rate K of the ligand on the surface of the quantum dotiIf less than 2 x 10-10mol/cm2The solubility of the quantum dots is poor, and the quality of a film prepared into the film subsequently is influenced. Require to be connected with KiAfter the value is increased, the application such as solution or ink preparation is carried out. Increase of KiValues may be entered by ligand re-exchangeAnd (6) rows. The specific process is as follows: the sample particles are firstly dissolved in a non-polar solvent, and then the same surface ligand is added to carry out exchange at the temperature of 25-150 ℃. The nonpolar solvent comprises chloroform, normal hexane, heptane, octane, toluene, chlorobenzene, dichlorobenzene, carbon tetrachloride, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, cyclodecane, cycloundecane, octadecene and the like. The amount of ligand added during said ligand re-exchange should not be less than (2 x 10)-10-K1)n1/K1(formula 3, K)0Representing the coverage rate of the ligand on the surface of the target quantum dot, K1Representing the coverage rate of the quantum dot ligand measured for the first time, and n1 is the amount of ligand added for the first time in the preparation process of the quantum dot). By using the process, KiThe value is increased to more than 2 x 10-10mol/cm2The quantum dots can be applied to other solution properties.
The present invention will be described in detail below with reference to examples.
Example 1
And determining the coverage rate of the octanethiol ligand on the surface of the CdZnSe/CdZnSe/ZnSe quantum dot.
And determining the average particle size d of the CdZnSe/CdZnSe/ZnSe quantum dots. And (2) dissolving CdZnSe/CdZnSe/ZnSe quantum dots with a surface ligand of octanethiol in a normal hexane solution to prepare a solution of 5mg/ml, after the solution is completely dissolved, dripping 5 drops of a small amount of quantum dot solution on a copper mesh, and placing the copper mesh in a transmission electron microscope analyzer for test analysis. The acceleration voltage was set at 200kV, the emission current was set at 10. mu.A, the working distance was set at 15mm, and the dead time was 20%. And (3) carrying out amplification analysis on the sample, firstly setting the amplification factor to be 70000 times, taking a region with concentrated and uniformly dispersed quantum dots for focusing analysis, and taking a TEM picture of the sample. And analyzing the TEM picture, firstly setting the length of a ruler, then calibrating 30-80 quantum dots, and calculating to obtain the average particle size d of the quantum dots, which is 11.6 nm.
And determining the content of the S element in the octanethiol ligand on the surface of the CdZnSe/CdZnSe/ZnSe quantum dot. Taking quantum dot powder, firstly bonding conductive adhesive or double-sided adhesive paper on a sample seat, then uniformly scattering the quantum dot powder sample on the sample seat, and plating a layer of PAnd (5) conducting film coating for 2min, and then placing the sample in a scanning electron microscope for observation. Setting the magnification to 500 times, selecting the quantum dot concentration area for analysis, and the analysis area is 5 x 5um2And acquiring data of element types contained in the quantum dots during region selection analysis to obtain a content curve of the elements in the quantum dots, calibrating Cd, Zn, Se and S of each element type in the content curve of the elements, and obtaining the content ratio of each element according to the integral area of each element peak. Selecting 5 areas from the sample for analysis, and then calculating to obtain the average value of the content ratio of each element, thereby obtaining m in the surface ligand of the quantum dotl/mQ. Table 1 shows the element content ratio in 5 selected regions of the sample, and FIG. 1 is a CdZnSe/CdZnSe/ZnSe quantum dot energy spectrum analysis selected region picture. Obtaining the content ratio of the S element in the surface ligand of the quantum dot, namely ml/mQThe content was 2.18%.
And determining the coverage rate of the thiol ligand on the surface of the CdZnSe/CdZnSe/ZnSe quantum dot. Known ml/mQ2.15 percent, the size d of the quantum dots is 11.6nm, and the density of the quantum dots is 5.6g/cm3Calculating according to the formula 2 to obtain the coverage rate K of the quantum dot surface ligandiIs 9.96 x 10-10mol/cm2This value is greater than 2 x 10-10mol/cm2The solution preparation can be directly carried out without ligand re-exchange.
TABLE 1 CdZnSe/CdyZnSe/ZnSe Quantum dot with the content ratio of each element
| Kind of element | Selection area 1 | Selection area 2 | Selection area 3 | Selection area 4 | Selection area 5 | Mean value of |
| S | 2.38 | 2.24 | 1.9 | 2.04 | 2.2 | 2.15 |
| Zn | 26.31 | 26.89 | 25.32 | 24.56 | 26.77 | 25.97 |
| Se | 44.78 | 45.81 | 46.45 | 47.77 | 44.61 | 45.88 |
| Cd | 26.53 | 25.06 | 26.33 | 25.63 | 26.42 | 25.99 |
Example 2
And determining the coverage rate of octadecyl phosphate on the surface of the CdZnSe quantum dot.
And determining the average particle size d of the CdZnSe quantum dots. And (2) dissolving CdZnSe quantum dots with surface ligands of octadecyl phosphoric acid in a normal hexane solution to prepare a solution of 3mg/ml, dripping 8 drops of a small amount of quantum dot solution on a copper net after the solution is completely dissolved, and placing the copper net in a transmission electron microscope analyzer for test analysis. The acceleration voltage was set at 300kV, the emission current was 20 μ A, the working distance was set at 20mm, and the dead time was 40%. And (3) carrying out amplification analysis on the sample, firstly setting the amplification factor to be 150000 times, taking a region with concentrated and uniformly dispersed quantum dots for focusing analysis, and taking a TEM picture of the sample. And analyzing the TEM picture, firstly setting the length of a ruler, then calibrating 30-80 quantum dots, and calculating to obtain the average particle size d of the quantum dots, which is 8.25 nm.
Determining the content of P element in octadecyl phosphate ligand on the surface of the CdZnSe quantum dot, taking quantum dot powder, firstly bonding conductive adhesive or double-faced adhesive tape on a sample seat, uniformly scattering a quantum dot powder sample on the sample seat, plating an Au conductive film for 10min, and then placing the sample in a scanning electron microscope for observation. Setting the magnification at 1200 times, selecting the concentrated region of the quantum dots for analysis, and the analysis region size is 20 × 20um2And in the field selection analysis, data of element types contained in the quantum dots are collected to obtain a content curve of the elements in the quantum dots, Cd, Zn, Se and P calibration is carried out on each element type in the content curve of the elements, and the content ratio of each element is obtained according to the integral area of each element peak. Selecting 5 areas from the sample for analysis, and then calculating to obtain the average value of the content ratio of each element, thereby obtaining the content ratio m of the P element in the ligand on the surface of the quantum dotl/mQ. Table 2 shows the elemental content ratios in 5 selected regions of the sample. Obtaining the content ratio of P element in the surface ligand of the quantum dot, namely ml/mQIt was 0.28%.
And determining the coverage rate of the phosphate ligand on the surface of the CdZnSe quantum dot. Known as ml/mQ0.28%, the quantum dot size d is 8.25nm, and the quantum dot density is 5.3g/cm3Calculating according to the formula 2 to obtain the octadecyl phosphate ligand coverage rate K on the surface of the quantum dot1Is 8.6 x 10-11mol/cm2This value is less than 2 x 10-10mol/cm2The ligand is needed to be exchanged again, and the solution preparation can be directly carried out.
And exchanging the surface ligands of the CdZnSe quantum dots. Knowing that the octadecyl phosphate added in the preparation process of the CdZnSe quantum dot is 6mmol, the adding amount of the octadecyl phosphate in the ligand exchange process cannot be less than 7.95 mmol. And (3) dissolving the CdZnSe quantum dots in a normal hexane solution, adding 9mmol of octadecyl phosphoric acid into the solution, heating and stirring at 40 ℃ for 4h, and cleaning to obtain the ligand-exchanged quantum dots. Detecting and analyzing the content of the surface ligand of the quantum dots after ligand re-exchange by the process 2 to obtain the content ratio of each element shown in the table 3, and calculating to obtain K2Is 3.3 x 10-10mol/cm2. Therefore, the CdZnSe quantum dots can be used for preparing other solutions after ligand re-exchange.
TABLE 2 CdZnSe Quantum dots with the content ratio of each element
| Kind of element | Selection area 1 | Selection area 2 | Selection area 3 | Selection area 4 | Selection area 5 | Mean value of |
| P | 0.66 | 0.21 | 0.06 | 0.18 | 0.3 | 0.28 |
| Zn | 33.56 | 32.52 | 31.73 | 31.26 | 32.57 | 32.33 |
| Se | 45.33 | 46.78 | 46.45 | 47.18 | 45.98 | 46.34 |
| Cd | 20.45 | 20.49 | 21.76 | 21.38 | 21.15 | 21.05 |
TABLE 3 Cd after ligand Reswap1-xZnxContent ratio of each element in Se quantum dot
| Kind of element | Selection area 1 | Selection area 2 | Selection area 3 | Selection area 4 | Selection area 5 | Mean value of |
| P | 0.64 | 1.94 | 0.97 | 1.09 | 0.8 | 1.09 |
| Zn | 33.25 | 32.46 | 32.35 | 32.26 | 32.37 | 32.54 |
| Se | 45.44 | 44.83 | 45.21 | 45.91 | 45.98 | 45.47 |
| Cd | 20.67 | 20.77 | 21.47 | 20.74 | 20.85 | 20.90 |
While the method for measuring the coverage of the quantum dot surface ligand provided by the embodiment of the present invention has been described in detail, for those skilled in the art, there may be variations in the specific implementation and application scope according to the concept of the embodiment of the present invention, and in summary, the content of the present specification should not be construed as a limitation to the present invention, and any variation made according to the design concept of the present invention is within the protection scope of the present invention.
Claims (12)
1. A method for measuring the coverage rate of a ligand on the surface of a quantum dot is characterized by comprising the following steps:
providing sample particles, wherein each particle in the sample particles comprises a quantum dot and an organic ligand bound on the surface of the quantum dot, wherein the organic ligand is selected from aliphatic carboxylic acid ligand, nitrogen-containing organic ligand, phosphorus-containing organic ligand or sulfur-containing organic ligand;
when the organic ligand on the surface of the quantum dot is an aliphatic carboxylic acid ligand, the quantum dot does not contain oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the quantum dot does not contain nitrogen element; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the quantum dot does not contain phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the quantum dot does not contain sulfur element;
determining the average particle size of the particles in the sample particles;
placing the sample particles in an energy spectrum analyzer, and collecting data of the content of each element in the sample particles to obtain a content curve of each element in the sample particles;
calibrating the element types in the content curve, and calculating to obtain the coverage rate K of the quantum dot surface ligandi；
The surface ligand coverage rate KiThe amount of substance binding to the surface ligand per unit area of the surface of the quantum dot, Ki=ml/(0.74MlmQSq/ρQVq) Wherein M1 is the mass of characteristic elements in special functional groups in the surface ligand of the quantum dot, M1Molar mass m of characteristic elements in special functional groups in the surface ligands of the quantum dotsQIs the total mass of the sample particles, pQIs density, SqIs the surface area of a single particle in the sample particle, VqIs a volume.
2. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 1, wherein the method comprises the steps of calibrating the types of elements in a content curve to obtain the mass ratio of the characteristic elements in the organic ligand to sample particles, and calculating to obtain the coverage rate K of the ligand on the surface of the quantum dotiWhen the organic ligand on the surface of the quantum dot is a fatty carboxylic acid ligand, the characteristic element in the organic ligand is oxygen element; when the organic ligand on the surface of the quantum dot is a nitrogen-containing organic ligand, the characteristic element in the organic ligand is a nitrogen element; when the organic ligand on the surface of the quantum dot is a phosphorus-containing organic ligand, the characteristic element in the organic ligand is a phosphorus element; when the organic ligand on the surface of the quantum dot is a sulfur-containing organic ligand, the characteristic element in the organic ligand is a sulfur-containing element.
3. The method for measuring the ligand coverage rate on the surface of the quantum dot according to claim 1, wherein the phosphorus-containing organic ligand is selected from alkyl phosphorus, alkyl phosphine oxide or alkyl phosphoric acid;
the sulfur-containing organic ligand is selected from the group consisting of a mono-thiol, a di-thiol, a mercapto alcohol, a mercaptoamine, or a mercaptoacid;
the nitrogen-containing organic ligand is organic amine with the carbon atom number more than 8;
the aliphatic carboxylic acid ligand is selected from aliphatic acid with 8-18C atoms.
4. The method for determining the coverage rate of the ligand on the surface of the quantum dot according to claim 1, wherein after the sample particle to be detected is selected, the sample particle is placed in an energy spectrum analyzer, data of the content of each element in the sample particle is collected, and a content curve of each element is obtained, and the step of selecting the sample particle to be detected comprises the following steps: and placing the particles on a sample seat in a scanning electron microscope, plating a layer of conductive film on the surfaces of the particles, setting the magnification of 200-1500 times, and selecting the particles in the particle concentration area as sample particles to be detected.
5. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 4, wherein the conductive film is selected from an Au conductive film, an Ag conductive film or a Pt conductive film.
6. The method for measuring the ligand coverage on the surface of the quantum dot according to claim 4, wherein the selected particle concentration region has an area size of 25-400 um2。
7. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 4, wherein the step of acquiring data of the content of each element in the sample particle to obtain a content curve of each element in the sample particle comprises the following steps: selecting particles in 5-10 particle concentration areas as sample particles to be detected, placing the sample particles to be detected in an energy spectrum analyzer, and collecting data of the content of each element in the sample particles to be detected to obtain a content curve of each element in 5-10 groups of sample particles to be detected.
8. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 2, wherein the relative mass of each element is obtained according to the integral area of each element in the content curve, and the mass ratio of the characteristic element in the organic ligand to the sample particle is calculated.
9. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to claim 1, wherein the size d of the particle is measured by a transmission electron microscope analyzer.
10. The method for determining the coverage rate of the ligand on the surface of the quantum dot according to claim 9, wherein the conditions for determining the average particle size of the particles in the sample particles by using a transmission electron microscope analyzer are as follows: setting the accelerating voltage between 200-300kV, the emission current between 7-20 muA, the working distance between 10-20mm and the dead time between 20-40%.
11. The method for determining the ligand coverage on the surface of the quantum dot according to claim 9 or 10, wherein the step of determining the average particle size of the particles in the sample particles by using a transmission electron microscope analyzer comprises the following steps: and (3) carrying out amplification analysis on the sample, wherein the amplification factor is 70000-150000 times, focusing the concentrated and uniformly dispersed area of the sample particles to obtain a TEM picture of the sample particles, analyzing the TEM picture by using software, calibrating 30-80 quantum dots, and calculating to obtain the average particle size of the sample particles.
12. The method for measuring the coverage rate of the ligand on the surface of the quantum dot according to any one of claims 1 to 10, wherein the coverage rate K of the ligand on the surface of the quantum dot is obtained by calibrating the types of elements in a content curve and calculatingiIf K isiLess than 2 x 10- 10mol/cm2And the ligand re-exchange method is adopted to improve the coverage rate of the ligand on the surface of the quantum dot.
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