Alkali metal gas chamber anti-relaxation self-assembly molecular coating adsorption energy quantification method

Abstract

The invention relates to an alkali metal gas chamber anti-relaxation self-assembly molecular coating adsorption energy quantification method, which finally realizes the physical quantification of the anti-relaxation coating adsorption energy by establishing a contact angle and surface topography collaborative characterization model and combining an adsorption-desorption dynamic formula, and is characterized by comprising the following steps: 1) establishing a contact angle and surface topography collaborative characterization model; depositing organosilane on a gas chamber glass substrate by adopting a liquid phase self-assembly method to form an anti-relaxation coating sample; step 2, selecting a plurality of measuring points on the anti-relaxation coating sample, dropping a 1 [mu] L ultrapure water liquid drop on each measuring point, determining a polarization retention angle of each measuring point according to the liquid drop height and the liquid drop substrate radius obtained by a contact angle measuring instrument, and scanning a local area of the corresponding measuring point by using an atomic force microscope (AFM), extracting an arithmetic mean value Ra of the surface roughness parameter and a root-mean-square value Rq of the surface roughness parameter as quantitative indexes of the polarization maintaining cross section; and step 3, taking free energy formed by the molecular layer of the coating as coating adsorption energy delta G.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of atomic optics and surface physics, and particularly to an alkali metal cell anti-relaxation self-assembled molecular coating adsorption energy quantification method. BACKGROUND

[0002] The alkali metal cell is the core component of quantum sensors such as atomic gyroscopes and atomic magnetometers, and its anti-relaxation property determines the upper limit of the sensitivity of the sensor. Among them, the spin-destroying collision relaxation is one of the dominant items of total relaxation. The traditional method usually uses the method of filling buffer gas in the alkali metal cell to slow down the spin-destroying collision relaxation. Another method is to plate an anti-relaxation coating on the inner wall of the cell, such as OTS (octadecyltrichlorosilane), paraffin or olefin molecular film, to reduce the polarization loss caused by the collision of atoms with the bubble wall. At present, the performance of the coating is often characterized by single indicators such as the number of alkali metal wall collisions and the surface roughness of the coating. However, this method cannot accurately reveal the interaction mechanism between the coating and the alkali metal atom interface, nor can it quantitatively compare the differences in adsorption strength of different coatings on alkali metal atoms.

[0003] Previous studies have shown that the anti-relaxation performance of alkali metal atoms is closely related to the adsorption energy of alkali metal on the coating, and the smaller the adsorption energy, the easier it is for alkali metal atoms to undergo elastic collision and retain the polarization state, thereby prolonging the spin lifetime and improving the detection sensitivity. Therefore, developing a high-precision, repeatable and quantitative adsorption energy evaluation method is the key to realizing the scientific design and engineering controllability of anti-relaxation coatings. At present, there is still a lack of a systematic multi-point collaborative measurement method to directly link the polarization retention angle, coating topography and adsorption energy. Although there are explorations in the literature to indirectly estimate the adsorption energy through molecular dynamics simulation or contact angle-surface energy model, there are still problems such as separation of measurement positions, simplification of quantitative models, and poor applicability of actual multi-layer coatings. In addition, the polarization retention angle on the rough surface of the coating surface has obvious non-uniformity, and the local change of roughness also has an important influence on the adsorption behavior of atoms, so it is urgent to develop a new adsorption energy evaluation scheme combining multi-point surface characterization and thermodynamic modeling.

[0004] Existing design schemes and their shortcomings:

[0005] Most of the existing literature and patents focus on the formulation or topography control of anti-relaxation materials, and have not yet proposed a unified path to quantify the adsorption energy from surface parameters, combining contact angle and roughness, which cannot provide a quantitative evaluation standard for coating performance, hindering the engineering design and optimization of the coating. After searching, there is no related patent on the adsorption energy quantification method of the coating of the alkali metal cell.

[0006] The searched existing scheme disclosure files are as follows:

[0007] The first disclosed scheme is CN201811452033.4 - A method for manufacturing an alkali metal cell based on Plasma hydroxylation to improve the anti-relaxation performance of the coating. This scheme improves the operation problems existing in the traditional wet hydroxylation in the tail pipe of the micro cell by introducing the plasma dry hydroxylation means, improves the process consistency and safety, and enhances the surface hydroxyl density, which provides a good foundation for the combination of the subsequent coating. However, this method still belongs to the preparation process control category, and the anti-relaxation mechanism of the coating performance after formation is not quantified and evaluated in depth.

[0008] The second disclosed scheme is CN110357451A - An anti-relaxation coating and an alkali metal cell and a method. This scheme optimizes the material structure layer, proposes a design idea of a double-layer composite coating of organic silane with different chain lengths, and improves the density and uniformity of the coating through the synergistic effect of short-chain and long-chain organic molecules, thereby improving the anti-relaxation performance. However, this scheme focuses on the design of the coating structure, lacks physical quantitative means for anti-relaxation performance, cannot systematically explain the performance changes from the adsorption behavior, and does not have the ability to compare the performance of various coating schemes.

[0009] The above two patents are related to the preparation of anti-relaxation coating and the optimization of anti-relaxation performance of alkali metal cell, but the existing patents mainly focus on the preparation method or the structure design of the anti-relaxation coating, and do not analyze and test the coating quality and quantitative indicators. The present application proposes an adsorption energy quantification method for anti-relaxation self-assembled molecular coating of alkali metal cell, which realizes high-precision quantification of adsorption energy through multi-parameter collaborative characterization and thermodynamic modeling. This method does not depend on specific coating structure or pretreatment method, has high applicability and expandability, can be applied not only to the performance research of typical anti-relaxation coatings such as OTS, but also as an evaluation method platform for various new self-assembled or hybrid molecular film materials, and has wide theoretical promotion and engineering application value. SUMMARY

[0010] The present application proposes an adsorption energy quantification method for anti-relaxation self-assembled molecular coating of alkali metal cell, aiming to solve the problems of lack of quantitative evaluation means for the anti-relaxation ability of the coating and inability to accurately deduce the adsorption energy of the alkali metal from the experimental measurement results in the prior art. By establishing a collaborative characterization model of contact angle and surface topography, combined with adsorption-desorption kinetics formula, the physical quantification of adsorption energy of anti-relaxation coating is finally realized. The core idea of the present application is to construct a complete parameter mapping path based on measurable surface parameters, and to deduce the internal relationship between coating adsorption energy and anti-relaxation performance.

[0011] The technical solution of the present application is as follows:

[0012] An alkali metal cell anti-relaxation self-assembled molecular coating adsorption energy quantization method, characterized in that it comprises the following steps:

[0013] Step 1, using a liquid phase self-assembly method to deposit a coating on the cell glass substrate to form an anti-relaxation coating sample;

[0014] Step 2, select multiple measurement points on the anti-relaxation coating sample, drop a drop of 1 μL ultrapure water on each measurement point, determine the polarization retention angle of each measurement point according to the liquid drop height and liquid drop base radius obtained by the contact angle measuring instrument, use an atomic force microscope (AFM) to scan the local area corresponding to the measurement point, and extract the arithmetic mean value Ra of the surface roughness parameter and the root mean square value Rq of the surface roughness parameter as the quantification index of the polarization retention section;

[0015] Step 3, take the free energy of the coating molecular layer as the coating adsorption energy ΔG:

[0016] ΔG=-RT ln(k eq )=-RT ln(k a / k d ),

[0017]

[0018] where R is the gas constant, T is the absolute temperature, k eq is the equilibrium constant, k a is the adsorption constant, k d is the desorption constant, is the coating surface coverage, t is time, θ is the polarization retention angle, c coat is the coating deposition solution concentration.

[0019] k a and k d in step 3 are determined by expression fitting.

[0020] Step 3 includes the following expression:

[0021]

[0022]

[0023] K2=k a c coat +k d ,

[0024] where is a function of t, K1 is a coverage coefficient, reflecting the maximum coverage of the surface ultimately, and K2 is an apparent rate coefficient, reflecting the rate at which the surface reaches adsorption equilibrium.

[0025] The following expression is included in step 2:

[0026]

[0027] Where θ is the contact angle, h is the droplet height, a is the droplet base radius, and V is the droplet volume.

[0028] In step 2, the Cassie-Baxter formula is introduced to modify the contact angle, and a function relationship between the contact angle and the effective adsorption area of the coating is established, realizing the collaborative matching of the two types of parameters at the spatial point, providing input variables for subsequent adsorption behavior modeling.

[0029] cosθ app = F1cosθ1 + f2cosθ2,

[0030] Where θ app is the apparent contact angle on the non-uniform surface, F1 is the effective adsorption area fraction of the coating, i.e., the surface area fraction of the first medium, θ1 is the contact angle of the first medium, F2 is the air surface area fraction hidden in the adsorption area of the coating due to surface roughness, i.e., the surface area fraction of the second medium, and θ2 is the contact angle of the second medium.

[0031] In step 1, the gas chamber glass substrate is a high borosilicate glass substrate, and the coating is octadecyltrichlorosilane OTS. A deposition time of 1h is used, and a 6mM OTS solution concentration is used. After deposition, the sample is heat treated at 150℃ for 24h to solidify the coating and enhance the molecular order and coating stability, forming a stable OTS anti-relaxation coating.

[0032] The technical effects of the present application are as follows: The alkali metal gas chamber anti-relaxation self-assembled molecular coating adsorption energy quantization method can be widely applied to multi-layer OTS coatings and other organic anti-relaxation materials, and can realize high-precision measurement of adsorption energy under different deposition conditions, and establish a mapping relationship between coating process parameters, surface structure, adsorption energy and anti-relaxation performance, providing reliable basis for structure design and performance evaluation of gas chamber coating.

[0033] The application provides an alkali metal cell anti-relaxation self-assembled molecular coating adsorption energy quantification method, high-precision quantification of adsorption energy is realized through multi-parameter collaborative characterization and thermodynamic modeling, the method does not depend on specific coating structures or pretreatment methods, has high applicability and expandability, can be applied to performance research of typical anti-relaxation coatings such as OTS, and can also be used as an evaluation method platform for various new self-assembled or hybrid molecular film materials, and has wide theoretical promotion and engineering application value.

[0034] Compared with the prior art, the application has the characteristics that:

[0035] 1. The coating alkali metal cell can be subjected to collaborative measurement of contact angle and AFM surface roughness through the method, the limitation of single parameter characterization is broken through, and measurement based on adsorption energy of alkali metal and the coating surface is realized.

[0036] 2. The problem of poor applicability of the traditional model in the anti-relaxation coating is solved. Through the combination of adsorption kinetics fitting and thermodynamic modeling, the microcosmic adsorption behavior is associated with the macroscopic surface parameter, and a reproducible quantitative standard is provided.

[0037] 3. The application is a universal method, and the coating surface of the alkali metal cell can be quantified based on the method, and the mechanism research of the alkali metal cell is carried out. The method is suitable for various anti-relaxation coatings, supports coating screening, performance evaluation and mechanism research, and promotes the engineering application of high-performance atomic cells. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a coating polarization retention angle and polarization retention cross section structure schematic diagram related to the alkali metal cell anti-relaxation self-assembled molecular coating adsorption energy quantification method of the application. Figure 1 The left drawing and the right drawing are included in the drawing. Figure 1 The left drawing schematically shows the motion trajectory of alkali metal atoms in the coating cell. Figure 1 The right drawing schematically shows the motion state of alkali metal in the cell without coating but containing buffer gas. Figure 1 In the drawing, K and Rb are both alkali metals, and SiO2 represents glass material silicon dioxide as a cell shell, that is, a coating deposition substrate. Figure 1 In the left drawing, OTS SAMul is an octadecyltrichlorosilane self-assembled multilayer film (OTS is octadecyltrichlorosilane, SAMul is self-assembled multilayer film, Self-assembled Multilayers), and the alkali metal atoms approximately elastically collide on the SAMul and are not completely depolarized on the cell wall, so that the relaxation time is improved. Figure 1 In the right drawing, the alkali metal atoms are completely depolarized after collision in the buffer gas (Ne). Compared with the two, the polarization retention angle in the cell without coating is much lower than that in the cell with coating.

[0039] Figure 2 is a flowchart of a method for quantifying the adsorption energy of an anti-relaxation self-assembled molecular coating of an alkali metal cell according to the present application. Figure 2 The method comprises the following steps: S1, preparing an anti-relaxation coating sample: by constructing a structurally stable and parameter controllable coating substrate sample, providing an experimental basis for subsequent adsorption performance testing; S2, surface parameter characterization and correction: obtaining key physical quantities of the coating as input parameters for adsorption thermodynamic modeling; S3, adsorption energy calculation and anti-relaxation ability evaluation: by fitting the model and calculating the Gibbs free energy, the adsorption energy is inversely calculated as the core index for evaluating the anti-relaxation performance of the coating. Step S1 includes: step S101, substrate preparation; step S102, substrate pretreatment; step S103, self-assembly preparation of the coating; step S104, heat curing. Step S2 includes: step S201, measurement of the polarization holding angle; step S202, measurement of the polarization holding section; step S203, calculation of the surface area fraction. Step S3 includes: step S301, fitting of the adsorption and desorption rate constants; step S302, calculation of the equilibrium constant; step S303, calculation of the adsorption energy. DETAILED DESCRIPTION

[0040] The present application will be described below with reference to the accompanying drawings Figures 1-2 ) and examples.

[0041] Figure 1 is a schematic diagram of the polarization holding angle and the polarization holding section structure of the coating involved in the method for quantifying the adsorption energy of an anti-relaxation self-assembled molecular coating of an alkali metal cell according to the present application. Figure 2 is a flowchart of a method for quantifying the adsorption energy of an anti-relaxation self-assembled molecular coating of an alkali metal cell according to the present application. Referring to Figures 1-2 , a method for quantifying the adsorption energy of an anti-relaxation self-assembled molecular coating of an alkali metal cell, comprising the following steps: step 1, using a liquid phase self-assembly method to deposit organosilane on a cell glass substrate to form an anti-relaxation coating sample; step 2, selecting multiple measurement points on the anti-relaxation coating sample, and dropping a drop of 1 μL ultrapure water on each measurement point, determining the polarization holding angle of each measurement point according to the liquid drop height and liquid drop base radius obtained by the contact angle measuring instrument, and using an atomic force microscope AFM to scan the local area corresponding to the measurement point, and extracting the arithmetic mean value Ra of the surface roughness parameter and the root mean square value Rq of the surface roughness parameter as the quantitative indicators of the polarization holding section; step 3, taking the free energy of the coating molecular layer as the coating adsorption energy ΔG:

[0042] ΔG=-RT ln(k eq )=-RT ln(k a / k d ),

[0043]

[0044] where R is the gas constant, T is the absolute temperature, k eq is the equilibrium constant, k a is the adsorption constant, k d is the desorption constant, is the coating surface coverage, t is time, θ is the contact angle hysteresis, c coat is the coating deposition solution concentration.

[0045] k a and k d in step 3 are determined by expression fitting.

[0046] Step 3 includes the following expression:

[0047]

[0048]

[0049] K2 = k a c coat + k d ,

[0050] where is a function of t, K1 is the coverage coefficient, reflecting the final maximum coverage of the surface, K2 is the apparent rate coefficient, reflecting the rate at which the surface reaches adsorption equilibrium.

[0051] Step 2 includes the following expression:

[0052]

[0053] where θ is the contact angle hysteresis, h is the droplet height, a is the droplet base radius, and V is the droplet volume.

[0054] Step 2 includes introducing a non-uniform wetting model Cassie-Baxter formula to correct the contact angle hysteresis, establishing a functional relationship between the contact angle hysteresis and the effective adsorption area of the coating, realizing the collaborative matching of the two types of parameters at the spatial point, providing input variables for subsequent adsorption behavior modeling, and the Cassie-Baxter formula is as follows:

[0055] cosθ app = f1cosθ1 + f2cosθ2,

[0056] where θ appis the apparent polarizing holding angle on the non-uniform surface, f1 is the effective adsorption area fraction of the coating, i.e., the first medium surface area fraction, θ1 is the polarizing holding angle of the first medium, f2 is the air surface area fraction hidden in the adsorption area of the coating due to surface roughness, i.e., the second medium surface area fraction, and θ2 is the polarizing holding angle of the second medium.

[0057] The gas chamber glass substrate in step 1 is a high borosilicate glass substrate, and the organosilane is octadecyltrichlorosilane OTS. A deposition time of 1 h is adopted, a 6 mM OTS solution concentration is adopted, after the deposition is completed, the sample is heat treated at 150 DEG C to solidify the coating to enhance the molecular order and the stability of the coating, and a structure-stable OTS anti-relaxation coating is formed.

[0058] The application provides an alkali metal gas chamber anti-relaxation self-assembled molecular coating adsorption energy quantization method, which comprises a cooperative quantization path construction, an adsorption-desorption thermodynamic model and an in-situ multi-point measurement scheme.

[0059] The cooperative quantization path construction adopts a contact angle test and an atomic force microscope (AFM) scanning technology to respectively acquire key characterization parameters such as a polarizing holding angle and a polarizing holding cross section of the coating surface; a non-uniform wetting model (Cassie-Baxter formula) is introduced to correct the contact angle, a functional relationship between the polarizing holding angle and the effective adsorption area of the coating is established, the cooperative matching of the two types of parameters at the spatial points is realized, and input variables for subsequent adsorption behavior modeling are provided.

[0060] The introduction of the adsorption-desorption thermodynamic model, the interaction process of alkali metal atoms and the coating surface conforms to a first-order adsorption-desorption kinetics equation, the polarizing holding angle and the surface area fraction are used to calculate the adsorption rate constant k a and the desorption rate constant k d , the equilibrium constant K eq is further obtained, and the adsorption free energy change ΔG is derived through a thermodynamic formula; the adsorption energy in eV units is converted from ΔG, which is used as an evaluation index of the real adsorption capacity of the coating to alkali metal atoms.

[0061] The in-situ multi-point measurement scheme, in view of the characteristics of the anti-relaxation coating such as non-uniform coverage and severe surface roughness changes, proposes a multi-point synchronous measurement strategy, the contact angle and roughness data of multiple positions of the same coating sample are paired and processed, the local polarizing holding angle is inversely deduced based on the liquid drop geometric parameters, the surface cross section value at the same position is extracted combined with the AFM image, and thus the spatial distribution reconstruction of the adsorption energy on the coating surface is realized.

[0062] In order to accurately quantify the OTS coating surface adsorption energy to optimize the coating quality, and thus greatly improve the anti-relaxation performance of the alkali metal gas chamber. The calculation process is as follows:

[0063] To characterize coating performance, an improved polarization retention angle (PSA) quantification method was used to evaluate OTS coatings. This improved PSA evaluation method starts from the droplet height and substrate radius after the polarization retention angle (θ) is formed:

[0064]

[0065] Where the droplet height h and a are the base radius. The droplet height and base radius are measured by observing an optical image of the water droplet. The specific values ​​of the droplet height and base radius are then obtained by simultaneously applying the droplet volume relationship. The formula for calculating the droplet volume is as follows:

[0066]

[0067] The polarization retention angle on rough surfaces manifests as non-uniform wetting. In this case, air is trapped below the liquid and within the turbid cavity during wetting. The apparent polarization retention angle for non-uniform wetting can be obtained using the following Cassie-Baxter (CB) equation.

[0068] cosθ app =f1cosθ1+f2cosθ2

[0069] Wherein, cosθ app Let θ1 and θ2 be the apparent polarization retention angles on the non-uniform surface, respectively, and let f1 and f2 be the surface integrals of media 1 and 2. For the case where media 2 is air, when θ2 = 180°, the above equation can be rewritten as follows:

[0070] cosθ app =f1(cosθ1+1)-1

[0071] Based on this method, the correspondence between the polarization retention angle at a specified point and the polarization retention cross section can be obtained.

[0072] The depolarization of alkali metals on coatings is essentially relaxation, while Gibbs free energy is a thermodynamic function describing the spontaneity and stability of a substance under certain temperature and pressure. The relationship between adsorption energy and Gibbs free energy can be expressed as follows: the adsorption process can be viewed as the transfer of alkali metal atoms from the gas phase to the solid surface. In thermodynamics, adsorption energy usually refers to the energy released by the adsorption of molecules or atoms on the surface, which is equivalent to the thermochemical energy of the surface adsorption reaction. If this process is spontaneous, then the change in Gibbs free energy should be negative. The adsorption and desorption process of alkali metal atoms on the coating can be described by the following first-order differential equation, and the rate of change of the coating surface coverage over time can be written as:

[0073]

[0074] in, k is the coating surface coverage, respectively a k is the adsorption constant and k d k is the desorption constant, c coat k is the coating deposition solution concentration. Integrating the above formula, the evolution of the coating surface coverage with time is obtained

[0075]

[0076]

[0077] K2=k a c coat +k d ,

[0078] Wherein, K1 is the coverage coefficient, reflecting the final maximum coverage of the surface, K2 is the apparent rate coefficient, reflecting the rate of the surface reaching adsorption equilibrium, and the values of K1 and K2 are given by the above formula. According to k a and k d , the equilibrium constant k eq can be calculated, and thus the free energy ΔG of the formation of the coating molecular layer is obtained:

[0079] ΔG=-RT ln(k eq )=-RT ln(k a / k d )

[0080] Wherein, R is the gas constant, T is the absolute temperature, k eq is the equilibrium constant. ΔG reflects the thermodynamic stability of the coating molecular layer on the surface of the gas chamber. The energy is negative, indicating that the process is spontaneous. In the adsorption process, the negative Gibbs free energy means that atoms or molecules spontaneously transfer from the gas phase to the surface, i.e. the adsorption process is spontaneous. The larger the negative value, the more inclined the adsorption process is to occur.

[0081] The present application relates to the field of atomic optics and surface physics, and in particular to a method for quantifying the adsorption energy of an alkali metal gas chamber anti-relaxation self-assembled molecular coating. Based on the synergistic characterization and thermodynamic modeling of the coating surface parameters, the method proposes to indirectly quantify the adsorption energy of alkali metal on the coating surface from the joint measurement of polarization retention angle and polarization retention cross section, providing an effective means for coating performance evaluation and anti-relaxation mechanism analysis.

[0082] In order to better understand the technical solutions of the present application, the specific implementation steps, principle derivation and application effects of the method described in the present application are further described in conjunction with typical embodiments. However, it should be understood that these embodiments are only used to illustrate the technical concept of the present application, and do not constitute a limitation on the protection scope of the present application.

[0083] To clearly illustrate the principle of the scheme, the method is introduced. Reference to the accompanying Figure 1 , the left graph is the trajectory of alkali metal atoms in the coating gas chamber, after a certain number of collisions, the alkali metal stays on the coating, but since the alkali metal chamber is sealed, the contact angle cannot be directly measured, so the water contact angle on the test substrate is used to measure the polarization retention ability of the coating, this contact angle is defined as the polarization retention angle. In addition, the quality of the coating is related to the surface roughness of the coating, and the total area of the anti-relaxation coating surface is defined as the polarization retention cross section, which can be measured by AFM roughness. The right graph shows the motion state of alkali metal in the gas chamber without coating but containing buffer gas, the alkali metal collides in the buffer gas atoms, and finally reaches the wall of the gas chamber and completely depolarizes. Its contact angle is much lower than that of the gas chamber containing the coating.

[0084] The following is a specific description of an embodiment of the present application.

[0085] Reference to the accompanying Figure 2 An alkali metal chamber anti-relaxation self-assembled molecular coating adsorption energy method comprises the following technical steps:

[0086] Step S1: preparing an anti-relaxation coating sample. Construct a structure-stable and parameter-controllable coating system to provide experimental sample basis for subsequent adsorption performance test. Prepare a multi-layer organosilane anti-relaxation coating by adjusting the deposition concentration and time to ensure that the sample has diversity and representativeness required for experimental comparison.

[0087] Among them, step S1 can be divided into four sub-steps S101-S104:

[0088] Step S101: select high borosilicate glass substrate as the coating deposition substrate.

[0089] Step S102: pretreat the glass substrate, including acid washing etching, deionized water cleaning and drying treatment, to ensure that the surface is clean and has sufficient hydroxyl density, which is beneficial to the subsequent organic molecule bonding.

[0090] Step S103: prepare a multi-layer anti-relaxation coating under humidity control conditions by using liquid phase self-assembly method, configuring 6mM OTS (octadecyltrichlorosilane) organic solution, and controlling the deposition time to be 1h.

[0091] Step S104: after completing the deposition, heat treat the sample at 150℃ to solidify the coating and enhance the molecular order and coating stability, forming a structure-stable OTS anti-relaxation coating.

[0092] Step S2: surface parameter characterization and correction. Obtain the key physical quantities of the coating, and introduce the wetting model to establish the cooperative relationship between them as the input parameters of the adsorption thermodynamic modeling. This step realizes the connection bridge between the adsorption capacity and the measurable characterization quantity.

[0093] Wherein step S2 can be divided into three sub-steps S201-S203:

[0094] Step S201: Select multiple measurement points on each coating sample, use the contact angle measuring instrument to carry out sessile drop test, adopt 1 μL ultrapure water droplet, and the polar retention angle value of each point is obtained by measuring the droplet height and the substrate radius.

[0095] Step S202: The local area corresponding to the measurement point is scanned by using an atomic force microscope (AFM), and the surface roughness parameters Ra (arithmetic mean) and Rq (root mean square) are extracted as the quantitative indicators of the polar retention section.

[0096] Step S203: Considering the non-uniform wetting phenomenon caused by the rough surface, the Cassie-Baxter model is used to correct the apparent polar retention angle, and the surface area fraction f is calculated, which provides basic data for adsorption modeling.

[0097] Step S3: Adsorption energy calculation and anti-relaxation ability evaluation. By fitting the adsorption-desorption kinetics model and calculating the Gibbs free energy, the adsorption energy of the coating to alkali metal atoms is obtained, which is the core index for evaluating the anti-relaxation performance of the coating, and the goal of performance quantification, material selection and process optimization is realized.

[0098] Wherein step S3 can be divided into three sub-steps S301-S303:

[0099] Step S301: Substitute the polar retention angle and the polar retention section data into the first-order adsorption-desorption kinetics equation: through the formula Fitting adsorption and desorption rate constants (ka and kd).

[0100] Step S302: By fitting the above equation, the experimental values of ka and kd are extracted, and the reaction equilibrium constant K is further calculated: eq = k a / k d .

[0101] Step S303: According to the equilibrium constant, the Gibbs free energy of the adsorption process is calculated: ΔG = -RT ln(k a / k d ). Convert it to the adsorption energy value in electron volts (eV), and the adsorption energy of alkali metal atoms under different coating conditions can be obtained.

[0102] Based on the synergistic characterization and thermodynamic modeling of the coating surface parameters, the present application proposes to measure the polar retention angle and the polar retention section jointly, and indirectly quantify the adsorption energy of alkali metal on the coating surface, which provides an effective means for coating performance evaluation and anti-relaxation mechanism analysis.

[0103] The content not described in detail in the specification of the present application belongs to the prior art known to the person skilled in the art. It is indicated here that the above description helps the person skilled in the art to understand the present application, but does not limit the protection scope of the present application. Any implementation of equivalent replacement, modification, improvement and / or deletion of the above description without departing from the essential content of the present application falls within the protection scope of the present application.

Claims

1. A method for adsorption energization of an alkali metal gas cell anti-relaxation self-assembled molecular coating, characterized in that, Includes the following steps: Step 1: An anti-relaxation coating sample is formed by depositing organosilane on a gas chamber glass substrate using a liquid-phase self-assembly method. Step 2: Select multiple measurement points on the anti-relaxation coating sample, and drop a 1μL drop of ultrapure water at each measurement point. Determine the polarization retention angle of each measurement point based on the droplet height and droplet substrate radius obtained by the contact angle measuring instrument. Use an atomic force microscope (AFM) to scan the local area of ​​the corresponding measurement point and extract the arithmetic mean Ra and the root mean square value Rq of the surface roughness parameters as quantitative indicators of the polarization retention section. Step 3: The free energy of the formation of the coating molecular layer is used as the coating adsorption energy ΔG: ΔG=-RTln(k eq )=-RTln(k a / k d ), Where R is the gas constant, T is the absolute temperature, and k is the gas constant. eq It is the equilibrium constant, k a It is the adsorption constant, k d It is the desorption constant. It is the coating surface coverage, t is time, θ is the polarization retention angle, and c is the polarization retention angle. coat It is the concentration of the coating deposition solution.

2. The adsorption energization method for alkali metal gas cell anti-relaxation self-assembly molecular coatings according to claim 1, characterized in that, In step 3, k a and k d pass The expression was determined by fitting.

3. The adsorption energization method for alkali metal gas cell anti-relaxation self-assembly molecular coatings according to claim 1, characterized in that, Step 3 includes the following expression: K2=k a c coat +k d , in yes The evolution function with respect to t is K1, which is the coverage coefficient, reflecting the final maximum coverage of the surface, and K2, which is the apparent rate coefficient, reflecting the rate at which the surface reaches adsorption equilibrium.

4. The adsorption energization method for alkali metal gas cell anti-relaxation self-assembly molecular coatings according to claim 1, characterized in that, Step 2 includes the following expression: Where θ is the polarization retention angle, h is the droplet height, a is the droplet base radius, and V is the droplet volume.

5. The adsorption energization method for alkali metal gas cell anti-relaxation self-assembly molecular coatings according to claim 1, characterized in that, Step 2 involves introducing the non-uniform wetting model Cassie-Baxter formula to correct the polarization retention angle, establishing a functional relationship between the polarization retention angle and the effective adsorption area of ​​the coating, achieving coordinated matching of the two types of parameters at spatial locations, and providing input variables for subsequent adsorption behavior modeling. The Cassie-Baxter formula is as follows: cosθ app =f1cosθ1+f2cosθ2, Where θ app θ1 is the apparent polarization retention angle on a non-uniform surface, f1 is the effective adsorption area fraction of the coating, i.e., the surface integral of the first medium, θ1 is the polarization retention angle of the first medium, f2 is the surface integral of the air trapped in the adsorption area of ​​the coating due to surface roughness, i.e., the surface integral of the second medium, and θ2 is the polarization retention angle of the second medium.

6. The adsorption energization method for alkali metal gas cell anti-relaxation self-assembly molecular coatings according to claim 1, characterized in that, In step 1, the gas chamber glass substrate is a borosilicate glass substrate, and the organosilane is octadecyltrichlorosilane OTS. A deposition time of 1 hour and a OTS solution concentration of 6 mM are used. After deposition, the sample is heat-treated at 150°C to cure the coating, enhance the molecular order and coating stability, and form a structurally stable OTS anti-relaxation coating.

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