Alpha particle backscattering thickness gauge for nanoscale liquid film and detection method thereof

Abstract

The application discloses an alpha particle backscattering thickness measuring device for nanoscale liquid film and a detection method thereof. The device comprises a vacuum sample inlet unit, a vacuum measurement unit and a detection unit connected in sequence. The vacuum measurement unit comprises a vacuum measurement chamber, a temperature-controlled sample table assembly and a radioactive source bin arranged in the vacuum measurement chamber. The temperature-controlled sample table assembly comprises a water-cooled base, a semiconductor temperature control element, a sample base, a metal base and an electrode ring arranged in sequence. The sample base is sealingly connected with the water-cooled base. The metal base and the electrode ring are connected through a plurality of insulating columns. An adjustable direct current voltage is loaded on the electrode ring, and the adjustable direct current voltage is ±500 V to ±1500 V. The thickness measuring device provided by the application realizes the thickness detection of the nanoscale liquid film by using alpha particles, and solves the problem that there is a long-term lack of in-situ and non-destructive liquid film thickness measuring devices and methods in the field.

Description

Technical Field

[0001] This invention belongs to the field of thin film detection technology, specifically relating to an alpha particle backscattering thickness measurement device and its detection method for nanoscale liquid films. Background Technology

[0002] In microelectronics, advanced materials, biointerfaces, and basic research, there is an urgent need for non-destructive, in-situ, absolute thickness measurement of nanoscale soft matter films (such as lubricating fluid films, self-assembled monolayers, and polymer films) on solid substrate surfaces.

[0003] Commonly used testing equipment in existing technologies and their inherent defects include: Ellipsometry: It relies heavily on optical models and assumptions about the optical constants of thin films. It has large measurement errors for thin films with unknown composition or complex structure, and its calibration of absolute thickness is indirect.

[0004] Quartz crystal microbalance: measures mass per unit area, requires known density to calculate thickness, is sensitive to viscoelasticity, and is an overall average measurement with no spatial resolution.

[0005] Atomic force microscopy: may cause mechanical disturbance to soft films and usually requires an exposed reference substrate to define “zero thickness”, making it difficult to obtain a reliable average thickness for films with poor uniformity.

[0006] Traditional alpha particle thickness gauges are designed based on the penetration of alpha particles through matter (transmission method), and are specifically designed for solid metal films at the micrometer level and above. However, they are fundamentally unsuitable for direct application to nanoscale soft material films. Firstly, the signal is weak; the blocking effect of nanoscale soft films on high-energy alpha particles is extremely weak, and the resulting signal change is far below the instrument's noise floor. Secondly, significant air interference occurs during detection; the strong scattering and energy attenuation of alpha particles by gas molecules in the air lead to severe signal degradation and energy spectrum broadening, making it impossible to distinguish the minute changes caused by nanoscale films. Finally, sample preparation is difficult; existing alpha particle thickness gauges cannot stably fix and measure volatile and flowing liquid films.

[0007] Therefore, existing technologies lack an effective means for in-situ, non-disturbance thickness measurement of nanoscale soft matter films.

[0008] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, this invention provides an alpha particle backscattering thickness measurement device and its detection method for nanoscale liquid films. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides an alpha particle backscattering thickness measurement device for nanoscale liquid films, comprising a vacuum sample introduction unit, a vacuum measurement unit, and a detection unit connected in sequence. The vacuum injection unit is used to inject samples into the vacuum measurement unit in a vacuum environment; The vacuum measurement unit includes a vacuum measurement chamber, in which a temperature-controlled sample stage assembly and a radiation source chamber are disposed. The vacuum measurement chamber is also connected to a first control assembly and a first vacuum pumping assembly. The radiation source chamber is used to place an alpha radiation source. The first control component is connected to the radiation source chamber and is used to control the position of the radiation source chamber in the vacuum measurement chamber; the first vacuum pumping component is used to ensure that the pressure in the vacuum measurement chamber is less than or equal to 1 × 10⁻⁶. - 6 Pa; The temperature-controlled sample stage assembly includes a water-cooled base, a semiconductor temperature control element, a sample base, a metal substrate, and an electrode ring, which are stacked in sequence. The upper surface of the water-cooled base is provided with a first receiving groove, and the semiconductor temperature control element is located in the first receiving groove; the sample base is sealed to the water-cooled base. The upper surface of the sample base is provided with a second receiving groove, and the metal substrate is disposed in the second receiving groove; the metal substrate is connected to the electrode ring through multiple insulating pillars, and an adjustable DC voltage is applied to the electrode ring, the adjustable DC voltage being ±500 V to ±1500 V; The detection unit is used to detect and analyze alpha particles scattered by the target liquid film.

[0010] Secondly, the present invention provides a detection method for the above-mentioned α-particle backscattering thickness measurement device for nanoscale liquid films, comprising the following steps: S1. Using a first vacuum pumping assembly, the pressure in the vacuum measurement chamber is adjusted to a first preset pressure; using a second vacuum pumping assembly, the pressure in the pre-evacuation chamber is adjusted to a second preset pressure; simultaneously, the temperature of the metal substrate is adjusted to a preset temperature according to the characteristics of the target liquid film. S2. Open the radiation source chamber, adjust its position using the first servo cylinder and the two-dimensional moving stage, and adjust the position of the detector using the second servo cylinder. When the alpha particle count rate measured by the detector is at its maximum, the position of the radiation source chamber and the detector is the optimal geometric position. At this optimal geometric position, collect the backscattered alpha particle count rate and energy spectrum within time t. The detection unit records the background measurement results and closes the radiation source chamber. The background measurement results include the total count rate N. b And plotting the energy spectrum curve S b (E); S3. Keep the measurement parameters in step S1 and the optimal geometric position in step S2 unchanged; Liquid under normal atmospheric pressure is quantitatively pushed through a piezoelectric micro-injection pump and enters the pre-vacuum chamber through a microtube. The vacuum gate valve is opened to introduce the liquid onto the metal substrate, and the DC voltage on the electrode ring is turned on at the same time. The microtube is immediately removed and the vacuum gate valve is closed, and the liquid forms a target liquid film on the surface of the metal substrate. S4. Open the radioactive source chamber, collect the backscattered alpha particle count rate and energy spectrum within the same time t, the detection unit records the measurement results of the target liquid film, and close the radioactive source chamber; the measurement results of the target liquid film include the total count rate N. f and energy spectrum curve S f (E); S5. Calculate the relative count rate value Δ(N) = (N b - N f ) / N b Analyze the energy spectrum curve S b (E) and the energy spectrum curve S f (E) Obtain the relative energy offset Δ(E); compare the relative count rate value Δ(N) and relative energy offset Δ(E) of the target liquid film with the pre-established database, calculate the thickness of the target liquid film, and output the measurement results of the target liquid film.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The alpha particle backscattering thickness measurement device for nanoscale liquid films provided by this invention operates under ultra-high vacuum conditions (pressure less than or equal to 1×10⁻⁶). -6The device measures the liquid film using an alpha particle absolute thickness measurement principle, avoiding the influence of air on the measurement. Simultaneously, the coordinated operation of the semiconductor temperature control element 202 and the water-cooled base 201 enables precise temperature control of the metal substrate 204, making the device applicable to various types of liquid films and allowing for precise temperature adjustment based on the properties of the target liquid film. Furthermore, by setting up an electrode ring and utilizing electrostatic confinement technology, a stable and measurable liquid film can be formed in real-time under vacuum conditions, providing a research device for dynamic processes such as film evaporation and spreading. Thus, this invention is the first to employ the alpha particle absolute thickness measurement principle to detect the thickness of nanoscale soft materials (liquids, polymers, and other organic thin films), solving the long-standing problem of lacking in-situ, non-destructive, absolute thickness benchmark measurements in this field.

[0012] 2. The core algorithm of the detection method provided by this invention relies on physical simulation. It only requires updating material parameters to adapt to the measurement of different types of thin films, without the need for experimental calibration. In addition, the automated process of detection reduces the difficulty of operation.

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of an alpha particle backscattering thickness measurement device for nanoscale liquid films provided in an embodiment of the present invention; Figure 2 This is an exploded structural diagram of a temperature-controlled sample stage assembly for an alpha particle backscattering thickness measurement device for nanoscale liquid films, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the detection status of an α-particle backscattering thickness measurement device for nanoscale liquid films provided in an embodiment of the present invention; Figure 4 This is a flowchart of a detection method for an alpha particle backscattering thickness measurement device for nanoscale liquid films provided in an embodiment of the present invention.

[0015] Explanation of reference numerals in the attached figures: 101-Pre-vacuum chamber; 102-Piezoelectric micro-injection pump; 103-Microtube vacuum feedthrough; 104-Microtube; 105-Vacuum gate valve; 106-Second mechanical pump; 107-Third vacuum conduit; 108-Second molecular pump; 109-First vacuum gauge; 201-Water-cooled base; 202-Semiconductor temperature control element; 203-Sample base; 204-Metal substrate; 205-Electrode ring; 206-Insulating post; 207-Water-cooled connector; 208-Semiconductor temperature control terminal; 209-Insulating support post; 210-First servo cylinder; 211-First servo... 212 - One-dimensional push rod of cylinder; 213 - Two-dimensional moving stage; 214 - Radiation source chamber; 215 - Collimator; 216 - Ion pump; 217 - First vacuum pipe; 218 - First molecular pump; 219 - Second vacuum pipe; 220 - First mechanical pump; 221 - Wiring electrode; 222 - Second vacuum gauge; 222 - Vacuum measurement chamber; 301 - Detector; 302 - Second servo electric cylinder; 303 - One-dimensional push rod of the second servo electric cylinder; 304 - Amplifier; 305 - Multichannel pulse amplitude analyzer; 306 - Computer; 307 - Signal line; 308 - Data line. Detailed Implementation

[0016] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail, with reference to the accompanying drawings and specific embodiments, an alpha particle backscattering thickness measurement device and its detection method for nanoscale liquid films proposed according to the present invention.

[0017] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0018] It should be noted that, in this document, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not explicitly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element.

[0019] The term "normal atmospheric pressure" refers to the atmospheric pressure of the laboratory or alpha particle backscattering thickness measurement environment.

[0020] Example 1 This invention provides an alpha particle backscattering thickness measurement device for nanoscale liquid films, see [link to relevant documentation]. Figures 1-3 It includes a vacuum sample introduction unit, a vacuum measurement unit, and a detection unit connected in sequence. The vacuum sample introduction unit is used to inject samples into the vacuum measurement unit in a vacuum environment.

[0021] The vacuum measurement unit includes a vacuum measurement chamber 222, within which a temperature-controlled sample stage assembly and a radiation source chamber 213 are disposed. The vacuum measurement chamber 222 is also connected to a first control assembly and a first vacuum pumping assembly. The radiation source chamber 213 is used to house an alpha radiation source. The first control assembly is connected to the radiation source chamber 213 and is used to control the position of the radiation source chamber 213 within the vacuum measurement chamber 222. The first vacuum pumping assembly is used to ensure that the pressure within the vacuum measurement chamber 222 is less than or equal to 1 × 10⁻⁶. -6 Pa.

[0022] like Figure 2 and Figure 3 As shown, the temperature-controlled sample stage assembly includes a water-cooled base 201, a semiconductor temperature control element 202, a sample base 203, a metal substrate 204, and an electrode ring 205 stacked sequentially. The upper surface of the water-cooled base 201 has a first receiving groove, within which the semiconductor temperature control element 202 is located. The sample base 203 is sealed to the water-cooled base 201 to ensure that the temperature-controlled sample stage assembly does not disrupt the vacuum level of the vacuum measurement chamber 222 in a vacuum environment. The upper surface of the sample base 203 has a second receiving groove, within which the metal substrate 204 is located. The metal substrate 204 serves to support the target liquid film formed during the use of the device. The metal substrate 204 is connected to the electrode ring 205 via multiple insulating pillars 206. An adjustable DC voltage is applied to the electrode ring 205, ranging from ±500 V to ±1500 V. In other words, the DC voltage applied to the electrode ring 205 needs to be determined based on the characteristics of the target liquid film being measured. The detection unit is used to detect and analyze alpha particles scattered by the target liquid film.

[0023] The alpha particle backscattering thickness measurement device for nanoscale liquid films provided in this invention embodiment can operate under ultra-high vacuum conditions (pressure less than or equal to 1×10⁻⁶). -6The device measures the liquid film using an alpha particle absolute thickness measurement principle, avoiding the influence of air on the measurement. Simultaneously, the coordinated operation of the semiconductor temperature control element 202 and the water-cooled base 201 enables precise temperature control of the metal substrate 204, making the device applicable to various types of liquid films and allowing for precise temperature adjustment based on the properties of the target liquid film. Furthermore, by setting up an electrode ring and utilizing electrostatic confinement technology, a stable and measurable liquid film can be formed in real-time under vacuum conditions, providing a research device for dynamic processes such as film evaporation and spreading. Thus, this invention is the first to employ the alpha particle absolute thickness measurement principle to detect the thickness of nanoscale soft materials (liquids, polymers, and other organic thin films), solving the long-standing problem of lacking in-situ, non-destructive, absolute thickness benchmark measurement methods in this field.

[0024] This alpha particle backscattering thickness measurement device has a high degree of integration. By organically integrating "noise reduction of vacuum measurement chamber", "electrostatic micro-nano manipulation of electrode ring for film formation" and "active precision temperature control of semiconductor temperature control element", it forms a dedicated liquid film thickness analysis instrument with a wide range of applications.

[0025] For example, the vacuum measurement chamber 222 can be a hollow cavity made of stainless steel, which, in conjunction with the first vacuum pumping assembly, controls the pressure in the vacuum measurement chamber 222 to meet a preset requirement (pressure less than or equal to 1×10⁻⁶). -6 Pa), thereby minimizing the scattering and energy attenuation of alpha particles by the air.

[0026] For example, a first vacuum gauge 109 is installed on the side wall of the vacuum measurement chamber 222 to monitor the pressure inside the vacuum measurement chamber 222.

[0027] For example, a wiring electrode 220 is also provided on the side wall of the vacuum measurement chamber 222. One end of the wiring electrode 220 is electrically connected to the electrode ring 205, and the other end is electrically connected to an external power supply.

[0028] For example, the temperature-controlled sample stage assembly can be disposed at the bottom of the vacuum measurement chamber 222 and fixedly connected to the bottom surface of the vacuum measurement chamber 222 by an insulating support column 209.

[0029] In one embodiment, the first vacuum pumping assembly includes a first vacuum pipe 216, an ion pump 215, a first molecular pump 217, a second vacuum pipe 218, and a first mechanical pump 219; the first vacuum pipe 216 is a three-way pipe, with its first end connected to the ion pump 215, its second end connected to the vacuum measurement chamber 222, and its third end connected to one end of the first molecular pump 217; the other end of the first molecular pump 217 is connected to the first mechanical pump 219 through the second vacuum pipe 218.

[0030] In one embodiment, the outer wall of the water-cooled base 201 is provided with a water-cooling connector 207 and a semiconductor temperature control terminal 208. The water-cooled base 201 has mutually isolated cooling water guide channels and wire channels; the cooling water guide channels communicate with the water channels of the water-cooling connector 207, and the wire channels communicate with the outlet holes of the semiconductor temperature control terminal 208. Thus, by injecting cooling water into the cooling water guide channels through the water-cooling connector 207, the temperature of the sample base 203 can be controlled in conjunction with the semiconductor temperature control element 202 (which achieves cooling and heating by changing the positive and negative terminals of the power supply). The metal substrate 204 is located in the second receiving groove on the sample base 203, thereby achieving temperature regulation of the metal substrate 204. For example, when the target liquid film to be detected requires a higher temperature, the positive and negative terminals of the semiconductor temperature control element 202 are adjusted to heat the sample base 203 and the metal substrate 204; when the target liquid film to be detected requires a lower temperature, the temperature can be quickly adjusted from high to low through the heat conduction of the water-cooled base 201 and the adjustment of the positive and negative terminals of the semiconductor temperature control element 202.

[0031] In one embodiment, a temperature sensor is disposed on the upper surface of the sample base 203. That is, the upper surface of the sample base 203 includes a groove area with a second receiving groove and a planar area surrounding the groove area, and the temperature sensor is disposed in the planar area. With the cooperation of the temperature sensor and the semiconductor temperature control element 202, the temperature control range of the metal substrate 204 is -30℃ to 100℃, and the temperature control error is less than ±0.1℃.

[0032] For example, the metal substrate 204 uses a metal element with an atomic number greater than 70 to generate a strong alpha particle backscattering background signal. For example, the metal substrate 204 can be made of platinum, gold, etc.

[0033] For example, the electrode ring 205 is a metal ring electrode, such as a ring electrode made of tungsten. In one example, the electrode ring 205 is insulated from the metal substrate 204 by three ceramic pillars, which are at a 120° angle to each other. During the use of the thickness measuring device, when a DC voltage is applied to the electrode ring 205, a non-uniform axisymmetric electric field is formed between the electrode ring 205 and the metal substrate 204. The introduced liquid is polarized under the action of dielectric force or electrostatic force, and is bound and spread flat directly below the electrode under the action of strong electric field force, forming a circular target liquid film of uniform thickness and fixed position on the surface of the metal substrate 204, while also effectively preventing the liquid from evaporating.

[0034] In one embodiment, a collimator 214 is provided at the end of the radiation source chamber 213 near the temperature-controlled sample stage assembly to ensure that the emission direction of the alpha radiation source is consistent. The collimation aperture of the collimator 214 is used to limit the incident direction of the alpha radiation source toward the metal substrate 204. In this way, the collimator 214 can both constrain the emission direction of the alpha radiation source and prevent some alpha particles from directly acting on the detector 301 without passing through the sample.

[0035] In one embodiment, the first control component includes a first servo cylinder 210 and a two-dimensional moving stage 212 connected to a one-dimensional push rod 211 of the first servo cylinder. The two-dimensional moving stage 212 is connected to the end of the radiation source chamber 213 away from the temperature-controlled sample stage assembly. Defined as the Z-direction of linear motion of the one-dimensional push rod 211 of the first servo cylinder, the one-dimensional lifting rod of the first servo cylinder is used to move the radiation source chamber 213 in the Z-direction, and the two-dimensional moving stage 212 is used to move the radiation source chamber 213 in the X and Y directions, wherein the X and Y directions are both perpendicular to the Z-direction, and the X-direction is perpendicular to the Y-direction. Thus, under the control of the one-dimensional push rod 211 of the first servo cylinder and the two-dimensional moving stage 212, the radiation source chamber 213 can move in three dimensions within the vacuum measurement chamber 222, adjusting the relative position of the radiation source chamber 213 and the temperature-controlled sample stage assembly.

[0036] For example, in the Z direction, the distance between the radiation source chamber 213 and the metal substrate 204 is 10 mm to 50 mm to optimize the detection signal intensity and spatial resolution.

[0037] For example, the two-dimensional moving stage 212 can be controlled by a servo motor to achieve movement in the X and Y directions.

[0038] For example, the alpha radiation source is either polonium-210 or plutonium-238. In this example, an alpha radiation source is used, such as... 210 Po (energy ~5.3 MeV) 238 Pu (energy ~5.5 MeV), etc. Its advantage lies in the moderate energy loss rate of alpha particles in this energy range within nanoscale liquid films. This ensures both the generation of detectable backscattered signals through the liquid film and a high-sensitivity response to minute fluctuations in film thickness. Combined with the path enhancement effect of alpha particles passing through the liquid film twice under the backscattering geometry, high-sensitivity and high-precision measurement of liquid film thicknesses in the 10-1000 nm range can be achieved by accurately measuring the energy spectrum shift of the emitted alpha particles.

[0039] In one embodiment, the vacuum injection unit includes a piezoelectric microinjection pump 102, a microtube 104, a pre-evacuation chamber 101, a vacuum gate valve 105, and a second vacuum pumping assembly connected to the pre-evacuation chamber 101. The microtube 104 is mounted on the side wall of the pre-evacuation chamber via a microtube vacuum feedthrough 103. One end of the microtube 104 is connected to the liquid outlet of the piezoelectric microinjection pump 102, and the other end extends into the pre-evacuation chamber 101. The vacuum gate valve 105 is located between the pre-evacuation chamber 101 and the vacuum measurement chamber 222. The volumetric accuracy of the injected liquid by the piezoelectric microinjection pump 102 can reach the pL level, and the pressure in the pre-evacuation chamber 101 is 1.0 × 10⁻⁶. -3 Pa ~ 4.0 × 10 -3 Pa.

[0040] For example, the diameter of the microtube 104 is 20 μm to 100 μm.

[0041] For example, the vacuum injection unit also includes an adjustment servo motor and a bellows. One end of the bellows is connected to the piezoelectric microinjection pump 102, and the other end is connected to the microtube vacuum feedthrough. The microtube 104 can be driven to reciprocate axially by adjusting the servo motor.

[0042] For example, the second vacuum pumping assembly includes a second mechanical pump 106, a third vacuum pipe 107, and a second molecular pump 108 connected in sequence, with the second molecular pump 108 connected to the pre-evacuation chamber 101.

[0043] For example, a second vacuum gauge 221 is installed on the side wall of the pre-evacuation chamber 101 to monitor the pressure inside the pre-evacuation chamber 101.

[0044] In one embodiment, the detection unit includes a detector 301, a second servo cylinder 302, and a signal processing component. The detector 301 is a silicon drift detector or a position-sensitive detector with high energy resolution. The detector 301 is used to receive alpha particles scattered by the target liquid film and output a pulse signal. The angle between the normal of the end face of the detector 301 near the temperature-controlled sample stage assembly and the axial direction of the collimation aperture of the collimator 214 is 150° to 175°.

[0045] like Figure 1As shown, the signal processing component includes an amplifier 304, a multichannel pulse amplitude analyzer 305, and a computer 306 connected in sequence. The amplifier 304 is positioned on the side of the detector 301 away from the temperature-controlled sample stage assembly, and is used for preliminary processing and amplification of the pulse signal output by the detector 301. The one-dimensional push rod 303 of the second servo cylinder 302 is connected to the detector 301 and is used to control the movement of the detector 301. The amplifier 304 is electrically connected to the multichannel pulse amplitude analyzer 305 via a signal line 307 (the signal line 307 can be placed in the gap of the second servo cylinder 302, allowing the signal line 307 to pass through without affecting the operation of the second servo cylinder 302). For example, the multichannel pulse amplitude analyzer 305 is connected to the computer 306 via a data line 308.

[0046] Example 2 Based on Example 1, this invention also provides a detection method for an alpha particle backscattering thickness measurement device for nanoscale liquid films, see [link to example]. Figure 4 This includes the following steps: S1. Using a first vacuum pumping assembly, the pressure in the vacuum measurement chamber 222 is adjusted to a first preset pressure; using a second vacuum pumping assembly, the pressure in the pre-evacuation chamber 101 is adjusted to a second preset pressure; simultaneously, the temperature of the metal substrate 204 is adjusted to a preset temperature according to the characteristics of the target liquid film. The characteristics of the target liquid film are its physicochemical features, such as the suitable temperature for film formation of the raw material liquid or the suitable temperature for application of the target liquid film.

[0047] S2. Open the radioactive source chamber 213. Adjust the alpha particle emission position using the first servo cylinder 210 and the two-dimensional moving stage 212, and adjust the position of the detector 301 using the second servo cylinder 302. When the alpha particle count rate measured by the detector 301 is at its maximum, the position of the radioactive source chamber 213 and the detector 301 is the optimal geometric position. Under the optimal geometric position, collect the backscattered alpha particle count rate and energy spectrum within time t, record the background measurement results through the detection unit, and close the radioactive source chamber 213. The background measurement results include the total count rate N. b And plotting the energy spectrum curve S b (E), the measurement result in this step is the substrate signal of the metal substrate material.

[0048] S3. Keep the measured parameters (first preset pressure, second preset pressure and preset temperature) in step S1 and the optimal geometric position in step S2 unchanged; quantitatively push the liquid under normal atmospheric pressure through the piezoelectric micro-injection pump 102, enter the pre-vacuum chamber 101 through the microtube 104, open the vacuum gate valve 105 to introduce the liquid onto the metal substrate 204, and at the same time turn on the DC voltage on the electrode ring 205; immediately remove the microtube 104 and close the vacuum gate valve 105, and the liquid forms a target liquid film on the surface of the metal substrate, realizing the capture and shaping of the injected liquid.

[0049] S4. Open the radioactive source chamber 213, collect the backscattered alpha particle count rate and energy spectrum within the same time t, record the measurement results of the target liquid film through the detection unit, and close the radioactive source chamber 213; the measurement results of the target liquid film include the total count rate N. f and energy spectrum curve S f (E).

[0050] S5. Calculate the relative count rate value Δ(N) = (N b -N f ) / N b And analyze the energy spectrum curve S b (E) and the energy spectrum curve S f (E) Obtain the relative energy shift Δ(E); compare the relative count rate value Δ(N) and relative energy shift Δ(E) of the target liquid film with a pre-established database, calculate the thickness of the target liquid film, and output the measurement results of the target liquid film. The measurement results of the target liquid film include the absolute thickness value of the target liquid film, uniformity assessment, and measurement uncertainty report.

[0051] In this step, the energy spectrum curve S is analyzed. b (E) and the energy spectrum curve S f (E) Obtaining the relative energy shift Δ(E) includes, from the energy spectrum curve S b (E) Extract the full-energy peak position E0 (i.e., the characteristic scattering peak position of the platinum substrate) of the backscattered α particles in the liquid-free state, from the energy spectrum curve S f (E) Extract the position of the full-energy peak E1 of the backscattered α particle in the liquid film state, and the relative energy shift Δ(E)=( E0- E1) / E0.

[0052] In one embodiment, in step S5, the pre-established database includes relative count rate values ​​and energy spectrum curves of various target liquid films under different thicknesses and different measurement parameters; the various target liquid films have different material compositions; the method for pre-establishing the database is to use Monte Carlo simulation.

[0053] In one implementation, the inversion calculation employs a nonlinear optimization algorithm to match the relative count rate value Δ(N) and relative energy shift Δ(E) of the target liquid film with data from a pre-established dataset; the nonlinear optimization algorithm can be nonlinear least squares or Bayesian inference. This detection method provides objective and reliable results, offering absolute thickness values ​​and statistical uncertainty results based on a physical model. It does not rely on empirical parameters or subjective assumptions, and exhibits high data repeatability and reliability.

[0054] This detection method utilizes three techniques—"ultra-high vacuum noise reduction," "backscattering sensitization," and "single-particle count rate"—to push the minimum detectable thickness change to the sub-nanometer level and provides an objective uncertainty assessment, with accuracy far exceeding that of traditional transmission measurement methods.

[0055] Example 3 The detection method of the alpha particle backscattering thickness measurement device for nanoscale liquid films provided by the present invention is applicable to the thickness detection of nanoscale liquid films and self-assembled molecular films.

[0056] This embodiment uses the liquid film of the ionic liquid [BMIM][Tf2N] (cation: 1-butyl-3-methylimidazolium ion; anion: bis(trifluoromethanesulfonyl)imide ion) as an example to perform thickness detection. The specific steps are as follows: 1. Device Pretreatment and Chamber Vacuum Conditioning: The cleaned metal substrate (platinum substrate) is mounted on the sample base. Based on the characteristics of the ionic liquid [BMIM][Tf₂N] liquid film, the temperature of the platinum substrate is adjusted to the preset temperature (30°C) to maintain temperature stability and prevent temperature fluctuations from causing liquid film evaporation or flow. A vacuum pumping assembly is used to maintain the pressure in the vacuum measurement chamber at the first preset pressure (5 × 10⁻⁶). -7 Pa).

[0057] 2. Alpha Source and Detector Debugging: Place the Po-210 alpha source (emitting alpha particles with an initial energy of 5.3 MeV) into the source chamber, activate the alpha source, and set the detector acquisition parameters to ensure stable reception of backscattered alpha particle signals and accurate recording of the energy spectrum. Adjust the positions of the source chamber and detector to maximize the count rate of alpha particles scattered from the substrate, and fix the positions of the source chamber and detector at their optimal geometric positions.

[0058] 3. Background Signal Measurement and Energy Spectrum Acquisition: Based on the parameters and optimal geometry set in steps 1 and 2, the alpha radiation source is activated, allowing the alpha particle beam to be incident on the platinum substrate surface. The detector is controlled to acquire the alpha particle backscattering signal from the platinum substrate. The acquisition time is set to 600 seconds, and the background count rate N is recorded. b =29.2 counts / s; simultaneously, the background backscattering energy spectrum curve S was acquired. b(E) The position of the full-energy peak E0 of the backscattered α particle in the liquid-free state (i.e. the characteristic scattering peak position of the platinum substrate) was extracted and obtained by energy spectrum analysis, and E0 = 4.92 MeV.

[0059] 4. Target liquid film preparation and stabilization: A vacuum pumping assembly is used to maintain the pressure in the pre-evacuation chamber at a second preset pressure (2×10). -3 Pa), 0.5 μL of ionic liquid [BMIM][Tf2N] is injected into the surface of a platinum substrate through a microtube injection assembly. A voltage of +1000 V is applied to the electrode ring, and the electric field confinement effect is used to form a uniform and stable nanoscale liquid film on the surface of the platinum substrate. The liquid film is maintained stable for 12 minutes to ensure that the liquid film is undamaged, does not volatilize, and the thickness uniformity meets the measurement requirements.

[0060] 5. Liquid Film Signal Measurement and Energy Spectrum Acquisition: Maintain the parameters of the alpha radiation source, detector, substrate temperature, and chamber vacuum, and ensure that the optimal geometry of the radiation source chamber and detector is completely consistent with S1 and S2. Control the detector to acquire the backscattered signal of alpha particles passing through the liquid film and platinum substrate. The acquisition time remains 600 seconds, and record the total count rate N. f =28 counts / s; Simultaneously acquire liquid film backscattering energy spectrum curve S f (E), the position of the full-energy peak E1 of the backscattered α particle in the liquid film state was extracted, and the energy spectrum analysis showed that E1 = 4.15 MeV.

[0061] S6. Data Calculation and Thickness Inversion: The measured relative count rate Δ(N) = (29.2-28) / 29.2 × 100% = 4.11% and the relative energy shift Δ(E) = (4.92-4.15) / 4.92 × 100% = 15.65%. The relative count rate and relative energy shift were compared with the pre-established MCNP simulated liquid film thickness, and the inverted liquid film thickness was found to be (18.5 ± 2.5) nm.

[0062] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0063] In the description of this specification, references to terms such as "an embodiment," "an example," "exemplary," or "furthermore" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0064] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A device for measuring the thickness of nanoscale liquid films using alpha particle backscattering, characterized in that, It includes a vacuum sample introduction unit, a vacuum measurement unit, and a detection unit connected in sequence; The vacuum injection unit is used to inject samples into the vacuum measurement unit in a vacuum environment; The vacuum measurement unit includes a vacuum measurement chamber (222), which is equipped with a temperature-controlled sample stage assembly and a radiation source chamber (213). The vacuum measurement chamber (222) is also connected to a first control assembly and a first vacuum pumping assembly. The radiation source chamber (213) is used to place an alpha radiation source. The first control component is connected to the radiation source chamber (213) and is used to control the position of the radiation source chamber (213) in the vacuum measurement chamber (222); the first vacuum pumping component is used to ensure that the pressure inside the vacuum measurement chamber (222) is less than or equal to 1 × 10⁻⁶. -6 Pa; The temperature-controlled sample stage assembly includes a water-cooled base (201), a semiconductor temperature control element (202), a sample base (203), a metal substrate (204), and an electrode ring (205) stacked in sequence. The upper surface of the water-cooled base (201) is provided with a first receiving groove, and the semiconductor temperature control element (202) is located in the first receiving groove; the sample base (203) is sealed to the water-cooled base (201); The upper surface of the sample base (203) is provided with a second receiving groove, and the metal substrate (204) is disposed in the second receiving groove; the metal substrate (204) and the electrode ring (205) are connected by a plurality of insulating pillars (206), and an adjustable DC voltage is applied to the electrode ring (205), the adjustable DC voltage being ±500 V to ±1500 V; The detection unit is used to detect and analyze alpha particles scattered by the target liquid film.

2. The α-particle backscattering thickness measurement device for nanoscale liquid films according to claim 1, characterized in that, The outer wall of the water-cooled base (201) is provided with a water-cooled connector (207) and a semiconductor temperature control terminal (208); The water-cooled base (201) has a cooling water guide groove and a wire groove that are isolated from each other; the cooling water guide groove is connected to the water channel of the water-cooled connector (207), and the wire groove is connected to the outlet hole of the semiconductor temperature control terminal (208).

3. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to claim 1, characterized in that, A temperature sensor is provided on the upper surface of the sample base (203); The temperature control range of the metal substrate (204) is -30℃ to 100℃, and the temperature control error is less than ±0.1℃.

4. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to claim 1, characterized in that, The first control component includes a first servo electric cylinder (210) and a two-dimensional moving stage (212) connected to a one-dimensional push rod of the first servo electric cylinder; the two-dimensional moving stage (212) is connected to the end of the radiation source chamber (213) away from the temperature control sample stage component; Defined as follows: the linear motion direction of the one-dimensional push rod of the first servo electric cylinder is the Z direction; the one-dimensional lifting rod of the first servo electric cylinder is used to realize the movement of the radiation source chamber (213) in the Z direction; the two-dimensional moving stage (212) is used to realize the movement of the radiation source chamber (213) in the X and Y directions, wherein the X and Y directions are both perpendicular to the Z direction and the X direction is perpendicular to the Y direction.

5. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to any one of claims 1-4, characterized in that, A collimator (214) is provided at one end of the radioactive source chamber (213) near the temperature-controlled sample stage assembly. The collimation hole of the collimator (214) is used to limit the incident direction of the α-radiation source toward the metal substrate (204). The alpha radiation source is either polonium-210 or plutonium-238; The metal substrate (204) uses a metal element with an atomic number greater than 70.

6. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to claim 5, characterized in that, The vacuum injection unit includes a piezoelectric micro-injection pump (102), a microtube (104), a pre-evacuation chamber (101), a vacuum gate valve (105), and a second vacuum pumping assembly connected to the pre-evacuation chamber (101); The microtube (104) is installed on the side wall of the pre-evacuation chamber (101) via a microtube vacuum feedthrough (103). One end of the microtube (104) is connected to the liquid outlet of the piezoelectric micro-injection pump (102), and the other end extends into the pre-evacuation chamber (101). The diameter of the microtube (104) is 20μm to 100μm. The vacuum gate valve (105) is located between the pre-evacuation chamber (101) and the vacuum measurement chamber (222). The pressure in the pre-evacuation chamber (101) is 1.0 × 10⁻⁶. -3 Pa ~ 4.0 × 10 -3 Pa.

7. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to claim 6, characterized in that, The detection unit includes a detector (301), a second servo electric cylinder (302), and a signal processing component; The detector (301) is used to receive α particles scattered by the target liquid film and output a pulse signal; the angle between the normal of the end face of the detector (301) near the temperature-controlled sample stage assembly and the axial direction of the collimation hole of the collimator (214) is 150° to 175°; the detector (301) is a silicon drift detector or a position-sensitive detector. The signal processing component includes an amplifier (304), a multichannel pulse amplitude analyzer (305), and a computer (306) connected in sequence; The amplifier (304) is located on the side of the detector (301) away from the temperature-controlled sample stage assembly, and is used to perform preliminary processing and shaping amplification of the pulse signal output by the detector (301); The one-dimensional push rod of the second servo electric cylinder is connected to the detector (301) and is used to control the movement of the detector (301).

8. The alpha particle backscattering thickness measurement device for nanoscale liquid films according to claim 7, characterized in that, The first vacuum pumping assembly includes a first vacuum pipe (216), an ion pump (215), a first molecular pump (217), a second vacuum pipe (218), and a first mechanical pump (219); the first vacuum pipe (216) is a three-way pipe, the first end of the first vacuum pipe (216) is connected to the ion pump (215), the second end of the first vacuum pipe (216) is connected to the vacuum measurement chamber (222), and the third end of the first vacuum pipe (216) is connected to one end of the first molecular pump (217); the other end of the first molecular pump (217) is connected to the first mechanical pump (219) through the second vacuum pipe (218); The second vacuum pumping assembly includes a second mechanical pump (106), a third vacuum pipe (107), and a second molecular pump (108) connected in sequence, with the second molecular pump (108) connected to the pre-evacuation chamber (101).

9. A detection method for an alpha particle backscattering thickness measurement device for nanoscale liquid films as described in claim 8, characterized in that, Includes the following steps: S1. Using the first vacuum pumping assembly, the pressure in the vacuum measurement chamber (222) is adjusted to the first preset pressure; using the second vacuum pumping assembly, the pressure in the pre-evacuation chamber (101) is adjusted to the second preset pressure; at the same time, the temperature of the metal substrate (204) is adjusted to the preset temperature according to the characteristics of the target liquid film. S2. Open the radioactive source chamber (213), adjust the position of the radioactive source chamber (213) using the first servo cylinder (210) and the two-dimensional moving stage (212), and adjust the position of the detector (301) using the second servo cylinder (302). When the alpha particle count rate measured by the detector (301) is at its maximum, the position of the radioactive source chamber (213) and the detector (301) is the optimal geometric position. Under the optimal geometric position, collect the backscattered alpha particle count rate and energy spectrum within time t, the detection unit records the background measurement results, and closes the radioactive source chamber (213). The background measurement results include the total count rate N. b And plotting the energy spectrum curve S b (E); S3. Keep the measurement parameters in step S1 and the optimal geometric position in step S2 unchanged; Liquid under normal atmospheric pressure is quantitatively pushed through a piezoelectric micro-injection pump (102) and enters the pre-vacuum chamber (101) through a microtube (104). The vacuum gate valve (105) is opened to introduce the liquid onto the metal substrate (204), and the DC voltage on the electrode ring (205) is turned on at the same time. The microtube (104) is immediately removed and the vacuum gate valve (105) is closed, and the liquid forms a target liquid film on the surface of the metal substrate (204). S4. Open the radioactive source chamber (213), collect the backscattered α particle count rate and energy spectrum within the same time t, the detection unit records the measurement results of the target liquid film, and close the radioactive source chamber (213); the measurement results of the target liquid film include the total count rate N. f and energy spectrum curve S f (E); S5. Calculate the relative count rate value Δ(N) = (N b - N f ) / N b Analyze the energy spectrum curve S b (E) and the energy spectrum curve S f (E) Obtain the relative energy offset Δ(E); compare the relative count rate value Δ(N) and relative energy offset Δ(E) of the target liquid film with the pre-established database, calculate the thickness of the target liquid film, and output the measurement results of the target liquid film.

10. The detection method for the α-particle backscattering thickness measurement device for nanoscale liquid films according to claim 9, characterized in that, In step S5, the pre-established database includes relative count rate values ​​and energy spectrum curves of various target liquid films under different thicknesses and different measurement parameters; the various target liquid films have different material compositions; the method for establishing the pre-established database is Monte Carlo simulation; The inversion calculation employs a nonlinear optimization algorithm to match the relative count rate value Δ(N) and relative energy shift Δ(E) of the target liquid film with data from a pre-established dataset; the nonlinear optimization algorithm is either nonlinear least squares or Bayesian inference.

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