Method for measuring work function of metal material based on ultraviolet photoelectron yield spectrum

Abstract

The application provides a method for measuring work function of metal material based on ultraviolet photoelectron yield spectrum, and relates to the technical field of material analysis, and comprises the following steps: determining actual incident photon number of a main light path at a target wavelength, wherein the target wavelength belongs to the vacuum ultraviolet and near ultraviolet wave band; measuring the number of photoelectrons excited by the main light path on the surface of a metal sample to be measured at the target wavelength; determining the ultraviolet photoelectron yield spectrum of the metal sample to be measured according to the actual incident photon number and the number of photoelectrons of the main light path at multiple wavelengths; fitting the ultraviolet photoelectron yield spectrum of the metal sample to be measured based on a Fowler photoelectron emission theoretical model, and determining the value of the work function of the metal material according to the fitting result. The application can accurately analyze the nonlinear variation law of the photoelectron yield near the threshold value through a nonlinear fitting process, and improves the accuracy of the work function measurement, and especially in a complex material system, the application shows stronger adaptability and higher measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of materials analysis technology, specifically to a method for measuring the work function of metallic materials based on ultraviolet photoelectron spectroscopy. Background Technology

[0002] In materials science, surface physics, and microelectronics, the work function of a material is a key physical quantity describing the ability of electrons to escape from the material's surface. Accurate measurement of the work function is crucial for understanding the electronic structure of materials, optimizing the performance of microelectronic devices, and conducting surface chemical reactions.

[0003] Traditional methods for measuring work function include the photoemission threshold method, Kelvin probe method, thermionic emission method, and field emission method. For example, ultraviolet light is irradiated onto the material surface to excite photoelectrons, and the work function value is calculated based on the kinetic energy of these photoelectrons. However, traditional photoemission methods typically rely on extrapolation to calculate the work function, especially when the number of experimental data collection points is limited. Extrapolation can lead to instability in the results. Due to the complexity of the material's electronic structure, surface state, and experimental conditions, extrapolation methods often cannot accurately predict unmeasured data points, thus affecting the accuracy of the work function. Summary of the Invention

[0004] This invention provides a method for measuring the work function of metallic materials based on ultraviolet photoelectron yield spectroscopy, aiming to solve the problems existing in the background art. To solve the above-mentioned technical problems, this invention is implemented as follows: This invention provides a method for measuring the work function of materials based on ultraviolet photoelectron yield spectroscopy, comprising: Determine the actual number of incident photons in the main optical path at the target wavelength, where the target wavelength belongs to the ultraviolet and near-ultraviolet bands; The number of photoelectrons excited by the main optical path on the surface of the metal sample under test at the target wavelength is measured. Based on the actual number of incident photons and photoelectrons in the main optical path at multiple wavelengths, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is determined. The horizontal axis of the ultraviolet photoelectron yield spectrum is the photon energy corresponding to the wavelength, and the vertical axis is the photoelectron yield, which characterizes the number of photoelectrons generated by each incident photon. Based on the Fowler photoelectron emission theory model, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is fitted, and the work function of the metal material is determined according to the fitting result. The work function of the metal material of the metal sample to be tested represents the critical photon energy corresponding to the inflection point of the ultraviolet photoelectron yield spectrum.

[0005] Optionally, based on the Fowler photoelectron emission theory model, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is fitted, and the value of the work function of the metal material is determined according to the fitting result, including: The vertical axis of the ultraviolet photoelectron yield spectrum is converted into logarithmic form to obtain the logarithm of the photoelectron yield corresponding to each data point in the ultraviolet photoelectron yield spectrum. From the ultraviolet photoelectron yield spectrum, a linear response segment of the logarithm of photoelectron yield as a function of photon energy was determined; Based on the Fowler photoelectron emission theory model, regression calculations are performed on the linear response region to obtain the value of the work function of the metallic material.

[0006] Optionally, based on the Fowler photoelectron emission theory model, regression calculations are performed on the linear response region to obtain the value of the work function of the metallic material, including: A nonlinear least squares fitting algorithm was used to fit the photon energy and the logarithm of the photoelectron yield in the linear response region using the Fowler photoelectron emission theory model, and the fitting results were obtained. Based on the fitting results, the value of the work function of the metallic material is determined.

[0007] Optionally, a nonlinear least squares fitting algorithm is used to fit the photon energy and the logarithm of the photoelectron yield in the linear response region using the Fowler photoelectron emission theory model, and the fitting result is obtained, including: A Fowler function is constructed with photon energy and work function of metallic material as variables. The Fowler function includes a piecewise defined statistical distribution function of electronic states and temperature parameters. Set the initial values ​​of the proportionality constant and the work function parameters of the metallic material in the Fowler function; Based on the initial values ​​of the proportionality constant and the work function parameters of the metallic material, the values ​​of the proportionality constant and the work function parameters of the metallic material are iteratively adjusted to minimize the sum of squared residuals between the logarithm of the theoretical yield output by the Fowler function and the logarithm of the photoelectron yield in the linear response segment. If the sum of squared residuals is below a preset threshold, the output includes a fitting result that includes the optimal work function parameters of the metallic material. Based on the fitting results, the value of the work function of the metallic material is determined, including: The optimal work function parameter of the metallic material in the fitting results is determined as the value of the work function of the metallic material.

[0008] Optionally, from the ultraviolet photoelectron yield spectrum, the linear response segment of the logarithm of photoelectron yield as a function of photon energy includes: Calculate the first derivative spectrum of the logarithm of photoelectron yield as a function of photon energy in the ultraviolet photoelectron yield spectrum; From the first derivative spectrum, the global maximum point is determined as the characteristic inflection point; Centered on the characteristic inflection point, the ultraviolet photoelectron yield spectrum is extended to the low-energy side and the high-energy side respectively to obtain the linear response segment. The low-energy side is the side where the photon energy decreases, and the high-energy side is the side where the photon energy increases.

[0009] Optionally, after obtaining the fitting result, the method further includes: Under the same test conditions as the metal sample to be tested, the ultraviolet photoelectron yield spectrum of a standard sample with a known work function value of the metal material was obtained and used as the reference yield spectrum. Based on the benchmark yield spectrum, establish the relationship curve between the temperature and work function offset of the standard sample; Based on the test temperature of the metal sample to be tested, the temperature compensation value is determined according to the relationship curve. Based on the fitting results, the value of the work function of the metallic material is determined, including: The temperature compensation value is superimposed on the fitting result of the metal sample to be tested to obtain the temperature-corrected work function value of the metal material.

[0010] Optionally, determining the actual number of incident photons in the main optical path at the target wavelength includes: Monochromatic light in the ultraviolet band is divided into a transmitted main optical path and a reflected reference optical path at the target wavelength. The number of incident photons in the reference optical path at the target wavelength is measured, and the number of incident photons in the main optical path at the target wavelength is also measured. The splitting ratio at the target wavelength is calculated based on the number of incident photons in the main optical path and the number of incident photons in the reference optical path at the target wavelength. Based on the splitting ratio at each wavelength, the number of incident photons in the main optical path at the corresponding wavelength is corrected to obtain the actual number of incident photons in the main optical path at each wavelength.

[0011] Optionally, the monochromatic light in the ultraviolet band is divided into a transmitted main optical path and a reflected reference optical path at the target wavelength, including: The control light source module generates monochromatic light in the ultraviolet band and processes the monochromatic light in the ultraviolet band into monochromatic light of the target wavelength; The focusing lens receives monochromatic light of the target wavelength and focuses the monochromatic light of the target wavelength onto the beam splitter; The beam splitter divides the monochromatic light of the target wavelength into the transmitted main optical path and the reflected reference optical path according to a preset ratio.

[0012] Optionally, the light source module includes a vacuum ultraviolet deuterium lamp, a ring mirror, a filter, and a vacuum ultraviolet monochromator; the light source module generates monochromatic light in the ultraviolet band and processes the monochromatic light in the ultraviolet band into monochromatic light of the target wavelength, including: The vacuum ultraviolet deuterium lamp is controlled to generate a continuous ultraviolet spectrum; The annular mirror reflects the light beam emitted by the vacuum ultraviolet deuterium lamp onto the filter; The filter removes stray light of non-target wavelength from the beam reflected by the annular mirror to obtain a filtered beam. The vacuum ultraviolet monochromator receives the light beam filtered by the filter and outputs monochromatic light of the target wavelength.

[0013] Optionally, measuring the number of incident photons in the reference optical path at the target wavelength includes: A photomultiplier tube measures the number of incident photons in the reference optical path at the target wavelength; Measuring the number of incident photons in the main optical path at the target wavelength includes: The four-dimensional sample operation stage carries the metal sample to be tested and adjusts the spatial pose of the metal sample to be tested so that the main optical path is focused on the surface of the metal sample to be tested; A wide-bandgap semiconductor photodetector mounted on a movable support measures the number of incident photons in the main optical path at the target wavelength at the location of the four-dimensional sample operation stage.

[0014] The technical solutions provided by the embodiments of the present invention bring at least the following beneficial effects: This invention eliminates the subjective errors of traditional extrapolation methods that rely on manual judgment of the cutoff edge by quantifying the actual number of incident photons and photoelectrons at each wavelength and combining it with spectrophotometer calibration. In terms of data processing, this invention utilizes the Fowler photoelectron emission theory model for nonlinear fitting to more scientifically process the experimentally measured ultraviolet photoelectron yield spectrum. The Fowler photoelectron emission theory model can deeply describe the photoelectron emission process and, combined with the electronic state statistical distribution function and temperature term, accurately captures the nonlinear variation of photoelectron yield near the threshold. In particular, in the threshold region, the photoelectron yield exhibits complex variations, and this invention can accurately analyze this variation through nonlinear fitting, avoiding the work function measurement errors caused by inaccurate data fitting in traditional methods. In summary, this invention improves the accuracy of work function measurement by quantifying the number of incident photons and photoelectrons and combining it with nonlinear fitting of the Fowler photoelectron emission theory model, demonstrating stronger adaptability and higher measurement accuracy, especially in complex material systems. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram of the steps of a method for measuring the work function of metallic materials based on ultraviolet photoelectron spectroscopy, provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the ultraviolet photoelectron yield testing principle in one embodiment of the present invention; Figure 3 This is a schematic diagram of a work function measurement system for metallic materials based on ultraviolet photoelectron yield spectroscopy, provided in one embodiment of the present invention. Figure 4 This is a schematic diagram of the ultraviolet photoelectron yield spectrum of a gold thin film sample fitted by Fowler in one embodiment of the present invention.

[0017] Labels in the diagram: 1—Vacuum ultraviolet deuterium lamp; 2—Ring mirror; 3—Filter; 4—Vacuum ultraviolet monochromator; 5—Collimating mirror; 6—Photomultiplier tube; 7—Beam splitter; 8—Electron shutter; 9—Neutralizing electron gun; 10—Electron multiplier; 11—Focusing lens; 12—Four-dimensional sample stage; 13—Wide bandgap semiconductor photodetector; 14—Argon ion gun; 15—Magnetic sample transfer rod; 16—Sample; 17—Photon; 18—Photoelectron detector. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Traditional work function measurement methods typically rely on extrapolation, which can lead to instability, especially when the number of experimental data collection points is limited. Due to the complexity of material electronic structure, surface state, and experimental conditions, extrapolation often fails to accurately predict unmeasured data points, thus affecting the accuracy of the work function. To address this issue, the core concept of this invention is to eliminate subjective errors in traditional methods by quantifying the actual number of incident photons and photoelectrons at each wavelength, combined with spectrophotometer calibration. Furthermore, it introduces the Fowler photoelectron emission theory model (proposed by RH Fowler to describe the photoelectron emission phenomenon of metals under ultraviolet light irradiation), effectively describing the physical response of the ultraviolet photoelectron emission spectrum through nonlinear fitting, particularly the nonlinear variation near the threshold. Compared to traditional methods, this approach offers higher accuracy and reliability, exhibiting significant advantages, especially in complex material systems and under low signal-to-noise ratio conditions.

[0020] Figure 1 This is a schematic diagram illustrating the steps of a method for measuring the work function of metallic materials based on ultraviolet photoelectron yield spectroscopy, as provided in one embodiment of the present invention. Figure 1 As shown, it includes: Step S11: Determine the actual number of incident photons in the main optical path at the target wavelength, wherein the target wavelength belongs to the ultraviolet and near-ultraviolet bands.

[0021] The ultraviolet (VUV) band has a wavelength range from 10 nm to 200 nm. Ultraviolet light cannot travel through air because air absorbs these wavelengths. Therefore, experiments with ultraviolet light in the VUV band must be conducted in a vacuum environment.

[0022] The near-ultraviolet (NUV) wavelength range is between 200 nm and 400 nm, which is close to the wavelength of visible light, but still falls within the ultraviolet light category. NUV light can penetrate air, so it can be used under normal experimental conditions without requiring a vacuum environment.

[0023] The target wavelength is the specific wavelength currently selected for the experiment in the ultraviolet and near-ultraviolet bands. In this embodiment, multiple different target wavelengths will be selected continuously in the ultraviolet and near-ultraviolet bands for testing in order to obtain the actual number of incident photons in the main optical path at multiple wavelengths.

[0024] In an optional implementation, step S11 specifically includes steps S111 to S114: Step S111: The monochromatic light in the ultraviolet band is divided into the main optical path that is transmitted and the reference optical path that is reflected at the target wavelength.

[0025] Before testing, the surface of the metal sample to be tested is cleaned using an argon ion gun 14 to remove contaminants. Specifically, the argon ion gun releases argon ions to bombard the sample surface, removing any contaminants or oxides that may be present on the surface of the metal sample, thereby ensuring the cleanliness of the sample surface and providing accurate measurement results for subsequent ultraviolet photoelectron spectroscopy.

[0026] The monochromatic light generated by the vacuum ultraviolet light source is split into two independent light paths at the target wavelength. One of these is the transmitted main light path (such as...). Figure 3 The middle direction points to the lateral optical path of the focusing lens 11. The main transmitted optical path is the optical path that directly illuminates the surface of the metal sample to be tested, used to excite photoelectrons. The second is the reflected reference optical path (such as...). Figure 3 The middle direction points to the longitudinal optical path of the photomultiplier tube 6. The reflected reference optical path serves as a reference signal for real-time monitoring of the stability of the light source and does not participate in the optical path for excitation of the metal sample under test.

[0027] Figure 2 This is a schematic diagram of the ultraviolet photoelectron yield testing principle in one embodiment of the present invention. Please refer to [link / reference]. Figure 2 The transmitted light beam (main light path) directly illuminates the surface of the metal sample 16 to be tested on the right side, and the excited photoelectrons are detected and counted by the wide-bandgap semiconductor photodetector 13 (i.e., photon detector) above the sample. The reflected light beam (reference light path) is received by a photomultiplier tube for synchronous monitoring of the number of incident photons. Simultaneously, the number of photoelectrons excited on the surface of the metal sample to be tested is synchronously captured by the photoelectron detector 18. In this embodiment, an electron multiplier and a pulse counter are combined into the photoelectron detector 18.

[0028] In an optional implementation, step S11 specifically includes steps S111 to S113: Step S111: Control the light source module to generate monochromatic light in the ultraviolet band, and process the monochromatic light in the ultraviolet band into monochromatic light of the target wavelength.

[0029] Monochromatic light covering the ultraviolet band is generated by a light source module. The light source module can be a xenon lamp, deuterium lamp, or other stable light source suitable for the ultraviolet band. The target wavelength is selected based on the photoelectric properties of the metal material under test and the measurement requirements of its work function.

[0030] Figure 3 This is a schematic diagram of a work function measurement system for metallic materials based on ultraviolet photoelectron yield spectroscopy, provided in one embodiment of the present invention. Please refer to [link / reference]. Figure 3 The light source module includes a vacuum ultraviolet deuterium lamp 1, a ring mirror 2, a filter 3, and a vacuum ultraviolet monochromator 4; in an optional embodiment, step S111 specifically includes steps S1111 to S1114: Step S1111: Control the vacuum ultraviolet deuterium lamp to generate a continuous ultraviolet spectrum.

[0031] First, a vacuum ultraviolet deuterium lamp (D2 lamp) is controlled to generate a continuous ultraviolet spectrum covering the ultraviolet and near-ultraviolet bands. The deuterium lamp (i.e., a vacuum ultraviolet deuterium lamp) is a commonly used ultraviolet light source, particularly suitable for providing high-brightness and highly stable ultraviolet spectra. Because it can produce a broad wavelength range from 115 nm to 400 nm, the deuterium lamp provides a relatively uniform ultraviolet spectrum for experiments. In practice, the deuterium lamp is started to emit light by adjusting the power supply and control system. During the emission process, the deuterium lamp can produce continuous ultraviolet light in the ultraviolet and near-ultraviolet bands. The output spectrum will include light of multiple different wavelengths.

[0032] In step S1112, the annular mirror reflects the light beam emitted by the vacuum ultraviolet deuterium lamp onto the filter.

[0033] A ring mirror is used to reflect the ultraviolet light beam from the vacuum ultraviolet deuterium lamp onto the filter. A ring mirror is an optical element used to reflect and guide light beams in the optical path. Its shape is designed so that the beam remains relatively focused and uniform after reflection by the ring mirror. The main function of the ring mirror is to concentrate the ultraviolet light emitted by the deuterium lamp and guide it to the filter for further processing.

[0034] In step S1113, the filter removes stray light of non-target wavelength from the light beam reflected by the annular mirror to obtain a filtered light beam.

[0035] Optical filters are used to remove stray light from the ultraviolet beam reflected from a ring mirror, retaining only the target wavelength. Stray light refers to extra spectral components outside the target wavelength range that may affect subsequent measurements. Filters are made of special materials that allow light to pass through a specific wavelength range while absorbing or reflecting other wavelengths. Through precise design and selection, it can be ensured that only monochromatic light matching the target wavelength passes through, while other wavelength components are effectively blocked. The filtered beam has a more uniform wavelength distribution, ensuring that the light source outputs monochromatic light close to the target wavelength. The choice of filter depends on the specific requirements of the target wavelength; for example, a bandpass filter (allowing the target wavelength while blocking other wavelengths) or high-pass / low-pass filters (allowing light greater than or less than a specific wavelength, respectively) can be used.

[0036] In step S1114, the vacuum ultraviolet monochromator receives the light beam filtered by the filter and outputs monochromatic light of the target wavelength.

[0037] The ultraviolet beam, after being processed by filters, is fed into a vacuum ultraviolet monochromator, where it is further filtered and output as monochromatic light of a specific target wavelength. A vacuum ultraviolet monochromator is a device capable of separating and outputting a specific wavelength from the spectrum; its core working principle is based on the dispersion effect of light. A vacuum ultraviolet monochromator contains optical elements such as gratings, lenses, or prisms to separate light of different wavelengths. By adjusting the angle of the grating, the desired target wavelength is selected. After the filtered beam emitted by the deuterium lamp enters the monochromator, the optical elements selectively separate the light of the desired wavelength according to the preset target wavelength, while other components outside the target wavelength range are filtered out. Through this process, the vacuum ultraviolet monochromator can output precise monochromatic light of the target wavelength for subsequent experiments or measurements.

[0038] The target wavelength monochromatic light, filtered by the vacuum ultraviolet monochromator 4, is received by the collimating lens 5. Located at the exit end of the vacuum ultraviolet monochromator 4, the collimating lens 5 collimates the monochromatic beam, converting it into a parallel beam. Subsequently, this parallel monochromatic beam is precisely guided and incident on the surface of the beam splitter 7, ensuring the parallelism of the light incident on the electronic shutter 8. This lays the necessary optical foundation for the beam splitter 7 to separate the beam into transmitted and reflected light paths in subsequent steps.

[0039] Step S112: Measure the number of incident photons in the reference optical path at the target wavelength, and measure the number of incident photons in the main optical path at the target wavelength.

[0040] The number of incident photons passing through the reference optical path and the main optical path at the selected target wavelength is measured. This measurement effectively reveals the photon intensity of the light source at the target wavelength, as well as the light energy transmitted through different optical paths, providing an accurate photon counting basis for subsequent experimental data analysis.

[0041] In an optional implementation, step S112 specifically includes steps S1121 to S1122: Step S1121: Using an electronic shutter, the main optical path is exposed according to a preset exposure cycle.

[0042] By controlling the electronic shutter 8, the exposure of the main optical path is controlled according to the preset exposure cycle. The electronic shutter is used to adjust the incident time of light, thereby precisely controlling the exposure duration and ensuring that the exposure time remains consistent each time.

[0043] Specifically, the main function of an electronic shutter is to periodically open and close the optical path, thereby limiting the time window for light to enter. The exposure period setting directly affects the measurement accuracy and signal-to-noise ratio. The exposure period should be set according to the required light intensity and the stability of the light source; it should not be too short, lest sufficient electronic information cannot be collected, nor should it be too long, lest overexposure cause measurement errors or saturation of the electron multiplier tube.

[0044] During this process, the light source in the main optical path will begin to illuminate the light under the control of the electronic shutter, and after a preset time, the shutter will close and stop the exposure.

[0045] Step S1122: The photomultiplier tube 6 measures the number of incident photons in the reference optical path at the target wavelength.

[0046] Photomultiplier tubes (PMTs) are used to measure the number of incident photons in a reference optical path at a target wavelength. A photomultiplier tube (PMT) is a highly sensitive detector that converts incident photons into electronic signals and amplifies these signals through a multiplication process, thereby enabling the detection of low-intensity signals.

[0047] In practice, the photomultiplier tube 6 receives the light signal from the reference optical path and counts according to a preset exposure cycle. Whenever a photon is absorbed by the photocathode of the photomultiplier tube, it releases electrons. These electrons are multiplied through multiple electrodes inside the multiplier tube, ultimately generating a measurable current signal.

[0048] During this process, photomultiplier tube 6 counts each incident photon and converts the number of photons into a corresponding electronic signal, facilitating subsequent data processing and analysis. It is important to note that the gain (amplification factor) of the photomultiplier tube should be adjusted according to the measurement requirements to ensure accurate measurement of the number of photons under low light intensity conditions.

[0049] In an optional implementation, step S112 further includes steps S1123 to S1124: In step S1123, the four-dimensional sample operation stage 12 carries the metal sample to be tested and adjusts the spatial pose of the metal sample to be tested so that the main optical path is focused on the surface of the metal sample to be tested.

[0050] The four-dimensional sample stage 12 is used to hold the metal sample to be tested and adjust its spatial orientation so that the light beam passing through the main optical path can be precisely focused on the surface of the metal sample. The four-dimensional sample stage 12 has multiple degrees of freedom, allowing for translation and rotation in three directions to adjust the position and angle of the sample, ensuring that the light beam is focused on a specific location on the sample. Specifically, the metal sample to be tested is first placed on the four-dimensional sample stage 12 via a magnetic transfer rod, ensuring it is in the appropriate position. Next, the spatial orientation of the sample is fine-tuned by manually or automatically adjusting the four-dimensional sample stage 12, ensuring that the light beam in the main optical path is concentrated and accurately illuminates the surface of the sample.

[0051] In step S1124, the wide bandgap semiconductor photodetector 13, mounted on the movable support, measures the number of incident photons in the main optical path at the target wavelength at the location of the four-dimensional sample operation stage 12.

[0052] A wide-bandgap semiconductor photodetector 13 mounted on a movable support is used to measure the number of incident photons that illuminate the sample surface through the main optical path at the location of the four-dimensional sample stage 12. The photodetector employs a wide bandgap semiconductor material, which exhibits excellent photoelectric response characteristics at the target wavelength, enabling effective detection of photon signals in the main optical path. The wide bandgap semiconductor photodetector 13 operates by absorbing photons and converting them into an electrical signal to measure the photon count. Due to the high bandgap of wide bandgap semiconductor materials, they exhibit strong photoelectric effects in the ultraviolet, visible, and near-infrared bands, effectively detecting photon signals within the target wavelength range. The wide bandgap semiconductor photodetector 13 is mounted on a movable support, allowing its position to be adjusted according to experimental needs. After the relative positions of the four-dimensional sample stage and the photodetector are adjusted, the detector can accurately receive incident photons in the main optical path at the target wavelength and convert them into measurable electrical signals.

[0053] Step S113: Calculate the splitting ratio at the target wavelength based on the number of incident photons in the main optical path and the number of incident photons in the reference optical path at the target wavelength.

[0054] spectral ratio This refers to a specific target wavelength. Below, the number of incident photons detected by the reference optical path The number of incident photons detected by the main optical path The ratio between them. Its mathematical expression is:

[0055] spectral ratio This reflects the beam splitter at the target wavelength. The optical beam-splitting characteristics (reflectivity to transmittance ratio) at a given wavelength. The reflection / transmission properties of the beam splitter may differ at different wavelengths, therefore... It is a function of wavelength. The splitting ratio also implicitly includes the wavelength difference between the reference optical path detector (photomultiplier tube, PMT) and the main optical path detector (wide-bandgap semiconductor photodetector). The relative response sensitivity difference at the location. Although the detector has been calibrated, The measured values ​​contain overall state information of the system at that wavelength.

[0056] In actual measurements, the output intensity of the vacuum ultraviolet deuterium lamp may fluctuate or drift slightly over time. This is because the photons in the reference and main optical paths originate from the same light source pulse (after beam splitting). and They will fluctuate proportionally. This proportional relationship is provided. In subsequent calculations of the actual number of photons irradiating the sample surface, Divide by The actual number of photons reaching the surface of the metal sample can then be obtained. More importantly, in subsequent measurements of the number of photoelectrons in the metal sample under test... In this way, it is not necessary to move the photodetector to the sample position for measurement every time. (This is both time-consuming and may disturb the sample position.)

[0057] Step S114: Based on the splitting ratio at each wavelength, correct the number of incident photons in the main optical path at the corresponding wavelength to obtain the actual number of incident photons in the main optical path at each wavelength.

[0058] At each wavelength Real-time measurement reference optical path And using the pre-determined wavelength point The number of photons actually reaching the sample surface at this moment and wavelength can be calculated using the following formula. That is, the actual number of incident photons in the main optical path:

[0059] In this way, even if the light source intensity fluctuates during the scanning process, the actual number of photons excited in the sample at each wavelength point can be accurately determined, thus ensuring the photoelectron yield. The accuracy of the calculations eliminates systematic errors caused by the instability of the light source.

[0060] Step S12: Measure the number of photoelectrons excited by the main optical path on the surface of the metal sample under test at the target wavelength.

[0061] The number of photoelectrons emitted from the surface of a metal sample under ultraviolet light of a target wavelength is quantified. The entire process is conducted in a vacuum environment because the behavior of photoelectrons can be affected by air molecules. Air molecules collide with electrons, causing scattering and energy loss, thus affecting the measurement results. Therefore, the experiment must be performed in a vacuum environment to preserve the pristine state of the photoelectrons, thereby ensuring high accuracy.

[0062] In one optional implementation, step S12 specifically includes steps S121 to S123: In step S121, the magnetic sample transfer rod transfers the metal sample to be tested to the four-dimensional sample operation stage in a vacuum environment.

[0063] The metal sample to be tested is accurately transferred to the four-dimensional sample handling stage under vacuum. For this purpose, a magnetic sample transfer rod 15 is used as the sample transfer tool. Through the action of magnetism, precise sample transfer can be achieved while maintaining high stability. The magnetic sample transfer rod consists of a coil generating a strong magnetic field and a transfer device with attached magnetic material. The sample is magnetically attracted to the transfer device and transferred to the four-dimensional sample handling stage under precise control.

[0064] In step S122, the electron multiplier applies a high-voltage electric field to amplify the photoelectron signal excited on the surface of the metal sample under test.

[0065] The weak photoelectron signal emitted from the surface of the metal sample under test is amplified by an electron multiplier 10. An electron multiplier is a precision electronic device that enhances the photoelectron signal emitted from the sample surface by applying a high-voltage electric field, making it more prominent and easier for subsequent counting. An electron multiplier typically consists of multiple multiplier tubes, each containing a cathode and multiple gain electrodes. Electrons generated by the photoelectric effect first strike the cathode of the multiplier, releasing primary electrons. These primary electrons are then accelerated and strike the gain electrodes in the multiplier, generating more secondary electrons. This process is repeated continuously at the multiple gain electrodes of the electron multiplier, ultimately amplifying the weak photoelectron signal into a sufficiently strong electrical signal. By applying a high-voltage electric field, the electron multiplier can control the acceleration and collision process of electrons, effectively amplifying the photoelectron signal.

[0066] Step S123: Using a pulse counter, based on the photoelectron signal amplified by the electron multiplier, measure the number of photoelectrons excited by the main optical path on the surface of the metal sample to be tested.

[0067] The number of photoelectrons excited by the main optical path on the surface of the metal sample under test is obtained by accurately measuring the photoelectron signal amplified by the electron multiplier using a pulse counter.

[0068] A pulse counter is a high-precision counting device. Its working principle is to convert the electrical signal amplified by an electron multiplier into a pulse signal. Each time a photoelectron passes through the counter, the counter records a pulse. These pulse signals are digitized and analyzed by a computer system. The pulse counter ultimately outputs the measured number of photoelectrons. That is, the number of photoelectrons excited on the surface of the metal sample under test by the main optical path. .

[0069] In one optional implementation, an embodiment of the present invention provides a work function measurement system for metallic materials based on ultraviolet photoelectron yield spectroscopy, which further includes a helium lamp and a neutralizing electron gun 9. The neutralizing electron gun 9 is located near the four-dimensional sample operating stage 12. The neutralizing electron gun emits a low-energy electron beam to neutralize the charge, ensuring that the photoelectron yield measurement is not disturbed, and cleaning the surface of the metal sample to be measured before measurement.

[0070] Step S13: Based on the actual number of incident photons and photoelectrons in the main optical path at multiple wavelengths, determine the ultraviolet photoelectron yield spectrum of the metal sample to be tested. The horizontal axis of the ultraviolet photoelectron yield spectrum is the photon energy corresponding to the wavelength, and the vertical axis is the photoelectron yield that characterizes the number of photoelectrons generated by each incident photon.

[0071] This invention constructs an ultraviolet photoelectron yield spectrum (PYS) by integrating optical parameters and photoelectron data. Specifically, the incident wavelength... Converted into photon energy The formula corresponding to the abscissa of the ultraviolet photoelectron yield spectrum is:

[0072] In the formula, h is Planck's constant. c It is the speed of light.

[0073] Calculate optoelectronic output The formula corresponding to the ordinate of the ultraviolet photoelectron yield spectrum is:

[0074] in,

[0075] therefore:

[0076] Step S14: Based on the Fowler photoelectron emission theory model, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is fitted, and the value of the material work function is determined according to the fitting result. The value of the material work function of the metal sample to be tested characterizes the critical photon energy corresponding to the inflection point of the ultraviolet photoelectron yield spectrum.

[0077] The core idea of ​​this invention is to extract the work function value of the material from the ultraviolet photoelectron yield spectrum of the metal sample to be tested. Among them, the Fowler photoelectron emission theory model quantitatively describes the photoelectron yield by introducing a temperature term and an electronic state statistical distribution function. Y With the energy of the incident photon hν Work function The physical relationship is determined by converting the ordinate of the ultraviolet photoelectron yield spectrum into logarithmic form to highlight the exponential change in yield near the threshold. Through first-order derivative analysis of the logarithmic spectrum, the characteristic inflection point of yield change is automatically located, and the optimal fitting interval is determined by expanding outwards from this point to both low-energy and high-energy sides. Finally, a nonlinear least squares algorithm is used to fit the Fowler photoelectron emission theoretical model with the linear response segment data, iteratively optimizing the work function parameters. Output until the residual is minimized. value.

[0078] In an optional implementation, step S14 specifically includes steps S141 to S143: Step S141: Convert the ordinate of the ultraviolet photoelectron yield spectrum into logarithmic form to obtain the logarithm of the photoelectron yield corresponding to each data point in the ultraviolet photoelectron yield spectrum.

[0079] Suppose that the ultraviolet photoelectron yield spectrum contains m data points, each point corresponding to a photon energy. Heguang Electronics Production Logarithmic transformation is performed according to the formula:

[0080] Linear response trend: near the threshold energy ( ≈ ), and It exhibits an approximately linear positive correlation. The inflection point location ( The maximum rate of change corresponds to the critical photon energy. (Right now = ).

[0081] Step S142: Determine the linear response segment of the logarithm of photoelectron yield as a function of photon energy from the ultraviolet photoelectron yield spectrum.

[0082] In the logarithmically transformed ultraviolet photoelectron yield spectrum ( - In the model, the linear transition interval that best fits the Fowler model is located. When the photon energy approaches the material work function threshold, the logarithm of the photoelectron yield... With photon energy They exhibit an approximately linear relationship.

[0083] In an optional implementation, step S142 specifically includes steps S1421 to S1423: Step S1421: Calculate the first derivative spectrum of the logarithm of photoelectron yield as a function of photon energy in the ultraviolet photoelectron yield spectrum.

[0084] Quantization can be achieved through differentiation. - The local rate of change of the curve provides a mathematical basis for inflection point identification. Therefore, this embodiment proposes that the first derivative at the threshold energy... The value reaches its maximum at a point corresponding to a sudden change in the photoelectron emission probability. The first derivative of the logarithm of the photoelectron yield as a function of photon energy is expressed as:

[0085] Specifically, in the logarithmically transformed ultraviolet photoelectron yield spectrum, for each photon energy point, the ratio of the difference in the logarithm of the photoelectron yield between adjacent data points to the difference in photon energy is calculated.

[0086] Step S1422: Determine the global maximum point as the characteristic inflection point from the first derivative spectrum.

[0087] The characteristic inflection point of the logarithm of photoelectron yield as a function of photon energy is determined from the first derivative spectrum. The characteristic inflection point is where the rate of change of yield in the photoelectron spectrum undergoes a significant shift. Specifically, the global maximum point of the first derivative spectrum corresponds to the region where the logarithm of photoelectron yield changes most drastically, marking a key turning point in the photoelectron emission process. In other words, the photon energy at the global maximum point is the location of the inflection point, corresponding to the work function value of the material.

[0088] Step S1423: Centered on the characteristic inflection point, extend the ultraviolet photoelectron yield spectrum to the low-energy side and the high-energy side respectively to obtain the linear response segment. The low-energy side is the side where the photon energy decreases, and the high-energy side is the side where the photon energy increases.

[0089] Based on the characteristic inflection point position determined in step S1422, the linear response segment is obtained by expanding outwards from this center towards both the low-energy and high-energy sides of the photon energy. The key to this process is ensuring that the logarithm of photoelectron yield in the selected segment exhibits a linear relationship with photon energy. Specifically, the expansion is first performed on both sides of the characteristic inflection point's photon energy, towards the low-energy and high-energy sides respectively. During expansion, an algorithm is used to determine whether the logarithm of photoelectron yield remains linear with photon energy on each side. If the logarithm of photoelectron yield exhibits a linear characteristic with photon energy on a certain side, then that part is determined to be part of the linear response segment. The linear response segment satisfies the following conditions: First, within the linear response segment, there is a clear linear relationship between the logarithm of photoelectron yield and photon energy. Second, the start and end points within the linear response segment should not exhibit large data fluctuations or deviate from the linear trend.

[0090] Step S143: Based on the Fowler photoelectron emission theory model, regression calculation is performed on the linear response segment to obtain the value of the work function of the metallic material.

[0091] Using the Fowler photoelectron emission theory model, regression calculations were performed on the linear response segment of the photoelectron yield as a function of photon energy to ultimately determine the work function value of the metal sample under test. In other words, by fitting data from the linear response segment, the accurate value of the material's work function was obtained using the Fowler photoelectron emission theory model.

[0092] In an optional implementation, step S143 specifically includes steps S1431 to S1432: Step S1431: Using a nonlinear least squares fitting algorithm, the photon energy and the logarithm of the photoelectron yield in the linear response region are fitted using the Fowler photoelectron emission theory model to obtain the fitting result.

[0093] A nonlinear least squares fitting algorithm was used for data fitting. Nonlinear least squares fitting is an optimization technique that determines the optimal fitting parameters within a given parameter range by minimizing the difference between model predictions and experimental data (i.e., the sum of squared residuals). In this step, the relationship between photon energy and the logarithm of photoelectron yield in the linear response region was fitted using the Fowler photoelectron emission theory model, ultimately obtaining the best fitting result. These fitting results will be used to calculate the work function of the material.

[0094] The input is a photon energy sequence of the linear response region. With the corresponding logarithmic sequence of optoelectronic output The output includes the optimal scaling constant. Sum of work function parameters The fitting results.

[0095] Figure 4 This is a schematic diagram of the ultraviolet photoelectron yield spectrum of a gold thin film sample fitted by Fowler, according to one embodiment of the present invention. Please refer to [link / reference]. Figure 4 The black discrete points represent the photoelectron yield values ​​measured in the experiment (which was conducted at room temperature). Photon energy The changing trend. The discrete points shown by the hollow circles are nonlinear least-squares fitting curves based on the Fowler photoelectron emission theoretical model (including temperature broadening effect), derived from... Figure 4 As can be seen, the fitting results are in high agreement with the experimental data.

[0096] In an optional implementation, step S1431 specifically includes steps S14311 to S14312: Step S14311: Construct a Fowler function with photon energy and material work function as variables. The Fowler function includes a piecewise defined statistical distribution function of electronic states and temperature parameters.

[0097] Construct a Fowler function that describes the photoelectron yield. With photon energy Material work function ,temperature The quantitative relationship between photon energy and electron yield is established. The variables in the Fowler function include photon energy and the material work function. In Fowler theory, electron emission is influenced by various factors, including the statistical distribution of electronic states and temperature parameters. Therefore, the Fowler function not only considers the relationship between photon energy and electron yield but also introduces a piecewise defined statistical distribution function of electronic states and temperature parameters. The Fowler function ensures that the fitting results accurately reflect the photoelectron emission phenomenon.

[0098] Specifically, the Fowler function can be represented as:

[0099] in, It is a proportionality constant; Let be the work function of the material to be fitted; Boltzmann's constant; The absolute temperature of the metal sample to be tested is . The temperature of the metal sample to be tested can be set between -160℃ and 120℃, controlled by the temperature control system of the four-dimensional sample operation stage. The electronic state statistical distribution function defined for the piecewise region is expressed as follows: when (Photon energy is below the threshold):

[0100] This is a convergent exponential series, reflecting the contribution of thermally excited electrons in the low-energy region.

[0101] when (Photon energy is above the threshold):

[0102] This includes a quadratic term and a decay exponential term, which dominate the nonlinear rise near the threshold.

[0103] Step S14312: Set the initial values ​​of the proportional constant and the material work function parameters in the Fowler function.

[0104] Specify reasonable initial values ​​for the proportionality constants and material work function parameters in the Fowler function. These proportionality constants and material work function parameters serve as the starting point for the fitting process. The selection of initial values ​​can be based on theoretical derivation, experimental data, or empirical values. For example, the proportionality constants... The initial value can be set to (Normalization assumption); Work function The initial values ​​are set according to the material type; for example, the initial values ​​of the material work function parameters for metal samples. eV (e.g., gold is 4.8 eV).

[0105] Step S14313: Based on the initial value of the proportionality constant and the initial value of the material work function parameter, iteratively adjust the value of the proportionality constant and the value of the material work function parameter to minimize the sum of squared residuals between the logarithm of the theoretical yield output by the Fowler function and the logarithm of the photoelectron yield in the linear response segment.

[0106] A nonlinear least squares fitting algorithm is used to iteratively adjust the proportionality constant and the work function parameters of the metallic material in the Fowler function, gradually minimizing the sum of squared residuals between the theoretical logarithm of photoelectron yield and the experimental data. Specifically, by continuously modifying the parameter values, the output of the Fowler function is optimized to make it closer to the actual value of the experimentally measured logarithm of photoelectron yield. During each iteration, the parameter values ​​are fine-tuned to ensure that the fitting process converges quickly to the optimal solution.

[0107] The Levenberg-Marquardt algorithm (nonlinear least squares) is used to minimize the sum of squared residuals:

[0108] Step S14314: If the sum of squared residuals is lower than a preset threshold, output the fitting result including the optimal work function parameters of the metal material.

[0109] Once the iteration process is complete and the sum of squared residuals is below a preset threshold, the fitting result is output. The fitting result contains the optimal work function parameters for the metallic material, which are the work function values ​​of the metal sample under test. At this stage, the fitting values ​​provided by the Fowler function accurately reflect the photoelectron emission characteristics of the metal sample under test, thus providing a scientific basis for further analysis and application.

[0110] In an optional implementation, after obtaining the fitting result, the method further includes: Step S21: Under the same test conditions as the metal sample to be tested, obtain the ultraviolet photoelectron yield spectrum of a standard sample with a known work function value of the metal material, and use it as the reference yield spectrum.

[0111] Under the same testing conditions as the metal sample to be tested, the ultraviolet photoelectron yield spectrum of a standard sample with a known work function value of the metal was obtained and used as the reference yield spectrum. Since the work function value of the standard sample has been accurately determined, its ultraviolet photoelectron spectrum can serve as a reliable reference for establishing the relationship between temperature and the shift in the work function of the metal.

[0112] Step S22: Based on the benchmark yield spectrum, establish the relationship curve between the temperature and work function offset of the standard sample.

[0113] Fitting is performed on the baseline yield spectrum at each temperature point to obtain the measured work function value of the standard sample at each temperature. For each temperature point, the measured work function value is subtracted from the work function value of the standard sample to obtain the corresponding work function temperature shift (positive values ​​indicate that the measured value is too high, and negative values ​​indicate that it is too low). Since temperature changes cause slight changes in the electron emission characteristics of the material surface, thus affecting the work function value, this temperature effect must be accurately modeled, and the work function shift at different temperatures must be compensated using a relationship curve to correct the work function temperature drift.

[0114] In practice, different temperature points and their corresponding offsets are plotted as relationship curves. These curves describe how the material's work function changes under different temperature conditions. These curves provide a basis for temperature correction in subsequent steps.

[0115] Step S23: Determine the temperature compensation value based on the relationship curve according to the test temperature of the metal sample to be tested.

[0116] Based on the actual test temperature of the metal sample under test, and using the established relationship curve between temperature and work function offset, the temperature compensation value is determined. The temperature compensation value represents the inherent deviation of the measurement system from the fitting result at the current temperature. The test temperature of the metal sample under test can be obtained experimentally or through sensors. By comparing the performance of the test sample with that of the standard sample at different temperatures, the offset of the work function of the metal material of the metal sample under test at that temperature can be calculated, i.e., the temperature compensation value.

[0117] Step S1432: Determine the value of the work function of the metallic material based on the fitting result.

[0118] In one optional implementation, step S1432 specifically includes: The optimal material work function parameter from the fitting results is determined as the value of the work function of the metallic material.

[0119] The optimal work function parameters of the metallic material are extracted from the fitting results obtained in step S1431. The optimal work function parameters of the metallic material are the values ​​of the work function of the metallic material.

[0120] In an optional implementation, step S1432 further includes: The temperature compensation value is superimposed on the fitting result of the metal sample to be tested to obtain the temperature-corrected work function value of the metal material.

[0121] By superimposing the temperature compensation value with the fitting result, a temperature-corrected work function value for the metallic material is obtained. This effectively eliminates the influence of temperature on the work function value of the metallic material, providing more accurate measurement data. If the temperature compensation value is positive, it indicates that the work function is overestimated at the current temperature, and the temperature compensation value needs to be subtracted from the original value (i.e., the result determined in step S1431). If the temperature compensation value is negative, it indicates that the work function is underestimated, and the absolute value of the temperature compensation value is added to the original value. Finally, the temperature-corrected work function value is output. This invention can effectively correct the temperature drift of the work function of metallic materials, thereby making the measurement results more accurate.

[0122] This invention eliminates the subjective errors of traditional extrapolation methods that rely on manual judgment of the cutoff edge by quantifying the actual number of incident photons and photoelectrons at each wavelength and combining it with spectrophotometer calibration. In terms of data processing, this invention utilizes the Fowler photoelectron emission theory model for nonlinear fitting to more scientifically process the experimentally measured ultraviolet photoelectron yield spectrum. The Fowler photoelectron emission theory model can deeply describe the photoelectron emission process and, combined with the electronic state statistical distribution function and temperature term, accurately captures the nonlinear variation of photoelectron yield near the threshold. In particular, in the threshold region, the photoelectron yield exhibits complex variations, and this invention can accurately analyze this variation through nonlinear fitting, avoiding the work function measurement errors caused by inaccurate data fitting in traditional methods. In summary, this invention improves the accuracy of work function measurement by quantifying the number of incident photons and photoelectrons and combining it with nonlinear fitting of the Fowler photoelectron emission theory model, demonstrating stronger adaptability and higher measurement accuracy, especially in complex material systems.

[0123] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, apparatus, electronic devices, and media. Therefore, embodiments of the present invention can take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, embodiments of the present invention can take the form of a computer program product embodied on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0124] Embodiments of the present invention are described with reference to flowchart illustrations and / or block diagrams of methods and apparatus according to embodiments of the present invention. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing terminal device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal device, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing terminal device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing terminal equipment to cause a series of operational steps to be performed on the computer or other programmable terminal equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable terminal equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0125] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0126] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element. The above provides a detailed description of a method for measuring the work function of metallic materials based on ultraviolet photoelectron spectroscopy provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas; at the same time, for those skilled in the art, based on the ideas of the present invention, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for measuring the work function of metallic materials based on ultraviolet photoelectron yield spectroscopy, characterized in that, include: Determine the actual number of incident photons in the main optical path at the target wavelength, where the target wavelength belongs to the ultraviolet and near-ultraviolet bands; The number of photoelectrons excited by the main optical path on the surface of the metal sample under test at the target wavelength is measured. Based on the actual number of incident photons and photoelectrons in the main optical path at multiple wavelengths, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is determined. The horizontal axis of the ultraviolet photoelectron yield spectrum is the photon energy corresponding to the wavelength, and the vertical axis is the photoelectron yield, which characterizes the number of photoelectrons generated by each incident photon. Based on the Fowler photoelectron emission theory model, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is fitted, and the work function of the metal material is determined according to the fitting result. The work function of the metal material of the metal sample to be tested characterizes the critical photon energy corresponding to the inflection point of the ultraviolet photoelectron yield spectrum. The ultraviolet photoelectron yield spectrum of the metal sample under test is determined based on the actual number of incident photons and photoelectrons in the main optical path at multiple wavelengths, including: incident wavelength Converted into photon energy The formula corresponding to the abscissa of the ultraviolet photoelectron yield spectrum is: In the formula, h is Planck's constant. c The speed of light; Calculate optoelectronic output The formula corresponding to the ordinate of the ultraviolet photoelectron yield spectrum is: in, The number of photoelectrons excited on the surface of the metal sample under test by the main optical path; This represents the actual number of photons reaching the surface of the metal sample under test. Among them, the ultraviolet photoelectron yield spectrum of the metal sample to be tested is fitted based on the Fowler photoelectron emission theory model, including: The ordinate of the ultraviolet photoelectron yield spectrum is converted to logarithmic form to obtain the logarithm of the photoelectron yield for each data point in the spectrum. When the photon energy approaches the work function threshold of the material, the logarithm of the photoelectron yield is... With photon energy The relationship is approximately linear; specifically, suppose the ultraviolet photoelectron yield spectrum contains m data points, each point corresponding to a photon energy. Heguang Electronics Production Logarithmic transformation is performed according to the formula: Calculate the first derivative spectrum of the logarithm of photoelectron yield as a function of photon energy in the ultraviolet photoelectron yield spectrum; the first derivative of the logarithm of photoelectron yield as a function of photon energy is expressed as: From the first derivative spectrum, the global maximum point is determined as the characteristic inflection point; the global maximum point of the first derivative spectrum corresponds to the region where the logarithmic change of photoelectron yield is most drastic, and the photon energy of the global maximum point is the position of the inflection point, corresponding to the work function value of the material; Centered on the characteristic inflection point, the ultraviolet photoelectron yield spectrum is extended towards both the low-energy and high-energy sides to obtain linear response segments, ensuring that the logarithm of photoelectron yield in the selected segment exhibits a linear relationship with the change in photon energy; the low-energy side is the side where photon energy decreases, and the high-energy side is the side where photon energy increases. A nonlinear least squares fitting algorithm is used to fit the photon energy and the logarithm of the photoelectron yield in the linear response region using the Fowler photoelectron emission theory model, and the fitting result is obtained; the input is the photon energy sequence of the linear response region. With the corresponding logarithmic sequence of optoelectronic output The output includes the optimal scaling constant. Sum of work function parameters The fitting results; The optimal work function parameter of the metallic material in the fitting results is determined as the value of the work function of the metallic material; Among them, a nonlinear least squares fitting algorithm is used to fit the photon energy and the logarithm of the photoelectron yield in the linear response segment using the Fowler photoelectron emission theory model, and the fitting results are as follows: A Fowler function is constructed with photon energy and work function of metallic material as variables. The Fowler function includes a piecewise defined statistical distribution function of electronic states and temperature parameters. Set the initial values ​​of the proportionality constant and the work function parameters of the metallic material in the Fowler function; Based on the initial values ​​of the proportionality constant and the work function parameters of the metallic material, the values ​​of the proportionality constant and the work function parameters of the metallic material are iteratively adjusted to minimize the sum of squared residuals between the logarithm of the theoretical yield output by the Fowler function and the logarithm of the photoelectron yield in the linear response segment. If the sum of squared residuals is below a preset threshold, the output includes a fitting result that includes the optimal work function parameters of the metallic material. After obtaining the fitting result, the method further includes: Under the same test conditions as the metal sample to be tested, the ultraviolet photoelectron yield spectrum of a standard sample with a known work function value of the metal material was obtained and used as the reference yield spectrum. Based on the benchmark yield spectrum, establish the relationship curve between the temperature and work function offset of the standard sample; Based on the test temperature of the metal sample to be tested, the temperature compensation value is determined according to the relationship curve. Based on the fitting results, the value of the work function of the metallic material is determined, including: The temperature compensation value is superimposed on the fitting result of the metal sample to be tested to obtain the temperature-corrected work function value of the metal material.

2. The method according to claim 1, characterized in that, Determining the actual number of incident photons in the main optical path at the target wavelength includes: Monochromatic light in the ultraviolet band is divided into a transmitted main optical path and a reflected reference optical path at the target wavelength. The number of incident photons in the reference optical path at the target wavelength is measured, and the number of incident photons in the main optical path at the target wavelength is also measured. The splitting ratio at the target wavelength is calculated based on the number of incident photons in the main optical path and the number of incident photons in the reference optical path at the target wavelength. Based on the splitting ratio at each wavelength, the number of incident photons in the main optical path at the corresponding wavelength is corrected to obtain the actual number of incident photons in the main optical path at each wavelength.

3. The method according to claim 2, characterized in that, Monochromatic light in the ultraviolet band is divided into a transmitted main optical path and a reflected reference optical path at the target wavelength, including: The control light source module generates monochromatic light in the ultraviolet band and processes the monochromatic light in the ultraviolet band into monochromatic light of the target wavelength; The focusing lens receives monochromatic light of the target wavelength and focuses the monochromatic light of the target wavelength onto the beam splitter; The beam splitter divides the monochromatic light of the target wavelength into the transmitted main optical path and the reflected reference optical path according to a preset ratio.

4. The method according to claim 3, characterized in that, The light source module includes a vacuum ultraviolet deuterium lamp, a ring mirror, a filter, and a vacuum ultraviolet monochromator; The process involves generating monochromatic light in the ultraviolet band using a light source module, and then processing the monochromatic light in the ultraviolet band into monochromatic light of the target wavelength, including: The vacuum ultraviolet deuterium lamp is controlled to generate a continuous ultraviolet spectrum; The annular mirror reflects the light beam emitted by the vacuum ultraviolet deuterium lamp onto the filter; The filter removes stray light of non-target wavelength from the beam reflected by the annular mirror to obtain a filtered beam. The vacuum ultraviolet monochromator receives the light beam filtered by the filter and outputs monochromatic light of the target wavelength.

5. The method according to claim 2, characterized in that, Measuring the number of incident photons in the reference optical path at the target wavelength includes: A photomultiplier tube measures the number of incident photons in the reference optical path at the target wavelength; Measuring the number of incident photons in the main optical path at the target wavelength includes: The four-dimensional sample operation stage carries the metal sample to be tested and adjusts the spatial pose of the metal sample to be tested so that the main optical path is focused on the surface of the metal sample to be tested; A wide-bandgap semiconductor photodetector mounted on a movable support measures the number of incident photons in the main optical path at the target wavelength at the location of the four-dimensional sample operation stage.

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