Device and method for measuring diffusion length of photon-generated carrier of photocatalytic material based on KPFM

Abstract

The invention discloses a KPFM-based photocatalytic material photon-generated carrier diffusion length measuring device and method. The device sequentially comprises a coordinate sample table support, a double-layer diaphragm assembly, a micro-displacement platform, an optical fiber fixing plate and a base from top to bottom. The method comprises the following steps: driving an AFM probe to a test area, and measuring a first potential distribution diagram of the surface of a to-be-tested sample by using a KPFM under a non-illumination condition; turning on an optical fiber light source, applying illumination to the back of the to-be-detected sample through a double-layer diaphragm assembly, and synchronously recording a second potential distribution diagram of the surface of the to-be-detected sample under the illumination condition; and calculating the diffusion length of the photon-generated carrier according to the first potential distribution diagram and the second potential distribution diagram. By improving the light path design and introducing a double-diaphragm regulation and control and precise positioning system, the quantitative analysis of the carrier diffusion length under the backlight surface illumination condition is realized, and a reliable micro-scale characterization means is provided for the performance optimization of a nano photocatalytic material.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a device and method for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM. Background Art

[0002] Two-dimensional semiconductor materials have important applications in the fields of photocatalysis and new energy, and their performance is closely related to the separation and migration efficiency of photo-generated carriers. In the prior art, Kelvin probe force microscopy (KPFM), a surface photovoltage characterization method based on atomic force microscopy (AFM), has been widely used for the analysis of carrier behavior at the micro-nano scale because it can be tested in an in-situ environment close to the real working environment of the material. However, due to the structural problems of existing instruments, the light application method mostly uses side illumination, which has the following defects: 1) It is difficult to accurately control the illumination area, and the scattering and reflection of light result in a large deviation between the actual illumination area and the target area, affecting the accuracy of experimental data; 2) It is impossible to quantitatively measure the relationship between the illumination intensity and the carrier separation depth, making it difficult to guide the thickness optimization of photocatalytic materials; 3) Since light is applied from the side, the thickness and volume of the sample to be tested must be large enough to receive sufficient photons. However, the thickness value of two-dimensional semiconductor materials is in the nanometer scale, and it is obvious that sufficient photons cannot be obtained through side illumination. Therefore, side illumination is currently only used to characterize the qualitative aggregation of photo-responsive carriers of photocatalysts with micron-sized dimensions on micron-sized volumes, and it is impossible to obtain carrier behavior information at the sub-micron scale, making it difficult to meet the characterization requirements of nano-scale photocatalysts. Summary of the Invention

[0003] In order to solve at least one of the above-mentioned technical problems, the present invention provides a device and method for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM.

[0004] In a first aspect, the present invention provides a device for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM, and the device includes:

[0005] A coordinate sample stage holder, which is arranged on the top of the sample stage frame and is used to fix a coordinate copper mesh covered with a single layer of graphene and mark the position of the sample to be tested;

[0006] A double-layer aperture assembly, which is arranged below the coordinate sample stage holder and includes an upper aperture and a lower aperture, and is used to control the size and position of the light spot by adjusting the stagger of the double-layer aperture holes;

[0007] A micro-displacement platform, which is arranged on the lower surface of the lower aperture and is used to calibrate the position of the sample to be tested and the position of the light spot;

[0008] An optical fiber fixing plate is provided below the micro-displacement platform assembly and is used to fix one end of the optical fiber so that the direction of light is perpendicular to the plane where the aperture is located, thereby determining the irradiation area of the light spot on the sample after passing through the aperture hole;

[0009] A base is provided below the optical fiber fixing plate, and a common positioning system is integrated inside; the common positioning system is used for synchronous positioning between the scanning electron microscope and the atomic force microscope;

[0010] Among them, the coordinate sample stage holder, the micro-displacement platform assembly, the optical fiber fixing plate, and the base are sequentially connected by an aperture holder.

[0011] Preferably, the upper aperture is fixed on the aperture holder, and the lower aperture is provided on the micro-displacement platform.

[0012] Preferably, the lower aperture is moved within a two-dimensional plane through the micro-displacement platform, and the moving range is (-5, +5) mm, and the spot size adjustment range is (1, 100) μm.

[0013] Preferably, the coordinate copper mesh and the coordinate sample stage holder are fixed through a detachable card slot.

[0014] Preferably, the aperture holder can be lifted and lowered in the vertical direction to adapt to the needs of focusing on samples with different thicknesses and different sizes of light spots.

[0015] Preferably, the common positioning system includes a coordinate marking module and an image synchronization module;

[0016] The coordinate marking module is used to ensure the unity of the coordinate reference of the SEM and the AFM;

[0017] The image synchronization module is used to collect SEM images and AFM images, and align the SEM images and AFM images at the pixel level through a feature matching algorithm.

[0018] In a second aspect, the present invention provides a method for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM, which is applied to the device for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM according to any one of the first aspects. The method includes:

[0019] Disperse the sample to be measured on the surface of the coordinate copper mesh, obtain an SEM image through the SEM, and record the marking coordinates of the target test area relative to the positioning marking points in the common positioning system;

[0020] Adjust the double-layer aperture assembly according to the marking coordinates, change the staggered area of the double-layer aperture holes to match the size of the target test area; synchronously adjust the micro-displacement platform assembly to horizontally move the coordinate sample stage holder to pre-align the light spot with the target test area;

[0021] Pixel - level alignment of the SEM image and the optical image of the target test area is performed through a shared positioning system, and the position of the light spot is finely adjusted through the micro - displacement platform component until the coincidence error between the light spot and the target test area is within the preset error.

[0022] Drive the AFM probe to the target test area, and measure the first potential distribution map of the surface of the sample to be measured using KPFM under the condition of no light; turn on the fiber - optic light source, apply a preset light intensity to the back of the sample to be measured through the double - layer diaphragm component, and synchronously record the second potential distribution map of the surface of the sample to be measured under the illumination condition; wherein, the test ranges of the first potential distribution map and the second potential distribution map are the same, and both are larger than the area irradiated by the light spot.

[0023] Calculate the diffusion length of photo - generated carriers according to the first potential distribution map and the second potential distribution map.

[0024] Preferably, calculating the diffusion length of photo - generated carriers according to the first potential distribution map and the second potential distribution map includes:

[0025] Perform matrix subtraction on the second potential distribution map and the first potential distribution map to obtain a third potential distribution map.

[0026] Perform binarization processing on the third potential distribution map to determine the background area and the annular area different from the background area.

[0027] Calculate the maximum width and the average width between the background area and the annular area; take the maximum width as the maximum diffusion distance of carriers, and take the average width as the average diffusion distance of carriers.

[0028] Preferably, after obtaining the third potential distribution map, it further includes:

[0029] Identify the potential values of the area corresponding to the sample in the third potential distribution map, and judge the type of carriers generated during the photocatalyst light response according to the positive or negative of the potential values, including:

[0030] When the potential value is positive, determine that the carrier type is a hole.

[0031] When the potential value is negative, determine that the carrier type is an electron.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention adds a method of applying light from the bottom surface and performing tests from the front surface. By designing a special sample clamping device, the regulation of the spot size and position is achieved. The surface photovoltage and current of micro-nano photocatalysts with specific compositions and thicknesses before and after illumination are studied using the shared sample positioning system of a scanning electron microscope - atomic force microscope. By controlling and monitoring the corresponding relationship between the test area and the spot illumination area in terms of position, the diffusion direction and distance of carriers in the photocatalyst under backside illumination conditions are quantitatively studied. In addition, this method can also determine the maximum depth at which a certain intensity of illumination can excite the effective separation of carriers by measuring the change in surface potential on the backside of thin-film photocatalysts with different thicknesses, thereby providing theoretical guidance for setting the coating thickness and illumination intensity of the photocatalyst. Through the improvement of the optical path design, the introduction of double aperture regulation, and the precise positioning system, the present invention realizes the quantitative analysis of the carrier diffusion length under backside illumination conditions, providing a reliable microscopic scale characterization means for optimizing the performance of nano-photocatalytic materials.

[0034] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the background art, the following will describe the drawings required to be used in the embodiments of the present invention or in the background art.

[0036] The drawings herein are incorporated into the specification and form a part of this specification. These drawings illustrate embodiments consistent with the present disclosure and, together with the specification, are used to explain the technical solutions of the present disclosure.

[0037] Figure 1 FIG. is a schematic structural diagram of a device for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM provided by an embodiment of the present invention;

[0038] Figure 2 FIG. is a schematic flowchart of a method for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM provided by an embodiment of the present invention;

[0039] Figure 3 For Figure 2 FIG. is a schematic flowchart of the sub-steps of step S50 in

[0040] Figure 4 FIG. is a schematic principle diagram of obtaining a potential distribution map provided by an embodiment of the present invention;

[0041] Figure 5 FIG. is a schematic principle diagram of subtracting the potential distribution maps provided by an embodiment of the present invention;

[0042] Figure 6Schematic diagram of the relationship between diffusion length and light intensity provided by the embodiments of the present invention. Detailed implementation manners

[0043] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0044] The terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0045] Referring to "embodiments" herein means that specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present invention. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0046] Photocatalytic and photovoltaic materials have important applications in the fields of environmental protection and new energy development. Their reaction processes involve steps such as light absorption, separation of photo-generated carriers, migration of carriers, and reactions on the interface. Since the separation and migration of carriers occur at the micro-nano scale, in order to better study the reaction mechanism, it is necessary to explore the separation and transport processes of photo-generated carriers in such materials at the nano level. Based on the surface photovoltage characterization technology of AFM, the change in the spatial distribution of the surface photovoltage of the material before and after illumination can be intuitively characterized at the micro-nano scale in a quasi-in-situ state, and it has gradually become a common means for characterizing photocatalysts. Its basic principle is to use the distribution of the surface potential values of individual catalyst nanoparticles before and after illumination to infer the regions where charges and holes are enriched, and to evaluate the distribution density of carriers according to the magnitude of the potential difference in different regions. This method provides an idea for solving the problem of characterizing the separation of photo-generated carriers on micro-nano scale catalysts.

[0047] At present, almost all the light application methods of the AFM-based carrier spatial distribution characterization method apply light from the side or obliquely above. This method can characterize the carrier behavior on the illuminated surface of the photocatalyst. However, due to light scattering and reflection in the experiment, the actual illumination area cannot be effectively controlled, and the potential and carrier behavior on the backlight side during illumination cannot be studied. Therefore, the present invention mainly adopts the method of applying light from the bottom surface and performing tests on the front surface. By designing a special sample clamping device, the spot size and position are regulated. The surface photovoltage and current of the micro-nano photocatalyst with a specific composition and thickness are studied before and after illumination by using the common sample positioning system of a scanning electron microscope - atomic force microscope. By controlling and monitoring the corresponding relationship between the test area and the spot illumination area in terms of position, the diffusion direction and distance of carriers in the photocatalyst under backlight illumination conditions are quantitatively studied.

[0048] In addition, this method can also determine the maximum depth at which a certain intensity of light can excite effective carrier separation by measuring the change in the surface potential on the back of the thin-layer photocatalyst with different thicknesses, thereby providing theoretical guidance for setting the coating thickness and light intensity of the photocatalyst. In previous photocatalysis research, the measurement of physical quantities such as carrier separation distance and potential difference caused by carrier separation was either based on macroscopic measurements or theoretical calculations. With the nanosizing of the photocatalyst size, these measurement methods can no longer provide effective characterization for nano-photocatalysts. Therefore, the present invention provides a method for measuring the diffusion length of carriers excited by light in nano-photocatalysts at the microscale. By improving the optical path design, introducing double-aperture regulation, and a precise positioning system, quantitative analysis of the carrier diffusion length under backlight illumination conditions is achieved, providing a reliable microscale characterization means for optimizing the performance of nano-photocatalytic materials.

[0049] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of a device for measuring the diffusion length of photo-generated carriers in a photocatalytic material based on KPFM provided by an embodiment of the present invention. As Figure 1 shown, the device includes:

[0050] A coordinate sample stage support 20, which is arranged on the top of the sample stage frame and is used to fix the coordinate copper mesh covered with graphene. The common positioning system is constructed by using the marking points on the coordinate copper mesh, and this system is used to mark the position of the sample to be measured 10;

[0051] A double-aperture assembly 40, which is arranged below the coordinate sample stage support 20 and includes an upper aperture 401 and a lower aperture 402, and is used to regulate the spot size and position by adjusting the stagger of the double-aperture holes;

[0052] The micro-displacement platform 50 is disposed on the lower surface of the lower diaphragm 402 and is used to calibrate the position of the sample 10 to be measured and the position of the light spot.

[0053] The optical fiber fixing plate 70 is disposed below the micro-displacement platform 50 assembly and is used to fix one end of the optical fiber 90 so that the direction of light is perpendicular to the plane where the diaphragm is located, thereby determining the irradiation area of the light spot on the sample 10 after passing through the diaphragm hole.

[0054] The base 80 is disposed below the optical fiber fixing plate 70.

[0055] Wherein, the coordinate sample stage holder 20, the micro-displacement platform 50 assembly, the optical fiber fixing plate 70 and the base 80 are sequentially connected by the diaphragm holder 30.

[0056] In this embodiment, the coordinate sample stage holder 20 selects a graphene-coated copper grid as the sample stage 10. During actual experiments, first observe in the SEM to confirm the position of the target to be tested on the copper grid of the coordinate sample stage holder 20, that is, the coordinate value relative to the marking point, so that the position to be tested can be quickly found after being transferred to the AFM.

[0057] In the diaphragm hole size and position adjusting device, usually a double-layer diaphragm is adopted. The upper diaphragm 401 and the lower diaphragm 402 can move relative to each other, and the size of the light spot is adjusted by adjusting the overlapping area of the two diaphragm holes. The lower diaphragm 402 is fixed on the micro-displacement platform 50 and can move with the micro-displacement platform instrument, thereby realizing the adjustment of the irradiation area of the light spot.

[0058] Preferably, the device uses the optical fiber 90 to provide the light source. The optical fiber 90 fixing bracket is used to fix the end of the optical fiber 90 and make the direction of light perpendicular to the plane where the diaphragm is located, so as to correctly evaluate the irradiation area of the light spot on the sample 10 after passing through the diaphragm hole.

[0059] The micro-displacement platform 50 is usually disposed on the lower surface of the lower diaphragm 402 and is used to calibrate the position of the sample 10 to be measured and the position of the light spot.

[0060] In one embodiment, the copper grid is fixed to the coordinate sample stage holder 20 through a detachable card slot.

[0061] A groove or convex structure matching the shape of the coordinate copper mesh is provided at the surface edge or specific position of the coordinate sample stage holder 20 to form a detachable card slot. For example, U-shaped grooves adapted to the thickness of the coordinate copper mesh are machined at the four peripheral edges of the sample stage 10, or a fixed frame with elastic buckles is designed in the central area of the sample stage 10. During installation, the coordinate copper mesh is aligned with the card slot of the coordinate sample stage holder 20, and gently pressed or pushed in so that the convex part of the copper mesh fits perfectly with the groove of the card slot. Some designs can use elastic buckles, which are locked into the card slot by pressing the edge of the copper mesh to ensure firm fixation. During disassembly, a reverse force can be applied to make the convex part of the copper mesh disengage from the card slot, and then the copper mesh can be removed from the coordinate sample stage holder 20. For the elastic buckle design, quick disassembly can be achieved by releasing the locked state of the buckle. Since the matching dimensions of the card slot and the copper mesh are precisely machined, it is ensured that the copper mesh is flush with the surface of the coordinate sample stage holder 20 after installation, and the position repeatability error is less than the micron level, avoiding the influence of copper mesh tilt or displacement on subsequent spot positioning and measurement results.

[0062] In one embodiment, the upper aperture stop 401 is disposed on the lower aperture stop 402, and 401 and 402 can move relative to each other, and the lower aperture stop 402 is fixed on the micro-displacement platform 50.

[0063] The aperture stop holder 30 is a vertical support structure, and a fixed card slot or threaded hole matching the size of the micro-displacement platform 50 is provided at its bottom. For example, an annular groove is machined at the bottom of the aperture stop holder 30, and the edge of the micro-displacement platform 50 is fixed in the groove by screws or buckles. The micro-displacement platform 50 can achieve high-precision displacement in two dimensions (X-Y directions). By controlling the movement of the micro-displacement platform 50, the position of the lower aperture stop 402 can be moved, thereby adjusting the position of the spot irradiating the sample 10 on the coordinate copper mesh. By translating or rotating the upper aperture stop 401, the degree of intersection of the two aperture stop holes is changed to achieve the adjustment of the spot size and position.

[0064] Preferably, the lower aperture stop 402 is moved within a two-dimensional plane by the micro-displacement platform 50, and the movement range is (-5, +5) mm, and the spot size adjustment range is (1, 100) μm.

[0065] In one embodiment, the common positioning system includes a coordinate marking module and an image synchronization module;

[0066] The coordinate marking module is used to ensure the unity of the coordinate reference of the SEM and the AFM;

[0067] The image synchronization module is used to collect SEM images and AFM images, and align the SEM images and AFM images at the pixel level through a feature matching algorithm.

[0068] The coordinate marking module is used to process high-precision coordinate marks on the surface of the coordinate copper mesh. For example, micron-scale crosshairs, circular or square marks are etched at the grid intersections of the copper mesh. During SEM observation, an SEM image containing the coordinate marks is obtained by electron beam scanning, and the coordinate positions of the marks are recorded based on the SEM coordinate system. During AFM measurement, an AFM image of the same area is obtained by probe scanning, and the positions of the coordinate marks are synchronously recorded based on the AFM coordinate system. The conversion relationship between the two coordinate systems, such as translation, rotation, and scaling parameters, is calculated through software algorithms to achieve the unification of the SEM and AFM coordinate references.

[0069] In the image synchronization module, a high-resolution topography image of sample 10 is collected using SEM, and at the same time, a surface potential or topography image of the same area is collected using AFM. The SEM image and the AFM image are preprocessed, such as noise reduction and contrast enhancement, to improve the accuracy of feature matching. Then, a feature detection algorithm is further used to extract key points in the images, and corresponding feature point pairs in the two images are found through a descriptor matching algorithm. The random sample consensus algorithm is used to remove mismatched points, and the transformation matrix between the images is calculated. Finally, the AFM image is geometrically corrected based on the transformation matrix to be precisely aligned with the SEM image at the pixel level.

[0070] The coordinate marking module ensures the positioning accuracy of the SEM image and the AFM image at the nanometer to micron scale through physical marking and coordinate system transformation, avoiding the deviation of the observation area caused by the difference in the device coordinate system. The image synchronization module realizes the pixel-level alignment of the SEM image and the AFM image, and can directly correlate the microstructure and electrical properties of the material.

[0071] Therefore, the device provided in this embodiment realizes spatial positioning with micron-level to nanometer-level accuracy through the combination of high-resolution SEM imaging and the coordinate copper mesh; the double-layer aperture assembly can flexibly adjust the spot size and position through the staggered design of the two layers of aperture holes, meeting the measurement requirements of photocatalytic materials from the nanometer scale to the micron scale, and improving the pertinence and accuracy of the experiment. The high-precision displacement ability of the micro-displacement platform ensures the precise alignment of the spot and the sample, effectively overcoming the problem of misalignment between the spot and the test area in the traditional method. The deployment of the common positioning system realizes the synchronous positioning of the SEM image and the AFM image, enabling morphological observation and electrical property measurement in the same microscopic area, avoiding the deviation of secondary sample positioning, and improving the data correlation. The optical fiber fixing plate ensures that the light beam 60 is incident perpendicular to the aperture plane, making the spot evenly irradiate the sample surface, reducing the light intensity attenuation or spot distortion caused by the optical path tilt, and improving the uniformity of photo-generated carrier excitation. Each component is vertically integrated through the aperture holder, with a compact structure, reducing the complexity of optical path calibration.

[0072] See Figure 2, based on the measuring device provided in the above embodiments, in one embodiment, a method for measuring the diffusion length of photo-generated carriers of a photocatalytic material based on KPFM is further provided. As Figure 2 shown, the method includes the following steps:

[0073] Step S10: Disperse the sample to be measured on the surface of the coordinate copper mesh, obtain an SEM image through SEM, and record the marking coordinates of the target test area relative to the positioning mark points in the common positioning system;

[0074] Step S20: Adjust the double-layer aperture assembly according to the marking coordinates, change the staggered area of the double-layer aperture holes to match the size of the target test area; synchronously adjust the micro-displacement platform assembly to laterally move the coordinate sample stage support 20 to pre-align the light spot with the target test area;

[0075] Step S30: Align the SEM image with the optical image of the target test area at the pixel level through the common positioning system, and fine-tune the position of the light spot through the micro-displacement platform assembly until the coincidence error between the light spot and the target test area is within the preset error;

[0076] Step S40: Drive the AFM probe to the target test area, use KPFM to measure the first potential distribution map on the surface of the sample to be measured under the condition of no light; turn on the fiber optic light source, apply a preset light intensity to the back of the sample to be measured through the double-layer aperture assembly, and synchronously record the second potential distribution map on the surface of the sample to be measured under the illumination condition; wherein, the test ranges of the first potential distribution map and the second potential distribution map are the same, and both are larger than the area irradiated by the light spot;

[0077] Step S50: Calculate the diffusion length of photo-generated carriers according to the first potential distribution map and the second potential distribution map.

[0078] In this embodiment, first, the target test area is located by SEM and the coordinates are recorded, and then the double-layer aperture and the micro-displacement platform are adjusted to initially align the light spot with the target area; then, the SEM image is aligned with the optical image at the pixel level by using the common positioning system, and the position of the light spot is further fine-tuned to a high-precision coincidence; then, under the conditions of no light and preset light intensity, the surface potential distribution of the sample is measured by KPFM respectively, ensuring that the two measurement ranges are the same and cover the light spot area; finally, the diffusion length of photo-generated carriers is calculated based on the two potential data, realizing the full process automation and precision from positioning, alignment to electrical property measurement.

[0079] In a specific embodiment, in order to measure the carrier diffusion length, the operation steps are as follows:

[0080] 1) First, fish out two-dimensional large-area graphene on the coordinate copper mesh;

[0081] 2) Disperse the sample to be tested in a suitable medium, configure it into a suitable concentration, then drop it on a coordinate copper mesh, and air-dry it under an infrared lamp or naturally to make the sample to be tested. Observe the sample in the SEM and record the coordinate values of the target position or the positional relationship between the target position and the marking point;

[0082] 3) Place the coordinate sample stage holder carrying the sample onto the coordinate sample stage holder and fix it with the corresponding card slot. Remove the optical fiber fixing frame part of the device and place it upside down under the SEM or optical microscope for observation. Confirm the irradiation area of the light spot on the coordinate sample stage holder and record the positional relationship between this area and the marking point on the coordinate sample stage holder. Take the device out of the SEM or optical microscope.

[0083] 4) Adjust the aperture and the micro-displacement platform connected to it according to the size of the target to be tested to obtain a light spot with a suitable size; according to the positional relationship between the target to be tested and the marking point, and the positional relationship between the marking point and the light spot, adjust the micro-displacement platform connected to the sample stage holder so that the target area to be tested is completely within the irradiation of the light spot. This step requires, after adjusting the two micro-displacement platforms respectively, removing the optical fiber fixing frame of the device and placing it upside down in the SEM for confirmation. The content to be confirmed includes the size and position of the light spot and the morphology of the sample to be tested after passing through the graphene film.

[0084] 5) After determining the above positional relationship, install the optical fiber fixing frame of the device and fix the optical fiber on it. According to the existing positioning method, find the target area to be tested in the AFM. First, perform the test under the condition of no light illumination, record the test result to obtain the first potential distribution map; then apply light illumination, record the test result to obtain the second potential distribution map, and finally calculate the diffusion length of photo-generated carriers according to the first potential distribution map and the second potential distribution map.

[0085] See Figure 3 , in one embodiment, calculating the diffusion length of photo-generated carriers according to the first potential distribution map and the second potential distribution map includes:

[0086] Step S501: Perform matrix subtraction on the second potential distribution map and the first potential distribution map to obtain a third potential distribution map;

[0087] Step S502: Perform binarization processing on the third potential distribution map to determine the background area and the annular area different from the background area;

[0088] Step S503: Calculate the maximum width and average width between the annular areas; take the maximum width as the maximum diffusion distance of the carriers and the average width as the average diffusion distance of the carriers.

[0089] First, explain the test principle in this embodiment. See Figure 4, Figure 4 Figure (a) in Figure 4 provides a schematic diagram of the illumination range during testing. By scanning on the graphene substrate, a first potential distribution map and a second potential distribution map can be obtained, as shown in Figure 4 Figure (b). Using the MATLAB tool to calculate the average distance and the maximum distance between two closed figures, which are denoted as the average diffusion length and the maximum diffusion length respectively. The maximum diffusion length is determined by the longest width between two regions, as shown in

[0090] Figure (c). The average diffusion distance is calculated based on the area and the average perimeter, including first calculating the area A between two curves, which can be calculated using Green's theorem or the pixel counting method; then calculating the average perimeter L of the two curves, that is, the sum of the perimeters of the inner curve and the outer curve divided by 2; finally, the average distance, i.e., the average diffusion length = A / L.

[0091] ;

[0092] wherein, is the point coordinate on the curve , is the infinitesimal change on the curve.

[0093] During the calculation, first parameterize the curve. If the curve is represented by the parametric equations , , then:

[0094] ;

[0095] wherein, the parametric equations , represent the function of the coordinates of the points on the curve changing with the parameter , are the lower and upper limits of integration, , are the derivatives, is the area of the closed region enclosed by the curve.

[0096] If the curve is composed of discrete points , such as polygon approximation, then the shoelace formula can be used to calculate :

[0097] ;

[0098] wherein, the discrete points In , it represents the vertices of a polygon; is the total number of discrete points.

[0099] If it is applied to the area between two curves, then:

[0100] Calculate the area enclosed by the outer curve and the inner curve enclosed area , and the area between the two curves is : .

[0101] In one embodiment, when calculating the area using the pixel counting method, the process is as follows:

[0102] First step, binarize the image first, convert the image into a black and white binary image, the curve area is black, and the pixel value is 1; the background is white, and the pixel value is 0;

[0103] Second step, count the pixels: For a single curve, the area is equal to the total number of white pixels multiplied by the actual area of a single pixel. For the area between two curves, the outer curve and the inner curve The pixel area between them can be extracted through morphological operations, and then the number of white pixels in this area is counted and multiplied by the area of a single pixel to obtain the final area.

[0104] In one embodiment, after obtaining the third potential distribution map, it further includes:

[0105] Identify the potential values of the regions corresponding to the samples in the third potential distribution map, and judge the types of carriers generated during the photocatalyst photo-response process according to the positive and negative of the potential values, including:

[0106] When the potential value is positive, it is determined that the carrier type is a hole;

[0107] When the potential value is negative, it is determined that the carrier type is an electron.

[0108] See Figure 5 , Figure 5The principle of performing matrix subtraction on the first potential distribution map and the second potential distribution map is provided. In this figure, a new potential distribution map, i.e., the third potential distribution map, is obtained through subtraction. In the third potential distribution map, all potential values are negative, indicating that the surface potential of the catalyst decreases after illumination and electrons accumulate on the surface, that is, the carrier type is electrons. On the contrary, if the potential value is positive, it means that the carrier type is holes. The outermost circle of the bright area in the third potential map is a darker ring. By binarizing the picture, the ring area is highlighted, and its maximum width and average width are calculated, corresponding to the maximum diffusion length of 1190 nm and the average diffusion length of 702 nm respectively.

[0109] In one embodiment, in order to further improve the accuracy of the measurement results, multiple light illumination condition experiments can be set up, and then multiple groups of second potential distribution maps can be obtained. Eventually, the average value of the calculated multiple groups of diffusion lengths can be taken to reduce the error of a single test. Among them, Figure 6 The variation law of the light intensity and the diffusion length is provided, as Figure 6 shown. As the light intensity increases, the diffusion length first increases, then stabilizes at a certain level and then slowly decreases. Therefore, when determining the light intensity of the light illumination test, the minimum light intensity when the diffusion length increases to the maximum value is used as the standard intensity value for measuring the diffusion length.

[0110] In summary, the method provided in this embodiment realizes the nano-precise synchronous positioning of SEM morphology observation and AFM electrical measurement through sharing a positioning system and SEM image marking, avoiding the target area deviation caused by the difference in the device coordinate system in the traditional method, ensuring multimodal analysis in the same microscopic area, and enhancing the data correlation. Under the conditions of no light illumination and a preset light intensity, potential distribution maps covering the same area are obtained through KPFM, and the range is larger than the spot illumination area, ensuring that the comparative analysis of potential changes is not affected by the spot edge effect. The backlight illumination design can reduce the interference of light scattering and improve the uniformity and stability of light intensity application. Based on the highly accurate aligned spot and potential data, combined with the analysis of the potential difference before and after illumination, the diffusion range of photo-generated carriers can be determined more accurately. The standardized measurement process and multimodal data fusion enhance the repeatability and scientific reliability of the experimental results. Therefore, this method realizes the quantitative analysis of the carrier diffusion length under the backlight illumination condition by improving the optical path design, introducing double aperture regulation, and a precise positioning system, providing a reliable microscopic scale characterization means for the performance optimization of nano-photocatalytic materials.

[0111] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professionals can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present invention.

Claims

1. A KPFM-based device for measuring the diffusion length of photogenerated carriers in photocatalytic materials, characterized in that: The device comprises: The coordinate sample support is located on the top of the sample stand and is used to fix the graphene-covered coordinate copper mesh and mark the position of the sample to be tested; A double-layer aperture assembly is provided below the coordinate sample stage support, comprising an upper aperture and a lower aperture, and is used to adjust the size and position of the light spot by adjusting the staggered double-layer aperture holes; A micro-displacement platform is provided on the lower surface of the lower aperture and is used to calibrate the position of the sample to be measured and the position of the light spot; An optical fiber fixing plate is provided below the micro-displacement platform assembly and is used to fix one end of the optical fiber so that the direction of the light is perpendicular to the plane where the aperture is located, so as to determine the irradiation area on the sample after the light spot passes through the aperture hole; A base, arranged below the optical fiber fixing plate, with a common positioning system integrated therein; the common positioning system is used for synchronous positioning between the scanning electron microscope and the atomic force microscope; Wherein, the coordinate sample stage support, the micro-displacement platform assembly, the optical fiber fixing plate and the base are sequentially connected through an aperture frame.

2. The device for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 1, characterized in that: The upper aperture is fixed on the aperture frame, and the lower aperture is arranged on the micro-displacement platform.

3. The device for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 2, characterized in that: The lower aperture is moved in a two-dimensional plane through the micro-displacement platform, the moving range is (-5, +5) mm, and the spot size adjustment range is (1, 100) μm.

4. The device for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 1, characterized in that: The coordinate copper mesh and the coordinate sample support are fixed via a detachable card slot.

5. The device for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 1, characterized in that: The aperture frame can be raised and lowered in the vertical direction to adapt to the focusing requirements of samples to be tested of different thicknesses and light spots of different sizes.

6. The device for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 1, characterized in that: The common positioning system includes a coordinate marking module and an image synchronization module; The coordinate marking module is used to ensure that the coordinate references of SEM and AFM are unified; The image synchronization module is used to collect SEM images and AFM images, and align the SEM images and AFM images at the pixel level through a feature matching algorithm.

7. A method for measuring the diffusion length of photogenerated carriers of a photocatalytic material based on KPFM, applied to the device for measuring the diffusion length of photogenerated carriers of a photocatalytic material based on KPFM as claimed in any one of claims 1 to 6, characterized in that: The method comprises: The sample to be tested is dispersed on the surface of the coordinate copper mesh, and the SEM image is obtained by SEM, and the marking coordinates of the target test area relative to the positioning marking point in the common positioning system are recorded; The double-layer aperture assembly is adjusted according to the marked coordinates to change the staggered area of ​​the double-layer aperture holes to match the size of the target test area; the micro-displacement platform assembly is synchronously adjusted to laterally move the coordinate sample stage support to pre-align the light spot with the target test area; The SEM image is aligned with the optical image of the target test area at the pixel level through a common positioning system, and the position of the light spot is fine-tuned through a micro-displacement platform assembly until the coincidence error between the light spot and the target test area is within a preset error. Drive the AFM probe to the target test area, and use KPFM to measure the first potential distribution map on the surface of the sample to be tested under no light conditions; turn on the fiber optic light source, apply a preset light intensity to the back of the sample to be tested through the double-layer aperture assembly, and simultaneously record the second potential distribution map on the surface of the sample to be tested under light conditions; wherein the test ranges of the first potential distribution map and the second potential distribution map are consistent, and both are larger than the area illuminated by the light spot; The photogenerated carrier diffusion length is calculated according to the first potential distribution diagram and the second potential distribution diagram.

8. The method for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 7, characterized in that: The calculating the photogenerated carrier diffusion length according to the first potential distribution diagram and the second potential distribution diagram comprises: Performing matrix subtraction on the second potential distribution map and the first potential distribution map to obtain a third potential distribution map; Binarization is performed on the third potential distribution map to determine a background area and a ring area different from the background area; The maximum width and average width between the background area and the annular area are calculated; the maximum width is taken as the maximum diffusion distance of the carriers, and the average width is taken as the average diffusion distance of the carriers.

9. The method for measuring the diffusion length of photogenerated carriers of photocatalytic materials based on KPFM according to claim 8, characterized in that: After obtaining the third potential distribution diagram, the method further includes: Identify the potential value of the area corresponding to the sample in the third potential distribution diagram, and determine the type of carriers generated in the photocatalyst light response process according to the positive and negative potential values, including: When the potential value is positive, the carrier type is determined to be a hole; When the potential value is negative, the carrier type is determined to be electron.

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