A method for determining the maximum uniform imaging range of a cathode fluorescence detector

Abstract

This invention belongs to the field of scanning electron microscopy and cathodoluminescence analysis technology, specifically relating to a method for determining the maximum uniform imaging range of a cathodoluminescence detector. This method is simple to operate and provides objective results in determining the maximum uniform imaging range of a cathodoluminescence detector. By calculating the standard deviation of image grayscale, this invention transforms the assessment of imaging uniformity from subjective judgment to objective data. The assessment results are accurate and reproducible, providing clear sample selection criteria, test locations, and data processing procedures. It is easy to promote and apply in laboratories. By determining the maximum uniform imaging range, it guides users to conduct large-field observations while ensuring image quality, effectively reducing analytical errors caused by imaging non-uniformity.

Description

Technical Field

[0001] This invention belongs to the field of scanning electron microscopy and cathodoluminescence analysis technology, and specifically relates to a method for determining the maximum uniform imaging range of a cathodoluminescence detector. Background Technology

[0002] Cathodoluminescence (CL) is a crucial analytical function in scanning electron microscopy (SEM). It obtains information about the microstructure, composition, and defects of materials by detecting the fluorescence signal generated when an electron beam excites a sample. This technology is widely used in semiconductors, geology and mineralogy, biomaterials, and nanophotonics. Imaging uniformity is a key indicator of CL detector performance. Non-uniform images cause variations in brightness and contrast within the field of view, affecting the accuracy and reliability of the analysis. Current techniques for assessing CL imaging uniformity largely rely on operator visual observation or subjective comparison with standard images. These methods have the following significant drawbacks: they depend on personal experience and cannot provide objective, quantifiable evaluation results; they are difficult to precisely define at which field of view (FOV) or magnification (Mag) the image can maintain acceptable uniformity; and visual methods are insufficient for systematically testing different parameter combinations and for quickly determining optimal imaging conditions.

[0003] Therefore, there is an urgent need in this field for an objective, quantitative, and standardized method to accurately determine the maximum uniform imaging range of a cathodoluminescence detector. Summary of the Invention

[0004] In view of this, the present invention provides a method for determining the maximum uniform imaging range of a cathodoluminescence detector, which is simple to operate and provides objective results in determining the maximum uniform imaging range of the cathodoluminescence detector.

[0005] To achieve the objectives of this invention, the following technical solutions are provided.

[0006] A method for determining the maximum uniform imaging range of a cathodoluminescence detector includes the following steps: Sample and parameter preparation: Select samples with stable and bright cathodoluminescence signals, and set and fix the key operating parameters of the scanning electron microscope and cathodoluminescence detector; Multi-location image acquisition: The sample is placed sequentially at multiple specific locations within the cathodoluminescence imaging field of view, and a cathodoluminescence image is acquired at each location under different field of view ranges or magnifications; Image data processing: Calculate the average gray value of each acquired cathodoluminescence image. For multiple images obtained under the same field of view or magnification, calculate the standard deviation of their corresponding average gray values. Uniformity determination and range determination: The calculated standard deviation is compared with a preset threshold. When the standard deviation is less than or equal to the preset threshold, the current field of view is determined to be a uniform imaging range. By testing a series of different field of view ranges, the maximum field of view range that can meet the uniformity condition is determined, which is the maximum uniform imaging range of the cathode fluorescence detector.

[0007] The key operating parameters include the accelerating voltage, beam current, and working distance of the scanning electron microscope, as well as the gain and contrast parameters of the cathode fluorescence detector.

[0008] The multiple specific locations include five locations: the center of the field of view, the upper left corner, the lower left corner, the upper right corner, and the lower right corner.

[0009] The preset threshold is set based on the visual limit of the human eye to grayscale differences, and the preset threshold is 5.

[0010] The sample in question is zircon.

[0011] Beneficial effects 1. This invention establishes a complete and quantifiable testing process through standardized sample preparation, systematic acquisition of images from multiple fixed locations under multi-field-of-view conditions, calculation of the standard deviation of image grayscale data, and comparison with objective thresholds. This method transforms the assessment of imaging uniformity from traditional reliance on subjective visual judgment by operators to scientific calculation based on objective image data, fundamentally eliminating inconsistencies caused by human factors. The assessment results are accurate, quantifiable, and reproducible, making performance evaluations conducted at different times, by different operators, or on different devices comparable. This method provides clear judgment criteria, accurately defining the maximum field of view achievable by the detector while maintaining acceptable uniformity. This scientifically guides users to conduct large-field-of-view observations while ensuring image quality, effectively avoiding problems such as image edge signal attenuation and brightness unevenness caused by blindly using large fields of view, and significantly improving the reliability and accuracy of cathodoluminescence analysis data.

[0012] 2. This invention clarifies the need to fix the core imaging parameters of the scanning electron microscope and detector during the testing process. By fixing the accelerating voltage, beam current, working distance, gain, and contrast, it ensures that the excitation and signal acquisition conditions remain constant throughout the entire testing sequence. This specification eliminates signal intensity variations introduced by parameter fluctuations, ensuring that the final calculated standard deviation variation uniquely reflects the uniformity difference of signal acquisition at a fixed position by the detector under different fields of view, rather than being caused by other interference factors. This guarantees the purity and reliability of the test results, enabling the determined maximum uniform imaging range to truly and accurately reflect the performance limits of the detector itself.

[0013] 3. This invention specifies the use of five representative locations—the center of the field of view and the four corners—for image acquisition. These five points systematically cover the core and edge regions of the imaging field of view, enabling comprehensive detection of signal distribution across the entire field of view. Compared to randomly selecting locations or testing only the center point, this five-point sampling strategy is more scientific and comprehensive, effectively capturing signal non-uniformity that may occur at the edges of the field of view. It ensures the spatial representativeness of the uniformity assessment, avoids misjudgments caused by unrepresentative sampling locations, and makes the final determination of the maximum uniform imaging range more rigorous and reliable. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram illustrating the trend of standard deviation of five points in a zircon CL image as a function of FOV in an embodiment of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] This invention provides a method for determining the maximum uniform imaging range of a cathode fluorescence detector, the process of which is as follows: Figure 1 As shown, it includes the following steps: S1. Sample and Parameter Preparation: Select a sample with stable and bright cathodoluminescence signal under electron beam bombardment, such as zircon; set and fix the accelerating voltage, landing current, working distance, resolution, and CL detector gain and contrast parameters of the scanning electron microscope (lower accelerating voltage and landing current result in weaker CL signal intensity, but excessively high accelerating voltage and landing current will affect image resolution and damage the sample; the working distance needs to be set according to the optimal distance of the CL detector, as the amount of CL signal received by the CL detector varies at different working distances; the gain and contrast of the CL detector need to be set according to the actual image, as lower gain and contrast parameters result in dark images with blurred details, which is not conducive to subsequent analysis, while excessively high gain and contrast parameters will increase image noise and reduce image quality) to ensure the stability of the signal source throughout the test. S2. Multi-Position Image Acquisition: Place the sample sequentially at five specific positions within the CL imaging field of view: the center of the field of view, the upper left corner, the lower left corner, the upper right corner, and the lower right corner. Acquire one CL image at each position at different field of view ranges or magnifications. S3. Image Data Processing: Process all CL images acquired in step S2 using image analysis software (such as ImageJ), and calculate the average gray value of each image. For five images obtained under the same field of view or magnification, calculate the standard deviation of their five average gray values. S4. Uniformity Determination and Range Determination: Compare the standard deviation calculated in step S3 with a preset threshold; when the standard deviation is less than or equal to the preset threshold, the current field of view is determined to be a uniform imaging range; by testing a series of different field of view ranges, the maximum field of view range that satisfies the uniformity condition is finally determined, which is the maximum uniform imaging range of the cathode fluorescence detector.

[0018] This invention transforms the assessment of imaging uniformity from subjective judgment to objective data by calculating the standard deviation of image grayscale, resulting in accurate and reproducible assessment results. It provides clear sample selection criteria, test locations, and data processing procedures, making it easy to promote and apply in laboratories. By determining the maximum uniform imaging range, it guides users to conduct large-field observations while ensuring image quality, effectively reducing analytical errors caused by imaging non-uniformity. This method is not dependent on specific equipment or samples and can be widely applied to various scanning electron microscope systems equipped with CL detectors, providing guidance for the study of different materials.

[0019] Preferably, the preset threshold is set based on the "visual limit of the human eye to grayscale differences" (Weber-Fechner law), and is preferably 5. The specific scientific setting of the threshold provides a clear, unified, and scientifically based quantitative standard for uniformity determination. The threshold, based on the visual characteristics of the human eye described by the Weber-Fechner law, ensures that the judgment standard conforms to the limits of human visual perception; that is, when the standard deviation of grayscale differences does not exceed this threshold, the human eye can hardly perceive obvious non-uniformity, thus having significance in engineering practice. Specifying the threshold as a value of 5 provides a clear and unambiguous operational benchmark, allowing different users to make judgments based on the same standard, greatly enhancing the consistency and generalizability of the method. This threshold is a verified effective value, capable of reasonably balancing the observation field of view and uniformity requirements while ensuring image visual quality.

[0020] Zircon is recommended as the standard test sample. Zircon is a commonly used mineral in cathodoluminescence analysis, producing a stable, bright, and well-defined fluorescence signal under electron beam bombardment. It is physically and chemically stable and not easily damaged or attenuated during testing. Using this recognized and stable standard sample ensures the reliability of the test signal source and avoids interference with detector performance evaluation due to sample signal instability. This further enhances the repeatability of this method and its benchmarking ability across different laboratories, facilitating the standardized application and promotion of this evaluation method within the industry.

[0021] Taking zircon as an example, the method of this invention is illustrated as follows: First, a zircon sample with a stable CL signal is prepared and fixed on the sample stage. The scanning electron microscope (SEM) parameters are set as follows: accelerating voltage 10 kV, working distance 10 mm, beam current 1 nA. The CL detector parameters are set as follows: gain medium, contrast 50%. All parameters remain unchanged in subsequent tests. Then, systematic testing begins. The field of view (FOV) is set to a small value (e.g., high magnification), and the sample is moved sequentially to five positions: center, upper left, lower left, upper right, and lower right. A CL image is acquired at each position. After completion, the FOV is gradually increased (i.e., the magnification is decreased), and the image acquisition process at the above five positions is repeated until the maximum field of view of the device is reached. Next, all acquired CL images are opened using ImageJ software. For each image, the entire sample area is selected, and the average gray value (range 0-255) is obtained using the software's "Measure" function. For each tested FOV, the standard deviation (σ) of the corresponding five average gray values ​​is calculated. Finally, a judgment is made. For example... Figure 2As shown, when the field of view (FOV) is 500 μm, the calculated standard deviation σ = 4.9, which is less than the threshold of 5, indicating that the imaging is uniform within this field of view. When the FOV increases to 600 μm, the calculated standard deviation σ = 7.4, which is greater than the threshold of 5, indicating that the imaging is non-uniform within this field of view. Therefore, it can be determined that under these test conditions, the maximum uniform imaging range is the field of view corresponding to 500 μm.

[0022] This invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the scope of protection of this invention.

Claims

1. A method for determining the maximum uniform imaging range of a cathode fluorescence detector, characterized in that, Includes the following steps: Sample and parameter preparation: Select samples with stable and bright cathodoluminescence signals, and set and fix the key operating parameters of the scanning electron microscope and cathodoluminescence detector; Multi-location image acquisition: The sample is placed sequentially at multiple specific locations within the cathodoluminescence imaging field of view, and a cathodoluminescence image is acquired at each location under different field of view ranges or magnifications; Image data processing: Calculate the average gray value of each acquired cathodoluminescence image. For multiple images obtained under the same field of view or magnification, calculate the standard deviation of their corresponding average gray values. Uniformity determination and range determination: The calculated standard deviation is compared with a preset threshold. When the standard deviation is less than or equal to the preset threshold, the current field of view is determined to be a uniform imaging range. By testing a series of different field of view ranges, the maximum field of view range that can meet the uniformity condition is determined, which is the maximum uniform imaging range of the cathode fluorescence detector.

2. The method according to claim 1, characterized in that, The key operating parameters include the accelerating voltage, beam current, and working distance of the scanning electron microscope, as well as the gain and contrast parameters of the cathode fluorescence detector.

3. The method according to claim 1 or 2, characterized in that, The multiple specific locations include five positions: the center of the field of view, the upper left corner, the lower left corner, the upper right corner, and the lower right corner.

4. The method according to claim 3, characterized in that, The preset threshold is set based on the visual limit of the human eye to grayscale differences, and the preset threshold is 5.

5. The method according to claim 4, characterized in that, The sample was zircon.

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