Delay calibration method, apparatus and system for electron beam shutter of electron microscope

Abstract

A delay calibration method, apparatus and system for an electron beam shutter of an electron microscope. The delay calibration method for an electron beam shutter of an electron microscope comprises: by means of a camera, controlling a shutter controller to open a shutter, and also controlling the camera to start the collection of the current image frame, wherein the camera sends a control signal to the shutter controller by means of a shutter control signal conversion module; controlling the camera to maintain a shutter opening and closing cycle during the subsequent image frame collection, and successively delaying an exposure start time of the camera on the basis of a preset time step; when the image brightness in a sequence of image frames collected by means of the camera drops below a preset threshold value, controlling the camera to end the image frame collection; and determining an exposure delay value of the camera on the basis of the image brightness in said sequence of image frames.

Description

Electron microscope electron beam shutter delay calibration method, device and system

[0001] This application claims priority to Chinese patent application filed on December 11, 2023, with application number 202311701183.5, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the technical field of electron microscopes, and in particular to a method, device and system for calibrating electron beam shutter delay of an electron microscope. Background Art

[0003] Transmission electron microscopy (TEM) uses an electron beam to pass through a sample, generating secondary electrons that carry the sample's image information. This image information is then amplified and focused before being collected by an imaging device (such as a CCD / CMOS electron microscope camera). When a TEM does not need to capture images, it is undesirable for the electron beam to reach the sample and imaging device to avoid aging damage. Therefore, a shutter control circuit is used to deflect the electron beam, turning it on and off. When the electron beam is on, the camera begins exposure, and when the camera stops exposure, the electron beam is turned off.

[0004] The shutter control signal is provided by the TEM system software or the camera. However, both methods suffer from control signal delay, and the amount of this delay is often unknown, making synchronization between the camera and shutter difficult. Commercial TEMs are factory-calibrated for synchronization, but replacing components like the camera or shutter control circuit necessitates recalibration of the camera and shutter synchronization. Currently, manual adjustment is commonly used, repeatedly adding delay to the shutter control signal until the optimal image is achieved. However, this approach is inefficient and not universally applicable. Summary of the Invention

[0005] One purpose of the present application is to propose a method for calibrating the electron beam shutter delay of an electron microscope to improve the efficiency of camera shutter synchronization calibration.

[0006] To achieve the above objectives, the first aspect of the present application provides

[0007] A method for calibrating electron beam shutter delay of an electron microscope, applied to an electron microscope, comprising:

[0008] The camera controls the shutter controller to open the shutter and simultaneously controls the camera to start capturing the current image frame; wherein the camera sends a control signal to the shutter controller via a shutter control signal conversion module;

[0009] Controlling the camera to maintain the shutter opening and closing cycle and to delay the exposure start time of the camera successively according to a set time step in subsequent image frame acquisition;

[0010] If the brightness of an image in the image frame sequence captured by the camera drops below a set threshold, controlling the camera to end image frame capture;

[0011] The camera exposure delay value is determined according to the image brightness of the image frame sequence captured by the camera.

[0012] Another object of the present application is to provide an electron microscope electron beam shutter delay calibration device to improve the efficiency of camera shutter synchronization calibration.

[0013] To achieve this goal, the second aspect of the embodiment of the present application provides the following technical solutions:

[0014] An electron microscope electron beam shutter delay calibration device is applied to an electron microscope, comprising:

[0015] An image frame acquisition module, configured to control a shutter controller to open a shutter through a camera, and simultaneously control the camera to start acquiring a current image frame; wherein the camera sends a control signal to the shutter controller through a shutter control signal conversion module;

[0016] An exposure delay control module, configured to control the camera to maintain the shutter opening and closing cycle and to delay the camera's exposure start time successively according to a set time step during subsequent image frame acquisition;

[0017] An acquisition ending module, configured to control the camera to end image frame acquisition if the image brightness in the image frame sequence acquired by the camera drops below a set threshold;

[0018] The exposure delay determination module is used to determine the camera exposure delay value according to the image brightness of the image frame sequence collected by the camera.

[0019] One purpose of the present application is to provide an electron microscope electron beam shutter delay calibration system to improve the efficiency of camera shutter synchronization calibration.

[0020] To achieve this purpose, the third aspect of the present application provides the following technical solutions:

[0021] A camera for acquiring image frames;

[0022] A shutter controller, connected to the shutter, for controlling the opening and closing of the shutter;

[0023] a shutter control signal conversion module, connected between the camera and the shutter controller, for converting the signal sent by the camera into a signal that complies with the electrical standard of the shutter controller;

[0024] A computer device, connected to the camera signal, comprising one or more processors; a memory for storing one or more programs;

[0025] When the one or more programs are executed by the one or more processors, the one or more processors implement the electron microscope electron beam shutter delay calibration method provided in an embodiment of the present invention.

[0026] As can be seen from the above, the technical solution provided by this application, by gradually increasing the camera exposure delay time, analyzing the image brightness of the image frame sequence, and automatically determining the camera exposure delay value, thereby adjusting the camera image acquisition, solves the problem of low efficiency of camera and shutter synchronization calibration after replacing components such as the camera and shutter control circuit, and realizes the improvement of the efficiency of camera shutter synchronization calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic structural diagram of an electron microscope electron beam shutter delay calibration system provided in Example 1 of the present application;

[0028] FIG2 is a flow chart of a method for calibrating electron beam shutter delay of an electron microscope provided in Example 2 of the present application;

[0029] FIG3 is a flow chart of a method for calibrating electron beam shutter delay of an electron microscope provided in Example 3 of the present application;

[0030] FIG4 is a flow chart of a method for calibrating electron beam shutter delay of an electron microscope provided in a fourth embodiment of the present application;

[0031] FIG5 is a schematic structural diagram of an electron microscope electron beam shutter delay calibration device provided in Example 5 of the present application;

[0032] FIG6 is a comparison diagram of shutter opening and closing time and camera exposure time in an embodiment of the present application;

[0033] FIG7 is a graph showing a delay time-image brightness curve according to an embodiment of the present application;

[0034] FIG8 is another delay time-image brightness curve diagram in an embodiment of the present application. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0036] Example 1

[0037] This embodiment is applicable to the case of synchronous calibration of a transmission electron microscope camera and shutter, and can also be applied to systems of scanning tunneling microscopes (SEMs) or other imaging media such as X-ray detectors, backscattered electron detectors, etc. As shown in FIG1 , an electron microscope electron beam shutter delay calibration system includes: a camera 5 for acquiring image frames;

[0038] A shutter controller 3, connected to the shutter, for controlling the opening and closing of the shutter;

[0039] A shutter control signal conversion module 8, connected between the camera and the shutter controller, for converting the signal sent by the camera into a signal that complies with the electrical standard of the shutter controller;

[0040] Computer device 10, connected to the camera signal, including one or more processors; memory for storing one or more programs;

[0041] When the one or more programs are executed by the one or more processors, the one or more processors implement the electron microscope electron beam shutter delay calibration method provided in any of the following embodiments.

[0042] As shown in Figure 1, taking TEM calibration as an example, the shutter controller 3 is an internal structure of the TEM, and the electron beam 2 and sample 4 are contained within the lens barrel 1. The sample 4 can be a standard sample, or it can be placed without a sample during calibration. The camera 5 can be a CCD / CMOS electron detection camera, but is not limited to CCD / CMOS cameras. For example, this embodiment verifies the use of a CMOS direct electron detection camera. The camera 5 can be connected to the shutter controller 3 via a shutter control signal line 9, thereby controlling the opening and closing of the shutter. The shutter control signal line 9 must pass through the shutter control signal conversion module 8 to convert the signal into a signal that meets the electrical standards of the shutter controller 3. When the shutter controller 3 controls the shutter to open, the electron beam 2 can pass through the sample 4 and hit the camera 5. If the camera 5 starts exposure synchronously, an image of the sample 4 can be captured on the camera 5. The camera 5 transmits the image data to the computer device 10 via the camera data line 7. The computer device 10 performs brightness analysis on the transmitted data image and controls the exposure delay time of the camera 5 via the camera communication signal line 6. The image and data analysis results can be displayed in real time on the display of the computer device 10.

[0043] Example 2

[0044] Figure 2 is a flowchart of an electron microscope electron beam shutter delay calibration method provided in Example 2 of the present invention. The method can be performed by an electron microscope electron beam shutter delay calibration device, which can be implemented by hardware and / or software and can generally be integrated into a computer device.

[0045] The electron microscope electron beam shutter delay calibration method specifically includes:

[0046] Step 210: Control the shutter controller via the camera to open the shutter, and simultaneously control the camera to start capturing the current image frame;

[0047] The camera sends a control signal to the shutter controller via a shutter control signal conversion module. A computer device sends instructions to the camera, which in turn controls the shutter controller, thereby controlling the opening and closing of the shutter. When the camera controls the shutter controller to open the shutter, the camera also begins exposure, i.e., capturing the current image frame. The shutter control signal conversion board is configured to convert the signal from the camera into a signal that complies with the electrical standards of the shutter controller. The shutter control signal conversion module performs signal conversion and effectively protects the shutter controller. The camera may be an electronic detection camera.

[0048] Step 220 : Control the camera to maintain the shutter opening and closing cycle and delay the exposure start time of the camera successively according to the set time step in subsequent image frame acquisition.

[0049] Because the shutter control signal from the camera experiences a delay as it passes through the shutter control signal conversion module and the shutter control signal line, the shutter is not yet open when the camera begins exposure, preventing the electron beam from striking the camera. The computer controls the camera via the camera communication signal line, delaying the exposure time by a set time step (represented by T) during subsequent image frame acquisition. As shown in Figure 6, T can be accurately measured to the microsecond level. The shutter opening width controlled by the shutter opening / closing signal can be adjusted based on the camera exposure time. The shutter opening / closing signal period can be adjusted to a variable width, thereby accelerating the acquisition rate.

[0050] Step 230: If the image brightness in the image frame sequence captured by the camera drops below a set threshold, control the camera to end image frame capture.

[0051] The delay between an uncalibrated camera and its shutter often prevents the shutter from opening after the camera exposure begins. Consequently, several frames captured by the camera may not be captured until the camera exposure ends and the shutter remains closed. This results in a blank image, meaning the image pixels are completely black or nearly black. As the exposure delay increases, the camera exposure duration and the shutter opening / closing duration overlap, and this overlap increases until the camera exposure duration is completely within the shutter opening / closing duration, at which point the image frame brightness reaches its maximum. Subsequently, as the exposure delay increases, the shutter may close but the camera exposure has not yet ended, until the camera exposure start time is later than the shutter opening time, and the image pixels are once again completely black or nearly black. The computer controls the camera to gradually increase the delay T until the entire image transition from zero to visible and then back to zero is traversed. By comparing the brightness of adjacent image frames and setting a threshold for image brightness, it can be determined whether the increased exposure delay has reached a point where the camera exposure duration is completely within the shutter opening / closing duration, resulting in the image frame brightness reaching its maximum.

[0052] Step 240: Determine a camera exposure delay value according to the image brightness of the image frame sequence captured by the camera.

[0053] The computer device collects image brightness statistics for each frame of the captured image and plots a graph of the delay time and image brightness. Based on the shape of the graph, the optimal exposure delay value for camera correction can be determined.

[0054] The technical solution of this embodiment, by gradually increasing the camera exposure delay time and analyzing the image brightness of the image frame sequence, automatically determines the camera exposure delay value, thereby adjusting the camera image acquisition, thereby solving the problem of low efficiency of camera and shutter synchronization calibration after replacing components such as the camera and shutter control circuit, and achieving improved efficiency of camera shutter synchronization calibration.

[0055] Example 3

[0056] FIG3 is a flow chart of a method for calibrating electron beam shutter delay of an electron microscope provided by a third embodiment of the present invention. This embodiment further refines the technical solution of the second embodiment. The method specifically includes:

[0057] Step 310: Control the shutter controller via the camera to open the shutter, and control the camera to start capturing the current image frame.

[0058] Step 320: Control the camera to maintain the shutter opening and closing cycle and delay the camera exposure start time successively according to the set time step in subsequent image frame acquisition;

[0059] Step 330: The average brightness of the pixels within a predetermined pixel region in the image frame is used as the image brightness. The predetermined pixel region may be the entire image region or the center of the image, as the electron beam typically strikes the center of the camera. Processing the pixel brightness of a portion of the image region improves processing efficiency.

[0060] Step 340: Determine whether the image brightness of the image frame sequence shows a downward trend; if the image brightness shows a downward trend, execute step 350; if the image brightness has not shown a downward trend, continue to determine whether the image brightness of the image frame sequence shows a downward trend;

[0061] The images in the image frame sequence are arranged according to the time of acquisition, and the brightness of adjacent image frames is compared. If the brightness decreases, it indicates a downward trend in image brightness. To avoid external interference, the brightness of multiple frames can be fitted into a curve, and the slope of the curve can be used to determine whether the image brightness is decreasing.

[0062] Step 350: Determine whether the image brightness of the image frame in the downward trend is less than the set threshold; if the image brightness of the image frame in the downward trend is less than the set threshold, execute step 360; if the image brightness of the image frame in the downward trend is not less than the set threshold, continue to determine whether the image brightness of the image frame in the downward trend is less than the set threshold;

[0063] The threshold value may be set to a pixel brightness of 0, or may be set to a lower brightness value, so that the image frame acquisition does not need to be terminated until the image completely disappears, thereby saving calibration time.

[0064] Step 360: Control the camera to end image frame acquisition.

[0065] Step 370: Determine a camera exposure delay value according to the image brightness of the image frame sequence captured by the camera.

[0066] The technical solution of this embodiment terminates image frame acquisition by analyzing the brightness changes of image frames in the image frame sequence and the relationship between the brightness value and the set threshold, thereby improving the efficiency of calibration. Moreover, it can be completed automatically by a computer device.

[0067] Example 4

[0068] FIG4 is a flow chart of a method for calibrating electron beam shutter delay of an electron microscope provided by a fourth embodiment of the present invention. This embodiment further refines the above technical solution. The method specifically includes:

[0069] Step 410: Control the shutter controller via the camera to open the shutter, and control the camera to start capturing the current image frame.

[0070] Step 420: Control the camera to maintain the shutter opening and closing cycle and delay the camera exposure start time successively according to the set time step in subsequent image frame acquisition;

[0071] Step 430: If the image brightness in the image frame sequence captured by the camera drops below a set threshold, control the camera to end image frame capture;

[0072] Step 440: Draw a curve graph of delay time-image brightness according to the exposure delay time and image brightness corresponding to each image frame in the image frame sequence;

[0073] Among them, the image frames captured by the camera can be analyzed by the computer equipment in real time to collect image data and draw the image brightness curve.

[0074] Step 450: If the curve graph has a vertex, the exposure delay time corresponding to the vertex of the curve is determined as the camera exposure delay value.

[0075] As shown in Figure 7, the shutter duration (the time from shutter opening to shutter closing) is equal to the camera exposure duration (the time from the start to the end of camera exposure), or slightly longer. The shutter opening time and the camera exposure start time coincide, and the electron beam is completely unobstructed during the camera exposure time. The optimal delay point can be quickly found. The camera exposure delay value is the exposure delay time corresponding to the vertex of the delay time-image brightness curve.

[0076] Step 460: If the curve graph has a flat top, the exposure delay time corresponding to the middle point of the flat top line segment is determined as the camera exposure delay value.

[0077] As shown in Figure 8, for the capture of a single image frame, the shutter opening and closing duration is greater than the camera exposure duration. The maximum image brightness in the delay-image brightness curve is a horizontal line segment of equal value. The camera exposure delay value is the exposure delay time corresponding to the midpoint of this line segment.

[0078] According to the technical solution of this embodiment, the computer device can analyze the collected image data in real time, draw the image brightness curve, and automatically determine the camera exposure delay value through image brightness analysis, so as to quickly find the optimal camera exposure delay point.

[0079] Example 5

[0080] FIG5 is a schematic structural diagram of an electron microscope electron beam shutter delay calibration device provided by a fifth embodiment of the present invention. As shown in FIG5 , the electron microscope electron beam shutter delay calibration device includes: an image frame acquisition module 510, an exposure delay control module 520, an acquisition end module 530, and an exposure delay determination module 540, wherein:

[0081] The image frame acquisition module 510 is used to control the shutter controller to open the shutter through the camera, and at the same time control the camera to start acquiring the current image frame; wherein the camera sends a control signal to the shutter controller through the shutter control signal conversion module;

[0082] An exposure delay control module 520 is used to control the camera to maintain the shutter opening and closing cycle and to delay the exposure start time of the camera successively according to a set time step in subsequent image frame acquisition;

[0083] The acquisition ending module 530 is configured to control the camera to end image frame acquisition if the image brightness in the image frame sequence acquired by the camera drops below a set threshold;

[0084] The exposure delay determination module 540 is configured to determine a camera exposure delay value according to the image brightness of the image frame sequence captured by the camera.

[0085] Optionally, the shutter control signal conversion board is configured to convert the signal sent by the camera into a signal that complies with the electrical standard of the shutter controller.

[0086] Optionally, the camera is an electronic detection camera.

[0087] Optionally, the acquisition end module 530 is specifically configured to:

[0088] Taking the average brightness of pixels within a set pixel area in the image frame as the image brightness;

[0089] Determining whether the image brightness of the image frame sequence shows a downward trend;

[0090] If the image brightness decreases, determining whether the image brightness of the image frame in the decreasing trend is less than the set threshold;

[0091] If the image brightness of the image frame in the downward trend is less than the set threshold, the camera is controlled to end image frame acquisition.

[0092] Optionally, the exposure delay determination module 540 is specifically configured to:

[0093] Optionally, a curve graph of delay time-image brightness is drawn according to the exposure delay time and image brightness corresponding to each image frame in the image frame sequence;

[0094] If the curve graph has a vertex, the exposure delay time corresponding to the vertex of the curve is determined as the camera exposure delay value.

[0095] Optionally, the exposure delay determination module 540 is further configured to:

[0096] If the curve graph has a flat top, the exposure delay time corresponding to the middle point of the flat top line segment is determined as the camera exposure delay value.

[0097] Optionally, for single image frame acquisition, the shutter opening and closing time is greater than the camera exposure time.

[0098] The electron microscope electron beam shutter delay calibration device provided by the embodiment of the present invention can execute the electron microscope electron beam shutter delay calibration method provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0099] Through the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented with the help of software and necessary general-purpose hardware, and of course it can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in each embodiment of the present invention.

[0100] It is worth noting that in the embodiment of the electron microscope electron beam shutter delay calibration device mentioned above, the various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of the functional units are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of the present invention.

[0101] Although the present invention has been described in detail above using general explanations, specific embodiments, and experiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An electron microscope electron beam shutter delay calibration method, applied to an electron microscope, includes: Control the shutter controller to open the shutter through the camera, and at the same time control the camera to start collecting the current image frame; wherein, the camera sends a control signal to the shutter controller through the shutter control signal conversion module; Control the camera to keep the shutter opening and closing cycle and delay the exposure start time of the camera successively according to the set time step in the subsequent image frame collection; If the image brightness in the image frame sequence collected by the camera drops below the set threshold, control the camera to end the image frame collection; Determine the camera exposure delay value according to the image brightness of the image frame sequence collected by the camera.

2. The electron microscope electron beam shutter delay calibration method according to claim 1, wherein, The shutter control signal conversion board is set to convert the signal sent by the camera into a signal that conforms to the electrical standard of the shutter controller.

3. The electron microscope electron beam shutter delay calibration method according to claim 1, wherein, The camera is an electronic detection camera.

4. The electron microscope electron beam shutter delay calibration method according to any one of claims 1-3, wherein, If the image brightness in the image frame sequence collected by the camera drops below the set threshold, control the camera to end the image frame collection, including: Take the average pixel brightness within the set pixel area in the image frame as the image brightness; Judge whether the image brightness of the image frame sequence shows a downward trend; If the image brightness decreases, judge whether the image brightness of the image frame in the downward trend is less than the set threshold; If the image brightness of the image frame in the downward trend is less than the set threshold, control the camera to end the image frame collection.

5. The electron microscope electron beam shutter delay calibration method according to claim 4, wherein, The determining the camera exposure delay value according to the image brightness of the image frame sequence collected by the camera includes: Draw a curve graph of delay time - image brightness according to the exposure delay time and image brightness corresponding to each image frame in the image frame sequence; If there is a vertex in the curve graph, determine the exposure delay time corresponding to the curve vertex as the camera exposure delay value.

6. The electron microscope electron beam shutter delay calibration method according to claim 5, wherein, It also includes: If there is a flat top in the curve graph, determine the exposure delay time corresponding to the midpoint of the flat top line segment as the camera exposure delay value.

7. The electron microscope electron beam shutter delay calibration method according to claim 6, wherein, For single image frame collection, the shutter opening and closing duration is longer than the camera exposure duration.

8. An electron microscope electron beam shutter delay calibration device, applied to an electron microscope, includes: An image frame collection module, used to control the shutter controller to open the shutter through the camera, and at the same time control the camera to start collecting the current image frame; wherein, the camera sends a control signal to the shutter controller through the shutter control signal conversion module; An exposure delay control module, used to control the camera to keep the shutter opening and closing cycle and delay the exposure start time of the camera successively according to the set time step in the subsequent image frame collection; An acquisition end module, used to control the camera to end the image frame collection if the image brightness in the image frame sequence collected by the camera drops below the set threshold; An exposure delay determination module, used to determine the camera exposure delay value according to the image brightness of the image frame sequence collected by the camera.

9. An electron microscope electron beam shutter delay calibration system, includes: A camera, used to collect image frames; A shutter controller, connected to the shutter, used to control the shutter to open and close; A shutter control signal conversion module, connected between the camera and the shutter controller, used to convert the signal sent by the camera into a signal that conforms to the electrical standard of the shutter controller; A computer device, signal-connected to the camera, including one or more processors; A memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method for calibrating the electron beam shutter delay of an electron microscope according to any one of claims 1-7.

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