CN111982945B - Method for acquiring time resolution dark field image based on ultra-fast transmission electron microscope system and application - Google Patents

Abstract

A method for obtaining high-contrast ultrafast time-resolved dark field images based on an ultrafast transmission electron microscope system and application thereof are provided. The method has the advantages that the high convergence angle incident beam imaging is adopted, the large-size objective diaphragm is adopted, the diffracted electrons are used as signals for imaging, the time resolution dark field image under the ultra-fast scale is obtained, compared with the ultra-fast transmission electron microscope bright field image, the dark field image with opposite contrast reduces the background signal, due to the combination of the high convergence angle and the large-size objective diaphragm, the signal to noise ratio of the acquired signals is improved through the optimized adjustment of double-beam diffraction and the dark field image, the change process of different areas inside a sample can be observed more directly relative to the diffraction mode signal, the method has high spatial resolution, the range of the sample represented by the ultra-fast electron microscope dark field mode is widened, contrast change details after the stimulated by nano particles are analyzed, and the method can be applied to characterization analysis of lattice structure relaxation and resonance dynamics processes of materials with different lattice orientations in the ultra-fast time scale.

Description

Method and application of time-resolved dark-field image acquisition based on ultrafast transmission electron microscopy system

technical field

The disclosure belongs to the field of dark field characterization of electron microscopy and ultrafast electron microscope technology, and relates to a method and application for obtaining time-resolved dark field images based on an ultrafast transmission electron microscope system, in particular to a method for obtaining time-resolved dark field images based on an ultrafast transmission electron microscope system. Method and application of high-contrast ultrafast time-resolved dark-field images.

Background technique

Transmission electron microscopy is an important tool for material characterization. After rapid development of transmission electron microscopy technology, the current spatial resolution has reached the sub-angstrom level, which has greatly met the experimental needs. Characterizing the change process of materials through transmission electron microscopy has become an important development trend at present. For example, in situ transmission electron microscopy and 4D ultrafast transmission electron microscopy.

Ultrafast transmission electron microscopy is combined with ultrafast optical means, which has the advantages of high spatial resolution of transmission electron microscopy and high time resolution of ultrafast optics, and breaks through the limitation of charge-coupled device (CCD) camera acquisition speed, achieving femtosecond to The dynamic change process of the material structure in the microsecond range, thus revealing the atomic scale change in the physical or chemical process. Ultrafast transmission electron microscopy has developed a variety of characterization techniques so far, which can analyze the plasma effect of materials based on image or diffraction information, or combined with electron energy loss spectroscopy (EELS).

At present, data collection based on ultrafast transmission electron microscopy is mainly based on bright field images and diffraction spots, to study the internal dynamics of materials after being excited by pulsed lasers. In 2018, some studies based on ultrafast transmission electron microscopy The change of contrast is to study the lattice vibration process generated by the pump inside and between the plasmonic gold nanoparticles. However, since the bright field image is mainly transmitted electrons, the lattice change leads to the signal of the contrast change of the bright field image. Compared with the transmitted electron signal, it only accounts for a small part, so there is a problem that the contrast change is not obvious. At the same time, the number of imaging electrons in the ultrafast transmission electron microscope is lower than that of the conventional transmission electron microscope, so the signal-to-noise ratio of the obtained result is relatively poor, and the image is finally obtained. The crystal lattice change process of the sample after laser excitation cannot be clearly revealed. The bright field image spectrum obtained by taking a large electron beam spot and the smallest objective aperture in the photoelectron mode is shown in Figure 1.

In the dark field image, diffracted electrons are used for imaging. Compared with the bright field image, the contrast is opposite. The sample area becomes a bright area, and the substrate area becomes a dark area. The background signal is weakened, and the change of the sample signal intensity is more obvious. Compared with the bright field image, it has been greatly improved. Compared with the ultrafast system bright field image, it can more intuitively show the changes of the sample in the ultrafast process.

In conventional transmission electron microscopes, taking dark field images often requires electron beams to be irradiated on the sample in an approximately parallel state, and the convergence angle is relatively small, so that dark field images can be taken with the smallest objective lens diaphragm to ensure the transmission of diffracted electrons and block The vast majority (inelastically) scatter electrons, but these methods are not directly applicable to ultrafast TEM. In the ultrafast transmission electron microscope, electrons are excited by laser pulses in the form of pulses, and the number of electrons generated is far less than that of conventional electron microscopes, so the dark field image contrast is very poor. The obtained dark field image atlas is shown in Figure 2.

At present, the dark-field imaging mode based on ultrafast transmission electron microscopy is mainly based on the observation of the mechanical movement of the sample, and the application range of the work based on dark-field imaging is relatively small, and there are great restrictions on the selection of samples, and small-sized samples cannot be applied, such as Characterization of samples such as nanoparticles. In addition, in the few existing studies that use dark-field images to characterize large-scale samples, the image contrast obtained is poor, and the obtained dark-field images have not analyzed the intensity change process of the time-resolved dark-field image itself in detail, and cannot clearly reflect the contrast of the contrast. The degree of change process cannot be applied to precise kinetic analysis. Therefore, there is still a need for an intuitive and high signal-to-noise ratio method to analyze the dynamic change process of the sample in the ultrafast time scale.

Contents of the invention

(1) Technical problems to be solved

The present disclosure provides a method and application for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system, so as to at least partially solve the above-mentioned technical problems.

(2) Technical solution

According to one aspect of the present disclosure, a method for obtaining time-resolved dark field images based on an ultrafast transmission electron microscope system is provided, including: Step S12: In the thermal electron mode, adjust to obtain the approximate double-beam diffraction of the sample and use an objective lens Cover the diffraction spot with the aperture to obtain a dark field image; Step S13: In the photoelectron mode, converge the electron beam spot at a larger convergence angle, and obtain the convergent beam diffraction of the sample in the diffraction mode; The tilt angle of the electron beam, using the objective lens diaphragm to select the diffraction spot, obtains the time-resolved dark field image of the sample in the photoelectron mode, where the larger convergence angle makes the diffraction spot area in the photoelectron mode larger than that in the thermal electron mode .

Wherein, the objective lens diaphragm is a large-sized objective lens diaphragm, and the diaphragm aperture of the large-sized objective lens diaphragm is between 10 microns and 100 microns; preferably, it is between 20 microns and 40 microns.

Wherein, before step S12, it also includes: step S11: In the ultrafast transmission electron microscope system, adjust the pump laser focus position to focus on the sample position, and focus the probe laser on the filament to generate probe electron pulses.

In some embodiments, step S11 includes: before the pump laser enters the sample chamber of the transmission electron microscope system, adding a visible light reflector to reflect the pump laser to the beam analyzer, and adjusting the position of the beam analyzer to find the focus position and focus of the pump laser. The size of the spot, the actual distance between the focus point and the focus lens and the size of the focus spot are obtained; according to the focus position, the position of the focus lens in the pump light path is adjusted through a three-dimensional translation stage; a carbon film is placed in the ultrafast transmission electron microscope, and the minimum energy pump light is used Excite the position of the carbon film to achieve the coincidence of the excitation position of the pump laser with the position of the photodetection electron; and finely adjust the position of the focusing lens to find the best focus position.

In some embodiments, after step S13, it further includes: step S14: using an automatic acquisition module to acquire images, and the automatic acquisition module realizes its functions through software, or hardware, or a combination of hardware and software. Step S14 can automatically collect and save time-resolved dark field images by controlling the one-dimensional electric translation stage and the imaging device of the transmission electron microscope system; or control the pump laser by controlling the mechanical shutter switch in the optical path of the pump laser to collect reference images and excitation images .

In some embodiments, after step S14, further includes: performing batch processing on the collected images.

In some embodiments, the batch processing of the collected images includes: one or more of image averaging as a reference image, image offset calibration, image intensity analysis, and result output; wherein the image intensity analysis includes: single pixel One or more of intensity analysis, area intensity analysis, and line intensity analysis; the result output includes: image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift output, Fourier analysis one or more of output and video output.

According to another aspect of the present disclosure, there is also provided a time-resolved dark field image acquired by the method described in the present disclosure to analyze the details of the contrast change of the nanoparticles after they are excited by laser light, and to characterize different Application of lattice structure relaxation and resonant dynamics processes of material lattice orientation.

(3) Beneficial effects

It can be seen from the above technical solutions that the method and application for obtaining time-resolved dark field images based on an ultrafast transmission electron microscope system provided by the present disclosure have the following beneficial effects:

1. By adopting high-convergence angle incident beam imaging, using a large-size objective lens aperture, and using diffracted electrons as signals for imaging, time-resolved dark-field images at ultrafast scales are obtained. Compared with ultrafast transmission electron microscope bright-field images, they have the opposite Contrast dark field images reduce the background signal, due to the combination of high convergence angle and large-size objective lens diaphragm, and through the optimal adjustment of double-beam diffraction and dark field images, the signal-to-noise ratio of the collected signal is improved. Compared with diffraction The mode signal can more directly observe the change process of different regions inside the sample, has high spatial resolution, expands the scope of ultrafast electron microscope dark field method to characterize samples, and can analyze the details of contrast changes after particles are excited by laser light. The time-resolved dark field image contrast obtained in the present disclosure is higher, and the lattice change is more obvious, and the dynamic change process of the sample in an ultrafast time scale can be observed, such as picoseconds, nanoseconds, or microseconds, etc., and the present disclosure contains electron-phonon interaction information and lattice direction tilt information, and also includes thermally scattered electrons, which can be used for thermally scattered electron signal analysis.

2. The image collection process of the present disclosure adopts automatic collection, and different reference modes can be selected to ensure that the collection process reduces external interference and improves collection efficiency.

3. This disclosure also proposes a corresponding data processing and analysis program, which can analyze the collected data images in batches, perform drift correction on the sample position, perform noise removal and filtering processing on the image, and output single pixel intensity analysis, regional pixel intensity analysis, Line strength analysis, output video, etc.

Description of drawings

Fig. 1 is a bright field image spectrum obtained by shooting with a relatively large electron beam spot and a minimum-sized objective lens diaphragm in the photoelectron mode in the prior art.

Fig. 2 is a dark field image spectrum obtained by shooting with a relatively large electron beam spot and a minimum-sized objective lens diaphragm in the photoelectron mode in the prior art.

FIG. 3 is a schematic structural diagram of an ultrafast transmission electron microscope system according to an embodiment of the present disclosure.

FIG. 4 is a dark field image spectrum obtained by using a high convergence angle and a large-sized objective lens diaphragm based on the method of the present disclosure.

FIG. 5 is a flow chart of a method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system according to an embodiment of the present disclosure.

6A-6C are schematic diagrams of determining the focus position according to the ablation area of the carbon film according to an embodiment of the present disclosure.

FIGS. 7A-7D are schematic diagrams of approximate double-beam diffraction and dark field images obtained through adjustment of a sample in a thermionic mode according to an embodiment of the present disclosure.

8A-8D are schematic diagrams of a time-resolved dark field image of an adjusted sample in an optoelectronic mode according to an embodiment of the present disclosure.

FIG. 9 is a flow chart of image acquisition and storage by the automatic acquisition module for acquiring negative time reference images according to an embodiment of the present disclosure.

FIG. 10 is a flow chart of image acquisition and storage by an automatic image acquisition module controlling a mechanical shutter according to an embodiment of the present disclosure.

Fig. 11 is a diagram illustrating a dark field image change process of a collected sample according to an embodiment of the present disclosure.

FIG. 12 is a standard deviation analysis result of a time-resolved dark field image according to an embodiment of the present disclosure.

FIG. 13 is an intensity change curve of a certain area of a time-resolved dark field image according to an embodiment of the present disclosure.

【Symbol Description】

01-laser; 02-one-dimensional electric displacement stage;

03-mechanical shutter; 04-filament;

05-sample; 06-ultrafast transmission electron microscope/electron microscope chamber;

07 - Imaging device.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present disclosure clearer, the present disclosure will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. "between" contains endpoint values.

In conventional transmission electron microscopy, the sample is in a stable state and the temperature is kept stable. The dark field image mainly studies the inhomogeneity inside the sample, providing a static characterization of the sample structure, such as the position of internal defects, the size of the grain or the enrichment of different regions The difference between particles, etc., so the observation in the conventional electron microscope is often a non-uniform sample. The time-resolved dark-field image obtained based on the present disclosure has high contrast, high signal-to-noise ratio, and high spatial resolution, and has become a means to study the dynamic signal of internal structure changes in a specific region, such as the study of phonons in the sample. The action, the process of phonon propagation, the process of phonon causing the lattice direction to tilt, etc., have no requirements on whether the sample is uniform or not. Therefore, the time-resolved dark-field image in the present disclosure represents a different meaning and process from the conventional electron microscope dark-field image.

In the present disclosure, the meaning of the terms "close" and "approximately" means equivalence within the allowable error range due to limitations of the instrument itself or limitations of experimental operations.

first embodiment

In a first exemplary embodiment of the present disclosure, a method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system is provided.

The ultrafast transmission electron microscopy system to which this method is applicable is introduced first.

FIG. 3 is a schematic structural diagram of an ultrafast transmission electron microscope system according to an embodiment of the present disclosure.

Referring to Fig. 3, the ultrafast transmission electron microscope system of the present disclosure includes: a laser system, which is used to generate ultrashort pulse laser, and is divided into two parts, a detection laser and a pump laser, after a beam splitter; Referred to as the electron microscope system), including electron microscope cavity 06, filament 04, electron microscope imaging device 07; and one-dimensional electric displacement stage 02, three-dimensional displacement stage and mechanical shutter 03 arranged in the optical path between the laser system and transmission electron microscope system; The electron microscope system can work in thermionic mode. By heating the filament in the cavity of the electron microscope to generate an electron beam, the probe laser can be introduced into the electron gun to generate photo-generated pulse electrons, and the photo-generated pulse electrons are accelerated through the sample area and finally imaged in the electron microscope. device; the pump laser can also be introduced into the sample area of the electron microscope to excite the sample to produce a transient lattice morphology change; among them, the three-dimensional translation stage adjusts the position of the focusing lens so that the incident detection laser and pump laser are respectively focused on the filament area and the sample area ; One-dimensional electric stage, controlling the optical path of the pump laser; mechanical shutter, controlling the switch of the pump laser.

In this embodiment, as shown in FIG. 3 , the ultrafast TEM system includes: a laser 01, a one-dimensional electric translation stage 02, a mechanical shutter 03, an ultrafast TEM 06, and a three-dimensional translation stage, wherein the ultrafast TEM 06 Contains a filament 04 and an imaging device 07, wherein the filament 04 is used to generate the detection electron pulse, and a sample 05 is placed in the area where the detection electron pulse is accelerated, and the laser light emitted by the laser 01 is divided into two beams by a spectroscope after frequency doubling, A beam of laser light is used as the detection light source, which is called the detection laser. After frequency doubling conversion again, it is finally focused on the filament 04 in the ultrafast transmission electron microscope 06 to generate detection electron pulses, which are accelerated through the cavity of the ultrafast transmission electron microscope 06. , penetrates through the sample 05; another beam of laser light is used as the excitation light source, called the pump laser, passes through the mechanical shutter 03, and finally focuses on the sample 05 in the ultrafast transmission electron microscope 06. The filament 04 , the sample 05 and the imaging device 07 are located on the same straight line, and the detection electron pulse sent by the filament penetrates through the sample 05 and forms an image on the imaging device 07 of the ultrafast transmission electron microscope 06 .

In this embodiment, the ultrafast transmission electron microscope 06 can generate thermal electron beams by heating the filament 04 , and can also irradiate the area of the filament 04 by introducing laser light to generate detection electrons.

In this embodiment, the three-dimensional translation stage is used to adjust the position of the focusing lens at the entrance of the sample chamber of the ultrafast transmission electron microscope system, and to adjust the position where the pump laser is focused on the sample 05 and the size of the focus area.

FIG. 4 is a dark field image spectrum obtained by using a high convergence angle and a large-sized objective lens diaphragm based on the method of the present disclosure. FIG. 5 is a flow chart of a method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system according to an embodiment of the present disclosure.

Referring to Figure 4, the time-resolved dark-field image obtained by this method can characterize small-sized nanoparticles, expanding the application range of the time-resolved dark-field image.

The method for obtaining time-resolved dark field images based on the ultrafast transmission electron microscope system is introduced below in conjunction with the ultrafast transmission electron microscope system of the present disclosure. Referring to FIG. 3 and FIG. 5 , the method includes:

Step S11: In the ultrafast transmission electron microscope system, adjust the focus position of the pump laser to focus on the sample position, and focus the detection laser on the filament to generate detection electron pulses;

In this embodiment, based on the structure of the ultrafast transmission electron microscope system, a preferred method for adjusting the focus position of the pump laser is proposed.

Adjustment methods for focusing the laser include:

Step 1. Before the pump laser enters the sample chamber of the TEM system, add a visible light mirror to reflect the pump laser to the beam analyzer. Adjust the position of the beam analyzer to find the pump laser focus position and focus spot size, and obtain the focus point The actual distance from the focusing lens and the size of the focusing spot;

Step 2, according to the focus position, adjust the position of the focus lens in the pump light path through the three-dimensional translation stage 02;

Step 3, put a carbon film (for example, a 50-mesh carbon film) into the ultrafast transmission electron microscope 06, and use the minimum energy pump light to excite the position of the carbon film, so that the excitation position of the pump laser coincides with the position of the photogenerated detection electron;

Step 4, finely adjust the position of the focus lens back and forth to find the best focus position.

6A-6C are schematic diagrams of determining the focus position according to the ablation area of the carbon film according to an embodiment of the present disclosure.

When the position of the carbon film is in front of the focal point of the focusing lens, the ablation area is shown in Figure 6A; when the position of the carbon film is behind the focal point of the focusing lens, the ablation area is shown in Figure 6B; , the ablation area is shown in Figure 6C, which is approximately a perfect circle.

Specifically, based on the following operation steps, the external optical path of the ultrafast transmission electron microscope is precisely adjusted to focus the pump laser and the probe laser on the exact position in the ultrafast transmission electron microscope, that is, both the pump laser and the probe laser are focused on the sample, and can achieve Focus area control. Step 1, put a 50-mesh carbon film in the electron microscope system as a sample, find small particles in the thermal electron mode as a reference, and adjust the particles at an appropriate magnification to appear on the electron microscope imaging device 07; Step 2, adjust the ultrafast transmission electron microscope The magnification of the system is 50 times, and the position of the particle under this magnification is obtained; step 3, a low-power pump laser can be used to ablate a low-contrast area on the carbon film, and adjust the focus area of the pump laser on the carbon film Make the small particles in the center of the low-contrast area, complete the coincidence of the pump laser focus position and the probe electron detection area; step 4, adjust the three-dimensional translation stage to make the focus lens move back and forth to change the focus position, and obtain the optimal focus according to the shape of the final ablation area lens position.

In some embodiments, chemically synthesized gold triangular nanoprisms are selected as samples and graphene copper meshes are selected as substrates, and the method based on the present disclosure can be used to characterize the lattice dynamics of gold nanosheets.

Step S12: In the thermal electron mode, adjust to obtain the approximate double-beam diffraction and dark field image of the sample;

7A-7D are schematic diagrams of approximate double-beam diffraction and dark field images of samples obtained through adjustment in thermal electron mode according to an embodiment of the present disclosure, wherein FIG. 7A is a bright field image of samples under thermal electrons Spectrum; Figure 7B is the approximate double-beam diffraction spectrum obtained by adjusting the sample under thermal electron; Figure 7C is the spectrum after selecting the aperture of the objective lens to cover the diffraction spot; Figure 7D is the final dark field image obtained in thermal electron mode.

As shown in FIG. 7A-FIG. 7D in conjunction with the accompanying drawings, in this embodiment, the method for adjusting the orientation (tape axis) of the electron microscope sample to obtain a dark field image in the thermal electron mode includes the following sub-steps:

Sub-step S12a: select a suitable sample area in the thermal electron mode;

In this embodiment, the filament 04 in the ultrafast transmission electron microscope 06 is heated to the state of the thermal electron beam, and a suitable sample area is selected in the thermal electron mode, for example, as shown in Figure 7A, a suitable particle sample is found, and the pump laser is introduced into the transmission Electron microscope system sample 05 area.

Sub-step S12b: Enclose the sample with a selective aperture, enter the diffraction mode, adjust the diffraction spots to the center of the screen, adjust the tilt angle of the sample so that the diffraction pattern under the electron microscope system is similar to double-beam diffraction, and ensure that there is basically no gap between the diffracted beam and the transmitted beam. interaction;

In this embodiment, the selected area diaphragm is used to cover the sample, enter the diffraction mode, adjust the diffraction spot to the center of the screen, and adjust the tilt angle of the sample so that the diffraction of the sample in the diffraction mode is close to the double-beam diffraction mode, as shown in Figure 7B. It shows the diffraction spot pattern corresponding to the sample chemically synthesized gold triangular nanoprisms, and the diffraction spots circled after calibration correspond to the Au(220) crystal plane.

It is particularly emphasized that in the present disclosure, the diffraction mode needs to be a double-beam diffraction mode, which is different from the operation of conventional electron microscope dark field images. In conventional electron microscope dark field images, it is only necessary to obtain the diffraction spots of the sample, and it is not necessary to use the double-beam diffraction mode.

Sub-step S12c: enter the dark field mode, adjust the incident angle of the incident electron beam so that the corresponding diffraction spot is located at the position of the original transmission spot, and the system will record the current tilt angle of the incident electron beam;

In this sub-step S12c, the recorded current tilt angle of the incident electron beam will be used in the subsequent step S13.

Sub-step S12d: select the aperture of the objective lens to cover the diffraction spot, and exit the diffraction mode to obtain a dark field image;

In the present disclosure, a large-sized objective lens diaphragm is adopted, and the minimum size of the diaphragm aperture of the selected objective lens diaphragm is greater than or equal to the size of the objective lens diaphragm used in the prior art, and the diaphragm aperture is between 10 microns and 100 microns For example, in an example, an objective diaphragm with a physical size of 20 μm can be used, and the corresponding collection half angle is about 7.6 mrad, as shown in FIG. 7C . Preferably, the aperture diameter of the objective lens (aperture) is greater than or equal to 20 μm and less than or equal to 40 μm, for example, in a specific example, the aperture of the 2# objective lens aperture is 20 μm, and the aperture of the 3# objective lens aperture is 40 μm.

In the conventional electron microscope, due to the high intensity of the electron beam current, the spot spreads evenly to ensure that the light is approximately parallel to the sample. When using the objective lens diaphragm to select the diffraction spot, the minimum size of the objective lens diaphragm is used to select the diffraction spot to ensure the least heat scattering. electrons pass through. In some examples of the present disclosure, the electron pulse is laterally broadened from the filament to the sample position due to the space charge effect, and the coherence is weakened. The incident electron beam irradiates the sample with an approximately converging beam. The larger the incident electron beam convergence angle, the larger the area of the diffraction spot in the reciprocal space, so the area of the diffraction spot obtained by the photogenerated electron mode is larger than that of the conventional electron microscope. Based on the above factors, the objective lens The size of the aperture should be large enough to ensure that most of the diffraction signal electrons pass through, so as to ensure that the obtained time-resolved dark-field image has sufficient signal intensity. In the reciprocal space, the large-size objective lens diaphragm will contain more angular scattered electrons, so based on the amorphous region in the dark field image, the change of the thermal scattering electron signal can be detected, so the dark field image can not only study the crystal sample region Diffraction contrast changes, and the scattering changes in the amorphous region can be studied at the same time. Compared with the traditional electron microscope dark field image, it contains more sample change information.

Sub-step S12e: fine-tuning the tilt angle of the sample according to the dark field image, so that the region of interest is a bright region.

The above sub-steps S12b-S12e are executed alternately until the target area of the obtained dark field image is in a bright state, and the diffraction spots are in the double-beam diffraction mode, which is an ideal dark field image. The result is shown in FIG. 7D.

In the process of converting from thermionic mode to optoelectronic mode, the following methods can be used for mode switching:

Reduce the heating current of the filament 04 of the TEM system to the state of no thermal electron emission, and electrons should not be detected based on the imaging device 07 of the TEM system;

Introduce the probe laser into the filament 04 area of the transmission electron microscope system to focus on the center of the filament surface, use photoelectron pulse imaging to find the sample area, and readjust the transmission electron microscope system until the sample obtains a bright field image without obvious aberration under the photoelectron pulse.

Step S13: In the photoelectron mode, converge the electron beam spot at a larger convergence angle, and obtain the convergent beam diffraction of the sample in the diffraction mode; in the dark field mode, based on the inclination angle of the incident electron beam in the thermal electron mode, use the objective lens diaphragm Select the diffraction spot to obtain the time-resolved dark field image of the sample in the photoelectron mode, wherein the larger convergence angle makes the diffraction spot area in the photoelectron mode larger than that in the thermal electron mode;

The objective aperture of the diffraction spot here is the same size as the objective aperture in step S12, and both are large-scale objective apertures.

In some examples of the present disclosure, the number of photogenerated electrons is less than that of conventional electron microscopes. In order to improve the brightness, the photogenerated electron beams are converged on the sample in an approximate converging beam mode to obtain approximate converging beam diffraction of the sample, and the aperture of the objective lens is selected to cover the diffraction spot. The larger the aperture of the objective lens, the more heat-scattered electrons will be transmitted, and the dark-field image will contain more angles of heat-scattered electrons. According to the different sizes of the objective aperture, the formed dark-field image will contain different angles. Therefore, the time-resolved dark-field images based on the present disclosure can be used to study heat-scattered electrons at different angles.

Therefore, in this operation, due to the Coulomb repulsion of electrons from the electron gun to the sample, the electron beam expands and the diffraction spot expands laterally. At the same time, the number of electrons in the photoelectron mode is relatively small compared with the thermal emission mode. Intensity, the incident electrons need to be converged on the gold particles at a large convergence angle, so that the diffraction spot area is larger than that of the thermal electron mode. Based on the above factors, when characterizing nanoparticle materials such as gold nanoparticles, it is necessary to use a large-sized objective lens diaphragm to ensure that most of the diffracted electrons pass through the objective lens diaphragm, and finally obtain a time-resolved dark field image with sufficient signal strength.

8A-8D are schematic diagrams of adjusting the time-resolved dark field image of a sample in the photoelectron mode according to an embodiment of the present disclosure, wherein, FIG. 8A is a bright field image spectrum obtained by converging incident beams in the photoelectron mode; FIG. 8B is the approximate convergent beam diffraction spectrum obtained in the photoelectron mode; FIG. 8C is the approximate convergent beam diffraction spot in the photoelectron mode where the objective lens diaphragm is caught; FIG. 8D is the dark field image spectrum obtained in the photoelectron mode.

In some examples, the method for obtaining a time-resolved dark field image in the photogenerated electron mode includes the following sub-steps:

Sub-step S13a: In the photoelectron mode, converge the photo-generated detection electron pulses on the sample, close to the convergent beam mode, and the bright field image spectrum obtained by converging the incident beam is shown in Fig. 8A;

Sub-step S13b: enter the diffraction mode, and obtain the approximate converging beam diffraction of the sample area under the photo-generated detection electron pulse;

The approximate converging beam diffraction pattern obtained in the photoelectron mode is shown in FIG. 8B . The converging angle can be calculated based on the diffraction spots. For example, in this embodiment, the converging angle calculated based on the diffraction spots is about 9.9 mrad.

Sub-step S13c: enter the dark field mode, adjust the electron beam tilt angle to the same angle according to the incident electron beam tilt angle recorded in the thermal electron mode, move the corresponding diffraction spot to the original transmission spot position, and adjust the spot position to make the diffraction spot brightness the highest;

Sub-step S13d: Select a large-sized objective lens diaphragm to cover the central diffraction spot. The size of the objective lens diaphragm should be large enough to ensure that most of the diffracted electrons pass through the objective lens diaphragm to block the transmitted beam electrons, exit the diffraction mode, and obtain a dark field image;

In this sub-step S13d, the approximate converging beam diffraction spot pattern in the photoelectron mode is covered by the objective lens diaphragm, as shown in Figure 8C, the size of the objective lens diaphragm is large enough to ensure that most of the diffracted electrons pass through the objective lens diaphragm and block the transmitted beam electronic.

Sub-step S13e: adjust the position of the electron beam, adjust the size of the electron beam spot, and obtain the best dark field image;

The final dark field image spectrum obtained in the photoelectron mode is shown in FIG. 8D .

Step S14: using the automatic acquisition module to acquire images;

FIG. 9 is a flow chart of image acquisition and storage by the automatic acquisition module for acquiring negative time reference images according to an embodiment of the present disclosure. The image acquisition process will be described below with reference to FIG. 9 .

In some embodiments, the automatic acquisition module can control the one-dimensional electric translation stage 02 and the imaging device 07 of the transmission electron microscope system to automatically acquire and save the time-resolved dark field images. As shown in Figure 9, the electron microscope system imaging device control software Gatan Digital Micrograph software is used to write scripts to control the movement of the one-dimensional translation stage and the imaging device to collect images. The automatic image acquisition process is as follows:

Sub-step S141a: Control the ultra-fast transmission electron microscope system according to the parameters set by the user. The automatic acquisition program parameters set by the user include one or more of the following parameters: the initial position, final position and step distance of the one-dimensional electric translation stage, etc., the transmission electron microscope The exposure time of the system imaging device, and the pixel value of the collected image, etc.

Sub-step S141b: the automatic acquisition module controls the one-dimensional electric displacement stage to move to a designated position, adjusts the optical path of the pump laser, and controls the interval between the arrival of the pump laser pulse at the sample and the arrival of the detection electron pulse at the sample 05;

Sub-step S141c: the automatic collection module collects the image according to the parameters, and assigns an ID to the image, and saves the image to a local file;

Sub-step S141d: determine whether to collect a reference image, if yes, execute sub-step S141e, otherwise execute sub-step S141g;

Sub-step S141e: Control the one-dimensional electric translation platform to move from the current position P (the original position as a reference) to the negative time position b, collect and save the reference image;

Sub-step S141f: Control the one-dimensional electric displacement platform to return to the original position P, re-acquire and save the image;

Sub-step S141g: the system judges whether the acquisition process is completed, and if so, ends the acquisition process, otherwise controls the one-dimensional electric displacement platform to the next position to acquire images;

Sub-step S141b to sub-step S141g are repeated to finally complete the acquisition process of all dark field images.

FIG. 10 is a flow chart of image acquisition and storage by an automatic image acquisition module controlling a mechanical shutter according to an embodiment of the present disclosure.

In other embodiments, at each position of the one-dimensional translation stage, the automatic acquisition module can control the mechanical shutter switch in the optical path of the pumping laser to control the pumping laser, and collect the reference image and the excitation image.

Referring to Figure 10, at each position of the one-dimensional translation stage, the automatic acquisition module can control the mechanical shutter switch in the optical path of the pump laser to control the pump laser. The process of acquiring reference images and excitation images is as follows:

Sub-step S142a: Control the imaging system of the transmission electron microscope system according to the parameters set by the user. The parameters of the automatic acquisition module set by the user are the same as the settings of the automatic acquisition module in the above-mentioned sub-step S141a.

Sub-step S142b: the automatic acquisition module controls the mechanical shutter to close, the pump laser light will not be introduced into the sample area of the TEM system, and the sample is in an unexcited state;

Sub-step S142c: the automatic acquisition module controls the one-dimensional translation stage to move to a designated position;

Sub-step S142d: the automatic collection module collects the reference image according to the parameters, assigns an ID to the image and saves the image to a local folder;

Sub-step S142e: the automatic acquisition module controls the opening of the mechanical shutter, the pump laser is introduced into the sample area of the transmission electron microscope system, and the sample is excited by the laser to produce instantaneous changes;

Step S142f: The automatic collection module collects the excitation image of the sample according to the parameters, assigns an ID to the image and saves it to another local folder;

Sub-step S142g: the system judges whether the acquisition process is completed, and if yes, ends the acquisition process; otherwise, controls the one-dimensional electric translation stage to acquire images at the next position.

Sub-step S142b to sub-step S142g are repeated, and the sample state when the sample is excited by the pump laser pulse and the sample state when it is not excited are collected as reference signals at different intervals to complete the entire image acquisition process.

The above-mentioned automatic collection module is described as being realized by software, but the present disclosure is not limited thereto. In other embodiments, different software, or hardware, or a combination of hardware and software may be used to implement the same function.

second embodiment

In a second exemplary embodiment of the present disclosure, a method of processing and analyzing time-resolved dark-field images is provided.

For example, batch processing can also be performed on obtained dark field images. In some examples, batch processing is performed on each image, including one or more of image sorting, noise removal, image averaging as a reference image, image offset calibration, image intensity analysis, and result output. Image intensity analysis, including one or more of single pixel intensity analysis, area intensity analysis, and line intensity analysis, the result output includes: image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift One or more of output, Fourier analysis output, and video output.

Fig. 11 is a diagram illustrating a dark field image change process of a collected sample according to an embodiment of the present disclosure.

Using a setting program, the sample changes can be visually displayed by video, and the obtained results are shown in Figure 11, which shows the corresponding dark field image output at zero time, 170 picoseconds (ps), 230 ps and 370 ps respectively. Video output includes the following:

The reference image A is used as the reference image B after the noise is removed, and the original image is calibrated with the reference image B after the noise is removed, and the video is output;

The reference image A is denoised and processed by the median filter as the reference image C, the original image is denoised and the position of the reference image C is calibrated, and the video is output after the median filter process;

The reference image A is used as the reference image B after denoising, the original image is calibrated with the reference image B after denoising, and the difference between the image position and the reference image B is processed after the image position is calibrated, and the video is output;

The reference image A is denoised and processed by the median filter as the reference image C. The original image is calibrated with the reference image C after denoising.

The image intensity output can select one or more pixels in the image, compare the pixel value changes under different delays, and perform Fourier transform on the pixel value change curve to obtain the intensity change frequency distribution. Either select pixels and output curves in a certain area around a certain position in the image, or rotate the image, perform multi-pixel superposition line intensity output on a certain position in the image, mark the position of the line intensity analysis area in the image, and output the two-dimensional result of the line intensity and 3D results. The cross-correlation value output includes the change curve of the maximum cross-correlation value of the image after the noise is removed and the reference image B, and the change curve of the maximum cross-correlation value of the image after the noise is removed and the reference image B after filtering.

The formula for calculating the cross-correlation value is as follows:

where the contrast C _x,y (t) is defined as:

为延时时间t时图像的平均像素强度。Among them, time t represents the laser pulse delay t when the one-dimensional translation stage is at the specified position, t' represents the time of the selected reference image, and I _{x, y} (t) is the delay time of the (x, y) position in the image. The pixel intensity of t, while

is the average pixel intensity of the image at the delay time t.

FIG. 12 is a standard deviation analysis result of a time-resolved dark field image according to an embodiment of the present disclosure.

Based on the output video of the analysis program of the present disclosure, quantitative analysis is performed on all pictures. Standard deviation analysis can obtain the change of data dispersion. Analyze the obtained series of images to obtain the area with the most significant change in pixel intensity in the particle area, and perform standard deviation analysis on the intensity of each pixel in the image. The result is shown in Figure 12. The brightness in the figure represents the intensity of the intensity change. Based on this, select one of the corner areas to observe the intensity change process. Fig. 13 is a time-resolved dark field image intensity change curve in a certain area according to an embodiment of the present disclosure. As shown in Fig. 13, the abscissa is the delay time of the pump laser pulse relative to the detection electron pulse, and the ordinate is the dark field Like the intensity average of the selected area, a clear intensity oscillation process can be observed, which is due to the pump laser excitation of the lattice oscillation in the sample, including the phonon coupling between the gold particles and the graphene substrate, resulting in a frequency of G Hz high-frequency oscillation, the crystal lattice direction changes, resulting in changes in the intensity of the dark field.

third embodiment

In a third exemplary embodiment of the present disclosure, an application of the above-mentioned method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system is provided.

In some embodiments, the method can be applied to lattice dynamics.

The disclosed method mainly reflects a single diffraction contrast. Nanoparticles (such as gold particles) are excited by the pump laser. After the electrons in the sample gain energy in the femtosecond order, the internal electrons interact with the phonons, resulting in a lattice temperature Elevated, according to the Debye-Waller effect, the intensity in the dark field image changes and thus the sample diffraction changes. At the same time, the increase in temperature causes changes such as expansion and tilt of the sample lattice, which also causes changes in the diffraction of the sample, and thus changes in the intensity of the dark field image. Therefore, the diffraction contrast (diffraction contrast) of the time-resolved dark-field image in the disclosed ultrafast process contains two effects, and can be used for the research of two different processes. The present disclosure has very good contrast and spatial resolution, and can directly observe the different change processes inside the gold nanoparticles, so the time-resolved dark field image contrast obtained by the present disclosure is more obvious, and the spatial resolution is higher, which can be observed Dynamics of lattice vibrations and phonon interactions in nanoscale samples in real space.

In some embodiments, compared with the bright field mode of the ultrafast transmission electron microscope, the present disclosure can select different diffraction spots of the sample for imaging, so as to obtain information on changes in different crystal planes, as shown in Figure 7B, which is the diffraction pattern of the Au nanoparticle sample, including Au For the diffraction spots of particles and substrate graphene, the {220} crystal plane of Au nanoparticles is selected as the diffraction spot imaging, and other diffraction spots can also be selected for imaging, such as {200}{400}.

In some examples, the substrate will affect the ultrafast process. Depending on the substrate, the ultrafast action behaves differently. The present disclosure can study the substrate scattering signal during the ultrafast action. At the same time, the present disclosure includes phonon interactions, which can be Indirectly reflects the interaction between the sample and the substrate in the ultrafast, so the present disclosure can study the influence of different substrates.

In reciprocal space, large objective apertures will contain more angles of scattered electrons, so this disclosure includes both the diffraction contrast signal of crystalline samples and the thermal scattering signal of amorphous regions, so it can also be used to study substrates Effects on ultrafast processes.

In some embodiments, the photogenerated electrons converge on the sample in an approximate converging beam mode to obtain approximate converging beam diffraction of the sample. The aperture of the objective lens is selected to cover the diffraction spot. The larger the aperture of the objective lens, the larger the angle will be included in the dark field image. According to the size of the objective lens aperture, the dark field image formed contains thermally scattered electrons at different angles, and different ranges of thermally scattered electrons can be selected for imaging. For example, the aperture size of the objective lens within the range of 20 microns to 40 microns can be used .

In some embodiments, the present disclosure can clearly show the existence of defects in the sample, and it is more obvious for the phonon interaction process, and the influence of defects on the interaction between electrons and phonons can be studied, such as point defects, dislocations, etc., or different The interaction between crystal grains, or the influence of different phases, the disclosure can directly characterize the change process of the heterogeneous region inside the material.

In some examples, the present disclosure can be used to study the change process of different regions inside metal nanoparticles, and the present disclosure can directly observe the change process of specific regions with high spatial resolution. In some embodiments, this disclosure can also study the internal change process of materials with different composition elements, different structures, and different shapes. The material shape can be one-dimensional materials, such as nanowires, nanorods, nanobelts, etc., or two-dimensional materials. Dimensional materials, nano-films, etc., are suitable for the research of various materials, such as metal elements and alloys, such as gold, silver, copper, etc. and their alloys, transition metal compounds, zinc oxide, molybdenum oxide, molybdenum sulfide, tungsten selenide, etc. The present disclosure is not limited to the above-mentioned substances.

The conventional TEM system requires electrons to irradiate the sample with an approximately parallel beam, and the minimum size of the objective lens diaphragm is used to reduce the scattered electrons in the dark field image. Since the photogenerated electrons irradiate the sample in the form of pulses in the ultrafast mode, the number of electrons is far less than that of the conventional electron microscope. It is difficult to directly apply this method to the ultrafast transmission electron microscope, and the obtained dark field image contrast is poor, and the requirements for the sample size are relatively high.

The method and application for obtaining time-resolved dark-field images based on an ultrafast transmission electron microscope system proposed in this disclosure adopts high-convergence angle incident beam imaging, adopts a large-sized objective lens diaphragm (such as 20 microns to 40 microns), and uses diffracted electrons as signals For imaging, compared with the bright field image of the ultrafast transmission electron microscope, the dark field image with opposite contrast reduces the background signal, thereby improving the signal-to-noise ratio of the collected signal, and can more directly observe different regions inside the sample compared to the diffraction mode signal With high spatial resolution, it expands the scope of ultrafast electron microscope dark field method to characterize samples, and can analyze the details of contrast changes after particles are excited by laser light. The time-resolved dark-field image contrast obtained in the present disclosure is higher, and the lattice change is more obvious, and the dynamic change process of the sample in an ultrafast time scale can be observed, such as picoseconds, nanoseconds, or microseconds, etc. At the same time, the present disclosure contains electron-phonon interaction information and lattice direction tilt information, and also includes thermally scattered electrons, which can be used for thermally scattered electron signal analysis. The disclosed image acquisition process adopts automatic acquisition, and different reference modes can be selected, and ensures that the acquisition process reduces external interference and improves acquisition efficiency. This disclosure also proposes corresponding data processing and analysis programs, which can analyze the collected data images in batches, perform drift correction on the sample position, perform noise removal and filtering processing on the image, and output single-pixel intensity analysis, regional pixel intensity analysis, and line intensity analysis. Analysis, output video, etc.

Unless specifically described or steps that must occur sequentially, the order of the above steps is not limited to that listed above and may be changed or rearranged according to the desired design. Moreover, the above-mentioned embodiments can be mixed and matched with each other or with other embodiments based on design and reliability considerations, that is, technical features in different embodiments can be freely combined to form more embodiments.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present disclosure in detail. It should be understood that the above descriptions are only specific embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims (10)

1. A method for obtaining a time-resolved dark field image based on an ultrafast transmission electron microscope system, characterized in that it comprises: Step S12: In the thermal electron mode, adjust to obtain the approximate double-beam diffraction of the sample and obtain a dark field image by trapping the diffraction spot with an objective lens diaphragm; Step S13: In the photoelectron mode, converge the electron beam spot at a larger convergence angle, and obtain the convergent beam diffraction of the sample in the diffraction mode; in the dark field mode, based on the inclination angle of the incident electron beam in the thermal electron mode, use the objective lens diaphragm Select the diffraction spot to obtain the time-resolved dark field image of the sample in the photoelectron mode, wherein the larger convergence angle makes the diffraction spot area in the photoelectron mode larger than that in the thermal electron mode; Wherein, step S12 comprises: Sub-step S12a: select the sample area to be characterized in the thermal electron mode; Sub-step S12b: Enclose the sample with a selective aperture, enter the diffraction mode, adjust the diffraction spots to the center of the screen, and adjust the tilt angle of the sample so that the diffraction pattern under the electron microscope system is double-beam diffraction; Sub-step S12c: enter the dark field mode, adjust the incident angle of the incident electron beam so that the corresponding diffraction spot is located at the position of the original transmission spot, and record the current tilt angle of the incident electron beam; Sub-step S12d: select the aperture of the objective lens to cover the diffraction spot, and exit the diffraction mode to obtain a dark field image; Sub-step S12e: fine-tuning the sample tilt angle according to the dark field image, so that the region of interest is a bright region; Alternately execute the above sub-steps S12b~S12e until the target area of the obtained dark field image is in a bright state, and the diffraction spots are in the double-beam diffraction mode at the same time; Described step S13 comprises: Sub-step S13a: In the photoelectron mode, converging the photo-generated detection electron pulses on the sample, close to the converging beam mode; Sub-step S13b: enter the diffraction mode, and obtain the approximate converging beam diffraction of the sample area under the photo-generated detection electron pulse; Sub-step S13c: enter the dark field mode, adjust the electron beam tilt angle to the same angle according to the incident electron beam tilt angle recorded in the thermal electron mode, move the corresponding diffraction spot to the original transmission spot position, and adjust the spot position to make the diffraction spot brightness the highest; Sub-step S13d: Select the objective aperture to cover the central diffraction spot, and the size of the objective aperture satisfies: about 90% of the electrons in the diffraction spot pass through the objective aperture or the imaging device shows that the size of the objective aperture accounts for 75% of the diffraction spot size. More than %; exit the diffraction mode and get a dark field image; Sub-step S13e: adjusting the position of the electron beam and adjusting the size of the electron beam spot to obtain an optimal dark field image. 2 . The method according to claim 1 , wherein the objective lens diaphragm is a large-sized objective lens diaphragm, and the aperture of the large-sized objective lens diaphragm is between 10 microns and 100 microns. 3. The method according to claim 2, wherein the aperture of the objective lens diaphragm is between 20 microns and 40 microns. 4. The method according to claim 1, further comprising: before step S12: Step S11: In the ultrafast transmission electron microscope system, adjust the pump laser focus position to focus on the sample position, and the probe laser focus on the filament to generate probe electron pulses. 5. The method according to claim 4, wherein said step S11 comprises: Before the pump laser enters the sample chamber of the TEM system, add a visible light reflector to reflect the pump laser to the beam analyzer, adjust the position of the beam analyzer to find the focal position of the pump laser and the size of the focused spot, and obtain the actual focus point and focus lens. distance and focus spot size; According to the focus position, the position of the focus lens in the pump light path is adjusted through the three-dimensional translation stage; Putting the carbon film in the ultrafast transmission electron microscope, using the minimum energy pump light to excite the position of the carbon film, so that the excitation position of the pump laser coincides with the position of the photogenerated detection electron; and Finely adjust the focus lens position to find the best focus position. 6. The method according to claim 1, characterized in that, after the step S13, further comprising: Step S14: using the automatic acquisition module to acquire images, and the automatic acquisition module realizes its functions through software, or hardware, or a combination of hardware and software. 7. The method according to claim 6, characterized in that, in step S14, the time-resolved dark-field image is automatically collected and saved by controlling the one-dimensional electric displacement stage and the imaging device of the transmission electron microscope system, and the method of automatically collecting and saving include: Sub-step S141a: set the ultrafast transmission electron microscope system according to the user setting parameters; Sub-step S141b: the automatic acquisition module controls the one-dimensional electric displacement stage to move to a designated position; adjusts the optical path of the pump laser, and controls the interval between the arrival of the pump laser pulse at the sample and the arrival of the detection electron pulse at the sample; Sub-step S141c: the automatic collection module collects the image according to the parameters, and assigns an ID to the image, and saves the image to a local file; Sub-step S141d: determine whether to collect a reference image, if yes, execute sub-step S141e, otherwise execute sub-step S141g; Sub-step S141e: Control the one-dimensional electric translation platform to move from the current position P to the negative time position, the above-mentioned current position P is used as the original position of reference, and the reference image is collected and saved; Sub-step S141f: Control the one-dimensional electric displacement platform to return to the original position P, re-acquire and save the image; Sub-step S141g: the system judges whether the acquisition process is completed, and if so, ends the acquisition process, otherwise controls the one-dimensional electric displacement platform to the next position to acquire images; Sub-step S141b to sub-step S141g are repeated to finally complete the acquisition process of all images. 8. The method according to claim 6, wherein the step S14 controls the pump laser by controlling the mechanical shutter switch in the optical path of the pump laser to collect reference images and excitation images; including: Sub-step S142a: Control the imaging system of the transmission electron microscope system according to the parameters set by the user; Sub-step S142b: the automatic acquisition module controls the mechanical shutter to close, and the sample is in an unexcited state; Sub-step S142c: the automatic acquisition module controls the one-dimensional translation stage to move to a designated position; Sub-step S142d: the automatic collection module collects the reference image according to the parameters, assigns an ID to the image and saves the image to a local folder; Sub-step S142e: the automatic acquisition module controls the opening of the mechanical shutter, the pump laser is introduced into the sample area of the transmission electron microscope system, and the sample is excited by the laser to produce instantaneous changes; Step S142f: The automatic collection module collects the excitation image of the sample according to the parameters, assigns an ID to the image and saves it to another local folder; Sub-step S142g: the system judges whether the acquisition process is completed, if yes, the acquisition process is ended, otherwise, the one-dimensional electric displacement platform is controlled to acquire images at the next position; Substep S142b~substep S142g are repeated, and the sample state when the sample is excited by the pump laser pulse and the sample state when it is not excited are collected as reference signals at different intervals to complete the acquisition process of all images. 9. The method according to claim 6, wherein said step S14 further comprises: Perform batch processing on the collected images; Wherein, the batch processing of the collected images includes: one or more of image averaging as a reference image, image offset calibration, image intensity analysis and result output; The image intensity analysis includes: one or more of single pixel intensity analysis, area intensity analysis, and line intensity analysis; The result output includes: one or more of image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift output, Fourier analysis output and video output. 10. A method as claimed in any one of claims 1 to 9 is used to analyze the details of the contrast change after the nanoparticle is excited by the laser, and to characterize the lattice structure relaxation of different material lattice orientations in the ultrafast time scale and the application of resonance dynamic process, characterized in that the time-resolved dark-field images obtained by the method are used to analyze the details of contrast changes of nanoparticles after being excited by laser light, and to characterize different materials in ultrafast time scales Lattice structure relaxation and resonance dynamics of lattice orientation.

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