CN111982945B - Method for acquiring time resolution dark field image based on ultra-fast transmission electron microscope system and application - Google Patents
Method for acquiring time resolution dark field image based on ultra-fast transmission electron microscope system and application Download PDFInfo
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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
Technical Field
The invention belongs to the technical field of dark field characterization of electron microscopy and ultra-fast electron microscopy, relates to a method and application for acquiring a time-resolved dark field image based on an ultra-fast transmission electron microscope system, and particularly relates to a method and application for acquiring a high-contrast ultra-fast time-resolved dark field image based on an ultra-fast transmission electron microscope system.
Background
Transmission electron microscopes are important material characterization tools, transmission electron microscope technologies are rapidly developed, the spatial resolution of the transmission electron microscope technology is in the sub-angstrom level at present, experimental requirements are greatly met, and the change process of the material characterization by the transmission electron microscope is an important development trend at present, such as in-situ transmission electron microscopes, 4D ultra-fast transmission electron microscopes and the like.
The ultra-fast transmission electron microscope is combined with an ultra-fast optical means, has the advantages of high spatial resolution and ultra-fast optical high time resolution of the transmission electron microscope, breaks through the limit of the acquisition speed of a Charge Coupled Device (CCD) camera, and realizes the dynamic change process of a material structure in the range of femtosecond to microsecond, thereby revealing the change of atomic scale in the physical or chemical process. Ultra-fast transmission electron microscopy has developed a variety of characterization techniques to date that analyze the plasma effects of materials based on image or diffraction information, or in combination with Electron Energy Loss Spectroscopy (EELS).
At present, based on ultrafast transmission electron microscope data acquisition, a bright field image and diffraction spots are taken as main materials, the dynamic change process of the interior of a material after the material is excited by pulse laser is studied, in 2018, some researches are based on the bright field image of the ultrafast transmission electron microscope, the lattice vibration process generated by pumping inside the plasma gold nanoparticles and among the particles is studied through the change of gold particle contrast, but the bright field image contrast change signals are mainly transmitted electrons under the bright field image, and compared with the transmitted electron signals, the contrast change is insignificant, meanwhile, the imaging electron quantity in the ultrafast transmission electron microscope is lower than that of a conventional transmission electron microscope, the obtained result has a poor signal-to-noise ratio, the lattice change process of a sample after laser excitation cannot be obviously revealed finally, and the bright field image obtained through shooting by using a larger electron beam spot and a minimum-size objective lens diaphragm in an optoelectronic mode is shown in a figure 1.
In the dark field image, diffraction electrons are adopted for imaging, compared with the bright field image, the contrast is opposite, the sample area becomes a bright area, the substrate area becomes a dark area, the background signal is weakened, the change of the signal intensity of the sample is more obvious, the signal to noise ratio is greatly improved relative to the bright field image, and the change of the sample in the ultrafast process can be more intuitively shown relative to the bright field image of the ultrafast system.
In a conventional transmission electron microscope, shooting a dark field image often requires that an electron beam irradiates a sample in an approximately parallel state, and a convergence angle is smaller, so that the minimum-size objective diaphragm can be used for shooting the dark field image, diffraction electrons are ensured to penetrate, and most (inelastic) scattered electrons are blocked, but the modes cannot be directly applied to an ultrafast transmission electron microscope. In the ultra-fast transmission electron microscope, electrons are excited by laser pulses in a pulse form, and the number of generated electrons is far less than that of a conventional electron microscope, so that the contrast of the obtained dark field image is very poor, and the dark field image map obtained by shooting with a larger electron beam spot and an objective diaphragm with the smallest size in an optoelectronic mode is shown in figure 2.
At present, the work of a dark field image mode based on an ultrafast transmission electron microscope is based on the mechanical movement of an observation sample, the working application range based on the dark field image is smaller, the selection of the sample is limited greatly, and the characterization of samples with small size, such as nano particles, cannot be applied. In addition, the image contrast obtained by representing a large-size sample by using a dark field image in the existing few researches is poor, the obtained dark field image does not analyze the intensity change process of the time-resolved dark field image in detail, the change process of the contrast cannot be obviously reflected, and the method cannot be applied to accurate dynamic analysis. There is therefore a need for a way to analyze the dynamic course of a sample in an ultrafast time scale that is intuitive and has a high signal-to-noise ratio.
Disclosure of Invention
First, the technical problem to be solved
The disclosure provides a method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system and application thereof, so as to at least partially solve the technical problems set forth above.
(II) technical scheme
According to one aspect of the present disclosure, there is provided a method for acquiring a time-resolved dark-field image based on an ultrafast transmission electron microscope system, including: step S12: in a hot electron mode, adjusting to obtain approximate double-beam diffraction of a sample, and sleeving a diffraction spot by adopting an objective diaphragm to obtain a dark field image; step S13: under the photoelectron mode, converging the electron beam spots at a larger converging angle, and obtaining the converging beam diffraction of the sample under the diffraction mode; the incident electron beam inclination angle based on the thermoelectric mode in the dark field mode adopts the objective diaphragm to select diffraction spots, so that a time resolution dark field image of the sample in the photoelectron mode is obtained, wherein the larger convergence angle enables the diffraction spot area in the photoelectron mode to be larger than that in the hot electron mode.
The objective diaphragm is a large-size objective diaphragm, and the diaphragm aperture of the large-size objective diaphragm is between 10 micrometers and 100 micrometers; preferably between 20 and 40 microns.
Wherein, before step S12, the method further comprises: step S11: in the ultra-fast transmission electron microscope system, the focusing position of the pumping laser is adjusted to focus on the sample position, and the detection laser focuses on the filament to generate detection electronic pulse.
In some embodiments, step S11 includes: before pump laser enters a sample chamber of a transmission electron microscope system, adding a visible light reflector to reflect the pump laser to a beam analyzer, and adjusting the position of the beam analyzer to find the focusing position and the focusing spot size of the pump laser to obtain the actual distance between a focusing point and a focusing lens and the focusing spot size; according to the focusing position, adjusting the position of a focusing lens in a pumping light path through a three-dimensional displacement table; a carbon film is put into an ultrafast transmission electron microscope, and the position of the carbon film is excited by pumping light with minimum energy, so that the excitation position of the pumping laser is overlapped with the position of photo-generated detection electrons; and fine adjusting the focus lens position to find the best focus position.
In some embodiments, step S13 further comprises, after: step S14: an automatic acquisition module is adopted to acquire images, and the automatic acquisition module realizes the functions thereof in a mode of software, hardware or a combination of hardware and software. Step S14, the time resolution dark field image can be automatically acquired and stored by controlling the one-dimensional electric displacement table and the transmission electron microscope system imaging device; or the pump laser is controlled by controlling a mechanical shutter switch in a pump laser light path, and a reference image and an excitation image are acquired.
In some embodiments, step S14 further comprises, after: and carrying out batch processing on the acquired images.
In some embodiments, batch processing the acquired images includes: image averaging as one or more of reference images, image offset calibration, image intensity analysis, result output, etc.; wherein the image intensity analysis comprises: one or more of single pixel intensity analysis, area intensity analysis, line intensity analysis; wherein the result output comprises: one or more of image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift amount output, fourier analysis output, and video output.
According to another aspect of the present disclosure, there is also provided an application of the time-resolved dark-field image obtained by the method of the present disclosure in analyzing contrast change details of nanoparticles after excited by laser, and in characterizing lattice structure relaxation and resonance dynamics processes of different material lattice orientations in an ultrafast time scale.
(III) beneficial effects
According to the technical scheme, the method for acquiring the time resolution dark field image based on the ultra-fast transmission electron microscope system and the application of the method have the following beneficial effects:
1. The time resolution dark field image under the ultra-fast dimension is obtained by adopting high convergence angle incident beam imaging and adopting a large-size objective diaphragm and taking diffracted electrons as signals for imaging, compared with the ultra-fast transmission electron microscope bright field image, the dark field image with opposite contrast reduces background signals, and due to the combination of the high convergence angle and the large-size objective diaphragm, the signal to noise ratio of 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 diffraction mode signals, the high spatial resolution is achieved, the range of the sample represented by the ultra-fast electron microscope dark field mode is widened, and the contrast change details of particles after excited by laser can be analyzed. The time resolution dark field image obtained by the method is higher in contrast, more obvious in lattice change, capable of observing the dynamic change process of the sample in an ultrafast time scale, such as picoseconds, nanoseconds, microseconds and the like, and meanwhile, the method comprises electron and phonon interaction information and lattice direction tilting information, also comprises heat scattering electrons, and can be used for heat scattering electron signal analysis.
2. The image acquisition process adopts automatic acquisition, different reference modes can be selected, the external interference is reduced in the acquisition process, and the acquisition efficiency is improved.
3. The disclosure also provides a corresponding data processing and analyzing program, which can analyze collected data images in batch, correct drift of sample positions, remove noise and filter the images, output single-pixel intensity analysis, regional pixel intensity analysis, line intensity analysis, output video and the like.
Drawings
Fig. 1 is a diagram of a bright field image taken with a larger electron beam spot and a minimum size objective stop in the prior art photoelectron mode.
Fig. 2 is a dark field image map taken with a larger electron beam spot and a minimum size objective stop in prior art photoelectron mode.
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 map taken using a high convergence angle and large size objective stop in accordance with the method of the present disclosure.
Fig. 5 is a flowchart 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.
FIGS. 6A-6C are schematic diagrams illustrating determining a focal position from a carbon film ablated region, according to one embodiment of the present disclosure.
Fig. 7A-7D are schematic diagrams of an approximate dual beam diffraction and dark field image of a sample adjusted in thermionic mode according to one embodiment of the present disclosure.
Fig. 8A-8D are schematic diagrams illustrating the time resolved dark field image of a conditioned sample in optoelectronic mode according to one embodiment of the disclosure.
Fig. 9 is a flowchart of image acquisition and saving by the automatic acquisition module for acquiring negative time reference images according to an embodiment of the present disclosure.
Fig. 10 is a flowchart of image acquisition and saving 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 process of acquiring a dark field image of a sample according to an embodiment of the present disclosure.
Fig. 12 is a standard differential analysis of a time resolved dark field image according to one embodiment of the present disclosure.
Fig. 13 is a graph showing a time-resolved dark-field image area intensity variation according to an embodiment of the present disclosure.
[ symbolic description ]
01-a laser; 02-one-dimensional electric displacement table;
03-a mechanical shutter; 04-filament;
05-sample; 06-ultra-fast transmission electron microscope/electron microscope cavity;
07-an imaging device.
Detailed Description
For the purposes of promoting an understanding of the principles and advantages of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. "between" includes endpoints.
In conventional transmission electron microscopy, the sample is in a stable state, the temperature is kept stable, and the dark field image mainly researches the non-uniformity inside the sample, providing static characterization of the sample structure, such as the position of internal defects, the size of crystal grains or the difference of enriched particles in different areas, and the like, so that the non-uniform sample is often observed in the conventional electron microscopy. The time-resolved dark field image obtained based on the method has high contrast, high signal-to-noise ratio and high spatial resolution, and is a means for researching dynamic signals of internal structural changes of a specific area, for example, researching the action of phonons in a sample, a phonon propagation process, a process of tilting a lattice direction caused by the phonons, and the like, and has no requirement on whether the sample is uniform or not. The time resolved dark field image in this disclosure therefore represents a different meaning and process than conventional electron microscopy dark field images.
In this disclosure, the terms "proximate" and "approximately" mean equivalents within an allowable error range due to limitations of the instrument itself or limitations of experimental operation.
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.
An ultrafast transmission electron microscope system suitable for the method is introduced.
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 ultra-fast transmission electron microscope system of the present disclosure includes: the laser system is used for generating ultrashort pulse laser and dividing the ultrashort pulse laser into two parts, namely detection laser and pumping laser after passing through the beam splitter; a transmission electron microscope system (hereinafter also referred to as electron microscope system) including an electron microscope cavity 06, a filament 04, an electron microscope imaging device 07; and a one-dimensional electric displacement table 02, a three-dimensional displacement table and a mechanical shutter 03 which are arranged on the light path between the laser system and the transmission electron microscope system; the transmission electron microscope system can work in a thermoelectric mode, electron beam current is generated by heating a filament in a cavity of the electron microscope, detection laser can be electrically introduced into an electron gun to generate photo-generated pulse electrons, and the photo-generated pulse electrons are accelerated to pass through a sample area and finally imaged on an electron microscope imaging device; the pumping laser can be introduced into the electron microscope sample area to excite the sample to generate transient lattice morphology change; the three-dimensional displacement table adjusts the position of the focusing lens to focus the incident detection laser and the pump laser to the filament area and the sample area respectively; a one-dimensional electric displacement table for controlling the optical path of the pumping laser; and a mechanical shutter for controlling the switching of the pumping laser.
In this embodiment, referring to fig. 3, an ultrafast transmission electron microscope system includes: the laser device 01, the one-dimensional electric displacement table 02, the mechanical shutter 03, the ultra-fast transmission electron microscope 06 and the three-dimensional displacement table, wherein the ultra-fast transmission electron microscope 06 comprises a filament 04 and an imaging device 07, the filament 04 is used for generating detection electronic pulses, a sample 05 is placed in an area after acceleration of the detection electronic pulses, laser emitted by the laser device 01 is divided into two beams through a spectroscope after frequency multiplication, one beam of laser is used as a detection light source, namely the detection laser, and finally focused at the filament 04 in the ultra-fast transmission electron microscope 06 after frequency multiplication conversion again to generate detection electronic pulses, and the detection electronic pulses are accelerated through a cavity of the ultra-fast transmission electron microscope 06 and penetrate through the sample 05; the other laser is used as an excitation light source, called pump laser, and finally focused at a sample 05 in the ultra-fast transmission electron microscope 06 through the mechanical shutter 03. The filament 04, the sample 05 and the imaging device 07 are positioned on the same straight line, and the detection electronic pulse emitted by the filament passes through the sample 05 and then is imaged on the imaging device 07 of the ultra-fast transmission electron microscope 06.
In this embodiment, the ultrafast transmission electron microscope 06 may generate a thermal electron beam by heating the filament 04, or may generate a detection electron by introducing laser to irradiate the area of the filament 04 and excite.
In this embodiment, the three-dimensional displacement table is used for adjusting the position of the focusing lens at the inlet of the sample chamber of the ultra-fast transmission electron microscope system, and adjusting the position and the focusing area of the pump laser focused on the sample 05.
Fig. 4 is a dark field image map taken using a high convergence angle and large size objective stop in accordance with the method of the present disclosure. Fig. 5 is a flowchart 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 fig. 4, the time-resolved dark field image obtained by the method can represent small-size nanoparticles, and the application range of the time-resolved dark field image is widened.
The following describes a method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system in conjunction with the ultrafast transmission electron microscope system of the present disclosure, and referring to fig. 3 and 5, the method includes:
step S11: in the ultra-fast transmission electron microscope system, the focusing position of the pumping laser is regulated to focus on the sample position, and the detection laser is focused on the filament to generate detection electronic pulse;
in this embodiment, a preferred method for adjusting the focal position of the pump laser is provided based on the structure of the ultrafast transmission electron microscope system.
The method for adjusting the focusing laser comprises the following steps:
Before the pump laser enters a sample chamber of a transmission electron microscope system, adding a visible light reflector to reflect the pump laser to a beam analyzer, and adjusting the position of the beam analyzer to find the focusing position and the focusing spot size of the pump laser so as to obtain the actual distance between a focusing point and the focusing lens and the focusing spot size;
step two, according to the focusing position, the position of a focusing lens in a pumping light path is adjusted through a three-dimensional displacement table 02;
step three, a carbon film (for example, a 50-mesh carbon film) is placed in the ultrafast transmission electron microscope 06, and the position of the carbon film is excited by pumping light with minimum energy, so that the excitation position of pumping laser is overlapped with the position of photo-generated detection electrons;
and fourthly, finely adjusting the position of the focusing lens back and forth to find the optimal focusing position.
FIGS. 6A-6C are schematic diagrams illustrating determining a focal position from a carbon film ablated region, according to one embodiment of the present disclosure.
When the carbon film is positioned in front of the focus lens, the ablated area is as shown in fig. 6A, when the carbon film is positioned behind the focus of the focus lens, the ablated area is as shown in fig. 6B, and when the carbon film is positioned at the focus of the focus lens, the ablated area is as shown in fig. 6C, and is approximately perfectly circular.
Specifically, the external optical path of the ultra-fast transmission electron microscope is accurately adjusted based on the following operation steps, so that the pump laser and the detection laser are focused at accurate positions in the ultra-fast transmission electron microscope, namely, the pump laser and the detection laser are both focused on a sample, and the control of the focusing area can be realized. Step one, putting a 50-mesh carbon film into an electron microscope system as a sample, finding small particles as a reference object in a hot electron mode, and adjusting the particles to be displayed on an electron microscope imaging device 07 under a proper multiple; step two, adjusting the magnification of the ultra-fast transmission electron microscope system to 50 times to obtain the position of the particles under the magnification; step three, a low-contrast area can be ablated on the carbon film by adopting low-power pump laser, and the focusing area of the pump laser on the carbon film is regulated to enable small particles to be positioned at the center of the low-contrast area, so that the superposition of the focusing position of the pump laser and a detection electronic detection area is completed; and step four, adjusting the three-dimensional displacement table to enable the focusing lens to be displaced forwards and backwards to change the focusing position, and obtaining the optimal focusing lens position according to the final shape of the ablation area.
In some embodiments, a chemical synthesis gold triangular nanoprism is selected as a sample, a graphene copper mesh is selected as a substrate, and a method based on the present disclosure may be used to characterize lattice dynamics of gold nanoplatelets.
Step S12: in the hot electron mode, adjusting to obtain an approximate double-beam diffraction and dark field image of the sample;
FIGS. 7A-7D are schematic diagrams illustrating an approximate dual-beam diffraction and dark-field image of a sample adjusted in a thermionic mode according to one embodiment of the present disclosure, wherein FIG. 7A is a bright-field image map of the sample in thermionic mode; FIG. 7B is an approximate dual beam diffraction pattern of a sample modulated under hot electrons; FIG. 7C is a graph showing the selected objective lens after the diffraction spot is covered by the diaphragm; fig. 7D shows the final dark field image obtained in hot electron mode.
Referring to fig. 7A to 7D of the drawings, in this embodiment, the method for adjusting the orientation (with axis) of the electron microscope sample to obtain a dark field image in the hot electron mode includes the following sub-steps:
substep S12a: selecting a suitable sample region in hot electron mode;
in this embodiment, the filament 04 in the ultrafast transmission electron microscope 06 is heated to a thermal electron beam state, and a suitable sample region is selected in a thermal electron mode, for example, as shown in fig. 7A, a suitable particle sample is found, and pump laser is introduced into the sample 05 region of the transmission electron microscope system.
Substep S12b: the sample is sleeved by adopting a selected area diaphragm, a diffraction mode is entered, diffraction spots are adjusted to the center of a screen, and the inclination angle of the sample is adjusted to enable the diffraction pattern to approximate double-beam diffraction under an electron microscope system, so that no interaction is basically caused between the diffraction beam and the transmission beam;
in this embodiment, a selected area diaphragm is used to cover the sample, enter a diffraction mode, adjust a diffraction spot to the center of the screen, adjust the tilt angle of the sample, and make the sample diffract in the diffraction mode to approach to a double-beam diffraction mode, as shown in fig. 7B, in which a diffraction spot pattern obtained by the sample corresponding to a chemical synthesis gold triangle nano prism is illustrated, and the diffraction spot circled after calibration corresponds to an Au (220) crystal face.
It is particularly emphasized that in the present disclosure, it is desirable that the diffraction mode be a dual beam diffraction mode, which is different from the operation of a conventional electron microscope dark field image. In the conventional electron microscope dark field image, a sample diffraction spot is obtained, and a double-beam diffraction mode is not necessarily adopted.
Substep S12c: entering a dark field mode, adjusting the incident angle of an incident electron beam to enable a corresponding diffraction spot to be positioned at the original transmission spot, and recording the tilting angle of the current incident electron beam by a system;
in this sub-step S12c, the recorded current incident electron beam tilt angle is used in a subsequent step S13.
Substep S12d: selecting an objective diaphragm to cover the diffraction spots, and exiting the diffraction mode to obtain a dark field image;
in the present disclosure, a large-sized objective lens stop is used, and the minimum size of the stop aperture of the selected objective lens stop is greater than or equal to the objective lens stop size used in the prior art, where the stop aperture is between 10 micrometers and 100 micrometers, for example, in an example, an objective lens stop with a physical size of 20 micrometers may be used, and the corresponding collection half angle is about 7.6mrad, as shown in fig. 7C. Preferably, the objective aperture diameter (aperture) is 20 μm or more and 40 μm or less, for example, in a specific example, the 2# objective aperture is 20 μm and the 3# objective aperture is 40 μm.
In a conventional electron microscope, due to higher electron beam intensity, light spots are uniformly dispersed, light is ensured to be approximately irradiated on a sample in parallel, when the diffraction spots are selected by adopting the objective diaphragm, the diffraction spots are selected by adopting the minimum-size objective diaphragm, and the least heat scattering electron transmission is ensured. In some examples of the disclosure, the electron pulses have a lateral spread from the filament to the sample location due to space charge effects, the coherence is reduced, the edges of the formed diffraction spots are blurred with respect to the thermionic mode, and in the optoelectronic mode, due to the smaller number of electrons, the incident electron beam irradiates the sample with an approximately converging beam, the larger the converging angle of the incident electron beam, the larger the diffraction spot area is obtained in the reciprocal space, so that the diffraction spot area obtained in the photogenerated electron mode is larger than that of a conventional electron microscope, and based on the above factors, the objective aperture size needs to be large enough to ensure that most of the diffraction signal electrons penetrate, thereby ensuring that the obtained time-resolved dark-field image has sufficient signal strength. In the reciprocal space, the large-size objective diaphragm can contain more angle scattered electrons, so that the change of thermal scattered electron signals can be detected based on an amorphous region in a dark field image, and therefore, the diffraction contrast change of a crystal sample region can be studied in the dark field image, meanwhile, the scattering change of the amorphous region can be studied, and compared with the traditional electron microscope dark field image, the thermal scattered electron signal detection device contains more sample change information.
Substep S12e: and fine-tuning the sample tilting angle according to the dark field image, so that the region of interest is a bright area.
The above sub-steps S12b to S12e are alternately performed until the target area where the dark field image is obtained is in a bright state, and the diffraction spots are in a double-beam diffraction mode, so that the ideal dark field image is obtained, and the result is shown in fig. 7D.
In the process of converting from the hot electron mode to the photoelectron mode, the following method can be adopted for mode switching:
reducing the heating current of the filament 04 of the transmission electron microscope system to a athermal electron emission state, wherein the imaging device 07 cannot detect electrons based on the transmission electron microscope system;
and introducing detection laser into a filament 04 area of the transmission electron microscope system, focusing the detection laser on the center of the surface of the filament, adopting photoelectron pulse imaging to find a sample area, and readjusting the transmission electron microscope system until the sample obtains a bright field image without obvious aberration under the photoelectron pulse.
Step S13: under the photoelectron mode, converging the electron beam spots at a larger converging angle, and obtaining the converging beam diffraction of the sample under the diffraction mode; the incident electron beam inclination angle based on the thermoelectric mode in the dark field mode adopts the objective diaphragm to select diffraction spots to obtain a time resolution dark field image of the sample in the photoelectron mode, wherein the larger convergence angle enables the diffraction spot area in the photoelectron mode to be larger than that in the hot electron mode;
The objective lens stop in the diffraction spot is a large-size objective lens stop, and the objective lens stop in the diffraction spot is the same size as the objective lens stop in step S12.
In some examples of the disclosure, the number of photo-generated electrons is smaller than that of a conventional electron microscope, in order to improve brightness, the photo-generated electron beams are converged on a sample in an approximate converging beam mode, so that approximate converging beam diffraction of the sample is obtained, an objective diaphragm is selected to cover a diffraction spot, the larger the size of the objective diaphragm is, the more the number of transmitted heat scattering electrons is, the dark field image contains more angle heat scattering electrons, and according to the different sizes of the objective diaphragm, the corresponding formed dark field image contains heat scattering electrons with different angles, so that the time-resolved dark field image based on the disclosure can be used for research of heat scattering electrons with different angles.
Therefore, in the operation, electron beam expansion is caused due to electron coulomb repulsion in the process of electron from the electron gun to the sample, so that diffraction spots are transversely expanded, meanwhile, the number of electrons in a photoelectron mode is smaller than that in a thermal emission mode, in order to generate enough signal intensity, incident electrons need to be converged on gold particles at a large convergence angle, and the area of the diffraction spots is larger than that of the thermal electron mode. Based on the above factors, when the nanoparticle material such as gold nanoparticles is characterized, a large-size objective diaphragm is required to be adopted, most of diffracted electrons are ensured to permeate the objective diaphragm, and finally, the obtained time-resolved dark field image has enough signal intensity.
FIGS. 8A-8D are diagrams illustrating adjusting a time-resolved dark-field image of a sample in an optoelectronic mode, wherein FIG. 8A is a bright-field image map obtained by converging an incident beam in the optoelectronic mode, according to one embodiment of the present disclosure; FIG. 8B is an approximate converging beam diffraction pattern obtained in photoelectron mode; FIG. 8C is an approximate converging beam diffraction spot in an optical mode with an objective stop encasing the photoelectron; fig. 8D is a dark field image map obtained in photoelectron mode.
In some examples, a method of obtaining a time resolved dark field image in a photogenerated electronic mode includes the sub-steps of:
substep S13a: in the photoelectron mode, converging the photoproduction detection electronic pulse on the sample, approaching to the converging beam mode, converging the incident beam to obtain a bright field image map, and referring to FIG. 8A;
substep S13b: entering a diffraction mode to obtain approximate converging beam diffraction of a sample area under the photo-generated detection electronic pulse;
the resulting approximate converging beam diffraction pattern in photoelectron mode is shown in fig. 8B, and the converging angle may be calculated from the diffraction spots, for example, in this embodiment, the converging angle calculated from the diffraction spots is about 9.9mrad.
Substep S13c: entering a dark field mode, adjusting the electron beam to tilt by the same angle according to the incident electron beam tilting angle recorded by the hot electron mode, moving the corresponding diffraction spot to the original transmission spot position, and adjusting the spot position to enable the diffraction spot brightness to be highest;
Substep S13d: selecting a large-size objective diaphragm to cover the central diffraction spot, wherein the size of the objective diaphragm is large enough to ensure that most of diffracted electrons penetrate through the objective diaphragm, blocking the electrons of the penetrating beam, exiting the diffraction mode and obtaining a dark field image;
in this substep S13d, the objective aperture is used to cover the approximately converging beam diffraction spot spectrum in the photoelectron mode, as shown in fig. 8C, and the objective aperture is large enough to ensure that most of the diffracted electrons penetrate the objective aperture and block the penetrating beam electrons.
Substep S13e: adjusting the position of the electron beam, and adjusting the size of the electron beam spot to obtain an optimal dark field image;
the resulting dark field image map in photoelectron mode is shown with reference to fig. 8D.
Step S14: an automatic acquisition module is adopted to acquire images;
fig. 9 is a flowchart of image acquisition and saving by the automatic acquisition module for acquiring negative time reference images according to an embodiment of the present disclosure. The image acquisition process is described below with reference to fig. 9.
In some embodiments, the automatic acquisition module may control the one-dimensional motorized displacement stage 02 and the transmission electron microscope system imaging device 07 to automatically acquire and store the time-resolved dark field image. As shown in fig. 9, a script is written by adopting electronic microscope system imaging device control software Gatan Digital Micrograph software, the one-dimensional displacement table is controlled to move and the imaging device is controlled to collect images, and the automatic image collection flow is as follows:
Substep S141a: controlling the ultra-fast transmission electron microscope system according to user set parameters, wherein the user set parameters of the automatic acquisition program comprise one or more of the following parameters: the initial position, the final position, the stepping distance and the like of the one-dimensional electric displacement table, the exposure time of the imaging device of the transmission electron microscope system, the pixel value of the acquired image and the like.
Substep S141b: the automatic acquisition module controls the one-dimensional electric displacement platform to move to a designated position, adjusts the optical path of the pumping laser, and controls the interval time between the arrival of the pumping laser pulse at the sample and the arrival of the detection electronic pulse at the sample 05;
substep S141c: the automatic acquisition module acquires images according to the parameters, allocates IDs for the images and stores the images into a local file;
substep S141d: judging whether a reference image is acquired, if yes, executing a sub-step S141e, otherwise, executing a sub-step S141g;
sub-step S141e: controlling a one-dimensional electric displacement table to move from a current position P (a home position serving as a reference) to a negative time position b, and acquiring and storing a reference image;
substep S141f: controlling the one-dimensional electric displacement table to return to the original position P, and re-acquiring and storing the image;
substep S141g: the system judges whether the acquisition process is finished, if yes, the acquisition process is finished, otherwise, the one-dimensional electric displacement table is controlled to acquire an image at the next position;
And repeating the substeps S141b to S141g to finally complete the acquisition process of all dark field images.
Fig. 10 is a flowchart of image acquisition and saving by an automatic image acquisition module controlling a mechanical shutter according to an embodiment of the present disclosure.
In other embodiments, the automatic acquisition module may control a mechanical shutter switch in the pump laser light path to control the pump laser to acquire the reference image and the excitation image at each one-dimensional displacement table position.
Referring to fig. 10, at each one-dimensional displacement stage position, the automatic acquisition module can control the mechanical shutter switch in the pump laser light path to control the pump laser, and the process of acquiring the reference image and the excitation image is as follows:
sub-step S142a: and controlling the imaging system of the transmission electron microscope system according to the user setting parameters, wherein the user setting parameters of the automatic acquisition module are the same as the automatic acquisition module setting in the substep S141 a.
Sub-step S142b: the automatic acquisition module controls the mechanical shutter to be closed, pump laser cannot be introduced into a sample area of the transmission electron microscope system, and the sample is in an unexcited state;
sub-step S142c: the automatic acquisition module controls the one-dimensional displacement platform to move to a designated position;
sub-step S142d: the automatic acquisition module acquires a reference image according to the parameters, allocates an ID for the image and stores the image into a local folder;
Sub-step S142e: the automatic acquisition module controls the mechanical shutter to open, pump laser is introduced into a sample area of the transmission electron microscope system, and the sample is excited by the laser to generate instantaneous change;
step S142f: the automatic acquisition module acquires the sample excitation image according to the parameters, allocates an ID for the image and stores the ID in another local folder;
substep S142g: and the system judges whether the acquisition process is finished, if yes, the acquisition process is finished, and otherwise, the one-dimensional electric displacement table is controlled to acquire an image at the next position.
And repeating the substeps S142b to S142g, collecting the sample state when the sample is excited by the pumping laser pulse and the sample state when the sample is not excited as reference signals at different intervals, and completing the whole image collection process.
The automatic acquisition module described above is described as being implemented in software, but the disclosure is not limited thereto. In other embodiments, the same functions may be implemented by different software, or hardware, or a combination of hardware and software.
Second embodiment
In a second exemplary embodiment of the present disclosure, a method of processing and analyzing a time-resolved dark-field image is provided.
For example, a batch process may also be performed on the obtained dark-field image. In some examples, batching each image includes: image ordering, noise removal, image averaging as one or more of reference images, image offset calibration, image intensity analysis, result output, and the like. Image intensity analysis, including one or more of single pixel intensity analysis, area intensity analysis, line intensity analysis, the resulting output includes: one or more of image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift amount output, fourier analysis output, and video output.
Fig. 11 is a diagram illustrating a process of acquiring a dark field image of a sample according to an embodiment of the present disclosure.
The sample change can be visually displayed in a video mode by using a setting program, and the obtained result is shown in fig. 11, and dark field image outputs corresponding to zero time, 170 picoseconds (ps), 230ps and 370ps are respectively displayed. Video output includes the following:
the reference image A is used as a reference image B after noise removal, and the original image is subjected to position calibration with the reference image B after noise removal, so that a video is output;
the reference image A is subjected to noise removal and median filtering treatment and then used as a reference image C, the original image is subjected to noise removal and position calibration of the reference image C, and the video is output after median filtering treatment;
the reference image A is used as a reference image B after noise removal, the original image is subjected to noise removal and is subjected to position calibration with the reference image B, and the difference value between the image position after the image position calibration and the reference image B is processed, so that a video is output;
the reference image A is used as a reference image C after noise removal and median filtering treatment, the original image is subjected to noise removal and position calibration with the reference image C, and the image position calibration is subjected to median filtering treatment and difference value treatment with the reference image C, so that a video is output.
The image intensity output can select one or more pixel points in the image, compare the pixel point value changes under different delays, and perform Fourier transform on the pixel point value change curve to obtain intensity change frequency distribution. Or selecting pixels and output curves in a certain area around a certain position of the image, or rotating the image, outputting multi-pixel superimposed line intensity at the certain position of the image, marking the position of an outgoing line intensity analysis area in the image, and outputting a two-dimensional result and a three-dimensional result of the line intensity. The cross-correlation value output comprises a cross-correlation value change curve of the image after noise removal and a reference image Bmax, and the cross-correlation value change curve of the image after noise removal is filtered and then is connected with the reference image Bmax.
The cross-correlation value calculation formula is as follows:
wherein contrast C x，y (t) is defined as:
wherein the time t represents the laser pulse delay t and t' represents the time of the selected reference image when the one-dimensional displacement table is at the designated position, I x，y (t) is the pixel intensity at the (x, y) position in the image at a delay time t, while
Is the average pixel intensity of the image at the time delay t.
Fig. 12 is a standard differential analysis of a time resolved dark field image according to one embodiment of the present disclosure.
And outputting video based on the analysis program disclosed by the disclosure, and carrying out quantization analysis on all pictures. The standard deviation analysis can obtain the data dispersion change, the obtained serial images are analyzed to obtain the region with the most obvious pixel intensity change in the particle region, and the standard deviation analysis is carried out on the intensity of each pixel of the images, and the result is shown in fig. 12. The intensity of the intensity change is represented by the brightness of the graph, and based on this, one corner region is selected to observe the intensity change process. Fig. 13 is a graph of a time-resolved dark-field image area intensity change, as shown in fig. 13, with the abscissa representing the delay time of the pump laser pulse relative to the probe electronic pulse, and the ordinate representing the average intensity of the selected area of the dark-field image, a significant intensity oscillation process is observed, because the pump laser excites lattice oscillations in the sample, including phonon coupling between gold particles and the graphene substrate, to generate high-frequency oscillations with a frequency of ghz, and the lattice direction changes, resulting in a change in dark-field intensity.
Third embodiment
In a third exemplary embodiment of the present disclosure, an application of the above method for acquiring a time-resolved dark field image based on an ultrafast transmission electron microscope system is provided.
In some embodiments, the method may be applied to lattice dynamics.
The method mainly reflects single diffraction contrast, nano particles (such as gold particles) are excited by pumping laser, after electrons in a sample acquire energy in the femtosecond order, the internal electrons interact with phonons to cause the temperature of a crystal lattice to be increased, and according to the Debye-Waller effect, the intensity in a dark field image is changed, so that the diffraction of the sample is changed. And meanwhile, the temperature rise causes the sample lattice to change such as expansion tilting and the like, and also causes the sample diffraction to change, so that the intensity in the dark field image changes. Therefore, the diffraction contrast (diffraction contrast) of the time-resolved dark-field image in the ultrafast process has two effects, and can be used for researching two different processes. The method has good contrast and spatial resolution, and can directly observe different change processes inside the gold nanoparticles, so that the time resolution dark field image contrast obtained by the method is more obvious, the spatial resolution is higher, and the dynamic process of lattice vibration and phonon interaction in a nanoscale sample in a real space can be observed.
In some embodiments, the present disclosure may select different diffraction spots of the sample for imaging, and thus obtain different crystal plane variation information, as shown in fig. 7B, which is a diffraction pattern of an Au nanoparticle sample, including Au particles and diffraction spots of the base graphene, select the {220} crystal plane of the Au nanoparticle as the diffraction spot for imaging, and may also select the remaining diffraction spots for imaging, e.g., {200} {400}.
In some examples, the substrate may have an effect on the ultrafast process, the ultrafast acting may behave differently based on the difference in substrate, the disclosure may study the base scattered signal during ultrafast acting while the disclosure includes phonon interactions that may indirectly reflect sample-to-substrate interactions in ultrafast, and thus the disclosure may study different substrate effects.
In reciprocal space, the large-sized objective stop will contain more angular scattered electrons, so the disclosure contains both diffraction contrast signals of crystalline samples and thermal scattering signals of amorphous regions, and thus can also be used to study the effect of substrates on ultrafast processes.
In some embodiments, the photo-generated electrons are converged on the sample in an approximately converging beam mode, so as to obtain the approximately converging beam diffraction of the sample, an objective diaphragm is selected to cover the diffraction spots, the larger the size of the objective diaphragm is, the larger angle of scattered electrons can be contained in the dark field image, the dark field image contains the heat scattered electrons with different angles according to the different sizes of the objective diaphragm, and the heat scattered electrons with different ranges can be selected for imaging, for example, the size of the objective diaphragm in the range of 20 micrometers to 40 micrometers can be used.
In some embodiments, the present disclosure may clearly show the presence of defects within a sample, and is more apparent to phonon interaction processes, and may investigate the effect of defects on electron-phonon interactions, such as point defects, dislocations, etc., or interactions between different grains, or the effect of different phases, and may directly characterize the process of variation of non-uniform regions within a material.
In some examples, the present disclosure may be used to study the course of change of different regions inside a metal nanoparticle, and the present disclosure may directly observe a specific region course of change with high spatial resolution. In some embodiments, the present disclosure may also study the internal variation process of materials of different constituent elements, different structures, and different morphologies, which may be one-dimensional materials, such as nanowires, nanorods, nanobelts, or the like, or two-dimensional material nanofilms, or the like, suitable for various material studies, such as elemental metals and alloys, such as gold, silver, copper, and the like, and alloys thereof, transition metal compounds, zinc oxide, molybdenum sulfide, tungsten selenide, and the like. The present disclosure is not limited to the above.
The conventional transmission electron microscope system requires electrons to irradiate a sample in an approximately parallel beam, and adopts a minimum-size objective diaphragm to reduce scattered electrons in a dark field image, and the number of electrons is far less than that of the conventional electron microscope because the photo-generated electrons irradiate the sample in a pulse mode in an ultrafast mode, so that the method is difficult to be directly applied to the ultrafast transmission electron microscope, the obtained dark field image has poor contrast, and the requirement on the size of the sample is higher.
The method for acquiring the time resolution dark field image based on the ultra-fast transmission electron microscope system and the application thereof adopt high-convergence-angle incident beam imaging, adopt a large-size objective diaphragm (for example, 20-40 microns), take diffraction electrons as signals for imaging, compared with the ultra-fast transmission electron microscope bright field image, the method has the advantages that the background signal is reduced by the dark field image with opposite contrast, the signal to noise ratio of acquired signals is improved, the change process of different areas inside a sample can be observed more directly relative to diffraction mode signals, the high spatial resolution is realized, the range of the sample represented by the ultra-fast electron microscope dark field mode is widened, and the contrast change details of particles after laser excitation can be analyzed. The time resolution dark field image obtained by the method is higher in contrast, more obvious in lattice change, capable of observing dynamic change processes of a sample in an ultrafast time scale, such as picoseconds, nanoseconds or microseconds, and meanwhile, the method comprises electron and phonon interaction information and lattice direction tilting information, also comprises heat scattering electrons, and can be used for heat scattering electron signal analysis. The image acquisition process adopts automatic acquisition, different reference modes can be selected, the external interference is reduced in the acquisition process, and the acquisition efficiency is improved. The disclosure also provides a corresponding data processing and analyzing program, which can analyze collected data images in batch, correct drift of sample positions, remove noise and filter the images, output single-pixel intensity analysis, regional pixel intensity analysis, line intensity analysis, output video and the like.
The order of the steps described above is not limited to the above list, and may be changed or rearranged according to a desired design, unless specifically described or the steps must occur sequentially. In addition, the above embodiments may be mixed with each other or other embodiments based on design and reliability, i.e. the technical features of the different embodiments may be freely combined to form more embodiments.
While the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be understood that the foregoing embodiments are merely illustrative of the invention and are not intended to limit the invention, and that any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the present disclosure are intended to be included within the scope of the present disclosure.
Claims (10)
1. The method for acquiring the time resolution dark field image based on the ultra-fast transmission electron microscope system is characterized by comprising the following steps of:
step S12: in a hot electron mode, adjusting to obtain approximate double-beam diffraction of a sample, and sleeving a diffraction spot by adopting an objective diaphragm to obtain a dark field image;
step S13: under the photoelectron mode, converging the electron beam spots at a larger converging angle, and obtaining the converging beam diffraction of the sample under the diffraction mode; the incident electron beam inclination angle based on the thermoelectric mode in the dark field mode adopts the objective diaphragm to select diffraction spots to obtain a time resolution dark field image of the sample in the photoelectron mode, wherein the larger convergence angle enables the diffraction spot area in the photoelectron mode to be larger than that in the hot electron mode;
Wherein, step S12 includes:
substep S12a: selecting a sample area to be characterized in a hot electron mode;
substep S12b: the sample is sleeved by adopting a selected area diaphragm, a diffraction mode is entered, diffraction spots are adjusted to the center of a screen, and the tilting angle of the sample is adjusted to enable the diffraction pattern to be double-beam diffraction under an electron microscope system;
substep S12c: entering a dark field mode, adjusting the incident angle of an incident electron beam to enable a corresponding diffraction spot to be positioned at the original transmission spot, and recording the tilting angle of the current incident electron beam;
substep S12d: selecting an objective diaphragm to cover the diffraction spots, and exiting the diffraction mode to obtain a dark field image;
substep S12e: fine-tuning a sample tilting angle according to the dark field image, so that the region of interest is a bright area;
the substeps S12 b-S12 e are alternately executed until a target area of the dark field image is in a bright state, and meanwhile, the diffraction spots are in a double-beam diffraction mode;
the step S13 includes:
substep S13a: in the photoelectron mode, converging the photoproduction detection electronic pulse on the sample, and approaching to the converging beam mode;
substep S13b: entering a diffraction mode to obtain approximate converging beam diffraction of a sample area under the photo-generated detection electronic pulse;
substep S13c: entering a dark field mode, adjusting the electron beam to tilt by the same angle according to the tilting angle of the incident electron beam recorded in the hot electron mode, moving the corresponding diffraction spot to the original transmission spot position, and adjusting the spot position to enable the diffraction spot brightness to be highest;
Substep S13d: selecting the objective diaphragm to cover the central diffraction spot, wherein the size of the objective diaphragm meets the following conditions: about 90% of the electrons in the diffraction spot penetrate through the objective diaphragm or the imaging device shows that the size of the objective diaphragm accounts for more than 75% of the size of the diffraction spot; exiting the diffraction mode to obtain a dark field image;
substep S13e: and adjusting the position of the electron beam, and adjusting the size of the electron beam spot to obtain the optimal dark field image.
2. The method according to claim 1, wherein the objective stop is a large-size objective stop having a stop aperture of between 10 and 100 microns.
3. The method according to claim 2, characterized in that the diaphragm aperture of the objective diaphragm is between 20 and 40 micrometers.
4. The method according to claim 1, further comprising, prior to step S12:
step S11: in the ultra-fast transmission electron microscope system, the focusing position of the pumping laser is adjusted to focus on the sample position, and the detection laser focuses on the filament to generate detection electronic pulse.
5. The method according to claim 4, wherein the step S11 includes:
before pump laser enters a sample chamber of a transmission electron microscope system, adding a visible light reflector to reflect the pump laser to a beam analyzer, and adjusting the position of the beam analyzer to find the focusing position and the focusing spot size of the pump laser to obtain the actual distance between a focusing point and a focusing lens and the focusing spot size;
According to the focusing position, adjusting the position of a focusing lens in a pumping light path through a three-dimensional displacement table;
a carbon film is put into an ultrafast transmission electron microscope, and the position of the carbon film is excited by pumping light with minimum energy, so that the excitation position of the pumping laser is overlapped with the position of photo-generated detection electrons; and
fine adjusting the focus lens position to find the best focus position.
6. The method according to claim 1, wherein after the step S13, further comprises:
step S14: an automatic acquisition module is adopted to acquire images, and the automatic acquisition module realizes the functions thereof in a mode of software, hardware or a combination of hardware and software.
7. The method according to claim 6, wherein the step S14 of automatically acquiring and storing the time-resolved dark field image by controlling the one-dimensional electric displacement stage and the transmission electron microscope imaging device comprises:
substep S141a: setting an ultrafast transmission electron microscope system according to user setting parameters;
substep S141b: the automatic acquisition module controls the one-dimensional electric displacement platform to move to a designated position; adjusting the optical path of the pump laser, and controlling the interval time between the arrival of the pump laser pulse at the sample and the arrival of the detection electronic pulse at the sample;
Substep S141c: the automatic acquisition module acquires images according to the parameters, allocates IDs for the images and stores the images into a local file;
substep S141d: judging whether a reference image is acquired, if yes, executing a sub-step S141e, otherwise, executing a sub-step S141g;
sub-step S141e: controlling a one-dimensional electric displacement table to move from a current position P to a negative time position, taking the current position P as a reference original position, collecting a reference image and storing the reference image;
substep S141f: controlling the one-dimensional electric displacement table to return to the original position P, and re-acquiring and storing the image;
substep S141g: the system judges whether the acquisition process is finished, if yes, the acquisition process is finished, otherwise, the one-dimensional electric displacement table is controlled to acquire an image at the next position;
and repeating the substeps S141b to S141g to finally complete the process of collecting all images.
8. The method of claim 6, wherein the step S14 is performed by controlling a mechanical shutter switch in an optical path of the pump laser to control the pump laser, and collecting the reference image and the excitation image; comprising the following steps:
sub-step S142a: controlling an imaging system of the transmission electron microscope system according to the user setting parameters;
sub-step S142b: the automatic acquisition module controls the mechanical shutter to be closed, and the sample is in an unexcited state;
Sub-step S142c: the automatic acquisition module controls the one-dimensional displacement platform to move to a designated position;
sub-step S142d: the automatic acquisition module acquires a reference image according to the parameters, allocates an ID for the image and stores the image into a local folder;
sub-step S142e: the automatic acquisition module controls the mechanical shutter to open, pump laser is introduced into a sample area of the transmission electron microscope system, and the sample is excited by the laser to generate instantaneous change;
step S142f: the automatic acquisition module acquires the sample excitation image according to the parameters, allocates an ID for the image and stores the ID in another local folder;
substep S142g: the system judges whether the acquisition process is finished, if yes, the acquisition process is finished, otherwise, the one-dimensional electric displacement table is controlled to acquire an image at the next position;
and repeating the substeps S142 b-S142 g, and collecting the sample state when the sample is excited by the pumping laser pulse and the sample state when the sample is not excited as reference signals at different intervals to complete the collection process of all images.
9. The method according to claim 6, wherein the step S14 further comprises:
carrying out batch processing on the acquired images;
wherein, the batch processing of the collected images comprises: image averaging as one or more of a reference image, image offset calibration, image intensity analysis, and outcome output;
Wherein the image intensity analysis comprises: one or more of single pixel intensity analysis, area intensity analysis, line intensity analysis;
wherein the result output comprises: one or more of image noise processing output, intensity curve output, position calibration output, image cross-correlation value output, image drift amount output, fourier analysis output, and video output.
10. Use of a method according to any one of claims 1 to 9 for analyzing details of contrast changes after laser excitation of nanoparticles and for characterizing lattice structure relaxation and resonance dynamics of lattice orientations of different materials in an ultrafast time scale, wherein time-resolved dark-field images obtained with said method are used for analyzing details of contrast changes after laser excitation of nanoparticles and for characterizing lattice structure relaxation and resonance dynamics of lattice orientations of different materials in an ultrafast time scale.
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