CN1862761A - Method and apparatus for receiving high stable energy filtering electronic microscopic image - Google Patents

Abstract

This invention relates to high stable energy filtration digital microscopic imaging receives method and its equipment. It belongs to energy filtration digital microscopic imaging technique field. Drift detection feedback method is used to eliminate the drift of different energy digital space distribution to energy selecting crack caused by high voltage fluctuation or interference of electromagnetic wave. So the energy filtration receive device can keep the filtrated electron energy stable all the time during signal acquisition process. Then energy selecting crack width is adjusted to make energy segment that contain sample excitatory feature spectrum information. So the high space distinguishing and high energy distinguishing energy filtration image can be got after accumulation.

Description

Method and device for receiving high-stable energy filtered electron microscopic images

technical field

The invention relates to a method and device for receiving high-stable energy-filtered electron microscopic images, belonging to the technical field of energy-filtered electron microscopic imaging.

Background technique

In recent years, energy-filtering electron microscopy has become an important tool for scientific research in the field of materials. It is developed based on the electron energy loss spectroscopy technique. The chemical properties or physical structure information of the sample can be obtained by using the electron energy loss spectrometer to detect the inelastically scattered electrons after interacting with the sample. Energy-filtered electron microscopy combines this chemical or structural information with spatial information, and can quantitatively or qualitatively obtain surface distribution maps that reflect specific chemical properties or physical structure information in the sample. The spatial resolution of energy-filtered electron microscopy can be better than 1nm, so it is an ideal tool for studying the chemical composition or structural information of materials at the nanometer scale. In addition, it can be combined with the transmission electron microscope to study various properties of the sample. Since energy-filtered electron microscopy is based on electron energy loss spectroscopy, it is an essential tool for the analysis of light elements. This technique has been widely used in the field of materials or biology.

Energy-filtered images can be obtained in STEM or conventional TEM. An energy-filtered image can be formed by adding a suitable electron energy filter to the light path of a conventional TEM. The electron energy filter first disperses the electron beams with different energies, selects the electron beams in a specific energy range through the energy selection slit, and then passes through the electron optical element and projects it to the detector for analysis. deal with. In the scanning transmission electron microscope, the electron beam is focused into a thin beam probe, and the electron probe can perform two-dimensional continuous scanning on the sample through the scanning coil placed in front of the sample, and a parallel detector is placed on the dispersion surface of the energy disperser. The electron beam intensity of the three-dimensional space quantity (x, y, E) can be obtained by continuous detection and recording of the energy loss spectrum of each scanning point. Then select a certain energy segment to process the three-dimensional energy spectrum record image, and then a surface distribution map corresponding to a certain element content can be obtained. This imaging method is called spectral imaging, which is currently the main imaging mode of energy-filtered imaging in scanning transmission electron microscopy.

There are two types of energy filtering that are used in TEM. One is the energy filtering technology in the lens barrel. The commonly used energy filters are omega type filter (see US Patent 4,740,704) and alpha type filter (see US Patent 4,760,261). The second is the energy filtering technology behind the lens barrel, which mainly adopts the method of adding a multipole mirror to eliminate aberrations behind the fan-shaped energy analyzer to obtain the energy filtering image (see US Patent 4,851,670). Compared with the energy filtering technology in the lens barrel, various important aberrations can be corrected due to the convenient addition of multipole lenses. In addition, the energy filter imaging device behind the lens barrel can be easily connected with various types of electron microscopes, including those with low aberration quality and extremely high accelerating voltage, and the energy filter in the lens barrel is compatible with these special electron microscopes. It is much more difficult to use together. Due to the above characteristics, the energy filtering method behind the lens barrel has been more widely used.

The series of energy-filtered images obtained in TEM mode can also be used to obtain electron energy loss spectra of localized parts of the material. This is done by systematically varying the energy filtering variables, obtaining an energy filtering image at each energy filtering volume. The localized electron energy loss spectrum of the region can be obtained by integrating the image intensity of a specific region in the energy-filtered image which can be arbitrarily defined. This energy loss spectrum is called image spectrum, which is widely used in the study of material valence band and electronic structure information.

Main Problems and Defects of Existing Energy-Filtering Electron Microscopy Technology

An important index to evaluate the performance of energy filtering images is the spatial resolution. In transmission electron microscopy, the spatial resolution obtained by elastic electron coherence imaging can be better than 1 angstrom; in contrast, the spatial resolution obtained by existing energy-filtered images is usually an order of magnitude worse. The reason for poor spatial resolution is mainly due to the influence of electromagnetic lens chromatic aberration, inelastic scattering electron off-position effect, spherical aberration of objective lens, sample drift, system noise, etc. on spatial resolution. In order to improve the spatial resolution of energy-filtered images, some related methods and devices have been proposed and applied.

Bernhard et al [see: Bernhard, et al. Automated spatial drift correction for EFTEM images series. Ultramicroscopy, Vol 102 (2004), 27-36] introduced digital imaging filters based on the traditional technique of correcting sample drift with cross-correlation algorithms and statistical evaluation techniques, a new method for automatic statistical correction of sample drift (SDSD) is proposed, which can precisely eliminate the degradation of imaging quality caused by sample drift.

Hiroki et al [see: Hiroki, et al.Attainable Resolution of Energy-Selecting ImageUsing High-Voltage Electron Microscope.J Electron Microscopy, Vol45 (1996): 79-84] add energy filter to FeCl ₃ made observations. Since the higher the accelerating voltage, the smaller the influence of the lens aberration, so this can improve the spatial resolution of the filtered image to a certain extent. Using this energy filtering technology to observe the energy filtering image of Cl _2,3 ionization edge of chlorine element shows that the spatial resolution of 1nm can be obtained.

In the post-lens energy filtering technology designed by Krivanek et al., the energy dispersion device uses a fan-shaped energy filter. Since the trajectory of the electron beam in the fan-shaped energy filter is asymmetrical with respect to the central mirror of the filter, there is Larger aberrations and distortions. People such as Koji [see U.S. Patent 6150657] introduce the energy filter (such as omega type filter) in the lens barrel into the energy filter technology behind the lens barrel, and make it rotate a certain angle so that the advancing direction of electron beam can resemble deflected 90 degrees like a fan diffuser. Since the electron beam trajectory of the energy filter in the lens barrel is symmetrical with respect to its central mirror, this method enables the energy filter imaging technology behind the lens barrel to save part of the multi-stage lens used to correct aberrations and distortions , so that the imaging electron optical path can be simplified.

However, the above methods and devices do not substantially improve the spatial resolution of the energy filter image, and the resolution of the inner shell electron loss filter image is only about 1nm. This is mainly because among the factors affecting energy resolution, chromatic aberration plays the most significant role, especially for high-energy loss energy filter images with energy loss greater than 100ev, chromatic aberration is an absolute factor restricting the performance of spatial resolution [see: O.L. Krivanek, et al. Spatial resolution in EFTEM elemental maps. Journal of electron microscopy, Vol 180, No 3, 1995: 277-287]. In addition to the intrinsic performance of the chromatic aberration coefficient of the electromagnetic lens, the influence of chromatic aberration is mainly related to the range of the scattering angle of the electron beam entering the image filter, that is, the energy interval width w determined by the energy selection slit. The larger the energy selection width, the more significant the influence of chromatic aberration. If the energy width w of the energy selection slit is reduced, the influence of chromatic aberration can be reduced theoretically, thereby improving the spatial resolution of the energy-filtered image, but in practice, this method does not necessarily improve the final resolution quality of the filtered image. The main reason is that the scattering cross-section of electrons in the inner shell of the atom is relatively small, and the high-energy loss signal formed by the inelastically scattered electrons is weak, so the resolution limit of the energy filter image will also be affected by the signal-to-noise ratio [see: Helmut Kohl, et al. The resolution limit for elemental mapping in energy-filtering transmission electron microscopy. Ultramicroscopy 59(1995): 191-194.]. The signal-to-noise ratio can be improved by increasing the incident dose of the electron beam, but even under the condition that the cold field emission gun with the highest brightness is selected as the illumination source, the electron beam current density that the detector finally receives and participates in imaging is very small. A more common method is to increase the signal-to-noise ratio by prolonging the exposure time (for example, more than 1 hour). However, due to the high-voltage fluctuations of the electron gun source, the interference of external electric fields and magnetic fields, or the mechanical vibration of the electronic energy filter device, the energy loss position of the entire received energy spectrum will drift, which may produce more than 1 eV in a short time energy drift. As shown in Figure 2, the drift of the energy relative to the position collected on the Jem2000ex electron microscope can be seen to produce a voltage fluctuation of up to 3 electron volts (ev) in just a few seconds.

Another important index to evaluate the performance of energy filtering image is energy resolution. The energy loss due to electrons is related to their electronic transitions within the atoms excited through the sample. The improvement of energy resolution enables us to subdivide the electronic transitions of different origins according to the transition energy, so as to obtain the surface distribution information of different electronic transitions in the sample through energy filtering images. For example, when the electron energy filter is 5-10 eV, we can distinguish the electronic transitions from the inner shell electron excitation of different atoms, and thus obtain the information of the chemical composition of the sample. The energy selection width is an important factor to determine the energy resolution, but due to the high-voltage fluctuation of the electron gun source, the interference of the external electric field and magnetic field, or the mechanical vibration of the electronic energy filter device, the spatial distribution of electrons on the energy dispersion surface or the conjugate plane will change. The position of the relative energy selection slit fluctuates, causing the actual energy resolution of the electron energy filtered image to be lower than its theoretical value.

The same problem also exists in the method of obtaining the local electron energy loss spectrum of the material by using a series of energy filtering images. Since the probability of inelastic electron scattering is very small, while being divided by energy loss and spatial distribution, it becomes even smaller. In order to obtain an energy-filtered image with a good signal-to-noise ratio, image reception needs a sufficiently long sampling time, so higher requirements are placed on the energy stability of the energy-filtering system during a series of image acquisitions. In addition, in order to ensure the one-to-one correspondence of the spatial regions of the energy-filtered images obtained in series, stringent requirements are placed on the stability of the mechanical and electronic components of the imaging system including the sample. When the stability of the system cannot meet the requirements, it is possible to detect and correct the small changes in the sampling area of the energy-filtered images generated during the acquisition of a series of energy-filtered images through associated image processing techniques. But correlative image processing techniques also require energy-filtered images with a certain signal-to-noise quality. Due to the limitation of the existing technology, the actual energy resolution of the local electron energy loss spectrum obtained by using a series of energy filtering images is lower than its theoretical energy resolution.

Contents of the invention

The purpose of the present invention is to provide a method and device for receiving high-stable energy filtered electron microscopic images, which eliminates the relative energy of electrons with different energy spatial distributions caused by high-voltage fluctuations or electromagnetic wave interference through drift detection and feedback methods. The drift of the slit is selected so that the energy filtering image receiving device keeps the energy of the filtering electrons stable during the signal acquisition period, and an energy filtering image with high spatial resolution or high energy resolution is obtained.

Technical scheme of the present invention is as follows:

The present invention proposes a method for receiving high-stable energy filtered electron microscopic images, which is characterized in that the method is carried out as follows:

1) The electron beam is transmitted from the sample or reflected from the surface of the sample to obtain the electronic wave reflecting the sample information, and the electron optical lens or electron optical lens group is used to focus the electron wave into an image. The electron wave is composed of electrons that have lost different energies in the sample composition;

2) Utilize the energy analyzer to form a spatial distribution of the electronic wave on the energy dispersion surface behind the energy analyzer according to its energy size;

3) The electron beam position detector placed on the energy dispersion surface or the conjugate position, under the excitation of the periodic scanning signal, repeatedly collects the spatial distribution information of the electron beam corresponding to a specific energy segment, forming a periodic spectrum of intensity changes in the time domain signal, and then send these signals with intensity changes in the time domain together with the periodic excitation signal to the drift detection system; the drift detection system extracts the spectral signal within a sampling period as a reference signal, and uses the spectral signal extracted in the subsequent acquisition period Compared with the reference signal, the difference is calculated and sent to the feedback controller as the energy drift; the feedback controller calculates the time domain drift output by the drift detection system, generates a feedback control signal for correcting the energy spectrum drift, and sends the The control signal is fed back to the front end to stabilize the spatial distribution position of the electron beam on the energy dispersion dispersion surface;

4) Adjust the width of the energy selection slit so that only the electrons in the energy range containing the excitation characteristic information of the sample pass through;

5) Using another electron-optical lens or electron-optic lens group to convert the electrons passing through the energy selection slit in step 4) into a high-stable energy filtered electron microscopic image and receive it by a two-dimensional detector.

The drift detection system described in the above-mentioned method calculates the method for time-domain drift amount to adopt integral difference method, cross-correlation function method, power spectral density function method or phase-locked loop method; The feedback control method that described feedback controller adopts is Speed feedback control method, robust feedback method or proportional-integral-derivative control method.

The periodic scanning signal described in the above method adopts sawtooth wave, triangular wave and sine wave.

The invention provides a receiving device for a high-stable energy-filtered image utilizing the above method, including an electron microscope, an entrance aperture, an energy analyzer, an energy selection slit, an image magnification and parallel receiving system, an energy-filtered image controller, a central A controller and an input device, the image magnification and parallel receiving system include a multi-pole lens group and a multi-channel parallel detector, according to the flow direction of the electron beam, the electron microscope, the entrance diaphragm, the energy analyzer, the energy selection narrow The slit, image amplification and parallel receiving system are sequentially placed in the optical path, and it is characterized in that: a fast response electron beam position detector is set between the energy analyzer and the energy selection slit, and at the position of the fast response electron beam The output end of the detector is provided with a detection feedback stabilizer and an adder, and the fast response electron beam position detector is placed in the optical path, which includes a linear motor, a line detector fixed at the front end of the linear motor, a photomultiplier tube and a set A scintillator near the detection window of the photomultiplier tube is used to receive the electrons generated by the line detector, the detection feedback energy stabilizer includes a drift detection system and a feedback controller, and the energy filter is like the controller output It is connected with the energy analyzer, the energy selection slit, the image amplification and parallel receiving system and the adder, the input end of the drift detection system is connected with the fast response electron beam position detector, and the output end is connected with the feedback controller. The drift detection system includes an A/D conversion circuit, a buffer and a drift detection module, and the feedback controller includes a feedback control module and a D/A conversion circuit, and the tube or deflection coil current obtained by the D/A conversion circuit On the control voltage, the input terminal of the central controller is connected to the electron beam drift device inside the energy analyzer after adding the input feedback control signal and the output signal of the energy filter image controller through an adder, and its output terminal is connected to the energy The filtering image controller, the drift detection module and the feedback control module are connected.

The technical feature of the present invention is also that a coupling lens group is added between the fast-response electron beam position detector and the energy selection slit, the coupling lens group produces an image plane conjugate to the energy dispersion surface, and the fast-response electron beam The beam position detector and the energy selection slit are respectively placed at the positions of the energy dispersion plane and its conjugate image plane.

The technical feature of the present invention is that: the energy selection slit is made of a flexible hinge structure.

Compared with the prior art, the present invention has the following advantages and outstanding progress:

① The spatial resolution of the energy-filtered image can be greatly improved. Since the energy filter image receiving device keeps the energy of filter electrons stable during the signal acquisition period, the signal-to-noise ratio can be improved through long-term signal acquisition, so that the width of the energy selection slit can be greatly reduced to improve the participation in imaging The monochromaticity of electrons reduces the most important factor of chromatic aberration, thus greatly improving the spatial resolution of the energy-filtered image.

② High energy resolution can be reflected in the energy filter image. Due to the small energy filter width that can be chosen, electronic transitions with different physical properties but close transition energies can be distinguished. The high spatial resolution energy filtered image collected in this way can reveal the spatial surface distribution information of different physical properties in the sample. For example, to obtain chemical bond state information requires at least an energy filter image with an energy resolution of more than 3 eV.

Description of drawings

Fig. 1 is a schematic diagram of the principle structure of the high-stable energy filter electron microscopic image receiving device provided by the present invention.

Fig. 2 is a structural diagram of an embodiment of the high-stable energy filter electron microscope image receiving device provided by the present invention.

Fig. 3 is a structural diagram of another embodiment of the high-stable energy filter electron microscope image receiving device provided by the present invention.

Figure 4 is a graph of the drift relationship of the electron gun source acceleration voltage with time collected in the JEM-2000EX transmission electron microscope.

In the figure: 1-electron gun source; 2-converging lens; 3-scanning coil; 4-sample; 5-objective lens; 6-intermediate mirror and projection lens group; 7-fluorescent screen; 8-electron microscope; ;10-energy analyzer; 11-image source; 12-fast response electron beam position detector; 13-drift detection system; 14-feedback controller; 15-energy selection slit; 16-image amplification and parallel receiving system; 17-linear motor; 18-line detector; 19-scintillator; 20-photomultiplier tube; 21-multipole lens group; 22-multi-channel parallel detector; 23-coupling lens group; 24-central controller; 25 -Energy filtering image controller; 26-Detection feedback stabilizer; 27-A/D conversion circuit; 28-Cache; 29-Drift detection module; 30-Feedback control module; 31-D/A conversion circuit; 32-Addition 33-input device; 34-signal changing in time domain; 35-scanning signal; 36-electron beam in high-energy section; 37-electron beam in low-energy section.

Detailed ways

The specific embodiment of the present invention will be further described below in conjunction with accompanying drawing:

Fig. 1 is a schematic diagram of the principle structure of a receiving device for obtaining high-stable energy filtering electron microscopic images. The device consists of an image source 11, an energy analyzer 10, a fast-response electron beam position detector 12, a detection feedback energy stabilizer 26, an energy selection slit 15, an image amplification and parallel receiving system 16, an energy filtering image controller 25, a central The controller 24 and the input device 33 are composed.

The electron beam emitted by the electron gun source 1 inside the image source 11 is transmitted through the sample 4 or reflected from the surface of the sample to obtain an electronic wave reflecting the information of the sample. The electron optical lens (group) focuses the electron wave into an image. electrons with different energies lost.

This electron wave containing the sample information then enters the fan-shaped energy analyzer 10 of the device. After receiving the instruction from the input device 33, the central controller 24 instructs the energy filtering image controller 25 to supply power to the electromagnetic coil inside the energy analyzer, so that the magnetic field generated inside the energy analyzer can disperse the electrons with different energies according to the size of the energy. In addition to forming a spatial distribution, electrons with the same energy but different incident directions can also be focused on the energy dispersion surface. In addition, when the energy filtering image controller 25 applies a certain voltage to the electron beam drift tube inside the energy analyzer, the electron distribution of energy dispersion will produce a certain proportion of translation along the energy dispersion direction, so by applying a certain voltage on the electron beam drift tube Different voltages can make the energy selection slit accept electrons in different energy ranges, and this characteristic is also applied to the feedback control in the detection feedback stabilizer. On the energy dispersion plane, the electron beam 36 and the electron beam 37 respectively correspond to the high-energy section and the low-energy section of the electron energy distribution. In addition, the selection of the type of energy analyzer needs to be based on the requirements of the trajectory characteristics of the electron beam, the size of the space where it is located, and the needs of use. Generally speaking, the energy filter image device in the lens barrel often chooses an omega (omega) energy analyzer. , The energy filter imaging device behind the lens barrel can use a fan-shaped energy analyzer or an omega energy analyzer with a certain deflection angle with the incident direction of the electron beam.

The fast-response electron beam position detector 12, under the excitation of a periodic signal, applies a relative position-modulated scanning signal to the electron beam on the energy dispersion surface behind the energy analyzer 10, so that the electrons with different energies are within a certain sampling period It is received sequentially by a fast-response electron beam position detector, and is converted into a signal of intensity variation in the time domain and then sent to the detection feedback stabilizer 26; the detection feedback stabilizer 26 is composed of a drift detection system 13 and a feedback controller 14 , under the instructions of the central controller 26, the drift detection system 13 extracts the spectral signal in a certain sampling period as the reference signal, and then extracts the time-domain drift of the spectral signal in each subsequent sampling period relative to the reference signal as the whole energy The basis of the energy drift detection of the spectrum; the feedback controller 14 calculates the time domain drift amount output by the drift detection system 13, and generates a feedback control signal for correcting the energy spectrum drift, and this feedback control signal is fed back to the front end to eliminate the energy drift to stabilize the entire electron The position of the beam on the energy distribution plane according to the spatial distribution of energy.

The energy drift detection mentioned above can be realized by various methods, such as integral difference method, cross-correlation function method, power spectral density function method, frequency response function and coherence function method, and phase-locked loop method. The feedback controller 14 mentioned above can also use various methods, such as speed feedback control method, robust (robust) feedback method, proportional-integral-derivative (PID) control method and so on.

The electron beam enters the energy selection slit 15 after passing through the fast-response electron beam position detector. The width of the energy selection slit is controlled by the energy filter image controller 25, whose function is to allow only the electron beams in the energy range containing the chemical properties or physical characteristic information of the sample to pass through the imaging, while blocking the rest of the electron beams. The energy selection slit needs to have sufficient opening precision, so as to ensure that the energy-filtered image obtained by the detection system is pure information corresponding to a certain chemical or structural feature of the sample.

The electron beam enters the image magnification and parallel receiving system 16 through the energy selection slit, which is composed of two parts, one is a multi-pole lens group 21 , and the other is a multi-channel parallel detector 22 . Under the excitation of the energy filter image controller 25, the multipole lens group can realize the following two functions, one is to form an energy filter image and amplify it, and the other is to eliminate aberrations, especially when the fan-shaped energy analysis with asymmetric electron beam trajectory is used The multipole lens group can eliminate the aberration and distortion produced by the energy analyzer when using the instrument. The multi-channel parallel detector 22 detects and receives the energy-filtered image after passing through the multipole lens group. In order to reduce the impact of the noise of the detector itself on the signal-to-noise ratio during long-time signal acquisition, low-noise detection components are necessary.

When using this device to collect energy-filtered images, first adjust the width of the energy selection slit according to the energy section corresponding to the sample characteristics, and then obtain a high-resolution energy-filtered image with a suitable signal ratio through long-term accumulation. Since the energy filtering image receiving device always keeps the energy of the filtering electrons stable during the signal acquisition time period, it is possible to collect energy filtering images in a small energy width interval. In addition, a series of energy-filtered images containing high-energy-resolution properties can be obtained by continuously changing the energy-filtering variables, and then the image intensities of arbitrarily defined specific regions in the energy-filtered images can be integrated to obtain localized high-resolution images close to the theoretical resolution limit. Resolve electron energy loss spectra.

Fig. 2 is a specific embodiment of the high-stable energy filter electron microscopic image receiving device provided by the present invention.

The high-stable energy filtering electron microscope imaging device includes an electron microscope 8, an entrance aperture 9, an energy analyzer 10, an energy selection slit 15, an image amplification and parallel receiving system 16, an energy filtering image controller 25, a central controller 24 and Input device 33, described image magnification and parallel receiving system include multipole lens group 21 and multichannel parallel detector 22, according to the flow direction of electron beam, described electron microscope, entrance diaphragm, energy analyzer, energy selection narrow The slit, image amplification and parallel receiving system are sequentially placed in the optical path, and a fast-response electron beam position detector 12 is arranged between the energy analyzer and the energy selection slit, and the fast-response electron beam position detector 12 The output end is provided with a detection feedback stabilizer 26 and an adder 32, and the fast response electron beam position detector is placed in the optical path, which includes a linear motor 17, a line detector 18 fixed at the front end of the linear motor, and a photomultiplier tube 20 And the scintillator 19 for receiving the electrons produced by the line detector near the photomultiplier tube detection window, the detection feedback energy stabilizer includes a drift detection system 13 and a feedback controller 14, and the energy filter The output end of image controller 25 is connected with energy analyzer, energy selection slit, image amplification and parallel receiving system and adder 32, the input end of described drift detection system is connected with fast response electron beam position detector, and the output end is connected with The feedback controller is connected, and the drift detection system includes an A/D conversion circuit 27, a cache memory 28 and a drift detection module 29, and the feedback controller includes a feedback control module 30 and a D/A conversion circuit 31, and the D The feedback control signal obtained by the /A conversion circuit and the output signal of the energy filter image controller are added by an adder and then connected to the control voltage of the electron beam drift tube or deflection coil current inside the energy analyzer. The central controller The input end is connected with the input device, and the output end is connected with the energy filter image controller, the drift detection module and the feedback control module.

In the present embodiment, the image source adopts scanning transmission or transmission electron microscope 8, electron gun source 1 emits electron beams, and scanning coil 3 deflects the electron beams emitted by electron gun source 1, along with the change of current in scanning coil 3 electron beams Scan over the sample. The converging lens 2 allows the electron beam to pass through the sample 4 in two ways: perpendicular to the sample surface and converging on the sample surface. The objective lens 5 , the intermediate mirror and the projection lens group 6 magnify and image the transmitted electron beam on the fluorescent screen 7 . The electron gun source 1, the converging lens 2, the scanning coil 3, the sample 4, the objective lens 5, the intermediate mirror and the projection lens group 6 and the fluorescent screen 7 are coaxially connected with the main axis of the electron optical path.

After the electron beam is emitted from the rear focal plane of the projection mirror, it enters the fan-shaped energy analyzer 10 of the device through the entrance aperture 9 . The entrance plane and exit plane of the energy analyzer in this device have a certain deflection relative to the central electron beam, so that the energy analyzer can also converge the electron beams with the same energy but different incident directions in the energy non-dispersive plane. The sector radius of the energy analyzer in this device is 100 mm, and the direction of the magnetic field is perpendicular to the surface of the paper, and the energy dispersion can be 1.1 μm/eV under the acceleration voltage of the electron gun source 1 of 200 kV. After the electron beam passes through the energy analyzer, the electron beam is dispersed according to its energy loss, and the distribution direction of its spatial position is perpendicular to the outgoing direction of the electron beam. Since electron beams with different energies correspond to different intensities, the energy distribution of the electron beams is transformed into the intensity distribution in space.

The fast-response electron beam position detector 12 detects the electron spatial distribution information corresponding to a specific energy range as a reference signal. The direction of the line detector 18 in the fast-response electron beam position detector is perpendicular to the direction of electron energy distribution, and under the irradiation of the electron beam, secondary electrons and backscattered electrons that are proportional to the intensity of the electron beam current are generated. In this device, a tungsten wire with a diameter matching the energy dispersion of the energy analyzer is selected as the line detector. This diameter is selected because the tungsten wire is too thick to reduce the energy resolution of the detection, and too thin will cause the photomultiplier tube to receive The number of electrons received decreases, and the detection accuracy decreases. When the line detector 18 is placed in different positions, signals of different intensities will be obtained, that is, different spatial positions correspond to energy spectrum signals of different energies. Under the excitation of the periodic signal, the linear motor 17 drives the front-end line detector to periodically vibrate along the direction of energy dispersion, so as to periodically detect the electronic energy spectrum signal of a specific energy range corresponding to the amplitude of the line detector. The scintillator 19 located near the line detector receives the secondary electrons and backscattered electrons produced by the line detector and converts them into optical signals, which are then received and amplified by the photomultiplier tube 20, so that the signal intensity can be periodically increased between The distribution of spatial positions is converted into a signal 34 of intensity variations in the temporal domain and gives a scan signal 35 representing the sampling period during repeated acquisitions. The linear motor 17 in this device has a unit step size of 0.1 μm and a maximum stroke of 18 mm. Its forward direction is parallel to the energy dispersion direction of electrons, and can generate high-frequency vibrations up to 1 kHz in this direction under external excitation.

The detection feedback stabilizer 26 receives the signal 34 and the scanning signal 35 that change in the time domain, calculates the energy drift and converts it into a control signal to feed back to the front end to stabilize the spatial distribution position of the electron beam on the energy dispersion surface. The signal 34 that changes in the time domain first passes through the A/D conversion circuit 27 to form a digital signal and then enters the buffer 28 for temporary storage; the scanning signal 35 enters the drift detection module 29 as a periodic signal for drift detection. The drift detection module uses the spectral signal in one of the sampling periods as a reference signal under the instruction of the central controller 26; then proposes the spectral signal of the next period from the buffer, and calculates the relative reference signal of the spectral signal in each sampling period. The amount of drift in the time domain is used as the basis for detecting the energy drift of the entire energy spectrum. This time-domain drift is output to the feedback control module 30. The feedback control module calculates the feedback control signal that can correct the energy spectrum drift under the instruction of the central controller. After the control signal is converted into an analog signal through the D/A conversion circuit 31, it is added The output signal of the controller 32 and the energy filter image controller is added and then fed back to the control voltage of the electron beam drift tube diameter or the deflection coil current inside the energy analyzer, so as to realize the stability of the spatial distribution position of the electron beam on the energy dispersion surface .

The drift detection module adopts the cross-correlation method to realize the energy spectrum drift detection function. After adopting the cross-correlation method, the drift detection system can extract useful signals in a very large noise background, so that when calculating the energy spectrum drift, instead of using the zero peak, the plasma peak or characteristic peak with lower energy can be selected as the reference spectrum, so that The acquisition range of energy-filtered images can be increased. The feedback control module adopts the method of proportional integral differential to realize, in order to eliminate the occurrence of harmful control such as self-oscillation.

The electron beam enters the energy selection slit 15 after passing through the fast-response electron beam position detector. The energy selection slit is made of a flexible hinge structure, and its minimum opening width is 0.1 μm. The upper and lower parts of the energy selection slit can move synchronously and reversely under the control of the energy filter image controller. The distance between the energy selection slit and the fast-response electron beam position detector is very close, only 5 mm, in order to ensure that both devices work near the energy dispersion surface.

Fig. 3 is another specific embodiment of the high-stable energy filter electron microscope image receiving device provided by the present invention. The difference with Fig. 2 is that a coupling lens group 23 is added between the fast-response electron beam position detector 12 and the energy selection slit 15, and the coupling lens group 23 produces an image plane conjugate with the energy dispersion surface, and the fast-response electron beam The position detector and the energy selection slit are respectively placed at the positions of the energy dispersion plane and its conjugate image plane. The advantage of this device is that it can avoid the problem that the fast-response electron beam position detector cannot detect the electron beam at the gathering position due to the deviation from the position of the energy dispersion surface, or the problem that the energy segment cannot be accurately selected due to the deviation of the energy selection slit from the position of the energy dispersion surface. . In addition, the coupling lens group 23 has a magnifying effect on the energy dispersion, so that when the energy filtering imaging device selects a certain energy segment, the requirement for the opening accuracy of the energy selection slit at the position where the energy dispersion is amplified is reduced. , so that the resolving power of the energy selective slit is improved.

Claims (6)

1. the method for reseptance of a high stable energy filtering electronic microscopic image is characterized in that this method carries out as follows:

1) electron beam reflects the electron waves that obtain the reflection sample message from the sample transmission or from sample surfaces, utilizes electro-optical lens or electro-optical lens group with this electron waves focal imaging, and these electron waves are made up of the electronics that has lost different-energy in sample;

2) utilize the energy spectrometer instrument that described electron waves are formed spatial distribution by its energy size on the energy dispersion face behind the energy spectrometer instrument;

3) place the electron-beam position detector of energy dispersion face or conjugate position under the excitation of periodic scan signal, gather the electron beam space distribution information of corresponding particular energy section repeatedly, form the periodicity spectrum signal of Strength Changes on the time domain, then the signal of Strength Changes on these time domains is delivered in the drift detection system together with periodic pumping signal; The drift detection system is extracted spectrum signal in the sampling period as the reference signal, and spectrum signal and this reference signal that later collection period is extracted compare, and calculates its difference and sends into feedback controller as the energy jitter amount; The time domain drift value that feedback controller is exported the drift detection system calculates, and produces the feedback control signal of proofreading and correct the power spectrum drift, and this control signal is fed back to front end to realize the stable of the spatial distribution position of electron beam on energy dispersion dispersion surface;

4) regulate energy selection slit width, the electronics in the energy section that comprises the sample excitation characteristic information is passed through;

5) utilize another electro-optical lens or electro-optical lens group that the electronics by the energy selection slit in the step 4) is converted into the high stable energy filtering electronic micro-image and receive by a two-dimensional detector.

2, according to the method for reseptance of the picture of high stable energy filtering described in the claim 1, it is characterized in that: the method that described drift detection system is calculated the time domain drift value adopts integral difference point-score, cross-correlation function method, power spectral density function method or phase-locked loop method; The feedback that described feedback controller adopted is speed feedback control method, robust feedback transmitter or proportion integration differentiation control method.

3, according to high stable energy filtering described in the claim 1 as method of reseptance, it is characterized in that: described periodic scan signal adopts sawtooth waveforms, triangular wave, sine wave.

4, a kind of utilization reception of the high stable energy filtering picture of method according to claim 1 connects and puts, comprise electron microscope (8), inlet diaphragm (9), energy spectrometer instrument (10), energy selection slit (15), picture amplifies and parallel receive system (16), energy filtering is as controller (25), central controller (24) and input unit (33), described picture amplifies and the parallel receive system comprises multipole lens group (21) and multi-channel parallel detector (22), the flow direction according to electron beam, described electron microscope, the inlet diaphragm, the energy spectrometer instrument, the energy selection slit, picture amplifies and the parallel receive system places light path successively, it is characterized in that: fast-response electron-beam position detector (12) is set between described energy spectrometer instrument and energy selection slit, the output of described fast-response electron-beam position detector be provided with detect feedback surely can device (26) and adder (32); Described fast-response electron-beam position detector places light path, this fast-response electron-beam position detector is put and is comprised linear electric motors (17), be fixed on the line detector (18) of linear electric motors front end, photomultiplier (20) and place near the photomultiplier detecting window the scintillator that is used to receive the electronics that produces by line detector (19); Described detection feedback surely can comprise drift detection system (13) and feedback controller (14) by device, described energy filtering is as controller (25) output and energy spectrometer instrument, the energy selection slit, picture amplification and parallel receive system and adder (32) link to each other, the input of described drift detection system links to each other with fast-response electron-beam position detector, output links to each other with feedback controller, described drift detection system comprises A/D change-over circuit (27), buffer memory (28) and drift detection module (29), described feedback controller comprises feedback control module (30) and D/A conversion circuit (31), feedback control signal that described D/A conversion circuit obtains and energy filtering are connected to after by the adder addition on the control voltage of the electron beam drift tube of energy spectrometer instrument inside or yoke current as the output signal of controller, described central controller input links to each other with input unit, and its output and energy filtering are as controller, the drift detection module links to each other with feedback control module.

5. according to the receiving system of the high stable energy filtering electronic microscopic image of the described method of claim 4, it is characterized in that: between described fast-response electron-beam position detector and energy selection slit, increased coupled lens group (23), the coupled lens group produces the image planes with energy dispersion face phase conjugate, and fast-response electron-beam position detector and energy selection slit are positioned over energy dispersion face and its conjugated image surface position respectively.

6. according to the receiving system of the high stable energy filtering electronic microscopic image of the described method of claim 4, it is characterized in that: described energy selection slit (15) is made by the flexible hinge structure.

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