High-resolution imaging system based on compact scanning transmission electron microscope

Abstract

The invention relates to the technical field of high-resolution imaging systems of compact scanning transmission electron microscopes, and discloses a high-resolution imaging system based on a compact scanning transmission electron microscope, which comprises a pulsed electron beam illumination system, a condenser, a 12-pole rapid deflector, an astigmatism corrector, an aberration corrector and a low-spherical-aberration objective lens. Only one pair of deflection electric fields is applied through the non-equal 12-pole field electrodes, the deflection speed problem is greatly relieved, three different functions can be achieved through a Tongzhi combination structure composed of quadruple octopoles and application of different electromagnetic signals, high-angle scattered electrons are collected through the dark field detector, and the high-angle scattered electrons are obtained through the pulse electron beam illumination system. Compared with bright field imaging, the method has the advantages that the imaging contrast ratio is higher, weak signals which are extremely easy to cover in bright field images are highlighted, the electron collection efficiency is improved, and it is guaranteed that images with higher quality are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of high-resolution imaging systems of compact scanning transmission electron microscopes, and in particular to a high-resolution imaging system based on a compact scanning transmission electron microscope. Background Art

[0002] In the field of structural biology, cryo-transmission electron microscopy (Cryo-TEM) has always been the preferred method for reconstructing the three-dimensional structure of biological molecules. However, the light element atoms contained in biological samples make them (i) sensitive to electron radiation and (ii) produce low phase contrast signal-to-noise ratio. In recent years, ultrafast and highly sensitive central dark field technology based on pulsed electrons has gradually been studied and is considered to be one of the most feasible technologies to avoid radiation damage and improve contrast.

[0003] The existing technology mostly integrates the pulse electron source and the hollow cone electron imaging system into the TEM, which is costly. We need to integrate the pulse electron source and the hollow cone electron imaging system into a compact STEM to meet the requirements of compactness and reduce costs. Summary of the invention

[0004] The object of the present invention is to provide a high-resolution imaging system based on a compact scanning transmission electron microscope to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a high-resolution imaging system based on a compact scanning transmission electron microscope, comprising a pulsed electron beam illumination system, a condenser, a 12-pole rapid deflector, an astigmatism corrector, an aberration corrector, and a low spherical aberration objective lens, wherein the condenser is arranged at the bottom of the pulsed electron beam illumination system, the 12-pole rapid deflector is arranged at the bottom of the condenser, the astigmatism corrector is arranged at the bottom of the 12-pole rapid deflector, the aberration corrector is arranged at the bottom of the astigmatism corrector, and the low spherical aberration objective lens is arranged at the bottom of the aberration corrector.

[0006] Preferably, the 12-pole fast deflector uses multi-pole field electrodes arranged along the central hollow cylindrical area to generate uniformly distributed deflection electric fields in the X and Y directions, and its optical properties depend on the axial potential distribution of the device. Using Laplace's equation Solve for the function of the electric potential distribution The 12-pole rapid deflector uses two mutually perpendicular dipole fields to control the deflection in the x and y directions respectively. Preferably, the length of the 12-pole rapid deflector is 15 mm, the electrode radius R=1.5 mm, the electrode bias is 80 V, two 12-level rapid deflectors are provided, and the distance between the two 12-level rapid deflectors is 30 mm, the 12-pole rapid deflector is a non-uniform 12-pole field electrode, and the 12-pole rapid deflector only applies a pair of deflection electric fields, which is convenient for using only a pair of positive and negative XY in the electronic circuit, greatly alleviating the problem of deflection speed. In terms of design, the 12-pole field can also completely eliminate the third-order term. Although a higher-pole deflector (such as a 20-pole field) can further eliminate the fifth-order term, the 20-pole electrode is more difficult to machine, the overall complexity is increased, and there are more error variables in engineering.

[0007] Preferably, the 12-pole rapid deflector generates hollow cone illumination. When deflected by φ, the 12-pole rapid deflector needs to illuminate the same area on the sample in one circle along the optical axis, so as to facilitate image data collection.

[0008] Preferably, the pulse electron beam illumination system uses a pulse electron light source to provide time resolution, and the repetition rate of the pulse electron light source can reach the megahertz (MHz) or even gigahertz (GHz) level, which can alleviate the radiation damage caused by continuous electrons while collecting sufficient signals in a single pixel.

[0009] Preferably, the pulse electron beam illumination system has two operating modes. One is to use an electron beam chopper to generate a transverse magnetic field in a specific mode and quickly deflect the electron beam to achieve the purpose of chopping. The second is to use a fiber needle tip electron gun to irradiate the metal coating of the fiber needle tip with a femtosecond laser to emit pulsed electrons. The time scales of the two light sources can cover the KHz-GHz range, which makes it easy to accurately control the electron dose by adjusting the duty cycle.

[0010] Preferably, the condenser uses two adjustable electromagnetic lenses, and the brightness and magnification of the adjustable electromagnetic lenses can be adjusted by changing the current value, which brings great convenience to the adjustment of the light path.

[0011] Preferably, the astigmatism corrector is composed of two quadrupole magnetic lenses maintaining an angle of 45°, so as to facilitate omnidirectional correction.

[0012] Preferably, the aberration corrector is composed of a lens group consisting of quadruple octopoles. When only quadruple signals are applied, the aberration corrector can be used as a quadruple quadruple lens group with M=-1. When octupole signals are applied, spherical aberration can be corrected. When quadruple electromagnetic signals are applied at the same time, a first-order Wien filter can also be integrated to correct chromatic aberration.

[0013] Preferably, a backscattered electron probe (BSE) and a secondary electron probe (SE) are arranged at the bottom of the aberration corrector, and an electron spectrometer (EDX) is arranged at the bottom of the aberration corrector. The electron spectrometer (EDX) can receive X-ray signals emitted by the interaction of electrons and samples and can simultaneously perform elemental analysis. A high-resolution, low-spherical-aberration objective lens is arranged at the bottom of the electron spectrometer (EDX), and the high-resolution, low-spherical-aberration objective lens is an immersion objective lens, and the focal length of the high-resolution, low-spherical-aberration objective lens is 1.6 mm, which is convenient for using a smaller focal length to have a smaller spherical aberration and chromatic aberration coefficient, to achieve a larger spatial resolution, and to achieve SEM and STEM imaging effects at the same time. When receiving X-ray signals emitted by the interaction of electrons and samples, elemental analysis can be performed simultaneously, and all-round characterization of the sample can be achieved. At the same time, the compact design of the device can greatly reduce costs and has huge market potential.

[0014] Compared with the prior art, the present invention provides a high-resolution imaging system based on a compact scanning transmission electron microscope, which has the following beneficial effects:

[0015] 1. The high-resolution imaging system based on a compact scanning transmission electron microscope uses a 12-pole fast deflector. During use, the non-uniformly divided 12-pole field electrodes are used to control the deflection electric field required for hollow cone illumination in the electronic circuit. Only one pair of deflection electric fields is applied by the non-uniformly divided 12-pole deflector, which greatly alleviates the problem of deflection speed.

[0016] 2. The high-resolution imaging system based on a compact scanning transmission electron microscope can realize three different functions by applying different electromagnetic signals through the lens group structure composed of quadruple octopoles through the aberration corrector set during use. When only quadrupole signals are applied, it can be used as a quadruple quadrupole lens group with M=-1. When octupole signals are applied, it can correct spherical aberration. At the same time, applying quadrupole electromagnetic signals can also integrate a first-order Wien filter to correct chromatic aberration, thereby improving the spatial resolution of low-voltage electron beams in scanning transmission mode in many aspects. The set aberration corrector can further reduce the probe size and improve the resolution by adjusting the spherical aberration and chromatic aberration.

[0017] 3. The high-resolution imaging system based on a compact scanning transmission electron microscope collects high-angle scattered electrons through a dark-field detector during use, which has a higher imaging contrast than bright-field imaging and highlights weak signals that are easily concealed in bright-field images. A weak electromagnetic lens is applied above the dark-field detector to increase the collection angle and improve the electron collection efficiency through the action of electromagnetic force, thereby ensuring higher quality images. The backscattered electron probe (BSE) and secondary electron probe (SE) can simultaneously achieve SEM and STEM imaging effects. The electron energy spectrometer (EDX) can simultaneously perform elemental analysis while receiving X-ray signals emitted by the interaction between electrons and samples, thereby achieving all-round characterization of the sample. At the same time, the compact design of the device can significantly reduce costs and has huge market potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative labor:

[0019] Figure 1 Schematic diagram of the hollow cone dark field illumination system of the double 12-electrode electrostatic deflector of the present invention;

[0020] Figure 2 Schematic diagram of two main hollow cone lighting generation methods of the present invention;

[0021] Figure 3 The structure of the unequally divided multi-pole electrostatic deflection system and its signal distribution diagram of the present invention;

[0022] Figure 4 This is a schematic diagram of the structure pulse electron hollow cone dark field high-resolution imaging system of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] See also Figure 1-4 The present invention provides a technical solution: a high-resolution imaging system based on a compact scanning transmission electron microscope, comprising a pulsed electron beam illumination system, a condenser, a 12-pole fast deflector, an astigmatism corrector, an aberration corrector, and a low spherical aberration objective lens,

[0026] See the attached drawings in the specification Figure 1-2 The pulsed electron beam illumination system uses a pulsed electron light source to provide time resolution. The repetition rate of the pulsed electron light source is at the level of megahertz (MHz) or even gigahertz (GHz), which can alleviate the radiation damage caused by continuous electrons while collecting enough signals in a single pixel. The pulsed electron beam illumination system has two operating modes. One is to use an electron beam chopper to generate a transverse magnetic field in a specific mode and quickly deflect the electron beam to achieve the purpose of chopping. The second is to use a fiber needle tip electron gun to irradiate the metal coating of the fiber needle tip with a femtosecond laser to emit pulsed electrons. The time scale of the two light sources can cover the KHz-GHz range, which makes it easy to accurately control the electron dose by adjusting the duty cycle.

[0027] See the attached drawings in the specification Figure 4 The condenser is set at the bottom of the pulse electron beam illumination system. The condenser adopts two adjustable electromagnetic lenses. The brightness and magnification of the adjustable electromagnetic lenses can be adjusted by changing their current values, which brings great convenience to the adjustment of the optical path.

[0028] See the attached drawings in the specification Figure 1-3 The 12-pole fast deflector is set at the bottom of the condenser. The 12-pole fast deflector uses multi-pole field electrodes arranged along the central hollow cylindrical area to generate uniformly distributed deflection electric fields in the X and Y directions. Its optical properties depend on its axial potential distribution. Using Laplace's equation Solve for the function of the electric potential distribution The 12-pole rapid deflector uses two mutually perpendicular dipole fields to control the deflection in the x and y directions respectively. The length of the 12-pole rapid deflector is 15mm, the electrode radius R=1.5mm, the electrode bias is 80V, there are two 12-level rapid deflectors, and the distance between the two 12-level rapid deflectors is 30mm. The 12-pole rapid deflector is a non-uniform 12-pole field electrode. The 12-pole rapid deflector only applies a pair of deflection electric fields, which is convenient for using a pair of ±X and ±Y on the electronic circuit to control the hollow cone type illumination. The deflection electric field required for illumination greatly alleviates the problem of deflection speed. In terms of design, the 12-pole field can also completely eliminate the third-order terms. Although a higher-pole deflector (such as a 20-pole field) can further eliminate the fifth-order terms, the 20-pole electrode is more difficult to machine, the overall complexity is increased, and there are more error variables in engineering. The 12-pole fast deflector produces hollow cone illumination. When the 12-pole fast deflector is deflected φ, it needs to go around the optical axis once to illuminate the same area on the sample, which is convenient for completing image data collection.

[0029] See the attached drawings in the specification Figure 4 The astigmatism corrector is set at the bottom of the 12-pole fast deflector. The astigmatism corrector consists of two quadrupole magnetic lenses maintaining a 45° angle, which facilitates omnidirectional correction.

[0030] See the attached drawings in the specification Figure 4 The aberration corrector is arranged at the bottom of the astigmatism corrector. The aberration corrector is composed of a lens group composed of quadruple octopoles. When only quadruple signals are applied, the aberration corrector can be used as a quadruple quadruple lens group with M=-1. When octupole signals are applied, spherical aberration can be corrected. At the same time, quadruple electromagnetic signals can also be applied to integrate a first-order Wien filter to correct chromatic aberration. A backscattered electron probe (BSE) and a secondary electron probe (SE) are arranged at the bottom of the aberration corrector. An electron spectrometer (EDX) is arranged at the bottom of the aberration corrector. The electron spectrometer (EDX) can receive X-ray signals emitted by the interaction between electrons and samples and can simultaneously perform To perform elemental analysis, a high-resolution, low-spherical-aberration objective lens is arranged at the bottom of the electron energy spectrometer (EDX). The high-resolution, low-spherical-aberration objective lens is an immersion objective lens, and the focal length of the high-resolution, low-spherical-aberration objective lens is 1.6 mm, which is convenient for using a smaller focal length to have a smaller spherical aberration and chromatic aberration coefficient, to achieve a larger spatial resolution, and to realize SEM and STEM imaging effects at the same time. When receiving the X-ray signal emitted by the interaction of electrons and samples, elemental analysis can be performed simultaneously to realize a full range of characterization of the sample. At the same time, the compact design of the device can greatly reduce costs and has huge market potential. The low-spherical-aberration objective lens is arranged at the bottom of the aberration corrector.

[0031] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

Claims

1. A high-resolution imaging system based on a compact scanning transmission electron microscope, comprising a pulsed electron beam illumination system, a condenser, a 12-pole fast deflector, an astigmatism corrector, an aberration corrector, and a low spherical aberration objective lens, characterized in that: The condenser is arranged at the bottom of the pulse electron beam illumination system, the 12-pole fast deflector is arranged at the bottom of the condenser, the astigmatism corrector is arranged at the bottom of the 12-pole fast deflector, the aberration corrector is arranged at the bottom of the astigmatism corrector, and the low spherical aberration objective lens is arranged at the bottom of the aberration corrector.

2. A high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The 12-pole fast deflector uses multi-pole field electrodes arranged along the central hollow cylindrical area to generate uniformly distributed deflection electric fields in the X and Y directions. Its optical properties depend on the axial potential distribution of the device. Using Laplace's equation Solve for the function of the electric potential distribution The 12-pole fast deflector uses two mutually perpendicular dipole fields to control the deflection in the x and y directions respectively.

3. A high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 2, characterized in that: The length of the 12-pole rapid deflector is 15 mm, the electrode radius R=1.5 mm, the electrode bias is 80 V, two 12-level rapid deflectors are provided, and the distance between the two 12-level rapid deflectors is 30 mm. The 12-pole rapid deflector is a non-uniform 12-pole field electrode. The non-uniform 12-pole field electrode uses a pair of ±X and ±Y to control the deflection electric field required for hollow cone lighting. The 12-pole rapid deflector only applies a pair of deflection electric fields.

4. A high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 3, characterized in that: The 12-pole fast deflector produces hollow cone illumination. When deflected φ, the 12-pole fast deflector needs to make a circle along the optical axis to illuminate the same area on the sample.

5. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The pulsed electron beam illumination system provides time resolution using a pulsed electron light source with a repetition rate in the order of megahertz (MHz) or even gigahertz (GHz).

6. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The pulse electron beam illumination system has two operating modes. One is to use an electron beam chopper to generate a transverse magnetic field in a specific mode and quickly deflect the electron beam to achieve the purpose of chopping. The second is to use a fiber needle tip electron gun to irradiate the metal coating of the fiber needle tip with a femtosecond laser to emit pulsed electrons. The time scales of the two light sources can cover the KHz-GHz range.

7. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The condenser uses two adjustable electromagnetic lenses, and the brightness and magnification of the adjustable electromagnetic lenses can be adjusted by changing their current values.

8. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The astigmatism corrector is composed of two quadrupole magnetic lenses maintaining an angle of 45 degrees.

9. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: The aberration corrector is composed of a lens group consisting of quadruple octopoles. When only quadruple signals are applied, the aberration corrector can be used as a quadruple quadruple lens group with M=-1. When octupole signals are applied, spherical aberration can be corrected. When quadruple electromagnetic signals are applied at the same time, a first-order Wien filter can also be integrated to correct chromatic aberration.

10. The high-resolution imaging system based on a compact scanning transmission electron microscope according to claim 1, characterized in that: A backscattered electron probe (BSE) and a secondary electron probe (SE) are arranged at the bottom of the aberration corrector, an electron spectrometer (EDX) is arranged at the bottom of the aberration corrector, the electron spectrometer (EDX) can receive X-ray signals emitted by the interaction of electrons and samples and can simultaneously perform element analysis, a dark field detector is arranged at the bottom of the electron spectrometer (EDX), a weak electromagnetic lens is arranged at the top of the dark field detector, a high-resolution low spherical aberration objective lens is arranged at the bottom of the electron spectrometer (EDX), the high-resolution low spherical aberration objective lens is an immersion objective lens, and the focal length of the high-resolution low spherical aberration objective lens is 1.6 mm.

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