阅读说明：本技术 一种测量待测样品四维电子能量损失谱的方法 (Method for measuring four-dimensional electron energy loss spectrum of sample to be measured ) 是由 高鹏 李跃辉 时若晨 于 2020-12-09 设计创作，主要内容包括：本发明提供一种测量待测样品四维电子能量损失谱的方法,所述方法包括如下步骤：S1、将制备好的待测样品放入电镜,旋转待测样品至待测的带轴；S2、在电镜的电子束的汇聚半角为第一汇聚半角下校正像散,再切换电子束的汇聚半角为第二汇聚半角；S3、调整电镜相机上的衍射斑使待测动量区位于狭缝光阑的预留区域内；S4、插入所述狭缝光阑使得所述狭缝光阑位于所述预留区域内；S5、插入单色仪,限制通过电子束的能量,提高能量分辨率；S6、调整像散；S7、获得待测样品当前位置的能量-动量图。该方法可以测量纳米结构的能量-动量谱,不需要大块的单晶样品,是角分辨光电子能谱和高分辨电子能量损失谱仪的有效补充。(The invention provides a method for measuring a four-dimensional electron energy loss spectrum of a sample to be measured, which comprises the following steps: s1, placing the prepared sample to be detected into an electron microscope, and rotating the sample to be detected to a belt shaft to be detected; s2, correcting astigmatism under the condition that the convergence half angle of an electron beam of the electron microscope is a first convergence half angle, and switching the convergence half angle of the electron beam to be a second convergence half angle; s3, adjusting diffraction spots on the electron microscope camera to enable the momentum zone to be measured to be located in the reserved area of the slit diaphragm; s4, inserting the slit diaphragm to enable the slit diaphragm to be located in the reserved area; s5, inserting a monochromator to limit the energy of the electron beam and improve the energy resolution; s6, adjusting astigmatism; and S7, obtaining an energy-momentum diagram of the current position of the sample to be detected. The method can measure the energy-momentum spectrum of the nano structure, does not need a large single crystal sample, and is an effective supplement for an angle-resolved photoelectron spectrum and a high-resolution electron energy loss spectrometer.)

1. A method for measuring a four-dimensional electron energy loss spectrum of a sample to be measured is characterized by comprising the following steps:

s1, placing the prepared sample to be detected into an electron microscope, and rotating the sample to be detected to a belt shaft to be detected;

s2, correcting astigmatism under the condition that the convergence half angle of an electron beam of the electron microscope is a first convergence half angle, and switching the convergence half angle of the electron beam to be a second convergence half angle;

s3, adjusting diffraction spots on the electron microscope camera to enable the momentum zone to be measured to be located in the reserved area of the slit diaphragm;

s4, inserting the slit diaphragm to enable the slit diaphragm to be located in the reserved area;

s5, inserting a monochromator to limit the energy of the electron beam and improve the energy resolution;

s6, adjusting astigmatism;

s7, obtaining an energy-momentum diagram of the current position of the sample to be detected;

the radian of the first convergence half angle is larger than that of the second convergence half angle, the radian range of the first convergence half angle is 15-35mrad, and the radian range of the second convergence half angle is 0.1-3 mrad.

2. The method of claim 1, wherein the four dimensions refer to two-dimensional x-y plane space, energy space, and momentum space.

3. The method of claim 1, wherein the slit diaphragm size is 1-3mm long and 0.02-0.15mm wide.

4. The method of any one of claims 1 to 3, wherein the electron microscope comprises a scanning transmission electron microscope;

preferably, the sweeping isThe types of scanning transmission electron microscopes include: nion UltraSTEM^TM 200，Nion UltraSTEM^TM100，Nion Ultra-HERMES^TM；

Preferably, the electron microscope has a spatial resolution of about 1 to 40nm and a momentum resolution of about 0.02 to 0.8nm^-1The energy resolution is about 6-20 meV;

preferably, the energy of the high-energy electron beam emitted by the light source of the electron microscope is 30-400 keV.

5. The method according to any one of claims 1 to 3, wherein the diffraction spot on the electron microscope camera is adjusted by a projection lens in S3;

preferably, adjusting the diffraction spot on the electron microscope camera by the projection lens comprises rotating, scaling and/or translating the projection lens;

preferably, the central transmission spot and the two first-order diffraction spots are located within a reserved position of the slit diaphragm.

6. The method according to any one of claims 1 to 3, further comprising, after step S7, the steps of: scanning an electron beam of the electron microscope on a sample to be detected to obtain a four-dimensional electron energy loss spectrum of the sample to be detected;

preferably, the electrons are collected using a charge coupled device CCD to obtain an energy-momentum diagram of the current position of the sample to be measured.

7. The method according to any one of claims 1 to 3, wherein the four-dimensional electron energy loss spectrum comprises phonon dispersion, and the energy interval is 10-500 meV;

preferably, the four-dimensional electron energy loss spectrum comprises an electron energy band structure, and the energy interval is 0.1-10 eV;

preferably, the four-dimensional electron energy loss spectrum comprises a dispersion curve of plasma, and the energy interval is 0.1-10 eV;

preferably, the four-dimensional electron energy loss spectrum comprises a core electron loss spectrum, and the energy interval is 20-1000 eV;

preferably, the sample to be detected comprises a diamond/cubic boron nitride heterojunction, an yttrium iron garnet and platinum heterojunction, a single-layer two-dimensional material or a carbon nano tube;

preferably, the single layer of two-dimensional material comprises a single layer of two-dimensional material WSe₂。

8. The method according to any one of claims 1-3, further comprising, after step S2 and before step S3, the steps of:

inserting the slit diaphragm into an electron microscope light path, wherein the slit diaphragm is positioned on a diffraction plane between the sample to be detected and the electron microscope camera;

marking the position of the slit diaphragm to obtain the reserved area;

and drawing out the slit diaphragm to enable the slit diaphragm not to be in the light path of the electron microscope.

Technical Field

The invention realizes the measurement of four-dimensional electron energy loss spectrum (two-dimensional space + energy + momentum) by using the novel slit diaphragm, can represent the electrical and magnetic properties of the material, and is applied to physics research.

Background

In recent years, with the development of electron microscopy, the general imaging modes such as annular dark field images, central bright field images and the like have more and more limitations because only intensity information can be obtained. Scientists have proposed a variety of methods to obtain more dimensional information, such as stacked diffraction imaging techniques: scanning a sample through an incident beam, and recording a two-dimensional diffraction intensity pattern at each scanning position, thereby constructing diffraction data with a four-dimensional space; ultrafast transmission electron microscope technique: the technology combines the spatial resolution of a transmission electron microscope and the time resolution of femtosecond laser, so that the dynamic process of researching substances under the ultrahigh space-time scale has possibility.

However, none of these techniques combines momentum and energy, and electron energy loss spectra, which contains rich information about inelastic scattering of electrons interacting with atoms, can be used to analyze a wide variety of physical and chemical properties of substances. The combination of energy and momentum is essential for our measurement of phonon dispersion, electronic band structure, analysis of electron-phonon interaction.

Disclosure of Invention

The invention provides a method for measuring a four-dimensional electron energy loss spectrum, which can measure an energy-momentum spectrum from 10meV to 1000eV, does not need a large single crystal, has high spatial resolution and provides a new research scheme for researching the physical problems of spatial dependence such as interfaces, surfaces and the like.

According to a first aspect, an embodiment of the present invention provides a method for measuring a four-dimensional electron energy loss spectrum, the method including the following steps:

s1, placing the prepared sample to be detected into an electron microscope, and rotating the sample to be detected to a belt shaft to be detected;

s2, correcting astigmatism under the condition that the convergence half angle of an electron beam of the electron microscope is a first convergence half angle, and switching the convergence half angle of the electron beam source to be a second convergence half angle;

s3, adjusting diffraction spots on the electron microscope camera to enable the momentum zone to be measured to be located in the reserved area of the slit diaphragm;

s4, inserting the slit diaphragm to enable the slit diaphragm to be located in the reserved area;

s5, inserting a monochromator to limit the energy of the electron beam and improve the energy resolution;

s6, adjusting astigmatism;

s7, obtaining an energy-momentum diagram of the current position of the sample to be detected;

the radian of the first convergence half angle is larger than that of the second convergence half angle, the radian range of the first convergence half angle is 15-35mrad, and the radian range of the second convergence half angle is 0.1-3 mrad.

Preferably, the four dimensions refer to two-dimensional x-y plane space, energy space and momentum space.

Preferably, the size of the slit diaphragm is 1-3mm in length and 0.02-0.15mm in width.

Preferably, the electron microscope comprises a scanning transmission electron microscope;

preferably, the types of the scanning transmission electron microscope include: nion UltraSTEM^TM 200，Nion UltraSTEM^TM 100，Nion Ultra-HERMES^TM；

Preferably, the electron microscope has a spatial resolution of about 1 to 40nm and a momentum resolution of about 0.02 to 0.8nm^-1The energy resolution is about 6-20 meV;

preferably, the energy of the high-energy electron beam emitted by the light source of the electron microscope is 30-400 keV.

Preferably, in S3, the diffraction spot on the electron microscope camera is adjusted by the projection lens;

preferably, adjusting the diffraction spot on the electron microscope camera by the projection lens comprises rotating, scaling and/or translating the projection lens;

preferably, the central transmission spot and the two first-order diffraction spots are located within a reserved position of the slit diaphragm.

Preferably, the following steps are further included after step S7: scanning an electron beam of the electron microscope on a sample to be detected to obtain a four-dimensional electron energy loss spectrum of the sample to be detected;

preferably, the electrons are collected using a charge coupled device CCD to obtain an energy-momentum diagram of the current position of the sample to be measured.

Preferably, the four-dimensional electron energy loss spectrum comprises phonon dispersion, and the energy interval is 10-500 meV;

preferably, the four-dimensional electron energy loss spectrum comprises an electron energy band structure, and the energy interval is 0.1-10 eV;

preferably, the four-dimensional electron energy loss spectrum comprises a dispersion curve of plasma, and the energy interval is 0.1-10 eV;

preferably, the four-dimensional electron energy loss spectrum comprises a core electron loss spectrum, and the energy interval is 20-1000 eV;

preferably, the sample to be detected comprises a diamond/cubic boron nitride heterojunction, an yttrium iron garnet and platinum heterojunction, a single-layer two-dimensional material or a carbon nano tube;

preferably, the single layer of two-dimensional material comprises a single layer of two-dimensional material WSe₂。

Preferably, the method further comprises the following steps after step S2 and before step S3:

inserting the slit diaphragm into an electron microscope light path, wherein the slit diaphragm is positioned on a diffraction plane between the sample to be detected and the electron microscope camera;

marking the position of the slit diaphragm to obtain the reserved area;

and drawing out the slit diaphragm to enable the slit diaphragm not to be in the light path of the electron microscope.

The invention provides a novel method for measuring a four-dimensional electron energy loss spectrum by combining a slit diaphragm with a scanning transmission electron microscope. The method is based on high spatial resolution of a scanning transmission electron microscope, high momentum resolution of a small convergence half angle and high energy resolution of a latest monochromator, realizes measurement of an energy-momentum spectrum by selecting a momentum direction to be measured through a slit diaphragm, and combines scanning electron beams to obtain a four-dimensional electron energy loss spectrum (two-dimensional space + energy space + momentum space). The method can efficiently obtain the four-dimensional information of the sample, is compatible with the existing electron microscope system, and is convenient for upgrading the existing electron microscope system. The method can measure the energy-momentum spectrum of the nano structure, can measure the energy-momentum spectrum of a small sample, and is an effective supplement for an angle-resolved photoelectron spectrum and a high-resolution electron energy loss spectrometer (requiring a large crystal).

The slit diaphragm of the existing TEM is under parallel electron beams and is not spatially resolved. The slit diaphragm of the invention has the advantages that under a certain convergence half angle, the slit width is matched with the corresponding convergence half angle, and the slit diaphragm has space resolution, momentum resolution and high energy resolution, which are not possessed by a common TEM.

Drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:

FIG. 1 shows a simplified structure diagram and an optical path diagram of an electron microscope for four-dimensional electron energy loss spectroscopy measurement according to the present invention.

Fig. 2 is an annular dark field image (a) near a diamond C-C/cubic boron nitride C-BN heterojunction interface, and dispersion images at three positions of a diamond side (b), an interface (C), and a cubic boron nitride side (d), respectively.

Fig. 3 is a correlation plot of magnetic circular dichroism spectra of iron near the yttrium iron garnet YIG/platinum Pt heterojunction interface, including annular dark field images (a) (b), diffraction patterns (c), and magnetic circular dichroism spectra (d) (e) (f) at different locations of the sample.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 shows a simplified structure diagram and an optical path diagram of an electron microscope for four-dimensional electron energy loss spectroscopy measurement according to the present invention, as shown in fig. 1, the electron microscope includes a light source, a slit diaphragm, a lens, and other components. The light source includes an electron beam light source that can generate a large converging half angle electron beam and a small converging half angle electron beam, wherein the large converging half angle is 15-35mrad, such as 15mrad, 20mrad, 25mrad, 30mrad, 35mrad, but not limited to the enumerated values, and other unrecited values within the numerical range are equally applicable. And the electron beams generated by the light source sequentially pass through the sample to be detected, the slit diaphragm and the lens and are collected by the signal collecting instrument. The small convergence half angle is between 0.1 and 3mrad, and can be, for example, 0.1mrad, 0.75mrad, 1.5mrad, 3mrad, but is not limited to the recited values, and other values within the range are equally applicable.

The size of the slit diaphragm is 1-3mm long and 0.02-0.15mm wide; in some specific embodiments, the slit diaphragm size is 2mm × 0.03mm, 2mm × 0.06mm, 2mm × 0.125mm, but is not limited to the enumerated values.

The lens comprises an electromagnetic lens which mainly comprises an electrostatic lens and a magnetic lens.

In some specific embodiments, the models of the electron microscope include: nion UltraSTEM^TM 200，Nion UltraSTEM^TM 100，Nion Ultra-HERMES^TM。

The slit diaphragm of the invention has the slit width matched with the corresponding convergence half angle under a certain convergence half angle, has high spatial resolution and momentum resolution and very high energy resolution, which is not possessed by a common TEM. Specifically, the spatial resolution of the electron microscope is about 1-40nm, and the momentum resolution is about 0.02-0.8nm^-1The energy resolution is about 6-20 meV. In one specific embodiment, at 60kV, 3mrad with a small convergence half angle, a slit size of 2mm x0.125mm, corresponding spatial resolution of about 2nm and momentum resolution of about 0.6nm^-1The energy resolution is about 15 meV; under 30kV, 1.5mrad is small in convergence half angle, the size of a slit is 2mm x0.125mm, the corresponding spatial resolution is about 8nm, and the momentum resolution is about 0.2nm^-1The energy resolution is about 10 meV. Other reasonable parameter combinations can also be used for the measurement of the four-dimensional electron energy loss spectrum, and corresponding spatial, momentum and energy resolutions can also be achieved.

The method for measuring the four-dimensional electron energy loss spectrum by adopting the electron microscope not only can measure the energy-momentum spectrum from 10meV to 1000eV, but also does not need a large single crystal, has high spatial resolution and provides a new research scheme for researching the physical problems of spatial dependence such as interfaces, surfaces and the like.

In a specific embodiment, the energy of the high-energy electrons in the electron beam is 30-400keV, such as 30keV, 60keV, 100keV, 200keV, 300keV, 400keV, but is not limited to the values recited, and other values not recited within the range of values are equally applicable.

The invention provides a novel method for measuring a four-dimensional electron energy loss spectrum by combining a slit diaphragm with a scanning transmission electron microscope. With reference to fig. 1, the method comprises the following steps: placing the prepared sample to be measured into an electron microscope, adjusting to a belt axis to be measured, correcting astigmatism under a large convergence half angle, switching to a small convergence angle (for example, 3mrad), adjusting (rotating, zooming and translating) diffraction spots on an electron microscope camera through a projection lens (projector lens) to enable a momentum zone to be measured to be located in a slit diaphragm, inserting a monochromator into the slit diaphragm, and adjusting EELS astigmatism to obtain an energy-momentum diagram (phonon dispersion, electron energy band, plasma dispersion and the like) of the current position of the sample to be measured. The electron beam is scanned on the sample, and a four-dimensional electron energy loss spectrum (two-dimensional space + energy space + momentum space) can be measured. Wherein a two-dimensional space refers to an x-y plane space. The monochromator is positioned between an electron gun of the electron microscope and a sample to be measured, and the electron beam irradiates the sample to be measured through the monochromator.

Wherein, after switching to the small convergence half angle, before adjusting the projection lens, the method further comprises the following steps: inserting the slit diaphragm into an electron microscope light path, wherein the slit diaphragm is positioned between the sample to be detected and the electron microscope camera; marking the position of the slit diaphragm to obtain a reserved area; and drawing out the slit diaphragm to enable the slit diaphragm not to be in the light path of the electron microscope.

The measurement of the four-dimensional electron energy loss spectrum can be understood with reference to fig. 1. The small convergent half-angle electron beam has high momentum resolution, forms diffraction spots on a diffraction surface after being scattered by a sample, selects a special set of diffraction spots by using a slit diaphragm, can limit the momentum in the x direction, and can be considered to be within the momentum resolution q_xEither 0 or, optionally, other valuesQ is collected_yThe momentum point of the direction passes through a magnetic prism, and then a momentum energy spectrum (q) is obtained_yE), scanning the electron beam in the xy plane to obtain a four-dimensional electron energy loss spectrum (x-y-q)_y-E)。

According to a first aspect, an embodiment of the present invention provides a method for measuring a four-dimensional electron energy loss spectrum, the method including the following steps:

the prepared sample to be measured is placed in an electron microscope, the sample is rotated to a belt shaft to be measured, astigmatism such as spherical aberration and coma aberration is adjusted under a large convergence half angle, the convergence half angle is switched to a small convergence half angle, diffraction spots are adjusted through a projection lens, a monochromator is inserted, the slit diaphragm selects momentum to be measured, EELS astigmatism is adjusted, an electron beam scans on the sample, and a CCD acquires a 4D-EELS signal.

Optionally, the energy momentum spectrum includes phonon dispersion, and the energy interval is 10-500 meV.

Optionally, the energy momentum spectrum comprises an electron band structure, and the energy interval is 0.1-10 eV.

Optionally, the energy momentum spectrum comprises a dispersion curve of the plasma, and the energy interval is 0.1-10 eV.

Optionally, the energy momentum spectrum comprises a core electron loss spectrum, and the energy interval is 20-1000 eV.

Optionally, the energy momentum spectrum includes dispersion spectra of various polaritons, including but not limited to phonon polaritons, exciton polaritons, plasma polaritons, and magneton polaritons.

Optionally, the energy momentum spectrum includes a first brillouin zone and a second brillouin zone, or may be a higher order brillouin zone.

Optionally, the large convergence half angle for adjusting astigmatism is 15-35mrad, such as 15mrad, 20mrad, 25mrad, 30mrad, 35mrad, but not limited to the recited values, and other values in the range of values not recited are equally applicable.

Optionally, the small convergence half-angle used in measuring the momentum-resolved spectra is between 0.1 and 3mrad, such as 0.1mrad, 0.75mrad, 1.5mrad, 3mrad, but not limited to the recited values, and other values within the range are equally applicable.

Optionally, the size of the slit diaphragm is 1-3mm long and 0.02-0.15mm wide; in some specific embodiments, the slit diaphragm size is 2mm × 0.03mm, 2mm × 0.06mm, 2mm × 0.125mm, but is not limited to the enumerated values.

Optionally, the convergence half-angle when measuring the momentum-resolved spectrum is best matched to the size of the diaphragm. Preferably, the converging half angles of 0.75mrad, 1.5mrad and 3mrad correspond to the sizes of the slit diaphragm of 2mm × 0.03mm, 2mm × 0.06mm and 2mm × 0.125mm one by one, and the effect is best.

Alternatively, the energy channel of the energy momentum spectrum may be determined according to the specific energy collection range, such as 0.5meV/ch, 1meV/ch, 2meV/ch for phonon dispersion, 0.005eV/ch, 0.01eV/ch for electron band structure, 0.16eV/ch, 0.3eV/ch for core electron energy loss spectrum, but not limited to the listed values.

Example one

The present embodiment provides a method for measuring phonon dispersion spectrum near diamond/cubic boron nitride heterojunction interface, comprising the steps of:

the prepared diamond/cubic boron nitride heterojunction electron microscope sample is placed into an electron microscope, a belt shaft is adjusted, after an optical path is adjusted under a convergence half angle of 20mrad (namely a large convergence half angle), the optical path is switched to a 3mrad convergence half angle (namely a small convergence half angle), a diffraction pattern is adjusted by using a projection lens, a central transmission spot and two first-order diffraction spots are located in a slit of a slit diaphragm, an energy channel is selected to be 0.0005eV/ch, EELS astigmatism is adjusted, and a dispersion signal of gamma 'M gamma' near an interface can be measured. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

Fig. 2 shows an annular dark field image (a) near the diamond/cubic boron nitride heterojunction interface, and dispersion data at three positions on the diamond side (b), the interface (c), and the cubic boron nitride side (d), respectively.

Example two

The present embodiment provides a method for measuring an electronic band structure near a diamond/cubic boron nitride heterojunction interface, the method comprising the steps of:

the prepared diamond/cubic boron nitride heterojunction electron microscope sample is placed into an electron microscope, a band axis is adjusted, after a light path is adjusted under a convergence half angle of 15mrad, the light path is switched to a convergence half angle of 0.1mrad, a diffraction pattern is adjusted by using a projection lens, a central transmission spot and two first-order diffraction spots are located in a slit of a slit diaphragm, an energy channel selects 0.01eV/ch, EELS astigmatism is adjusted, and the electron energy band structure of gamma 'M gamma' near an interface can be measured. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

EXAMPLE III

This example provides a method for measuring the d-d exciton dispersion relationship from bulk state of nickel oxide NiO to the surface, comprising the steps of:

and (2) placing the prepared NiO electron microscope sample into an electron microscope, adjusting a belt axis, adjusting a light path under a convergence half angle of 35mrad, switching to a convergence half angle of 0.5mrad, adjusting a diffraction pattern by using a projection lens to enable a central transmission spot and two first-order diffraction spots to be positioned in a slit of a slit diaphragm, selecting an energy channel to be 0.005eV/ch, adjusting EELS astigmatism, scanning an electron beam to the surface of the sample from a bulk state, and measuring the change of dispersion of a d-d exciton of NiO from the inside of the body to the surface. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

Example four

The embodiment provides a method for measuring dichroism of a magnetic circle near an interface of yttrium iron garnet and platinum heterojunction by using four-dimensional electron energy loss spectrum, which comprises the following steps:

referring to fig. 3, the prepared yttrium iron garnet/platinum heterojunction electron microscope sample (YIG/Pt) is placed in an electron microscope, adjusted to a [112] band axis, switched to a 3mrad convergence half angle after adjusting a light path under a convergence half angle of 20mrad, a projection lens is used for adjusting a diffraction pattern, as shown in fig. 3, an energy channel is selected to be 0.16eV/ch, EELS astigmatism is adjusted, an electron beam is scanned from a YIG layer to a Pt layer, and the change of an L-edge momentum resolution spectrum of Fe near a YIG/Pt interface can be measured. The lower 3 panels (d) (e) (f) of fig. 3 show the electron magnetic circular dichroism spectra at 3 locations near the interface, after data processing. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

EXAMPLE five

The embodiment provides a method for measuring WSe of a single-layer two-dimensional material by utilizing a four-dimensional electron energy loss spectrum₂A method of exciton dispersion, the method comprising the steps of:

the prepared monolayer WSe₂Placing a sample into an electron microscope, adjusting a light path under a convergence half angle of 20mrad, switching to a convergence half angle of 0.15mrad, adjusting a diffraction pattern by using a projection lens to enable a central transmission spot and two first-order diffraction spots to be positioned in a slit of a slit diaphragm, selecting an energy channel to be 0.005eV/ch, adjusting EELS astigmatism, and enabling an electron beam to pass through a WSe₂Internally scanning to the edge, WSe can be measured₂The effect of the edge states on exciton dispersion. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

EXAMPLE six

The embodiment provides a method for measuring phonon dispersion of a carbon nano tube by utilizing a four-dimensional electron energy loss spectrum, which comprises the following steps:

the prepared carbon nano tube sample is placed into an electron microscope, after the light path is adjusted under the condition that the convergence half angle is 20mrad, the convergence half angle is switched to 3mrad, the diffraction pattern is adjusted by using a projection lens, the central transmission spot and the two first-order diffraction spots are positioned in a slit of a slit diaphragm, an energy channel is selected to be 0.0005eV/ch, EELS astigmatism is adjusted, an electron beam scans from the center to the edge of the carbon nano tube, and the dispersion of phonons of the carbon nano tube along with the change of the inclination angle of the tube wall can be measured. A monochromator may be interposed between the electron gun and the sample to limit the energy passing through the electron beam and improve energy resolution.

The foregoing embodiments are merely illustrative of the principles of this invention and its efficacy, rather than limiting it, and various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention, which is defined in the appended claims.