TWI609402B - A low energy electron microscopy - Google Patents

Description

Transmission type low energy electron microscopy system

The invention relates to the field of micro-nano technology, in particular to a transmissive low-energy electronic display Microsystems and methods for characterizing two-dimensional nanomaterials.

Nanomaterials offer the potential to create new logic devices and increase device integration. New energy, detection, flexible electronics, biomedical and other aspects also have many excellent features and broad application prospects. A key step in achieving the ultimate application of nanomaterials is the uniform preparation of large areas. At present, two-dimensional nanomaterials such as graphene and molybdenum disulfide can be prepared by large-area chemical vapor deposition. For example, the preparation of graphene single crystals reaches the centimeter level, the molybdenum disulfide single crystal can reach the sub-millimeter size, and the tungsten selenide and the molybdenum diselenide are also several hundred micrometers in size. Therefore, it is an important requirement for current material research to develop a convenient and rapid characterization method and instrument for the structure and performance of large-area samples obtained.

Material structure and properties have different characterization methods and corresponding equipment, due to electronics The wavelength is close to the atomic distance of the material, and the energy and motion are easy to control. At the same time, because the electron is mainly scattered by the nucleus, the diffraction angle is small, the diffraction spot is strong, the radiation depth and the volume of the active sample are relatively small, and the electron microscopy is characterized. Nanomaterials include one of the most suitable means of structure and morphology of two-dimensional materials. Transmitted electron microscopy (TEM) allows atomic-level structural analysis and imaging of very small samples. However, mature transmission electron microscopy devices are designed for three-dimensional materials in order to achieve large magnification. Multiples and good resolution, the working voltage of the electron microscope is mostly from 20kV to 300kV, the electron beam spot is as small as possible, and the sample holder is also a metal ring with a diameter of only 3 mm. The high-energy electron irradiation will damage the structure of the material. The effect of nanomaterials is very obvious, and the area of sample analysis should not be too large. Low energy electron diffraction (LEED) and low energy electron microscopy (LEEM) mining The use of lower energy electrons to characterize the structure of the atomic surface of the material is ideal for analyzing the two-dimensional structure of the material and its adsorption. However, since this characterization is also designed for conventional material structures, it has the same problem of smaller electron beam spot than TEM, and the efficiency of characterizing large-area materials is not high. At the same time, LEED and LEEM observe the reflected electron beam. The material grown on the substrate, such as graphene, is only a layer of atoms on the surface. After the electron beam passes through the sample, it will continue to interact with the substrate material to reflect. Therefore, in the LEED pattern. There is also a signal for the substrate material.

Thus, the development of suitable transmission-type low-energy electron microscopy with large electron beam spots The analytical method will be expected to solve the intrinsic characterization problem of large-area samples in the current nanomaterial characterization, which is the inherent requirement of the research and development of current nanomaterials, especially two-dimensional materials.

The present invention provides a transmission type low energy electron microscopy system.

A transmissive low-energy electron microscopy system comprising: a vacuum chamber; a setting An electron gun in the vacuum chamber, an electron beam for emitting; a diffraction cavity connected to the vacuum chamber; an imaging device disposed in the diffraction cavity; and a sample holder for fixing the two-dimensional nai a sample of a rice material, the electron beam may be formed from the two-dimensional nanomaterial sample to form a transmitted electron beam and a diffracted electron beam entering the diffraction cavity, and imaged on the imaging device; a core column connected to the cavity; a vacuuming device connected to the vacuum chamber; and a control computer for controlling the entire system operation and data processing; wherein the control computer further includes a working mode switching module The working mode switching module can switch between the imaging mode of the large beam spot and the diffraction mode of the small beam spot; the imaging mode of the large beam spot is to irradiate the entire sample surface with an electron beam larger than the sample, and perform diffraction imaging; The diffraction pattern of the beam spot is that a partial surface of the sample is irradiated with an electron beam smaller than the sample or the entire surface is scanned, and diffraction imaging is performed.

A transmissive low energy electron microscopy system as described above, wherein the control computer further comprises An image processing module and a distance control module; the image processing module is configured to process the acquired image to obtain a diffraction ring radius R, and the distance control module can adjust between the sample and the imaging device Distance D.

The transmissive low-energy electron microscopy system, wherein the control computer further comprises a calculation module, wherein the calculation module is configured to calculate a radius R of the diffraction ring and a distance D between the sample and the imaging device. the diffraction angle θ between the transmitted electron beam with an electron beam, and calculating according to the formula dsinθ = λ Weinai Mi lattice period of the two material samples d, wherein, [lambda] is the wavelength of the electron beam.

A transmissive low energy electron microscopy system as described above, wherein the imaging device is a fluorescent screen.

A transmissive low-energy electron microscopy system as described above, wherein the imaging device is a CCD image sensor, and an image of the transmitted electrons and the diffracted electrons is collected by the CCD image sensor and sent to the control computer.

A transmissive low-energy electron microscopy system as described above, wherein the electron gun provides an electron beam energy of 800 eV to 3000 eV, an electron beam current of 0.1 microamperes to 1 microamperes, and an electron beam spot diameter of 100 micrometers.

A transmissive low-energy electron microscopy system as described above, further comprising a shower member disposed adjacent to the sample holder such that molecular material ejected from the shower member can be adsorbed on the surface of the sample.

A transmissive low-energy electron microscopy system as described above, further comprising a conductive rod, the conductive rod being rotatable such that the conductive rod can be rotated to the front of the imaging device to block the transmission spot, thereby obtaining only a winding Shoot the pattern.

A transmissive low energy electron microscopy system as described above, wherein the sample holder further comprises a heating element and a temperature sensor, the heating range being from room temperature to 1500K.

A transmissive low energy electron microscopy system as described above, wherein the sample holder further comprises a moving device for moving the sample to effect scanning of the sample by the electron beam.

The transmissive low-energy electron microscopy system provided by the invention can be directly used for observing a single layer to a plurality of layers of two-dimensional nanomaterials, and obtaining an electron transmission and diffraction image of the two-dimensional nano material; in particular, the large beam spot The imaging mode is to irradiate the entire sample surface with an electron beam larger than the sample, and perform diffraction imaging, which greatly improves the characterization efficiency of the large-area two-dimensional nano material.

10‧‧‧Transmission type low energy electron microscopy system

11‧‧‧Vacuum chamber

12‧‧‧Electronic gun

13‧‧‧Diffraction cavity

132‧‧‧ imaging device

134‧‧‧Anode electrode

14‧‧‧ sample holder

142‧‧‧electrode

15‧‧‧core

16‧‧‧ Vacuuming device

161‧‧‧ ion pump

162‧‧‧First Molecular Pump

163‧‧‧Second molecular pump

164‧‧‧ mechanical pump

165‧‧‧Control device

166‧‧‧Pre-extraction room

17‧‧‧Control computer

18‧‧‧Spray parts

19‧‧‧Mobile Station

20‧‧‧ samples

22‧‧‧ incident electron beam

24‧‧‧Diffractive electron beam

26‧‧‧Transmission electron beam

28‧‧‧ crystal face

29‧‧‧ Conducting rod

FIG. 1 is a schematic structural view of a transmission type low energy electron microscopy system according to an embodiment of the present invention.

2 is an electron winding of a transmission type low energy electron microscope system according to an embodiment of the present invention. Schematic diagram of the method of radiation and transmission.

3 is an evacuation of a transmission type low energy electron microscope system according to an embodiment of the present invention Schematic diagram of the structure of the device.

4 is an electron winding of a transmission type low energy electron microscope system according to an embodiment of the present invention. Schematic diagram of the principle of radiation and transmission.

5 is an optical micrograph of a graphene island sample used in Example 1 of the present invention, wherein Ab is an optical micrograph of a graphene island grown on a copper foil by a CVD method, and c is an optical display of a CGF (CNT/graphene hybrid film) sample formed by placing a graphene island on a cross-mounted carbon nanotube film. Micro photo.

6a-6b are central transmission images and diffraction patterns of graphene islands 1 according to Embodiment 1 of the present invention; Image, where a is a transmission image and b is a diffraction image.

6c-6d are schematic views of a transmission image and a diffraction image of a single-layer single crystal graphene sheet, In the middle, c is a schematic diagram of a transmission image, and d is a schematic diagram of a diffraction image.

7a-7b are central transmission images and diffraction patterns of graphene island 2 according to Embodiment 1 of the present invention. Image, where a is a transmission image and b is a diffraction image.

7c-7d are schematic views of a transmission image and a diffraction image of a three-layer single crystal graphene sheet, In the middle, c is a schematic diagram of a transmission image, and d is a schematic diagram of a diffraction image.

8 is a diffraction diagram of a selection region of four different regions of graphene island 1 according to Embodiment 1 of the present invention; image.

Figure 9 is a plan view of a selected area of four different regions of graphene island 2 according to Embodiment 1 of the present invention; image.

10a is a sample of a large-area continuous polycrystalline graphene film used in Example 2 of the present invention; Optical micrograph.

10b is a sample of a large-area continuous polycrystalline graphene film used in Example 2 of the present invention; The selection of the area is diffracted.

10c-10d are diffractions of an electron beam covering the entire graphene island 2 according to Embodiment 1 of the present invention; An image in which c is the focus of the electron beam and d is after the electron beam is focused.

Figure 11a is an optical micrograph of a MoS ₂ sheet sample used in Example 3 of the present invention.

Figure 11b is a diffraction image of an electron beam covering the entire MoS ₂ sheet sample in Example 3 of the present invention.

Figure 11c is a diffraction image of an example of a MoS ₂ sheet sample having only one crystal orientation in an electron beam in Example 3 of the present invention.

Figure 11d is a diffraction image of an electron beam covering a small number of MoS ₂ sheet samples having two crystal orientations in Example 3 of the present invention.

12 is a view showing a transmission electron diffraction of a single crystal graphene after adsorbing water molecules according to Embodiment 4 of the present invention; The diffracted image appears first and then disappears as the image changes over time, with exposure every 15 seconds.

Figure 13 is a transmission diffraction diagram of different samples after adsorbing water molecules according to Example 5 of the present invention; For example, where a is a polycrystalline graphene film having only one main crystal orientation, b is a polycrystalline graphene film having two main crystal orientations, and c is a polycrystalline graphene film having three main crystal orientations.

Figure 14 is a transmission diffraction image before and after rotation of a sample according to Embodiment 6 of the present invention, wherein a As a transmission diffraction image of the polycrystalline graphene film before rotation, b is a transmission diffraction image of the polycrystalline graphene film rotated by 90 degrees.

15 is a series of transmission diffraction images obtained after scanning a sample according to Embodiment 7 of the present invention, Among them, the arrow indicates the direction in which the electron beam moves, first up and down.

Figure 16 is a graph showing the relationship between the sin θ of different crystal faces of the sample of Example 8 of the present invention and the wavelength of the electron beam.

The transmissive low energy provided by the present invention will be described below in conjunction with the above drawings and different embodiments. An electron microscopy system and a method of characterizing a two-dimensional nanomaterial.

Referring to FIG. 1-2, a transmission type low energy electron microscopy system 10 package provided by an embodiment of the present invention is provided. A vacuum chamber 11, an electron gun 12, a diffraction cavity 13, a sample holder 14, a stem 15, a vacuuming device 16, and a control computer 17 are included.

The electron gun 12 is disposed in the vacuum chamber 11 . The vacuum chamber 11 and the The diffraction cavity 13 is connected. The sample holder 14 is disposed at a junction of the vacuum chamber 11 and the diffraction cavity 13 such that electrons emitted by the electron gun 12 can be transmitted after being transmitted from the sample 20 on the sample holder 14. Inside the diffraction cavity 13. The stem 15 and the diffraction cavity 13 connection. The vacuuming device 16 is connected to the vacuum chamber 11. The control computer 17 is used to control the operation of the entire transmission type low energy electron microscopy system 10.

The diffraction cavity 13 has an imaging device 132 and an anode electrode 134 therein. Said The image device 132 is disposed between the electron gun 12 and the anode electrode 134. The electrons emitted by the electron gun 12 are moved toward the anode electrode 134 by the anode electrode 134, and after being transmitted from the sample 20 on the sample holder 14, a diffraction imaging point is performed on the imaging device 132 or / And performing diffraction imaging. The structure of the two-dimensional nanomaterial sample 20 can be analyzed by diffraction spots or/and diffraction imaging on the imaging device 132. The imaging device 132 can be a fluorescent screen or a CCD image sensor. An image of the transmitted electrons and the diffracted electrons is collected by the CCD image sensor and sent to the control computer 17.

The electron gun 12 provides an electron beam energy of 800 eV to 3000 eV, and the electron beam current is 0.1 microamperes - 1 microamperes, and the electron beam spot diameter is 100 micrometers to 1 centimeter. The electron source of the electron gun 12 may be a hot cathode or a field emission cold cathode. Referring to FIG. 2, in the embodiment, the electron gun 12 is a pre-focusing multi-lens fine beam electron gun, which adopts a quadrupole electrostatic focusing system, specifically including a cathode emitter C, and four focusing electrodes A1 and A2 disposed at a time. , A3, A4. The electron beam spot diameter can be adjusted by the focusing electrode. It can be understood that the electron gun 12 can also use other electron guns, such as a laminar flow gun. The laminar flow gun can achieve more uniform beam spot and greater current density, which is expected to improve the quality of imaging and diffraction. Further, the transmissive low energy electron microscopy system 10 can also include a mobile station 19. The electron gun 12 can be moved by the mobile station 19 to effect scanning of the sample 20 by the electron beam.

The sample holder 14 is used to fix the sample 20. Structure and ruler of the sample holder 14 Inch is not limited and can be designed as needed. In this embodiment, the sample holder 14 is a copper disk having a circular through hole in the middle. The through hole diameter is slightly smaller than the size of the sample 20. The sample holder 14 also includes a moving device so that the sample 20 can be moved in the xyz direction. Scanning of the sample 20 by an electron beam can be achieved by moving the sample 20. Further, the sample holder 14 further includes a heating element to investigate the structure and interaction phenomenon of the sample 20 as a function of temperature. The heating range is from room temperature to 1500K. In this embodiment, the sample holder 14 includes two spaced apart electrodes 142. When the sample 20 is attached to the sample holder 14, an electrically conductive support carrying the sample 20, such as a copper mesh or a carbon nanotube film, can be electrically connected to the two spaced apart electrodes 142. Passing the electrode 142 to the conductive support The current is applied to heat the sample 20 disposed on the conductive support. The sample holder 14 can also include a temperature sensor for monitoring the temperature of the sample 20.

Further, the transmission type low energy electron microscope system 10 may further include a shower portion Item 18. The shower member 18 is disposed adjacent to the sample holder 14 such that molecular material ejected from the shower member 18 can be adsorbed on the surface of the sample 20. As such, the adsorption and reaction of the sample 20 to different materials can be investigated.

Further, the transmission type low energy electron microscope system 10 may further include a conductive rod 29. One end of the conductive rod 29 is fixed on the side wall of the diffraction cavity 13 and can be rotated, so that the conductive rod 29 can be rotated to the front of the imaging device 132, thereby blocking the zero-order spot or the transmission spot, so that only A diffraction pattern is obtained. It will be appreciated that the transmissive low energy electron microscopy system 10 can also include a Faraday cup (not shown) to measure the intensity of a certain diffracted beam.

Referring to Fig. 3, the specific structure of the vacuuming device 16 is not limited and can be designed as needed. In this embodiment, the vacuuming device 16 includes an ion pump 161, a first molecular pump 162, a second molecular pump 163, a mechanical pump 164, and a control device 165. The ion pump 161 and the second molecular pump 163 are directly connected to the vacuum chamber 11 respectively. The first molecular pump 162 is coupled to the vacuum chamber 11 via a pre-extraction chamber 166. The mechanical pump 164 is coupled to the first molecular pump 162 and the second molecular pump 163, respectively. The control device 165 is used to control the operation of the entire vacuuming device 16. By the vacuuming device 16, the vacuum degree of the vacuum chamber 11 can be made 10 ^-3 -10 ^-6 Pa, and diffraction spots and diffraction imaging of the transmitted electrons can be observed in this vacuum range.

The control computer 17 includes a working mode switching module, a computing module, and an image processing module. Group and distance control module. The working mode switching module can switch between an imaging mode of a large beam spot and a diffraction mode of a small beam spot. Wherein, the imaging mode of the large beam spot is to irradiate the entire surface of the sample 20 with an electron beam larger than the sample 20, and perform diffraction imaging. The diffraction pattern of the beam spot is to irradiate a partial surface of the sample 20 with an electron beam smaller than the sample 20 or to scan the entire surface, and to perform diffraction imaging. The calculation module is used to calculate a lattice period of the sample 20, as described later. The image processing module is configured to process the acquired image, for example, to obtain a diffraction ring radius R. The distance control module can adjust the distance D between the sample 20 and the imaging device 132.

Unlike traditional electronic diffraction, this instrument is aimed at large-area two-dimensional materials. Fast structure characterization, two-dimensional materials, especially the diffraction principle with only one layer of atomic structure, will be different from the three Dimensional material. The principle of diffracting a two-dimensional nanomaterial by the transmission type low-energy electron microscopy system 10 provided by the present invention and the principle of diffracting a three-dimensional material by a conventional electron microscope are described below.

Referring to FIG. 4, for the two-dimensional material shown in FIG. 4(a), the condition of the diffraction to be satisfied is dsin θ = λ , where d is the lattice period of the two-dimensional material, and θ is the diffracted electron beam 24 The angle between the transmitted electron beam 26 and the transmitted electron beam 26. For the conventional three-dimensional material as shown in Fig. 4(b), the diffraction condition is 2 d'sin θ' = λ , where d' is the interplanar spacing of the three-dimensional material, and θ' is the incident electron beam. 22 is at an angle to the crystal face 28 of the three-dimensional material. In the diffraction of a conventional three-dimensional material, the angle between the transmitted electron beam 26 and the diffracted electron beam 24 is 2θ' . It should be noted that in the usual selection of electronic diffraction, θ is very small, satisfying θ. Sin θ Tanθ . For two-dimensional materials Where θ is the angle between the diffractive electron beam 24 and the transmitted electron beam 26. For three-dimensional materials, Where θ' is the angle between the incident electron beam 22 and the crystal facet 28, and 2θ' is the angle between the transmitted electron beam 26 and the diffracted electron beam 24.

The computing module of the control computer 17 passes The lattice period d of the sample 20 can be calculated. Specifically, referring to FIG. 2, in the same crystal orientation, the diffracted electron beam 24 forms a diffraction ring on the imaging device 132, and the transmitted electron beam 26 forms a transmission spot on the imaging device 132. The distance of the diffraction ring from the transmitted spot is equal to the radius R of the diffraction ring. This radius R can be obtained by the image processing software. The distance between the sample 20 and the imaging device 132 is D. The angle θ between the diffractive electron beam 24 and the transmitted electron beam 26 can be calculated by R and D. In addition, when the energy of the incident electron beam 22 is determined, its wavelength λ is also a determined value. In this way, according to The lattice period d of the corresponding crystal orientation of the sample 20 can be calculated.

It can be understood that the selection diffraction and micro-diffraction of the transmission electron microscope are parallel. Or an approximately parallel electron beam, due to the focus of the objective lens and the spherical aberration, the diffraction range of the selection is 0.5-1 micron, and the micron diffraction below 0.5 micron is called micro-diffraction. Converging beam diffraction focuses the electron beam at a large convergence angle on the surface of the sample, and the diverging beam expands the transmitted and diffracted spots into a disk. In a transmission electron microscope, a diffraction beam can be used to obtain a dark field image. However, usually only the transmission image and the diffraction image are observed. Conventional electronic diffractors also use small electron beam spots, and because traditional material samples are still relatively thick, they are generally only used for diffraction in a small size range. LEED can also integrate LEEM mode. However, LEEM only selects a diffraction beam for imaging, and the beam spot is also small. The instrument is oriented to the structural characterization of large-area samples. The imaging of single crystal and polycrystalline samples can be seen separately. The bright field image and the diffraction spot of the zero-order spot. The dark field image is obtained at the same time. The imaging and diffraction under the condition of large beam spot will be different from the rule of the existing instrument for small beam spot, which requires new considerations for electron optics and diffraction physics.

The transmission type low-energy electron microscopy system 10 provided by the present invention can be used for observing single-layer to multi-layer graphene and two-dimensional materials such as MoS ₂ , and has the following beneficial effects. First, the size of the sample 20 at a time can be on the order of ten micrometers to millimeters. By moving the sample 20, a rapid structural characterization can be performed on a range of dimensions in the order of centimeters. Second, the transmission design is adopted, and the electron beam energy is low, which reduces the damage to the sample. Moreover, the transmission-type low-energy electron diffraction proposed in this design can study the adsorption state of the surface of two-dimensional materials, which will be helpful for the study of the characteristics of two-dimensional materials and applications in the fields of detection, energy and catalysis. Adding an in-situ function to provide different types of molecular sources in the instrument can change the type of adsorption on the surface of the material. This study of the state of adsorption on the surface of a suspended material avoids the influence of the substrate and is more indicative of the properties of the material itself. Thirdly, in order to achieve complete degassing of the material itself, the local heating function of the sample is integrated. For the sake of simplicity, since most of the material systems used are electrically conductive, they can be transferred to the carbon nanotube film for non-conductive sample systems, so Joule heating can be used. Even for the study of the properties of the material itself, the integrated heating function makes it possible to study the structural properties of the sample with temperature. Fourth, the sample holder is xyz movable while integrating rotation in one direction. A conductive rod is placed in front of the imaging device to block the zero-order spot, and the intensity of a certain diffraction beam can be measured when a Faraday cup is mounted.

Embodiments for observing two-dimensional materials such as graphene and MoS ₂ using the transmission type low-energy electron microscopy system 10 provided by the present invention are described below.

Example 1

Referring to Figures 5a-5b, the sample of Example 1 of the present invention is a graphene island grown on a copper foil. Two of the graphene islands, on the order of square millimeters, are labeled 1 and 2, respectively. Referring to Figure 5c, the two graphene islands labeled 1 and 2 were transferred to a carbon nanotube film. Since the carbon nanotube film comprises a plurality of spaced and ordered carbon nanotubes, the two graphene islands are partially suspended by the carbon nanotube film. The carbon nanotube film supported by the graphene island is suspended on the central through hole of the circular copper piece. Because the carbon nanotube film is an ultra-thin, sparse porous structure, the effect on the sample is relatively small. In addition, because the most important diffraction spot of the carbon tube film is the diffraction between the tube walls, it is located at a low angle. It will affect the diffraction spots of the material being studied.

The sample was observed using a transmission type low energy electron microscopy system 10 provided by the present invention. When electricity The beamlet covers the entire graphene island 1, and the central transmission image and the diffraction image of the graphene island 1 are as shown in Figs. 6a-6b. Shown. As can be seen from Figures 6a-6b, the transmission pattern and diffraction pattern of the graphene island 1 coincide with the pattern of the graphene island 1. Referring to Figures 6c-6d, a schematic representation of a transmission image and a diffraction image of a single layer single crystal graphene sheet. Comparing Figures 6a-6b and Figures 6c-6d, graphene island 1 is illustrated as a single layer single crystal graphene sheet.

When the electron beam covers the entire graphene island 2, the central transmission image and the winding of the graphene island 2 The image is shown in Figures 7a-7b. 7a-7b, the transmission pattern of the graphene island 2 is similar to the transmission pattern of the graphene island 1, but the diffraction pattern of the graphene island 2 is more complicated than the diffraction pattern of the graphene island 1. . Referring to Figures 7c-7d, there are schematic views of transmission and diffraction images of a three-layer single crystal graphene sheet. Comparing Figures 7a-7b and 7c-7d, graphene island 2 is illustrated as a three layer single crystal graphene sheet.

Since electrons penetrate different graphene sheets and then diffract at different azimuth angles, The diffraction image of the plurality of layers of single crystal graphene sheets is a superposition of the diffraction images of each layer of graphene sheets. When the electron beam is focused, an image similar to selected area electron diffraction (SAED) is obtained. Figure 8 is a selected area diffraction image of four different regions of the graphene island 1. Figure 9 is a selected area diffraction image of four different regions of the graphene island 2. As can be seen from Fig. 8, the selected area diffraction image of the graphene island 1 is a single hexagonal diffraction lattice, indicating that the graphene island 1 is a single layer single crystal graphene sheet. As can be seen from FIG. 9, the selected area diffraction image of the graphene island 2 is three different hexagonal diffraction lattices, indicating that the graphene island 2 is a three-layer single crystal graphene sheet. In Figure 9, the different hexagonal diffraction lattices are labeled with different digits.

Example 2

Referring to FIG. 10a, the sample of Embodiment 2 of the present invention is a large-area continuous polycrystalline graphene film. It is transferred to a layer of ruthenium dioxide on the surface of a substrate. As seen from the selected area diffraction image of Figure 10b, the sample is a single layer graphene film. Figures 10c-10d are diffraction patterns of an electron beam covering the entire sample. Figures 10c-10d are electron transmission diffraction images of the sample of Example 2. As can be seen from Fig. 10c, the electron diffraction image of the large-area continuous polycrystalline graphene film is different from the electron diffraction image of the single-layer single crystal graphene sheet of Fig. 6e. The electron diffraction image of the large area continuous polycrystalline graphene film includes two sets of identical diffraction lattices. As shown in Figure 10d, after focusing the electron beam, it can be obtained that the transmitted diffracted image comprises two sets of identical hexagonal diffraction lattices. Figures 10c-10d show the crystal distribution of a large area continuous large polycrystalline graphene film of this millimeter size. Since the polycrystalline graphene film of Example 2 includes a plurality of minute single crystal graphene sheets, the diffraction pattern of the square millimeter-sized polycrystalline graphene film is thousands of tiny single crystals. Superposition of diffraction patterns of graphene sheets. The same set of hexagonal diffraction lattices of Figure 2d shows that the polycrystalline graphene film has two preferred crystal orientations.

Example 3

Referring to Fig. 11a, the sample of Example 3 of the present invention is a MoS ₂ sheet which is grown on a layer of ruthenium dioxide on the surface of a substrate. As can be seen from Figure 11a, the MoS ₂ sheet is discontinuous and has a coverage of about 19% on the tantalum substrate. Figure 11b is a diffraction pattern of an electron beam covering the entire sample. As can be seen from Figure 11b, the MoS ₂ sheet is polycrystalline and includes a plurality of diffraction lattices. Therefore, the MoS ₂ flakes have no preferred crystal orientation. When the electron beam covers only a few MoS ₂ sheets, the crystal orientation of these MoS ₂ sheets can be clearly seen. Figure 11c shows a transmission electron diffraction image of two crystal oriented MoS ₂ sheets. Figure 11d shows a transmission electron diffraction image of a single crystal oriented MoS ₂ sheet. Since the size of the MoS ₂ sheet is several tens of micrometers, which is much smaller than the electron beam spot size, the resolution of the transmission type low energy electron microscopy system 10 provided by the present invention exceeds the limitation of its electron beam size.

Example 4

The sample of the embodiment 4 of the present invention is basically the same as that of the embodiment 1, and the difference is that the sample is transparent. The sampled low energy electron microscopy system 10 was washed with deionized water prior to observation. In the present embodiment, the transmission type low energy electron microscopy system 10 provided by the present invention observes an additional diffraction lattice other than graphene. As shown in Figure 12a, initially, a set of hexagonal diffraction lattices were observed near the transmission point. The diffraction angle of these diffraction lattices is the same as the rotation angle of the graphene {10-10} diffraction lattice. However, as shown in Figures 12b-12d, after a few seconds, these additional diffraction lattices gradually disappear. Move the gun to a new position and the same diffracted image appears and disappears again. However, the sample was heated to illuminate in a vacuum and no additional diffraction lattice was observed. When the sample was irradiated with an electron beam or after the sample was heated, water spray was sprayed using a spray member, and it was found that the additional diffraction lattice appeared again and then disappeared. Therefore, the additional diffraction lattice may be caused by the adsorption of water molecules by the sample.

Example 5

The sample of the embodiment 5 of the present invention is basically the same as the embodiment 2, and the difference is that the embodiment Includes a polycrystalline graphene film with only one major crystal orientation, with multiple major crystal orientations A crystalline graphene film and a polycrystalline graphene film having three main crystal orientations. As shown in Fig. 13, in this example, transmission diffraction images of three samples after adsorption of water molecules were observed, respectively.

Example 6

The sample of Example 6 of the present invention is a large-area continuous polycrystalline graphene film which is transferred To a nano carbon tube film. In this embodiment, the electronic diffraction patterns of the samples at different rotation angles are respectively observed. As shown in FIG. 14, after the sample is rotated by 90 degrees, its corresponding electronic diffraction pattern is also rotated by 90 degrees.

Example 7

The sample of Example 7 of the present invention is a large-area continuous polycrystalline graphene film which is transferred To a nano carbon tube film. The sample of Example 7 of the present invention was substantially the same as that of Example 6, except that the present example was etched on the sample to form a slit having a width of 1 mm. In this embodiment, the electron beam is used to scan the sample in a direction perpendicular to the slit, and the slit is drawn across the slit to obtain a series of electronic diffraction patterns. As shown in Fig. 15, when the electron beam is drawn across the slit, the diffraction point of the electron diffraction pattern gradually becomes dark, disappears, and then becomes brighter. It can be seen that the electronic diffraction pattern is caused by the sample rather than the gap.

Example 8

The sample of Example 8 of the present invention was a single crystal graphene sheet which was transferred onto a carbon nanotube film. In this embodiment, the interplanar spacing d of the crystal faces (10-10) and the crystal faces (11-20) of the sample are respectively measured. As shown in FIG. 16, it is a function of the sin θ of the single crystal graphene sheet sample and the wavelength λ of the incident electron beam 22. Where θ ₁ is the angle between the diffracted electron beam 24 corresponding to the crystal plane (10-10) and the transmitted electron beam 26. θ ₂ is the angle between the diffracted electron beam 24 corresponding to the crystal plane (11-20) and the transmitted electron beam 26. The lattice period d of the corresponding crystal plane of the sample can be calculated from d = λ / sin θ .

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by those skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

Claims (10)

A transmissive low-energy electron microscopy system comprising: a vacuum chamber; an electron gun disposed in the vacuum chamber, an electron beam for emitting; a diffraction cavity connected to the vacuum chamber; An imaging device in the diffraction cavity; a sample holder for fixing a two-dimensional nano material sample, wherein the electron beam can be transmitted from the two-dimensional nano material sample to form a transmission electron entering the diffraction cavity And diffracting an electron beam and imaging the imaging device; a stem coupled to the diffraction cavity; a vacuuming device coupled to the vacuum cavity; and a control computer for controlling the entire system Work and data processing; the improvement is that the control computer further comprises a working mode switching module, wherein the working mode switching module can switch between an imaging mode of the large beam spot and a diffraction mode of the small beam spot; The imaging mode of the plaque is to irradiate the entire sample surface with an electron beam larger than the sample, and perform diffraction imaging; the diffraction pattern of the small beam spot is to irradiate the sample with an electron beam smaller than the sample. Scan the entire surface or partial surface, and the diffraction image. The transmission type low-energy electron microscopy system of claim 1, wherein the control computer further comprises an image processing module and a distance control module; the image processing module is configured to process the collected image Obtaining a diffraction ring radius R, the distance control module can adjust the distance D between the sample and the imaging device. The transmission type low-energy electron microscopy system of claim 2, wherein the control computer further comprises a calculation module for using the radius R of the diffraction ring and the sample and the imaging device It calculates the distance D between the diffraction angle θ between the transmitted electron beam with an electron beam, and the equation calculating the two dsinθ = λ Weinai Mi lattice period material sample according to d, where, [lambda] is the wavelength of the electron beam. The transmission type low energy electron microscopy system of claim 1, wherein the imaging device is a fluorescent screen. The transmission type low energy electron microscopy system according to claim 1, wherein the image forming apparatus It is set as a CCD image sensor, and an image of the transmitted electrons and the diffracted electrons is collected by the CCD image sensor and sent to the control computer. The transmission type low energy electron microscopy system according to claim 1, wherein the electron gun provides an electron beam energy of 800 eV to 3000 eV, an electron beam current of 0.1 microamperes to 1 microamperes, and an electron beam spot diameter of 100. Micron - 1 cm. The transmission type low-energy electron microscopy system of claim 1, further comprising a shower member disposed adjacent to the sample holder such that molecular material ejected from the shower member can be adsorbed The surface of the sample. The transmissive low-energy electron microscopy system of claim 1, further comprising a conductive rod, the conductive rod being rotatable such that the conductive rod can be rotated to the front of the imaging device to block the transmission spot Thus, only the diffraction pattern is obtained. The transmission type low energy electron microscopy system of claim 1, wherein the sample holder further comprises a heating element and a temperature sensor, the heating range being from room temperature to 1500K. The transmission type low energy electron microscopy system of claim 1, wherein the sample holder further comprises a moving device to move the sample to effect scanning of the sample by the electron beam.