The thickness of TEM sample is preferably less than 100nm. Too thick electron beam is not easy to penetrate and the analysis effect is not good.
2. What are the obvious features of transgranular fracture and intergranular fracture in SEM images?
In SEM photos, it can be clearly seen that cracks develop along grain boundaries, and the grain boundaries are obvious. Transgranular fracture is that the crack propagates in the grain and the grain boundary is blurred.
3. What are the requirements for samples when doing TEM test?
It's simple, as long as there is no water. If the sample is a solution, it needs to be dropped on a certain substrate (such as glass), then dried and sprayed with carbon. If the sample itself is conductive, carbon spraying is not needed.
4. How do nanoparticles do TEM in aqueous solution?
Transmission electron microscope samples must be detected under high vacuum, and nanoparticles in aqueous solution cannot be directly detected. Generally, the samples are picked up by micro-grid or copper mesh, then put into the sample pre-extractor, dried and put into the electron microscope for testing. If the sample size is very small, only a few nanometers, you can fish the sample with a non-porous carbon film.
5. How to do TEM for powder samples?
In scanning electron microscope (SEM) testing, powder samples are mostly prepared by double-sided tape dry method and ultrasonic wet method, and mixed with appropriate solutions. Dispersants are not effective in SEM sample preparation, and sometimes they have the opposite effect, such as crystallization when drying.
6.6 What is the difference between sampling depths? EDS and XPS?
The sampling depth of XPS is 2-5nm, and the sampling depth of EDS is about 1um.
7. Energy spectrum, some called EDS, some called EDX, which is more suitable?
The full name of energy spectrum is energy dispersive X-ray spectroscopy.
International standardized terms:
alpha ray spectrometer
EDX spectroscopy
What is the aperture of 8.8 copper mesh? TEM？
Carbon supporting film and micro-grid with holes are commonly used in powder fishing, and there is actually an ultra-thin carbon film on the micro-grid with holes. For high resolution, it is best to control the thickness of the sample below 20nm, so the powder with a diameter less than 20 nm is generally fished out directly. If the particle is large, it is best to dilute the ions after embedding.
9. Nanocrystals were observed by transmission electron microscope, and there were amorphous region around the nanocrystals. I want to raise the temperature of the amorphous region or give it a certain voltage (current) to make it change, and observe the change in situ?
Atomic force microscope should solve this problem.
How to make SEM of 10? Magnesium-aluminum alloy, secondary electron?
The correct measurement of this sample should be polished first and then corroded. If there is evaporation, you can cross a layer of gold on the surface of the sample.
1 1. How to make TEM samples of ceramics?
Slicing, grinding, ion refining, FIB (highly recommended)
12. Application information of transmission electron microscope in polymer materials research?
Modern Polymer Physics (Volume II), edited by Yin Jinghua and Mo, Science Press, 200 1[ Chapter 18 Application of Electron Microscope in Polymer Structure Research]
13. What is the difference between microscopic diffraction and selective diffraction in transmission electron microscopy?
The difference lies in the size of the electron beam spot. The selected diffraction beam spot is about 50 microns or more, and the beam spot is micron or micro-diffraction. Microscopic diffraction is mainly used to identify some small phases.
14. What does SEM think of the thickness of oxide layer? Is it accurate to look at the thickness of the oxide layer of the sample by scanning electron microscope and directly cut the section?
The thickness of the oxide layer of the sample was observed by scanning electron microscope. If it's glass or ceramic, just cut it off. If it is a metal material, the sample structure may not change when cutting, so it depends on the oxide layer of what material.
15. Requirements for preparation of glass-ceramics samples by transmission electron microscope
Firstly, the thickness of the thin slice is less than 500um, then it is nailed to the sample preparation room of the central transmission electron microscope, and then ion thinning is carried out.
16. What parts does the electron energy loss spectrum consist of?
EELS and HREELS are different systems. The former is generally used with high-resolution transmission electron microscope, and it is best to use field emission gun and energy filter. The general resolution can reach 0. 1 ev- 1 ev, which is mainly used to obtain the content of elements, especially the content of light elements. But also the thickness of the corresponding sample area can be easily obtained. HREELS is a high vacuum independent equipment, which can study the adsorption and dissociation of gas molecules on solid surfaces.
17. To study the vesicles formed by surfactants, many literatures are made of cryoTEM, and the shape is really clear, but only negative staining can be done in the laboratory. Can you see the wall of the bubble clearly?
The structure of polymer samples is easily destroyed by electron beam, and freezing table is the best method. You can see the outline of the wall by negative dyeing, but you should observe it carefully. It's impossible without a freezing table, right? All the polymer samples I have seen are satisfied by looking at the outline, and no higher requirements have been mentioned.
18. What do HKL and HKL mean?
(hkl) denotes the crystal plane index {hkl} denotes the crystal plane family index.
[hkl] indicates that the crystal orientation index indicates the crystal orientation group index.
The coordinate representation of (h, k, -h-k, l) hexagonal system is infinite.
19. what will happen to the brightness and size of the light spot after the magnification is increased in the electron microscope test?
Darkening, because the objective lens is stronger and the focal length is smaller, it blocks part of the current, and the brightness is proportional to the current. Because the intensity of the total beam is fixed, if the magnification is too large, the electron beam passing through the lens will be less, and vice versa. The brightness is adjusted to focus the limited light,
20. What mode does alumina TEM choose?
It is best to adopt low dosage mode for alumina, so as not to destroy the crystal structure as much as possible.
How to sample 2 1? ZSM-5 under transmission electron microscope?
Adding alcohol into agate mortar, grinding, dispersing with ultrasonic wave, and dropping on a micro-grid. The sensitivity of irradiation is related to the SiAl ratio, and the greater the SiAl ratio, the more stable it is.
22. For polymer samples with weak diffraction intensity and short life, is the exposure time long or short?
Due to the weak diffraction, long-time exposure is a method to increase the contrast, and the enhancement range of transmission spots is large, but it is easy to cover up much weaker spots and the samples are easy to be damaged, so short-time exposure is more suitable. I have photographed the diffraction of mesoporous molecular sieve, which is weak, and the effect is better after 6-8 s than after a long time.
23. How to write the ordinate of EDXS?
The EDXS spectrum was made, and it was found that the ordinate of the spectrum in various publications was inconsistent. Perhaps because the absolute intensity value is not very important, there is no uniform standard for labeling the ordinate of X-ray energy spectrum. In addition to I/CPS, CPS, Counts and other writing methods, there are unmarked, marked with strength or relative strength and so on. The specific form of marking depends on the requirements of the magazine you submit. Generally, there are many CPS, that is, the count per second, that is, the count per second of the spectrometer counter.
24. Both are 24. Is EDAX the same as Ed?
EdAX has two meanings, one is X-ray energy dispersion analysis, also known as EDS method or EDX method, which is rarely expressed by ED; Second, it refers to the earliest company that produces spectrometers-American EDAX Company. Of course, EDAX is not the only company that produces energy spectrometers, and so is Oxford in Britain.
EDAX refers to the auxiliary analytical equipment used in scanning electron microscope (SEM) or transmission electron microscope (TEM)-energy spectrometer, or the company that first produced energy spectrometer-American Idax Co., Ltd., or this analytical technology. When we observe the electron microscopic image on the electron microscope, we can use this attachment to analyze the energy and intensity of X-rays emitted by a point on the microscopic image, or a point on a line or a surface, so as to determine the elemental information (species and content) of the point we are interested in on the microscopic image.
25. Secondary diffraction
Because electrons are scattered many times in matter, emission often occurs where the first scattering should not occur. This phenomenon is called secondary diffraction. When determining the regularity of small light reflection index caused by crystal symmetry, we must pay attention to this second diffraction phenomenon. The second diffraction point is the result of the second diffraction of the first diffraction wave. The second diffraction point can appear at the position where the sum of the inverse vectors of the two diffraction points with approximate kinematics is located. Especially, there is a great possibility of secondary diffraction points on the axis passing through the origin. In addition, we should pay full attention to its strength.
26. What is a superlattice?
1970, the concept of superlattice was put forward by He Zhu of IBM laboratory in the United States. They imagine that if two kinds of semiconductor materials with good lattice matching are used to alternately grow periodic structures, and the thickness of each layer is below 100nm, as shown in the figure, the movement of electrons along the growth direction will oscillate. It can be used to make microwave equipment. Two years later, their idea was realized on molecular beam epitaxy equipment. It can be seen that superlattice material is a multilayer thin film with two different components alternately growing in thin layers of several nanometers to tens of nanometers and maintaining strict periodicity, which is actually a specific form of layered fine composite materials.
27. Are the white dots in the bright-field image lattice metal atoms?
Because of the influence of electron beam coherence, lens aberration, defocus and sample thickness, it is impossible to directly interpret high-resolution images, and image simulation is needed, so it is difficult to say whether the white spots in the images are metal atoms or not, and we can only know by calculation.
28. How to disperse carbon tubes for TEM?
It is best to look at carbon tubes with micro-grids, because the contrast between carbon films and carbon tubes is too weak, and it will be difficult to observe them with carbon films. Especially single-wall pipes. In addition, be careful not to dip the carbon film into it for fishing (there will be samples on both sides and it will be difficult to focus). Samples can be dripped, coated, rubbed and stained with carbon film on the surface, and the carbon film is easy to burst when the surface tension is too high.
29. Resolution of different pole shoes
Pole shoes are divided into: ultra-high resolution pole shoes, high resolution pole shoes and high inclination pole shoes. The ultra-high resolution pole shoe point resolution is 0. 19nm, and the high resolution pole shoe point resolution is 0.24nm, but it can't reach the actual situation. The resolution of field emission is the same as that of LaB6, but the fast current is more stable and the brightness is 100 times higher than that of LaB6.
30. If the machine discharges-there is enough freon in the electron gun to reach the specified index.
When the voltage is normal and the filament current is normal, all the diaphragms are retracted, but there is still no light-the valve of the electron gun is not opened.
Withdraw all stations, there is a beam of light, but half of it is blocked. I don't know why-the closed valve blocks some light.
3 1. How do you write the size of the ruler?
Only numbers such as 1, 2, 5 can be used in the ruler, such as 1, 2, 5, 10, 20, 50, 100, 200,500, and nothing else.
32. What's the difference between TEM and STEM images?
TEM imaging: illuminating parallel beams, imaging coherence, result simultaneity and contrast are inversely proportional to sample thickness and defocus. Because more electrons pass through the collected scattering interface, the contrast of the image is better!
STEM imaging: focused beam illumination, incoherent imaging and cumulative results. In the case of completely incoherent reception, the contrast of the image will not be reversed with the sample thickness and defocus, and thicker samples can be imaged.
33. How to sample nanorings?
Tufa, put the copper net in your sample and shake your hand for a while. In this way, the sample can be dispersed without ethanol, and the large particles can be blown off by ear washing balls before observation, so that the general nano-scale samples can be hung. It's just that the uniformity of scraping is poor.
You can also take a sample and put it in a mortar, and copy it several times with a copper mesh similar to a sand screen on site.
34. About the radioactivity of uranium dioxide acetate.
The half-life of uranium 236 in uranium dioxide acetate is as long as 24 million years, which is not a big problem and can be used safely!
35. Internal standard method
Using known lattice samples (gold particles), under the same electron microscope state (high pressure), corresponding to some camera lengths, the camera length L is 0.4, 0.8 and 1 m. Through the basic formula of electron microscope H=Rd=Ls, (H camera constant S is wavelength), a set of camera constants can be obtained and kept well. It can be used very conveniently in the future.
36. What software can simulate Ju Chi diagram?
JEMS: Yes, when drawing the electron diffraction pattern, just choose the Ju Chi line.
37. What about the metal samples of transmission electron microscope?
Including metal slicing, sandpaper grinding, disc punching, pit grinding, double jet electrolysis and ion thinning, FIB sample preparation (sample preparation artifact of block samples).
38. Several methods for preparing transmission electron microscope film samples (vacuum evaporation, solution solidification, ion bombardment thinning, ultra-thin slicing, and planting of metal film samples) are introduced.
You can refer to Mr. Zhang of electron microscope and Mr. Liu Ansheng of analytical electron microscope method for material evaluation.
39. The problem of osmium tetroxide.
Soaking the sample in osmium tetroxide solution can dye the elastomer on the one hand and harden the plastic on the other. If the volatility of osmium tetroxide is really strong, nick the ampoule, put it in a thick glass bottle, plug it with a rubber stopper, shake it well, and inject distilled water into a syringe to dissolve it. When the rubber plug was removed and replaced with a glass plug, it was found that the rubber plug mouth was completely black! When using, be sure to add protection, wear protective masks and gloves, and operate in the gas holder. The exhaust on the gas holder must be good. This is good for yourself and others!
40. Make electron microscope samples of polymer films.
Generally, a thin film is spin-coated on a glass or ITO substrate, soaked in water, and then the film is uncovered. However, for films with a thickness less than 100nm, it is difficult to peel off by this method. Spin-coat the polymer solution on smooth glass (the glass should be treated with plazmaor uv ozon), and put it into water immediately after film formation. Don't heat and dry, or you won't get it off. Using the tension of water, the film can be separated from the glass from the edge with plastic tweezers, and the film of about 70nm can be treated. Then put the membrane on the grid!
4 1. How to convert three crystal plane indices into four crystal plane indices?
Triaxial crystal plane index (hkl) is converted into tetraxial crystal plane index (hkil), where i=-(h+k).
Hexagonal crystal system needs to be calibrated by four-axis graduation, and cubic and orthogonal crystal systems can be calibrated by three-axis graduation.
42. The lowest detection limit of energy spectrum
Under the best experimental conditions, the minimum detection limit of energy spectrum is about 0.0 1-0. 1%, which is still a long way from ppm. If you can make a TEM sample, maybe you can try electron holography. In this way, several ppm impurities in semiconductor can be observed.
43. Advantages of CCD over film
At present, TEM CCD can completely replace negative film, and it is superior to film in pixel size (less than 20um), sensitivity, linearity, dynamic range, detection efficiency and gray scale. Because CCD has a very high dynamic range, it is especially suitable for recording strong features and weak fine structures in images and electron diffraction spectra.
44. Small-angle double injection, how to choose double injection?
There is a formula in teacher Wu Xingfang's book:
Chemical polishing of copper: 50% nitric acid +25% acetic acid +25% phosphoric acid at 20℃.
CuNi alloy: electrolytic polishing 30mL nitric acid +50mL acetic acid+10mL phosphoric acid.
—— Practical methods of electron microscopic analysis, edited by Wu Xingfang and Liu Deli.
45. When non-metallic materials are sprayed with gold, will there be gold particles sprayed out on the vertical plane of the material perpendicular to the gold spraying machine?
When spraying gold, the plane gold particles facing the nozzle are the most, which is also the area observed by electron microscope. There should be few or no sides, so when spraying gold, the surrounding sides are generally wrapped with aluminum foil to increase conductivity.
46. The Z contrast image is imaged by the high-angle dark field detector of STEM, namely HAADF. Can ordinary ADF get Z contrast image?
Atomic resolution STEM is not patented by HAADF, ADF or bright field probe can also be used, but the direct interpretation is too poor, and the advantage of Z contrast is lost. In addition to high collection angle, HAADF has much higher collection sensitivity than common ADF probe. There are not many electrons with high scattering angle, and sensitivity is more needed. The position of ADF is usually very low, the acquisition angle is not high (even if the camera length is very short), and the sensitivity is low, so it is not suitable for weak signal acquisition.
47. Simple classification of transmission electron microscope?
Transmission electron microscope can be divided into thermionic emission type and field emission type according to the different ways of generating electrons. Thermionic emission filament mainly includes tungsten filament and lanthanum hexaboride filament; Field emission types can be divided into thermal field emission and cold field emission.
According to the different pole shoes of objective lens, it can be divided into high tilt, high contrast, high resolution and ultra-high resolution types.
48. Does TEM need liquid nitrogen for normal operation?
Different from the energy spectrum probe, TEM liquid nitrogen cooling is not necessary, but it is helpful to the vacuum around the sample and to quickly restore the working state after the sample is replaced.
49. Does the electron microscope need to pay attention to magnetic particles?
1. magnetic particles need to be cautious when doing electron microscopy. I suggest reading related posts.
2. Surfactants can be used as dispersants, but local surfactants will decompose under electron beam irradiation, forming pollution rings during observation, which hinders observation.
50. Adjustment of voltage center and current center?
HT wobbler adjusts the voltage center, OBJ wobbler adjusts the current center, and wobbler-imagex and imagey help focus.
5 1. How do materials prepared by hydrothermal method do electron microscopy?
The materials prepared by hydrothermal method are easy to contain crystal water, and the structure is easy to be destroyed under electron beam irradiation. It is beneficial to remove some crystal water if the sample stays overnight under high vacuum of electron microscope. It is estimated that after you talked to the operation teacher, he won't let you put the samples in advance.
52. What is the magnetic deflection angle of TEM for a while and how to correct it?
Generally, the old electron microscope needs to correct the magnetic deflection angle, but the new electron microscope doesn't need to do it. At present, the imported electron microscope automatically corrects the magnetic deflection angle.
53. Why does molecular sieve conduct electricity?
The molecular sieve should be similar to silicon. Pure silicon is basically non-conductive, and the electron bonding in a single silicon atom is not as tight as that in an insulator. A very small amount of electrons will also be separated from silicon atoms due to the action of electron beams, forming a small amount of free electrons. Leave holes for electrons, which are positively charged and conduct electricity.
54. There will be a black shadow in the electron diffraction diagram, which is the shadow of the indicator bar, and one end of the shadow points to the diffraction center. Why should this shadow be marked in the diffraction pattern?
The beam blocker is mainly used to block the center transmission spot that is too bright, so that the weaker diffraction spots around can also be clearly displayed.
55.HAADF-STEM high-angle annular dark field image of scanning transmission electron microscopy.
Z-contrast imaging with high resolution or atomic resolution can also be called high-angle annular dark field image (HAADF-STEM) of scanning transmission electron microscope. The incoherent high-resolution image produced by this imaging technology is different from the coherent phase contrast high-resolution image, and the phase contrast will not change greatly with the thickness of the sample and the focal length of the electron microscope. The bright spots in the image always reflect the real atoms. The intensity of the point is proportional to the square of the atomic number, so the chemical composition information of atomic resolution can be obtained.
56. Pan Ning specification in transmission electron microscope.
The Pan Ning gauge for measuring the vacuum degree was not measured, so the engineer asked it to be removed and cleaned. Because there is no "internal caliper", it can't be completely dismantled, so we have to blow it with N2 for a while, and it will return to normal after reassembly. However, according to the project, it is best to polish it with sandpaper and clean it with alcohol after taking it out.
57. Can automatic exposure time be used for electron diffraction? If manual exposure is used, how long is appropriate?
Electron diffraction can't use automatic exposure, it depends on experience. Generally 1 1 or 16 seconds. If the spots are weak, the exposure time should be extended.
58. What is the meaning of CCD in CCD camera?
Charge coupled device
For details, please refer to page 35-42, Analytical Electron Microscope Method for Material Evaluation.
59. There are commensurability modulation and incommensurability modulation.
Under certain conditions, the long-range correlation of many substances makes the structure of local atoms in the crystal modulated by periodic modulation waves. If the modulation period is an integer multiple of the lattice translation vector of the basic structure, it is called commensurability modulation; If the ratio of the modulation period to the lattice translation vector of the basic structure is an irrational number, it is called incommensurate modulation. The modulation structures involved can be structural modulation, component modulation and magnetic structure modulation. Modulation can be one-dimensional, two-dimensional and three-dimensional.
60. How fine is the high-resolution powder sample?
To make a high-resolution powder sample, the particles are ground so finely that they cannot be distinguished by the naked eye. Dozens of nanometers is not small. The smaller the particle, the easier it is to find the thin edge region with high resolution, which is more conducive to the energy loss spectrum analysis; The larger the particle, the easier it is for the crystal to tilt to the band axis (such as diffraction analysis), and the higher the X-ray count.
6 1. Working mode of electron microscope filament?
When the heating current of tungsten wire or lanthanum hexaboride wire is zero, its emission current is also zero. Only by increasing the heating current can the emission current be generated, and increasing the heating current after the saturation point will not increase the emission current too much. There is no heating current, only emission current, which is actually the working mode of cold field emission. But it also needs a strong extraction voltage to act on the tip of the filament.
62. What is the crystal growth direction?
The crystal growth direction is the plane with the lowest crystal face index, which is the same as the electron diffraction direction, and then it can be simplified to the coprime index. For example, if it is (222) along the crystal growth direction, it should be (11) as the growth direction.
63.N-A mechanism
Small single crystals gradually expand and finally recrystallize into single crystals, which is called N-A mechanism and nucleation-aggregation mechanism.
64. Can three-dimensional images be obtained by transmission electron microscope?
Three-dimensional reconstruction can be done, but special sample sticks and software are needed.
65. Nanofiber transmission electron microscope
When making PAN-based carbon fiber, the feeling drift may be caused by two reasons: one is that the sample is not fixed well, and the other is that the conductivity is too poor. When analyzing fiber samples with electron microscope, we usually use the method of embedding fibers and then making ultra-thin sections. If the fiber is cut very fine (30 ~ 50 nm), we can fish it directly into the copper net for observation without spraying gold.
66. Ion dilution process
Before ion thinning, the sample should be mechanically thinned with sandpaper and nailing machine, and the thickness of the mechanically thinned sample is about 10 micron, and then ion thinning is carried out.
When the ions are thinned, the ions are rapidly thinned at a large angle of 15-20 degrees, and then narrowed to a perforation at a small angle of 8- 10 degrees.
67. What is the working principle of 48 spherical aberration corrector?
Want to know the principle, just look at the relevant articles.
take for example
Max Haider et al., Ultramicroscopy 75 (1998) 53-60.
Max Haider et al., ultramicroscope 81(2000)163-175.
68. Bright field images and dark field images
Bright-field images are imaged by projecting and diffracting electron beams,
The dark field image is imaged by diffracted electron beam (1 10), showing interference fringes.
69. When taking pictures, you need to switch between different magnifications. The original adjusted condenser diaphragm often changes its position after the magnification is changed, that is, the spot is no longer strictly concentric. Why?
This is normal. Generally, the aperture alignment of condenser is done at low magnification (40K), and there will be deviation at high magnification (500K), because the alignment at low magnification will not be accurate.
Generally speaking, I am the first to correct the condenser diaphragm, and I have to readjust the project after moving it. When preparing for high resolution, it is generally convenient to combine them when preparing for high resolution shooting.
70. What is the working principle of energy filtering?
The working principle of energy filtering imaging can be simply understood as the beam splitting phenomenon of prism, and then the light imaging that cannot be energy is selected.
The principle of energy filtering is that the deflection radius of electrons with different energy (velocity) is different in the magnetic field (it is often done in middle schools to calculate the deflection radius of electrons acting on Rolenc force), so a slit is added at different positions to filter out the energy.
7 1. Consequences of vacuum damage
It will not affect the life of electron microscope, but it will definitely affect the life of filament.
72. The results of EDX composition analysis are changing every time.
The situation that the results of EDX component analysis change every time is actually very simple. In the energy spectrum analysis software, there is a periodic table under the view menu. In the case of its ROI, select the elements to be quantized, and right-click the mouse to select the peak to be quantized for each element. If you re-quantify, the problem you mentioned will not appear.
73. When using 20 10 transmission electron microscope, it is found that when the brightness is gathered together, two concentric circles are presented according to IMAG X. Adjusting foucs will make DV not equal to zero. I want to ask you, if you want to keep dv=0, what adjustments need to be made?
Adjust dv to +0, and then adjust the height of the sample with Z axis to minimize the jitter of imagex.
74. Image contrast problem
Le Kai's film contrast is worse than Kodak's, but the price/performance ratio has always been good. It is recommended to try Gao Fancha developer.
You can use dark fields to improve the contrast. I've been shooting the form of organic matter with dark field! Wang Heshang (June 07: 33: 02, 2009)
75. The problem of polymer dyeing
Phosphotungstic acid is a dye solution used for negative dyeing samples. We usually use the concentration of 1% or 2%. When the concentration is high, there will be many black spots or crystal blocks. In addition, the concentration of the sample itself is very important, so you can try several more concentrations. If there are components in the sample that are easy to combine with the dye solution, black spots or black clusters will also appear. Phosphotungstic acid can be used to dye nylon or polyamide to make it black, so as to increase the contrast of polymer materials. Osmium acid can make polymer materials with double bonds appear black.
Choosing the right dye according to your own requirements is the key to observation!
76. What is a sub-crystal?
Sub-crystals are simply separated by small-angle grain boundaries, which are mainly composed of dislocations, and the crystal orientation difference between adjacent sub-crystals is very small.
77. What is the corresponding relationship between FFT diagram and diffraction diagram?
Both of them are two-dimensional vector projections in frequency space, which are related to structural factors and can be used for phase calibration, but they have different meanings and operational formulas in diffraction physics and cannot be confused.
FFT is the mathematical calculation of pixel gray value of TEM image, and diffraction is the special arrangement of electrons after diffraction of the sample.
78. What is the diffraction pattern of amplitude modulation structure?
There are obvious elongated stripes between diffraction spots.
80. What are bright field, dark field and high resolution images?
In diffraction mode, a small objective diaphragm is added, and only the transmitted light beam passes through, so as to obtain a bright field image; Obtaining a dark field image by only one diffracted beam; With or without a large objective lens aperture, the high-power (more than 500,000 times) imaging mode is switched to obtain a high-resolution image. Of course, whether a high-resolution image can be obtained depends on the axial direction of the ribbon, the thickness of the sample and the defocus amount.