Development Trend of New Generation Electron Microscope
1. High-performance field emission gun electron microscopes are increasingly popular and applied. The field emission gun transmission electron microscope can provide high brightness and high coherence electron light source. Therefore, the atomic arrangement and types of materials can be comprehensively analyzed on the atomic-nanometer scale. In the mid-1990s, there were only a few dozen units in Taiwan; now it has soared to thousands. At present, there are more than one hundred field emission gun transmission electron microscopes in our country. Conventional hot tungsten filament (electron) gun scanning electron microscopes can only reach a resolution of 3.0nm at the highest; the new generation of field emission gun scanning electron microscopes can have a resolution better than 1.0nm; The resolution is as high as 0.5nm-0.4nm. Among them, the environmental scanning electron microscope can achieve: real "environmental" conditions, samples can be observed under 100% humidity conditions; biological samples and non-conductive samples do not need to be coated, and can be directly on the machine for dynamic observation and analysis; Three uses of the machine". Three working modes of high vacuum, low vacuum and "ambient".
2. Efforts should be made to develop a new generation of monochromators and spherical aberration correctors to further improve the resolution of electron microscopes. Spherical aberration coefficient: the spherical aberration coefficient Cs of the conventional transmission electron microscope is about mm; the spherical aberration coefficient of the current transmission electron microscope has been reduced to Cs<0.05mm. Chromatic aberration coefficient: the chromatic aberration coefficient of the conventional transmission electron microscope is about 0.7; The chromatic aberration coefficient of the TEM has been reduced to 0.1. Field emission transmission electron microscopy, STEM technology, and energy filtering electron microscopy have become analytical means and tools for material science research, and even biomedicine. The spherical aberration corrector of the objective lens improves the resolution of the field emission transmission electron microscope to the information resolution. That is, it improves from 0.19nm to 0.12nm or even less than 0.1nm. Using a monochromator, the energy resolution will be less than 0.1eV. But the beam current of the monochromator is only about one tenth of that without a monochromator. Therefore, while using a monochromator , but also to consider the reduction of the beam current of the monochromator. While the spherical aberration corrector of the condenser improves the resolution of STEM to less than 0.1nm, the spherical aberration corrector of the condenser increases the beam current by at least 10 times, which is very beneficial to improve the spatial resolution. While correcting the spherical aberration, the chromatic aberration increases by about 30%. Therefore, while correcting the spherical aberration, the chromatic aberration should also be considered.
3. Electron microscope analysis is moving toward computerization and networking. In terms of instruments and equipment, the current operating system of the scanning electron microscope has used a brand-new operation interface. The user only needs to press the mouse to realize the control of the electron microscope lens barrel and electrical parts, as well as the automatic memory and adjustment of various parameters. Between different regions, demonstrations such as moving samples, changing imaging modes, and adjusting electron microscope parameters can be performed through the network system. In order to realize the remote control of the electron microscope.
4. The important application of electron microscope in the study of nanomaterials. Since the analysis accuracy of the electron microscope is close to the atomic scale, using a field emission gun transmission electron microscope and an electron beam with a diameter of 0.13nm can not only collect the Z-contrast image of a single atom, but also collect the electron energy of a single atom loss spectrum. That is, the electron microscope can simultaneously obtain the atomic and electronic structure information of materials at the atomic scale. Observing individual atomic images in samples has always been a long-term pursuit of the scientific community. The diameter of an atom is about 2-3mm in 10 millionths. Therefore, to distinguish the position of each atom, an electron microscope with a resolution of about 0.1nm is required, and it must be magnified about 10 million times. It is predicted that when the scale of the material is reduced to the nanoscale, the optical, electrical and other physical and mechanical properties of the material may be unique. Therefore, the preparation of nanomaterials such as nanoparticles, nanotubes, and nanowires, as well as the research on the relationship between their structures and properties have become a research hotspot that people have paid close attention to. Using an electron microscope, generally on a transmission electron microscope with an ultra-high vacuum field emission gun above 200KV, high-resolution electron microscope images of nanophases and nanowires, electron diffraction patterns and electron energy loss spectra of nanomaterials can be observed. For example, carbon nanotubes with an inner diameter of 0.4nm, Si-C-N nanorods, and Li-doped Si semiconductor nanowires were observed on the electron microscope. In the field of biomedicine, nano-colloidal gold technology, nano-selenium health care capsules, nano-level organelle structures, and nano-robots that can be as small as bacteria, monitor blood concentrations in blood vessels, and remove blood clots in blood vessels can be said to be all researches. Inseparable from the tool electron microscope. In short: SEM and TEM are becoming more and more important in materials science, especially nanotechnology. The improvement of stability and operability makes the electron microscope no longer an instrument used by a few experts, but a popular tool; higher resolution is still the most important direction for the development of the electron microscope; the application of scanning electron microscope and transmission electron microscope has changed from characterization and Analysis has developed to in-situ experiments and nano-visible processing; Focused ion beam (FIB) has been used more and more in the scientific research of nano-materials; The most powerful tool for nanoprototyping; the goal of corrective STEM (Titan): 3D structure characterization at 0.5Å resolution in 2008.
5. Cryo-electron microscopy and three-dimensional reconstruction technology are the current research hotspots in bioelectron microscopy. Cryo-electron microscopy technology and three-dimensional reconstruction technology are current research hotspots in bio-electron microscopy. It mainly discusses the use of cryo-electron microscopy (which also includes the application of cryo-electron microscopy on a liquid helium cold stage) and computer three-dimensional image reconstruction technology to determine biological Three-dimensional structure of macromolecules and their complexes. Such as the use of cryo-electron microscopy to determine the three-dimensional structure of viruses and the growth of two-dimensional crystals of membrane proteins on monolayer lipid membranes and their electron microscope observation and analysis. Structural biology has aroused people's high attention nowadays, because looking at the biological world from a systemic point of view, it has different hierarchical structures: individual ® organ ® tissue ® cell ® biomacromolecule. Although biomacromolecules are at the lowest level, they determine the differences between high-level systems. Three-dimensional structure determines function. Structure is the basis of application: drug design, genetic modification, vaccine research and development, artificial protein construction, etc. Some people predict that breakthroughs in structural biology will bring revolutionary changes to biology. Electron microscopy is one of the important means of structure determination. The advantages of low-temperature electron microscopy are: the sample is in a water-containing state, and the molecules are in a natural state; because the sample is damaged by radiation, low-dose technique must be used for observation; the observation temperature is low, which enhances the radiation resistance of the sample; Samples can be frozen in different states to observe changes in molecular structures. Through these techniques, the observation and analysis results of various biological samples are closer to the real state.
6. High-performance CCD cameras are becoming more and more popular. The advantages of CCDs used in electron microscopes are high sensitivity, low noise, and high signal-to-noise ratio. Under the same pixel, CCD imaging often has good transparency and sharpness, and color reproduction and exposure can be guaranteed to be basically accurate. The image resolution/resolution of the camera is how many pixels we often say. In practical applications, the camera The higher the pixels, the better the quality of the captured image. For the same picture, the higher the pixels, the stronger the ability to analyze the image, but the amount of data it records will be much larger, so the storage device requirements are much higher. In today's TEM field, the newly developed products are completely computer-controlled, and the image acquisition is completed by a high-resolution CCD camera instead of a photographic film. The trend of digital technology is driving the revolution of TEM application and even the whole laboratory work from all aspects. Especially in terms of image processing software, many things that were considered impossible in the past are becoming a reality.
