Original:  Main Achievement Research Summary In 1985, Li Fanghua deduced a new and practical approximate analytical expression for high-resolution image intensity, established a practical image contrast theory, and solved the theoretical basis for the application of electronic crystallographic image processing in practice. Her research promotes the development of related disciplines and provides crystal structure information of new materials, which helps to draw the laws of the relationship between material properties, structure and technology. Her research content includes: (1) High-resolution electron microscopy and electronic crystallography In the early 1960s, Li Fanghua first carried out electron diffraction in China to determine the structure of a single crystal. In China, he determined the position of hydrogen atoms in the crystal for the first time. The relevant literature is still cited by foreign colleagues. In the 1970s, Li Fanghua and Fan Haifu cooperated to explore the combination of diffraction methods and high-resolution electron microscopy, and created a new image processing theory and technology in high-resolution electron microscopy. Later, she and her students established an unwinding processing technology based on the principle of maximum entropy. It provides an important way to determine the tiny crystal structure. It has been successfully applied to determine the crystal structure of materials such as high-temperature superconductors. While studying in Japan in the 1980s, Li Fanghua summarized new experimental rules and developed a method for determining the position of light atoms. On this basis, after returning to China, she proposed a new image contrast theory: "pseudo-weak phase object approximation". This theory clarified the relationship between image intensity and crystal thickness for the first time, and revealed the law of changes in the intensity of different atomic images. , Is the theoretical basis of the above-mentioned image processing technology. Under the guidance of this theory, Li Fanghua et al. observed lithium atoms in crystals for the first time experimentally. In addition, she participated in the early research of high-temperature superconducting materials by means of high-resolution electron microscopy, and was one of the first groups in the world to report the presence or absence of commensurate modulation structures of bismuth superconductors. (2) Quasi-crystal The research team led by Li Fanghua first discovered and reported the almost continuous transition process between quasicrystals and crystals, and she gave a theoretical explanation. Li Fanghua used the phase sub-strain field to derive some formulas reflecting the relationship between the quasicrystal and the crystal, and on this basis, proposed a new method to determine the structure of the quasicrystal, as well as the determination of the local phase sub-strain in the quasicrystal. method. And successfully applied to Al-Cu-Li and Al-Mn-Si quasicrystals. (3) Crystal defects For the newly developed field emission electron microscope, Li Fanghua proposed a new research direction for measuring crystal defects with atomic resolution. At present, she has successfully measured the 60-degree dislocation at the SiGe/Si epitaxial film interface into two incomplete dislocations of 90 degrees and 30 degrees, and a piece of stacking fault sandwiched between them. This is also the first report on the defect of atomic resolution at the interface of SiGe/Si epitaxial film .
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