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ENCYCLOPEDIA O FMATERIALS CHARACTERIZATIONC phần 3

Năng lượng-Loss Quang phổ học điện tử (cá chình) là một phương pháp phân tích nguồn gốc thông tin của mình từ các phép đo thay đổi trong việc phân phối năng lượng và góc của một chùm tia ban đầu trên danh nghĩa monoenergetic của các điện tử đã được rải rác trong quá trình truyền thông qua một mẫu vật mỏng. | 3.2 EELS Electron Energy-Loss Spectroscopy in the Transmission Electron Microscope NESTOR J. ZALUZEC Contents Introduction Basic Principles Low-Loss Spectroscopy Inner Shell Spectroscopy Quantification Limitations and Specimen Requirements Conclusions Introduction Electron Energy-Loss Spectroscopy EELS is an analytical methodology which derives its information from the measurement of changes in the energy and angular distribution of an initially nominally monoenergetic beam of electtons that has been scattered during transmission through a thin specimen. This geometry is identical to that which is used routinely in a transmission or Scanning Transmission Electron Microscope TEM or STEM and thus in the last decade the technique has been closely associated with these two types of instruments. EELS is an absorption spectroscopy and is similar in many respects to X-Ray Absorption Spectroscopy XAS . Its characteristic spectral signature termed the edge profile is derived from the excitation of discrete inner shell levels to empty states above the Fermi level. Conservation of energy requires that the incident electron beam lose the corresponding amount of energy and intensity expended in exciting each inner shell level and these are the parameters which are recorded in each experiment. From an analysis of the transmitted electron intensity distribution the experiment can 3.2 EELS 135 derive the local elemental concentration of each atomic species present. Additionally by studying the detailed shape of the spectral profiles measured in EELS the analyst may derive information about the electronic structure chemical bonding and average nearest neighbor distances for each atomic species detected. A related variation of EELS is Reflection Electron Energy-Loss Spectroscopy REELS . In REELS the energy distribution of electrons scattered from the surface of a specimen is studied. Generally REELS deals with low-energy elecưons 10 keV while TEM STEM-based EELS deals with incident