EXAFS là một không phá hủy, yếu tố cụ thể spectroscopictechnique wt appliih cation để tất cả các yếu tố từ lithium uranium. Nó được sử dụng như một tàu thăm dò trực tiếp của môi trường nguyên tử của một yếu tố hấp thụ tia X và cung cấp thông tin liên kết hóa học. | EXAFS is a nondestructive element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids . crystalline and amorphous materials solid surfaces and interfaces its use is not limited to the solid state. As a structural tool EXAFS complements the familiar X-ray diffraction technique which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers types and interatomic distances of neighboring atoms. EXAFS is part of the field of X-ray absorption spectroscopy XAS in which a number of acronyms abound. An X-ray absorption spectrum contains EXAFS data as well as the X-ray absorption near-edge structure XANES alternatively called the near-edge X-ray absorption fine structure NEXAFS . The combination of XANES NEXAFS and EXAFS is commonly referred to as X-ray absorption fine structure or XAFS. In applications of EXAFS to surface science the acronym SEXAFS for surface-EXAFS is used. The principles and analysis of EXAFS and SEXAFS are the same. See the article following this one for a discussion of SEXAFS and NEXAFS. Experimental Aspects An EXAFS experiment involves the measurement of the X-ray photoabsorption of a selected element as a function of energy above its core-shell electron binding energy. The most direct measurement of EXAFS is the transmission method wherein the sample is placed in the X-ray beam and the incident and ttansmitted X-ray intensities ỈQ and Iv respectively are recorded see Figure 1 . The measurement of Iq and It is accomplished with two ion chamber proportional counters that are gas filled typically with nitrogen and argon to provide about 10-20 absorption of q and 80 90 absorption of It. As shown in Figure 1 it is useful
