材料分析測(cè)試技術(shù)chapter5透射電鏡的結(jié)構(gòu)(已修改)
2025-04-25 22:35 本頁(yè)面
【正文】 第五章 透射電鏡的結(jié)構(gòu) 光學(xué)顯微鏡的發(fā)明為人類認(rèn)識(shí)微觀世界提供了重要的工具。隨著科學(xué)技術(shù)的發(fā)展，光學(xué)顯微鏡因其有限的分辨本領(lǐng)而難以滿足許多微觀分析的需求。上世紀(jì) 30年代后，電子顯微鏡的發(fā)明將分辨本領(lǐng)提高到納米量級(jí)，同時(shí)也將顯微鏡的功能由單一的形貌觀察擴(kuò)展到集形貌觀察、晶體結(jié)構(gòu)、成分分析等于一體。人類認(rèn)識(shí)微觀世界的能力從此有了長(zhǎng)足的發(fā)展。 Definitions Microscope A device with a lens or series of lenses that enlarge (magnify) the appearance of an object. Does not apply to SEM. Lens A lens is an optical ponent which is used to focus beams of radiation. Lenses for light are usually made of a glassy material, whereas nonuniform electromagic fields are used as lens for electrons. Image Perception of an object using your eyes (vision). One can sense an object without vision (touch, etc..). Requires visible light. Lenses Curved glass or mirror for Visible light Concave surface of metal (. satellite dish) Radio waves Concave mirror or Fresnel lens Heat Solenoid (electromagic fields that can be varied) Subatomic particles (electrons, protons, positrons) concave convex Resolution The point at which two or more objects can be distinguished as separate. Magnification The ratio between image size to the object size. Can be varied by changing the distance between the object and the final lens (of the eye) or by inserting a second lens between the two. History: First record of using glass lens for magnification was by an Arabian from what is now known as Iran, Alhazen, in the 10 and 11th century. He contradicted Ptolemy39。s and Euclid39。s theory of vision that objects are seen by rays of light emanating from the eyes。 according to him the rays originate in the object of vision and not in the eye. Because of his extensive research on vision, he has been considered by many as the father of modern optics. 15th century on Studies done with glass magnifiers to study objects in detail mostly as a curiosity by nonscientists Antonie van Leeuwenhoek (linen draper) described three shapes of bacterial cells using his simple, single lens microscope (glass bead in metal holder). By mid19th century, became evident that theoretical limits of light were reached. Above magnification of 1500, resolution lost. Image was larger, but blurred (empty magnification). In 1870, Ernst Abbe derived mathematical expression for resolution of microscope: Resolution is limited to approx. 1/2 the wavelength of illuminating source. Wavelength distance between peaks of the waveform Blue light has a wavelength of um Resolution max um (200 nm) Cannot go beyond this even with better optics. Solution? Use illumination of shorter wavelength Antone de Broglie (1924) Theory of wave nature of electrons Hermann Busch (1924) axial magic fields refract electrons Electron optics ?1935 Max Knoll demonstrates the theory of the scanning ele
教學(xué)課件相關(guān)推薦
鄂ICP備17016276號(hào)-1