第五章透射电镜的结构 光学显微镜的发明为人类认识微观世界提供了重要的工具。随着科学技术的发展,光学显微镜因其有限的分辨本领而难以满足许多微观分析的需求。上世纪30年代后,电子显微镜的发明将分辨本领提高到纳米量级,同时也将显微镜的功能由单一的形貌观察扩展到集形貌观察、晶体结构、成分分析等于一体。人类认识微观世界的能力从此有了长足的发展。 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 ponent which is used to focus beams of radiation. Lenses for light are usually made of a glassy material, whereas non-uniform ic 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 (ic 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 Ptolemy's and Euclid'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 non-scientists - Antonie van Leeuwenhoek (linen draper) described three shapes of bacterial cells using his simple, single lens microscope (glass bead in metal holder). By mid-19th century, became evident that theoretical limits of light were re
