tailieunhanh - Volume 10 - Materials Characterization Part 13

Tham khảo tài liệu 'volume 10 - materials characterization part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 11 Influence of Burgers vector orienta tion on the FIM contrast from dislocations a Dislocations in tungsten. The Burgers vector in this material has a component normal to the surface producing the spiral images shown. Courtesy of . Godfrey University of Oxford b Origin of image cont rast. 1 one pole of a field ion tip when perfect 2 same as 1 but after cutting and displacing an amount b introducing a dislocation at point A 3 same as 2 but after field evaporation Figure 12 shows grain-boundary contrast. A high-angle boundary appears as a line of discontinuity running across th pattern. The images of the crystals on either side of the boundary appear regular up to the plane of the interface ind that the disordered region at a grain boundary is narrow. Fig. 12 Grain boundary in tungsten. See text for discussion. Courtesy of . Godfrey University of Oxford Images of Alloys and Semiconductors The FIM images of disordered solid solutions are less regular than those of pure metals because first the field-evapc behavior varies due to variations in the local environment of different surface atoms. Therefore the end-form of the Sc becomes less uniform on an atomic scale. Second chemical differences between alloy species result in formation 0 surface dipoles which in turn affect the extent of field adsorption and the local tunneling probability for field ionizath Micrographs of disordered solid solutions are provided in Examples 1 and 2 in the section Applications in this article ordered alloys the images appear more regular but on super-lattice planes the brightness of successive atom layers V systematically for the reasons outlined above stacking-fault and grain-boundary-like contrast are also found in ordered i because of the presence of antiphase boundaries. Figure 13 shows an FIM image of an ordered nickel-molybdenun containing several domain .