Tham khảo tài liệu 'nanomaterials for nanoscience and nanotechnology part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Characterization of Nanophase- Materials. Edited by Zhong Lin Wang Copyright 2000 Wiley-VCH Verlag GmbH ISBNs 3-527-29837-1 Hardcover 3-527-2960009-4 Electronic 3 Transmission Electron Microscopy and Spectroscopy of Nanoparticles Zhong Lin Wang One of the typical characters of nanophase materials is the small particle sizes. Although some structural features can be revealed by x-ray and neutron diffraction direct imaging of nanoparticles is only possible using transmission electron microscopy TEM and scanning probe microscopy. TEM is unique because it can provide a real space image on the atom distribution in the nanocrystal and on its surface 1 . Today s TEM is a versatile tool that provides not only atomic-resolution lattice images but also chemical information at a spatial resolution of 1 nm or better allowing direct identification the chemistry of a single nanocrystal. With a finely focused electron probe the structural characteristics of a single nanoparticle can be fully characterized. To reveal the capabilities of a modern TEM this chapter is designed to illustrate the fundamentals of TEM and its applications in characterization of nanophase materials. The fundamentals and applications of scanning transmission electron microscopy STEM will be given in Chapter 4. A transmission electron microscope A modern TEM can be schematically shown in Figure 3-1 which is composed of a illumination system a specimen stage an objective lens system the magnification system the data recording system s and the chemical analysis system. The electron gun is the heart of the illumination system which typically uses LaB6 thermionic emission source or a field emission source. The LaB6 gun gives a high illumination current but the current density and the beam coherence are not as high as those of a field emission source. Field emission source is unique for performing high coherence lattice imaging electron holography and high spatial resolution microanalysis. The illumination .
