文档介绍：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. Al-
though some structural features can be revealed by x-ray and neutron diffraction,
direct imaging of nanoparticles is only possible using transmission electron micros-
copy "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, allow-
ing direct identification the chemistry of a single nanocrystal. With a finely focused
electron probe, the structural characteristics of a single nanoparticle can be fully char-
acterized. To reveal the capabilities of a modern TEM, this chapter is designed to
illustrate the fundamentals of TEM and its applications in characterization of nano-
phase 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 posed of a
illumination system, a specimen stage, an objective lens system, the magnification sys-
tem, 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