Scanning transmission with EELS

In addition to its power of directly imaging atomic structures of crystals, H RTEM is often equipped with several other powerful devices for characterization of solids, such as electron diffraction (ED), EDX, electron energy loss spectroscopy (EELS), scanning transmission electron microscopy (STEM) and so on. In this chapter, only the most commonly used supporting techniques for HRTEM, ED and EDX, are discussed in detail. 

Figure 17.3.2 Detection limits, sampling depth, and spot size for several surface spectroscopic techniques. XRP (x-ray fluorescence) EMP (electron microprobe) EEL (electron energy loss), SAM (scanning Auger microprobe) STEM (scanning transmission electron microscopy). Other abbreviations in Figure 17.3.1. This figure is meant to provide a graphic summary of the relative capabilities of different methods modem instmments have somewhat better quantitative performance characteristics than the 1986 values given here. [From A. J. Bard, Integrated Chemical Systems, Wiley, New York, 1994, pp. 103, with permission adapted from Texas Instmments Materials Characterizations Capabilities, Texas Instmments, Richardson, TX, 1986, with permission.]...

This article will focus on the use of electron energy loss spectrometry (EELS) in a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). In a TEM or STEM, a beam of electrons is accelerated to energies typically between 100 keV and IMeV. The beam of electrons is transmitted through a sample that consists of a thin piece of material (typically less than 50 nm thickness). Interaction of the beam with the sample enables the operator to learn something about the sample, such as the chemical elements present, stoichiometry, energy levels, electronic structure, and more. 

Minor concentrations of foreign compositions at grain boundaries and three-grain junctions in a sintered ceramic can be characterized using transmission electron microscopy (TEM) and electron diffraction, scanning transmission electron microscopy (STEM) with EDS or electron energy loss spectroscopy (EELS), and AES. ... 

XAS requires synchrotron radiation and a relatively large amount of material but no vacuum condition. On the other hand, EELS can be performed directly using an electron spectrometer fitted to a scanning transmission electron microscope (STEM). Here, the main advantage is the high spatial resolution attainable. (The incident electron beam can be as. small as I nm in diameter.) EELS can also be coupled with conventional transmission electron microscope (TEM) facilities and particularly high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). 

The morphology and composition of the specimens were examined using an AMRAY scanning electron microscope. The sections, of nominal thickness of 15 nm, were examined in a JEOL 200FX II transmission electron microscope. High resolution observation employed a Philips Tecnai 30 FEG analytical electron microscope equipped with EDX and EELS facilities. 

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