Transmission electron with EELS

Historically, EELS is one of the oldest spectroscopic techniques based ancillary to the transmission electron microscope. In the early 1940s the principle of atomic level excitation for light element detection capability was demonstrated by using EELS to measure C, N, and O. Unfortunately, at that time the instruments were limited by detection capabilities (film) and extremely poor vacuum levels, which caused severe contamination of the specimens. Twenty-five years later the experimental technique was revived with the advent of modern instrumentation. The basis for quantification and its development as an analytical tool followed in the mid 1970s. Recent reviews can be found in the works by Joy, Maher and Silcox " Colliex and the excellent books by Raether and Egerton. ... 

This kind of estimation of the relative concentration is the most widely used method for quantitative EELS analysis. It is advantageous because the dependence on the primary electron current, Iq, is cancelled out this is not easily determined in a transmission electron microscope under suitable analytical conditions. Eurthermore, in comparison with other methods, e. g. Auger electron spectroscopy and energy-disper-... 

Several structural characterisations of carbon nanotubes (CNTs) with the cylindrical graphite are reviewed from the viewpoint of transmission electron microscopy (TEM). Especially, electron energy loss spectroscopy (EELS) by using an energy-fdtered TEM is applied to reveal the dependence of fine structure of EELS on the diameter and the anisotropic features of CNTs. 

We have used both transmission electron microscopy (TEM) and Raman spectroscopy to characterize the different DWNTs samples. TEM allows direct imaging of the DWNTs and gives indications for the presence of other species along with the DWNTs. In the TEM images, we seldom encountered SWNTs or MWNTs. Besides providing information on the nature and dimensions of DWNTs, Raman spectroscopy helps to characterize the purity and quality of the DWNTs. Electron energy loss spectroscopy (EELS), carried out in a high-resolution electron microscope, and X-ray photoelectron microscopy have been employed to determine the elemental composition of the DWNTs. 

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. 

Recent development of transmission electron microscope enables us to make microscopic observation with sub-nanometer spatial resolution, because the electron beam can be focused within 1 nm diameter. The advantage of the use of EELS technique is that an investigation of electronic state at very small local space of sub-nanometer scale is feasible when it is combined with the high resolution electron microscopic(HREM) technique. A schematic illustration of the combination of HREM and ELNES is indicated in Fig. 17. 

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.]...

---