Electron energy-loss spectrometry EELS

Local composition is very useful supplementary information that can be obtained in many of the transmission electron microscopes (TEM). The two main methods to measure local composition are electron energy loss spectrometry (EELS), which is a topic of a separate paper in this volume (Mayer 2004) and x-ray emission spectrometry, which is named EDS or EDX after the energy dispersive spectrometer, because this type of x-ray detection became ubiquitous in the TEM. Present paper introduces this latter method, which measures the X-rays produced by the fast electrons of the TEM, bombarding the sample, to determine the local composition. As an independent topic, information content and usage of the popular X-ray powder dififaction database is also introduced here. Combination of information from these two sources results in an efficient phase identification. Identification of known phases is contrasted to solving unknown stmctures, the latter being the topic of the largest fiaction of this school. 

The need for both qualitative and quantitative analyses of light elements in the transmission electron microscope has stimulated the development of electron energy loss spectrometry (EELS). In this technique. 

Once the breakdown location is identified using DBIE, electron energy loss spectrometry (EELS) was performed using a FEI-TITAN 300 kV TEM/STEM to analyze the chemical nature of the percolation path [10,11]. Fig. 2 illustrates a close-up view of the sample configuration and beam-sample interaction. STEM/EELS spectra were collected at 80 keV beam voltage using point-to-point vertical and horizontal scans as shown in Fig. 2b across the dielectric layer at the breakdown site identified by a DBIE and at the non-breakdown site that were far away from the DBIE. 

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. 

Electron energy loss spectrometry (EELS) Thin section TEM Chemical information... 

Figure 12.41 Profile of distribution of nitrogen in cross-section of Torayca T-300 carbon fiber, determined by electron energy loss spectrometry (EELS). RID is the ratio of the distance into the fiber for measurement to the fiber diameter. Source Reprinted with permission from Serin V, Fourmeaux R, Kihn Y, Sevely J, Guigon M, Nitrogen distribution in high tensile strength carbon fibers, Carbon, 28, 573, 1990. Copyright 1980, Elsevier.

Every effort is made here to achieve the highest possible absolute power of detection. Microdistribution analysis represents the primary field of application for microprobe techniques based on beams of laser photons, electrons, or ions, including electron microprobe analysis (EPMA), electron energy-loss spectrometry (EELS), particle-induced X-ray spectrometry (PIXE), secondary ion mass spectrometry (SIMS), and laser vaporization (laser ablation). These are exploited in conjunction with optical atomic emission spectrometry and mass spectrometry, as well as various forms of laser spectrometry that are still under development, such as laser atomic ab.sorption spectrometry (LAAS), resonance ionization spectrometry (RIS). resonance ionization mass spectrometry (RIMS), laser-enhanced ionization (LEI) spectrometry, and laser-induced fluorescence (LIF) spectrometry [36]-[44],... 

Electron Energy Loss Spectrometry (EELS) (- Surface Analysis) [190]... 

R. F. Egerton. Electron Energy Loss Spectrometry in the Electron Microscope. Plenum Press, 1986. This is a comprehensive text on the use of EELS in the TEM. It covers instrumentation, theory and practical applications. 

Knowledge of the stracture and bonding of molecnles to snrfaces has been obtained from such techniques as LEED, electron energy-loss spectroscopy (EELS), secondaiy-ion mass spectrometry (SIMS), infrared spectroscopy (IRS), Raman spectroscopy, and NMR spectrometiy. The scope of snch studies needs to be greatly expanded to include the effects of coadsorbates, promoters, and poisons. Greater emphasis should be given to developing new photon spectroscopies that would permit observation of adsorbed species in the presence of a gas... 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

Ahn, C.C., (2004), Transmission Electron Energy Loss Spectrometry in Materials Science and the EELS Atlas, New York, John Wiley Sons. 

Chemical reactions at the gas-surface interface can be followed by monitoring gas-phase products with, for example, a mass spectrometer, or by directly analyzing the surface with a spectroscopic technique such as Auger electron spectroscopy (AES), photoelectron spectroscopy (PES), or electron energy loss spectroscopy (EELS), all of which involve energy analysis of electrons, or by secondary ionization mass spectrometry (SIMS), which examines the masses of ions ejected by ion bombardment. Another widely used surface probe is low-energy electron diffraction (LEED), which can provide structural information via electron diffraction patterns. At the gas-liquid interface, optical reflection elHpsometry and optical spectroscopies are employed, such as Eourier transform infrared (ET IK) and laser Raman spectroscopies. 

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