Energy Loss Spectroscopy ELS

Another more serious defect of the EDS technique concerns the inherent sensititivy of the measurements for light (low-Z) elements. Several factors prevent the efficient detection of elements within the first row of the Periodic Table and limit information from the second. Instrumentally, the efficiency of the Li-drifted Si detector, its resolution, and the transparency of the Be window commonly used between the former and the system vacuum all concern us here. Detection sensitivities may be as low as 10 , thereby limiting MDM at a given S/N, whilst the resolution (typically 150— 200 eV) may make the analysis of, for example, magnesium (hco = 1253.6 eV) in the presence of aluminium (hcu = 1486.6 eV) difficult. The presence of the Be window presents a more immediate practical problem in that characteristic Z-rays softer than, say, Na Kct may be absorbed, and this certainly precludes the analysis of the majority of the first-row elements (Li to F). 

The physics of the Z-ray-emission process presents an even more fundamental barrier to the usefulness of EDS in low-Z element analysis. The electron beam incident on a sample excites characteristic Z-rays (as distinct from bremstrahlung) via the radiative decay of core holes created as a primary event within the inner electronic structure of the element in question. However, these core holes can decay via competing channels, the most important of these being the Auger process in this, the energy associated with the neutralization of the core holes is transmitted to another electron in a shallower level, which is then ejected from the atom. The probability of radiative as opposed to Auger decay decreases with Z, so that for sodium the relative probabilities are 1 40, for carbon 1 400. Instrumental factors notwithstanding, this 

Quantum-mechanically, the process of energy loss by electrons can be considered as formally equivalent to the absorption of photons, so that we may express the differential cross-section for inelastic scattering (energy loss) under the dipole approximation as  

To attempt to summarize the impact of a relatively new experimental technique is, at this early stage, difficult. The diversity of applications outlined in the present review should be regarded only as early indications of great promise. The author is indebted to Dr. S. M. Allen (MIT), Dr. P. E. Baston (IBM), Dr. A. J. Craven (Glasgow University), Dr. H. L. Frazer (United Technology Inc.), Dr. E. L. Hall (General Electric), and Professor J. B. Vandersande (MIT) for permission to reproduce their results. 

Fraser in Proceedings 9th International Congress on Electron Microscopy , ed., J. M. Sturgis, 1978, p. 552. 

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Inelastic effects are exploited in the rapidly developing technique of high resolution electron energy loss spectroscopy (ELS or EELS) which permits identification of adsorbed molecules or molecular fragments by their vibrational spectra. Thus the method has much in common with the infrared spectroscopy of surfaces and, not surprisingly, the classic case of CO adsorption has received attention on Ni(lOO) and on stepped Ni and Pt surfaces. Other recent investigations of interest include H2 on organic species on Ni and Pt, and the observation of... 

Changes in energy of incident electrons after scattering by a solid Energy loss spectroscopy ELS... 

Energy loss spectroscopy ELS Monoenergetic electrons 12 and 13 Derivative electron... 

SEELS surface electron energy loss spectroscopy (= ELS)... 

ELS Electron Energy Loss Spectroscopy Monoenergetic electrons 5-50 eV are scattered off a surface the energy losses are measured. This gives information on the electronic excitations of the surface and adsorbed molecules (see HREELS). Sometimes called EELS. 

Fig. 24. XPS spectra of SmS and electron energy loss spectroscopy data of the cleaved (100 surface-the ELS transitions are identified in Table II.

The X-ray diffraction patterns for Ge02 (H) and Ge02 (T) have been accurately determined and can be used to identify films as thin as 500 A (using low angle diffraction). Here again, the monoxide phase cannot be identified by this means since no diffraction pattern has been observed for that phase. Some other non-destructive techniques have been used such as low energy electron diffraction (LEED), electron loss spectroscopy (ELS), Raman scattering, etc. but usually they are so sensitive to contamination that the results cannot easily be used for simple phase identification. Such techniques are therefore more useful for physical property studies. 

REELS, ELS (reflection electron energy loss spectroscopy) and EELES, EXELES (extended electron energy loss fine structure) work with a higher fixed energy of the primary electrons (50 200 eV and 10 80 keV, respectively) and higher energy losses of the scattered primary electrons ranging from 0.005 eV to several hundred and from 200—4000 ey respectively. 

ELS = electron energy loss spectroscopy 0 - = lattice oxygen ion... 

In electron energy loss spectroscopy an electron incident on a surface is inelastically scattered and the distribution of electrons n(AE) having transferred an energy AE to the target is measured. Both vibrational and electronic transitions can be excited, but this section will be confined to ELS in the range of electronic excitations. 

DAPS Disappearance potential spectroscopy CLS Cathodoluminescence spectroscopy IPES Inverse photoemission spectroscopy BIS Bremsstrahlung isochromat spectroscopy AES Auger electron spectroscopy SAM Scanning Auger microscopy ELS (electron) Energy loss spectroscopy HREELS High-resolution electron energy loss spec-... 

Energy Loss Spectroscopy and Core-Electron Energy Loss Spectroscopy. The techniques of ELS and CEELS can be discussed together because they use the same experimental arrangement, basically that of conventional AES, A beam of primary electrons interacts with electrons in surface... 

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