Reflection Electron Energy Loss Spectroscopy

Acronyms REELS reflection electron energy loss spectroscopy (sometimes abbreviated also to EELS). 

The electron beam from a simple electron gun is directed at the sample surface. The beam normally has an energy spread -1—2 eV at a typical primary beam energy of between 100—2000 eV. The reflected electrons pass through an electron energy analyser before being detected. 

Samples should have reasonably flat surfaces and preferably be conducting. 

The source of information is dependent on electron current, primary beam energy and electron energy loss. The plasmon losses are typically of the order of 10 eV and can provide information on the permitivity of the material under study. EELS is thus complementary to optical reflectivity techniques. Interband transitions can be compared with theoretical models of the electronic structure of the material. 

The method is sensitive to energy losses of greater than 1 eV. Hence it cannot detect vibrational losses as in high resolution electron energy loss spectroscopy (HREELS). The detection volume is limited to the top few atomic layers for metals. 

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Reflected Electron Energy-Loss Spectroscopy (REELS)... 

Reflected Electron Energy-Loss Spectroscopy (REELS) has elemental sensitivities on the order of a few tenths of a percent, phase discrimination at the few-percent level, operator controllable depth resolution from several nm to 0.07 nm, and a lateral resolution as low as 100 nm. 

REELS Reflection electron energy loss spectroscopy... 

How then, can one recover some quantity that scales with the local charge on the metal atoms if their valence electrons are inherently delocalized Beyond the asymmetric lineshape of the metal 2p3/2 peak, there is also a distinct satellite structure seen in the spectra for CoP and elemental Co. From reflection electron energy loss spectroscopy (REELS), we have determined that this satellite structure originates from plasmon loss events (instead of a two-core-hole final state effect as previously thought [67,68]) in which exiting photoelectrons lose some of their energy to valence electrons of atoms near the surface of the solid [58]. The intensity of these satellite peaks (relative to the main peak) is weaker in CoP than in elemental Co. This implies that the Co atoms have fewer valence electrons in CoP than in elemental Co, that is, they are definitely cationic, notwithstanding the lack of a BE shift. For the other compounds in the MP (M = Cr, Mn, Fe) series, the satellite structure is probably too weak to be observed, but solid solutions Coi -xMxl> and CoAs i yPv do show this feature (vide infra) [60,61]. 

Au and Pt compounds. The Tougaard method gave approximately 3% RSD from theory, which is of the order of the expected uncertainty due to the effects of instrumental stability and the errors in the ratio of photoionization cross-sections258. Additional considerations for background correction were made from reflection electron energy-loss spectroscopy (REELS) measurements at different take-off angles259. 

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. 

RAIS Reflection-Absorption Infrared Spectroscopy, 33 RBS Rutherford Backscattering Spectrometry, 36 REELS Reflection Electron Energy Loss Spectroscopy, 18, 34 REM Reflection Electron Microscopy ... 

Modern reflection electron energy loss spectroscopy has its origins in work by Powell (1960), Robins and Swan (1960) and Best (1962), while Gerlach et al. (1970) and Gerlach and Du Charme (1972) showed that core ionisation could be studied in reflection. Surprisingly there is no comprehensive review of this field as far as electronic excitations are concerned, but the article by Froitzheim (1977) may be a useful starting point. 

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