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. 

The principal applications of REELS are thin-film growth studies and gas-surface reactions in the few-monolayer regime when chemical state information is required. In its high spatial resolution mode it has been used to detect submicron metal hydride phases and to characterize surface segregation and difRision as a function of grain boundary orientation. REELS is not nearly as commonly used as AES orXPS. 

It is a fundamental principle of quantum mechanics that electrons bound in an atom can have only discrete energy values. Thus, when an electron strikes an atom its electrons can absorb energy from the incident electron in specific, discrete amounts. As a result the scattered incident electron can lose energy only in specific amounts. In EELS an incident electron beam of energy Eq bombards an atom or collection of atoms. After the interaction the energy loss E of the scattered electron beam is measured. Since the electronic energy states of different elements, and of a single element in different chemical environments, are unique, the emitted beam will contain information about the composition and chemistry of the specimen. 

Valence electrons also can be excited by interacting with the electron beam to produce a collective, longitudinal charge density oscillation called a plasmon. Plas-mons can exist only in solids and liquids, and not in gases because they require electronic states with a strong overlap between atoms. Even insulators can exhibit 

Perhaps the most common use for REELS is to monitor gas—solid reactions that produce surface films at a total coverage of less than a few monolayers. When Eq is a few hundred eV, the surface sensitivity of REELS is such that over 90% of the signal originates in the topmost monolayer of the sample. A particularly powerfiil application in this case involves the determination of whether a single phase of variable composition occurs on the top layer or whether islands occur that is, whether 

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

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 Reflection electron energy loss spectroscopy... 

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. 

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

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

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