High Resolution Electron Loss Spectroscopy HREELS

HIGH RESOLUTION ELECTRON LOSS SPECTROSCOPY (HREELS) 

EELS can be applied in conjunction with several techniques. We have just discussed its use in association with TEM or STEM, where the losses predominantly occur in 

Another technique is spin polarised EELS, or SPEELS, which can provide information on phenomena such as magnetic coupling and exchange excitation processes, but SPEELS will not be discussed further here. 

The interpretation of HREELS is similar to that of RAIRS (pp. 41 et seq.), although RAIRS spectra are usually expressed in wavenumbers, while HREELS are in meV (1 meV = 8.065 cm-1). The resolution in RAIRS is typically 0.25meV, while it is about 20meV for HREELS (despite the HREELS acronym ). 

In spectral identification, the first step is a comparison of the observed losses with vibrational frequencies measured by IRS in the gas phase, to see if any correlations exist. When a molecule is attached to a surface it is fettered by forces due to the chemical bonds to the surface, and there will be stretching modes of vibration 

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High Resolution Electron Loss Spectroscopy (HREELS) 194... 

High resolution electron loss spectroscopy (HREELS) Identify adsorbed species Electrons in, electrons out... 

Surface Characterization Using Spectroscopic Techniques. The elemental composition and the oxidation states of surfaces are most frequently determined by x-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), Auger spectroscopy, and high-resolution electron loss spectroscopy (HREELS). 

Several techniques that provide information about composition and structure on the molecular level were discussed. For instance, secondary ion mass spectroscopy (SIMS), XPS which provide information about surface composition and the chemical environment and bonding of surface species, and ultraviolet photoelectron spectroscopy (UPS), which probes the density of electronic states in the valence band of materials. Also, the low energy electron diffraction (LEED) and high resolution energy electron loss spectroscopy (HREELS) are electronscattering techniques that are uniquely suited to yield the structure of the surface... 

HREELS High-resolution electron energy-loss spectroscopy [129, 130] Same as EELS Identification of adsorbed species through their vibrational energy spectrum... 

As the table shows, a host of other teclmiques have contributed a dozen or fewer results each. It is seen that diffraction teclmiques have been very prominent in the field the major diffraction methods have been LEED, PD, SEXAFS, XSW, XRD, while others have contributed less, such as NEXAFS, RHEED, low-energy position diffraction (LEPD), high-resolution electron energy loss spectroscopy (HREELS), medium-energy electron diffraction (MEED), Auger electron diffraction (AED), SEELFS, TED and atom diffraction (AD). 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

High-Resolution Electron Energy-Loss Spectroscopy, HREELS 442... 

In this chapter, three methods for measuring the frequencies of the vibrations of chemical bonds between atoms in solids are discussed. Two of them, Fourier Transform Infrared Spectroscopy, FTIR, and Raman Spectroscopy, use infrared (IR) radiation as the probe. The third, High-Resolution Electron Enetgy-Loss Spectroscopy, HREELS, uses electron impact. The fourth technique. Nuclear Magnetic Resonance, NMR, is physically unrelated to the other three, involving transitions between different spin states of the atomic nucleus instead of bond vibrational states, but is included here because it provides somewhat similar information on the local bonding arrangement around an atom. 

Another spectroscopic technique, high-resolution electron energy loss spectroscopy (HREELS), has been used by Wagner and Moylan211 in combination with cyclic voltammetry to estimate ffs0of a Pt(lll) electrode from the reaction of H30+ formation. 

Hartree-Fock wave functions, 269 High resolution electron energy loss spectroscopy, HREELS, 43, 69 Highest occupied molecular orbital, HOMO, 269... 

HREELS high-resolution electron energy loss spectroscopy... 

Ammonia oxidation was a prototype system, but subsequently a number of other oxidation reactions were investigated by surface spectroscopies and high-resolution electron energy loss spectroscopy XPS and HREELS. In the case of ammonia oxidation at a Cu(110) surface, the reaction was studied under experimental conditions which simulated a catalytic reaction, albeit at low... 

Figure 8.14 High-resolution electron energy loss spectroscopy (HREELS) and low-energy electron diffraction of CO adsorbed on a Rh(l 11) surface, along with structure models. The HREELS spectra show the C-O and metal-CO stretch vibrations of linear and threefold CO on rhodium (from R.Linke etal. [56]).

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