Surface high-resolution electron energy loss

Fig. VIII-10. (a) Intensity versus energy of scattered electron (inset shows LEED pattern) for a Rh(lll) surface covered with a monolayer of ethylidyne (CCH3), the structure of chemisorbed ethylene, (b) Auger electron spectrum, (c) High-resolution electron energy loss spectrum. [Reprinted with permission from G. A. Somoijai and B. E. Bent, Prog. Colloid Polym. ScL, 70, 38 (1985) (Ref. 6). Copyright 1985, Pergamon Press.]...

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. 

Figure 2 Schematic of a 127° high-resolution electron energy-loss spectrometer mounted on an 8-in flange for studies of vibrations at surfaces.

In recent years there is a growing interest in the study of vibrational properties of both clean and adsorbate covered surfaces of metals. For several years two complementary experimental methods have been used to measure the dispersion relations of surface phonons on different crystal faces. These are the scattering of thermal helium beams" and the high-resolution electron-energy-loss-spectroscopy. ... 

AC Impedance spectroscopy, 237 Auger electron spectroscopy, AES, 254 High resolution electron energy loss spectroscopy, HREELS, 43, 69 Infrared spectroscopy, IRS, 39, 69 Surface enhanced Raman spectroscopy, SERS, 256... 

HRELS = high-resolution, electron-energy-loss spectroscopy. " Surf. Sci. (in press). Ref. (123). Ref (101). Softened pCHj surface-mode. Weak band observed around 1500 cm could be a surface-dipole-forbidden, Pfc mode. Hidden under intense SCHj mode of free C2H4 in the matrix. " One of these bands belongs to Ni2(C2H4)2. 

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]).

Recent studies using high resolution electron energy loss and photoelectron spectroscopy to investigate the effect of sulfur on the CO/Ni(100) system are consistent with an extended effect by the impurity on the adsorption and bonding of CO. Sulfur levels of a few percent of the surface nickel atom concentration were found sufficient to significantly alter the surface electronic structure as well as the CO bond strength. 

In order to elucidate the results of the CO TPD experiment, the detailed structure of the oxygen-modified Mo(l 12) surfaces and the adsorption sites of CO on these surfaces have been considered. Zaera et al. (14) investigated the CO adsorption on the Mo(l 10) surface by high-resolution electron-energy-loss spectroscopy (HREELS) and found vatop sites. Francy et al. (75) also found a 2100 cm loss for CO on W(IOO) and assigned it to atop CO. Recently, He et al. (16) indicated by infrared reflection-absorption spectroscopy that at low exposures CO is likely bound to the substrate with the C-0 axis tilted with respect to the surface normal. They, however, have also shown that CO molecules adsorbed on O-modified Mo(l 10) exhibi Vc-o 2062 and 1983 cm L characteristic to CO adsorbed on atop sites. Thus it is supposed that CO adsorbs on top of the first layer Mo atoms. 

Welipitiya etal. [132] have studied adsorption and desorption of ferrocene on Ag(lOO), applying photoemission and thermal desorption. The initially adsorbed surface species closely resembled that of molecular ferrocene. The molecule was adsorbed with the cyclopentadienyl ring ligands parallel to the surface. Wood-bridge etal. [133] have performed the high-resolution electron energy loss spectroscopy (HREELS) andXPS studies of ferrocene on Ag(lOO). Researchers from the... 

In this paper, we will report the electronic and catalytic reactivities of the model VC/V(110) surface, and our attempt to extend them to VC powder catalysts. By using high-resolution electron energy loss spectroscopy (HREELS) and NEXAFS techniques, we observed that the surface properties of V(110) could be significantly modified by the formation of vanadium carbide some of the experimental results on these model surfaces were published previously.3-5 We will discuss the selective activation of the C-H bond of isobutane and the C=C bond of isobutene on V(110) and on VC/V(110) model systems. These results will be compared to the catalytic performances of vanadium and vanadium carbide powder materials in the dehydrogenation of isobutane. 

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