High resolution electron energy loss surface studies

B.E. Koel, J.E. Crowell, C.M. Mate, and G.A. Somoijai. A High Resolution Electron Energy Loss Spectroscopy Study of the Surface Structure of Benzene Adsorbed on the Rhodium (111) Crystal Face. J. Chem. Phys. 88 1988 (1984). 

Gorodetskii, V.V. and Drachsel, W., Kinetic oscillations and surface waves in catalytic CO - - O2 reaction on Pt surface field electron microscope, field ion microscope and high resolution electron energy loss spectroscope studies, Appl. Catal. A Gen., 188, 267-275, 1999. 

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. ... 

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... 

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. 

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... 

The success of the isotope dilution experiment for CO on Pt(lll) was accompanied by a serious difficulty in reconciling the magnitude of the shift, which determines Oy/3Q), with the intensity of the band, which also determines Oy/3Q). When due allowance is made for the resultant surface field and geometric factors (36) in RAIR spectroscopy the intensity is almost consistent with the vibrational polarizability av = 0.057 X3 (39), corresponding to the gas phase intensity, as has been concluded for CO adsorbed on copper films (40) from infrared studies and for CO on Pt(lll) (41) and Cu(100) (42) from high resolution electron energy loss spectroscopy. This value of av is an order of magnitude smaller than that deduced from the frequency shift. 

In contrast to the acetaldehyde decarbonylation, reactions with ethanol over Rh (111) did not lead to formation of methane but rather to an oxametallocycle via methyl hydrogen abstraction. These data suggest that ethanol formed over supported rhodium catalysts may not be due to hydrogenation of acetaldehyde. This study shows how surface science studies of model catalysts and surfaces can be used to extract information about reaction mechanisms since the nature of surface intermediates can often be identified by methods such as temperature programmed desorption and high resolution electron energy loss spectroscopy. 

Most studies on deposition of fullerenes on semiconductor surfaces have focused on silicon9 28 and, to a much less extent, on GaAs. Earlier experimental work using HREELS (high-resolution electron energy loss spectroscopy) on C60 adsorption on Si (100)2 x 1 surface suggested that the molecular attachment to the... 

There is a number of vibrational spectroscopic techniques not directly applicable to the study of real catalysts but which are used with model surfaces, such as single crystals. These include reflection-absorption infrared spectroscopy (RAIRS or IRAS) high-resolution electron energy loss spectroscopy (HREELS, EELS) infrared ellipsometric spectroscopy. 

High Resolution Electron Energy Loss Spectroscopy has been "discovered" at about the same time as the previous cited techniques - die first reported experiment is related to a study of small molecules adsorbed on a (100)W surface and is dated from 1967 (1). During the last 15 years, the characterization of adsorption states of molecules on metal and semiconductor surfaces was the principal attribute of HREELS information on the elemental composition, on the chemistry, and the kinetics of surface reactions (versus temperature and/or time) were studied. One significant "plus" of HREELS is its ability to identify adsorption sites on a metal, by using the "dipole-selection rule" it is therefore possible to gain information on the short-scale structure or morphology of a surface with HREELS. 

Previous studies have shown that a trend exists in the behavior of some evaporated metals on polyimide surfaces x-ray and ultraviolet photoelectron (XPS, UPS) as well as high resolution electron energy loss (HREELS) measurements have indicated that while for some metals such as aluminum, titanium and chromium there is bond formation with the PMDA carbonyl oxygen of the polyimide (2, 10-13). other metals such as copper, palladium and gold undergo little reaction or interaction (10,12,14,15). It has, however, since been postulated that metals, in order to adhere well at all to a polymer under a wide variety of conditions, must form metal- polymer bonds (10). 

Another class of techniques monitors surface vibration frequencies. High-resolution electron energy loss spectroscopy (HREELS) measures the inelastic scattering of low energy ( 5eV) electrons from surfaces. It is sensitive to the vibrational excitation of adsorbed atoms and molecules as well as surface phonons. This is particularly useful for chemisorption systems, allowing the identification of surface species. Application of normal mode analysis and selection rules can determine the point symmetry of the adsorption sites./24/ Infrarred reflectance-adsorption spectroscopy (IRRAS) is also used to study surface systems, although it is not intrinsically surface sensitive. IRRAS is less sensitive than HREELS but has much higher resolution. 

In order to show that the strongly bound species was actually an EpB molecule, high-resolution electron energy loss spectroscopy (HREELS) was used to study the species present at the various dosing temperatures. When dosed at lower temperatures, most of the observed peaks in the HREELS matched those of the vibrational spectrum of liquid EpB, suggesting that intact EpB is interacting with the silver surface at lower temperatures. However, the silver surface dosed with EpB at 300 K showed noticeable differences in the HREELS spectrum. In addition, DPT calculated vibrational frequencies of the surface bound oxaraetallacylce matched well with those determined experimentally. 

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