Electron energy-loss spectroscopy, recent

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. ... 

Although there are no published data (which can be compared directly with the results obtained with nickel, iron, and aluminum surfaces), several studies with NO have been reported recently with platinum, ruthenium, and iridium 49, 50). In the main, these have relied on electron energy loss spectroscopy... 

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. 

Local chemical composition from areas less than 1 nm in diameter can be measured by energy dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy (EELS). Such spectroscopic information may be presented in 2D maps showing the spatial element distribution in the specimen (13). Furthermore, information about the local density of unoccupied electron states of a specific element can be extracted from EELS data and used to estimate the oxidation state and the local coordination geometry of the excited atoms (14). In some favorable cases, electronic structure information with a resolution of about 1 eV from individual atomic columns has been attained (15,16). Recent developments of monochromators and spectrometers have brought the resolution down to 0.1 eV (17,18), and this capability may offer new opportunities to determine relationships between electronic structure information, the atomic arrangements and the catalytic activities of solids. 

The final chapters of this book review the progress of three recently developed techniques that provide information about the vibrational states of adsorbed molecules. Perhaps the most important of these techniques is electron energy loss spectroscopy that, despite its inherent low resolution, gives valuable information on vibrational modes that are either inactive in the IR, or inaccessible because of experimental difficulties. The applications of this technique are discussed in two chapters by Somorjai and Weinberg. The review of new experimental techniques concludes with presentations on inelastic electron tunneling spectroscopy and neutron scattering by Kirtley and Taub. 

Very recently, spectroscopic investigations have provided evidence that at least two types of molecular NO can exist simultaneously on transition metal surfaces (12,15.19,20, 21, 22), thus supporting the interesting possibility that the rich diversity of nitrosy1-metal chemistry extends from metal complexes to metal surfaces. Two states of molecular NO have been observed on Ru(001) by electron energy loss spectroscopy (EELS) (13), and also by X-ray photo-... 

Li et al. made extraordinarily perfect artificial c-axis twist bicrystal junctions.[3] These junctions were extensively characterized using high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy, and low energy electron diffraction, etc., and the results were compared with computer simulations. [4] More recently, off-axis electron holography provided compelling evidence of the remarkable atomic perfection and reproducibility of the twist junctions.[5]... 

Inelastic effects are exploited in the rapidly developing technique of high resolution electron energy loss spectroscopy (ELS or EELS) which permits identification of adsorbed molecules or molecular fragments by their vibrational spectra. Thus the method has much in common with the infrared spectroscopy of surfaces and, not surprisingly, the classic case of CO adsorption has received attention on Ni(lOO) and on stepped Ni and Pt surfaces. Other recent investigations of interest include H2 on organic species on Ni and Pt, and the observation of... 

Vibrational spectroscopy is an important probe used to determine the bonding and structural properties of molecules. Powerful techniques such as electron energy loss spectroscopy (EELS) have been developed, which allow one to obtain the vibrational properties of molecules chemisorbed upon surfaces. Due to low concentration, the highly reactive nature of the clusters, and the large number of possible species which are typically present in the cluster beams used to date, unconventional techniques are required in order to obtain spectroscopic information. One unconventional but powerful technique, infrared multiple photon dissociation (IRMPD), has recently been applied to the study of the vibrational properties of gas-phase metal clusters upon which one or more molecules have been chemisorbed. This same technique, IRMPD, has previously been used to obtain the vibrational spectra of ions, species for which it is difficult to apply conventional absorption techniques. 

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