High-resolution electron energy loss spectra

Kuzuo, R. Terauchi, M. Tanaka, M. Saito, Y. Shinohara H. High resolution electron energy loss spectra of solid Cgo, 1991, 30, no. 10a, p. L1817... 

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.]...

Cox, P. A., EgdeD, R. G., Eriksen, S. and Elavell, W. R. (1986) The high-resolution electron-energy-loss spectrum of TiO2(110)./. Electron Spectrosc. Relat. Phenom., 39, 117-126. 

Figure 23 High-resolution electron energy-loss spectrum of CO adsorbed at different coverages on Rh(l 11)...

As demonstrated by the results presented above, the probability of dissociative chemisorption can be readily probed by measuring the extent of carbon deposition by Auger electron spectroscopy. However, a complete picture of the dissociative adsorption process requires that the product of the dissociative chemisorption event be spectroscopically identified. For example, although the discussion has assumed that a single C-H bond cleaves upon dissociation, no evidence for this has been presented. In order to identify chemically the product of the dissociative chemisorption event, we have measured the high resolution electron energy loss spectrum for methane deposited on the Ni(lll) surface at 140 K with an incident energy of 17 kcal/mole. The spectrum is shown in Fig. 4a. A low surface temperature is chosen in order to trap the nascent product of the dissociative chemisorption and not a thermal decomposition product. The temperature of the surface has no effect on the probability for dissociative chemisorption since the dissociation occurs immediately upon impact of the molecule on the surface. 

Figure 8.2.6 High-resolution electron energy loss spectrum for a CO-covered Ru(OOl) surface. The total energy resolution as is directly measured by the width (full width at half maximum (FWHM)) of the quasi-elastic peak at AE = 0 is 0.78 meV (6.3 cm ).

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

The invariance of IETS in an M-A-M junction vs an M-I-A-M device is exceptionally well demonstrated by the work of Reed [30], Figure 7 shows the Au-alkanedithiol-Au structure he used to create a single barrier tunnel diode. The IET spectra obtained from this device were stable and repeatable upon successive bias sweeps. The spectrum at 4.2 K is characterized by three pronounced peaks in the 0-200 mV region at 33,133, and 158 mV. From comparison with previously reported IR, Raman, and high-resolution electron energy-loss (HREEL) spectra of... 

Fig. 4.8. High-resolution electron energy loss speetra for H and D adsorbed atomically on W(IOO). The elastic peak is shown at left. The loss energy for hydrogen is plotted along the horizontal axis. The coverage varies from 0 = 0.4 to 6 = 2.0 (saturation), exhibiting a change in adsorption site, while the deuterium spectrum is shown at 0 = 2.0 only. [After H. Froitzheim, H. Ibach and S. Lehwald, Phys. Rev. Lett. 36, 1549 (1976).]...

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. 

The product of the collision-induced dissociative chemisorption event is identified by high resolution electron energy loss spectroscopy. Fig. 9a shows the vibrational spectrum of a monolayer of methane at 46 K before bombardment with Ar. The vibrational frequencies are unperturbed from the gas phase values within the resolution of this technique ( 20 cm-1). The loss observed at 1305 cm" is assigned to the V4 mode, the loss at 1550 cm- to the >2 mode and the losses at 2895 cm 1 and 3015 cm- to the vi and V3 modes, respectively. Fig. 9b shows the vibrational spectrum after exposure of the methane monolayer at 46 K to a beam of Ar atoms with a translational energy of 36 kcal/mole. This spectrum has been assigned previously to an adsorbed methyl radical. 

The adsorption of ethylene on the Rh(lll) surface provides a typical example. The high-resolution electron-energy-loss (HREEL) spectrum at 77 K in Figure 2.25 has been attributed to ethylene adsorbed molecularly intact on the Rh(lll) surface [101]. However, vibrational frequencies measured are markedly different from those for gas-phase ethylene, indicating a strong interaction between ethylene and the rhodium surface. 

Figure 16 High-resolution electron energy loss (HREEL) spectrum of a metallized PET sample (a) clean PET (b)-(g) increasing coverage of the PET by Al atoms. (From Ref. 78.)...

Fig. 22. High-resolution electron energy loss vibrational spectrum of ethylidyne (CCHj) and ethylidyne-rfj on Rh(lll) the stable, room temperature, chemisorbed structure for ethylene...

Figure 1 An overview of high resolution electron energy loss spectroscopy. Top left the incident electron beam is shown as a narrow, intense peak on the intensity vs energy loss axes. The specularly reflected beam is shown with loss peaks due to adsorbed molecules, with modes tuo. Centre The scattering mechanism is illustrated with the three diatomic molecules adsorbed on the sur ce with perpendicular and parallel orientation relative to the sur ce. Mode has a dynamic dipole moment pa which is perpendicular to the sur ce, and induces a second image dipole in the same direction, so that the electron scatters from a combined dipole moment of 2p . This is the dipole scattering process. The mode o>2 is parallel to the surface, and the induced image dipole cancels the molecular dynamic dipole moment. The mode is screened and is not present in the spectrum if there is no impact contribution to the scattering. Mode (03 is shown with the dynamic dipole moment equal to zero (the orientation is not relevant). The mode will be observed as an impact mode.

The geometry of N2 is assigned to side-on based on detailed interpretation of the X-ray photoelectron spectroscopy spectrum [460, 461] and of the high-resolution electron-energy-loss spectroscopy spectrum [470]. 

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

As noted in the introduction, vibrations in molecules can be excited by interaction with waves and with particles. In electron energy loss spectroscopy (EELS, sometimes HREELS for high resolution EELS) a beam of monochromatic, low energy electrons falls on the surface, where it excites lattice vibrations of the substrate, molecular vibrations of adsorbed species and even electronic transitions. An energy spectrum of the scattered electrons reveals how much energy the electrons have lost to vibrations, according to the formula ... 

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