Metastable impact electron spectroscopy

Bifunctional spacer molecules of different sizes have been used to construct nanoparticle networks formed via self-assembly of arrays of metal colloid particles prepared via reductive stabilization [88,309,310]. A combination of physical methods such as TEM, XAS, ASAXS, metastable impact electron spectroscopy (MIES), and ultraviolet photoelectron spectroscopy (UPS) has revealed that the particles are interlinked through rigid spacer molecules with proton-active functional groups to bind at the active aluminium-carbon sites in the metal-organic protecting shells [88]. 

Figure 7.38. XPS spectrum of an ionic liquid, [EMIM][Tf2N], detailing the C(ls) and N(ls) regions. Since there are no peaks from the Au substrate, the film thickness is hkely >10nm. Also shown (right) is the comparison between XPS, ultraviolet photoelectron spectroscopy (UPS, Hel = 21.2eV, Hell = 40.8 eV radiation), and metastable impact electron spectroscopy (MIES). Whereas XPS and UPS provide information from the first few monolayers of a sample, MIES is used for zero-depth (surface only) analysis, since the probe atoms are excited He atoms that interact with only the topmost layer of sample. Full interpretations for these spectra may be found in the original work Hofft, O. Bahr, S. Himmer-lich, M. Krischok, S. Schaefer, J. A. Kempter, V. Langmuir 2006, 22, 7120. Copyright 2006 American Chemical Society.

The different reactivity of MgO versus CaO surfaces predicted by cluster calculations [95] has been recently confirmed by metastable impact electron spectroscopy (MIES) experiments on CO2 adsorption on MgO [100] and CaO [101] as well as by synchrotron based photoemission spectroscopy on the same systems [102,103] while the CaO surface exposed to CO2 is highly reactive and becomes terminated by carbonate complexes, on the MgO surface CO2 chemisorption does not take place at regular sites but only at defect sites, presumably the O " ions at the step or comer sites. 

The combination of Metastable Impact Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy, UPS(Hel) has been applied to the study of the interaction between halides (Csl, CsF, and Nal) with solid water and methanol around their respective Tg values [11,12]. Surface segregation of iodide, but not of fluoride or Cs ions, took place from ASW, exposed to Csl or CsF vapour, during annealing [11]. The same behaviour was also derived from molecular dynamics (MD) simulations of the corresponding aqueous salt solutions. In contrast, no appreciable surface segregation of ions was observed in methanol under similar conditions, neither in the experiment nor in the simulation of the corresponding liquid solution. It was pointed out that, as far as solvation phenomena are concerned, water and methanol ices, when heated above their respective Tg values, behave remarkably similar to the corresponding liquid solutions. The surface propensity of iodide is also seen when Cs is replaced by Na [12]. 

INS is very similar to MIES (metastable impact electron spectroscopy) or PIES (penning ionisation electron spectroscopy) except that in INS ions are used instead of metastable atoms. 

M., Krischok, S., Schaefer, J.A., and Kempter, V. (2006) Electronic structure of the surface of the ionic liquid [EMIM][Tf2N] studied by metastable impact electron spectroscopy (MIES), UPS, and XPS. Langmuir, 22, 7120-7123. 

Penning ioni2ation electron spectroscopy is also called (i) metastable atom electron spectroscopy (MAES), (ii) metastable deexdtation spectroscopy (MDS), (iii) metastable quenching spectroscopy (MQS), and (iv) metastable impact electron spectroscopy (MIES), where atom at metastable state is used instead of photon to ionize the target material When a slow, long-lived, electronically excited metastable atom hits a solid surface, most of its excitation energy is used to eject electrons from the surface. Unlike photons used for UPS, metastable atoms do not penetrate into the bulk of the solid. PIES, therefore, excites the outermost surface layer selectively (39). 

Morgner, H., Oberbrodhage, J., and Richter, K., The first stages of lipid layer formation. A metastable impact electron spectroscopy study of egg lecithin dissolved in hydroxypro-pionitrile. Mol Phys., 76, 813,1992. 

Characterization and analysis are performed using the following surface science techniques temperature programmed desorption/reaction (TPD/TPR), pulsed molecular beam reactive scattering (pMBRS) (IRRAS), metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and auger electron spectroscopy (AES). First the experimental setup is briefly described, followed by the support preparation and characterization as well procedures utilized in this work. These descriptions include a concise introduction to the underlying physical principles of the applied techniques (including experimental details). 

Because UPS delivers information from several top atomic layers, it is difldcult to characterize trace amounts of adsorbates. This limitation can be overcome e.g. by photoemission of adsorbed xenon (PAX) [90]. This technique is a site-selective titration technique, in which Xe adsorption sites are revealed by means of UPS it has been used effectively to characterize catalytic systems [91, 92]. An alternative surface sensitive technique capable of determining trace amounts of adsorbates is metastable impact electron spectroscopy (MIES). 

Metastable impact electron spectroscopy MIES (MAES) Metastable rare gas atom 19.81 eV (Hel Si)... 

With metastable impact electron spectroscopy (MIES) and UPS, an additional electronic state within the band gap, about 1-2 eV above the 02p valence band, of MgO thin films has been detected and attributed to F centers (Figure 15.31b) [142]. The position of the defect-related peak within the MgO band gap is in line with theoretically predicted energy levels of F centers in MgO. However, the signals are... 

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