“…The lower curves in Figure , parts a and b, respectively show the Mg KLL and the Mg 2p regions of the XPS spectrum of the Mg film. They are characteristic of metallic Mg, with the most pronounced of the Mg KLL peaks at 1185.5 eV and the Mg 2p peak at 50.0 eV, in agreement with the literature values. ,,− 1 Mg film deposition on polycrystalline Au followed by the exposure to TiCl 4 and the reaction with AlEt 3 . Mg KLL, Mg 2p, and Ti 2p regions of the XPS spectra are shown.…”
Two new synthetic routes for the preparation of model Ziegler−Natta catalysts under UHV conditions are
described. The exposure of metallic magnesium to TiCl4 produced titanium chloride films with Ti in the 4+,
3+, 2+, and 0 oxidation states. Stable titanium chloride films could also be obtained by TiCl4 and Mg
codeposition on MgCl2 and Au. A TiCl4/TiCl2 film was obtained in this case. The reaction of these systems
with AlEt3 produced model catalysts for the polymerization of both ethylene and propylene. XPS is a proper
technique for the characterization of the oxidation state of Ti in a variety of titanium chloride surface species.
The stability of MgCl2 surfaces with a high concentration of undercoordinated Mg atoms was studied in
UHV by Mg gas-phase deposition on a MgCl2 multilayer film. The Mg adatoms were readily coordinated
by the Cl ions diffusing from the halide bulk to the surface. Mg-containing MgCl2 faces are thermodynamically
unstable, and the fast diffusion of the Cl ions in the MgCl2 matrix allows the recovery of the chlorine termination
to lower the system surface energy. The high mobility of the chlorine ions is of central importance for the
molecular level understanding of the dynamic equilibrium among the MgCl2 surface, TiCl4, and the electron
donors used in the synthesis of high performance microporous Ziegler−Natta catalysts. The deposition of
MgCl2 in the presence of TiCl4 was studied for the stabilization of high Miller index faces during the MgCl2
film growth. The interaction between the two halides is too weak to influence the MgCl2 deposition, and
TiCl4 could not be chemisorbed at 300 K.
“…The lower curves in Figure , parts a and b, respectively show the Mg KLL and the Mg 2p regions of the XPS spectrum of the Mg film. They are characteristic of metallic Mg, with the most pronounced of the Mg KLL peaks at 1185.5 eV and the Mg 2p peak at 50.0 eV, in agreement with the literature values. ,,− 1 Mg film deposition on polycrystalline Au followed by the exposure to TiCl 4 and the reaction with AlEt 3 . Mg KLL, Mg 2p, and Ti 2p regions of the XPS spectra are shown.…”
Two new synthetic routes for the preparation of model Ziegler−Natta catalysts under UHV conditions are
described. The exposure of metallic magnesium to TiCl4 produced titanium chloride films with Ti in the 4+,
3+, 2+, and 0 oxidation states. Stable titanium chloride films could also be obtained by TiCl4 and Mg
codeposition on MgCl2 and Au. A TiCl4/TiCl2 film was obtained in this case. The reaction of these systems
with AlEt3 produced model catalysts for the polymerization of both ethylene and propylene. XPS is a proper
technique for the characterization of the oxidation state of Ti in a variety of titanium chloride surface species.
The stability of MgCl2 surfaces with a high concentration of undercoordinated Mg atoms was studied in
UHV by Mg gas-phase deposition on a MgCl2 multilayer film. The Mg adatoms were readily coordinated
by the Cl ions diffusing from the halide bulk to the surface. Mg-containing MgCl2 faces are thermodynamically
unstable, and the fast diffusion of the Cl ions in the MgCl2 matrix allows the recovery of the chlorine termination
to lower the system surface energy. The high mobility of the chlorine ions is of central importance for the
molecular level understanding of the dynamic equilibrium among the MgCl2 surface, TiCl4, and the electron
donors used in the synthesis of high performance microporous Ziegler−Natta catalysts. The deposition of
MgCl2 in the presence of TiCl4 was studied for the stabilization of high Miller index faces during the MgCl2
film growth. The interaction between the two halides is too weak to influence the MgCl2 deposition, and
TiCl4 could not be chemisorbed at 300 K.
“…Our measurements correspond both to these initial stages of oxidation, for exposures less than 2 L for Mg and 100 L for Al, and to much higher exposures (200 L for Mg and 500 L for Al) corresponding to formation of an oxide film [21]. The high exposure region for Al(111) was recently studied in ultraviolet photoemission spectroscopy (UPS) and metastable He scattering (MIES) [22].…”
Electron capture processes on oxygen covered surfaces were investigated on the example of H 2 formation in H 1 scattering. A strong increase in H 2 production occurs with increasing coverage from the submonolayer to oxide formation range. At low coverages these modifications are interpreted as resulting from competing local effects at oxygen chemisorption sites and nonlocal effects corresponding to work function changes. At high coverages scattering on an ionic solid is considered, with capture occurring at O d2 sites. Strong H 1 to H 2 conversion on an oxide provides an interesting method of negative ion production for injection into fusion devices. [S0031-9007(96)01643-2] PACS numbers: 79.20. Rf, 34.70.+e, 73.30.+y, 82.65.My Oxide surfaces play an important role in fields like catalysis, microelectronics, gas sensors, and in many manufacturing processes in ceramic and glass industries [1,2]. Despite their importance, the proportion of surface science work that has been devoted to date to them remains very limited as opposed to the case of metal and semiconductor surfaces. It is well known that the majority of reactions at surfaces and the formation of transient species involve charge transfer processes: the exchange of an electron or a proton [3]. The acid-base properties of an oxide catalyst are characterized by its capacity to retain an electron or a proton. The study of these transfer phenomena, which along with the surface structure play a fundamental role in determining its reactivity, is thus of great interest. On the theoretical side, efforts at a systematic investigation of the acid-base properties of a series of insulating oxides (BaO, MgO, TiO 2 , SiO 2 ) have been performed recently by Noguera et al. [4,5], who investigated the adsorption of H 1 and OH 2 and discussed charge transfer for this static case. On the experimental side, an interesting method of investigation was suggested by Souda et al. [6], who qualitatively discuss the backscattering of H 1 and He 1 in terms of the ionic-covalent nature of the surface. However, neutralization probabilities, which carry quantitative information, were not determined.A related topic, the study of oxygen adsorption on metal and semiconductor surfaces, has been the subject of numerous experimental and theoretical studies. However, here also electron transfer processes have not been studied in detail experimentally and there do not exist accurate theoretical descriptions of resonant and Auger electron transfer processes. It is common knowledge that oxygen adsorption results in an enhanced emission of secondary ions, as observed in, e.g., secondary-ion mass spectroscopy (SIMS) measurements, attributed to a decrease of electron capture. Our recent studies [7][8][9] have demonstrated that strong modifications in the rearrangement of atomic states near a surface occur in the very initial stages of oxygen uptake. These modifications were tentatively attributed to changes in such surface properties as the work function ͑f͒ and density of states.Here we investiga...
“…For both Be and Mg, the calculated core-electron binding energies are within 0.3 eV of experimental values. [45][46][47][48][49][50][51][52][53] Finally we turn our attention to the prediction of coreelectron binding energies of adsorbed molecules. We have carried out calculations for four molecules, H 2 O, OH, CO and HCOO, on Cu(111).…”
Core-electron x-ray photoelectron spectroscopy is a powerful technique for studying the electronic structure and chemical composition of molecules, solids and surfaces. However, the interpretation of measured spectra and the assignment of peaks to atoms in specific chemical environments is often challenging. Here, we address this problem and introduce a parameter-free computational approach for calculating absolute core-electron binding energies. In particular, we demonstrate that accurate absolute binding energies can be obtained from the total energy difference of the ground state and a state with an explicit core hole when exchange and correlation effects are described by a recently developed meta-generalized gradient approximation and relativistic effects are included even for light elements. We carry out calculations for molecules, solids and surface species and find excellent agreement with available experimental measurements. For example, we find a mean absolute error of only 0.16 eV for a reference set of 103 molecular core-electron binding energies. The capability to calculate accurate absolute core-electron binding energies will enable new insights into a wide range of chemical surface processes that are studied by x-ray photoelectron spectroscopy. arXiv:1904.04823v1 [cond-mat.mtrl-sci]
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