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ABSTRACT: Photoelectron spectroscopy with synchrotron radiation, low energy electron diffraction, and ion-scattering spectroscopy were used in order to study the Ti/MgCl(2) interface grown on an atomically clean Si(111) 7 × 7 substrate. A series of high resolution spectra after deposition of a thick MgCl(2) layer, step by step deposition of Ti and gradual annealing, indicated a very reactive interface even at room temperature. Strong interaction between the incoming Ti atoms and the MgCl(2) layer, leads to the formation of Ti(2+) and Ti(4+) oxidation states. The interfacial interaction continues even at multilayer Ti coverage mainly by the partial disruption of Mg-Cl bonds and the formation of Ti-Cl sites, rendering this interface a very promising UHV-compatible model of a pre-catalyst for olefin polymerization. After the final annealing, the MgCl(2) multilayers desorb while Ti remains on the surface forming a silicide layer on which Cl and Mg atoms are attached.
The Journal of chemical physics 06/2012; 136(22):224703. · 3.09 Impact Factor
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11th Greek National Symposium on Catalysis, Athens, 2010; 10/2010
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XXVI Greek National Conference on Solid State Physics and Material Science, Ioannina, 2010; 09/2010
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ABSTRACT: Photoelectron spectroscopy with synchrotron radiation (SRPES), temperature programmed desorption (TPD), low energy electron diffraction (LEED), and ion-scattering spectroscopy (ISS) were used in order to study the MgCl(2)/Ti(0001) interface. A clear hexagonal LEED pattern confirmed the presence of a quite large grain of Ti(0001) on the substrate while no new superstructure was formed after deposition of MgCl(2) either at room or at elevated temperatures. A series of high resolution spectra after step by step MgCl(2) deposition and gradual annealing indicated strong interaction between MgCl(2) and the substrate while ISS measurements showed that there is no migration of Ti atoms into the deposit layers. Additional quantities of deposited MgCl(2) grew stoichimetrically on top of the chemically active interface. Annealing at approximately 350 degrees C caused clustering of the MgCl(2) multilayer and TPD results showed that they desorbed stoichimetrically at temperatures between 360 and 380 degrees C. The interfacial TiCl(x)Mg(y) species dissociated by the disruption of the Cl-Mg bonds at temperatures higher than 400 degrees C and metallic Mg evaporated. The Cl atoms remained attached on the Ti surface but they did not form any ordered structure even after annealing at 730 degrees C. The present results indicate the occurrence of charge transfer at the Ti/MgCl(2) interface through the Cl ligands and provide valuable information for catalyst design.
The Journal of chemical physics 08/2010; 133(7):074701. · 3.09 Impact Factor
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ABSTRACT: The interaction between MgCl2 and SiO2 was investigated by X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS) and contact potential difference (CPD) measurements. A thin SiO2 layer was grown for this purpose on a Si(1 0 0) wafer and MgCl2 was applied on this support at room temperature by evaporation under UHV conditions. It was found that magnesium chloride is deposited molecularly on the SiO2 substrate, growing in layers and covering uniformly the oxide surface. The interaction with the substrate is initially very weak and limited to the interfacial layer. Above 623 K, most of the molecular MgCl2 is re-evaporated and the interfacial interaction becomes stronger, as Mg–Cl bonds in the remaining sub-monolayer chloride break and Cl atoms desorb. This leaves on the surface sub-stoichiometric MgClx, which interacts with oxygen atoms from the substrate to form a complex surface species. At 973 K all Cl atoms desorb and Mg remains on the surface in the form of an oxide.
Applied Surface Science 08/2009; 255(21):8941. · 2.10 Impact Factor
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XXIV Greek National Conference on Solid State Physics and Material Science, Heraklion, 2008; 01/2008
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S. Karakalos, A. Siokou,
V. Dracopoulos,
S. Ladas,
F. Sutara,
T. Skala,
M. Skoda,
V. Nehasil,
K. Prince,
V. Matolin,
V. Chab
VIII European Conference on Catalysis, Europacat, Turku, Finland, 2007, Turku, Finland; 08/2007
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6th Greek National Conference on Chemical Engineering, Athens, 2007; 01/2007
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XXIII Greek National Conference on Solid State Physics and Material Science, Athens, 2007; 01/2007
