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.
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.
ABSTRACT
The electronic states of diamond-like hydrogenated carbon (DLC) films were studied by synchrotron radiation photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p-pi band in relation to the sample annealing and ion bombardment amorphization. The p-pi band of the annealed DLC was characterized by localized p(z) states, while the formation of the amorphous carbon surface was accompanied by appearance of the delocalized p(z) states, which reduce the optical gap. A simple approach permitting the extraction of the 2p band shape from the photoelectron spectra is proposed.
