G. Zampieri

Highly under-coordinated atoms at Rh surfaces: interplay of strain and coordination effects on core level shift

The electronic structure of highly under-coordinated Rh atoms, namely adatoms and ad-dimers, on homo-metallic surfaces has been probed by combining high-energy resolution core level photoelectron spectroscopy and density functional theory calculations. The Rh3d5/2 core level shifts are shown to be proportional to the number of Rh nearest-neighbours (n = 3, 4 and 5). A more refined analysis shows that the energy position of the different core level components is correlated with the calculated changes of the individual inter-atomic bond length and to the energy changes of the d-band centre, which is known to be a reliable descriptor of local chemical reactivity.

TiO2-Photocatalytic Reduction of Pentavalent and Trivalent Arsenic: Production of Elemental Arsenic and Arsine

Heterogeneous photocatalytic reduction of As(V) and As(III) at different concentrations over TiO(2) under UV light in deoxygenated aqueous suspensions is described. For the first time, As(0) was unambiguously identified together with arsine (AsH(3)) as reaction products. As(V) reduction requires the presence of an electron donor (methanol in the present case) and takes place through the hydroxymethyl radical formed from methanol oxidation by holes or hydroxyl radicals. On the contrary, As(III) reduction takes place through direct reduction by the TiO(2)-conduction band electrons. Detailed mechanisms for the photocatalytic processes are proposed. Although reduction to solid As(0) is convenient for purposes of As removal from water as a deposit on TiO(2), attention must be paid to formation of AsH(3), one of the most toxic forms of As, and strategies for AsH(3) treatment should be considered.

Charge transfer from core-excited argon adsorbed on clean and hydrogenated Si(100): ultrashort timescales and energetic structure

Using the well-established core hole-clock method under resonant Auger Raman conditions we have measured the charge transfer (CT) times for the 4s electron on 2p3/2 core excited Ar atoms adsorbed on Si(100). The influences of the doping (p- or n-type), surface condition (clean or covered with monohydride) and varied excitation energy have been examined. The data for the Si–H surfaces are most extensive and distinct and undisturbed by background or losses. The CT times, which are identical for n- and p-type materials, are found to be about 2 fs at resonance. They show a distinct energy dependence when broadly tuning the excitation energy through the Ar core resonance. The CT times on clean Si(100), for which the data are not as extensive, are shorter by a factor of ~2 compared to the Si–H surfaces and again about the same for n- and p-type Si(100). The unexpectedly short CT times found, as well as the energetic structure seen, are discussed in terms of possible influences of the projected surface electronic structure of Si(100) in the energy range of the Ar 4s electron, and of other explanations. Theoretical modeling would be highly desirable.

Resistive Switching in Ferromagnetic

Ferromagnetic thin films of La2/3Ca1/3MnO3 manganite were grown by pulsed laser deposition, under different oxygen atmospheres, on silicon substrates. We performed structural, magnetic, spectroscopic, and electrical characterization of the films. Resistive switching between high and low resistance states was obtained upon pulsing with opposite polarities voltages. The I-V curves exhibit sharp transitions between these states. The RS properties are strongly dependant on the films oxygen stochiometry and on the compliance current used for producing the high to low transition. ON/OFF ratios as high as 1000 were obtained for optimal RS conditions. Obtained results are discussed within the framework of mobile oxygen vacancies.

{\rm La}_{2/3}{\rm Ca}_{1/3}{\rm MnO}_{3}

We have measured the angular distribution of electrons reflected from Cu(001) having excited: i) an interband transition, ii) a plasmon, and iii) a core electron. We have found that the angular patterns in cases i) and ii) are similar to the angular pattern of elastically reflected electrons; in particular, the inelastic electrons are reflected along the Bragg directions at low energies and along the main crystallographic axes at intermediate energies. The angular pattern of the electrons reflected having created a Cu‐3p vacancy is also concentrated along the crystallographic axes at intermediate energies but at low energies the maxima of intensity are not along the Bragg directions.