The orbital symmetries of electron-doped iron-arsenide superconductors Ba(Fe{sub 1-x}Co)As have b... more The orbital symmetries of electron-doped iron-arsenide superconductors Ba(Fe{sub 1-x}Co)As have been measured with x-ray absorption spectroscopy. The data reveal signatures of Fe d electron itinerancy, weak electronic correlations, and a high degree of Fe-As hybridization related to the bonding topology of the Fe d{sub xz+yz} states, which are found to contribute substantially at the Fermi level. The energies and detailed
Here we report the absolute characterization of a spin polarimeter by measuring the Sherman funct... more Here we report the absolute characterization of a spin polarimeter by measuring the Sherman function with high precision. These results have been obtained from the analysis of the spin and angle-resolved photoemission spectra of Au(111) surface states. The measurements have been performed with a 250 kHz repetition rate Ti:sapphire amplified laser system combined with a high energy-, angle-, and spin-resolving time-of-flight electron spectrometer.
We report polarization-dependent on-resonance and off-resonance photoemission and x-ray absorptio... more We report polarization-dependent on-resonance and off-resonance photoemission and x-ray absorption measurements to probe the character and the symmetry of the occupied and empty valence-band (VB) states of the four-layered misfit cobaltate [Bi2Ca2O4]RSs[CoO2]1.67 . These experiments bring clear evidence that the one-electron removal VB photoemission spectra, between the Fermi energy (EF) and ˜4.5eV , contain Co3d states, which are strongly hybridized
We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function... more We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function of growth conditions and annealing time via soft and hard x-ray absorption spectroscopies in order to find out if short range ordering (SRO) in the group-V sublattice is present. SRO is one of the potential origins of the huge blueshift of the band gap observed upon annealing in these materials. By combining a Sb K - and L - and N K -edge x-ray absorption fine structure spectroscopy analysis, we demonstrate that neither strong Sb clustering nor preferential Sb-N association is possible, and that Sb atoms see a random number of N next nearest neighbors except for growth temperatures smaller than 400°C , for which Sb-N neighbors in the type-V sublattice are in excess with respect to statistical disorder. On the other hand, the evolution of SRO around N anions (breaking of nitrogen pairs and randomization) can play a role in the annealing-induced band gap blueshift. Varying growth conditions and concentration modifies the band gap but, surprisingly, it does not affect the position of the conduction band minimum when Sb is incorporated.
We use core-valence-valence Auger spectra to probe the Coulomb repulsion between holes in the val... more We use core-valence-valence Auger spectra to probe the Coulomb repulsion between holes in the valence band of Fe pnictide superconductors. By comparing the two-hole final-state spectra to density functional theory calculations of the single-particle density of states, we extract a measure of the electron correlations that exist in these systems. Our results show that the Coulomb repulsion is highly screened
The search for high dielectric constant (high-k) oxides to replace silicon dioxide for future CMO... more The search for high dielectric constant (high-k) oxides to replace silicon dioxide for future CMOS devices is a formidable task. Key issues are definitely good structural and electrical properties as well as high quality interfaces between the high-k and the semiconductor substrate. In this work we study the local structure of ultra thin Y2O3 films and Y2O3/Si interface, by using
The adsorption of dopamine onto an anatase TiO(2)(101) single crystal has been studied using phot... more The adsorption of dopamine onto an anatase TiO(2)(101) single crystal has been studied using photoemission and NEXAFS techniques. Photoemission results suggest that the dopamine molecule adsorbs on the surface in a bidentate geometry, resulting in the removal of band gap states in the TiO(2) valence band. Using the searchlight effect, carbon K-edge NEXAFS spectra indicate that the phenyl rings in the dopamine molecules are orientated normal to the surface. A combination of experimental and computational results indicates the appearance of new unoccupied states arising following adsorption. The possible role of these states in the charge-transfer mechanism of the dopamine-TiO(2) system is discussed.
A detailed study of resonant photoemission at Ti L(2,3) edges of insulating rutile TiO(2-x) thin ... more A detailed study of resonant photoemission at Ti L(2,3) edges of insulating rutile TiO(2-x) thin film is presented. Pure TiO(2) resonating structures, defect-related resonances, resonant Raman-Auger and normal LVV Auger emissions are tracked, including an unpredicted two-hole correlated satellite below the non-bonding part of the valence band. The analysis of excitation dynamics unambiguously addresses the origin of these features and, in particular, the extent of charge transfer effects on the Ti-O bonding in the valence band of rutile, disclosing further applications to the more general case of, formally, d(0) oxides.
The orbital symmetries of electron-doped iron-arsenide superconductors Ba(Fe{sub 1-x}Co)As have b... more The orbital symmetries of electron-doped iron-arsenide superconductors Ba(Fe{sub 1-x}Co)As have been measured with x-ray absorption spectroscopy. The data reveal signatures of Fe d electron itinerancy, weak electronic correlations, and a high degree of Fe-As hybridization related to the bonding topology of the Fe d{sub xz+yz} states, which are found to contribute substantially at the Fermi level. The energies and detailed
Here we report the absolute characterization of a spin polarimeter by measuring the Sherman funct... more Here we report the absolute characterization of a spin polarimeter by measuring the Sherman function with high precision. These results have been obtained from the analysis of the spin and angle-resolved photoemission spectra of Au(111) surface states. The measurements have been performed with a 250 kHz repetition rate Ti:sapphire amplified laser system combined with a high energy-, angle-, and spin-resolving time-of-flight electron spectrometer.
We report polarization-dependent on-resonance and off-resonance photoemission and x-ray absorptio... more We report polarization-dependent on-resonance and off-resonance photoemission and x-ray absorption measurements to probe the character and the symmetry of the occupied and empty valence-band (VB) states of the four-layered misfit cobaltate [Bi2Ca2O4]RSs[CoO2]1.67 . These experiments bring clear evidence that the one-electron removal VB photoemission spectra, between the Fermi energy (EF) and ˜4.5eV , contain Co3d states, which are strongly hybridized
We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function... more We investigated the local structure around N and Sb atoms in GaAsSbN/GaAs epilayers as a function of growth conditions and annealing time via soft and hard x-ray absorption spectroscopies in order to find out if short range ordering (SRO) in the group-V sublattice is present. SRO is one of the potential origins of the huge blueshift of the band gap observed upon annealing in these materials. By combining a Sb K - and L - and N K -edge x-ray absorption fine structure spectroscopy analysis, we demonstrate that neither strong Sb clustering nor preferential Sb-N association is possible, and that Sb atoms see a random number of N next nearest neighbors except for growth temperatures smaller than 400°C , for which Sb-N neighbors in the type-V sublattice are in excess with respect to statistical disorder. On the other hand, the evolution of SRO around N anions (breaking of nitrogen pairs and randomization) can play a role in the annealing-induced band gap blueshift. Varying growth conditions and concentration modifies the band gap but, surprisingly, it does not affect the position of the conduction band minimum when Sb is incorporated.
We use core-valence-valence Auger spectra to probe the Coulomb repulsion between holes in the val... more We use core-valence-valence Auger spectra to probe the Coulomb repulsion between holes in the valence band of Fe pnictide superconductors. By comparing the two-hole final-state spectra to density functional theory calculations of the single-particle density of states, we extract a measure of the electron correlations that exist in these systems. Our results show that the Coulomb repulsion is highly screened
The search for high dielectric constant (high-k) oxides to replace silicon dioxide for future CMO... more The search for high dielectric constant (high-k) oxides to replace silicon dioxide for future CMOS devices is a formidable task. Key issues are definitely good structural and electrical properties as well as high quality interfaces between the high-k and the semiconductor substrate. In this work we study the local structure of ultra thin Y2O3 films and Y2O3/Si interface, by using
The adsorption of dopamine onto an anatase TiO(2)(101) single crystal has been studied using phot... more The adsorption of dopamine onto an anatase TiO(2)(101) single crystal has been studied using photoemission and NEXAFS techniques. Photoemission results suggest that the dopamine molecule adsorbs on the surface in a bidentate geometry, resulting in the removal of band gap states in the TiO(2) valence band. Using the searchlight effect, carbon K-edge NEXAFS spectra indicate that the phenyl rings in the dopamine molecules are orientated normal to the surface. A combination of experimental and computational results indicates the appearance of new unoccupied states arising following adsorption. The possible role of these states in the charge-transfer mechanism of the dopamine-TiO(2) system is discussed.
A detailed study of resonant photoemission at Ti L(2,3) edges of insulating rutile TiO(2-x) thin ... more A detailed study of resonant photoemission at Ti L(2,3) edges of insulating rutile TiO(2-x) thin film is presented. Pure TiO(2) resonating structures, defect-related resonances, resonant Raman-Auger and normal LVV Auger emissions are tracked, including an unpredicted two-hole correlated satellite below the non-bonding part of the valence band. The analysis of excitation dynamics unambiguously addresses the origin of these features and, in particular, the extent of charge transfer effects on the Ti-O bonding in the valence band of rutile, disclosing further applications to the more general case of, formally, d(0) oxides.
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Papers by M. Malvestuto