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6 results on '"Lollobrigida, Valerio"'

1. Space-charge effects in high-energy photoemission

Author

Verna, Adriano, Greco, Giorgia, Lollobrigida, Valerio, Offi, Francesco, and Stefani, Giovanni

Subjects
Condensed Matter - Materials Science
Abstract

Pump-and-probe photoelectron spectroscopy (PES) with femtosecond pulsed sources opens new perspectives in the investigation of the ultrafast dynamics of physical and chemical processes at the surfaces and interfaces of solids. Nevertheless, for very intense photon pulses a large number of photoelectrons are simultaneously emitted and their mutual Coulomb repulsion is sufficiently strong to significantly modify their trajectory and kinetic energy. This phenomenon, referred as space-charge effect, determines a broadening and shift in energy for the typical PES structures and a dramatic loss of energy resolution. In this article we examine the effects of space charge in PES with a particular focus on time-resolved hard X-ray (~10 keV) experiments. The trajectory of the electrons photoemitted from pure Cu in a hard X-ray PES experiment has been reproduced through $N$-body simulations and the broadening of the photoemission core-level peaks has been monitored as a function of various parameters (photons per pulse, linear dimension of the photon spot, photon energy). The energy broadening results directly proportional to the number $N$ of electrons emitted per pulse (mainly represented by secondary electrons) and inversely proportional to the linear dimension $a$ of the photon spot on the sample surface, in agreement with the literature data about ultraviolet and soft X-ray experiments. The evolution in time of the energy broadening during the flight of the photoelectrons is also studied. Despite its detrimental consequences on the energy spectra, we found that space charge has negligible effects on the momentum distribution of photoelectrons and a momentum broadening is not expected to affect angle-resolved experiments. Strategy to reduce the energy broadening and the feasibility of hard X-ray PES experiments at the new free-electron laser facilities are discussed., Comment: 15 pages, 2 tables, 8 figures

Published
2016
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2. Electrical, optical, and electronic properties of Al:ZnO films in a wide doping range.

Author

Valenti, Ilaria, Benedetti, Stefania, di Bona, Alessandro, Lollobrigida, Valerio, Perucchi, Andrea, Di Pietro, Paola, Lupi, Stefano, Valeri, Sergio, and Torelli, Piero

Subjects
PHOTOEMISSION, SPECTRUM analysis, INFRARED absorption, CONDUCTIVITY of electrolytes, FILMSTRIPS
Abstract

The combination of photoemission spectroscopies, infrared and UV-VIS absorption, and electric measurements has allowed to clarify the mechanisms governing the conductivity and the electronic properties of Al-doped ZnO (AZO) films in a wide doping range. The contribution of defect-related in-gap states to conduction has been excluded in optimally doped films (around 4 at. %). The appearance of gap states at high doping, the disappearance of occupied DOS at Fermi level, and the bands evolution complete the picture of electronic structure in AZO when doped above 4 at. %. In this situation, compensating defects deplete the conduction band and increase the electronic bandgap of the material. Electrical measurements and figure of merit determination confirm the high quality of the films obtained by magnetron sputtering, and thus allow to extend their properties to AZO films in general. [ABSTRACT FROM AUTHOR]

Published
2015
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3. Role of Oxygen Deposition Pressure in the Formation of Ti Defect States in TiO2(001) Anatase Thin Films

Author

Gobaut, Benoit, primary, Orgiani, Pasquale, additional, Sambri, Alessia, additional, di Gennaro, Emiliano, additional, Aruta, Carmela, additional, Borgatti, Francesco, additional, Lollobrigida, Valerio, additional, Céolin, Denis, additional, Rueff, Jean-Pascal, additional, Ciancio, Regina, additional, Bigi, Chiara, additional, Das, Pranab Kumar, additional, Fujii, Jun, additional, Krizmancic, Damjan, additional, Torelli, Piero, additional, Vobornik, Ivana, additional, Rossi, Giorgio, additional, Miletto Granozio, Fabio, additional, Scotti di Uccio, Umberto, additional, and Panaccione, Giancarlo, additional

Published
2017
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5. Role of Oxygen Deposition Pressure in the Formation of Ti Defect States in TiO2(001) Anatase Thin Films

Author

Fabio Miletto Granozio, A. Sambri, Pranab Kumar Das, Regina Ciancio, Giancarlo Panaccione, Emiliano Di Gennaro, Carmela Aruta, Piero Torelli, Pasquale Orgiani, Francesco Borgatti, Chiara Bigi, Umberto Scotti di Uccio, V. Lollobrigida, Jean-Pascal Rueff, Denis Céolin, Jun Fujii, Damjan Krizmancic, B. Gobaut, Ivana Vobornik, Giorgio Rossi, Gobaut, Benoit, Orgiani, Pasquale, Sambri, Alessia, DI GENNARO, Emiliano, Aruta, Carmela, Borgatti, Francesco, Lollobrigida, Valerio, Céolin, Deni, Rueff, Jean Pascal, Ciancio, Regina, Bigi, Chiara, Das, Pranab Kumar, Fujii, Jun, Krizmancic, Damjan, Torelli, Piero, Vobornik, Ivana, Rossi, Giorgio, Miletto Granozio, Fabio, SCOTTI DI UCCIO, Umberto, and Panaccione, Giancarlo

Subjects
In situ, defect, Anatase, Materials science, shear planes, Analytical chemistry, chemistry.chemical_element, 02 engineering and technology, 01 natural sciences, Oxygen, oxygen vacancies, Pulsed laser deposition, X-ray photoelectron spectroscopy, 0103 physical sciences, General Materials Science, Thin film, 010306 general physics, defects, Range (particle radiation), 021001 nanoscience & nanotechnology, chemistry, resonant photoemission, oxygen vacancie, interdiffusion, anatase, Electron configuration, 0210 nano-technology, in-gap state
Abstract

We report the study of anatase TiO2(001)-oriented thin films grown by pulsed laser deposition on LaAlO3(001). A combination of in situ and ex situ methods has been used to address both the origin of the Ti(3+)-localized states and their relationship with the structural and electronic properties on the surface and the subsurface. Localized in-gap states are analyzed using resonant X-ray photoelectron spectroscopy and are related to the Ti(3+) electronic configuration, homogeneously distributed over the entire film thickness. We find that an increase in the oxygen pressure corresponds to an increase in Ti(3+) only in a well-defined range of deposition pressure; outside this range, Ti(3+) and the strength of the in-gap states are reduced.

Published
2017
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6. Electron trajectory simulations of time-of-flight spectrometers for core level high-energy photoelectron spectroscopy at pulsed X-ray sources

Author

Adriano Verna, Giorgia Greco, Daniela Simeone, Giovanni Stefani, Francesco Offi, V. Lollobrigida, Lollobrigida, Valerio, Greco, Giorgia, Simeone, Daniela, Offi, Francesco, Verna, Adriano, Stefani, Giovanni, and Verna, A

Subjects
Free electron model, Atomic and Molecular Physics, and Optic, Photoionization, Electron, Condensed Matter Physic, Optics, Cylindrical lens, Physical and Theoretical Chemistry, Spectroscopy, Electro-optics simulation, Physics, Radiation, Spectrometer, business.industry, Electronic, Optical and Magnetic Material, Free-electron laser, Condensed Matter Physics, Hard X-ray photoemission spectroscopy, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Time of flight, Time-of-flight analyzers, Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, business, Time-of-flight analyzer
Abstract

The advent of Free Electron Lasers (FELs), able to provide short (2-100 fs) and intense (10(33) photons/s/mm(2)/mrad(2)/0.1%bandwidth) pulses of light also in the hard X-ray regime (h omega> 2000 eV), opens new possibilities to study the ultrafast dynamics of processes, exploiting the capability of Hard X-ray Photoelectron Spectroscopy (HAXPES) to measure core-level spectra of elements with bulk sensitivity. In order to detect the intense bursts of high kinetic energy electrons generated by the X-ray pulses with an energy resolution comparable to the existing category of electron analyzers, a new class of spectrometers must be designed. We present a characterization of two different TOF spectrometers, namely one based on a retarding cylindrical lens and another one based on the spherical reflector geometry. SIMION (R) software has been used in order to evaluate electron trajectories of high kinetic energy electrons (5000-10,000 eV) and extract transmission properties, angular acceptance and energy resolution. It resulted that while the linear system is able to accept a larger solid angle (similar to 50 msr), the spherical mirror offers a better resolving power (around 71,000). Both analyzers are capable of a transmission above 90% within range of kinetic energies wide enough to measure the full line-shape of a core photoionization peak. Furthermore, we proved that both instruments are able to discriminate between two consecutive electron bunches having a temporal separation inferior than 220 ns, which is the distance between two consecutive photon pulses at the European X-ray Free Electron Laser (EXFEL), which is currently under construction in Hamburg.

Published
2015

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