M. Pedio - Academia.edu (original) (raw)
Papers by M. Pedio
Physical review. B, Condensed matter, Jan 15, 1992
An investigation of the metal-induced electronic states, the dielectric properties, and the growt... more An investigation of the metal-induced electronic states, the dielectric properties, and the growth morphology of Bi/GaAs(110) and Sb/GaAs(110)-as model systems, for epitaxial and unreactive interfaces-is presented. The electronic transitions involving surface and Bi (Sb) -induced states, investigated by means of high-resolution electron-energy-loss spectroscopy, are discussed and compared with previous results. In the Bi/GaAs(110) interface, a clear absorption structure appears within
Langmuir, 2012
Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-d... more Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-dimensional molecular chains, whose spatial distribution evolves into different structural phases at increasing molecular density. The plasticity of the Au channels first induces an ordered phase with a 5×5 symmetry, followed by a second long-range ordered structure composed by denser chains with a 5×7 periodicity with respect to the bare Au surface, as observed in the low-energy electron-diffraction (LEED) and grazing incidence X-ray diffraction (GIXRD) patterns. The geometry of the FePc molecular assemblies in the Au nanorails is determined by scanning tunneling microscopy (STM). For the 5×7 phases, the GIXRD analysis identifies a "4-3" rows profile along the [001] direction in the Au surface and an on-top FePc adsorption site, further confirmed by density functional theory (DFT) calculations. The latter also reveals the electronic mixing of the interface states. The chain assembly is driven by the molecule−molecule interaction and the chains interact with the Au nanorails via the central metal atom, while the chain−chain distance in the different structural phases is primarily driven by the plasticity of the Au surface.
Physical Review B, 2002
The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum... more The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum has been measured for in situ prepared potassium superoxide. The experimental data have been analyzed in detail by multiple scattering calculations using self-consistent field potentials. In particular, the so-called pi resonance at the rising edge, which presents a double-peak structure, has been totally resolved and reproduced by the
Surface Science, 2006
Epitaxial cobalt films on CaF2(110) buffer layers on Si(001) were grown by molecular beam epitaxy... more Epitaxial cobalt films on CaF2(110) buffer layers on Si(001) were grown by molecular beam epitaxy. It is found that Co grows in a face-centered cubic lattice forming nanodimensional islands. The islands tend to align along the parallel grooves which characterize the self-patterned CaF2(110) surface grown on Si(001). Photoemission was used to probe the uniformity of the film and the occurrence
Physica Scripta, 2005
We report a near-edge X-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C 60 molecu... more We report a near-edge X-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C 60 molecules interacting with Si(100) and Si(111) surfaces. Annealing the C 60 /Si systems at 1050 K induces fullerene fragmentation and leads to SiC nucleation. Tuning the probing depth and studying polarization dependence, the NEXAFS results shed light on the evolution of the molecular states after thermal treatment, up to the fullerene fragmentation and SiC formation. The NEXAFS spectra of a single layer of C 60 deposited at 670 K onto both surfaces show a strong C 60 -substrate interaction. A polarization dependence of the spectra can be detected; this behaviour is similar to the results obtained on C 60 covalently chemisorbed on Al surfaces. We find, for both substrates, that fullerene fragmentation starts at the C-Si interfaces, involving the C atoms lying close to the Si substrate, implying an increase of the number of C-Si bonds at the fragmentation stage.
Applied Surface Science, 2004
In particle accelerators with intense positively charged bunched beams, an electron cloud may ind... more In particle accelerators with intense positively charged bunched beams, an electron cloud may induce beam instabilities and the related beam induced electron multipacting (BIEM), result in an undesired pressure rise and, in a cryogenic machine such as the Large Hadron Collider (LHC), introduce addition heat loads. When present, synchrotron radiation (SR) may generate a significant number of photoelectrons, that may play a role in determining the onset and the detailed properties of the electron-cloud related instability. Since electrons are constrained to move along field lines, those created on the accelerator equator in a strong vertical (dipole) field cannot participate in the ecloud build-up. Therefore, for the LHC there has been a continuous effort to find solutions to absorb the photons on the equator. The solution adopted for the LHC dipole beam screens is a saw-tooth structure on the illuminated equator. SR from a bending magnet beamline at ELETTRA, Italy (BEAR) has been used to measure the reflectivities (forward, backscattered and diffuse), for a flat and a saw-tooth structured Cu co-laminated surface using both white light SR, similar to the one emitted by LHC, and monochromatic light. Our data show that the saw-tooth structure does reduce the total reflectivity and modifies the photon energy distribution of the reflected photons. The implications of these results on the LHC arc vacuum system are discussed.
Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task.... more Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C 60 with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C 60 molecules and the clean Pt(111) surface results in the formation of an ordered √ 13 × √ 13R13.9 • reconstruction based on the creation of a surface vacancy lattice. The C 60 molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.
We report a study of the electronic properties of Cs overlayers on the narrow-band-gap III-V semi... more We report a study of the electronic properties of Cs overlayers on the narrow-band-gap III-V semiconductor InSb(110) as determined by means of photoemission and high-resolution electron-energy-loss spectroscopy. The electric and electronic properties of Cs-deposited on InSb(110) present two distinguishable phases, which can be related to the morphological transition observed in the scanning tunneling microscopy from one-dimensional chains to the two-dimensional (2D) Cs layer. The earlier stages of Cs adsorption induce an accumulation layer, while an additional Cs deposition results in a depletion of carriers in coincidence with the appearance of Cs-induced states in the semiconductor gap. When a 2D layer of cesium is formed on the InSb(110) surface, the interface is insulating with the surface band gap at 0.65 eV, larger than the underlying InSb bulk gap (0.175 eV at room temperature).
Physical review. B, Condensed matter, Jan 15, 1992
An investigation of the metal-induced electronic states, the dielectric properties, and the growt... more An investigation of the metal-induced electronic states, the dielectric properties, and the growth morphology of Bi/GaAs(110) and Sb/GaAs(110)-as model systems, for epitaxial and unreactive interfaces-is presented. The electronic transitions involving surface and Bi (Sb) -induced states, investigated by means of high-resolution electron-energy-loss spectroscopy, are discussed and compared with previous results. In the Bi/GaAs(110) interface, a clear absorption structure appears within
Langmuir, 2012
Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-d... more Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-dimensional molecular chains, whose spatial distribution evolves into different structural phases at increasing molecular density. The plasticity of the Au channels first induces an ordered phase with a 5×5 symmetry, followed by a second long-range ordered structure composed by denser chains with a 5×7 periodicity with respect to the bare Au surface, as observed in the low-energy electron-diffraction (LEED) and grazing incidence X-ray diffraction (GIXRD) patterns. The geometry of the FePc molecular assemblies in the Au nanorails is determined by scanning tunneling microscopy (STM). For the 5×7 phases, the GIXRD analysis identifies a "4-3" rows profile along the [001] direction in the Au surface and an on-top FePc adsorption site, further confirmed by density functional theory (DFT) calculations. The latter also reveals the electronic mixing of the interface states. The chain assembly is driven by the molecule−molecule interaction and the chains interact with the Au nanorails via the central metal atom, while the chain−chain distance in the different structural phases is primarily driven by the plasticity of the Au surface.
Physical Review B, 2002
The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum... more The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum has been measured for in situ prepared potassium superoxide. The experimental data have been analyzed in detail by multiple scattering calculations using self-consistent field potentials. In particular, the so-called pi resonance at the rising edge, which presents a double-peak structure, has been totally resolved and reproduced by the
Surface Science, 2006
Epitaxial cobalt films on CaF2(110) buffer layers on Si(001) were grown by molecular beam epitaxy... more Epitaxial cobalt films on CaF2(110) buffer layers on Si(001) were grown by molecular beam epitaxy. It is found that Co grows in a face-centered cubic lattice forming nanodimensional islands. The islands tend to align along the parallel grooves which characterize the self-patterned CaF2(110) surface grown on Si(001). Photoemission was used to probe the uniformity of the film and the occurrence
Physica Scripta, 2005
We report a near-edge X-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C 60 molecu... more We report a near-edge X-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C 60 molecules interacting with Si(100) and Si(111) surfaces. Annealing the C 60 /Si systems at 1050 K induces fullerene fragmentation and leads to SiC nucleation. Tuning the probing depth and studying polarization dependence, the NEXAFS results shed light on the evolution of the molecular states after thermal treatment, up to the fullerene fragmentation and SiC formation. The NEXAFS spectra of a single layer of C 60 deposited at 670 K onto both surfaces show a strong C 60 -substrate interaction. A polarization dependence of the spectra can be detected; this behaviour is similar to the results obtained on C 60 covalently chemisorbed on Al surfaces. We find, for both substrates, that fullerene fragmentation starts at the C-Si interfaces, involving the C atoms lying close to the Si substrate, implying an increase of the number of C-Si bonds at the fragmentation stage.
Applied Surface Science, 2004
In particle accelerators with intense positively charged bunched beams, an electron cloud may ind... more In particle accelerators with intense positively charged bunched beams, an electron cloud may induce beam instabilities and the related beam induced electron multipacting (BIEM), result in an undesired pressure rise and, in a cryogenic machine such as the Large Hadron Collider (LHC), introduce addition heat loads. When present, synchrotron radiation (SR) may generate a significant number of photoelectrons, that may play a role in determining the onset and the detailed properties of the electron-cloud related instability. Since electrons are constrained to move along field lines, those created on the accelerator equator in a strong vertical (dipole) field cannot participate in the ecloud build-up. Therefore, for the LHC there has been a continuous effort to find solutions to absorb the photons on the equator. The solution adopted for the LHC dipole beam screens is a saw-tooth structure on the illuminated equator. SR from a bending magnet beamline at ELETTRA, Italy (BEAR) has been used to measure the reflectivities (forward, backscattered and diffuse), for a flat and a saw-tooth structured Cu co-laminated surface using both white light SR, similar to the one emitted by LHC, and monochromatic light. Our data show that the saw-tooth structure does reduce the total reflectivity and modifies the photon energy distribution of the reflected photons. The implications of these results on the LHC arc vacuum system are discussed.
Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task.... more Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C 60 with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C 60 molecules and the clean Pt(111) surface results in the formation of an ordered √ 13 × √ 13R13.9 • reconstruction based on the creation of a surface vacancy lattice. The C 60 molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.
We report a study of the electronic properties of Cs overlayers on the narrow-band-gap III-V semi... more We report a study of the electronic properties of Cs overlayers on the narrow-band-gap III-V semiconductor InSb(110) as determined by means of photoemission and high-resolution electron-energy-loss spectroscopy. The electric and electronic properties of Cs-deposited on InSb(110) present two distinguishable phases, which can be related to the morphological transition observed in the scanning tunneling microscopy from one-dimensional chains to the two-dimensional (2D) Cs layer. The earlier stages of Cs adsorption induce an accumulation layer, while an additional Cs deposition results in a depletion of carriers in coincidence with the appearance of Cs-induced states in the semiconductor gap. When a 2D layer of cesium is formed on the InSb(110) surface, the interface is insulating with the surface band gap at 0.65 eV, larger than the underlying InSb bulk gap (0.175 eV at room temperature).