Salvatore Altieri - Academia.edu (original) (raw)

Papers by Salvatore Altieri

Physical Review B, 2002

The morphology of ultrathin epitaxial MgO layers reactively grown on Ag͑001͒ was investigated by ... more The morphology of ultrathin epitaxial MgO layers reactively grown on Ag͑001͒ was investigated by using scanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from the substrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individual substrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensates in form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islands and on the vacancy islands as well. The largest Ag͑001͒ fractional coverage by monoatomic MgO islands is 70%. A limited amount of MgO bilayers or trilayers has also been detected ͑about 1% fractional coverage͒. At the nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, with edges along the ͓110͔ directions. The actual substrate fractional coverage is about 85% and the occurrence of bilayers and multilayers becomes significant ͑about 30 and 5% fractional coverage, respectively͒, resulting in the formation of three-dimensional pyramidal MgO islands.

Physical Review Letters, 1997

We report the measurement of the local Ni 3d spin polarization, not only below but also above the... more We report the measurement of the local Ni 3d spin polarization, not only below but also above the Curie temperature ͑T C ͒, using the newly developed spin-resolved circularly polarized 2p ͑L 3 ͒ resonant photoemission technique. The experiment identifies the presence of 3d 8 singlets at high energies and 3d 8 triplets at low energies extending all the way to the Fermi energy, both below and above T C , showing that it is the orbital degeneracy of the 3d band and the Hund's rule splitting which is of utmost importance to understand Ni and other 3d ferromagnets. [S0031-9007(97)04363-9]

Physical Review B, 2009

We have tested the concept of image charge screening as a new approach to enhance magnetic orderi... more We have tested the concept of image charge screening as a new approach to enhance magnetic ordering temperatures and superexchange interactions in ultra thin films. Using a 3 monolayer NiO(100) film grown on Ag(100) and an identically thin film on MgO(100) as model systems, we observed that the Néel temperature of the NiO film on the highly polarizable metal substrate is 390 K while that of the film on the poorly polarizable insulator substrate is below 40 K. This demonstrates that screening by highly polarizable media may point to a practical way towards designing strongly correlated oxide nanostructures with greatly improved magnetic properties.

Surface Science, 1995

We investigated the electron emission induced by energetic sputter-deposited Si particles during ... more We investigated the electron emission induced by energetic sputter-deposited Si particles during ion beam sputter deposition of Si on Ge substrate. Electron emission is strictly similar to the ion-induced Auger (IAE) Si spectra and originates in Si-Si collisions. Monitoring this "IAE-like" Si yield during the Si layer-by-layer growth, we measured the surface sensitivity of particle-induced electron emission for different energies of the involved particles and for different experimental geometries. We found that the depth sampled by IAE spectroscopy critically depends on the experimental parameters. The surface sensitivity of IAE is, in several cases, larger than that of the corresponding, conventional electron-induced Auger electron emission.

Physical Review B, 2009

... G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá di Modena e Reggio Em... more ... G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá di Modena e Reggio Emilia, via G. Campi 213/A, 41100 Modena, Italy (Received ... Integral XPS spectral intensities were analyzed after standard x-ray satellite filtering and Shirley background sub-traction. ...

Physical Review B, 2007

... at Surfaces, via G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá diMo... more ... at Surfaces, via G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá diModena e Reggio Emilia, via G. Campi 213/A, 41100 Modena, Italy (Received ... The XPS spectra were analyzed af-ter standard x-ray satellite filtering and Shirley background subtraction. ...

The existence and the properties of metal-oxide boundaries, and, more in generai, metalceramic bo... more The existence and the properties of metal-oxide boundaries, and, more in generai, metalceramic boundaries, play a crucial role in determining many physical processes and technological applications in a wide variety of traditional areas of the materials science and technology. Coating of oxide which function as thermal barriers or as a natural corrosion protection are of concern to the manufacturers of jet engines and equipment for power generation, who seek to improve lifetimes and efficiency. In the chemicai industry, strong metal-support interactions and the performance of a metallic catalyst supported on a ceramic substrate depend on the properties of metal-ceramic interfaces, and also the electronic industry depends on the properties of such interfaces for packaging and in components such as rectifiers and MOSFETs. ... Ziee: Summary

Thin Solid Films, 2001

ABSTRACT Growth, morphology and structure of thin MgO films prepared on Ag(001) substrates by dif... more ABSTRACT Growth, morphology and structure of thin MgO films prepared on Ag(001) substrates by different preparation procedures have been investigated by AES, LEED and modulated electron emission. Oxide layers were prepared by Mg MBE in an oxygen atmosphere or sputter deposition from bulk MgO target. In both cases stoichiometric MgO forms, which initially grows in a rocksalt tetragonally distorted structure. For 3-ML films, 3.6% expansion of the interlayer spacing along the growth axis has been measured. The misfit strain progressively reduces as the film thickness increases, and the equilibrium spacing is completely recovered at 8–10 ML thickness. In spite of the similarity in structure and strain, different deposition procedures lead to different film morphology. Sputter deposited films only partially cover the substrate. Fractional coverage (50%) has been evaluated for the 3-ML thick film, and full coverage only occurs at approximately 10 ML thickness. The MBE procedure results in almost complete layers. Fourfold broadening of spot profiles has been observed in LEED patterns of both MBE and sputter deposited films, indicating the occurrence of a similar large-scale atomic arrangement and surface morphology.

Surface Science, 2002

Thin MgO films (1-20 ML) were synthesised by evaporating the metallic component in oxygen atmosph... more Thin MgO films (1-20 ML) were synthesised by evaporating the metallic component in oxygen atmosphere on Ag(0 0 1). The reduced lattice misfit (3.1%) between the (0 0 1) surface unit meshes of the Ag fcc and MgO rock salt structure leads to the formation of epitaxial MgO layers with the (0 0 1)MgOk(0 0 1)Ag and [1 0 0]MgOk[1 0 0]Ag orientation relationships. The oxide layers were structurally characterized by LEED and modulated electron emission, while their surface morphology was studied by STM. In spite of the weak interaction between the oxide overlayer and the substrate, the occurrence of a significant tetragonal distortion of the MgO structure has been detected. We investigated in detail the strain in the oxide layer as a function of the thickness. Thin (<6 ML) films exhibit an expansion along the growth axis with respect to the equilibrium phase. This vertical strain progressively reduces as the thickness increases and disappears at about 9 ML. A Poisson ratio larger than the bulk MgO value has been obtained for the 3 ML film, while the bulk value is appropriate films thicker than 6 ML. STM data indicate that an almost complete substrate coverage is obtained at 3 ML deposition. Ó

Physical Review B, 2002

ABSTRACT The morphology of ultrathin epitaxial MgO layers reactively grown on Ag(001) was investi... more ABSTRACT The morphology of ultrathin epitaxial MgO layers reactively grown on Ag(001) was investigated by using scanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from the substrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individual substrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensates in form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islands and on the vacancy islands as well. The largest Ag(001) fractional coverage by monoatomic MgO islands is 70%. A limited amount of MgO bilayers or trilayers has also been detected (about 1% fractional coverage). At the nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, with edges along the [110] directions. The actual substrate fractional coverage is about 85% and the occurrence of bilayers and multilayers becomes significant (about 30 and 5% fractional coverage, respectively), resulting in the formation of three-dimensional pyramidal MgO islands.

Thin Solid Films, 2003

The structure and morphology of thin NiO films prepared on Ag(001) by reactive growth at 460 K ha... more The structure and morphology of thin NiO films prepared on Ag(001) by reactive growth at 460 K has been investigated as a function of the film thickness in the 3-20 monolayers range. Emphasis was on the study of the oxide layer misfit strain. Primary beam diffraction modulated electron emission and low energy electron diffraction experiments allowed the determination of the in-plane and out-of-plane strain in the oxide layer, while scanning tunneling microscopy, X-ray photoelectron spectroscopy and secondary electron imaging have been used to monitor the film morphology, stoichiometry and structure, respectively. The film strain begins to be removed at a critical thickness of 10 ML, while at 20 ML the film is fully relaxed. Strain analysis indicates that the Poisson ratio of the oxide layer is nearly equal to that of the bulk material. ᮊ

Physical Review B, 2003

We calculate the classical dipole interaction energy in fcc collinear antiferromagnetic films. We... more We calculate the classical dipole interaction energy in fcc collinear antiferromagnetic films. We find that the presence and the type of strain strongly conditions the dipolar anisotropy, while the finite thickness introduces an additional perturbation to the dipolar energy, similar to the well known shape anisotropy of ferromagnetic films, with sizable effects due to surface roughness. An analytic expression relating

Thin Solid Films, 2001

NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O atmosphere. The thickness... more NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O atmosphere. The thickness range 5-50 ML has 2 been investigated. X-ray photoelectron spectroscopy has been used to study the stoichiometric composition and chemical purity of the oxide films. We found completely oxidized stoichiometric NiO films. Their contamination has been found to be limited to the topmost layers. Photoelectron diffraction has given information concerning the local crystal structure of the films. The film atomic geometry has been found to be the same independent of thickness in the 0-50 ML range. The films have the expected (001) rock-salt structure with the same in plane orientation as the Ag(001) substrate. Specular X-ray reflectivity has allowed a very accurate thickness evaluation and has given information on the width of the density gradients at the film-substrate and vacuum-film interfaces, found to be of the order of a few atomic layers. ᮊ

The Journal of Physical Chemistry C, 2011

ABSTRACT We obtained assemblies of Ni/MgO core/shell nanoparticles (NPs) by using a special exper... more ABSTRACT We obtained assemblies of Ni/MgO core/shell nanoparticles (NPs) by using a special experimental setup, in which a beam of preformed Ni nanoclusters, obtained by sputtering and aggregation, is co-deposited with evaporated Mg on a substrate, in a controlled O2 atmosphere. In situ X-ray photoelectron spectroscopy (XPS) and ex situ energy-filtered transmission electron microscopy (EF-TEM) show that the Ni core remains metallic, whereas Mg, located in the shell, is completely oxidized. Detailed high-resolution transmission electron microscopy and geometric phase analyses reveal the multitwinned icosahedral structure of the Ni core and details the arrangement of the MgO shell. This combined effort of controlled assembly of NPs and fine analysis offers intriguing possibilities in the design of nanoscale materials.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1995

ABSTRACT Sputter deposition of thin films and multilayers involves, in the initial stage, the ene... more ABSTRACT Sputter deposition of thin films and multilayers involves, in the initial stage, the energetic interaction of reflected ions and/or sputter ejected target particles with the substrate surface and with the overlayer‐substrate interface.The present work reports on the c‐Si(111) surface amorphization when Ge is deposited by 4 keV Ar+ ion sputtering in different experimental geometries. The incidence angle of the Ar+ beam was 65°, with respect to the surface normal, to emphasize prompt collision sputtering. Attempts have been made to clarify the role of the different particles involved in the process. New, unconventional approaches to Auger spectroscopy were used for this study. Substrate structural characterization during overlayer growth has been performed by primary‐beam diffraction modulated electron emission (PDMEE) technique, a powerful tool for the investigation of ‘‘buried’’ surfaces. Auger electron kinetic emission from the growing interface was used to determine the occurrence and importance of the different collisional processes. The high average kinetic energy of the Ge atoms ejected from the target in prompt, first‐order collisions was found to be responsible for the large substrate amorphization we observed with a specular geometry but not on off‐specular geometry. Reflected, energetic Ar+ ions do not play a relevant role. © 1995 American Vacuum Society

Applied Surface Science, 2012

ABSTRACT In this work it is reported a detailed investigation of the structure in Ni/NiO core–she... more ABSTRACT In this work it is reported a detailed investigation of the structure in Ni/NiO core–shell nanoparticles (NP). An experimental set-up was realized for the preparation and the study of pre-formed NP films. NiO shell was obtained with controlled dosing of O2 gas in the experimental system. A comparison of HR-TEM experimental images with theoretical simulations shows that the Ni NP core has a regular multitwinned icosahedral structure, composed with single crystal tetrahedra with (1 1 1) faces. NiO phase is clearly observed forming islands on the NP surface. In order to better investigate the oxide shell, the exit wave reconstruction method was applied to the images. It was found evidence of oxide island formation with direct or opposite (twinned) stacking on Ni (1 1 1) surfaces.

Surfaces, Interfaces, and Thin Films, 2010

Physical Review B, 2002

The morphology of ultrathin epitaxial MgO layers reactively grown on Ag͑001͒ was investigated by ... more The morphology of ultrathin epitaxial MgO layers reactively grown on Ag͑001͒ was investigated by using scanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from the substrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individual substrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensates in form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islands and on the vacancy islands as well. The largest Ag͑001͒ fractional coverage by monoatomic MgO islands is 70%. A limited amount of MgO bilayers or trilayers has also been detected ͑about 1% fractional coverage͒. At the nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, with edges along the ͓110͔ directions. The actual substrate fractional coverage is about 85% and the occurrence of bilayers and multilayers becomes significant ͑about 30 and 5% fractional coverage, respectively͒, resulting in the formation of three-dimensional pyramidal MgO islands.

Physical Review Letters, 1997

We report the measurement of the local Ni 3d spin polarization, not only below but also above the... more We report the measurement of the local Ni 3d spin polarization, not only below but also above the Curie temperature ͑T C ͒, using the newly developed spin-resolved circularly polarized 2p ͑L 3 ͒ resonant photoemission technique. The experiment identifies the presence of 3d 8 singlets at high energies and 3d 8 triplets at low energies extending all the way to the Fermi energy, both below and above T C , showing that it is the orbital degeneracy of the 3d band and the Hund's rule splitting which is of utmost importance to understand Ni and other 3d ferromagnets. [S0031-9007(97)04363-9]

Physical Review B, 2009

We have tested the concept of image charge screening as a new approach to enhance magnetic orderi... more We have tested the concept of image charge screening as a new approach to enhance magnetic ordering temperatures and superexchange interactions in ultra thin films. Using a 3 monolayer NiO(100) film grown on Ag(100) and an identically thin film on MgO(100) as model systems, we observed that the Néel temperature of the NiO film on the highly polarizable metal substrate is 390 K while that of the film on the poorly polarizable insulator substrate is below 40 K. This demonstrates that screening by highly polarizable media may point to a practical way towards designing strongly correlated oxide nanostructures with greatly improved magnetic properties.

Surface Science, 1995

We investigated the electron emission induced by energetic sputter-deposited Si particles during ... more We investigated the electron emission induced by energetic sputter-deposited Si particles during ion beam sputter deposition of Si on Ge substrate. Electron emission is strictly similar to the ion-induced Auger (IAE) Si spectra and originates in Si-Si collisions. Monitoring this "IAE-like" Si yield during the Si layer-by-layer growth, we measured the surface sensitivity of particle-induced electron emission for different energies of the involved particles and for different experimental geometries. We found that the depth sampled by IAE spectroscopy critically depends on the experimental parameters. The surface sensitivity of IAE is, in several cases, larger than that of the corresponding, conventional electron-induced Auger electron emission.

Physical Review B, 2009

... G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá di Modena e Reggio Em... more ... G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá di Modena e Reggio Emilia, via G. Campi 213/A, 41100 Modena, Italy (Received ... Integral XPS spectral intensities were analyzed after standard x-ray satellite filtering and Shirley background sub-traction. ...

Physical Review B, 2007

... at Surfaces, via G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá diMo... more ... at Surfaces, via G. Campi 213/a, 41100 Modena, Italy 2Dipartimento di Fisica, Universitá diModena e Reggio Emilia, via G. Campi 213/A, 41100 Modena, Italy (Received ... The XPS spectra were analyzed af-ter standard x-ray satellite filtering and Shirley background subtraction. ...

The existence and the properties of metal-oxide boundaries, and, more in generai, metalceramic bo... more The existence and the properties of metal-oxide boundaries, and, more in generai, metalceramic boundaries, play a crucial role in determining many physical processes and technological applications in a wide variety of traditional areas of the materials science and technology. Coating of oxide which function as thermal barriers or as a natural corrosion protection are of concern to the manufacturers of jet engines and equipment for power generation, who seek to improve lifetimes and efficiency. In the chemicai industry, strong metal-support interactions and the performance of a metallic catalyst supported on a ceramic substrate depend on the properties of metal-ceramic interfaces, and also the electronic industry depends on the properties of such interfaces for packaging and in components such as rectifiers and MOSFETs. ... Ziee: Summary

Thin Solid Films, 2001

ABSTRACT Growth, morphology and structure of thin MgO films prepared on Ag(001) substrates by dif... more ABSTRACT Growth, morphology and structure of thin MgO films prepared on Ag(001) substrates by different preparation procedures have been investigated by AES, LEED and modulated electron emission. Oxide layers were prepared by Mg MBE in an oxygen atmosphere or sputter deposition from bulk MgO target. In both cases stoichiometric MgO forms, which initially grows in a rocksalt tetragonally distorted structure. For 3-ML films, 3.6% expansion of the interlayer spacing along the growth axis has been measured. The misfit strain progressively reduces as the film thickness increases, and the equilibrium spacing is completely recovered at 8–10 ML thickness. In spite of the similarity in structure and strain, different deposition procedures lead to different film morphology. Sputter deposited films only partially cover the substrate. Fractional coverage (50%) has been evaluated for the 3-ML thick film, and full coverage only occurs at approximately 10 ML thickness. The MBE procedure results in almost complete layers. Fourfold broadening of spot profiles has been observed in LEED patterns of both MBE and sputter deposited films, indicating the occurrence of a similar large-scale atomic arrangement and surface morphology.

Surface Science, 2002

Thin MgO films (1-20 ML) were synthesised by evaporating the metallic component in oxygen atmosph... more Thin MgO films (1-20 ML) were synthesised by evaporating the metallic component in oxygen atmosphere on Ag(0 0 1). The reduced lattice misfit (3.1%) between the (0 0 1) surface unit meshes of the Ag fcc and MgO rock salt structure leads to the formation of epitaxial MgO layers with the (0 0 1)MgOk(0 0 1)Ag and [1 0 0]MgOk[1 0 0]Ag orientation relationships. The oxide layers were structurally characterized by LEED and modulated electron emission, while their surface morphology was studied by STM. In spite of the weak interaction between the oxide overlayer and the substrate, the occurrence of a significant tetragonal distortion of the MgO structure has been detected. We investigated in detail the strain in the oxide layer as a function of the thickness. Thin (<6 ML) films exhibit an expansion along the growth axis with respect to the equilibrium phase. This vertical strain progressively reduces as the thickness increases and disappears at about 9 ML. A Poisson ratio larger than the bulk MgO value has been obtained for the 3 ML film, while the bulk value is appropriate films thicker than 6 ML. STM data indicate that an almost complete substrate coverage is obtained at 3 ML deposition. Ó

Physical Review B, 2002

ABSTRACT The morphology of ultrathin epitaxial MgO layers reactively grown on Ag(001) was investi... more ABSTRACT The morphology of ultrathin epitaxial MgO layers reactively grown on Ag(001) was investigated by using scanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from the substrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individual substrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensates in form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islands and on the vacancy islands as well. The largest Ag(001) fractional coverage by monoatomic MgO islands is 70%. A limited amount of MgO bilayers or trilayers has also been detected (about 1% fractional coverage). At the nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, with edges along the [110] directions. The actual substrate fractional coverage is about 85% and the occurrence of bilayers and multilayers becomes significant (about 30 and 5% fractional coverage, respectively), resulting in the formation of three-dimensional pyramidal MgO islands.

Thin Solid Films, 2003

The structure and morphology of thin NiO films prepared on Ag(001) by reactive growth at 460 K ha... more The structure and morphology of thin NiO films prepared on Ag(001) by reactive growth at 460 K has been investigated as a function of the film thickness in the 3-20 monolayers range. Emphasis was on the study of the oxide layer misfit strain. Primary beam diffraction modulated electron emission and low energy electron diffraction experiments allowed the determination of the in-plane and out-of-plane strain in the oxide layer, while scanning tunneling microscopy, X-ray photoelectron spectroscopy and secondary electron imaging have been used to monitor the film morphology, stoichiometry and structure, respectively. The film strain begins to be removed at a critical thickness of 10 ML, while at 20 ML the film is fully relaxed. Strain analysis indicates that the Poisson ratio of the oxide layer is nearly equal to that of the bulk material. ᮊ

Physical Review B, 2003

We calculate the classical dipole interaction energy in fcc collinear antiferromagnetic films. We... more We calculate the classical dipole interaction energy in fcc collinear antiferromagnetic films. We find that the presence and the type of strain strongly conditions the dipolar anisotropy, while the finite thickness introduces an additional perturbation to the dipolar energy, similar to the well known shape anisotropy of ferromagnetic films, with sizable effects due to surface roughness. An analytic expression relating

Thin Solid Films, 2001

NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O atmosphere. The thickness... more NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O atmosphere. The thickness range 5-50 ML has 2 been investigated. X-ray photoelectron spectroscopy has been used to study the stoichiometric composition and chemical purity of the oxide films. We found completely oxidized stoichiometric NiO films. Their contamination has been found to be limited to the topmost layers. Photoelectron diffraction has given information concerning the local crystal structure of the films. The film atomic geometry has been found to be the same independent of thickness in the 0-50 ML range. The films have the expected (001) rock-salt structure with the same in plane orientation as the Ag(001) substrate. Specular X-ray reflectivity has allowed a very accurate thickness evaluation and has given information on the width of the density gradients at the film-substrate and vacuum-film interfaces, found to be of the order of a few atomic layers. ᮊ

The Journal of Physical Chemistry C, 2011

ABSTRACT We obtained assemblies of Ni/MgO core/shell nanoparticles (NPs) by using a special exper... more ABSTRACT We obtained assemblies of Ni/MgO core/shell nanoparticles (NPs) by using a special experimental setup, in which a beam of preformed Ni nanoclusters, obtained by sputtering and aggregation, is co-deposited with evaporated Mg on a substrate, in a controlled O2 atmosphere. In situ X-ray photoelectron spectroscopy (XPS) and ex situ energy-filtered transmission electron microscopy (EF-TEM) show that the Ni core remains metallic, whereas Mg, located in the shell, is completely oxidized. Detailed high-resolution transmission electron microscopy and geometric phase analyses reveal the multitwinned icosahedral structure of the Ni core and details the arrangement of the MgO shell. This combined effort of controlled assembly of NPs and fine analysis offers intriguing possibilities in the design of nanoscale materials.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1995

ABSTRACT Sputter deposition of thin films and multilayers involves, in the initial stage, the ene... more ABSTRACT Sputter deposition of thin films and multilayers involves, in the initial stage, the energetic interaction of reflected ions and/or sputter ejected target particles with the substrate surface and with the overlayer‐substrate interface.The present work reports on the c‐Si(111) surface amorphization when Ge is deposited by 4 keV Ar+ ion sputtering in different experimental geometries. The incidence angle of the Ar+ beam was 65°, with respect to the surface normal, to emphasize prompt collision sputtering. Attempts have been made to clarify the role of the different particles involved in the process. New, unconventional approaches to Auger spectroscopy were used for this study. Substrate structural characterization during overlayer growth has been performed by primary‐beam diffraction modulated electron emission (PDMEE) technique, a powerful tool for the investigation of ‘‘buried’’ surfaces. Auger electron kinetic emission from the growing interface was used to determine the occurrence and importance of the different collisional processes. The high average kinetic energy of the Ge atoms ejected from the target in prompt, first‐order collisions was found to be responsible for the large substrate amorphization we observed with a specular geometry but not on off‐specular geometry. Reflected, energetic Ar+ ions do not play a relevant role. © 1995 American Vacuum Society

Applied Surface Science, 2012

ABSTRACT In this work it is reported a detailed investigation of the structure in Ni/NiO core–she... more ABSTRACT In this work it is reported a detailed investigation of the structure in Ni/NiO core–shell nanoparticles (NP). An experimental set-up was realized for the preparation and the study of pre-formed NP films. NiO shell was obtained with controlled dosing of O2 gas in the experimental system. A comparison of HR-TEM experimental images with theoretical simulations shows that the Ni NP core has a regular multitwinned icosahedral structure, composed with single crystal tetrahedra with (1 1 1) faces. NiO phase is clearly observed forming islands on the NP surface. In order to better investigate the oxide shell, the exit wave reconstruction method was applied to the images. It was found evidence of oxide island formation with direct or opposite (twinned) stacking on Ni (1 1 1) surfaces.

Surfaces, Interfaces, and Thin Films, 2010