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Transparent conductive oxides (TCO) have the unique characteristics of combining optical transparency with high electrical conductivity; such a property makes them uniquely alluring for applications in visible and infrared photonics. One of their most interesting features is the large sensitivity of their optical response to the doping level. We performed the active electrical manipulation of the dielectric properties of aluminum-doped ZnO (AZO), a TCO-based on Earth-abundant elements. We actively tuned the optical and electric performances of AZO films by means of an applied voltage in a parallel-plate capacitor configuration, with SrTiO

Expanding the activity of wide bandgap semiconductors from the UV into the visible range has become a central goal for their application in green solar photocatalysis. The hybrid plasmonic/semiconductor system, based on silver nanoparticles (Ag NPs) embedded in a film of CeO2, is an example of a functional material developed with this aim. In this work, we take advantage of the chemical sensitivity of free electron laser (FEL) time-resolved soft X-ray absorption spectroscopy (TRXAS) to investigate the electron transfer process from the Ag NPs to the CeO2 film generated by the NPs plasmonic resonance photoexcitation. Ultrafast changes (

Nanomaterials can be game-changers in the arena of sustainable energy production because they may enable highly efficient thermoelectric energy conversion and harvesting. For this purpose, doped thin film oxides have been proven to be promising systems for achieving high thermoelectric performances. In this work, the design, realization, and experimental investigation of the thermo electric properties exhibited by a set of five Al:ZnO thin films with thicknesses of 300 nm and Al doping levels ranging from 2 to 8 at.% are described. Using a multi-technique approach, the main structural and morphological features of the grown thin films are addressed, as well as the electrical and thermoelectrical transport properties. The results show that the samples exhibited a Seebeck coefficient absolute value in the range of 22–33 µV/K, assuming their maximum doping level was 8 at.%, while the samples’ resistivity was decreased below 2 × 10−3 Ohm·cm with a doping level of 3 at.%. The findings shine light on the perspectives of the applications of the metal ZnO thin film technology for thermoelectrics., This research was funded by MIUR-PON, scholarship PhD program “Physics and nano sciences”021/22.“Nanotecnologie per la termoelettricità e l’energy harvesting” (Azione IV.5 “Dottorati su tematiche green”) and by project QUANTEP, INFN CSN5. VB was supported by the project “Brosynano”MICINN-FEDER (PID2019-106820RB-C22). C.T. acknowledges the funding from FCT/PIDDAC through the Strategic Funds project reference UIDB/04650/2020-2023. A.M., G.P. acknowledge support by the Italian Ministry of University and Research through PRIN UTFROM N. 20178PZCB5. This work was also partially funded under the National Recovery and Resilience Plan (NRRP), Mission 04 Component 2 Investment 1.5 – NextGenerationEU, Call for tender n. 3277 dated 30/12/2021. Award Number: 0001052 dated 23/06/2022.

Understanding the interaction between plasmonic nanoparticles and transparent conductive oxides is instrumental to the development of next-generation photovoltaic, optoelectronic, and energy-efficient solid-state lighting devices. We investigated the optical response of hybrid media composed of gold nanoparticles deposited on aluminum-doped zinc oxide thin films with varying doping concentration by spectroscopic ellipsometry. The dielectric functions of bare AZO were addressed first, revealing doping-induced effects such as the band gap shift and the appearance of free carriers. In the hybrid media, a blue-shift of the localized surface plasmon resonance of Au NPs as a function of increasing Al doping of the substrate was observed, ascribed to the occurrence of a charge transfer between the two materials and the doping-dependent variation of the polarizability of the substrate.

Space and mirror charge effects in time-resolved photoemission spectroscopy can be modeled to obtain relevant information on the recombination dynamics of charge carriers. We successfully extracted from these phenomena the reneutralization characteristic time of positive charges generated by photoexcitation in CeO2-based films. For the above-band-gap excitation, a large fraction of positive carriers with a lifetime that exceeds 100 ps are generated. Otherwise, the sub-band-gap excitation induces the formation of a significantly smaller fraction of charges with lifetimes of tens of picoseconds, ascribed to the excitation of defect sites or to multiphoton absorption. When the oxide is combined with Ag nanoparticles, the sub-band-gap excitation of localized surface plasmon resonances leads to reneutralization times longer than 300 ps. This was interpreted by considering the electronic unbalance at the surface of the nanoparticles generated by the injection of electrons, via localized surface plasmon resonance (LSPR) decay, into CeO2. This study represents an example of how to exploit the space charge effect in gaining access to the surface carrier dynamics in CeO2 within the picosecond range of time, which is fundamental to describe the photocatalytic processes.

The morphology, epitaxy, band-alignment and optical response of silver nanoparticles on ZnO(1010) has been analysed by microscopy, photoemission, electron diraction and dier-ential reectivity. At 700 K, clusters tend to nu-cleate and grow exclusively along [010]-oriented polar steps and corners, and not on at terraces or non-polar [001] steps. This preference leads to a specic epitaxy Ag(111)[110] ZnO[010](1010) with a large lattice mismatch along the dense row of the metal. The experiments have been rationalized through ab ini-tio simulations. A much lower adsorption energy is obtained for the O-terminated steps with a charge transfer from silver to oxygen, that corroborates the variation of ionization energy observed in photoemission and the presence of cationic silver. This anisotropy of growth reverberates in the plasmonic response of the metallic particles. The growth and epitaxy of metals on the polar (0001) and non-polar (1010) ori-entations of ZnO is discussed in terms of sur-face/step polarity compensation in the light of the present ndings.

Expanding the activity of wide bandgap semiconductors from the UV into the visible range has become a central goal for their application in green solar photocatalysis. The hybrid plasmonic/semiconductor system, based on silver nanoparticles (Ag NPs) embedded in a film of CeO2, is an example of a functional material developed with this aim. In this work, we take advantage of the chemical sensitivity of free electron laser (FEL) time-resolved soft X-ray absorption spectroscopy (TRXAS) to investigate the electron transfer process from the Ag NPs to the CeO2 film generated by the NPs plasmonic resonance photoexcitation. Ultrafast changes (

The femtosecond evolution of the electronic temperature of laser-excited gold nanoparticles is measured, by means of ultrafast time-resolved photoemission spectroscopy induced by extreme-ultraviolet radiation pulses. The temperature of the electron gas is deduced by recording and fitting high-resolution photo emission spectra around the Fermi edge of gold nanoparticles providing a direct, unambiguous picture of the ultrafast electron-gas dynamics. These results will be instrumental to the refinement of existing models of femtosecond processes in laterally-confined and bulk condensed-matter systems, and for understanding more deeply the role of hot electrons in technological applications.

A ferromagnetic (FM) thin film deposited on a substrate of $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}{\mathrm{PbTiO}}_{3}$ (PMN-PT) is an appealing heterostructure for the electrical control of magnetism, which would enable nonvolatile memories with ultralow-power consumption. Reversible and electrically controlled morphological changes at the surface of PMN-PT suggest that the magnetoelectric effects are more complex than the commonly used ``strain-mediated'' description. Here we show that changes in substrate morphology intervene in magnetoelectric coupling as a key parameter interplaying with strain. Magnetic-sensitive microscopy techniques are used to study magnetoelectric coupling in Fe/PMN-PT at different length scales, and compare different substrate cuts. The observed rotation of the magnetic anisotropy is connected to the changes in morphology, and mapped in the crack pattern at the mesoscopic scale. Ferroelectric polarization switching induces a magnetic field-free rotation of the magnetic domains at micrometer scale, with a wide distribution of rotation angles. Our results show that the relationship between the rotation of the magnetic easy axis and the rotation of the in-plane component of the electric polarization is not straightforward, as well as the relationship between ferroelectric domains and crack pattern. The understanding and control of this phenomenon is crucial to develop functional devices based on FM/PMN-PT heterostructures.

We investigate the mechanism of H-2 activation on Ag-modified cerium oxide surfaces, of interest for different catalytic applications. The study is performed on thin epitaxial cerium oxide films, investigated by X-ray photoemission spectroscopy to assess the changes of both the Ag oxidation state and the concentration of Ce3+ ions, O vacancies, and hydroxyl groups on the surface during thermal reduction cycles in vacuum and under hydrogen exposure. The results are interpreted using density functional theory calculations to model pristine and Ag-modified ceria surfaces. Although the reactivity of ceria toward H-2 oxidation improves when a fraction of Ce cations is substituted with Ag, the concentration of reduced Ce3+ ions in Ag-modified ceria is found to be lower than in pure ceria under the same conditions. This behavior is observed even though the number of surface oxygen vacancies caused by the thermal treatment under hydrogen exposure is larger for the Ag-modified surface. These results are explained in terms of a change of the oxidation state of the surface Ag, which is able to acquire some of the extra surface electrons created by the oxygen vacancies and the adsorbed hydrogen atoms. Our findings provide new insights into the reactivity of Ag-modified ceria, which has been proposed as a promising alternative to platinum electrodes in electrochemical devices.

In this work, we present an investigation on the effects of thermal annealing on the magnetic response of Lithium Niobate/Fe samples. Fe thin films have been deposited on Lithium Niobate Z-cut ferroelectric substrates by vapor phase epitaxy. A series of annealing treatments were performed on the samples, monitoring the evolution of their magnetic properties, both at the surface and on the volume. The combination of structural, magnetic, chemical and morphological characterizations shows that the modification of the chemical properties, i.e. the phase decomposition, of the substrate upon annealing affects drastically the magnetic behavior of the interfacial Fe layer. By tuning the annealing temperature, the magnetic coercive field value can be increased by an order of magnitude compared to the as-grown value, keeping the same in-plane isotropic behavior. Since no evident differences were recorded in the Fe layer from the chemical point of view, we attribute the origin of this effect to an intermixing process between a fragment of the substrate and the Fe thin film upon critical temperature annealing, process that is also is responsible for the observed changes in roughness and morphology of the magnetic thin film.

In the framework of piezoelectric/ferromagnetic patterned heterostructures, the purpose of this work is to electrically control the magnetic properties by tuning the morphology, especially by modifying the magnetic shape anisotropy through patterned strain. We have thus designed and studied a heterostructure with bottom nano-striped and top full film electrodes. ZnO piezoelectric and CoFeB magnetic materials were chosen to respond at critical criteria of its geometry. In addition, numerical simulations and magnetostatic calculations were performed to understand the reproduction of the pattern across the multiferroic heterostructure. Calculations have shown that the geometry of the heterostructure presents strict constraints, as for instance the distance between stripes versus the piezoelectric thickness. This study is a preliminary step towards reversible patterning of magnetic properties.

Converse magnetoelectric coupling in artificial multiferroics is generally modeled through three possible mechanisms: charge transfer, strain mediated effects or ion migration. Here the role played by electrically controlled morphological modifications on the ferromagnetic response of a multiferroic heterostructure, specifically FexMn1-x ferromagnetic films on piezoferroelectric PMN-PT [001] substrates, is discussed. The substrates present, in correspondence to electrical switching, fully reversible morphological changes at the surface, to which correspond reproducible modifications of the ferromagnetic response of the FexMn1-x films. Topographic analysis by atomic force microscopy shows the formation of surface cracks (up to 100 nm in height) upon application of a sufficiently high positive electric field (up to 6 kV cm-1). The cracks disappear after application of negative electric field of the same magnitude. Correspondingly, in operando X-ray magnetic circular dichroic spectroscopy at Fe edge in FexMn1-x layers and micro-MOKE measurements show local variations in the intensity of the dichroic signal and in the magnetic anisotropy as a function of the electrically driven morphological state. This morphologic parameter, rarely explored in literature, directly affects the ferromagnetic response of the system. Its proof of electrically reversible modification of the magnetic response adds a new possibility in the design of electrically controlled magnetic devices.

In this work we report the interfacial charge transfer between the Fe core and Ag shell in self-organized nanoparticles on MgO films on Mo(001). Predeposited Fe nanoparticles organize in a square network with long-range order on the oxide surface guided by the MgO coincidence lattice. When Ag is added, it covers the Fe nanoparticles, forming a shell. By means of XPS and UPS we show that a charge transfer occurs between the Fe core and the Ag shell, determining the oxidation of part of the Fe atoms and a negative charging of the Ag shell. This is confirmed by band bending and core level shifts. As a consequence of the Fe@Ag morphology and composition the plasmonic response of the nanoparticles is modified with respect to pure Ag nanoparticles.

The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light. The processes which come into play after the excitation of localized surface plasmon resonances (LSPRs) in the NPs largely determine the efficiency of the charge/ energy transfer from the metal NP to the oxide. We report a study of plasmon-mediated energy transfer from mass-selected silver NPs into the cerium oxide matrix in which they are embedded. Femtosecond transient absorption spectroscopy is used to probe the dynamics of charge carrier relaxation after the excitation of the LSPR of the silver nanoparticles and to evaluate the plasmon-mediated electron transfer efficiency from the silver nanoparticles to the cerium oxide. High injection efficiencies in the 6-16% range have been identified for excitation between 400 and 600 nm. These high values have been explained in terms of plasmon-mediated direct electron injection as well as indirect hot electron injection from the NPs to the oxide. The information obtained provides an important contribution towards a knowledge- driven design of efficient cerium oxide based nanostructured materials for solar to chemical energy conversion.

Incorporation of Cr into a crystalline MgO(001) thin film has been investigated by means of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and diffraction. For this purpose, samples of different Cr content (0-33 at %) and postannealing treatments (300-1050 K) have been analyzed. The Cr impurities mainly adopt a 3+ oxidation state, which renders the formation of compensating Mg vacancies necessary to maintain charge neutrality. Only at 33 at % doping amount are Cr6+ species detected in the as-grown films, indicating the development of a metastable CrO3 phase. At low doping level, the Cr ions fully dissolve in the MgO lattice, while segregation toward the surface is observed for Cr-rich films. In the latter case, a new surface oxide develops that is characterized by a lower binding energy of the Mg is and Cr 2p core levels and a (2 x 1) superstructure with respect to weakly doped MgO. In combination with a distinct 4-fold symmetric XPD pattern, the new surface phase resembles Mg chromite (MgCr2O4), growing on top of the heavily doped MgO film. Our study provides insight into the technologically relevant transition region between doped binary and ternary oxides.

Transparent conductive oxides are a class of materials that combine high optical transparency with high electrical conductivity. This property makes them uniquely appealing as transparent conductive electrodes in solar cells and interesting for optoelectronic and infrared-plasmonic applications. One of the new challenges that researchers and engineers are facing is merging optical and electrical control in a single device for developing next-generation photovoltaic, optoelectronic devices and energy-efficient solid-state lighting. In this work, the authors investigated the possible variations in the dielectric properties of aluminum-doped ZnO (AZO) upon gating by means of spectroscopic ellipsometry (SE). The authors investigated the electrical-bias-dependent optical response of thin AZO films fabricated by magnetron sputtering within a parallel-plane capacitor configuration. The authors address the possibility to control their optical and electric performances by applying bias, monitoring the effect of charge injection/depletion in the AZO layer by means of in operando SE versus applied gate voltage.

The conduction and optoelectronic properties of transparent conductive oxides can be largely modified by intentional inclusion of dopants over a very large range of concentrations. However, the simultaneous presence of structural defects results in an unpredictable complexity that prevents a clear identification of chemical and structural properties of the final samples. By exploiting the unique chemical sensitivity of Hard X-ray Photoelectron Spectra and Near Edge X-ray Absorption Fine Structure in combination with Density Functional Theory, we determine the contribution to the spectroscopic response of defects in Al-doped ZnO films. Satellite peaks in O1s and modifications at the O K-edge allow the determination of the presence of H embedded in ZnO and the very low concentration of Zn vacancies and O interstitials in undoped ZnO. Contributions coming from substitutional and (above the solubility limit) interstitial Al atoms have been clearly identified and have been related to changes in the oxide stoichiometry and increased oxygen coordination, together with small lattice distortions. In this way defects and doping in oxide films can be controlled, in order to tune their properties and improve their performances.

We report a growth study of MgO thin films on an Au(111) support, performed with scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy-electron and X-ray-diffraction techniques. Depending on the deposition temperature, the O2 partial pressure, and the availability of water during oxide formation, two growth regimes can be distinguished. At high oxygen pressure, the MgO mainly adopts a square-lattice configuration and exposes the nonpolar (001) surface, whereas at low O2 pressure a hexagonal lattice develops that resembles the (111) surface of rocksalt MgO. For films beyond the monolayer limit, the emerging electrostatic dipole along theMgO(111) direction becomes important for the film morphology. Depending on the preparation conditions, the system takes either structural or adsorption-mediated routes to remove the polarity. Whereas surface roughening is identified as main polarity-compensation mechanism at perfect vacuum conditions, hydroxylation becomes important if water is present during oxide growth.

Scanning tunnelling microscopy and X-ray photoelectron spectroscopy have been used to study the adsorption of Mg on 12 ML thick MgO films grown either on Ag(001) or Mo(001) supports. The initially arriving Mg atoms spontaneously oxidize on the MgO surface, whereas metallic aggregates only form at higher exposure. The total amount of cationic Mg is considerably larger on the Mo- compared to the Ag-supported oxide films. The charge transfer is suggested to be induced by Mg attachment to MgO line defects with high electron-trapping potential. The density of those defect lines and hence the oxidation power of the film is governed by the lattice mismatch with the underlying metal support

We used nuclear hyperfine spectroscopies and a 57 Fe probe layer approach to study the depth-dependent magnetic properties of ultrathin Fe films on NiO(0 0 1), a system exhibiting exchange bias. Conversion electron Mossbauer spectroscopy and nuclear resonance scattering of synchrotron radiation were employed. The samples were two Fe films with a thickness (8–10 ML) slightly above the critical thickness for the onset of ferromagnetism at room temperature, in which a 2 ML-thick probe layer, enriched in the 57 Fe Mossbauer isotope, was embedded at different depths from the Fe/NiO interface. Both techniques indicate that inside the film Fe has a metallic character, while at the interface with NiO different Fe phases are present. The main conclusion is that already a few monolayers from the interface with NiO the magnetic properties of Fe are bulk-like.

In this work we present a study of Fe self-organization on the surface of stepped MgO as a function of deposition temperature and thickness. The Fe morphology results in being very much influenced by the presence on the MgO terraces of a roughness due to exposure of the sample to the air. Because of the additional sites introduced by the MgO roughness, at room temperature Fe nucleates indistinctly on steps and terraces. Dramatic changes in the Fe nucleation appear on increasing the deposition temperature to 800 K. Here Fe diffuses on the MgO terraces and 40% of the clusters nucleate on step edges. This effect is more evident on decreasing the amount of Fe deposit.

X-ray photoelectron spectroscopy reveals spontaneous atom diffusion from a Mo(001) support into a MgO thin film doped with transition-metal ions. The amount of interfacial mixing depends on the nature of the dopants and is considerably larger for Fe than for Cr impurities. DFT calculations find the reason for Mo diffusion in the ability of the dopants to change oxidation state. Cr exclusively occurs as 3+ ion in the rocksalt lattice, whereby the charge mismatch to native Mg2+ ions is compensated for by Mg vacancies. Iron, on the other hand, switches its thermodynamically preferred configuration from 3+ to 2+ with increasing temperature. As a result, Mo atoms from the support move into the Mg vacancies upon sample annealing and become oxidized via charge transfer into the Fe3+ species. Our study unravels a new charge-compensation scheme in doped oxides that proceeds via chemical intermixing at a metal-oxide interface. The mechanism may rationalize the often observed inactivity of doped oxides in charge-transfer reactions.

Thin MgO films with a nominal thickness ranging between 1 and 60 ML have been grown on a Mo(001) surface. The film morphology was studied by LEED and STM, revealing the presence of a coincidence pattern with the Mo support in the low coverage regime, a dislocation network at medium thickness and a rather flat and defect-poor MgO surface for thicker layers. The MgO optical properties were investigated as a function of film thickness by analyzing electro-luminescence spectra obtained via electron injection from the STM tip into well-defined surface areas. The spectra are characterized by two distinct emission bands at 3.1 and 4.4 eV. Their origin is discussed in the light of earlier photo-luminescence measurements on MgO nanocubes and smokes. (c) 2006 Elsevier B.V. All rights reserved.

Biological activities of a putative mature sea bass interleukin-1beta peptide, produced as a recombinant protein (rIL-1beta) in Escherichia coli, have been investigated. The rIL-1beta contains a 6-histidine tag at the N-terminus, and protein purification has been achieved through this tag by affinity chromatography. Biological activities have been investigated both at the cellular and gene expression levels. In in vitro assays sea bass rIL-1beta induced the proliferation of murine D10.G4.1 cells and increased yeast phagocytosis by sea bass head kidney leukocytes. The purified cytokine was also tested in a lymphocyte-activation factor assay, where it induced the proliferation of sea bass thymocytes. Finally, in an in vivo assay, rIL-1beta administered intraperitoneally increased expression levels of the IL-1beta gene and activated macrophages to produce a cyclooxygenase 2 homologue (COX-2) gene in the head kidney.

The interaction between Fe and NiO(0 0 1) surface for increasing metal deposition at RT was studied by means of X-ray photoelectron spectroscopy and X-ray photoelectron diffraction. NiO reduces to an extent that depends on the amount of deposited Fe, up to a maximum of 1 ML for Fe deposition of 5 ML or larger. The overlayer initially grows in a 3D island mode, with partial intermixing between the deposited Fe atoms and the metallic Ni atoms resulting from the reduction process. The intermixed region extends up to about 3 ML. For 5 ML Fe deposition, the islands coalesce into a continuous film.

In this paper we have determined the role of oxidizing pressure and annealing temperature in the formation of ZnO nanostructures on the Mo surface. ZnO has been grown on Mo(001) by means of physical vapor deposition of Zn in molecular oxygen pressure. Combining STM, XPS, and XRD we have studied the relation between morphology, composition, and structure. ZnO grows as a film with (101¯1) preferential orientation up to a thickness of 10 Å, catalyzed by the Mo surface that provides oxygen available for oxide formation and limited by the residual polarity of the surface. Increasing the deposited amount, the role of the Mo interface becomes less effective, and part of the Zn remains metallic, forming clusters on the surface that catalyze the further growth of ZnO in the form of polycrystalline nanostructures. Surfactant Zn is removed by annealing, and peculiar oxide nanostructures are left on the surface. Increasing O pressure or reducing Zn flux allows control of nanostructure density and shape, while the continuous film underneath does not modify.

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. (C) 2015 AIP Publishing LLC.

International audience; The coincidence lattice formed between a crystalline MgO film and a Mo(001) support is found to be an ideal template to produce long-range ordered ensembles of Fe and Cr particles for electronic, magnetic and chemical applications. The structural and electronic properties of this super-lattice are analyzed by means of scanning tunnelling microscopy and density functional theory. The different registers of atoms at the interface induce periodic changes in the MgO lattice parameter, in the metal-oxide binding length, and the workfunction. These variations modulate the adsorption landscape for Cr and Fe atoms and give rise to the observed ordering phenomena. Preferred nucleation and growth is revealed in those regions of the coincidence lattice that have a small lattice mismatch with the ad-particles and enable electron-transfer processes with the support.

Using scanning tunneling microscopy and density functional theory (DFT), we have analyzed the local electronic properties of (111)-oriented MgO nanoislands on Au(111). Conductance and barrier-height measurements revealed substantial modulations in the electronic structure and electrostatic potential across the islands, with particularly high and low values for band onsets and surface potential occurring at the perimeter and in the island center, respectively. DFT calculations showed that MgO(111) monolayer structures exhibit a strongly reduced distance between the Mg${}^{\ensuremath{\delta}+}$ and O${}^{\ensuremath{\delta}\ensuremath{-}}$ plane as compared to bulk MgO, which in turn suppresses the polar character of the film. The spatial modulations in the electronic properties originate from gradual changes of the interface registry when approaching the island edges, driven by a small mismatch between the Au(111) and MgO(111) lattices. At the periphery of the islands, additional effects such as band shifts and low-lying electronic states are observed, which arise from the interplay of residual edge polarity and unsaturated chemical bonds. We expect that the peculiar edge properties of MgO(111) islands are decisive for the chemical behavior of the nanostructures.

There is a steadily growing interest in the research on oxide surfaces and films, due to their challenging fundamental properties and to their actual and potential applications in catalytic systems, chemical sensors, electronic and magnetic devices, and functional and aesthetic coatings. Special efforts have been directed at the study of ultrathin oxide films [1–11]. Such two-dimensional systems are emerging as important new materials where the relevant phenomena are induced by the extreme vertical confinement, and new phases and structures are stabilized, which cannot be obtained in bulk form. Last but not least, the possible use of thin oxide films as model systems to substitute for bulk oxides has been shown to be very appealing. Critical properties basically depend on the reduced dimensionality, as well as on the stoichiometry, defectivity, and morphology of the films, on the extent of the crystalline order, and on the sharpness of the interfaces between film and substrate or between different films in multilayers, which are to a great extent determined by the preparation method. Therefore a main driving force in the development of oxide materials in the form of ultrathin films has been the progressive improvement of the fabrication procedures. Since the 1950s, studies of finite size effects in ferroelectrics pointed to a critical film thickness (typically 10 nm) below which ferroelectricity disappears [12]. Improved fabrication techniques have completely changed the picture. Studies on singlecrystal, “perfect” ultrathin films have led to the conclusion that perovskite layers down to a very few nanometers in thickness remain ferroelectric [13]. New fabrication methods, alternatives to the conventional thermal oxidation, have enabled the thickness of the gate silicon oxide in metal–oxide–semiconductor field effect transistors (MOSFETs) to decrease to sub-nanometric dimensions, thus reducing both power consumption and power dissipation [14]. The expected, unprecedented properties of ultrathin NiO remained undisclosed until the stabilization of a stoichiometric (1 1)–1ML NiO/Ag(001) phase with

We investigate the depth-dependent magnetization reversal and spin structure of Fe/NiO epitaxial bilayers before and after field cooling. Using nuclear resonant scattering of synchrotron radiation we selectively probe the spin structure of the interfacial layers in contact with NiO. We provide a direct evidence that magnetization reversal involves a rotation in the film plane perpendicular to the applied field, except for the interfacial Fe layers. Moreover, we show that the spin structure of the ferromagnetic layer is not modified by field cooling and that the exchange bias in the Fe layer is independent of the distance from the antiferromagnetic phase.

Monolayer films of MgO(001) have been prepared on an Au(111) surface and explored by means of scanning tunneling microscopy (STM) and spectroscopy. The symmetry mismatch between the hexagonal substrate and the squared overlayer results in the formation of a (6 \ifmmode\times\else\texttimes\fi{} 1) superlattice, as revealed from the distinct stripe pattern observed in the STM images. The presence of the oxide film also modifies the potential situation at the interface, which induces a substantial upshift of the Shockley-type surface band on Au(111). The resulting MgO/Au interface band is characterized by a pseudogap at around 500 mV that opens at the position of the new Brillouin zone of the enlarged (6 \ifmmode\times\else\texttimes\fi{} 1) unit cell. In addition the oxide layer gives rise to a drastic decrease of the Au(111) work function, as deduced from the energy position of the first field-emission resonance on the bare and MgO-covered surface. The work-function drop is explained by an interfacial charge transfer from the oxide film into the electro-negative gold surface.

Using scanning tunnelling microscopy and photoelectron diffraction, we have analyzed the nucleation and growth behavior of simple (Mg and Ca), transition (Ni and Fe), and noble metals (Ag and Au) on MgO films grown on Mo(001). With the exception of gold, the particles develop interface planes that are in registry with the surface-oxygen lattice of the MgO(001). To achieve this commensurability, the particles expose facets that differ from the low-energy surfaces of the respective metals and adopt crystallographic structures that are unknown in the bulk materials. This peculiar growth behavior demonstrates the importance of interfacial interactions between the metal deposits and the MgO film, despite the inert nature of the oxide support. The observed equilibrium shapes of the particles have been analyzed with a simple growth model that includes the interfacial interactions, the surface energies, and the elastic distortion of the particle lattice to reach commensurability with the MgO(001). Experimental particle densities have been explained with a scheme that considers formation of metal cations at certain MgO defects to be the initial nucleation step. Although the model is in reasonable agreement with the experimental results for most metals, it fails for gold. We relate this deviation to the large tendency of gold to charge up negatively on MgO thin films, in correspondence with earlier experimental and theoretical work.

Using nuclear resonant scattering of synchrotron radiation and density functional theory calculations we have resolved the magnetic properties of the different Fe phases present at the Fe/NiO(001) interface, an epitaxial ferromagnetic/antiferromagnetic system. We have detected the presence of an interfacial antiferromagnetic FeO-like phase with a significantly increased magnetic moment compared to the case of a sharp interface. Already a few atomic layers above the interface, the Fe atoms have a bulk-like metallic character and the reversal of their magnetization is strongly influenced by the antiferromagnetic layer.

We report an investigation of the magnetic properties of Fe films epitaxially grown on NiO layers with (001) orientation. The results are interpreted with the help of a morphological characterization of the system. The onset of ferromagnetic behavior for the Fe layer is observed at 8 ML and it is ascribed to the coalescence of the islands, formed by Fe at the first stages of the growth, into larger interconnected islands. At larger Fe layer thickness the magnetization reversal is explained by taking into account the interplay between a unidirectional anisotropy, due to coupling with NiO, and the uniaxial growth anisotropy of Fe, which develops around 50 ML Fe layer thickness. No significant chemical modification of the interface is observed for thermal treatments up to 540 K. Exchange bias can be induced only for NiO layer thickness above 25 ML and its value can be tuned by changing the ferromagnetic to antiferromagnetic layer thickness ratio, reaching 220 Oe. No training effect is observed for this system.

The charge state of Au nanoparticles deposited on MgO/Fe(001) ultrathin films has been investigated experimentally by means of X-ray photoemission spectroscopy and theoretically by performing density functional theory (DFT) calculations. The binding energy of the Au 4f(7/2) core-level peak has been studied as a function of the Au coverage and of the MgO film thickness. The Au 4f(7/2), peak presents a high binding energy value (about 600 meV higher than that of bulk Au) for the smallest Au nanoparticles deposited oil thick MgO films. The binding energy shift is only 200 meV for Au particles on very thin MgO films, indicating a different electronic configuration in this case. For larger Au coverages, the binding energy of the Au 4f(7/2) peak converges to the bulk value for both thick and thin MgO films. In view of the results from DFT calculations, we show that this behavior is consistent with the occurrence of a charge flow from the MgO/Fe(001) interface to the Au nanoparticles. We also show that, on ultrathin MgO films, the Au 4f(7/2), photoemission line width is much sharper than that for thicker oxide films, a result which is rationalized based on the different growth mode of Au nanoclusters when a charge-transfer process takes place.

Using a combination of reciprocal and real-space techniques, the structural evolution and its effect on the surface morphology is investigated for MgO films of 1--30 ML thickness epitaxially grown on Mo(001). The strain induced by the mismatch with the substrate is relieved between 1 and 7 ML MgO due to the formation of an ordered network of interfacial misfit dislocations aligned along the MgO $⟨110⟩$ directions, particularly evident after annealing the film at 1070 K. A dislocation periodicity of about $60\text{ }\text{\AA{}}$ has been determined by means of grazing incidence x-ray diffraction. The dislocations induce a tilting of the surface that appears in electron diffraction along the $⟨100⟩$ MgO directions for thin films and changes to $⟨110⟩$ directions when the oxide thickness increases. Scanning tunneling microscopy (STM) shows the presence of a regular pattern on the surface below 7 ML thickness associated to the dislocation network. With increasing thickness, screw dislocations connected by nonpolar steps appear on the oxide surface. Thanks to the combination of different diffraction techniques and STM measurements, a comprehensive picture of the relaxation mechanisms in MgO films on Mo(001) can be drawn.

We present and discuss X-ray absorption spectroscopy and resonant photoemission measurements on Fe nanostructures self-assembled on MgO(001). For Fe coverages below 1 ML equivalent we measured an increase of the Fe L-23 branching ratio and changes in the splitting, widths and relative intensities of the different final states in the L3M23M23 resonant Auger peak. Scanning tunnelling microscopy indicates that the average lateral dimensions of the self-aggregated structures decrease with decreasing Fe amount, from 12 nm at 15 ML nominal Fe amount to 5 nm at 2 ML Fe. This observation allows to interpret the observed changes in the 3d band electronic properties in terms of the evolution of the Fe local atomic coordination from a bulk-like situation to a configuration where low dimensionality effects are significant. (C) 2007 Elsevier B.V. All rights reserved.

We present a study of the preparation procedure for stepped MgO surfaces which can be used as templates for the deposition of metallic nanostructures. A cleaved sample of MgO(001) was mechanically polished to reach the desired miscut angle along the [110] direction. Then a thermal annealing was performed. The effect of an intermediate chemical etching has been also studied. The surface was analyzed by means of contact AFM in air, LEED and XPS in UHV. The role of the chemical etching and the dependence of the final morphology on the annealing time and temperature were investigated. The influence of the miscut angle on the final surface topography is also briefly discussed. (C) 2006 Elsevier B.V. All rights reserved.

In this investigation a number of “in vitro” activities of sea bass peripheral blood leucocytes (PBL) against allogeneic PBL inactivated by irradiation were studied. Stimulator PBL were cultured with inactivated allogeneic PBL, and direct counting of lymphocytes was done after 2 weeks by immunofluorescence and flow cytometry using mAbs DLT15 and DLIg3 specific for T-cells and B-cells, respectively. In a one-way mixed leucocyte reaction (MLR), results showed an increase of T lymphocytes, whereas B lymphocytes had values similar to those in control PBL. The increase of T-cells in MLR cultures was also confirmed using RT-PCR by analyzing the expression of the T-cell receptor (β-subunit) mRNA. The addition of 5 μg/ml of cyclosporin A (CsA) to the MLR caused a significant decrease in T-cell proliferation. Leucocytes from MLR cultures displayed an enhanced cytotoxic activity against xenogeneic target cells with respect to control PBL, raising the possibility of the presence of cytotoxic-like T lymphocytes. Cellular activation of PBL was confirmed in 2 weeks MLR by measuring antibody-induced intracellular Ca ++ mobilization with Fura-2 AM. This work represents the first direct quantitative determination of an “in vitro” T-cell activity in a teleost species.

We present a study focussed at the atomic level characterization of the Fe/MgO(0 0 1) interface by means of X-ray photoelectron spectroscopy, X-ray photoelectron diffraction and X-ray absorption spectroscopy. The data show a good crystalline quality of the Fe films grown on MgO(0 0 1) at room temperature. The films have a bcc structure with the Fe(0 0 1)//MgO(0 0 1) and Fe[1 1 0]//MgO[1 0 0] orientation. The Fe growth in the 1–10 ML thickness range proceeds by the formation of islands covering a fraction of the MgO surface. The oxidation of Fe and the consequent reduction of MgO can be excluded, thus proving that the interface is locally abrupt, with a very weak interaction between the two sides. The interface is stable with temperature up to 670 K.

The initial stages of cobalt film growth on a MgO(001) surface was studied by methods of sample surface structure imaging by reflected electrons, low-energy electron diffraction, and Auger electron spectroscopy. The measurements were performed at room temperature for cobalt layer thicknesses up to 40 angstrom. It is established that cobalt film growth proceeds according to the island mechanism. In the interval of cobalt film thicknesses below similar to 10 angstrom, the dominating surface phase has the form of cobalt islands with an fcc structure; at greater layer thicknesses, the surface film consists predominantly of cobalt grains with an hcp structure. (C) 2005 Pleiades Publishing, Inc.

We have grown Au films of different thicknesses, ranging from 1 to 30 MonoLayers Equivalent, on 10 MLE of NiO deposited on Ag(1 0 0) single crystal. XPS and STM measurements were performed in order to study the chemical activity at the interface and the morphology of the system. The Au growth on the NiO film starts in a 2D mode and becomes a 3D island growth after the formation of an almost complete layer. After Au deposition, the formation of about 0.3 MLE of metallic Ni (Ni0) is observed. The absence of significant attenuation of the PE signal of Ni0 after successive Au depositions indicates that Ni does not remain confined to the interface between Au and NiO. The density of defects at the surface of the NiO film is shown to be fundamental in determining the chemical activity at the Au/NiO interface.

In this paper we review our recent studies on the structure, morphology and interface chemistry of different metal systems on simple rock- salt oxides, providing a basis for the understanding of their properties. Fe on both MgO and NiO grows in the cubic structure with the (001) Fe parallel to ( 001) oxide and [110]Fe parallel to [100] oxide orientation. The Fe/ MgO interface is sharp at the atomic level up to 400 degrees C, thus showing that MgO can allow the growth of 'free standing' Fe films and low-dimensional structures. Submicrometric Fe dots on MgO have been prepared by FIB milling and characterized by the magneto-optical Kerr effect. At the Fe/NiO(001) interface an Fe-Ni body centred tetragonal alloyed phase is formed on top of a two-dimensional FeO layer situated at the interface. The FeO layer presents an expansion of the interplanar distance at the interface and a buckling in the Fe and O atomic positions. The presence of the structurally distorted FeO phase is predicted by ab initio density functional theory calculations to increase the spin magnetic moment of Fe atoms by 0.6 mu B compared to the ideally abrupt interface. A reduction of NiO is also induced by the deposition of (supposedly) inert Au films, which incorporate the metallic Ni atoms. The reduction takes place at the low-coordination sites at the surface of the NiO film. The Co/MgO( 001) system has also been studied. In all the investigated cases, given the lower surface free energy of the oxide surfaces compared to the metal ones, the deposited metals tend to form islands, which coalesce above a few monolayers.