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Anodic oxidation of niobium has been investigated in an electrolyte solution containing calcium phosphate and calcium acetate. The oxide layer morphology has been determined by combining 3D Atomic Force Microscopy images and cross-sectional Field Emission SEM measurements. The surface sensitivity of high-resolution X-ray Photoemission Spectroscopy has been exploited to evaluate the chemical composition of the outermost oxide surface, a key feature in view of implant development. Anodic Spark Deposition (ASD) results in the formation of micrometer-thick oxide layers showing a porous morphology suitable for osseointegration purposes. Increasing the maximum potential attained during oxidation leads to an increase of the oxide thickness and pore size accompanied by a noticeable surface enrichment with calcium and phosphorus. Remarkably, a maximal Ca/P ratio of 1.8 was achieved for anodization at 250 V, promising for osseointegration thanks to the similarity with hydroxyapatite stoichiometry. Parallel experiments performed on titanium under the same conditions indicated a maximal Ca/P ratio of 1.3 and pores of smaller dimensions. The comparative analysis suggests that niobium may represent a promising alternative to titanium to be explored for implant development.

The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system's electron gas, lattice, and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution of the system subcomponents. We measured the dynamic optical response of ensembles of plasmonic Au nanoparticles following ultra-short-pulse excitation, and we compared it with the corresponding static optical response as a function of the increasing temperature of the thermodynamic bath. Evaluating the two sets of data, the optical fingerprints of equilibrium or off-equilibrium responses could be clearly identified, allowing us to extract a dynamic thermometric calibration scale of the relaxation process, yielding the experimental ultrafast temperature evolution of the plasmonic particles as a function of time.

Electromagnetically-heated metal nanoparticles can be exploited as efficient heat sources at the nanoscale. The assessment of their temperature is, however, often performed indirectly by modelling their temperature-dependent dielectric response. Direct measurements of the optical properties of metallic nanoparticles in equilibrium with a thermodynamic bath provide a calibration of their thermo-optical response, to be exploited for refining current thermoplasmonic models or whenever direct temperature assessments are practically unfeasible. We investigated the plasmonic response of supported Au nanoparticles in a thermodynamic bath from room temperature to 350 °C. A model explicitly including the temperature-dependent dielectric function of the metal and finite-size corrections to the nanoparticles' permittivity correctly reproduced experimental data for temperatures up to 75 °C. The model accuracy gradually faded for higher temperatures. Introducing a temperature-dependent correction that effectively mimics a surface-scattering-like source of damping in the permittivity of the nanoparticles restored good agreement with the data. A finite-size thermodynamic effect such as surface premelting may be invoked to explain this effect.

Titanium dioxide (TiO2) thin films were prepared by means of electrochemical anodisation or anodic spark deposition (ASD) from thin and flat metallic titanium (Ti) films pre-deposited on high quality quartz substrates by electron beam evaporation. AFM analysis indicates the formation of uniform mesoporous layers and a definite increase about 50% of the film thickness upon anodisation and about 90% upon annealing. Anodised mesoporous TiO2films have been characterized by Raman spectroscopy, which indicates the presence of well-defined peaks related to anatase structure. Phase transformation from anatase to rutile was observed after annealing at temperatures up to 900°C for 3h.

Small aluminum nanoparticles have the potential to exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum, however technical and scientific challenges make it difficult to attain this limit. We report the fabrication of arrays of Al/Al 2O3 core/shell nanoparticles with a metallic-core diameter between 12 and 25 nm that display sharp plasmonic resonances at very high energies, up to 5.8 eV (down to ? = 215 nm). The arrays were fabricated by means of a straightforward self-organization approach. The experimental spectra were compared with theoretical calculations that allow the correlation of each feature to the corresponding plasmon modes.

The proper exploitation of the plasmon resonance typical of metallic nanoparticles can allow for the confinement of the electromagnetic field in nanometric volumes, thus creating the so called "hot spots". These nanometric volumes are characterized by high field, remarkably useful characteristic for a huge variety of applications in photonics and optics. The most commonly employed plasmonic metals, Au and Ag, yield resonances only reaching up to the near-UV electromagnetic range, in fact stretching upwards the energy of plasmon resonances requires the use of different materials. Deep-ultraviolet plasmon resonances were indeed predicted exploiting one of the cheapest and most abundant materials available on earth. Aluminium holds the promise of a broadly-tuneable plasmonic response, theoretically extending far into the deep-ultraviolet (DUV). Complex fabrication issues, including the strong Al reactivity, have however stood in the way of achieving this ultimate DUV response. We report the successful realization of 2-dimensional arrays of ultrafine aluminium nanoparticles that exhibit a remarkable plasmonic response up to the DUV electromagnetic range. Careful nanofabrication allowed to maintain the mean NP size below 20 nm, preserving a purely-metallic core. These systems exhibit a striking high-energy plasmon resonance up to 6.8 eV photon energy, and preserve their DUV plasmon response when exposed to atmosphere [1,2]. These observations pave the way to the full exploitation of aluminium plasmonic tunability, hence extending the numerous applications of plasmonics to the high-energy side of the spectral range.

We have studied Cu electrodeposition on well defined Au films using real time Spectroscopic Ellipsometry (SE). SE allows to discriminate the under-potential (UP) and over-potential (OP) regimes. In the UP regime, tiny yet reproducible variations of Ψ and Δ parameters indicate the formation of two phases with slightly different optical behavior. The phase at the largest coverage is assigned to a Cu monolayer. The SE response in the OP regime shows a marked dependence on the potential scan rate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report first results about the interaction of a He ∗ beam with nanometer thick layers of l -cysteine, a fundamental amino-acid, deposited under ultra high vacuum conditions on Cu and Au surfaces. Electronic properties of adsorbed molecules have been investigated by metastable deexcitation spectroscopy (MDS). Deexcitation of He ∗ on molecular layers gives rise to well defined Penning ionization spectra. In these spectra, we distinguish contributions of the molecules strongly bound to the surface through the thiol group and of molecules weakly bound to the surface, as for example those belonging to multilayers. The beam (whose intensity on the sample is of the order of 10 11 at/s with a spot diameter of 1 mm) induces slow rate desorption of weakly bound molecules. Mild annealing to 330 K induces the desorption of weakly bound molecules as well. Cleavage of intra-molecular bonds is observed for annealing temperatures above 420 K. Beam-induced damage of first layer molecules appears not significant on the time scale (tens of seconds) of the MDS experiment. The data demonstrate the full applicability of MDS to the investigation of self-assembled monolayers of small biomolecules.

The effects of a chemical alteration of the antiferromagnet surface in the exchange-biased ultrathin epitaxial antiferromagnetic/ferromagnetic bilayer Mn/Co/Cu(001) have been investigated. The formation of a nanometer-thick paramagnetic oxide at the surface of the Mn layer was induced through the controlled exposure to oxygen. Although the buried Mn/Co interface was not affected by the oxidation, strong changes of the exchange-bias properties of the system, which cannot be accounted for by the mere reduction of the antiferromagnetic Mn thickness, were observed. We propose that the produced surface modification affects the magnetic configuration of the near-surface region and the domain structure in the whole antiferromagnet layer which, in turn, influences the pinned uncompensated spin density responsible for the exchange bias.

Growth and oxidation of Na adlayers on Ag(0 0 1) have been investigated by means of metastable de-excitation spectroscopy (MDS) and He reflectivity ( R He ) measurements. During Na deposition at 180 K, R He exhibits maxima at the formation of the c (2 × 2)-Na phase and at the completion of the first layer. Oxidation of the Na film at 180 K by exposure to O 2 goes through the incorporation of dimeric molecular ions and, at larger exposure, of neutral O 2 molecules. Successive annealing of the oxidised Na film leads first to the loss of the neutral oxygen molecules at 400 K and finally to the removal of the Na–O film at 750 K. Both Na condensation and oxidation of the Na film induce the lowering of the work function. In both cases (Na deposition and oxidation), the singlet-to-triplet conversion was found to be hindered if the work function is lower than 2.5 eV.

International audience; The metastable deexcitation spectrum of Ag(100) is measured and information on the effective density of states probed by the metastable atom is obtained by deconvolution of the experimental spectrum, under the hypothesis that it reflects the self-convolution of the surface density of states. Layer resolved semi-empirical LCAO calculations are compared to the deconvolution curve, showing poor agreement as far as the branching ratios of sp versus d contributions are concerned. The agreement between theory and experiment strongly improves if an energy dependent exponential decay factor is included in the first layer calculated density of states to account for the energy dependent increased overlap between electronic states of the solid and metastable atom outside the surface. © 2003 Elsevier B.V. All rights reserved.

Structural and electronic properties of ultrathin Mg films on Ag(1 0 0) have been investigated by means of metastable de-excitation spectroscopy (MDS), work function change (Δφ), electron diffraction and helium reflectivity (RHe) measurements. At room temperature Mg grows on Ag(1 0 0) following the Stranski–Krastanov growth mode. Successive annealing of a 10 ML thick Mg film leads to its almost complete desorption at about 390 K and to the formation of a Mg–Ag alloy. RHe and electron diffraction measurements indicate that for annealing temperatures between 480 and 570 K, the alloy orders with a c(2×2) periodicity. Further annealing at higher temperatures restores the initial Ag(1 0 0) surface.

We have studied cadmium stearate Langmuir–Blodgett (LB) films by spectroscopic ellipsometry (SE) and we have compared the results with those obtained by using X-ray reflectivity and atomic force microscopy. The measurements on cadmium stearate LB films deposited on silicon wafers capped by a native oxide layer provide sound results for films formed by 1–25 molecular layers. The experimental data are well fitted by a Cauchy-type model over the whole examined wavelength range (245–725 nm). The model, which takes into account the anisotropy of the film, uses the film thickness of several mono- and multi-layers films, together with the in-plane and the out-of-plane components of the refraction index as free parameters. The obtained mean thickness of the monolayer (ML), 2.50±0.02 nm, very well agrees with X-rays reflectivity measurements and with literature data.

The surface magnetic properties of ultrathin Cr films grown on O(1×1)-Fe(0 0 1) have been studied by means of spin-polarised metastable de-excitation spectroscopy (SPMDS). The spin-selected surface density of states extracted from the experimental SPMDS data provides information on both composition and magnetic properties of the topmost layer. We find that oxygen floats on the surface of the growing Cr film and that Cr/Fe intermixing is restricted to the first Cr layer. Concerning the magnetic properties, a strong polarisation of Cr3d electrons is found in agreement with theoretical calculations. Oxygen 2p states are polarised too and their polarisation is opposite to that of Cr3d states. Surface magnetisation as a function of the Cr film thickness shows an oscillatory behaviour induced by the layered antiferromagnetic structure of Cr. At variance with the results of other experimental investigation in this case the layered antiferromagnetic structure of Cr is already present in the 3 ML thick film.

Codeposition of oxygen and Fe on Cu 3 Au(0 0 1) has been investigated in order to look at the modifications of the growth regime induced by the chemical additive. Oxygen deeply modifies the growth modes both at relatively low temperature (150 K) and at room temperature (RT). The bilayer growth mode active at earlier stages of growth in absence of the surfactant element is suppressed. We concentrated our investigation on RT deposition. A relatively ordered, pseudomorphic iron film has been found only at low thickness (up to 4 ML). This film is covered with an oxygen layer, whose coverage and order depends on the post-growth annealing treatment. The annealed oxygen layer has been used as a surfactant for further Fe deposition cycles. During deposition, part of the oxygen remains trapped into the film. Restoration of the chemisorbed layer is obtained after annealing at moderate temperature (700 K). As the film thickness increases as a result of successive depositions, the film is first characterized by coexistence of pseudomorphic and bcc patches. The pseudomorphic patches seem stabilized not only by presence of the oxygen, but also by Cu and Au impurities in the film. For relatively large thickness (above 25 ML) bcc domains become majority.

The structure of the Cu 3 Au(0 0 1) surface has been studied by Ne + scattering spectroscopy under impact collision conditions (ICISS) at room temperature. Scattering of low energy ions (Ne + , 0–3 keV) provides scarce structural information due to the high neutralization probability. Using a Ne ++ beam with energy up to 6 keV and profiting also of the relatively high cross-section for Ne + production in violent collisions with Cu atoms well-defined focusing peaks were detected in ICISS polar scans. The ICISS patterns clearly reflect meaningful structural information, consistent with the 50% Cu–50% Au surface truncation proposed by theoretical investigation and supported by previous ISS works. A comparison of experimental scans with Monte Carlo simulations of ion trajectories, taking into account the Ne–Cu and Ne–Au interaction potentials, thermal disorder, neutralization and reionization processes, is presented and the theoretically predicted rippling between Cu and Au atoms in the first layer is discussed.

The magnetic properties of Ag/Fe/MgO and Cr/Fe/MgO multilayers have been studied in air by both linear (MOKE) and non-linear (MSHG) magneto-optics. Thanks to the different probing sensitivities of the two techniques, film and interface properties can be separately measured. In the Ag/Fe/MgO case, coercive field values measured with linear and non-linear optics are very similar, indicating that a sharp interface is formed and that the presence of silver on top of iron does not alter its magnetic properties. The values of coercive field measured with MOKE for the Cr/Fe/MgO multilayer differ significantly with respect to the Ag case, and furthermore different coercive fields have been measured on this system with MOKE and MSHG. We ascribe the observed effects to spin frustration caused the layered antiferromagnetic Cr spin structure along with the presence of steps at the Cr/Fe interface.

We report on the initial stages of growth of Fe on a well-defined Cu 3 Au (0 0 1) substrate as a function of the temperature of deposition in the range 150–350 K. The structure and morphology of the deposit have been studied by low energy ion scattering (LEIS) under the so-called impact collision conditions (ICISS). Comparison of ion scattering results with simulations in two dimensions of the particle trajectories allowed us to obtain information on the structure and morphology of Fe islands. Ion scattering results have been analysed in combination with He diffraction data obtained in the same apparatus, under the same experimental conditions. Both ICISS and He scattering indicate that growth initially proceeds through nucleation of many small islands. The two techniques provide independent and fully compatible estimates of the average separation between islands that at one layer equivalent increases from ∼30 A at 165 K to ∼60 A at 350 K. ICISS data are fully consistent with the model of initial growth of two-layer thick islands proposed in a recent He scattering investigation [Phys. Rev. B 62 (2000) 13121]. The bilayer growth mode is effective at temperatures up to 350 K, even if at this temperature Fe intermixing with substrate atoms cannot be ruled out. Bilayer islands grow pseudomorphically with a relevant tetragonal strain.

The surface magnetism of an iron film grown on a MgO(1 0 0) substrate has been studied by means of spin polarized metastable de-excitation spectroscopy (SPMDS) as a function of the exposure to oxygen. The O 2p states are magnetically coupled to the iron film and exhibit a splitting in energy Δ E O 2p between the majority and the minority components. The behavior of Δ E O 2p with oxygen exposure demonstrates that the magnetic coupling of the O 2p states is strongly dependent on the local environment of the adsorbed oxygen atoms and provides a clear indication of the magnetic shielding induced by oxygen diffusion in sub-surface sites.

We report a study of the effects of chlorine adsorption on the interaction of positive ions (H+, Ne+, Ar+ with a Ag(111) surface from the submonolayer Cl chemisorption to initial stages of AgCl formation. Cl adsorption on Ag(111) proceeds through different phases and we observed that the neutralization probabilities oscillate in this range, attaining an intermediate minimum at about 2/3 coverage and reach a maximum at full coverage. The subsequent appearance of AgCl phase again leads to a reduction in neutralization. These results are described in terms of changes in Auger neutralization rates due to modifications in the adsorbate density of states.

X-ray specular reflectivity, in-plane grazing incidence X-ray diffraction (GIXRD) and photoelectron diffraction (PED) have been employed to study the Fe/Cu3Au(001) system at the ALOISA beamline (Trieste Synchrotron, Italy). In-plane GIXRD has been used to determine the epitaxial strain of the film lattice by (H00) radial scans around the Cu3Au(200) diffraction peak. FED has been employed in forward scattering conditions to determine the vertical spacing of the topmost layers and to look at atomic exchange processes. At very low coverage, Fe grows pseudomorphically on the fee substrate; the bulk-like Fe bcc structure has been observed for an 18-Angstrom thick Fe film. The PED analysis suggests that, at 1 ML Fe coverage, a full Au layer is segregated onto the surface with the Au atoms sitting in their fee sites. A consistent fraction of a monolayer of Au is still present on top of the 18-Angstrom Fe bcc film.

He diffraction measurements show that preadsorption of an O(1×1) phase on Fe(001) promotes two-dimensional growth of Fe at temperatures below 400 K, in contrast to the island growth observed on the bare Fe(001) surface. Oxygen floats at the surface, acting as a surfactant. After repeated cycles of film annealing and Fe re-deposition, a beat is observed in the pattern of He reflectivity measured as a function of deposition time. The beat is assigned to the growth on surface domains characterized by a different surfactant efficiency.

The surface magnetic properties of ultrathin Cr films grown on an O/Fe/Ag(100) substrate have been studied by means of spin polarized metastable de-excitation spectroscopy. The presence of oxygen on top of the Fe film inhibits the segregation of Ag and strongly reduces Fe/Cr intermixing. The magnetization of the outermost Cr layer is zero immediately after its deposition, whereas, upon annealing up to 500 K, a net magnetization is observed which reverse its direction as a function of the film thickness already from a 3 ML thick film. The magnetization reversal is in agreement with the layered antiferromagnetic structure of Cr clearly observed for thicker films.

The correlation between crystallographic order and surface magnetism has been investigated by studying the chemisorption of oxygen on iron films grown on Ag(100) and MgO(100). The exchange splitting of O 2p states depends strongly on surface order as it decreases from Δ E O 2p ≃0.5 eV for the O(1×1) phase to Δ E O 2p ≃0.2 eV for the O/Fe/MgO disordered phase. Even smaller values of Δ E O 2p are obtained for the highly disordered O/Fe/Ag system, demonstrating that the coupling of oxygen states with the magnetic film underneath is strongly affected by crystallographic order.

We present the results of a helium diffraction study of the morphology of a Cu 3 Au(001) surface at 140 K. Biatomic steps only are not able to describe the terrace morphology, and monoatomic steps must be included. The step height (1.855±0.015 A) is closely comparable to the bulk interlayer spacing of Cu 3 Au along the 〈001〉 direction (1.865 A). Two kinds of terraces have been identified. The first class (A-terraces) are the majority. They are large terraces that display the well-known c(2×2) ordering of the Au–Cu termination. The second type (B-terraces) consists of much smaller terraces of uncertain composition. B-terraces are separated from A-terraces by a monoatomic step. Monoatomic steps are probably bunched into pairs.

XPS spectra acquired on anodized niobium during a thermal treatment from 300 to 1223 K are reported. The anodization process consists of growing a layer of oxide of known thickness on the metal surface; the sample is kept in a solution of ammonia inside an electrochemical cell and a d.d.p. is applied to the electrodes. We acquired XPS spectra by using a PHI 5600 ESCA multitechnique spectrometer with an Al Kα monochromatized source. The spherical capacitor analyzer operated in the constant energy mode at a pass energy of 5.85 eV. Measurements at two emission angles, 0° and 70°, and at temperatures between 300 and 1223 K are reported. This XPS study puts in evidence the existence of a transition on the Nb surface from Nb pentoxide to Nb pure metal during the heating phase.

The influence on surface magnetism of oxygen adsorption at T = 120 K on an iron film grown on Ag(100) has been analysed by spin polarized metastable deexcitation spectroscopy. The low temperature has been chosen in order to reduce the segregation of silver at surface. SPMDS data have been interpreted by a model that provides the effective charge and magnetization densities. At 120 K, oxygen chemisorbs atomically, the O2p states are spin polarized and show a ferromagnetic coupling with the substrate. The energy shift between the majority and the minority density of states is a function of exposure as it decreases from 0.24 eV at 0.25 L to zero for exposures higher than 1.6 L. At exposures of about 1 L, oxygen starts a process that leads, at 3–4 L, to the formation of a layer that is magnetically dead as observed by He∗.

The localized surface plasmon resonance of metal nanoparticles allows confining the eletromagnetic field in nanosized volumes, creating high-field "hot spots", most useful for enhanced nonlinear optical spectroscopies. The commonly employed metals, Au and Ag, yield plasmon resonances only spanning the visible/near-infrared range. Stretching upward, the useful energy range of plasmonics requires exploiting different materials. Deep-ultraviolet plasmon resonances happen to be achievable with one of the cheapest and most abundant materials available: aluminum indeed holds the promise of a broadly tunable plasmonic response, theoretically extending far into the deep-ultraviolet. Complex nanofabrication and the unavoidable Al oxidation have so far prevented the achievement of this ultimate high-energy response. A nanofabrication technique producing purely metallic Al nanoparticles has at last allowed to overcome these limits, pushing the plasmon resonance to 6.8 eV photon energy (approximate to 180nm) and thus significantly broadening the spectral range of plasmonics' numerous applications.

Introduction Anodisation of pure titanium has been carried out in sulphuric and in phosphoric acid solutions at potentials ranging from 50 to 150V. The SEM and AFM morphological analysis indicates that, within this potential range, oxidation in sulphuric acid solution produces better developed mesoporous oxide layers. XPS analysis of the Ti2p core level region and Raman spectroscopy measurements show that oxide layers grown in sulphuric acid are characterised by a better defined oxidation state of titanium and by a higher content in anatase crystalline phase. XPS measurements indicate that oxidation in phosphoric acid solution produces oxide layers with two components of stoichiometric oxide and with the presence of phosphate inclusions which can be interesting in view of biomedical applications. Titanium and its alloys are largely employed for the development of orthopaedic and dental implants because of their good mechanical strength and low density. Thanks to its thin native oxide layer which prevents ion release, titanium offers good resistance to corrosion in body fluids and good biocompatibility. These properties can be further improved by surface treatments able to grow thicker oxide layers with controlled morphological and physico-chemical properties. Several methods have been used to this purpose, from thermal treatment [1-3], to acid solution immersion [4], peroxide immersion [5], anodic-plasma chemical treatment [6], plasma immersion ion implantation [7] and anodisation [8,9]. Volume 1 | Issue 1

The initial stages of growth of Fe on a well-defined single crystal Ag(100) surface have been investigated by means of thermal energy helium diffraction. We report on specular beam spot profiles obtained at 0.5 monolayer for several temperatures of deposition in the range of 135–300 K. Typical sidebands ("satellites") in diffraction patterns allow one to estimate the mean separation between islands. Experimental data in the range of 135–228 K show a linear dependence of ln < L> as a function of the inverse of the temperature of deposition, while at higher temperatures a clear deviation from this law is found, indicating a change in the regime of growth. The nucleation of small islands turns out to be the factor which favors two-dimensional growth at low temperature.

Interference conditions for atom-surface scattering from small islands are proposed and demonstrated for ultrathin films of Fe grown on Ag(100). We show that the local variation of the van der Waals forces causes a sizable change of the step induced phase shift. We propose a simple square well model that allows the quantitative reproduction of the observed effect.

The growth of ultrathin iron films on Ag(100) at 135 K has been studied by means of thermal-energy helium diffraction. Film deposition has been monitored by measuring the oscillations of the specular beam intensity during the growth. Information on the island morphology of the deposited film has been obtained by exploiting the dependence of the scattered intensity on the momentum transfer. The set of data indicates that there are definite differences between the growth mode of the first and subsequent layers. The surface of the first monolayer exhibits a two-dimensional morphology, while the estimate of the interface width $w$ [J. W. Evans, Phys. Rev. B 43, 3897 (1991)] from a kinematic analysis of data provides values of ${w}^{2}$ ranging from 0.28 at 2 ML to 0.37 at 5 ML. The obtained values are consistent with the so-called one-hop transient mobility model with adsorption at the fourfold hollow site and show that from the second layer on the morphology gradually deviates towards island growth. The analysis of rocking curves also provides the step height ${(h}^{\ensuremath{'}})$ of the growing interface. At 2, 3, 4, and 5 ML, ${h}^{\ensuremath{'}}$ assumes values that are slightly larger than the value of bulk bcc iron ${h}_{\mathrm{Fe}}=1.43$ \AA{}. This finding is assigned to the occurrence of intermixing through simple arguments based on the conservation of the atomic volumes. The Ag population at the surface of the film is found to decrease with film thickness consistently with recent ion-scattering measurements.

The influence of adsorption of O 2 and CO on the surface magnetism of a 10 ML film of Fe grown at 120 K on Ag(100) has been investigated by spin polarized metastable deexcitation spectroscopy. The extreme surface sensitivity of this spectroscopy allows us to study the effects of adsorption from exposures as low as ∼0.1 L. Oxygen adsorbs dissociatively at 120 K and the O 2p states are spin polarized. At this low temperature, oxidation starts from exposures of the order of 1 L and above 3-4 L a non-magnetic oxide layer is formed. CO adsorbs molecularly at T = 120 K and then dissociates above room temperature. Following dissociation, carbon atoms do not have any effect on the spin polarization of oxygen and iron states at the surface.

We report on the thermal evolution of the OHAg(110) phase at coverage θ(OH) = 0.66. Combined information, provided by thermal energy helium scattering and angle resolved ultraviolet photoemission spectroscopy, show that recombination of the OHγ, sub-state, in the range 235–255 K produces a new phase consisting of a mosaic of large and ordered oxygen domains and OHδ domains. The former present a (2 × 1) geometric structure with AgO added rows aligned along the 〈001〉 direction while the latter show a (1 × 2) structure with OHAg chains placed along the 〈110〉 direction. Further recombination of the OHδ sub-state starting around 260 K and leading to the final O(3 × 1) phase around room temperature, proceeds through a continuous rearrangement between large ordered oxygen domains and OH disordered domains.

The present paper is devoted to the application of metastable deexcitation spectroscopy (MDS) for studying interface formation with reference to Yb GaAs (110) and Sb GaAs (110) . These systems are prototypical examples of intermixed disordered and ordered interfaces. In the discussion, emphasis is given to the potentiality offered by MDS in interface formation studies. A comparison with photoemission is discussed.

""Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to. probe electronic structure in antiferromagnetic thin films. In particular, exploiting the AR-APECS capability to. discriminate Auger electron emission events characterized by a different spin of the ion in its final state, a sharp. multiplet structure in the Ni MVV Auger line shape of NiO\\\/Ag(001) thin films is measured below the critical. Néel temperature. The assignment of multiplet terms follows from a close comparison of the experimental. AR-APECS line shapes with the predictions based on semiempirical calculations on a cluster model and an. open-band extension of the Cini-Sawatzky approach. In analogy to CoO, also in NiO, above the Néel temperature. a more featureless Auger spectrum appears and AR-APECS does not disentangle anymore high-spin and low-spin. contributions to the total Auger intensity. Such a behavior, which seems to be a general result for metal oxide. antiferromagnetic systems, is discussed.""

Metastable deexcitation spectroscopy (MDS) was applied to the study of the electronic structure of Sb/GaAs (110) and H:GaAs(110) systems. For both systems valuable insights into the surface electronic structure (effective surface density of states and surface charge density) were obtained. A surface to volume ratio extremely higher than photoemission was obtained for MDS. For both systems new features, never observed by more conventional surface spectroscopies, were detected.

Water adsorption on the oxygen-covered Ag (110) surface has been studied by a combined analysis of structural properties (by helium diffraction) and of electronic states at the surface (by metastable deexcitation and angle-resolved ultraviolet photoemission spectroscopies) . H2O adsorption on well ordered O (n × 1) phases (n even) leads to the observation of pure OH (1 × m ) phases with m = 00n 2 . Spectroscopic data indicate that OH is bonded to the surface via the O atom. The most distinctive spectral feature induced by OH(a) is the dispersion of electronic states in the 2–4 eV binding energy range, above Ag 4d bands, along 〈110〉. These levels are interpreted as anti-bonding states originating from the covalent mixing between OH 1π and Ag 4d states. A donation of s-p metal charge to the adsorbate is suggested by work function and metastable deexcitation spectroscopy measurements. The band structure of the induced levels and the surface corrugation experienced by helium diffraction indicate, for all phases, that -Ag-OH- chains are formed along the 〈110〉 azimuthal direction of the substrate. A different local geometry of adsorption for OH in the (1 × 1) phase with respect to (1 × 2) and (1 × 3) cases is suggested. An adsorption site of C2v symmetry is expected on the latter phases. Helium diffraction data on OH phases are incompatible with the missing-row reconstruction model, which is known to be effective on oxygen phases.

We report on the dispersion relations of surface plasmon resonance (SPR) modes in spatially extended self-organized two-dimensional arrays of closely spaced gold nanoparticles (NPs). The arrays are supported on uniaxially rippled LiF substrates that trigger the organization of the metallic gold NPs in sequences of closely spaced chains. We measured the dispersion of the longitudinal and transverse SPR modes of these chains and successfully reproduced the experimental data by means of a modified effective-medium model. The calculations show that the interchain electromagnetic coupling increases by almost one order of magnitude the SP group velocity in well-defined regions of the Brillouin zone with respect to isolated chains.

We report the fabrication of 2-dimensional arrays of Au nanoparticles (NPs) with flexibly tunable shape and arrangement, realized by deposition onto self-organized ridge-valley structures at the LiF(110) surface. Tuning the array fabrication conditions, the NP mean size, spacing, and aspect ratio could be controllably varied, allowing us to achieve a variety of 2-dimensional array morphologies. We discuss the consequences of the morphological tuning on the plasmonic response focusing on two particularly instructive cases: in-plane circular NPs arranged on a rectangular array and coherently aligned elongated ellipsoidal NPs laid on a square lattice. Comparing the data with model calculations allowed us to ascribe the optical birefringence of the arrays to the interplay of intrinsic and collective effects. The remarkably narrow width of the plasmonic resonance in these arrays is shown to arise as a consequence of the partial compensation of the dipolar coupling fields between neighboring nanoparticles.

Water dissociation on O(n × 1)−Ag(110) phases has been studied as a function of oxygen coverage and surface temperature by He scattering at thermal energy and photoemission spectroscopy. A new phase of OH with (1 × 1) periodicity with respect to the Ag(110) substrate has been observed following H2O adsorption at Ts = 130 K on the O(2 × 1) phase and annealing at Ts = 210 K. OH groups arrange in chains along the 〈110〉 direction. Hydroxyl groups strongly interact along the chain as shown by the dispersion of electronic states along 〈110〉.

We report a spectroscopic ellipsometry investigation of the interaction of nanoporous cluster-assembled Au films with pure ethanol in a liquid environment. The Au films were first characterized in atmosphere in terms of the mean size of the constituent clusters and their porosity. Upon immersion in liquid, a clear correlation between the relative density of the films and the corresponding fraction of pores that could be filled by ethanol molecules was observed. Low-density porous Au structures exhibit abundant open pores, accessible by molecules from the ambient, whereas for higher-density structures the fraction of accessible pores sharply drops. We found evidence that the pore accessibility in cluster-assembled films with pore dimension in the sub-10 nm range is strongly dependent on fine morphological details of the solid scaffold.

We report on a metastable deexcitation spectroscopy investigation of the growth of L-cysteine layers deposited under UHV conditions on well-defined Au(110)- (1 × 2) and Au(111) surfaces. The interaction of He(*) with molecular orbitals gave rise to well-defined UPS-like Penning spectra which provided information on the SAM assembly dynamics and adsorption configurations. Penning spectra have been interpreted through comparison with molecular orbital DFT calculations of the free molecule and have been compared with XPS results of previous works. Regarding adsorption of first-layer molecules at room temperature (RT), two different growth regimes were observed. On Au(110), the absence of spectral features related to orbitals associated with SH groups indicated the formation of a compact SAM of thiolate molecules. On Au(111), the data demonstrated the simultaneous presence, since the early stages of growth, of strongly and weakly bound molecules, the latter showing intact SH groups. The different growth mode was tentatively assigned to the added rows of the reconstructed Au(110) surface which behave as extended defects effectively promoting the formation of the S-Au bond. The growth of the second molecular layer was instead observed to proceed similarly for both substrates. Second-layer molecules preferably adopt an adsorption configuration in which the SH group protrudes into the vacuum side.

We have investigated the exchange bias (EB) in ultrathin epitaxial Cr/Fe/Ag(001) nanopatterned bilayers characterized by atomic-scale-tailored interfaces consisting of nanoripples aligned along the ${[100]}_{\text{Fe}}$ direction. Precisely measuring the magnetic anisotropy of the system, we quantitatively characterized the energetics of the magnetization reversal in terms of domain-wall propagation in the Fe layer and discussed the influence of the interface structure in determining the exchange bias and promoting the domain-wall processes. We found no influence of the relative orientation of the field-cooling direction with respect to the nanoripple orientation in determining the EB magnitude, but we observed that the anisotropic morphology generates characteristic spin frustrations affecting the energetics of different domain-wall processes.

The combined use of the photoemission and metastable deexcitation spectroscopy, because of the extreme surface sensitivity of the latter, allows for the observation of electronic states related to molecular chemisorption located in the energy region of the d bands of the metal where ultraviolet photoemission spectroscopy alone cannot give definite information because of strong bulk contributions. In the adsorption of CO on Ag(110), we have detected the following states: E1=3.3±0.15, E2=7.0±0.3, E3=9.6±0.15, E4=12.8±0.15, E5=14.9±0.15 eV (binding energies) obtaining the first evidence of weak chemisorption in this system and a quantitative measure of the mutual influence between the electronic states of the molecule and of the surface.

We addressed the thermal stability and corrosion resistance of the magnetic anisotropy of surface-step atoms in nanopatterned ultrathin Fe/Ag(001) films. The step-induced anisotropy was remarkably stable, in ultrahigh vacuum, for flashing temperature up to 520 K, but showed no resistance to atmospheric oxidation. Capping the nanopatterned films with ultrathin chromium overlayers allowed to preserve the magnetic anisotropy due to step atoms while extending its thermal stability to above 670 K and greatly enhancing its resistance under oxidizing atmospheric environment.

We have investigated the optical response of thiolate self-assembled monolayers (SAMs) deposited from the liquid phase on well characterized, (111)-textured gold films based on the use of in situ and ex situ optical spectroscopic ellipsometry. We considered SAMs formed by several molecules with thiol functionality, focusing on the octadecanethiol (C 18) SAM model system. We were able to show the tiny spectroscopic variations induced by the monolayer thick films with great reproducibility and high signal-to-noise ratio. We identified spectral features related to the alkyl chain and to the S-Au interface, providing a reliable spectral "fingerprint" of the formation of densely packed thiolate layers. By comparing data with simulations based on several effective models developed within the framework of Fresnel approach, we identified the main optical features related to the thiolate interface and in particular an absorption band whose spectral weight increases regularly from 500 nm toward the IR limit. We also obtained reliable estimations of the SAM thickness. The interface absorption properties have been tentatively assigned to a modification of the nearly free electron behavior, related to nanoscale morphological modifications following the formation of Au-thiolate moieties.