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The growth of vapour-deposited silver nanoparticles on &agr;-Al2O3 was studied in situ from 190 to 675 K by surface differential reflectivity spectroscopy in the UV-visible range. Changes in size, shape and density were derived from the plasmonic response modelled in the framework of interface susceptibilities by assuming that supported clusters were in the form of truncated spheres. The sticking coefficient of silver on alumina is close to one up to T ' 575 K before entering a regime of incomplete condensation. The Arrhenius dependence of the saturation density indicates a nucleation on defects at low temperature (T ≤ 300 K) and detrapping above. The particle size D evolution follows temporal power laws, independent of temperature and flux, which characterize the growth (D ∼ t0:31) and coalescence (D ∼ t0:55) of the film. These are indicative of the growth of isolated particles at constant density and dynamic coalescence, respectively. The wetting angle of the silver clusters is shown to increase during the growth regime, which is assigned to a combination of surface stress and mismatch-induced strain, and to decrease upon coalescence, which is attributed to plastic relaxation. For particles larger than 10 nm in size, the values of contact angle and adhesion energy level off with asymptotic limits (&thgr;c D =127:5° ± 1° and 0:48 ±0:02 J m-2) that nicely agree with tabulated data. This work highlights the ability of nanoplasmics to monitor in situ the growth kinetics of thin supported films. [ABSTRACT FROM AUTHOR]

Abstract: The etching of MgO smoke in wet conditions – an archetype for aqueous dissolution of oxide crystals – is explored on the basis of transmission electron microscope (TEM) analyses. In pure water with neutral pH, in acid solutions and in moist air, the MgO cubic crystallites show first (110) truncations of the 〈110〉 edges and then (111) cuts at the corners. Criteria are given to characterize (110) and (111) cuts on the TEM images. It is shown that (110) truncations appear independently of the formation of the (111) cuts and are associated with a stationary state. The picture is fully consistent with the previous suggestion of a “constrained Wulff profile” which explains the formation of (110) cuts by excluding (111) facets. [Copyright &y& Elsevier]

Abstract: Upon dissolution in liquid water at neutral pH, the cubic MgO smoke crystals give rise to octahedra with (111) facets, an evolution which is fully consistent with theoretical predictions. The first changes to show up during the dissolution process are jagged (110) cuts of the 〈100〉 cube edges. Then, (111) cuts develop at the cube corners till they become the dominant features of the dissolving crystals. [Copyright &y& Elsevier]

The growth of a titanium thin film on the α-Al2O3(0 0 0 1) surface occurs in two steps. In the first stage, titanium is oxidised via a chemical reaction with the surface oxygen species which are characterised by a shift of 1.5 eV of the O 1s level. These species involve removable OH groups ((5±2)×1014/cm2 at saturation) and—likely—residual OH groups ((3±1.5)×1014/cm2, minimum value). At higher titanium coverage, the titanium film becomes metallic. [Copyright &y& Elsevier]

Determines the local structure centered on sodium after diffusion in silica. Use of extended X-ray absorption fine structure; Representation of soda-silica glass in local structure; Presence of ionic conductivity in oxide glasses.

This comment article introduces a series of four review papers about oxide surfaces which are published in this journal.[sup 1 - 4] It is emphasized that oxides concern a very broad area of applications and that the examination of the extreme surface of these materials is crucial to the understanding of an increasing number of phenomena. [ABSTRACT FROM AUTHOR]

A new spectral restoration algorithm of reflection electron energy loss spectra is proposed. It is based on the maximum likelihood principle as implemented in the iterative Lucy-Richardson approach. Resolution is enhanced and point spread function recovered in a semi-blind way by forcing cyclically the zero loss to converge towards a Dirac peak. Synthetic phonon spectra of TiO2 are used as a test bed to discuss resolution enhancement, convergence benefit, stability towards noise, and apparatus function recovery. Attention is focused on the interplay between spectral restoration and quasi-elastic broadening due to free carriers. A resolution enhancement by a factor up to 6 on the elastic peak width can be obtained on experimental spectra of TiO2(110) and helps revealing mixed phonon/plasmon excitations. [ABSTRACT FROM AUTHOR]

The reflection coefficients of a nanoparticle film are driven to a large extent by perpendicular and parallel interfacial susceptibilities that have the meaning of 'dielectric thicknesses' which combine the actual geometry of the film and its dielectric properties. The direct determination of these parameters faces the long-standing issue of the derivation of complex optical constants from Fresnel coefficients via a unique spectroscopic measurement. The present work sets up an iterative algorithm based on inversion of the reflection coefficients recorded in the UV-visible range for two polarization states s and p and Kramers-Kronig (KK) analysis. To calculate the KK integrals over a limited energy window, the strategy was to complement measurements by spectra calculated in the framework of the spheroidal dipole approximation. The algorithm has been successfully tested on synthetic data of differential reflectivity for supported truncated spheres. These were chosen to span different dielectric behaviors, involving (a) for the particles, metals whose optical response is dominated by plasmonic excitations with a noticeable Drude behavior (Ag and Au) and (b) for the substrate, either nonabsorbing wide bandgap (alumina) or semiconducting (zincite and titania) oxides. Unlike the thin plate model, the approach was proven to apply to 'dielectric thicknesses' of several tens of nanometres in cases in which, even for geometric sizes of the order of the nanometer, the classical long-wavelength dielectric approximation fails because of strong plasmon resonances. Therefore, the disentanglement of dielectric behaviors along the parallel and perpendicular directions simplifies the understanding on the interface polarization process by removing substrate contribution. The present work that deals with plasmonics in nanoparticles can be easily generalized to different morphologies as well as to other combinations of Fresnel coefficients. [ABSTRACT FROM AUTHOR]

Abstract: A method to determine the van der Waals forces from phase–distance curves recorded by atomic force microscopy (AFM) in tapping mode is presented. The relationship between the phase shift and the tip–sample distance is expressed as a function of the product of the Hamaker constant by tip radius. Silica-covered silicon tips are used to probe silica-covered silicon substrate in dry conditions to avoid capillary effects. Tips being assumed spherical, radii are determined in situ by averaging profiles recorded in different directions on hematite nanocrystals acting as nanotemplates, thus accounting for tip anisotropy. Through a series of reproducible measurements performed with tips of various radii (including the in-situ characterization of a damaged tip), a value of (6.3±0.4)×10−20 J is found for the Hamaker constant of interacting silica surfaces in air, in good agreement with tabulated data. The results demonstrate that the onset of the tip–surface interaction is dominated by the van der Waals forces and that the total force can be modeled in the framework of the harmonic approximation. Based on the tip radius and the Hamaker constant associated to the tip–substrate system, the model is quite flexible. Once the Hamaker constant is known, a direct estimate of the tip size can be achieved whereas when the tip size is known, a quantitative evaluation of the van der Waals force becomes possible on different substrates with a spatial resolution at the nanoscale. [Copyright &y& Elsevier]

Thanks to a dedicated modelling of intensities, the depth sensitivity of X-ray photoemission is used to probe the segregation profile of aluminium at the (110), (100) and (111) low index surfaces of the body-centred Fe 0.85 Al 0.15 random alloy. Sputtered surface composition is close to the nominal bulk one, thus excluding preferential sputtering. Surface enrichment in aluminium upon annealing starts at around 700 K before reaching a stationary state above 1000 K. The average surface composition is close to Fe 0.5 Al 0.5 , corresponding to the B 2 CsCl structure of the phase diagram. The impacted depth, that is in the range of 2.5–3.5 nm, is quite significant. Although not evidenced previously in surface science conditions at FeAl single crystal surfaces, it is qualitatively in agreement with the segregation at grain boundaries and shear planes of Al-alloyed steels. This segregation tendency is rationalized through ab initio calculations. Unlabelled Image • Severe aluminium segregation above 700 K at the surfaces of bcc Fe 0.85 Al 0.15 • Photoemission determination of the concentration profile in a random alloy • Nanometer deep impacted layer with a Fe 0.5 Al 0.5 composition • Ab initio modelling of segregation trends [ABSTRACT FROM AUTHOR]

For self‐assembling of TiO2 nanoparticles in multiple layers by layer‐by‐layer deposition to be applied to TiO2 thin films with defined and homogeneous thickness for large‐scale applications, the proper functionalization of substrate surface is a prerequisite to guarantee sufficient adhesion. The substrates selected and tested in the present paper were conductive, fluorine‐doped tin oxide (FTO) glass, nonconductive silica glass, and titanium alloy. The current study focusses on the analytical control of the stepwise functionalization of the substrates with 3‐aminopropyltriethoxysilane and glutaraldehyde (GA) for both the FTO glass and silica glass and with 3‐aminepropyl phosphonic acid and GA for Ti alloy. The analyses have been conducted by means of surface sensitive methods, X‐ray photoelectron spectroscopy, Auger electron spectroscopy, and time‐of‐flight secondary ions mass spectrometry. Chemical composition of surface of functionalized substrates shows differences in the degree and type of modification in dependence on substrate. It could be demonstrated that the best functionalized substrates were the conductive FTO glasses. The analysis of the functionalized Ti substrates has revealed that the surface coverage with 3‐aminepropyl phosphonic acid and GA molecules is an inhomogeneous one, and further optimization of the two‐step functionalization on the Ti alloy substrate is necessary. [ABSTRACT FROM AUTHOR]

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (1 1 0) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900  K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5  nm that run along the [ 0 0 1 ] B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements. [ABSTRACT FROM AUTHOR]

Antibiotic resistance has impelled the research for new agents that can inhibit bacterial growth without showing cytotoxic effects on humans and other species. We describe the synthesis and physicochemical characterization of nanostructured ZnMgO whose antibacterial activity was compared to its pure nano-ZnO and nano-MgO counterparts. Among the three oxides, ZnO nanocrystals-with the length of tetrapod legs about 100 nm and the diameter about 10 nm-were found to be the most effective antibacterial agents since both Gram-positive ( B. subtilis) and Gram-negative ( E. coli) bacteria were completely eradicated at concentration of 1 mg/mL. MgO nanocubes (the mean cube size ~50 nm) only partially inhibited bacterial growth, whereas ZnMgO nanoparticles (sizes corresponding to pure particles) revealed high specific antibacterial activity to Gram-positive bacteria at this concentration. Transmission electron microscopy analysis showed that B. subtilis cells were damaged after contact with nano-ZnMgO, causing cell contents to leak out. Our preliminary toxicological study pointed out that nano-ZnO is toxic when applied to human HeLa cells, while nano-MgO and the mixed oxide did not induce any cell damage. Overall, our results suggested that nanostructured ZnMgO, may reconcile efficient antibacterial efficiency while being a safe new therapeutic for bacterial infections. [ABSTRACT FROM AUTHOR]

Abstract: Under well-controlled synthesis conditions, MgO was produced in powdered form by means of conventional metal combustion technique. Resulting so-called smoke nanoparticles consist of single crystallites with exceptionally regular cubic shape. We demonstrate that their size and distribution are strongly dependent on the synthesis parameters. The effect of the oxygen partial pressure on the synthesis has been systematically studied by transmission electron spectroscopy. It was shown that an increase in oxygen partial pressure leads to a decrease in MgO particle size . This is rationalized on the basis of the classical theory of nucleation and growth. More general applications of this approach are discussed. [Copyright &y& Elsevier]

Abstract: New features are observed in photoluminescence spectra of MgO smokes produced in controlled conditions, an experiment inspired by previous measurements on cleaved MgO(100). Upon photoexcitation at 5.17–5.45eV, most luminescence spectra observed can be decomposed into two bands, peaking at 3.82–3.86eV (the highest energy ever recorded in such experiment) and 3.20eV, respectively. It is assumed that the 3.82–3.86eV band is related to the luminescence at four-coordinated (4C) defect-free edge sites and that the 3.20eV band arises from the excitation transfer from 4C edge sites towards less-coordinated 3C sites. A minor contribution to the 3.20eV band observed upon excitation with 4.6eV photons is assigned to a direct excitation of 3C sites. Within these assumptions, water chemisorption–desorption is suggested to produce less-coordinated sites (the 3.20eV band increases in intensity) at the expense of 4C sites (the 3.84eV band decreases). The huge sensitivity of the 3.84eV/3.20eV branching ratio to the formation of defects on 4C edges is suggested to explain the lack of consensus about the photoluminescence of MgO. [Copyright &y& Elsevier]

One challenge in the production of nanometer-sized objects with given properties is to control their growth at a macroscopic scale in situ and in real time. A dedicated ultrahigh-vacuum grazing-incidence small-angle x-ray scattering setup has been developed, yielding high sensitivity and dynamics. Its capabilities to derive the average particle shape and size and the film growth mode and ordering and to probe both surfaces and buried interfaces are illustrated for two prototypical cases: the model catalyst Pd/MgO(100) and the self-organized Co/Au(111) system. A wide range of technologically important systems can potentially be investigated in various gaseous environments. [ABSTRACT FROM AUTHOR]

• Similar aluminium segregation deep profile at the surfaces of bcc Fe 0.85 Al 0.15. • Orientation (1 1 0)/(1 0 0)/(1 1 1) dependent surface structures. • Al-rich long-range nanometer size surface reconstruction at (1 1 0) surface. • Pronounced nano-faceting at (1 1 1) surface. Based on previous photoemission findings, the influence of newly observed aluminum surface segregation at the low (1 1 0), (1 0 0) and (1 1 1) index surfaces of the A 2 body-centered Fe 0.85 Al 0.15 random alloy is explored. Scanning Tunneling Microscopy, Low-Energy Electron Diffraction and Grazing-Incidence X-ray Diffraction are combined to explore surface structures and topographies. The formation of a surface composition close to the B 2 Fe 0.5 Al 0.5 occurs with the appearance of (i) a long-range pseudo-hexagonal incommensurate superstructure with a periodicity of ~ 18 Å on the (1 1 0) surface, (ii) a (1 × 1) termination on the (1 0 0) surface and (iii) a intense vicinal faceting of the (1 1 1) surface in the form of triangular pits. [ABSTRACT FROM AUTHOR]

Periodic arrays of anisotropic silver nanoparticles having peculiar optical properties are fabricated at a macroscopic scale. The proposed scalable method is based on temperature‐assisted solid‐state dewetting of a continuous thin layer deposited on a silica substrate patterned by the nanoimprint technique. The resulting nanoparticles are shaped like diamonds and are half‐embedded into the patterned silica. A period‐dependent optimum in film thickness for the quality of spatial organization is found and discussed in terms of thermodynamics and, for the first time, in terms of the role of grains in the dewetting process. The optical properties of the arrays are driven by not only simply the particle shape but also the lattice period and the degree of order. A surface lattice resonance that disperses with the underlying period is evidenced experimentally and confirmed by optical simulations. The opportunity to fabricate and tune such an assembly of plasmonic particles on transparent substrate opens interesting perspectives for not only fundamental photonics but also potential optical applications. [ABSTRACT FROM AUTHOR]

The spectroscopic fingerprints of the point defects of titanium dioxide remain highly controversial. Seemingly indisputable experiments lead to conflicting conclusions in which oxygen vacancies and titanium interstitials are alternately referred to as the primary origin of the Ti 3d band-gap states. We report on experiments performed by electron energy loss spectroscopy whose key is the direct annealing of only the very surface of rutile TiO2 (110) crystals and the simultaneous measurement of its temperature via the Bose-Einstein loss/gain ratio. By surface preparations involving reactions with oxygen and water vapor, in particular, under electron irradiation, vacancy- and interstitial-related band-gap states are singled out. Off-specular measurements reveal that both types of defects contribute to a unique charge distribution that peaks in subsurface layers with a common dispersive behavior. [ABSTRACT FROM AUTHOR]