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In this work sintered thick microcrystalline films as well as micro and nanostructures of In(2)O(3) have been studied. The results obtained by XPS microscopy show that the boundary regions of the microcrystalline films present a higher amount of oxygen, as well as a different O (1s) core level XPS spectrum with respect to the grains. CL images recorded at room temperature show that the emission is preferentially associated with the grain boundaries and the main emission band appeared at 1.9 eV in the recorded CL spectra. Core level and valence band spectromicroscopy measurements of the indium oxide arrows grown at the surface of the sintered InN revealed the incorporation of nitrogen, coming from the starting material. In these structures the N (1s) core level splits into two components, showing a higher amount of nitrogen in the pyramid surface than in the columns of the structures which correlates with an increase of CL intensity. (C) 2008 Elsevier Ltd. All rights reserved.

The spreading of MoO 3 crystallites on a flat Al 2 O 3 support has been investigated by means of integrative X-ray photoelectron spectroscopy and laterally resolving photoelectron spectromicroscopy. The effect of different heat treatments on the spreading of the MoO 3 crystallites has been studied by systematically varying the temperature, the total pressure, and the humidity of the oxygen atmosphere. The chemical images and the quantitative analysis of the lateral expansion of the spread phase around a single MoO 3 crystallite provided insight in the effect of the parameter changes, since the same crystallite could be monitored and the spread layer was removed prior to each heat treatment. The obtained data set strongly supports that gas-phase transport is responsible for the spreading and wetting of molybdate species on the support surface. A model is discussed that consistently explains all experimental observations.

The initial stage of spreading of micron-sized MoO3 crystals deposited on a flat Al2O3 support have been studied by synchrotron radiation spectromicroscopy. The lateral resolution of 150 nm and the surface sensitivity of the microscope allowed us to detect submonolayer quantities of Mo–oxide, spread on the support in the vicinity of the MoO3 crystals after annealing in oxygen atmosphere. Detailed analyses of the Mo–oxide wetting the support have been performed combining chemical imaging with spectroscopy. The concentration of the spread Mo–oxide was quantified as a function of the distance from the MoO3 crystals. The determined concentration profiles were fitted to the analytical solution of an equivalent diffusion model for the MoO3 mass transport in dry oxygen at 630 K yielding a diffusion constant of D=7.8×10−11 cm2/s. The results are discussed in the framework of the possible mass transport mechanisms causing the spreading. The simple unrolling carpet was ruled out as an active process.

The adsorption of CO on a Rh(100) surface and the interaction of CO with p(2 × 2) and (2 × 2)p4g oxygen layers on Rh(100) at different temperatures have been studied by means of Thermal Programmed Desorption (TPD), X-Ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED). As a measure of the reaction rate the changes in the partial pressure of CO2 (mass 44) during titration of the oxygen layers with CO were used. The composition of the surface layer and the surface structure were monitored at various stages of the reaction. The CO O 1s XPS spectra showed that CO adsorption occurs in two bonding configurations characterized by O 1s binding energies of 532.4 and 531.5 eV, assigned to occupation of on-top and bridge sites, respectively. The on-top sites are occupied first yielding an ordered c(2 × 2) layer at coverage of 0.5 ML. At higher coverages a fraction of CO adsorbs in bridge sites and conversion to compressed p(4√2 × √2) and ‘split’ (2 × 1) structures occurs. Three CO desorption states were observed in the CO TPD curves which correlate well with the development of the three ordered structures with increasing CO coverage. The desorption parameters of each ordered structure and their variations with CO coverage were evaluated. The rate of CO oxidation reaction during titration of p(2 × 2) and (2 × 2)p4g layers was studied at temperatures ranging from 290 to 670 K. The variation of the CO2 production revealed dependence on the temperature, reactant surface structure and coverages. It has been found that the following factors are of importance for the reaction rate: (i) the mobility of CO which at the same reaction temperature is affected by the actual oxygen surface structure; (ii) the ordering of the reactants and the structural changes in the course of the titration reaction.

Valence band and spatially resolved x-ray photoemission studies of the Al growth on sexiphenyl films, in both an ultrahigh vacuum (UHV) and in a partial pressure of oxygen, are reported. We show that in an UHV, even for very high coverages, the Al balls up on the organic film and is discontinuous. In contrast, for growth in an oxygen partial pressure, similar to that in standard high-vacuum systems used in organic device production, very thin continuous conducting wetting layers are formed. We suggest that the oxygen acts like a surfactant that allows the high surface free-energy metal to wet low surface free-energy organic films.

The chemical and structural evolution of supported PtRh alloy nano- and microparticles during oxidation has been studied by means of scanning photoelectron microscopy (SPEM) and low energy electron...

Photoemission spectromicroscopy data on Si–GaSe with 0.2 μm lateral resolution revealed laterally inhomogeneous interface Se–Si chemical reactions. The local Si 2p fits agrees with interface Si selenide parameters; the Se 3d peaks indicate a Si–selenide component; the Ga 3d peaks exhibit a metallic component whose intensity increases with Si coverage. This local interface reaction is related to lateral changes in the band lineup.

The formation conditions, morphology, and reactivity of thin oxide films, grown on a Rh(110) surface in the ambient of atomic or molecular oxygen, have been studied by means of laterally resolved core level spectroscopy, scanning tunneling microscopy and low energy electron diffraction. Exposures of Rh(110) to atomic oxygen lead to subsurface incorporation of oxygen even at room temperature and facile formation of an ordered, laterally uniform surface oxide at approximately 520 K, with a quasi-hexagonal structure and stoichiometry close to that of RhO(2). In the intermediate oxidation stages, the surface oxide coexists with areas of high coverage adsorption phases. After a long induction period, the reduction of the Rh oxide film with H(2) is very rapid and independent of the coexisting adsorption phases. The growth of the oxide film by exposure of a Rh(110) surface to molecular oxygen requires higher pressures and temperatures. The important role of the O(2) dissociation step in the oxidation process is reflected by the complex morphology of the oxide films grown in O(2) ambient, consisting of microscopic patches of different Rh and oxygen atomic density.

The capabilities of the Scanning Photo Electron Microscope (SPEM) at ELETTRA as a unique probing tool in the field of catalysis and surface science are illustrated presenting results of two recent investigations. The lateral resolution and the high surface sensitivity of the SPEM has enabled imaging the initial steps of the spreading processes of MoO3 crystals on an alumina support surface, a model system of a catalyst used in petrochemistry. In the second study the local adsorbate coverage inside a pulse of a chemical wave occurring in the catalytic NO+H2 reaction on a Rh(110) single crystal surface has been determined. The microscope was used to monitor the sample surface in situ during the reaction and thus characterizing a temporal and spatial inhomogeneous system. The so-called excitation cycle of the pulse formation has been verified and the adsorbate gradient inside a chemical wave was measured.

1. 1. Acid phosphomonoesterase activity has been observed in midguts from normal and starved cockroaches. 2. 2. Partially purified acid phosphomonoesterases have two pH optima of 5.2 and 2.8 . 3. 3. Five acid phosphatases can be demonstrated by polyacrylamide gel electrophoresis. 4. 4. Two of these protein bands are non-specific esterases which suggests that three bonafide acid phosphatases are present. 5. 5. The four most active enzymes all reach a concentration maximum 4 days after the removal of food and exhibit maximal activity at pH 5.2 . 6. 6. Only the autophagic vacuole-mitochondria fraction shows increased enzyme activity after midgut homogenates are subjected to differential centrifugation. 7. 7. It is suggested that both phosphatase and esterase activity are contained in the vacuoles and that the increased enzyme activity is due to the increased number of vacuoles.

In view of improved durability, the study of electrocatalyst supports for PEMFCs alternative to carbon is raising notable research interest. In this paper we investigated the oxidation of ethanol on WC-supported electrodeposited Pt, in pristine and aged conditions by: (i) electrochemical measurements, (ii) in situ spectroscopy (FTIR and sum-frequency generation spectroscopy (SFG)) carried out during the electro-oxidation of ethanol and (iii) ex situ synchrotron-based space-resolved photoelectron spectroscopy (SPEM). The complementarity of FTIR and SFG allows an insightful understanding of the electrochemical interface as a function of applied potential and catalyst ageing. In situ FTIR and SFG revealed adsorbed acetate and ethanol, in addition to linearly and bridge-bonded CO and solution-phase CO2. The Stark tuning of CO indicates that it is less strongly bonded to aged electrodes. Quantitative analysis of potential-dependent FTIR and SFG spectra reveals that the population of adsorption sites for CO, acetate and ethanol changes with ageing and correlates with loss of catalytic activity. Changes in catalyst morphology as well as Pt and WC chemical state have been pinpointed by SPEM: electrodeposited Pt nanoparticles tend to agglomerate and the distribution of oxidised and reduced forms of Pt and W correlates with the attack of the catalyst support.

Cobalt/polypyrrole ORR electrocatalysts has been electrochemically synthesized by a potentiostatic anodic/cathodic pulse-plating procedure. The deposition electrochemistry has been studied by cyclic voltammetry and in-situ Micro Raman Spectroscopy complemented with scanning X-ray microscopy and micro-spot X-ray absorption spectroscopy (mu-XAS). Linear sweep voltammetry (LSV) under oxygen reduction has been used to assess the electrocatalytic effect of as-electrodeposited Co/PPy. The obtained results have provided new information about the concomitant electropolymerisation and metal incorporation processes occurring under different pulsed co-electrodeposition conditions, important for optimising the electrosynthesis procedure. The colocation of O and Co, evidenced by the O and Co XRF maps indicates that the Co in the formed composite is in oxidized state and for composites formed at low currents using shorter Co pulses coexistence of both CoO and Co3O4 is evidenced by the Co L-3 XAS spectra. Bimodal Co distribution as micro-grains on a background of nano-grains and co-nulcleation of PPy and Co is evidenced by correlation of Co and N XRF maps.

The control of the doping in nanowires (NWs) is of fundamental importance for the implementation of NW-based devices. A method is presented to obtain local information about doping by monitoring the Fermi-energy position within the bandgap at the surface along single NWs through spatially resolved x-ray photoemission spectroscopy. The experimental results are complemented by theoretical simulations of the carrier profile, taking into account the presence of electronic surface states and quantifying the impact of carrier depletion at the NW surface. This combined approach allows to determine the effect of the incorporation of Si dopants in GaAs NWs following different growth protocols, such as vapor-liquid-solid axial growth or vapor-solid radial growth, and in the resulting core-shell structures and axial junctions. The method also revelaed the strong dependence of the resulting doping on the morphology of the single NW (orientation, shell thickness). This approach can be easily applied to other nanoscale objects, allowing the direct observation of how doping (or junctions, or adsorbates,.) may locally affect the position of the Fermi level at the surface, which is a crucial factor in several application fields, such as photovoltaic and photocatalysis. (C) 2013 AIP Publishing LLC.

Fuel cells are one of the most appealing environmentally friendly devices for the effective conversion of chemical energy into electricity and heat, but still there are key barriers to their broad commercialization. In addition to efficiency, a major challenge of fuel-cell technology is the durability of the key components (interconnects, electrodes, and electrolytes) that can be subject to corrosion or undesired morphology and chemical changes occurring under operating conditions. The complementary capabilities of synchrotron-based soft X-ray microscopes in terms of imaging, spectroscopy, spatial and time resolution, and variable probing depths are opening unique opportunities to shed light on the multiple processes occurring in these complex systems at microscopic length scales. This type of information is prerequisite for understanding and controlling the performance and durability of such devices. This paper reviews the most recent efforts in the implementation of these methods for exploring the evolving structure and chemical composition of some key fuel cell components. Recent achievements are illustrated by selected results obtained with simplified versions of proton-exchange fuel-cells (PEFC) and solid-oxide fuel-cells (SOFC), which allow in situ monitoring of the redox reactions resulting in: 1) undesired deposits at interconnects and electrodes (PEFC); 2) material interactions at the electrode-electrolyte interface (PEFC); 3) release of corrosion products to the electrolyte phase (PEFC, and 4) mass-transport processes and structural changes occurring at the high operation temperatures of SOFC and promoted by the polarization.

Replacement of hydrogen with hydrocarbon fuels in solid-oxide fuel cells (SOFCs) is an appealing alternative for reducing the implementation costs of SOFCs technology, but the electrode stability and susceptibility to carbon deposition still remain important issues to be solved. The present in situ photoelectron microscopy study of a prototype hydrocarbon-fuelled SOFC, operated at 650 °C in C2H4 + H2O gas mixture and voltages in the range 0−3 V, provides insights into morphologychemistry changes of the Ni electrodes and Cr interconnects with decisive impact on the electrochemical activity and durability. The results reveal the combination of thermal and electromigration of Ni across the electrode−electrolyte interface that can cause sensible material losses and structural changes responsible for the deterioration of device performance. The C 1s spectra evidence deposition of C and formation of carbides on the Ni electrodes and Cr interconnects at 650 °C as result of C2H4 dissociation, the process being promoted applying cathodic potential and reversed by switching to anodic potential. Following the attenuation of the C signal under anodic potential, the effect of the stability of different carbides on the reaction rate was observed.

The extraction of the light produced by an organic light emitting diode has been made possible by the use of transparent conductive materials which should have well defined electronic and optical properties. All the requirements are satisfied by indium tin oxide which has rapidly become the most common conductive substrate used for the growth of organic light emitting sources. Atomic force microscope, conventional X-ray photoemission spectroscopy and scanning photoemission spectromicroscopy have been used to investigate the morphology and the chemical properties of commercial thin indium tin oxide films after several treatments commonly used prior to the organic layer growth for smoothing/cleaning/patterning the surface. Unambiguous smoothing effects of the potassium hydroxide-based solutions have not been observed while Si contaminations of the surfaces have been found after the application of different patterning procedures.