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A single-step ultrasonic method (20 kHz) is demonstrated for the complexation of acetylsalicylic acid (ASA)–ZnO–graphene oxide (GO) nanoparticles with an average size of

Tin oxide is a material that attracts attention due to variety of technological applications. The main parameters that influence its properties are morphology, crystalline structure and stoichiometry. Researchers try to develop nanostructured thin films with tunable parameters that would conform its technological applications. Herein, we report on the preparation and characterization of highly porous SnO2 and Pd-doped SnO2 thin films. These films were deposited in the form of nanorods with controllable geometry. Such morphology was achieved by utilizing glancing angle deposition (GLAD) with assisted magnetron sputtering. This arrangement allowed preparation of slanted pillars, zig-zag structure, vertically standing posts, spiral posts and “bush”-like structures. We calculated that slanted pillars feature the highest surface area among the listed. Then, sets of slanted pillars were deposited and studied in more details. Tin oxide films were thoroughly characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoelectron spectroscopy (SRPES). The influence of substrate annealing during the deposition and Pd doping on the morphology, crystalline structure and stoichiometry of the films are discussed. GLAD with assisted magnetron sputtering allowed us to deposit broad range of SnO2 nanostructures while annealing of the substrate during deposition affected the films crystallinity. Also, we found out that doping of the SnO2 films with Pd leads to alloy phase formation. These findings can be applied in variety of applications including gas sensing, catalysis, optics and electronics.

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnO

Small : nano micro (2104356), (2021). doi:10.1002/smll.202104356, Published by Wiley-VCH, Weinheim

The first layer of atoms on an oxide catalyst provides the first sites for adsorption of reactants and the last sites before products or oxygen are desorbed. We employ a unique combination of morphological, structural, and chemical analyses of a model ceria catalyst with different surface terminations under an H2 environment to unequivocally establish the effect of the last layer of atoms on surface reduction. (111) and (100) terminated epitaxial islands of ceria are simultaneously studied in situ allowing for a direct investigation of the structure–reducibility relationship under identical conditions. Kinetic rate constants of Ce4+ to Ce3+ transformation and equilibrium concentrations are extracted for both surface terminations. Unlike the kinetic rate constants, which are practically the same for both types of islands, more pronounced oxygen release, and overall higher reducibility were observed for (100) islands compared to (111) ones. The findings are in agreement with coordination-limited oxygen vacancy formation energies calculated by density functional theory. The results point out the important aspect of surface terminations in redox processes, with particular impact on the catalytic reactions of a variety of catalysts.

We present a study of temperature dependent growth of nano-sized ceria islands on a Cu (100) substrate. Low-energy electron microscopy, micro-electron diffraction, X-ray absorption spectroscopy, and photoemission electron microscopy are used to determine the morphology, shape, chemical state, and crystal structure of the grown islands. Utilizing real-time observation capabilities, we reveal a three-way interaction between the ceria, substrate, and local oxygen chemical potential. The interaction manifests in the reorientation of terrace boundaries on the Cu (100) substrate, characteristic of the transition between oxidized and metallic surface. The reorientation is initiated at nucleation sites of ceria islands, whose growth direction is influenced by the proximity of the terrace boundaries. The grown ceria islands were identified as fully stoichiometric CeO2 (100) surfaces with a (2 × 2) reconstruction.

This work reports the effect of different processing parameters on the structural and morphological characteristics of MoSe2 layers grown by chemical vapour deposition (CVD), using MoO3 and Se powders as solid precursors. It shows the strong dependence of the size, shape and thickness of the MoSe2 layers on the processing parameters. The morphology of the samples was investigated by field emission scanning electron microscopy (FESEM) and the thickness of the deposited layers was determined by atomic force microscopy (AFM). Raman and photoluminescence (PL) spectroscopies were used to confirm the high quality of the MoSe2 layers. Surface composition was examined by photoelectron spectroscopy (XPS). Moreover, the MoSe2/SiOx/Si heterojunctions exhibit diode behaviour, with a rectification ratio of 10, measured at ±2.0 V, which is due to the p-i-n heterojunctions formed at the p-Si/SiOx/MoSe2 interface. A photovoltaic effect was observed with a short circuit current density (Jsc), open circuit voltage (VOC) and efficiency of -0.80 mA/cm2, 1.55 V and 0.5%, respectively. These results provide a guide for the preparation of p-i-n heterojunctions based on few-layer MoSe2 with improved photovoltaic response., Tis work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UID/CTM/04540/2019 and UID/FIS/04650/2019. Part of this work was supported by the COST Action MP1406 “Multiscale in modeling and validation for solar photovoltaics (MultiscaleSolar)”. Te authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and fnancial support under proposal 20182042.

Here, the ability of using p-type tin oxide (SnO

In today´s developed world, there is a huge pressure on increasing the amount of electricity produced by renewable sources. With growing percentage of electricity from wind and solar power plants, new challenges arise. The biggest issue seems to be the instability of generated electricity during the days. Possible solution can be offered by Proton Exchange Membrane Water Electrolyzers (PEM-WE) and Proton Exchange Membrane Fuel Cell (PEM-FC) through electricity-hydrogen-electricity conversion cycle. Although PEM-WE technology is well suited for scale-up, one major drawback – its dependence on noble metal catalysts remains to be solved. Both, Ir on the anode and Pt on the cathode, which are traditionally used, are extremely rare and expensive, thus their partial replacement by other materials can lead to the noticeable decrease of PEM-WE price. More focus is usually laid on the anodic oxygen evolution reaction (OER) which is catalytically much more demanding. Ruthenium catalyst appears to be an interesting alternative due to its high activity towards OER. However, low electrochemical stability of Ru renders it inapplicable in its pure form. This problem can be solved by using mixed iridium-ruthenium catalyst which benefits from stability of iridium and from the lower price and high activity of ruthenium. In this work we present magnetron sputtered thin-film iridium-ruthenium mixed catalyst for the OER on the anode of PEM-WE. Magnetron sputtering is a mean of catalyst deposition which allows the preparation of a thin films of exact concentration and thickness. Moreover, it is also possible to use it on industrial scales. Usage of magnetron sputtering provides several important advantages. Firstly, we are able to cut down the amount of used catalyst significantly -- usually 10 times less than in the case of powder catalyst. Secondly, it is possible to prepare small systems for detailed electrochemical and surface analysis and also bigger systems for testing of our catalysts at real electrolyzer. This allows us to narrow the gap between the model and controlled studies and real industrial systems. In our work, we present four concentration of mixed iridium-ruthenium catalyst prepared by magnetron sputtering. Each catalyst was prepared either on Glassy Carbon electrode, or on Nafion® NR212. Measurement on Nafion® NR212 helps us to pick the industrially most suitable candidate. Measurements on the Glassy Carbon electrodes allows to investigate the activity and stability of given catalysts and correlate it with their structural and chemical properties. Numerous techniques were used, specifically Rotation Disk Electrode (RDE), Potential Electrochemically Impedance Spectroscopy (PEIS), Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). Combination of these techniques revealed that 25:75 Ir:Ru sputtered thin-film catalyst outperforms the benchmark pure Ir counterpart while retaining comparable electrochemical stability. Figure 1

The stability and the conversion of atomically dispersed Pt2+ species to sub-nanometer Pt particles have been investigated as a function of the Sn concentration in Pt–CeO2 films by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, and angle-resolved X-ray photoelectron spectroscopy in combination with density functional calculations. The deposition of Sn onto the Pt–CeO2 films triggers the reduction of Ce4+ cations to Ce3+ yielding Sn2+ cations. Consecutively, the redox coupling between the Ce3+ and Pt2+ species triggers the reduction of Pt2+ species yielding sub-nanometer Pt particles. The onset of reduction of Pt2+ species is directly related to the concentration of Ce3+ centers which, in turn, is controlled by the concentration of Sn2+ cations in the Pt–CeO2 film. On average, the formation of 6Ce3+ centers corresponding to the adsorption of 3Sn atoms gives rise to the reduction of one Pt2+ species. The analysis of the depth distribution of Sn atoms in the Pt–CeO2 films revealed preferential adsorption of Sn2+ at the surface followed by diffusion of Sn2+ ions into the bulk at higher Sn coverages. Density functional modeling suggested that the adsorption of three Sn atoms in the vicinity of the Pt2+ species results in a rearrangement of the local coordination accompanied by substantial destabilization of the Pt2+ species followed by its conversion to Pt0 atoms. The formation of sub-nanometer Pt particles is coupled with re-oxidation of two Ce3+ centers per one Pt2+ species reduced. Annealing of the Pt–CeO2 films in the presence of metallic Sn also leads to the reduction of the Pt2+ species due to thermally triggered oxidation of metallic Sn residues followed by diffusion of Sn2+ into the bulk. Annealing of the Pt–CeO2 films to temperatures above 600 K results in a loss of Sn yielding sub-nanometer Pt particles supported on nearly stoichiometric and Sn-free CeO2 films.

Reaktivní magnetronové naprašování s hlubokými oscilacemi, pulzní kontrolou toku reaktivního plynu a vstupem reaktivního plynu, orientovaným k substrátu a umístěným v zóně hustého plazmatu před Mo terčem, bylo použito pro nízkoteplotní (< 120 °C) přípravu vrstev MoOx a MoOxNy s 2,5 < x < 3,0 a y < 0,2. Vysvětlujeme výhody použité depoziční techniky umožňující hladkou a reprodukovatelnou kontrolu složení vrstev a tím i jejich struktury a vlastností. Speciální pozornost věnujeme silnému dopadu malého snížení x ve vrstvách MoOx a malého zvýšení y ve vrstvách MoOxNy na jejich optické a elektrické vlastnosti, které přímo souvisí s proměnnou elektronovou strukturou těchto vrstev. Diskutujeme možné aplikace těchto vrstev v oblasti solárních článků, organické elektroniky a lithium-iontových baterií. Reactive deep oscillation magnetron sputtering with a pulsed reactive gas flow control and to-substrate reactive gas injection into the high-density plasma in front of the sputtered Mo target was used for a low-temperature (< 120 °C) preparation of MoOx and MoOxNy films with 2.5 < x < 3.0 and y < 0.2. We explain the advantages of this deposition technique, allowing us to control smoothly and reproducibly the film composition and thus the film structure and properties. Special attention is paid to the strong effect of slightly decreasing x in MoOx films and slightly increasing y in MoOxNy films on their optical and electrical properties which are directly related to varying electronic structure of the films. We discuss possible applications of these films in the field of solar cells, organic electronic devices and lithium-ion batteries.

Reversible structural changes of As-rich As–Se nanolayers occurring during in situ thermal annealing and above-bandgap laser illumination were studied by synchrotron radiation photoelectron spectroscopy. It was found that the first thermal annealing of As56Se44 nanolayers led to a decrease of the concentration of As that can be connected with evaporation of more volatile As-rich fractions from the surface. This process is accompanied by structural rearrangements in the nanolayers. In situ green laser illumination of annealed samples causes an increase in the concentration of homopolar As–As bonds associated with As-Se2As s.u., while the opposite effect was detected during further thermal treatment. These processes appeared to be reversible for three sequences of annealing and illumination. The observed effect of the reversible photoinduced structural modification is discussed in detail, and possible applications as an active optical medium for photonics are proposed.

Due to promising catalytic properties of cerium oxide, such based materials have been recognized as a suitable candidate for catalysts at the anode side of fuel cells. In order to achieve the largest active surface area, a commercially available gas diffusion layer used as Pt-CeOx catalyst support has been enhanced by the application of a CNx interlayer. Herein, the surface morphology modification, into the form of individual needles, observed by Scanning Electron Microscopy and Transmission Electron Microscopy, is presented. Furthermore, spectroscopy techniques, namely X-ray Photoelectron Spectroscopy, Electron Energy Loss Spectroscopy, and Energy Dispersive X-ray Spectroscopy reveal important role of nitrogen incorporated in the CNx interlayer that enables formation of very porous surface structures. In addition, it is demonstrated that tuning of catalyst film morphology provides a viable strategy towards higher performance in the PEMFC tests, complemented by better corrosion resistance of CNx interlayers under the start-up conditions of fuel cells.

In this study, PtxNi100-x (0 ≤ x ≤ 100) alloy catalysts were prepared using magnetron co-sputtering in order to reveal the correlation between their composition and catalytic properties as a cathode in proton exchange membrane fuel cells (PEMFCs). Fine power adjustment on magnetrons allowed to deposit alloys with precise composition and at the same time with identical thickness of 10 nm and similar morphologies. The powerful surface characterization techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) were applied to thoroughly investigate the catalytic layers. The desired composition of the films was confirmed by EDX and XRD results. All deposited layers showed similar morphologies with vertical and horizontal roughness of ~0.35 nm and ~6 nm, respectively. XRD confirmed the alloy nature of the films with one crystalline phase of the fcc PtNi. The PtxNi100-x alloys showed significant enhancement of specific power (SP) comparing to the pure Pt in PEMFC. Particularly, the Pt25Ni75 sample exhibited the highest SP of 24 kW/g(Pt). This catalyst showed a 2- and almost 10-fold improvement in SP with respect to the Pt film and commercial nanopowder Pt catalyst, respectively.

Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F−–Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.

This work reports thermal annealing induced effect on the structural, optical, chemical and ferroelectric properties of ion-beam sputtered lead-free ferroelectric 0.5 Ba(Zr0.2Ti0.8)O3 – 0.5 (Ba0.7Ca0.3)TiO3-δ (0.5BZT–0.5BCT) thin films. X-ray diffraction studies reveal that the tetragonality increases with the annealing temperature (Ta), while photoluminescence and X-ray photoelectron spectroscopy studies confirm that this effect is associated with the annihilation of the oxygen vacancies as well as changes in the Ba2+ coordination. The films annealed at 750 °C show a remarkable remnant polarization of Pr = 45.0 μC/cm2, with a coercive field of 32 kV/cm. The temperature dependence of the spontaneous polarization of the 0.5BZT–0.5BCT film reveals a mean field behavior of the polarization and the fatigue study reveals that Pr only decreases 3% after passing 109 cycles. Therefore the high remnant polarization and its high Pr stability make these films as promising candidates for memory applications, Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UID/FIS/04650/2013; (ii) Project Norte-070124-FEDER-000070 Nanomateriais Multifuncionais. The author J.P.B.S. is grateful for financial support through the FCT Grant SFRH/BPD/92896/2013. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal CERIC-ERIC-20167010. The author K.C. Sekhar acknowledge UGC and DST-SERB, Govt. of India for the funds through the grant no. F.4-5(59-FRP/2014(BSR)) and ECR/2017/000068, info:eu-repo/semantics/publishedVersion

A novel and simple method is presented for the preparation of a well-defined CeO2(100) model system on Cu(111) based on the adjustment of the Ce/O ratio during growth. The method yields micrometer-sized, several nanometers high, single-phase CeO2(100) islands with controllable size and surface termination that can be benchmarked against the known (111) nanostructured islands on Cu(111). Furthermore, we demonstrate the ability to adjust the Ce to O stoichiometry from CeO2(100) (100% Ce4+) to c-Ce2O3(100) (100% Ce3+), which can be readily recognized by characteristic surface reconstructions observed by low-energy electron diffraction. The discovery of the highly stable CeOx(100) phase on a hexagonally close packed metal surface represents an unexpected growth mechanism of ceria on Cu(111), and it provides novel opportunities to prepare more elaborate models, benchmark surface chemical reactivity, and thus gain valuable insights into the redox chemistry of ceria in catalytic processes.

Structural transitions affect electronic structure of materials and consequently their catalytic properties. We report the observation of faceting of a low index metal surface at an oxide–metal interface in a catalytically relevant system of ceria on Cu(110). We observe formation of (13 13 1) facets on the Cu(110) surface covered by ceria upon annealing above 500 °C. The faceting transition occurs in spite of a weak adsorbate–substrate interaction, which manifests itself in ceria adopting a carpet-like growth mode. We rationalize the surface faceting under such conditions by oxide overlayer-induced modification of the roughening temperature of Cu(110). We describe the carpet-like ceria film in terms of elasticity theory and show that the specific structure of the ceria supported on Cu(13 13 1) can lead to a periodic modulation of the electronic structure of the ceria–copper interface. The reported structural transition indicates that surface faceting of metal can occur at the oxide–metal interface at rela...

We have conducted resonant angle-resolved photoemission spectroscopy of well-defined ${\mathrm{CeO}}_{2}$(111) and $c--{\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$(111) model surfaces, revealing distinct $f$ contributions in the valence band of the two compounds. In conjunction with density functional theory calculations, we show that the $f$ contribution in ${\mathrm{CeO}}_{2}$ is of a covalent nature, arising from hybridization with the $\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$ bands. In contrast, $c--{\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ exhibits an almost nondispersive $f$ state at 1.3 eV, which is indicative of almost negligible c-f hybridization.

Changes of stoichiometry in reducible oxides are inevitably accompanied by changes of the oxide structure. We study the relationship between the stoichiometry and the structure in thin epitaxial fi...

Thin films of reduced ceria supported on metals are often applied as substrates in model studies of the chemical reactivity of ceria based catalysts. Of special interest are the properties of oxygen vacancies in ceria. However, thin films of ceria prepared by established methods become increasingly disordered as the concentration of vacancies increases. Here, we propose an alternative method for preparing ordered reduced ceria films based on the physical vapor deposition and interfacial reaction of Ce with CeO2 films. The method yields bulk-truncated layers of cubic c-Ce2O3. Compared to CeO2 these layers contain 25% of perfectly ordered vacancies in the surface and subsurface allowing well-defined measurements of the properties of ceria in the limit of extreme reduction. Experimentally, c-Ce2O3(111) layers are easily identified by a characteristic 4 x 4 surface reconstruction with respect to CeO2(111). In addition, c-Ce2O3 layers represent an experimental realization of a normally unstable polymorph of Ce2O3. During interfacial reaction, c-Ce2O3 nucleates on the interface between CeO2 buffer and Ce overlayer and is further stabilized most likely by the tetragonal distortion of the ceria layers on Cu. The characteristic kinetics of the metal-oxide interfacial reactions may represent a vehicle for making other metastable oxide structures experimentally available.

Proper consideration of length-scales is critical for elucidating active sites/phases in heterogeneous catalysis, revealing chemical function of surfaces and identifying fundamental steps of chemical reactions. Using the example of ceria thin films deposited on the Cu(111) surface, we demonstrate the benefits of multi length-scale experimental framework for understanding chemical conversion. Specifically, exploiting the tunable sampling and spatial resolution of photoemission electron microscopy, we reveal crystal defect mediated structures of inhomogeneous copper-ceria mixed phase that grow during preparation of ceria/Cu(111) model systems. The density of the microsized structures is such that they are relevant to the chemistry, but unlikely to be found during investigation at the nanoscale or with atomic level investigations. Our findings highlight the importance of accessing micro-scale when considering chemical pathways over heteroepitaxially grown model systems.

SO2 poisoning of methane oxidation over alumina-supported, Pd@CexZr1−xO2 nanoparticle catalysts was systematically studied by means of advanced PhotoElectron Spectroscopy (PES) methods. The Pd@CexZr1−xO2 units were synthesized and deposited on two modified-alumina supports, i.e. high surface area modified alumina and a model alumina prepared by Atomic Layer Deposition (ALD) of alumina on Indium Tin Oxide (ITO)/quartz slides. The model support was designed to be suitable for PES analysis and was stable to high temperature treatments (850 °C). Characterization of the high-surface-area (HSA) catalysts by X-Ray Diffraction (XRD), N2 physisorption, CO chemisorption and Transmission Electron Microscopy (TEM) indicated formation of CeO2–ZrO2 (CZ) mixed-oxide crystallites that stabilize the Pd active phase against sintering. Correlation of methane-oxidation rates with PES results demonstrated two distinct mechanisms for deactivation by SO2. Below 450 °C, the presence of SO2 in the feed led to partial reduction of the active PdO phase and to the formation of sulfates on the Pd. Above 500 °C, poisoning by SO2 was less severe due to spillover of the sulfates onto the oxide promoter. Pd@ZrO2 catalysts showed the best resistance to SO2 poisoning, outperforming analogous Pd@CZ mixed-oxide catalysts, because there was less sulfate formation and the sulfates that did form could be removed during regeneration. The authors acknowledge CERIC-ERIC for open access to instrumentation and user support. This paper was also made possible by a NPRP Grant #6-290-1-059 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. Scopus

Aluminum oxide structures were grown on Cu–9 at.%Al(111) single crystals. Usually alumina grows in the form of an epitaxial thin film. The process is based on Al atom segregation and subsequent oxidation of the Al topmost surface. Strong temperature dependence of the alumina growth mode was observed during the oxidation of a Cu–9 at.%Al single crystal. In this work we have reported for the first time the formation of alumina wire-like nanostructures on the substrate surface during high-temperature oxidation at low pressure. The nanowire growth was observed during substrate annealing at 1070 K while annealing at 910 K led to the formation of a flat and continuous thin alumina layer. Morphology, chemical composition, and structure characterization of the prepared nanostructures was done by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The experimental results point to the formation of Θ alumina phase nanowires due to surface segregation of Al atoms. Mechanism of alumina nanostructure formation is discussed. The experiment clearly showed that nanowire oxide structure growth can be obtained by a bottom-up process with a mass transfer from the substrate to the assembled nanostructure.

Silver has rarely been considered as the catalyst for CO oxidation, although it has been recognized to be very active in several partial oxidation reactions such as ethylene epoxidation and formaldehyde synthesis. It is generally believed that a metal support interaction plays an important role in catalytic processes. Therefore in our study, we examined electronic and adsorption properties of cerium deposited onto a polycrystalline silver substrate. Layers of approximately one monolayer of cerium deposited on a clean silver substrate were examined in situ using surface-sensitive techniques—by XPS, ultraviolet photoelectron spectroscopy (UPS) and low energy ion scattering (LEIS). CO molecular adsorption was observed by UPS and LEIS; experimental results exhibited CO adsorption on Ce atoms sites. Oxygen adsorption on deposited layers led to a strong oxidation; stoichiometry of oxidized layers was given by amount of adsorbed oxygen and by temperature. Copyright © 2011 John Wiley & Sons, Ltd.

The super-bandgap laser irradiation of the in situ prepared As-S chalcogenide films was found to cause drastic structural transformations and unexpected selective diffusion processes, leading to As enrichment on the nanolayer surface. Excitation energy dependent synchrotron radiation photoelectron spectroscopy showed complete reversibility of the molecular transformations and selective laser-driven mass transport during "laser irradiation"-"thermal annealing" cycles. Molecular modeling and density functional theory calculations performed on As-rich cage-like clusters built from basic structural units indicate that the underlying microscopic mechanism of laser induced transformations is connected with the realgar-pararealgar transition in the As-S structure. The detected changes in surface composition as well as the related local and molecular structural transformations are analyzed and a model is proposed and discussed in detail. It is suggested that the formation of a concentration gradient is a result of bond cleavage and molecular reorientation during transformations and anisotropic molecular diffusion.

Platinum shows excellent catalytic activity in electrochemical oxidation of methanol. It is widely used in direct methanol fuel cells, but it is readily poisoned by CO-like intermediates generated in methanol activation process. To increase Pt CO tolerance, oxophilic metals such as Ru or Ni are incorporated into Pt. In our model study we present results of the adsorption and decomposition of methanol on a Pt-Ni ordered surface alloy prepared by Pt evaporation on Ni(111) surface, examined by conventional and synchrotron radiation XPS. Methanol adsorbed at low temperature formed adsorbate multilayers, which were consecutively desorbed upon heating to 600 K. Reaction intermediates arising during desorption were measured. Reaction pathways are discussed and compared with those obtained on a clean Ni{111} single crystal.

The interaction of Pt with CeO 2 in Pt-doped cerium oxide layers deposited on a Si wafer at normal and grazing incidence, and on multiwall carbon nanotubes (MWCNTs), was investigated by using X-ray photoelectron spectroscopy (XPS). 30-nm-thick Pt-doped CeO 2 layers were deposited by rf-magnetron sputtering of a composite CeO 2 -Pt target. XPS showed formation of cerium oxide with completely ionized species Pt 2+,4+ embedded in the film. The Pt 2+ /Pt 4+ ratio depends on the deposition angle and increases in the case of the film deposition on the MWCNTs. This behavior was explained by the dependence of the poiycrystalline film grain morphology on a deposition angle.

The photoelectron spectroscopy (PES) study compares electronic states in three different ceria thin film surfaces prepared on a Cu(111) single-crystal surface by vapour deposition under different conditions: at 250 °C, at room temperature and finally Au-doped ceria film obtained by simultaneous deposition of Au and CeO 2 at room temperature (RT). Electronic properties of the layers and interaction of gold with CeO 2 were investigated using synchrotron-radiation-excited PES and resonant photoemission (Ce 4d → 4f transitions). We observed partial Ce 4+ → Ce 3+ reduction induced by the decrease of deposition temperature to RT instead of 250 °C and also by doping ceria with gold, accompanied by a 4f resonance enhancement of the Ce 3+ species. In the case of the Au-doped sample the surface reduction degree is stronger and can be explained by the possible creation of a new ionic Au + state observed in the Au 4f spectra.

We report a systematic evaluation of the influence of the use of nitric acid at elevated temperature (80 degrees C) as purification and functionalization treatment for four different types of multi wall carbon nanotubes (MWCNTs) and for carbon microparticles upon their physico-chemical properties. We used BET, Raman spectroscopy, high resolution X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy measurements for MWCNTs characterization. We found that nitric acid treatment significantly changes physico-chemical properties of MWCNTs and that these changes vary significantly between different MWCNTs. Therefore we urge researchers to be careful when relying on the physico-chemical properties measured on different MWCNTs samples.

Photoelectron spectroscopy at different photon energies was used to optimize the photoexcitation cross section for valence band study of diamond-like hydrogenated carbon films. The electronic states of diamond-like carbon (DLC) were studied by synchrotron radiation photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p–π band in relation to the sample annealing and ion bombardment amorphization. The p–π band of the annealed DLC was characterized by localized pz states whilst the formation of the amorphous carbon surface was accompanied by appearance of the delocalized pz states in the gap. Secondary ion mass spectrometry and thermal desorption spectroscopy showed that sample annealing was accompanied by hydrogen content decrease.

We have studied Pd–Sn layers with different composition prepared by magnetron sputtering. Layers were sputtered onto Al 2 O 3 and SiO 2 substrates and studied by X-ray photoelectron spectroscopy (XPS). Spectra confirmed that after vacuum annealing residual oxygen and carbon have been removed and bimetallic bonds have been created. The shift of Pd 3d 5/2 core level to higher binding energy followed by the peak narrowing in dependence on the composition was observed, accompanied by the shift of the Pd 4d in the valence band region, induced by hybridization of Pd-d and Sn-s,p states. Experiments carried out on a gas-flow reactor indicate increasing temperature of the CO oxidation with tin ratio in the alloy.

The Au/Ti(0 0 0 1) adsorption system was studied by low energy electron diffraction (LEED) and photoemission spectroscopy with synchrotron radiation after step-wise Au evaporation onto the Ti(0 0 0 1) surface. For adsorption of Au at 300 K, no additional superstructures were observed and the (1 × 1) pattern of the clean surface simply became diffuse. Annealing of gold layers more than 1 ML thick resulted in the formation of an ordered Au–Ti surface alloy. Depending on the temperature and annealing time, three surface reconstructions were observed by LEED: (√3 × √3) R30°, (2 × 2) and a one-dimensional incommensurate (√3 × √3) rectangular pattern. The Au 4f core level and valence band photoemission spectra provided evidence of a strong chemical interaction between gold and titanium. The data indicated formation of an intermetallic interface and associated valence orbital hybridization, together with diffusion of gold into the bulk. Au core-level shifts were found to be dependent on the surface alloy stoichiometry.

We have studied the Sn/Pd(1 1 0) adsorption system by synchrotron radiation photoelectron spectroscopy and low-energy electron diffraction (LEED). For room temperature evaporation, two surface reconstructions were observed: c(2 × 2) and (3 × 1), corresponding to about 0.5 ML and 0.75 ML of Sn adlayer coverage. The Pd 3d and Sn 4d core levels as well as valence band spectra indicate a strong chemical interaction between Sn and Pd, and the formation of an intermetallic interface. Structural models are proposed for both of these phases based on the photoemission and CO adsorption results. We show that at coverage higher than 0.7 ML, tin is alloyed with the Pd crystal forming a subsurface layer of Pd–Sn intermetallic compound of stoichiometry which varies with tin coverage. CO adsorption occurs only at low temperature (120 K) and depends on the Sn coverage and reconstruction of the Pd(1 1 0) surface. We estimate the CO adsorption energy for the c(2 × 2)- and (3 × 1)-Sn/Pd(1 1 0) surfaces to be reduced by 40% compared to the clean palladium (1 1 0) surface.

Carbon monoxide (CO) adsorption properties of Pd/Al systems have been studied using X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS) and static secondary ion mass spectroscopy (SSIMS) under UHV conditions. Measured XPS and TDS spectra were compared to that of clean bulk metals (Pd, Al). Pd adlayers, prepared by vacuum evaporation onto a pure polycrystalline Al surface, exhibited a strong interaction with Al atoms resulting in formation of a Pd–Al alloy of a noble metal-like electronic structure. The shifts of the Pd 3d core levels and the Pd 4d-band centroid toward higher binding energies due to bimetallic bond formation were observed. The CO TDS spectra consisted of two desorption peaks, both lying lower than the one typical for a Pd foil, indicating distinct weakening of the Pd–CO chemisorption bond. Partial CO dissociation on the Pd/Al surface during adsorption/desorption cycles, accompanied by CO 2 and H 2 O production, was observed. CO dissociation caused creation of Pd–C and Al–O chemical bonds on the Pd/Al surface resulted in weakening of the Pd–Al bimetallic bond.

Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by synchrotron radiation photoelectron spectroscopy using photon excitation energies of 600, 250 and 73 eV. Depth resolved results were compared to the results of the SIMS profiling. The measurements confirmed the disappearance of the superficial oxide layer covering the air-exposed Zr–V surfaces via its progressive reduction during the thermal activation. The depth sensitive results showed that the activated getter surface is covered by a residual zirconium sub-oxide.

In this work the study of a redox process on Pd/SnOx system by means of X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) is presented. SnOx substrates were prepared by spray pyrolysis onto Si(1 1 1). Palladium ultra-thin films were evaporated in UHV chamber and then stabilised in air at 720 K for 2 h. Results obtained after thermal treatment in 1% H2 containing air and in pure air showed the reversible change in palladium chemical state.

SnO 2 system is known to be very universal in gas sensing applications. Sensing properties can be improved by adding of a small amount of transition metals. The exact mechanism of this enhancement is not known yet. In this work we used X-ray photoelectron spectroscopy to study the chemical state changes during heating in usual and hydrogen containing atmosphere on Pd-doped SnO 2 powder prepared by microwave irradiation wet method. Reversible oxidation and reduction of Pd additive during the treatment were observed. We found out a dependence of the redox process on heating temperature and gas mixture proportion.

Polycrystalline Ni 3 Al alloy surface was investigated during CO adsorption–desorption experiments by means of X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) and temperature programmed desorption (TPD). It was shown that CO partially dissociates giving nickel bonded carbon and carbon monoxide species and aluminum bonded oxygen. Thermal desorption was characterized by both low temperature CO desorption peaks typical for Ni–Al alloy, and high temperature one of highly reactive sites with lower CO dissociative barrier.

Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by photoelectron spectroscopy using two photon excitation energies of 600 eV (synchrotron light) and 1253.6 eV (Mg Kα laboratory source). During the activation by heating from 120 to 320 °C, the adsorbed carbon was transformed to metal carbides and diffused to the subsurface region.

The metal–substrate and metal–metal interactions (MSI, MMI) represent important effects which can determine properties of supported catalysts. We investigated Pd–Al bimetallic interactions of Pd thin films vapor deposited onto non-stoichiometric aluminum oxide surfaces by means of X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). The formation of a Pd–Al surface alloy phase exhibiting noble metal-like electronic structure was observed. Changes of the Pd 3d and Pd 4d photoemission features and a modification of surface stoichiometry as a function of degree of aluminum surface oxidation as well as during CO adsorption–desorption cycles are discussed.

Thin films of the Zr–V getter alloy were prepared on stainless steel substrates using magnetron sputtering. The getter surface chemical composition was investigated by X-ray photoelectron spectroscopy (XPS) for four air exposure/activation cycles. The experimental results show the decrease of the activation capacity after several oxidation/activation cycles. The adsorbed carbon is transformed simultaneously to zirconium and vanadium carbides, which are inactive for both oxidation and reduction processes. Higher affinity of V to carbon atoms was confirmed by secondary ion mass spectroscopy (SIMS) study of CO adsorption.