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For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field emission scanning electron microscopy (FESEM), and current density–voltage (J–V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP‐XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J‐V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J‐V sweeps., Solar cell deactivation: For similar exposures, the soaking of light proves more detrimental to the perovskite film than water vapor. Absorbed photons create Frenkel defects in the perovskite crystal. The number of created Frenkel defects depends strongly on the used illumination. The higher the photon flux, the higher the creation of Frenkel defects, and thus the stronger the degradation of power conversion efficiency and the stronger the hysteresis in the J–V characteristics.

In this work, we present a complex study of photoregeneration of a zinc phthalocyanine (ZnPc) sensor by illumination from light-emitting diodes (LEDs). It includes an investigation of photoregeneration effectivity for various wavelengths (412–723 nm) of incident light carried out at sensor operating temperatures of 55 °C. It is demonstrated that the efficiency of photoregeneration is increasing with a decrease in the light wavelength. In the region of longer wavelengths (723–630 nm), the regeneration degree (RD) was low and ranged from 12% to 15%. In the region of shorter wavelengths (518–412 nm), the RD rose from 35% for 518 nm to 94% for 412 nm. The efficiency of photoregeneration is also shown to be higher in comparison with the temperature regeneration efficiency. In order to understand the chemism of photoregeneration processes, the electrical measurements are supplemented with Raman and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) studies. The spectroscopic results showed that nitrogen dioxide bonds to the Zn atom in ZnPc in the form of NO2− and NO−, i.e., partial decomposition of NO2 molecules occurs during the interaction with the surface. NAP-XPS spectra proved that light illumination of the ZnPc surface is essential for almost complete desorption of NOx species. At the same time, it is demonstrated that in case of long-time exposure or exposure of a ZnPc chemiresistor with a high concentration of NO2, the oxygen, released due to the NO2 decomposition, slowly but irreversibly oxidizes the layer. This oxidation process is most probably responsible for the sensor deactivation observed in sensor experiments with high NO2 concentrations. Based on these studies, the mechanism of nitrogen dioxide interaction with zinc phthalocyanine both under LED illumination and in dark conditions is proposed, and a special method for the sensor operation called “constant exposure dose” is established.

Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt3Y films sputtered from an alloy target. The Pt3Y catalyst surface is investigated using synchrotron radiation X-ray photoelectron spectroscopy before and after acid treatment. A new substoichiometric oxide component is identified. The oxide layer extends into the alloy surface, and although it is not completely removed with acid treatment, the catalyst still achieves the expected high ORR activity. Other surface-sensitive techniques show that the sputtered films are smooth and bulk X-ray diffraction reveals many defects and high microstrain. Nevertheless, sputtered Pt3Y exhibits a very high activity regardless of the film's oxide content and imperfections, highlighting Pt3Y as a promising catalyst. The obtained results will help to support its integration into fuel cell systems.

This article presents an investigation of the sensing properties of chemiresistors based on Cu2O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conven...

Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al2 O3 ) film on top of a methyl ammonium lead triiodide (CH3 NH3 PbI3 ) absorber showed excellent stability of the power conversion efficiency (PCE) over a long time. Under the same environmental conditions (for 355 d), the average PCE of solar cells without the ALD layer decreased from 13.6 to 9.6 %, whereas that of solar cells containing 9 ALD cycles of depositing RT-ALD-Al2 O3 on top of CH3 NH3 PbI3 increased from 9.4 to 10.8 %. Spectromicroscopic investigations of the ALD/perovskite interface revealed that the maximum PCE with the ALD layer is obtained when the so-called perovskite cleaning process induced by ALD precursors is complete. The PCE enhancement over time is probably related to a self-healing process induced by the RT-ALD-Al2 O3 film. This work may provide a new direction for further improving the long-term stability and performance of perovskite solar cells.

This study used non-reactive magnetron sputtered polycrystalline cerium oxide thin films as model substrates to mimic the surface morphology of cerium oxide nanoparticles. We investigated the interaction between dextran and polycrystalline cerium oxide surfaces by atomic force microscopy, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy. A simplified sample preparation method probing solid-liquid interface was set up by conducting aqueous adsorption procedures in an argon-filled glove bag connected to an ultra-high vacuum chamber. We found that the adsorption of dextran from aqueous solution onto the polycrystalline cerium oxide surface leads to a mutual charge transfer between dextran and cerium ions, creating a surface accumulation of Ce3+. In the aqueous environment, dextran hydroxyl groups adsorbs on the polycrystalline cerium oxide surface competitively with the dissociated hydroxyl groups from water. By investigating glucose adsorbed onto polycrystalline ceria prepared by physical vapor deposition, we further confirmed the role of hydroxyl groups from polysaccharide during interaction with ceria. Thermal annealing of the dextran adsorbed polycrystalline cerium oxide surface results in desorption of weakly bonded dextran below 100 °C and decomposition of dextran above 100 °C.

A Pt-Co nanoalloy thin film catalyst was prepared by using simultaneous magnetron sputtering of Pt and Co. The catalyst was characterized during accelerated degradation test using in-situ electrochemical atomic force microscopy complemented with ex-situ techniques such as energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and synchrotron radiation photoelectron spectroscopy. The combined results gave the full step-by-step picture of the catalyst behavior during the aging test.

Recently we have tested a magnetron sputtered Pt-Co catalyst in a hydrogen-fed proton exchange membrane fuel cell and showed its high catalytic activity for the oxygen reduction reaction. Here we present further investigation of the magnetron sputtered Pt-Co thin film catalyst by both experimental and theoretical methods. Scanning electron microscopy and transmission electron microscopy experiments confirmed the nanostructured character of the catalyst. The surface composition of as-deposited and annealed at 773 K Pt-Co films was investigated by surface analysis techniques, such as synchrotron radiation photoelectron spectroscopy and X-ray photoelectron spectroscopy. Modeling based on density functional theory showed that the surface of 6 nm large 1:1 Pt-Co nanoparticles is almost exclusively composed of Pt atoms (>90%) at typical operation conditions and the Co content does not exceed 20% at 773 K, in agreement with the experimental characterization of such films annealed in vacuum. According to experiment, the density of valence states of surface atoms in Pt-Co nanostructures is shifted by 0.3 eV to higher energies, which can be associated with their higher activity in the oxygen reduction reaction. The changes in electronic structure caused by alloying are also reflected in the measured Pt 4f, Co 3p and Co 2p photoelectron peak binding energies.

The progress in the design of a perspective alloy catalyst relies on correct interpretation of its photoelectron spectra. Particularly, X-ray photoelectron spectroscopic (XPS) analysis of platinum-copper alloys represents a serious challenge for both qualitative and quantitative analyses due to the complexity of the Pt 4f spectra arising from its overlapping with the Cu 3p region. Studies regarding XPS investigation of Pt-Cu alloys often ignore the Cu 3p contribution while fitting Pt 4f spectra, which leads to partially incorrect interpretation of measured XPS data. This is most noticeable for alloys containing more than 50 % of platinum where the low-intensity Cu 3p core levels can be hidden under a more intense contribution of Pt 4f. In this work, we present the correct way of processing photoemission spectra of such systems. First, we thoroughly examine the XPS Cu 3p spectra of pure copper surfaces of different oxidation states, namely Cu°, Cu+, and Cu2+. Then, the obtained results are applied for the fitting of Pt 4f spectra of both metallic and oxidized Pt-Cu systems. The precise curve-fitting and data analysis procedure showcased in this study can be utilized to eliminate uncertainties in the analysis of Pt-Cu photoemission spectra.

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.

In this work changes in surface chemistry and morphology of PtNi alloy induced by redox environments were investigated by photoelectron spectroscopy, atomic force microscopy and substantiated by theoretical calculations. PtNi was exposed to alternating oxidation (O2) and reduction (H2) gaseous atmospheres at different temperatures (298, 373, 523 K) to simulate its behavior as a cathode catalyst in proton exchange membrane fuel cells. Results showed that the PtNi alloy undergoes surface nickel enrichment under switched reactive environments. The most significant effects occurred at 523 K, when the Ni/Pt surface atomic ratio increased from 0.8 to 6.7 after five redox cycles, while the bulk Ni/Pt value reached 2.3. Along with compositional changes catalyst coarsening was observed. The revealed behavior of the PtNi alloy allows a better understanding of the structural dynamics of a bimetallic catalyst during its interaction with reactive environments that is a prerequisite for development of efficient fuel cell catalyst.

CO oxidation on platinum oxide deposited by magnetron sputtering on flat (Si) and highly porous (multi-walled carbon nanotubes, MWCNT) substrates were examined using X-ray photoelectron spectroscopy, scanning tunneling microscopy, temperature-programmed desorption and temperature-programmed reaction in both UHV and ambient pressure conditions. Platinum in the freshly deposited thin film is present entirely in the 4+ oxidation state. The intrinsic CO oxidation capability of such catalyst proved to be significantly higher under approx. 480 K than that of pure platinum, presumably due to the interplay between metallic and cationic platinum entities, and the reaction yield can be further enhanced by increasing effective surface area when MWCNT is used as a support. The thermo-chemical stability of the platinum oxide, however, has its limitations as the thin film can be gradually thermally reduced to metallic platinum (with small residuum of stable Pt2+ species) and this process is further facilitated in the presence of reducing CO atmosphere.

The high catalytic activity of Pt-Co nanoalloys in oxygen reduction and other reactions is usually attributed to their Pt-rich surfaces. However, identification of the precise near-surface structure is by no means easily achievable experimentally. In this work we systematically analyzed the chemical ordering and surface composition of PtXCo(79-X) and PtXCo(140-X) bimetallic nanoparticles by means of a recently developed method based on topological energy expressions and electronic structure calculations. Pt is found to segregate on the surface, especially on corner and edge sites, forming a one atomic layer thick skin independent of the size and composition of the nanoparticle. In turn, the subsurface shell of the particle is composed mostly of Co, whereas the core area has a mixed composition, which depends on the overall stoichiometry. The formation of an outer Pt shell is corroborated by thoroughly analyzed data of X-ray photoelectron spectroscopy experiments performed with various photon energies on annealed Pt-Co particles prepared in vacuum by magnetron sputtering. The core-shell structure of Pt-Co particles is calculated to be more stable than the respective L10 structure. The obtained topological energy expressions are shown to depend only very moderately on the nanoparticle size, which allowed us to apply them to determine the ordering in ∼4 nm big PtXCo(1463-X) species. The presented results deepen our understanding of the intrinsic structure of Pt-Co nanoparticles depending on their size and composition.

Interfacial properties including configuration, porosity, chemical states, and atomic diffusion greatly affect the performance of supported heterogeneous catalysts. Hard X-ray photoelectron spectroscopy (HAXPES) can be used to analyze the interfaces of heterogeneous catalysts because of its large information depth of more than 20 nm. We use HAXPES to examine Pt-doped CeO2 and related thin film catalysts evaporated on Si, carbon, and carbon nanotube substrates, because Pt-doped CeO2 has great potential as a noble metal-based heterogeneous catalyst for fuel cells. The HAXPES measurements clarify that the dopant material, substrate material, and surface pretreatment of substrate are important parameters that affect the interfacial properties of Pt-doped CeO2 and related thin film catalysts. Another advantage of HAXPES measurement of heterogeneous catalysts is that it can be used for chemical analysis of trace elements by detecting photoelectrons from deep core levels, which have large photoionization cross-sections in the hard X-ray region. We use HAXPES for chemical analysis of trace elements in Pd nanoparticle catalysts immobilized on sulfur-terminated substrates and Pt3Ni nanoparticle catalysts enveloped by dendrimer molecules.

The elevated price of Pt limits the large-scale implementation of commercial proton exchange membrane fuel cells, which effectively convert chemical energy into electricity. In order to increase the cost-efficiency in proton-exchange membrane fuel cells, we have designed a family of novel anode catalysts consisting of thin films of ceria with low Pt loadings sputtered on a nanostructured carbon support. Remarkably, only such small amounts of Pt are necessary for achieving power density values comparable to the reference commercial catalysts, which results in excellent specific activities of our samples. By combining photoelectron spectroscopy and catalytic performance analysis, we have shown that the surface Pt 2+ species in cerium oxide exhibit high electrocatalytic activity. Density functional theory calculations show that the great stability of Pt 2+ species on ceria makes these resistant to reduction by hydrogenation and suggests that the formation of such stable surface complexes prevents degradation of the nanostructured composite.

Interaction of water with fully oxidized and partially reduced CeO2(1 1 1) thin film model catalyst grown on a Cu(1 1 1) surface was investigated by photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). On the stoichiometric surface water adsorbs molecularly at low temperatures (

The interaction of Pt with CeO2 layers was investigated by using high resolution hard X-ray photoelectron spectroscopy. Pt doped CeO2 layers were deposited simultaneously by rf-magnetron sputtering on a SiO2/Si substrate and carbon nanotubes (CNTs) grown on a carbon diffusion layer of a polymer membrane fuel cell. In the case of the CNT support photoelectron spectra showed the formation of ionic platinum rich cerium oxide with Pt2+,4+ species, and with the Pt2+/Pt4+ ratio strongly dependent on the amount of platinum. Ce reveals 4+/3+ mixed valent character with Ce3+ concentration increasing with Pt content. In the case of the SiO2/Si substrate the film revealed Ce4+ and Pt4+ species only.

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.

The RF magnetron sputtering of polytetrafluoroethylene target is studied with the aim to find out conditions leading to the deposition of super-hydrophobic thin films. It is shown that such coatings can be prepared at elevated pressures and a longer distance between the sputtered target and the substrate. This is explained by an increase in the density of longer C x F y molecules that reach the substrate and a lower flux of ions and CF 2 radicals on the surface of growing film under such deposition conditions, as observed by optical emission spectroscopy and mass spectrometry. Such changes in plasma composition result in a deposition of rough films having F / C ratio close to 2 as observed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. These findings clearly distinguish our results from the previous investigations of polytetrafluoroethylene sputtering performed at shorter distances from the target, where either low F / C ratio or low roughness of the deposited films did not allow reaching super-hydrophobic character of the coatings.

Adjustable morphology and degree of reduction represent desirable properties of model oxide substrates for heterogeneous catalysis. We investigate these properties in CeO2 (ceria) thin films on Cu(111) using scanning tunneling microscopy and photoelectron spectroscopy. We identify growth mechanisms of ceria on Cu(111): formation of incomplete oxide interfacial layer and formation of three-dimensional ceria pyramids by stacking of monolayer-high islands. Using these mechanisms, we control the coverage, the number of open monolayers, and the step density of ceria thin films on Cu(111). Annealing in vacuum allows us to control besides the morphology also the degree of ceria surface reduction. We find a correlation between surface reduction and morphological stability in annealed ceria layers. Oriented and stoichiometric thin films of ceria on Cu(111) can be prepared at temperatures as low as 150 and 250 °C. Both the morphology and the surface reduction of these films readily change with increasing temperatur...

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.

Cerium oxide films equivalent to 2 ML of CeO2 were grown at 520 K in an oxygen atmosphere on a clean Cu(111) substrate in order to prepare a model catalytic system. This “inverse model catalyst” was characterized by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core levels, and resonant photoelectron spectroscopy (RPES) of the valence band. Samples annealed at 770 K exhibited a LEED pattern corresponding to the (1.5 × 1.5) CeO2(111)/Cu(111) structure that can be interpreted as formation of a flat, well-ordered cerium oxide overlayer aligned with the principal crystallographic axes of the substrate. The model catalytic system corresponds well to a copper-loaded ceria nanopowder catalyst that exhibits growth of Cu(111) film structure on CeO2(111) planes. Lowering of the CO oxidation temperature due to the Cu loading is explained by CO adsorption on copper in the vicinity of highly active ceria planes providing oxygen for the reaction.

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 morphology and composition of CeOx films prepared by r.f. magnetron sputtering on a graphite foil have been investigated mainly by using microscopy methods. This study presents the formation of nanocrystalline layers with porous structure due to the modification of a carbon support and the formation of cerium carbide crystallites as a result of the deposition process. Chemical analyses of the layers with different thicknesses performed by energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and X-ray photoelectron spectroscopy have pointed to the reduction of the cerium oxide layers. In the deposited layers, cerium was present in mixed Ce(3+) and Ce(4+) valence. Ce(3+) species were located mainly at the graphite foil-CeOx interface and the chemical state of cerium was gradually changing to Ce(4+) going to the layer surface. It became more stoichiometric in the case of thicker layers except for the surface region, where the presence of Ce(3+) was associated with oxygen vacancies on the surface of cerium oxide grains. The degree of cerium oxide reduction is discussed in the context of particle size.

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.

In this work, properties of non-evaporable getter (NEG) films prepared on stainless steel substrates by magnetron sputtering were investigated. Changes of the sample surface during thermal activation were studied by means of secondary ion mass spectroscopy (SIMS). Static SIMS observation of a superficial layer as well as dynamic profiling of the surface region were performed. Two samples of the same Ti:Zr:V stoichiometry were investigated following two different procedures of thermal activation. Step-by-step heating up to 320 °C (as model activation) and direct long time heating to 240 °C (continuous thermal activation) were applied. The SSIMS measurements are highly surface sensitive and reflect changes of the superficial oxide layer covering air-exposed surfaces during activation. To compare the final states of activation, depth profiles of surface layers have been used as well. Molecular ion intensity ratios MX + /M + (X=O, H; M=Ti, Zr, V) have been considered to be directly coverage-sensitive and were monitored during the processes. The results were checked by comparison to corresponding XPS experiments.

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.

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.

The activated ZrV non-evaporable getter (NEG) film has been studied by means of X-ray photoelectron spectroscopy, low-energy ion scattering and secondary ion mass spectrometry. In this work, we found that the first atomic layer of the thermally activated ZrV NEG consists mainly of zirconium atoms, which are partly oxidized. The residual zirconium suboxides observed on thermally activated ZrV NEG diminish during ion sputtering of NEG surface. It indicates that residual suboxides are located mainly in the top surface layer.

Pd x Co 1− x thin layers with different stoichiometry, prepared by DC magnetron sputtering on α -Al 2 O 3 (sapphire) substrates, were investigated by X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS) and temperature programmed desorption (TPD). The shifts of Pd 3d, XPS Auger Pd-MNN and the valence-band centre toward higher binding energies due to the formation of a bimetallic bond were observed. CO adsorption properties of the alloys were strongly dependent on alloy stoichiometry. The common property was the lowering of the CO desorption temperature with respect to the desorption from pure metals. The SSIMS study showed that CO partially dissociated on Co–Pd alloy surfaces.

In2O3 belongs to the group of metal oxides used successfully for gas detection, with sensitivity for CO and H2 comparable with that of SnO2 and excellent for O3. The sensing properties of these sensors could be greatly improved by adding small amount of transition metals such as Pd, Pt, Au, etc. In this work, we used X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to study the growth of Pd particles on In2O3 substrates prepared by spray pyrolysis method. Surface stoichiometry and its changes during Ar+ ion bombardment used for surface cleaning were checked with XPS and ISS. The Pd growth was studied stepwise in situ using the micro-electron beam evaporation source (MEBES) with controlled evaporation rate. XPS and ISS measurements were carried out with special attention to metal–substrate interaction (MSI), which was observed for Pd–In and resulted in the formation of Pd–In alloy with noble metal-like electronic structure. Further, we studied reduction of these samples after oxidation in air. A lower reduction temperature than with bulk PdO was observed. The results are compared with the experiment of Pd deposition performed on a pure In foil.

The reactive vacuum deposition of CeO 2 on Cu(1 1 1) surface in oxygen atmosphere provides high quality epitaxial ceria overlayers. We report the growth characteristics of Ce oxide, the structures, and the temperature stability of the oxide phases as investigated by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. We find that Ce oxide on the Cu(1 1 1) grows initially in the form of islands giving sharp hexagonal LEED pattern of the CeO 2 (1 1 1) structure corresponding to the (1.5 × 1.5) structure. The CeO 2 –Cu(1 1 1) films exhibited mixed valence states and temperature dependent CeO 2 –Ce 2 O 3 transition above 900 K due to the vacuum annealing. The transition progressed more rapidly at the surface, probably by formation of oxygen vacancies.

Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0001) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core states and resonant photoelectron spectroscopy (RPES) of the valence bands. Copper adsorption on stoichiometric ceria caused reduction of CeO2, while on the oxygen-defficient ceria it partially reoxidized the substrate. This is in agreement with DFT+U calculations of copper adsorption on stoichiometric and defective ceria surfaces. (C) 2012 Elsevier B. V. All rights reserved.

The interaction of oxygen with gold adsorbed on Ti(0001) was studied by synchrotron radiation photoelectron spectroscopy. Two kinds of surfaces were explored: as-deposited 0.38, 1.16 and 1.85 monolayer (ML) thick Au overlayers on the Ti(0001) surface, and the same samples after thermal treatment, which resulted in the formation of Au-Ti intermetallic surfaces. The Ti 3p core level was strongly affected by reaction with oxygen, while the Au 4f core level showed only minor changes other than a decrease in intensity. The Ti 3p peak was fitted with several components which were identified as Ti atoms in different oxidation states, namely TiO, Ti(2)O(3), TiO(2) and Ti-OH. Titanium oxide phase formation is accompanied by Au-Ti bond dissociation and outward diffusion of Ti. The presence of an Au-Ti intermetallic phase on the Ti(0001) surface promotes oxidation of the Ti atoms.

Adsorption and desorption of methanol on Pt particles on a CeO(2)(111)/Cu(111) thin film surface and on an ion-eroded Pt(111) single crystal were investigated by X-ray photoelectron spectroscopy and soft X-ray synchrotron radiation photoelectron spectroscopy (PES). Resonant PES was used to determine the occupancy of the Ce 4f states with high sensitivity. Multilayers of methanol were adsorbed at low temperature and subsequently desorbed by heating to 600 K. Methanol desorption is accompanied by the formation of chemisorbed methoxy -OCH(3). Cerium oxide surface is strongly reduced by methanol, which was detected via the transition Ce(4+) --> Ce(3+) and an increase of the Ce 4f electronic state occupancy. Partial C-O bond scission and formation of atomic carbon was observed on the Pt particles as well as on the rough Pt(111) surface. On Pt/CeO(2)(111), all traces of surface carbon and residual hydrocarbons disappear at 500 K.

The interaction of Pt with CeO(2) layers was investigated by using photoelectron spectroscopy. The 30 nm thick Pt doped CeO(2) layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) substrate, multiwall carbon nanotubes (CNTs) supported by a carbon diffusion layer of a polymer membrane fuel cell and on CNTs grown on the silicon wafer by the CVD technique. The synchrotron radiation X-ray photoelectron spectra showed the formation of cerium oxide with completely ionized Pt(2+,4+) species, and with the Pt(2+)/Pt(4+) ratio strongly dependent on the substrate. The TEM and XRD study showed the Pt(2+)/Pt(4+) ratio is dependent on the film structure.

The interaction of Pt with CeO2 layers was investigated by using photoelectron spectroscopy. Thirty-nanometre-thick Pt and Sn doped CeO2 layers were deposited simultaneously by rf-magnetron sputtering on a Si(001) substrate and a carbon diffusion layer of a polymer membrane fuel cell by using a composite CeO2–Pt–Sn target. The laboratory XPS and synchrotron radiation soft X-ray and hard X-ray photoemission spectra showed the formation of cerium oxide with completely ionised Pt2+,4+ species, and with Pt4+ embedded in the film bulk. Hydrogen/air fuel cell activity measurements normalised to the amount of Pt used revealed high specific power of up to 5.4 × 104 mW mg–1 (Pt). The activity of these materials is explained by the strong activity of embedded Ptn+ cations.

We have studied the adsorption of low dimensional gold on ceria, produced by evaporation onto the surface. The interaction of gold with CeO(2)(111) layers was investigated with x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, and resonant photoelectron spectroscopy (RPES). Gold was deposited in steps onto a 1.5 nm thick CeO(2)(111) layer epitaxially grown on a Cu(111) substrate. The RPES showed a partial Ce(4+)--Ce(3+) reduction, observed as a resonant enhancement of the 4f level of the Ce(3+) species. This can be explained by possible creation of a new Au(+) ionic state. The observed effects are stronger for Au deposition at room temperature than at 250 degrees C. The obtained results are in agreement with already published density functional theory calculations reporting weakening of bond between the oxygen and the Ce atoms in ceria caused by the presence of gold.

Self-organized straight nanowires of WO3 have been epitaxially grown on muscovite mica in low super-saturation conditions. Morphology, structure and chemical composition of the prepared nanostructures have been investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). SEM permits us to observe nanowire networks and substrate electron channeling patterns (ECP) simultaneously and thus to determine crystallographic direction of nanowire growth. The experimental results show that straight WO3 nanowires are orientated preferentially parallel to two of three high symmetry crystallographic directions of mica [100] and [110] or [100] and [Formula: see text]. XRD and XPS measurements indicated self-assembly of very thin nanowires of hexagonal tungsten bronze in the first stage of growth followed by the formation of stoichiometric WO3. The growth mechanism has been studied as a function of different preparation conditions with special focus on the role of potassium ions present on the mica surface. Based on obtained results a growth model of tungsten oxide nanowires on mica is proposed.

Cerium 4f level occupation determines the properties of cerium oxide based catalysts in a significant way. The Ce 4f level of nanosized cerium oxide particles was investigated with the use of resonant photoelectron spectroscopy in the Ce 4d-4f photoabsorption region. A strong interaction of ceria with different additives, e.g. Pd and Sn, led to a partial Ce4+-->Ce3+ transition that was observed as a significant resonance enhancement of 4f photoemission intensity. Increases of the CO oxidation catalytic activity were observed simultaneously. The ratio of resonance enhancement of Ce photoemission intensity DCe(3+)/DCe(4+) was used to monitor Ce(3+) and Ce(4+) state occupation. The relative parameter DCe(3+)/DCe(4+) was found to be particularly useful in the case of photoemission studies of nanopowder ceria catalysts.

The interaction of gold with CeO2 layers was investigated using photoelectron spectroscopy. 65 nm thick Au doped CeO2 layers were deposited by rf-magnetron sputtering on a Si(0 0 1) substrate by using a composite CeO2–Au target. The laboratory XPS and synchrotron radiation soft x-ray and hard x-ray photoemission spectra showed the formation of stoichiometric Ce4+ (CeO2) and the appearance of new Au+,3+ states with ionized Au species in excess of 50% of the total Au amount. Depth resolved measurements, by varying the emission angle or photon energy, indicated the formation of an Au0 overlayer and deeper Au+,3+ species. The formation of Au+,3+ ions was found to be strongly dependent on the cerium oxide stoichiometry. The amount of ionized Au can be reversibly decreased and increased by surface reduction (removal of O by sputtering) and subsequent surface re-oxidation.