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Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO2. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO2RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O2-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu2O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate's orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu2O is formed during the initial growth phase, both Cu2O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu2O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments., A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.

The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply. Supercapacitors are high-power devices, particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability. Additionally, they can function with two carbon electrodes, which is an advantage due to the abundance of carbon in biomass and other waste materials (i.e., plastic waste). Newly developed supercapacitive nanocarbons display extremely narrow micropores (100 kW kg−1), using fourty times less activating agent than traditionnal chemically activated carbons. We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores. Finally, this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry.

Carbon dots (CDs) are an emerging class of photoluminescent material. Their unique optical properties arise from the discrete energy levels in their electronic states, which directly relate to their crystalline and chemical structure. It is expected that when CDs go through structural changes via chemical reduction or thermal annealing, their energy levels will be altered, inducing unique optoelectronic properties such as solid-state photoluminescence (PL). However, the detailed structural evolution and how the optoelectronic characteristics of CDs are affected remain unclear. Therefore, it is of fundamental interest to understand how the structure of CDs prepared by hydrothermal carbonisation (HTC) rearranges from a highly functionalised disordered structure into a more ordered graphitic structure. In this paper, detailed structural characterisation and in situ TEM were conducted to reveal the structural evolution of CDs during the carbonisation process, which have demonstrated a growth in aromatic domains and reduction in oxidation sites. These structural features are correlated with their near-infrared (NIR) solid-state PL properties, which may find a lot of practical applications such as temperature sensing, solid-state display lighting and anti-counterfeit security inks.

As a new class of sustainable carbon material, "carbon dots" is an umbrella term covering many types of materials. Herein, a broad range of techniques was used to develop the understanding of hydrothermally synthesized carbon dots, and it is shown how fine-tuning the structural features by simple reduction/oxidation reactions can drastically affect their excited-state properties. Structural and spectroscopic studies found that photoluminescence originates from direct excitation of localized fluorophores involving oxygen functional groups, whereas excitation at graphene-like features leads to ultrafast phonon-assisted relaxation and largely quenches the fluorescent quantum yields. This is arguably the first study to identify the dynamics of photoluminescence including Stokes shift and allow the relaxation pathways in these carbon dots to be fully resolved. This comprehensive investigation sheds light on how understanding the excited-state relaxation processes in different carbon structures is crucial for tuning the optical properties for any potential commercial applications.

We offer a comprehensive approach to determine how physical confinement can affect the water formation reaction. By using free-standing crystalline SiO2 bilayer supported on Ru(0001) as a model system, we studied the water formation reaction under confinement in situ and in real time. Low-energy electron microscopy reveals that the reaction proceeds via the formation of reaction fronts propagating across the Ru(0001) surface. The Arrhenius analyses of the front velocity yield apparent activation energies (Eaapp) of 0.32 eV for the confined and 0.59 eV for the nonconfined reaction. DFT simulations indicate that the rate-determining step remains unchanged upon confinement, therefore ruling out the widely accepted transition state effect. Additionally, H2O accumulation cannot explain the change in Eaapp for the confined cases studied because its concentration remains low. Instead, numerical simulations of the proposed kinetic model suggest that the H2 adsorption process plays a decisive role in reproducing the Arrhenius plots.

Polymer electrolyte membrane fuel cells require cheap and active electrocatalysts to drive the oxygen reduction reaction. Nitrogen-doped carbons have been extensively studied regarding their oxygen reduction reaction. The work at hand looks beyond the nitrogen chemistry and brings to light the role of oxygen. Nitrogen-doped nanocarbons were obtained by a radio-frequency plasma route at 0, 100, 250, and 350 W. The lateral size of the graphitic domain, determined from Raman spectroscopy, showed that the nitrogen plasma treatment decreased the crystallite size. Synchrotron radiation photoelectron spectroscopy showed a similar nitrogen chemistry, albeit the nitrogen concentration increased with the plasma power. Lateral crystallite size and several nitrogen moieties were plotted against the onset potential determined from oxygen reduction reaction curves. There was no correlation between the electrochemical activity and the sample structure, as determine from Raman and synchrotron radiation photoelectron spectroscopy. Near-edge X-ray absorption fine structure (NEXAFS) was performed to unravel the carbon and nitrogen local structure. A difference analysis of the NEXAFS spectra showed that the oxygen surrounding the pyridinic nitrogen was critical in achieving high onset potentials. The work shows that there were more factors at play, other than carbon organization and nitrogen chemistry.

The oxidation and reduction of a bimetallic Ni/Rh model catalyst during the water forming ${\mathrm{O}}_{2}+{\mathrm{H}}_{2}$ reaction is studied with low-energy electron microscopy, microspot-low-energy electron diffraction, and x-ray photoemission electron microscopy. Oxidation of a submonolayer Ni film results in the formation of three-dimensional (3D) NiO nanoparticles. Reduction of 3D-NiO in ${\mathrm{H}}_{2}$ produces a dispersed two-dimensional film of metallic Ni. Chemical waves during the ${\mathrm{O}}_{2}+{\mathrm{H}}_{2}$ reaction involve a cyclic transformation between 3D-NiO and 2D-NiO.

A constant increase in the need of clean energy demands more innovation from the research community. Active and stable materials that can make use of the solar radiation to promote different reactions are the cornerstone of emerging technologies. Polymeric carbon nitrides that harvest solar radiation to drive electrochemical reactions are considered solid candidates. In this respect, polymeric carbon nitrides were prepared by the thermal polycondensation of melamine. As-obtained materials were characterized by synchrotron radiation and lab-based techniques. The electron band structure was fully characterized by a combined electrochemical optoelectronic study. Electron microscopy studies before and after the photoelectrochemical experiments showed morphological and structure degradation. The work at-hand concludes that polymeric carbon nitrides are prone to photoelectrochemical degradation at high overpotentials., 25 pages, 4 figures + SI

The large-scale formation of patterned, quasi-freestanding graphene structures supported on a dielectric has so far been limited by the need to transfer the graphene onto a suitable substrate and contamination from the associated processing steps. We report μm scale, few-layer graphene structures formed at moderate temperatures (600–700 °C) and supported directly on an interfacial dielectric formed by oxidizing Si layers at the graphene/substrate interface. We show that the thickness of this underlying dielectric support can be tailored further by an additional Si intercalation of the graphene prior to oxidation. This produces quasi-freestanding, patterned graphene on dielectric SiO2 with a tunable thickness on demand, thus facilitating a new pathway to integrated graphene microelectronics.

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition metal treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around $450-500^\circ\text{C}$. From the chemical reaction between SiC and thin films of Fe or Ru, $\text{sp}^{3}$ carbon is liberated from the SiC crystal and converted to $\text{sp}^{2}$ carbon at the surface. The quality of the graphene is demonstrated using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate is verified using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene based device structures., 10 pages, 4 figures, 51 references

Manganese is deposited at high temperature on (001) oriented ferroelectric lead zirco-titanate prepared in two different ways: sputter-annealed or just simply annealed in ultrahigh vacuum. Room temperature ferromagnetism (FM) is obtained for Mn deposited on sputter-annealed substrates, while for the other sample preparation a paramagnetic behaviour is obtained. Also, for the first case a clear inwards component of the polarization P(−) is observed by X-ray photoelectron spectroscopy and piezoresponse force microscopy. Composition analysis evidenced formation of Pb vacancies in the case of FM – P(−) sample, consistent with hole formation near the surface, needed both to stabilize the inwards polarization state and to intermediate ferromagnetism between Mn2+ ions. The indirect exchange ferromagnetism mediated by holes is stronger, most probably because the interaction energy is proportional with the carrier effective mass. Also, whereas in the case of unsputtered substrate a stable surface Mn oxide is formed, defect formation by sputtering seems to favor Mn migration inside the sample. This also induces the formation of a thin film where ferromagnetism and the orientation of ferroelectric polarization might have the same origin, i. e. holes accumulated near the outer surface.

Metal alloy catalysts can develop complex surface structures when exposed to reactive atmospheres. The structures of the resulting surfaces have intricate relationships with a myriad of factors, such as the affinity of the individual alloying elements to the components of the gas atmosphere, and the bond strengths of the multitude of low-energy surface compounds that can be formed. Identifying the atomic structure of such surfaces is a prerequisite for establishing structure-property relationships, as well as for modeling such catalysts in ab initio calculations. Here we show that an alloy, consisting of an oxophilic metal (Cu) diluted into a noble metal (Ag), forms a meta-stable 2-dimensional oxide monolayer the more oxophilic metal, when the alloy is subjected to oxidative reaction conditions. The presence of this oxide is correlated with selectivity in the corresponding test reaction of ethylene epoxidation. In the present study, using a combination of in-situ, ex-situ and theoretical methods (NAP-XPS, XPEEM, LEED, and DFT) we determine the structure to be a 2-dimensional analogue of Cu2O, resembling a single lattice plane of Cu2O. The overlayer holds an pseudo-epitaxial relationship with the underlying noble metal. Spectroscopic evidence shows that the oxide’s electronic structure is qualitatively distinct from its 3-dimensional counterpart, and due to weak electronic coupling with the underlying noble metal, it exhibits metallic properties. These findings provide precise details of this peculiar structure, and valuable insights into how alloying can enhance catalytic properties.

In this study, we compared the structural, morphological, and optical properties of a series of Zn1-xFexO (x = 0.00, 0.01, and 0.03) powders synthesized via a hydrothermal route with and without cetyltrimethylammonium bromide as a cationic surfactant. Our results highlighted the critical effects of the surfactant and the iron concentration on the structure, morphology, and optical properties of ZnO. X-ray diffraction, Mossbauer spectroscopy, and X-ray photoelectron spectroscopy analyses indicated the presence of a single phase comprising ZnO with a hexagonal wurtzite structure in all samples and a single oxidation state (+3) for the iron (Fe3+) that replaced Zn2+ in the ZnO structure. Morphological investigations by scanning electron microscopy showed that the surfactant and Fe3+ dopant greatly affected the shape of the ZnO grains, which varied between sheets and rod-like flowers. We found that the morphological and photocatalytic properties of the two series of samples comprising iron-doped ZnO with and without the surfactant were in opposition. We propose a possible growth mechanism for the ZnO polycrystalline grains in the presence of the Fe dopant and/or surfactant. The photocatalytic properties increased for the samples prepared with surfactant as the iron content increased, which was confirmed by ultraviolet-visible reflection measurements. The photocatalytic activities of the samples prepared without surfactant decreased in both the ultraviolet and visible spectral regions as the iron content increased in the samples.

By platinum deposition on a 150 nm thick film of lead zirco-titanate oriented PZT(001), grown on strontium titanate (001) single crystals with a strontium ruthenate buffer layer, which did not show initial preferential out-of-plane orientation of its ferroelectric polarization, a band bending near the interface towards lower energies is observed using photoelectron spectroscopy, by following all core levels from the substrate (Pb 4f, Zr 3d, Ti 2p, O 1s). This is unexpected given the fact that platinum has a larger work function than PZT and a rectifying contact for electrons is expected to be built at the interface. This observation may have two explanations: (i) platinum forms an alloy with elements from PZT yielding a metal with considerable lower work function; (ii) platinum provides electrons to the substrate which are able to compensate the depolarization field generated by the outwards polarization state. Several arguments are brought in favor of the second hypothesis, especially the attenuation of core levels from the substrate which is well described by exponential functions with reasonable values of the photoelectron inelastic mean free path, suggesting the formation of a sharp interface. High resolution transmission electron microscopy confirmed the sharpness of the interface.

International audience; We report a direct photoelectrochemical response from low cost carbon dots (CDs) prepared from chitosan via a solvothermal method. The carbon dots were covalently linked to an indium tin oxide (ITO) surface through a self-assembled silane monolayer. We attribute the photocurrent of the ITO–silane–CD surface to a photogenerated electron-transfer process by CDs under illumination with a wavelength of 420 nm to 450 nm. The self-assembled monolayer of CDs was used for ac-photocurrent imaging of the surface with micron scale lateral resolution. This discovery opens up new applications for CDs as biocompatible, light-addressable electrochemical sensors in bioanalytical and bioimaging applications.

We report the molecular beam epitaxy growth of Ni on a clean Ge(001) surface with an intermediate NiGe layer forming at the interface at room temperature. The crystallinity of the substrate is lost after the deposition of more than 2 Ni monolayers. The Schottky barrier formation is investigated by X-ray photoelectron spectroscopy. The method allows us to infer a 0.39–0.45 eV band bending at the interface between the compound and Ge(001). Magneto-optical Kerr effect measurements were conclusive in detecting the ferromagnetic ordering of Ni outermost layers.

Establishing the rather complex correlation between the structure and the charge transfer in organic−organic heterostructures is of utmost importance for organic electronics and requires spatially resolved structural, chemical, and electronic details. Insight into this issue is provided here by combining atomic force microscopy, Kelvin probe force microscopy, photoemission electron microscopy, and low-energy electron microscopy for investigating a case study. We select the interface formed by pentacene (PEN), benchmark among the donor organic semiconductors, and a p-type dopant from the family of fluorinated fullerenes. As for Buckminsterfullerene (C60), the growth of its fluorinated derivative C60F48 is influenced by the thickness and crystallinity of the PEN buffer layer, but the behavior is markedly different. We provide a microscopic description of the C60F48/PEN interface formation and analyze the consequences in the electronic properties of the final heterostructure. For just one single layer of PEN, a laterally complete but noncompact C60F48/PEN interface is created, importantly affecting the surface work function. Nonetheless, from the very beginning of the second layer formation, the presence of epitaxial and nonepitaxial PEN domains dramatically influences the growth dynamics and extremely well packed two-dimensional C60F48 islands develop. Insightful elemental maps of the C60F48/PEN surface spatially resolve the nonuniform distribution of the dopant molecules, which leads to a heterogeneous work function landscape., This work has been supported by the Spanish government under the projects MAT2016-77852-C2-1-R (AEI/FEDER, UE) and the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2015-0496) and by the European Union’s Horizon 2020 Research and Innovation Program under grant Agreement No. 730872 and the Marie Skłodowska-Curie Grant Agreement No. 722651 (SEPOMO project). We also acknowledge the Generalitat de Catalunya grant 2017 SGR668. F.S. has been developing this work as part of his doctorate in Materials Science at the Universitat Autonoma de Barcelona (UAB). The SMART instrument was ̀ financially supported by the Federal German Ministry of Education and Research (BMBF) under the contract 05 KS4WWB/4, as well as by the Max-Planck Society. We thank the Helmholtz-Center Berlin for Materials and Energy (HZB) for the allocation of beamtime 192-08486-ST. L.d.S.C. is grateful for the funding through the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany′s Excellence StrategyEXC 2008390540038 (UniSysCat). O.S. acknowledges the support from the Israel Ministry of Science, the Center for Absorption in Science of the Ministry of Immigrant Absorption, the Committee for Planning and budgeting of the Council for Higher Education under the framework of the KAMEA Program.

Tuneable nitrogen doped carbogels have been synthesised by a simple one-pot hydrothermal carbonisation, followed by pyrolysis at 1000 °C, using highly available and low cost precursors such as glucose and ovalbumin. Different physical activation ratios of nitrogen/oxygen were used to demonstrate a sustainable and easy method for changing surface area, pore size and elemental composition in order to investigate their effect on the oxygen reduction reaction when used as electrocatalysts. A ratio of nitrogen mixed with 2% of oxygen was found to be most beneficial for enhancing the catalytic activity by creating a high surface area of 874 m2 g−1 as well as a favourable ratio of pyridinic to graphitic nitrogen. The influence of sulphur doping and/or boron on the carbogel structure was investigated. Incorporation of sulphur does not interfere with the structure formation, but decreases the surface area and nitrogen content resulting in diminished ORR performance. However, boron doping with boric acid results in a different carbogel structure by acting as a catalyst, creating an altered morphology, surface area, pore properties and higher nitrogen content by fully utilising ovalbumin as a nitrogen source instead of as a structure directing/surface stabilising agent. Nitrogen content is found to determine the limiting current, while the oxygen content has a small influence on the onset potential. An assumed synergistic effect between nitrogen and boron generates higher electron transfer numbers and lower hydrogen peroxide yields in boron nitrogen co-doped carbogels than those observed in purely nitrogen doped systems.

We propose a novel idea to improve the surface properties of carbon-based Pt-free electrocatalysts in Polymer Electrolyte Membranes (PEMs) and Alkaline Fuel Cells (AFCs). Our concept is based on the addition of oxygenophilic and hydrophobic ionic liquids (ILs) to form a thin passivating layer at the triple point between the electrocatalyst–electrolyte–gas interface where the Oxygen Reduction Reaction (ORR) takes place.

We report the structural, electronic and magnetic investigation using extended X-ray absorption fine structure spectroscopy (EXAFS), photoelectron microscopy, spin-resolved photoemission and magneto-optical Kerr effect on the properties of Mn $$_{x}$$ Ge $$_{1-x}$$ systems obtained by molecular beam epitaxy deposition of manganese on Ge(001) wafers annealed on temperatures between 50 and 450 $$^{\circ }$$ C. Magnetic ordering can be achieved when the substrate temperature is higher than 250 $$^{\circ }$$ C, when the manganese tends to diffuse into the Ge matrix and segregate in Mn $$_{5}$$ Ge $$_{3}$$ -like compounds, as proved by EXAFS. High spatial resolution photoelectron spectroscopy reveals Mn inhomogeneities in the 5–10 $$\upmu $$ m range, even though Mn is found mostly in the same chemical state all over the surface.

We investigate band bending effects occurring at the interface between atomically clean Ge(001) and molecular beam epitaxy (MBE) deposited copper and platinum. Low energy electron diffraction (LEED) confirmed the crystallinity of the surface, evidenced the formation of (2 × 1) and (1 × 2) reconstructions, and revealed that it is strongly affected with metal deposition. X-ray photoelectron spectroscopy (XPS) data let us assume a Stranski–Krastanov growth mechanism and confirmed that the observed band bending is associated to an ohmic contact in both cases. For the platinum contact, the high values of the apparent inelastic mean free path (IMFP) derived from the evolution of the XPS intensities indicate a prevalence of mixture of Pt with Ge nearby the interface. Pt deposited on Ge(001) does not behave like a Schottky contact, as one may have expected due to the higher work function of platinum. The observed effect is similar to the case where interfacial Pt had a lower work function by 2.25/1.96 eV than that of metallic Pt. We propose a model to explain this fact by the effective mass variation or to the conduction band broadening due to the strong intermixing of platinum with germanium under the surface.

The direct synthesis from elements of tungsten semicarbide, W 2 C, taking place in a narrow concentration range and at high temperatures, is unsuited for some applications requiring small particle sizes. We report an efficient synthesis method for obtaining pure phase W 2 C at low temperatures ( in situ . A 1:5 (at.) Pd:W ratio or higher yields pure phase W 2 C, while increasing the Pd content decreases the carburization temperature. The resulting composite materials contain Pd(0) and W 2 C particles well-dispersed on carbon, with sizes between 50 and 500 nm. The samples have been tested using cyclic voltammetry and chronoamperometry as potential anode materials for the electrooxidation of formic acid and show improved stability in comparison with commercial Pd and comparable current densities, up to 2 times higher than the commercial catalyst.

The orientation of polarization in ferroelectric thin films is important for applications of these materials in nonvolatile memory and field-effect transistors with ferroelectric gates, and in catalysis and photocatalysis. One means of control is to choose a well defined substrate, but the influence of a substrate's electronic properties on polarization orientation is not well understood. In this investigation of model systems, the experimental findings are integrated with electrostatic models to determine the magnitudes and orientations of the interfacial electric fields that are useful for setting the polarization of the thin ferroelectric epilayer.

Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature TC (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (ΔSM) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg−1, somewhat lower than that of bulk Gd (410 J kg−1) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating ΔSM in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (ΔSM)max around TC is proportional to (μ0H/TC)2/3 in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.

We report the applicability of a hybrid system comprising a La3+-based catalyst and an Au/TiO2 photocatalyst in the decomposition of chemical weapons. This system is able to perform complete degradation of soman, sarin and VX in less than 1 minute under low basic conditions and visible light irradiation.

International audience; Supported Pd nanocatalysts were prepared by deposition of Pd nanoparticles (NPs) onto spherical mesoporous carbon beads (MB) functionalized by thermal or acidic treatement The Pd NPs were synthesized by decomposition of [Pd-2(dba)(3)] (dba: dibenzylideneacetone) under dihydrogen either directly on the carbon supports without stabilizer leading to naked Pd NPs (Pd/MB series) or in solution in the presence of a stabilizer (polymer (PVP series) or triphenylphosphine (TPP series)) to obtain stable colloidal solutions that were further used to impregnate the carbon materials to have carbon-deposited Pd NPs. The NPs deposited on carbon displayed a Pd loading from 0.5 to 14.8 wt.% and were characterized by different techniques (nitrogen physisorption at 77 K, H-2-chemissorption and TPD, XRD, XPS and HRTEM). Their catalytic performance in deoxygenation of oleic acid was evaluated in batch and flow reaction conditions. Flow conditions led to superior results compared to batch. No aromatic compounds were detected as side products, but in the case of the Pd/MB series, octadecanol and octadecane were significantly formed suggesting the involvement of a deoxygenation mechanism in which the hydrocarbons were produced via both decarbonylation/decarboxylation and dehydration steps. Further experiments carried out in H-2/N-2 mixture or in pure N-2 highlighted the key role of hydrogen. For a N-2/H-2 of 2.5:1 the dehydration route was crossing out and even no traces of octadecanol nor octadecane were detected. Then, complete removal of H-2 produced heptadecene in a high excess compared to heptadecane (almost 7-1) thus suggesting the decarbonylation/decarboxylation steps as the main route. ICP-OES measurements indicated no leaching of palladium and simple washing of catalysts with mesitylene allowed recycling without any change in conversion or product distribution.

The formation of separate phases in crystalline materials is promoted by doping with elements with different valences and ionic radii. Control of the formation of separate phases in multiferroics is extremely important for their magnetic, ferroelectric and elastic properties, which are relevant for multifunctional applications. The ordering of dopants and incipient phase separation were studied in lead titanate-based multiferroics with the formula (Pb0.88Nd0.08)(Ti0.98-xFexMn0.02)O3 (x = 0.00, 0.03, 0.04, 0.05) by means of a combination of Mössbauer spectroscopy, XPS, HRTEM, dielectric and anelastic spectroscopy. We found that Fe ions are substituted as Fe3+ at Ti sites and preferentially exhibit pentahedral coordination, whereas Ti ions have coexisting valences of Ti4+/Ti3+. Fe3+ ions are preferentially ordered in clusters, and there exists a transition temperature TC1, below which phase separation occurs between a tetragonal phase T1 free of magnetic clusters and a cubic phase, and a lower transition temperature TC2, below which the cubic phase rich in magnetic clusters is transformed into a tetragonal phase T2. The phase separation persists at the nanoscale level down to room temperature and is visible in HRTEM images as a mixing of nanodomains with different tetragonality ratios. This phase separation was observed over the whole studied concentration range of xFe values. It occurs progressively with the value of xFe, and the transition temperature TC2 decreases with the concentration from about 620 K (xFe = 0.03) to about 600 K (xFe = 0.05), while TC1 remains nearly constant.

The positions of the low energy electron diffraction (LEED) spots from ferroelectric single crystal films depend on its polarization state, due to electric fields generated outside of the sample. One may derive the surface potential energy, yielding the depth where the mobile charge carriers compensating the depolarization field are located ($\ensuremath{\delta}$). On ferroelectric $\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}$(001) samples, surface potential energies are between 6.7 and 10.6 eV, and $\ensuremath{\delta}$ values are unusually low, in the range of $1.8\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\AA{}$. When $\ensuremath{\delta}$ is introduced in the values of the band bending inside the ferroelectric, a considerably lower value of the dielectric constant and/or of the polarization near the surface than their bulk values is obtained, evidencing either that the intrinsic `dielectric constant' of the material has this lower value or the existence of a `dead layer' at the free surface of clean ferroelectric films. The inwards polarization of these films is explained in the framework of the present considerations by the formation of an electron sheet on the surface. Possible explanations are suggested for discrepancies between the values found for surface potential energies from LEED experiments and those derived from the transition between mirror electron microscopy and low energy electron microscopy.

The stability of thin films of lead zirco-titanate (PZT) under intense soft X-ray beams is investigated by time-resolved photoelectron spectromicroscopy with a lateral resolution below 1 micrometer. Surface dissociation is observed when samples are irradiated with intense (5 × 1023 photons per s per m2) soft X-rays, with promotion of reduced lead on the surface. On areas exhibiting outwards polarization (P(+)), the reduced lead is formed at the expense of P(+)-PZT. On areas presenting co-existing P(+) states with areas without out-of-plane polarization (P(0)), the reduced lead is formed at the expense of the P(0)-PZT component, while the P(+)-PZT remains constant. The main dissociation mechanism was found to be triggered by 'hot' electrons in the conduction band, with energies exceeding the surface dissociation energies. Dissociation occurs basically when the electron affinity is larger than the dissociation energy of PbO (for P(+) areas) or PbO- (for P(0) areas). Such mechanisms may be adapted for dissociation of other molecules on surfaces of ferroelectric thin films or for quantifying the stability of ferroelectric surfaces interacting with other radiation, with applications in the fields of photocatalysis or photovoltaic devices.

We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

This work presents a systematic investigation by X-ray photoelectron spectroscopy of the mechanisms of interface formation and band bending for Au/Pb(Zr,Ti)O 3 (PZT) layers grown on SrTiO 3 (001) with a SrRuO 3 buffer layer, as function on the initial state of the PZT surface. After isolating the chemical effects, such as the formation of metal Pb at some surfaces, the evolution of the core levels with Au deposition allows one to simultaneously investigate the Schottky barrier formation and the built-in potential effects (charging induced by the static ferroelectric polarization). Areas of the sample with outwards P (+) and no polarization perpendicular to the surface P (0) are identified for all samples. Only the freshly prepared sample exhibited inward polarization areas P (−) . The built-in potential is on the order of 0.9 eV, while the Schottky band bending ranges from 0.2 to 0.6 eV towards lower absolute energies, therefore indicating that the work function of PZT exceeds that of Au deposited. We report also a chemically differentiate value of the built-in potential, manifested by a preferential distribution of the charge accumulated at the surface on Ti and O atoms. The O 1s and Ti 2p core levels manifest quite strong variations with the Au thickness for freshly prepared samples, resulting in shifts on the order of 2 eV towards lower binding energies. Au deposited on areas with an outward polarization is positively charged by the same potential as atoms from the PZT film (0.8–0.9 eV), whereas Au deposited on areas with an inward polarization forms a continuous grounded layer, which progressively pumps the accumulated charge and removes the polarization of these areas.

TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe–N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe–N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent, the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

This contribution is a review of recent aspects connected with photoelectron spectroscopy of free ferroelectric surfaces, metals interfaced with these surfaces, graphene-like layers together with some exemplifications concerning molecular adsorption, dissociations and desorptions occurring from ferroelectrics. Standard photoelectron spectroscopy is used nowadays in correlation with other characterization techniques, such as piezoresponse force microscopy, high resolution transmission electron spectroscopy, and ferroelectric hysteresis cycles. In this work we will concentrate mainly on photoelectron spectroscopy and spectro-microscopy characterization of ferroelectric thin films, starting from atomically clean ferroelectric surfaces of lead zirco-titanate, then going towards heterostructures using this material in combination with graphene-like carbon layers or with metals. Concepts involving charge accumulation and depolarization near surface will be revisited by taking into account the newest findings in this area.

TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe–N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe–N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

Epitaxial La

Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(−), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(−) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(−) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(−) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface.