The dehydration mechanism of Na and K birnessites: a comprehensive multitechnique study.

The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions (bir) to complete dehydration, and the involved mechanisms were scrutinized. Density Functional Theory (DFT) simulations were employed to derive structural models for lamellar AMnO·HO (A = Na or K, = 0 or 0.66), subsequently compared with the experimental results obtained for NaMnO·0.

Revealing CO dissociation pathways at vicinal copper (997) interfaces.

Size- and shape-tailored copper (Cu) nanocrystals can offer vicinal planes for facile carbon dioxide (CO) activation. Despite extensive reactivity benchmarks, a correlation between CO conversion and morphology structure has not yet been established at vicinal Cu interfaces. Herein, ambient pressure scanning tunneling microscopy reveals step-broken Cu nanocluster evolutions on the Cu(997) surface under 1 mbar CO(g).

Bimolecular Reaction Mechanism in the Amido Complex-Based Atomic Layer Deposition of HfO.

The surface chemistry of the initial growth during the first or first few precursor cycles in atomic layer deposition is decisive for how the growth proceeds later on and thus for the quality of the thin films grown. Yet, although general schemes of the surface chemistry of atomic layer deposition have been developed for many processes and precursors, in many cases, knowledge of this surface chemistry remains far from complete. For the particular case of HfO atomic layer deposition on a SiO surface from an alkylamido-hafnium precursor and water, we address this lack by carrying out an atomic layer deposition experiment during the first cycle of atomic layer deposition.

Intercalation and reactions of CO under single layer graphene/Ni(111): the role of vacancies.

We use synchrotron radiation-induced core level photoemission spectroscopy to investigate the influence of vacancies, produced by ion bombardment, on monolayer graphene/Ni(111) exposed to CO at pressures ranging from ultra-high vacuum (10 mbar) up to near ambient (5.6 mbar) conditions. CO intercalates at a rate which is comparable to the one observed in absence of defects and reacts the Boudouard reaction producing additional carbon atoms and CO.

Self-Metalation of Porphyrins at the Solid-Gas Interface.

Self-metalation is a promising route to include a single metal atom in a tetrapyrrolic macrocycle in organic frameworks supported by metal surfaces. The molecule-surface interaction may provide the charge transfer and the geometric distortion of the molecular plane necessary for metal inclusion. However, at a metal surface the presence of an activation barrier can represent an obstacle that cannot be compensated by a higher substrate temperature without affecting the layer integrity.

The Fermi level as an energy reference in liquid jet X-ray photoelectron spectroscopy studies of aqueous solutions.

To advance the understanding of key electrochemical and photocatalytic processes that depend on the electronic structure of aqueous solutions, X-ray photoemission spectroscopy has become an invaluable tool, especially when practiced with liquid microjet setups. Determining vertical ionization energies referenced to the vacuum level, and binding energies referenced to the Fermi level, including the much-coveted reorganization energy of the oxidized species of a redox couple, requires that energy levels be properly defined. The present paper addresses specifically how the vacuum level "just outside the surface" can be known through the energy position of the rising edge of the secondary electrons, and how the Fermi level reference is uniquely determined via the introduction of a redox couple.

Hydrogen Bonding of Ammonia with (H,OH)-Si(001) Revealed by Experimental and Ab Initio Photoelectron Spectroscopy.

Combining experimental and ab initio core-level photoelectron spectroscopy (periodic DFT and quantum chemistry calculations), we elucidated how ammonia molecules bond to the hydroxyls of the (H,OH)-Si(001) model surface at a temperature of 130 K. Indeed, theory evaluated the magnitude and direction of the N 1s (and O 1s) chemical shifts according to the nature (acceptor or donor) of the hydrogen bond and, when confronted to experiment, showed unambiguously that the probe molecule makes one acceptor and one donor bond with a pair of hydroxyls. The consistency of our approach was proved by the fact that the identified adsorption geometries are precisely those that have the largest binding strength to the surface, as calculated by periodic DFT.

Correlation between structural phase transition and surface chemical properties of thin film SrRuO/SrTiO (001).

The correlation between the structural phase transition (SPT) and oxygen vacancy in SrRuO (SRO) thin films was investigated by in situ X-ray diffraction (XRD) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In situ XRD shows that the SPT occurs from a monoclinic SRO phase to a tetragonal SRO phase near ∼200 °C, regardless of the pressure environment. On the other hand, significant core level shifts in both the Ru and Sr photoemission spectra are found under ultrahigh vacuum, but not under the oxygen pressure environment.

Different Reactivity of Rutile and Anatase TiO Nanoparticles: Synthesis and Surface States of Nanoparticles of Mixed-Valence Magnéli Oxides.

Magnéli phases Ti O (3 View Article and Find Full Text PDF

Adsorbate-driven reactive interfacial Pt-NiO nanostructure formation on the PtNi(111) alloy surface.

The origin of the synergistic catalytic effect between metal catalysts and reducible oxides has been debated for decades. Clarification of this effect, namely, the strong metal-support interaction (SMSI), requires an understanding of the geometric and electronic structures of metal-metal oxide interfaces under operando conditions. We show that the inherent lattice mismatch of bimetallic materials selectively creates surface segregation of subsurface metal atoms.

Highly active nano-sized iridium catalysts: synthesis and spectroscopy in a proton exchange membrane electrolyzer.

A stable and cost effective oxygen evolution reaction (OER) catalyst is crucial for the large-scale market penetration of proton exchange membrane (PEM) water electrolyzers. We show that the synthesis of iridium nanoparticles in either low purity ethanol or water, or in the absence of a surfactant, is detrimental to the electrocatalytic properties of the materials. Adding NaBH in excess improves the purity of the catalyst enhancing the OER activity up to 100 A g at 1.

Soft X-ray Heterogeneous Radiolysis of Pyridine in the Presence of Hydrated Strontium-Hydroxyhectorite and its Monitoring by Near-Ambient Pressure Photoelectron Spectroscopy.

The heterogeneous radiolysis of organic molecules in clays is a matter of considerable interest in astrochemistry and environmental sciences. However, little is known about the effects of highly ionizing soft X-rays. By combining monochromatized synchrotron source irradiation with in situ Near Ambient Pressure X-ray Photoelectron Spectroscopy (in the mbar range), and using the synoptic view encompassing both the gas and condensed phases, we found the water and pyridine pressure conditions under which pyridine is decomposed in the presence of synthetic Sr-hydroxyhectorite.

CO oxidation activity of Pt, Zn and ZnPt nanocatalysts: a comparative study by in situ near-ambient pressure X-ray photoelectron spectroscopy.

The investigation of nanocatalysts under ambient pressure by X-ray photoelectron spectroscopy gives access to a wealth of information on their chemical state under reaction conditions. Considering the paradigmatic CO oxidation reaction, a strong synergistic effect on CO catalytic oxidation was recently observed on a partly dewetted ZnO(0001)/Pt(111) single crystal surface. In order to bridge the material gap, we have examined whether this inverse metal/oxide catalytic effect could be transposed on supported ZnPt nanocatalysts deposited on rutile TiO2(110).

How a tertiary diamine molecule chelates the silicon dimers of the Si(001) surface: a real-time scanning tunneling microscopy study.

The patterning of silicon surfaces by organic molecules emerges as an original way to fabricate innovative nanoelectronic devices. In this regard, we have studied how a diamine, N,N,N',N'-tetramethylethylenediamine (TMEDA, (CH)N-[CH]-N(CH)), chelates the silicon dimers of the Si(001)-2 × 1 surface. Starting from very low coverage to surface saturation (at 300 K), we used real-time scanning tunneling microscopy (STM) in a scanning-while-dosing approach.

Synthesis of CeOS and GdCeOS Nanoparticles and Reactivity from in Situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy.

Lanthanide oxysulfide nanoparticles have recently attracted interest in view of their potential applications, such as lighting devices and MRI contrast agents, which requires a good stability in air and a controlled surface. In order to address these issues, in this work, air-sensitive CeOS nanoparticles of hexagonal shape were successfully prepared and characterized under inert conditions. Bimetallic GdCeOS nanoparticles of similar shape and size were also synthesized for the whole composition range (y from 0 to 1).

Chemical and kinetic insights into the Thermal Decomposition of an Oxide Layer on Si(111) from Millisecond Photoelectron Spectroscopy.

Despite thermal silicon oxide desorption is a basic operation in semiconductor nanotechnology, its detailed chemical analysis has not been yet realized via time-resolved photoemission. Using an advanced acquisition system and synchrotron radiation, heating schedules with velocities as high as 100 K.s were implemented and highly resolved Si 2p spectra in the tens of millisecond range were obtained.

Chemical states of surface oxygen during CO oxidation on Pt(1 1 0) surface revealed by ambient pressure XPS.

The study of CO oxidation on Pt(1 1 0) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure conditions, both the α-phase of PtO oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to the exothermic nature of CO oxidation, the temperature of the Pt surface increases as CO oxidation takes place.

Energy-Level Alignment of a Hole-Transport Organic Layer and ITO: Toward Applications for Organic Electronic Devices.

2,2',6,6'-Tetraphenyl-4,4'-dipyranylidene (DIPO-Ph) was grown by vacuum deposition on an indium tin oxide (ITO) substrate. The films were characterized by atomic force microscopy as well as synchrotron radiation UV and X-ray photoelectron spectroscopy to gain an insight into the material growth and to better understand the electronic properties of the ITO/DIPO-Ph interface. To interpret our spectroscopic data, we consider the formation of cationic DIPO-Ph at the ITO interface owing to a charge transfer from the organic layer to the substrate.

In Situ Solid-Gas Reactivity of Nanoscaled Metal Borides from Molten Salt Synthesis.

Metal borides have mostly been studied as bulk materials. The nanoscale provides new opportunities to investigate the properties of these materials, e.g.

Insights into the Surface Reactivity of Cermet and Perovskite Electrodes in Oxidizing, Reducing, and Humid Environments.

Understanding the surface chemistry of electrode materials under gas environments is important in order to control their performance during electrochemical and catalytic applications. This work compares the surface reactivity of Ni/YSZ and LaSrCrFeO, which are commonly used types of electrodes in solid oxide electrochemical devices. In situ synchrotron-based near-ambient pressure photoemission and absorption spectroscopy experiments, assisted by theoretical spectral simulations and combined with microscopy and electrochemical measurements, are used to monitor the effect of the gas atmosphere on the chemical state, the morphology, and the electrical conductivity of the electrodes.

Silica-Supported Au-Ag Catalysts for the Selective Hydrogenation of Butadiene.

Gold and silver are miscible over the entire composition range, and form an attractive combination for fundamental studies on bimetallic catalysts. Au-Ag catalysts have shown synergistic effects for different oxidation and liquid-phase hydrogenation reactions, but have rarely been studied for gas-phase hydrogenation. In this study 3 nm particles of Au, Ag and Au-Ag supported on silica (SBA-15) were investigated as catalysts for selective hydrogenation of butadiene in an excess of propene.

Room temperature differential conductance measurements of triethylamine molecules adsorbed on Si(001).

We have measured the differential conductance of the triethylamine molecule (N(CH2CH3)3) adsorbed on Si(001)-2 × 1 at room temperature using scanning tunneling spectroscopy. Triethylamine can be engaged in a dative bonding with a silicon dimer, forming a Si-Si-N(CH2CH3)3 unit. We have examined the datively bonded adduct, either as an isolated molecule, or within an ordered molecular domain (reconstructed 4 × 2).

Static and dynamic electronic characterization of organic monolayers grafted on a silicon surface.

Organic layers chemically grafted on silicon offer excellent interfaces that may open up the way for new organic-inorganic hybrid nanoelectronic devices. However, technological achievements rely on the precise electronic characterization of such organic layers. We have prepared ordered grafted organic monolayers (GOMs) on Si(111), sometimes termed self-assembled monolayers (SAMs), by a hydrosilylation reaction with either a 7-carbon or an 11-carbon alkyl chain, with further modification to obtain amine-terminated surfaces.

Propanoate grafting on (H,OH)-Si(0 0 1)-2 × 1.

We have examined the reactivity of water-covered Si(0 0 1)-2 × 1, (H,OH)-Si(0 0 1)-2 × 1, with propanoic (C2H5COOH) acid at room temperature. Using a combination of spectroscopic techniques probing the electronic structure (XPS, NEXAFS) and the vibrational spectrum (HREELS), we have proved that the acid is chemisorbed on the surface as a propanoate. Once the molecule is chemisorbed, the strong perturbation of the electronic structure of the hydroxyls, and of their vibrational spectrum, suggests that the molecule makes hydrogen bonds with the surrounding hydroxyls.