X-ray Photelectron Spectroscopy Research Articles

Structure-Property-Performance Relationship of Ultrathin Pd-Au Alloy Catalyst Layers for Low-Temperature Ethanol Oxidation in Alkaline Media.

Pd-containing alloys are promising materials for catalysis. Yet, the relationship of the structure-property performance strongly depends on their chemical composition, which is currently not fully resolved. Herein, we present a physical vapor deposition methodology for developing PdxAu1-x alloys with fine control over the chemical composition. We establish direct correlations between the composition and these materials' structural and electronic properties with its catalytic activity in an ethanol (EtOH) oxidation reaction. By combining X-ray diffraction (XRD) and X-ray photelectron spectroscopy (XPS) measurements, we validate that the Pd content within both bulk and surface compositions can be finely controlled in an ultrathin-film regime. Catalytic oxidation of EtOH on the PdxAu1-x electrodes presents the largest forward-sweeping current density for x = 0.73 at ∼135 mA cm-2, with the lowest onset potential and largest peak activity of 639 A gPd-1 observed for x = 0.58. Density functional theory (DFT) calculations and XPS measurements demonstrate that the valence band of the alloys is completely dominated by Pd particularly near the Fermi level, regardless of its chemical composition. Moreover, DFT provides key insights into the PdxAu1-x ligand effect, with relevant chemisorption activity descriptors probed for a large number of surface arrangements. These results demonstrate that alloys can outperform pure metals in catalytic processes, with fine control of the chemical composition being a powerful tuning knob for the electronic properties and, therefore, the catalytic activity of ultrathin PdxAu1-x catalysts. Our high-throughput experimental methodology, in connection with DFT calculations, provides a unique foundation for further materials' discovery, including machine-learning predictions for novel alloys, the development of Pd-alloyed membranes for the purification of reformate gases, binder-free ultrathin electrocatalysts for fuel cells, and room temperature lithography-based development of nanostructures for optically driven processes.

Self-assembled chitosan-zirconium phosphate nanostructures for adsorption of chromium and degradation of dyes

Nano zirconium phosphate (ZrP) was synthesized hydrothermally using an autoclave and was further self-assembled with chitosan to form bionanocomposite CZrP. The structural characteristics of ZrP and CZrP were investigated by Fourier Transform Infrared (FT-IR), X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX), X-Ray Photelectron Spectroscopy (XPS), Electron Spin Resonance (ESR), Raman spectroscopy and Transmission Electron Microscopy (TEM) techniques. During the course of characterization, unique surface defects and superoxide anions stabilized on ZrP and CZrP were observed for the first time. The potential of the synthesized nanocomposite was investigated for adsorption of Cr(VI), a copper phthalocynanine dye- Reactive blue-21 (RB-21), azo dye- Reactive Red 141 (RR-141), a xanthene dye-Rhodamine-6G as well as binary mixtures of the dyes. Further the potential of CZRP as catalyst for the hydrogen peroxide degradation of dyes was investigated. The dyes were degraded in ˜10 min and CZrP exhibited stability during multiple runs of degradation of the dyes.

Stability of Nanopyramids of Pt/W(111) in Sulfuric Acid Medium

We report on the electrochemical behavior of Pt/W(111) nanfaceted surface in sulfuric acid. The Pt/W(111) nanofaceted surface was characterized by X-ray photelectron spectroscopy (XPS) and Scanning Tunneling Micrsocopy (STM) before and after the electrochemical measurements. The X-ray photoelectron spectroscopy (XPS) have shown a partial oxidation of W(111) during electrochemical measurements. Comparison of STM images before and after the electrochemical measurements enabled to locate the region where the oxidation process took place.

Gelatin functionalised porous titanium alloy implants for orthopaedic applications

In the present work, we studied the immobilisation of the biopolymer gelatin onto the surface of three dimensional (3D) regular Ti6Al4V porous implants to improve their surface bio-activity. The successful immobilisation of the gelatin coating was made possible by a polydopamine interlayer, a polymer coating inspired by the adhesive nature of mussels. The presence of both coatings was first optimised on two dimensional titanium (2D Ti) substrates and confirmed by different techniques including X-ray photelectron spectroscopy, contact angle measurements, atomic force microscopy and fluorescence microscopy. Results showed homogeneous coatings that are stable for at least 24h in phosphate buffer at 37°C. In a next step, the coating procedure was successfully transferred to 3D Ti6Al4V porous implants, which indicates the versatility of the applied coating procedure with regard to complex surface morphologies. Furthermore, the bio-activity of these stable gelatin coatings was enhanced by applying a third and final coating using the cell-attractive protein fibronectin. The reproducible immobilisation process allowed for a controlled biomolecule presentation to the surrounding tissue. This newly developed coating procedure outperformed the previously reported silanisation procedure for immobilising gelatin. In vitro cell adhesion and culture studies with human periosteum-derived cells showed that the investigated coatings did not compromise the biocompatible nature of Ti6Al4V porous implants, but no distinct biological differences between the coatings were found.

Synthesis, Characterization, and Catalytic Properties of Two Zwitterionic Hybrid SBA‐15 Mesoporous Silicas

AbstractZwitterionic hybrid SBA‐15 mesoporous silica materials containing both amine and sulfonic acid groups have been synthesized through cocondensation from as‐synthesized zwitterionic siloxane precursors (ZS) with tetraethoxysilane (TEOS). Characterization by XRD, TEM, and N2 adsorption–desorption measurements show that the as‐synthesized materials have ordered mesostructures. Analysis with UV, 29Si/13C cross‐polarization magic angle spinning (CP‐MAS) NMR, and X‐ray photelectron spectroscopy (XPS) and elemental analysis demonstrates that the zwitterionic parts have been successfully introduced into the silica framework, and the organic contents of 15 % hybrid samples are over 1.0 mmol/g. The presence of a secondary organoamine group enables the hybrid material to be further alkalized to achieve the desired basic properties. The materials were used as catalysts for the aldol condensation of acetone with 4‐nitrobenzaldehyde. With a good catalytic performance, the catalyst could be easily separated, recycled, and reactivated by secondary basification.

On the Surface Chemistry of LiMO2 Cathode Materials (M = [ MnNi ] and [MnNiCo]): Electrochemical, Spectroscopic, and Calorimetric Studies

This study examined the aging mechanisms of layered cathode materials for lithium batteries upon exposure to air and the influence of this aging on the thermal stability and electrochemical performance of these materials composed of solid solutions of ( or [MnNiCo]) in Li cells. A unique methodology for the quantitative characterization of surface carbonates on compounds based on differential scanning calorimeter (DSC) measurements was developed. Correlations were made between the formation of and other carbonates on the surface of the lithiated metal oxide powders and the changes in the structure and electrochemical performance of the cathode materials. The techniques used included solid-state NMR, X-ray photelectron spectroscopy, Fourier transform IR, high resolution scanning electron microscopy, high resolution transmission electron microscopy and the thermal analysis, DSC, and accelerating rate calorimetry in conjunction with electrochemical measurements.

Bifunctional Oxygen Reduction Reaction Mechanism on Non-Platinum Catalysts Derived from Pyrolyzed Porphyrins

A study on the oxygen reduction reaction (ORR) mechanism that occurs on non-platinum electrocatalysts, specifically materials derived from pyrolyzed cobalt tetramethoxyphenyl porphyrin in acidic media, is presented here. Reactant and product flux analysis is performed on rotating ring-disk electrode (RRDE) data to evaluate the non-platinum-based materials. An in-depth X-ray photelectron spectroscopy surface characterization analysis is performed and discussed in the context of structure-to-property correlations that are established using a multivariant analysis technique. Pyrolyzed cobalt porphyrin catalysts are highly heterogeneous materials that include both Co species that are associated with nitrogen and Co nanoparticles coated by “native” Co oxides. This study proposes an ORR mechanism that occurs on this class of non-Pt electrocatalysts based on structure-to-property correlations and qualitative analysis of the RRDE flux data. The combined flux analysis and structural characterization suggests that the series type, peroxide ORR pathway is supported on the bifunctional catalyst materials. In this model, two distinct active sites are involved following a bifunctional catalysis scheme. It is suggested that oxygen is initially adsorbed and reduced to peroxide on a -type site. The intermediate product, peroxide, can be further reduced to water in a series reaction step on a decorating active cobalt oxide species on the catalyst surface.

The Influence of Yb Substitution on the Magnetic, Electric Properties and Electronic Structure οf YbxGd1-xNi5System

The crystal and electronic structure, magnetic and electric properties of intermetallic compounds YbxGd1ixNi5 (x = 0:0, 0.2, 0.4, 0.5) are presented. The whole series crystallize in the hexagonal CaCu5 type of crystal structure. The ordering temperatures TC and the efiective magnetic moments decrease with increase in ytterbium concentration. The electronic structure studied by X-ray photelectron spectroscopy method shows the domination of Ni 3d states nearby the Fermi level. The multiplet structure visible in valence bands is typical of Yb 3+ ions.

Growth and photoluminescence properties of PbS nanocubes

This paper reports the synthesis of semiconductor nanocrystals of PbSthrough a facile and inexpensive synthetic route between lead acetate[Pb(Ac)2·3H2O] anddithioglycol (HSCH2CH2SH) without any surfactant. The products were characterized by x-ray diffraction (XRD),transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Ramanspectroscopy, x-ray photelectron spectroscopy (XPS) and infrared (IR) spectroscopy. Thesize of cube-shaped PbS nanocrystals can be controlled by changing the relative amount ofPb(Ac)2·3H2O and dithioglycol. Smaller cube-shaped PbS nanocrystals were obtained at higher sulfurcontent in the reaction system. The nanometre-sized single crystals of PbS measure∼83 nm × 59 nm × 22 nm and 39 nm × 10 nm × 7 nm, for lead acetate:dithioglycol ratios of 1:0.375 (denoted as PbS-1) and1:1.5 (denoted as PbS-2), respectively, when a mixture of NaOH solutionof lead acetate and ethyl alcohol solution of dithioglycol is maintained at220 °C for 4 h in a Teflon-lined autoclave. XRD patterns and HRTEM images confirm thecrystalline structure of the PbS crystals. TEM helped to determine the dimension of thesingle crystals. Raman, XPS and IR helped to further demonstrate the purity of theas-synthesized samples. The optical absorption spectra of suspensions of the thesecrystals in glycol show shifts in absorption band edge for as-prepared sample PbS-1from 246 to 271 nm and for PbS-2 from 246 to 275 nm, after four days of storage,respectively. The photoluminescence peaks from the two samples are located at 434 and433 nm for photoexcitation radiation of 315–355 nm, thus exhibiting a Stokes shiftcompared with band edge energy. The principal contribution of this work is that thenanometre-size PbS single crystals are prepared without using a surfactant ortemplating agent. The formation of a five-membered ring via the chelation between thePb2+ ion and dithioglycol is considered to be crucial in this mechanism.

Near-edge valence-band structure of amorphous hydrogenated Si–C thin films characterized by Auger and photoemission processes

A core–valence–valance Auger transition contains information about the local valence electronic structure of the probed atom. This is due to the direct coupling of the core and valence levels involved in the Auger process. In this work, a combined use of the Auger and photoemission processes to study near-edge valence-band structures of amorphous hydrogenated silicon carbide is described. Experimentally, a-Si1−xCx:H thin films were fabricated by plasma-enhanced chemical-vapor deposition using methylsilane precursors. Hydrogen was incorporated in the plasma to control the carbon composition from 0.36 to 0.83. The valence-band edge in the Si-rich region (x<0.6) was lead by both Si 3p and C 2p states, while the C 2p states from the C–C bonding configuration dominates the near-edge structure in the C-rich region (x⩾0.6). Due to the large difference in the photoionization cross sections for Si 3p and C 2p, the valance spectrum measured from x-ray photelectron spectroscopy failed to represent the near-edge structure in a-Si1−xCx:H.

Effect of HCl catalyst in the formation of flat structures of Ta2O5 thin films by sol-gel technique

Ta 2 O 5 thin films have been prepared from tantalum ethoxide solutions [Ta(C2H5O)5] by sol-gel spin coating technique on Si (100) substrates and annealed at different temperatures ranging from 500 to 800 °C for 1 h. The physical, chemical and morphological characteristics of both fine powders and thin films have been characterized by bulk techniques like N2 adsorption and He porosimetry, thermogravimetry, differential thermal analysis and surface techniques like x-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), and x-ray photelectron spectroscopy (XPS). Additions of acid catalyst (HCl) and proper thermal treatment enable the formation of highly dense flat like films of Ta2O5, as observed by AFM observations. Films prepared from neutral precursor solutions show a micrometer-range porous network and a strongly marked rough polycrystalline surface structure. HCl catalyst resulted in a decrease of the crystallization temperature to 630 °C, with respect to a crystallization temperature of 732 °C found for the neutral prepared films. The evolution of dense structures upon HCl treatment has been confirmed by surface area and density measurements on the fine powders. XPS measurements have confirmed the formation of stoichiometric Ta2O5 for the HCl prepared films. The pH of the precursor solution as well as the annealing thermal treatment have resulted in the key process parameters for controlling the microstructural characteristics of the deposited films.

Dielectric losses of self-supporting chemically vapour deposited diamond materials

Abstract The dielectric properties of microwave-assisted plasma chemical vapour deposition diamond are investigated over a wide frequency range. The dielectric losses of several grades of diamond from three different origins are measured from 1 kHz to 15 GHz by resonant methods. Very low losses were measured in some samples, but high losses were also found in similar grades. This gives rise to a great dispersion in the results, with dielectric loss values ranging from 10 −5 to 10 −1 . This shows that the dielectric loss is still an uncontrolled parameter in the commercially available diamond grades. A characterisation of the samples by X-ray photelectron spectroscopy and radioluminescence is also reported. The measured dielectric spectrum does not show a clear relationship with any of the parameters analysed.

Electronic structure of HgBa2CaCu2O6+ delta epitaxial films measured by x-ray photoemission.

The electronic structure and chemical states of ${\mathrm{HgBa}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{6+\mathrm{\ensuremath{\delta}}}$ epitaxial films have been studied with x-ray photelectron spectroscopy. Signals from the superconducting phase dominate all the core-level spectra, and a clear Fermi edge is observed in the valence-band region. The Ba, Ca, Cu, and O core levels are similar to those of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$, but distinct differences are observed in the valence bands which are consistent with differences in the calculated densities of states.

Surface Treatment of Carbon Fibers Using Low Temperature Plasma

Abstract Low temperature plasma treatment experiments were conducted on AS4 and AU4 type fibers in the presence of air, argon and nitrogen to study their effects on the resulting fiber-matrix adhesion in the composites fabricated with the fibers. Optimum conditions for the introduction of maximum surface oxygen and nitrogen functional groups on AS4 and AU4 fiber surfaces were derived. X-ray photelectron spectroscopy was performed on the fiber surfaces to determine the effect of plasma treatment on the amount and types of surface functional groups introduced. Scanning electron microscopy was performed on the fiber surfaces and the amount of surface etching and pitting was correlated to the plasma treatment conditions. Transverse tensile specimens were fabricated from treated fibers representing a few plasma treatment conditions, and their transverse tensile strengths were measured experimentally. An attempt was made to determine the effects of factors such as amount of chemical groups on the fiber surfaces...

The influence of oxygen partial pressure on the properties of DC reactive magnetron sputtered titanium oxide films

Titanium oxide thin films were grown on glass substrates by DC reactive magnetron sputtering at various oxygen partial pressures. The films were characterized using X-ray diffraction (XRD), X-ray photelectron spectroscopy (XPS), scanning electron microscopy (SEM) and optical transmittance spectra. The effects of the oxygen partial pressure on the structural and optical properties of titanium oxide films were investigated.

Characterization of the oxidation of tantalum nitride

AbstractSputter‐deposited non‐stoichiometric tantalum nitride films are used for laser‐trimmed thin‐film resistors owing to their stability and processability. The films are stabilized by heating in air to form a passive Ta2O5 film. This passive film can be destroyed if the resistors are exposed to aggressive thermal or chemical conditions. Thus we have studied sputtered TaN films and resistors deposited on SiO2 and Al2O3 substrates and exposed to either KOH solutions or air at 250–500 °C for various times. The oxidized films have been characterized with Auger electron spectroscopy (AES), x‐ray photelectron spectroscopy (XPS), x‐ray absorption near‐edge spectroscopy (XANES) and extended x‐ray absorption fine structure (EXAFS). Chemical shifts in the NOO Auger spectrum have been used to show that the initial fraction of deposited TaN reacts with the SiO2 surface to form Ta2O5. X‐ray photoelectron spectroscopy showed that although significant amounts of oxygen can be present in the sputered films, little of the tantalum is fully oxidized to Ta2O5. X‐ray photoelectron spectroscopy was also used to show that the oxide layer slowly increases in thickness when heated in air. Finally, KTaO3 was identified by XANES on the surface of films exposed to KOH. Once the passive Ta2O5 is converted to KTaO3, further oxidation of the underlying films occurs. The mechanism of oxidation of these films and the unique advantages of each spectroscopic technique are discussed.

Chemical, structural, and electronic properties of sulfur-passivated InP(001) (2×1) surfaces treated with (NH4)2Sx

Some chemical, structural, and electronic properties of (NH4)2Sx-treated InP(001) surfaces have been studied using x-ray photelectron spectroscopy, x-ray photoelectron diffraction and reflection high-energy electron diffraction. A (2×1) surface reconstruction is observed for substrates heated in vacuum at a transition temperature of about 200–350 °C. Sulfur atoms are only bonded to indium atoms and the exchange between phosphorus and sulfur occurs in the first five atomic planes leading to the formation of an InP1−xSx pseudomorphic overlayer. The sulfur surface concentration varies from about 0.85±0.15 after annealing at 350 °C to 0.5±0.15 monolayer at 550 °C. The sulfidation treatment results in (2×1) reconstructed surfaces of high thermal stability up to 560 °C and of high chemical stability. Unpinned ultraclean surfaces, free of carbon and oxygen, are obtained after vacuum annealing at 550 °C.

Adhesion characteristics of plasma-treated polypropylene to mild steel

The ability of polypropylene (PP) to adhere to mild steel depends to a large extent on the surface characteristics of both PP and steel. The adhesion of PP was improved by treatment in a cold plasma from oxidizing gases (O2, H2O, etc.). This surface functionalization was followed ex situ by means of contact angle measurements and XPS (X-ray photelectron spectroscopy) analysis. The polymer/steel assembly was fabricated by hot-pressing in vacuum, or after exposure to ambient air. Adhesion to steel, as determined by the lap-shear test, increased when the PP was treated with Ar-containing plasma gas and joined to steel after exposure to room atmosphere. Correlations between the polarity, the atomic (O/C, N/C) ratio, the dispersive component of the surface energy, and the degree of PP/steel adhesion are discussed.

The graphite intercalation compounds: A route to metallic supported clusters

New preparations of metallic-supported clusters (Fe, Co, Ni) using a graphite intercalation compound as precursor are described. The graphite-metallic halides derivatives were reduced by potassium at 300°C, and metallic particles were obtained within a graphite matrix. The reduction of a metallic halide salt dissolved in tetrahydrofuran by KC 8 leads to the formation of clusters at the edge of the graphite flakes. The products of the reactions were studied by X-ray diffraction (XRD), X-ray photelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Mechanisms based on the structure of the initial graphite intercalation compound explain the formation of these supported metallic particles.