XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

Combined analysis methods for investigating titanium and nickel surface contamination after plasma deep etching

Plasma etching techniques can result in damage and contamination of materials, which, if not removed, can interfere with further processing. Therefore, characterisation of the etched surface is necessary to understand the basic mechanisms involved in the etching process and enable process control and cleaning procedures to be developed. A detailed investigation by means of the combined use of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM) has been carried out on deep titanium trenches etched by plasma. This innovative approach has provided a further insight into the microchemical structure of the surface contamination layer on both the titanium and the nickel hard mask surfaces. The described experiments were conducted on 25 to 100-μm wide trenches, first etched in bulk titanium by an optimised Cl₂/SF₆/O₂-based inductively coupled plasma process, through an electroplated nickel hard mask. The results allow to identify chlorine, fluorine and carbon as the main contaminating agents of the nickel mask and to associate three oxidation states around the etched trenches highlighting certain specific aspects related to the passivation mechanism. These observations reinforce the scientific relevance of the combined use of complementary optical and imaging analytical techniques.     

A Study of Nickel Electrodeposition on Paraffin‐Impregnated Graphite Electrode

The aim of the present work was to elucidate the mechanism of electrolytic deposition of Ni on paraffin‐impregnated graphite electrode (PIGE). This process is influenced by H₂ evolution, which occurs in the same potential region. On the basis of the results obtained by linear and cyclic voltammetry, elimination voltammetry with linear scan (EVLS) was used to evaluate both processes. H₂ Evolution alone was studied in sulfate supporting electrolyte, and the previously suggested mechanism for this process according to Volmer–Heyrovsky was confirmed by EVLS. It was found that both the Ni²⁺ concentration and pH affect the polarization behavior of PIGE significantly. Two separated cathodic peaks were observed at low Ni²⁺ and high H⁺ concentrations, and the separation was better at higher scan rates. EVLS confirmed the most‐probable mechanism of Ni deposition as being controlled by slow transfer of the first electron under formation of [NiOH]⁺ as an intermediate. EVLS also indicated slow reduction of H⁺ preceding the reduction of Ni²⁺. The same was confirmed by studying the anodic dissolution at different switching potentials. The results were complemented by scanning electron microscopy (SEM).     

玻璃表面特性的XPS研究

本文用XPS表征了玻璃表面铜、铅和锡离子的价态,并测定在浮法玻璃底表面锡离子价态的深度分布。对沾锡现象与锡离子价态之间的关系进行了讨论。     

XPS Analysis of the Aging of Thin,Adhesion Promoting,Fluorocarbon Treatments of DC Plasma Polymers

Plasma polymer treatment of aluminum alloys has recently been shown to improve adhesion of primer coatings, thereby reducing the corrosion of thusly protected panels to the levels afforded by conventional chromate conversion coating. One particular plasma polymer system, comprised of a 50 nm trimethylsilane DC plasma polymer capped by an ultrathin layer modified by DC hexafluoroethane plasma treatment, has shown tremendous adhesion increases to a wide variety of primers, yielding a coating that is virtually unremovable with conventional stripping applications. An application window was empirically deduced regarding this improved adhesion, indicating that the primer needed to be applied within 5 days of plasma treatment to display the tenacious adhesion to panels. In an effort to elucidate the differences between fresh and aged panels, an X-ray photoelectron spectroscopy (XPS) time study of this system was undertaken. Some direct correlation to this time frame was observed in the XPS data, indicating that a particular fluorocarbon structure in the films modified upon continued atmospheric exposure, rearranging the local bonding environment by introducing additional C—C bonding with an increase in oxygen incorporation.     

Structure and electrical properties of a-C∶H films deposited from CH4 decomposition in a low frequency discharge

a-C∶H films have been deposited from methane in a 20 KHz discharge. The Current Voltage characteristics of the plasma have been plotted as a function of the CH₄ pressure. It was shown that below 0.1 mbar the graphitic content in the films estimated from Raman Spectroscopy and Electron Energy Loss Spectroscopy is high enough to give electrical conductivity controlled by a percolation mechanism. It was also found that the a:c electrical responses of the deposited films are more sensitive to the structure than any other chemical analysis. The electrical analysis might be a good tool for structural investigations on a-C∶H films.     

Boron‐Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction

Molybdenum‐based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo₂B, α‐MoB, β‐MoB, and MoB₂ by arc‐melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X‐ray photoelectron spectroscopy (XPS) for the first time; MoB₂ and β‐MoB show excellent activity in the same range as the recently reported α‐MoB and β‐Mo₂C phases, while the molybdenum richest phase Mo₂B show significantly lower HER activity, indicating a strong boron‐dependency of these borides for the HER. In addition, MoB₂ and β‐MoB show long‐term cycle stability in acidic solution.     

Synthesis of TiO2 photocatalysts with abundant surface defects using a TiO2@NaCl precursor

TiO2 nanoparticles have been synthesized by using a TiO2@NaCl core-shell structure as the precursor. The surface defects were well preserved by the NaCl shell, and therefore high oxygen adsorption capacity was observed. After the NaCl shell was removed, the resulting pure TiO2 nanoparticles were of anatase phase and uniform size of around 20?24 nm. The presence of an abundance of surface defects contributes to the high photocatalytic activity of the synthesized materials, and the TiO2 materials obtained from the TiO2@NaCl precursor can be used as efficient photocatalysts for degradation of rhodamine B under UV light irradiation.     

Additional evidence for the migration of clay upon heating of clay-polypropylene nanocomposites from X-ray photoelectron spectroscopy (XPS)

The explanation for reduction in the peak heat release rate of polymer-clay nanocomposites which is normally accepted is that clay accumulates at the surface, forming a thermal shield which is also a barrier to mass transport. The process by which this clay arrives at the surface has never been described in print but the common assumption is that pyrolysis is required for clay accumulation to occur. In this work, X-ray photoelectron spectroscopy, a tool much more sensitive in surface analysis than conventional techniques, is used to probe the surface of polypropylene-clay nanocomposites that have been annealed at relatively low temperatures, well below that required for pyrolysis. The composition of the surface changes with time and temperature of annealing, which provide a strong indication that the clay at the surface undergoes chemical change at fairly low temperatures.     

高活性多羟基结构态亚铁FHC(Cl~-)去除Se(Ⅳ)的性能与机制

通过慢速滴定法合成了高活性的多羟基结构亚铁FHC(Cl~-),对FHC(Cl~-)去除Se(Ⅳ)的动力学进行了研究,并对体系中的投加量、pH值、溶解氧和氯化钠浓度进行了响应面分析.研究结果表明,FHC(Cl~-)去除Se(Ⅳ)的表观速率常数k_(obs)=0.60 min~(-1),约为纳米零价铁的4倍和零价铁的16倍.由Box-Benhnken设计拟合得出响应值对编码自变量的二次多项回归方程为Y(c/c_0)=0.14-0.20A+0.017B-0.27C-0.019D-0.047AB-0.095AC+0.13AD-0.010BC-0.082BD+0.33A~2+0.023B~2+0.097C~2+0.065D~2,最优条件为:FHC(Cl~-)投加量98 mg/L,溶液的pH=7.5,氯化钠浓度1 mmol/L,体系为封闭.产物XPS分析结果表明,Se(Ⅳ)最终被FHC(Cl~-)还原为Se(0)或Se(-Ⅱ).     

Modulation of the crystallinity of hydrogenated nitrogen-rich graphitic carbon nitrides

An hydrogenated nitrogen-rich graphitic carbon nitride, structurally related to the theoretical graphitic phase of C₃N₄, has been synthesized in a bulk well-crystallized form. This new material was prepared by thermal decomposition of thiosemicarbazide up to 600 °C at ambient pressure under nitrogen flow. Its composition was determined by elemental combustion analysis. Powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and C¹³ MAS NMR characterizations were performed. This material can be schematically described with a two-dimensional framework and a composition close to C₃N_4.17H_1.12. In this nitrogen-rich material, C₃N₃ voids are fully occupied by water molecules which are strongly trapped into the material. A loss of crystallinity associated with a modification of the thermal behavior is observed when the amount of trapped molecules decreases in the graphitic material, order being damaged both between and in the graphitic planes.     

X-ray photoelectron spectroscopy: A new method for determination of copolymer composition,and monomer reactivity ratios and monomer sequence distribution therefrom

Copolymer compositions and reactivity ratios for the radical copolymerization of styrene with acrylonitrile have been determined by x-ray photoelectron spectroscopy (XPS). The results obtained by this technique were confirmed by elemental as well as ¹H-NMR (nuclear magnetic resonance) analysis. The monomer sequence distributions have also been calculated utilizing the monomer reactivity ratio values obtained by three different techniques viz., XPS, ¹H-NMR, and elemental analysis. The agreement between the monomer sequence distributions in the copolymer chain by these methods is very satisfactory. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2049–2056, 1997     

Determination of Arsenic Speciation in Complex Environmental Samples by the Combined Use of TEM and XPS

Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) have been used to refine the solid-state speciation of As in mine waste materials and stream-bed sediments from the Baccu Locci mine area in Sardinia, Italy. The combined use of TEM and XPS confirmed previous studies and pointed out that: (i) As is contained in plumbojarosite in substitution of S, (ii) As-bearing Fe(III) hydroxides are represented by arsenical 2-line ferrihydrites with most Fe/As molar ratios in the range of 1.6–3.2, (iii) scorodite often lacks long range order. Arsenatian plumbojarosite will tend to dissolve incongruently in ferrihydrite, releasing Pb and As into water. However, Pb is fated to precipitate as Pb(OH)₂ or to be adsorbed onto ferrihydrite, whereas As mobility is favoured since the adsorptive capacity of ferrihydrite for As(V) is notably reduced under the neutral to alkaline pH conditions occurring in the Baccu Locci stream water. Arsenical ferrihydrites will tend to be converted into goethite or hematite with time, releasing As into the water as a consequence of the notably lower density of the adsorption sites of the crystalline Fe(III) phases. Also scorodite is relatively unstable under the Baccu Locci system conditions, and its stability is further decreased owing to the higher solubility of the amorphous form compared to the crystalline one.     

Understanding the Buoy Effect of Surface-Enriched Pt Complexes in Ionic Liquids: A Combined ARXPS and Pendant Drop Study**

Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C₄C₁Im][PF₆] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our previous angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5 %_mol down to 1 %_mol and present complementary surface tension pendant drop (PD) measurements under ultraclean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface derived from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1 %_mol. It also displays a strong temperature dependence, which was not observed for 5 %_mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of IL-based catalyst systems with large contact areas to the surrounding reactant/product phase, such as in supported IL phase (SILP) catalysis.     

Surface chemical analysis of copper powder used in additive manufacturing

Additive manufacturing (AM) has during years gained significant interest owing to its endless component design possibilities. One of the most popular AM techniques is laser powder bed fusion (LPBF), which selectively melts metal powder layer-by-layer in a chamber with protective argon atmosphere. This technique is attractive for realizing Cu-based products in which the high electrical conductivity of Cu is combined with component design possibilities. The successful use of Cu powder not only poses challenges owing to the high reflectivity and thermal conductivity of Cu but also involves the important concern of controlling the powder surface chemistry since the powder surface constitutes the main source of oxygen. It is of crucial importance to control the oxygen level in order to maintain good electrical conductivity and brazing ability of the AM-fabricated Cu-part. In LPBF, fine spherical powder with size of 10–60 μm is used, providing significant specific surface area, and this powder is also usually recycled several times, and hence, the role of powder surface chemistry is evident. Two kinds of copper powder with purities 99.70 and 99.95 wt% were analysed in both virgin and in used conditions after numerous printing cycles using LPBF. The powder was analysed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A clear difference between the two powder grades in terms of surface chemistry was observed. The oxide thickness and bulk oxygen content increased for both powder grades after recycling. The surface oxides under different conditions are identified and the effect of powder purity on the oxide formed is discussed.     

Surface properties of fluorinated single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) were fluorinated at several different temperatures. The change of atomic and electronic structures of fluorinated SWCNTs was investigated using X-ray photoelectron spectroscopy (XPS), electrical resistivity measurements and transmission electron microscopy (TEM). The amount of doped fluorine increases with increasing doping temperature, and the fluorine atoms are covalently attached to the side-wall of the SWCNTs. From Raman spectra and HRTEM study, the strong fluorination on the SWCNTs leads to the breaking of carbon–carbon bonds and the disintegration of tube structure. Several intermediate phases of fluorinated SWCNTs are observed during e-beam irradiation in HRTEM.     

Reactions at the interface of ultrathin Fe films deposited on ZnO(0 0 0 1) and ZnO(0 0 0−1) single crystal substrates

In this work we focus on the chemical interactions at the interface formed during the room temperature deposition of thin Fe films on polar ZnO surfaces via electron beam evaporation. The Fe is found to grow in layers and to form polycrystalline, disordered films. At the interface a considerable reaction takes place. By X-ray photoelectron spectroscopy, the formation of Fe²⁺ and metallic zinc species is detected.     

The effect of glow discharge sputtering on the analysis of metal oxide films

The potential of radiofrequency glow discharge optical emission spectrometry (rf-GD-OES) for the quantification and the solid-state speciation of metal oxide films has been investigated in this work. Two types of oxide coatings, an iron oxide film deposited on silicon and a chromate conversion coating (CCC), were studied at 700 Pa of pressure and 30 W of forward power. The metal to oxygen ratios in the quantitative depth profiles (Fe/O and Cr/O, respectively) were used to evaluate the oxidation states of iron and chromium in the oxide films, demonstrating the capability of GD-OES technique for depth-resolved solid-state speciation. Furthermore, the effect of glow discharge sputtering on the samples surface in terms of modifications in the surface morphology and species transformations, were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The iron and chromium oxidation states were carefully studied by XPS at the original samples surface and at the bottom of GD craters, and a systematic reduction of metal elements was observed after rf-GD-OES analysis. In the case of thin oxide films, preferential sputtering can be considered as a critical factor since oxygen atoms can be preferentially sputtered, leaving a metal-enriched surface and, therefore, promoting the reduction of metal elements. In the present study preferential sputtering was found to be sample dependent, changing the proportion of the metal reduction in the oxide film with its composition. Additionally, alternative sputter-depth-profiling techniques such as secondary ion mass spectrometry (SIMS), femtosecond laser ablation (fs-LA), and XPS ion gun were used for the analysis of the CCC in order to evaluate the reduction of Cr⁶⁺ to Cr³⁺ depending on the sputtering mechanism.     

Formation of ultra-thin prussian blue layer on carbon steel that promotes adherence of hybrid polypyrrole based protective coating

Electrodeposition of well-adhering polypyrrole-based hybrid films containing hexacyanoferrate(II,III) anions from neutral solutions of pyrrole and potassium hexacyanoferrate(II) on medium carbon (0.48% C) steel has been described. The resulting polypyrrole coatings that are doped with hexacyanoferrate(II,III) anions show protective properties against pitting corrosion of carbon steel substrates in strongly acidic media containing chlorides (0.1 mol dm^–3 HCl + 0.4 mol dm^–3 NaCl). Polypyrrole acts as a stable host matrix for inorganic anions. The presence of negatively charged species (hexacyanoferrates) in the polymer backbone tends to block the access of pitting-causing anions (chlorides) to the surface of steel. The Fe(CN)₆^3-/4– anions existing in the vicinity of steel substrate stabilizes its surface by forming an overcoating in the form of sparingly soluble metal hexacyanoferrate, mostly Prussian blue (PB), microstructures. It has been demonstrated that by applying cyclic voltammetry and X-ray photoelectron spectroscopy, the presence of traces of free cyanide anions promotes the formation of PB on carbon steel surface which results in increasing the adherence of polypyrrole-based films to the metallic substrate. Morphology of the protective composite films is also addressed.Dedicated to Prof. G. Horanyi on the occasion of his 70th birthday     

Electrochemical Reduction and Oxidation of Six Natural 2′‐Deoxynucleosides at a Pyrolytic Graphite Electrode in the Presence or Absence of Ambient Oxygen

Recently we have demonstrated that pyrolytic graphite electrodes (PGE) offer a broad analytically useful potential window, ranging from about ?2.0 V to +1.6 V vs. Ag|AgCl|3 M KCl, which enables to use the PGE not only for anodic measurements, but also for direct reduction of nucleobases in DNA oligonucleotides. In this follow‐up study, we have focused on the electrochemical behavior of four 2′‐deoxynucleosides derived from adenine, guanine, cytosine, thymine, uracil, and 5‐methyl cytosine on the PGE. On one hand we have obtained analogous primary redox responses as previously with the oligonucleotides. On the other hand, significant differences were observed, particularly when considering secondary responses involving products of the primary conversions, suggesting involvement of different mechanisms. Further we have found that presence of the ambient oxygen in the electrolyte does not dramatically affect the redox signals of the nucleosides. This finding is in contrast with DNA responses measured at the mercury‐based electrodes, where deaeration prior to the measurements was necessary. We demonstrate that all studied nucleosides can be analyzed using a simple ex situ (medium exchange) procedure.