Development of Surface Fluorescence X‐Ray Absorption Fine Structure Spectroscopy Using a Laue‐Type Monochromator

Surface fluorescence X‐ray absorption fine structure (XAFS) spectroscopy using a Laue‐type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X‐rays from the bulk even in the presence of solution. We applied the technique to submonolayer (～10¹⁴ atoms cm^?2) Pt on HOPG and successfully obtained high signal/noise in situ XAFS data in combination with back‐illuminated fluorescence XAFS (BI‐FXAFS) spectroscopy. This technique allows in situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes.     

Consequences of x‐ray absorption fine structure for quantitative core‐level photoelectron spectroscopy

The dependence of x‐ray absorption fine structure (XAFS) on the chemical environment implies a corresponding environmental dependence of photoionization cross‐sections. The practical consequences of the XAFS for quantitative core‐level photoelectron spectroscopy have been studied for a number of materials with the help of simulations based on the ab initio FEFF code. The XAFS effects are predicted to be significant only for photoelectron kinetic energies below 250–300 eV. These effects take the form of systematic sensitivity factor variations between different chemical structural environments (e.g. compound materials quantified with reference to elemental standards). Apart from a few exceptions (e.g. the 2p core levels of Zn, Ga, Ge and As in metallic environments), the XAFS should introduce no significant errors when conventional Mg Kα or Al Kα sources are used for excitation. For core‐level spectra excited with synchrotron radiation or He II radiation sources, the quantification errors can readily approach or exceed 10% at room temperature (and are expected to increase at lower temperatures). Copyright © 2003 John Wiley & Sons, Ltd.     

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum‐Supported Cerium‐Zirconium Oxide Three‐Way Catalyst Particles by Hard X‐ray Spectro‐Ptychography

The cerium density and valence in micrometer‐size platinum‐supported cerium–zirconium oxide Pt/Ce₂Zr₂O_x (x=7–8) three‐way catalyst particles were successfully mapped by hard X‐ray spectro‐ptychography (ptychographic‐X‐ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic‐XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce₂Zr₂O_x particles. Ptychographic‐XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.     

Operando XAFS Imaging of Distribution of Pt Cathode Catalysts in PEFC MEA

Three‐dimensional imaging using X‐ray as a probe is state‐of‐the‐art for the characterization of heterogeneous materials. In addition to simple imaging of sample morphology, imaging of elemental distribution and chemical states provides advanced maps of key structural parameters of functional materials. The combination of X‐ray absorption fine structure (XAFS) spectroscopy and three‐dimensional imaging such as computed tomography (CT) can visualize the three‐dimensional distribution of target elements, their valence states, and local structures in a non‐destructive manner. In this personal account, our recent results on the three‐dimensional XAFS imaging for Pt cathode catalysts in the membrane electrode assembly (MEA) of polymer electrolyte fuel cell (PEFC) are introduced. The distribution and chemical states of Pt cathode catalysts in MEAs remarkably change under PEFC operating conditions, and the 3D XAFS imaging revealed essential events in PEFC MEAs.     

X‐ray photoemission spectroscopy investigation of Ce1 − xEuxCrO3 nano‐powders

To reveal the surface elemental composition and chemical states of the Ce_{1 ? x} Eu_x CrO₃ nano‐powders (x= 0.0, 0.3, 0.5, 0.7, 0.8, 1.0), X‐ray photoelectron spectroscopy was carried out in two conditions of before and after surface cleaning. This surface characterization described the core level binding energies of cerium, europium and chromium with different oxidation states. These results verified the morphology of the particles' surface which can be a confirmation of the spin disorder in these core‐shell structures. The effect of surface Ar sputtering on the oxidation states were studied. Copyright © 2016 John Wiley & Sons, Ltd.     

Advances in Synchrotron Radiation‐based X‐ray Absorption Spectroscopy to Characterize the Fine Atomic Structure of Single‐atom Nanozymes

Single‐atom nanozymes (SAzymes) with high atomic utilization, excellent catalytic activities, and selectivity have recently attracted significant interest. Usually, they contain only isolated metal atoms embedded in host matrices. However, traditional measuring instruments are extremely difficult to obtain their useful structural information due to ultra‐low metal loading, amorphous structure, coordination with light‐weight surface atoms and/or co‐existing of other metal elements. Synchrotron radiation‐based X‐ray absorption fine structure spectroscopy (XAFS) has demonstrated its usefulness for this type of catalyst. In this mini‐review, we have summarized the recent progress using XAFS to characterize the fine atomic structure of these nanozymes. The synthetic strategies of SAzymes, the principle of XAFS, delicate structural information by XAFS, and the applications of SAzymes have been presented. Furthermore, the outlook and challenges in this active research field have also been discussed. We expect that the help of XAFS can offer a wealth of opportunities to design and develop more efficient SAzymes and apply them to various fields.     

Surface heterogeneity study of some reference Cu–Ag alloys using laser‐induced breakdown spectroscopy

Investigation of the chemical composition, surface structure, metallurgical features, corrosion mechanism, and surface modification techniques of archeological metallic artifacts from Romans and pre‐Roman times aimed to simulate the most commonly used Cu‐based and Ag‐based alloys. These simulated reference alloys will be used as sacrificial materials to study the most appropriate conservation materials and procedures. In the present work, laser‐induced breakdown spectroscopy (LIBS) is introduced as a new validated surface mapping technique to study the micro‐chemical distribution of elements in binary reference copper–silver alloy samples. Using different techniques for surface and bulk analysis, such as SEM coupled with energy‐dispersive X‐ray spectroscopy and X‐ray diffraction, it has been proven that LIBS is a simple, sensitive, and direct technique in the determination of heterogeneity of the sample's surface. By changing the laser wavelength (λ/nm) and focal length of the used focusing lens (f/cm), different spot sizes can be obtained. It was possible to control the spatial resolution in mapping the investigated samples' surface and to achieve local chemical information. In the present work, Q‐switched neodymium‐doped yttrium aluminum garnet laser has been used at its fundamental wavelength 1064 nm and its second harmonic 532 nm. The studied samples were specially manufactured heterogeneous copper–silver alloys with known grain size as studied via SEM investigation. The obtained LIBS results are in good agreement with those by other analytical techniques and extend the applicability of the surface techniques to study metallic ancient objects. Copyright © 2015 John Wiley & Sons, Ltd.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

Summary of ISO/TC 201 Standard: XIX ISO 17331:2004—Surface chemical analysis—Chemical methods for the collection of elements from the surface of silicon‐wafer working reference materials and their determination by total‐reflection x‐ray fluorescence (TXRF) spectroscopy

This international standard specifies chemical methods for the collection of iron and/or nickel from the surface of silicon‐wafer working reference materials by the vapour‐phase decomposition method or the direct acid droplet decomposition method. The determination of the elements collected may be carried out by total‐reflection x‐ray fluorescence spectroscopy, as well as by graphite‐furnace atomic absorption spectroscopy or inductively coupled plasma mass spectroscopy. This international standard applies to iron and/or nickel atomic surface densities from 6 × 10⁹ to 5 × 10¹¹ atoms cm^?2. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface modification of polystyrene biochip for biotin‐labelled protein/streptavidin or neutravidin coupling used in fluorescence assay

A polystyrene biosensing chip to be used as a medical diagnostic tool has been developed. Its surface functionalization is optimized to bind the bioanalytes with high efficiency. Coatings of allyldextran monolayers were carried out on polystyrene chips activated with γ‐irradiation. The effect of the concentration of allyldextran solution on the coating efficiency was studied by surface‐sensitive x‐ray photoelectron spectroscopy (XPS) and contact‐angle measurements. In a second step, sodium periodate chemistry was applied to functionalize the dextran layer, followed by coupling with streptavidin or neutravidin. Copyright © 2004 John Wiley & Sons, Ltd.     

Preparation of Polyfunctional Biaryl Derivatives by Cyclolanthanation of 2‐Bromobiaryls and Heterocyclic Analogues Using nBu2LaCl⋅4 LiCl

Various aryl‐ and heteroaryl‐substituted 2‐bromobiaryls are converted to cyclometalated lanthanum intermediates by reaction with nBu₂LaCl?4 LiCl. These resulting lanthanum heterocycles are key intermediates for the facile preparation of functionalized 2,2′‐diiodobiaryls, silafluorenes, fluoren‐9‐ones, phenanthrenes, and their related heterocyclic analogues. X‐ray absorption fine structure (XAFS) spectroscopy was used to rationalize the proposed structures of the involved organolanthanum species.     

Wet‐Chemical Synthesis of Nanoscale Iron Boride,XAFS Analysis and Crystallisation to α‐FeB

The reaction of lithium tetrahydridoborate and iron bromide in high boiling ether as reaction medium produces an ultrafine, pyrophoric and magnetic precipitate. X‐ray and electron diffraction proved the product to be amorphous. According to X‐ray absorption fine structure spectroscopy (XAFS) the precipitate has FeB structure up to nearly two coordination spheres around an iron absorber atom. Transmission electron microscopy (TEM) confirms the ultrafine powder to be nanoscale. Subsequent annealing at 450 °C causes the atoms to arrange in a more distinct FeB structure, and further thermal treatment to 1050 °C extends the local structure to the α‐modification of FeB. Between 1050 °C and 1500 °C α‐FeB is transformed into β‐FeB.     

Monte‐Carlo simulation of x‐ray photoelectron emission from silver

Silver 3d x‐ray photoelectron spectroscopy (XPS) spectra were simulated with the Monte‐Carlo method using an effective energy‐loss function that was derived from a reflected electron energy‐loss spectroscopy (REELS) analysis based on an extended Landau approach. After confirming that Monte‐Carlo simulation based on the use of the effective energy‐loss function can successfully describe the experimental REELS spectrum and Ag 3d XPS spectrum, we applied Monte‐Carlo simulation to predict the angular distribution of Ag 3d x‐ray photoelectrons for different x‐ray incidence angles and different photoelectron take‐off angles. The experimental photoelectron emission microscope that we are constructing was confirmed as being close to the optimum configuration, in which the x‐ray incident angle as measured from the surface normal direction is 74° and the photoelectron take‐off angle is set normal to the surface. The depth distribution functions of the Ag 3d X‐ray photoelectrons for different energy windows suggest that the photoelectron emission microscope will exhibit greater surface sensitivity for narrower photoelectron energy windows. Copyright © 2003 John Wiley & Sons, Ltd.     

X‐Ray Scattering and Imaging Studies of Electrode Structure and Dynamics

We will review structures and dynamics of electrode interfaces studied in situ using x‐ray scattering and imaging techniques. The examples cover single‐crystal and nanocrystal structures relevant to electrocatalytic activities, anodic oxidation and corrosion, aqueous dissolution reactions, surface reconstructions, and surface modifications by under potential deposition. The x‐ray techniques include the widely used traditional surface x‐ray scattering, such as crystal truncation rods and x‐ray reflectivity, as well as recently developed resonance surface scattering, coherent surface x‐ray photon correlation spectroscopy, coherent x‐ray Bragg diffraction imaging, and surface ptychography. Results relevant to various electrochemical phenomena will be highlighted.     

Summary of ISO/TC 201 Technical Report: ISO/TR 19319: 2003—Surface chemical analysis—Auger electron spectroscopy and x‐ray photoelectron spectroscopy—Determination of lateral resolution,analysis area and sample area viewed by the analyser

ISO Technical Report 19319:2003 contains information on the determination of lateral resolution, analysis area and sample area viewed by the analyser in surface analyses by Auger electron spectroscopy and x‐ray photoelectron spectroscopy. This article provides a brief summary of this information. Copyright © 2004 John Wiley & Sons, Ltd.     

1,1′‐Nitramino‐5,5′‐bitetrazoles

1,1′‐Dinitramino‐5,5′‐bitetrazole and 1,1′‐dinitramino‐5,5′‐azobitetrazole were synthesized for the first time. The neutral compounds are extremely sensitive and powerful explosives. Selected nitrogen‐rich salts were prepared to adjust sensitivity and performance values. The compounds were characterized by low‐temperature X‐ray diffraction, IR and Raman spectroscopy, multinuclear NMR spectroscopy, elemental analysis, and DTA/DSC. Calculated energetic performances using the EXPLO5 code based on calculated (CBS‐4M) heats of formation and X‐ray densities support the high performances of the 1,1′‐dinitramino‐5,5′‐bitetrazoles as energetic materials. The sensitivities toward impact, friction, and electrostatic discharge were also explored. Most of the compounds show sensitivities in the range of primary explosives and should only be handled with great care!     

Summary of ISO/TC201 standard: ISO/TR 18394:2006—surface chemical analysis—Auger electron spectroscopy—derivation of chemical information

ISO/TR 18394 provides guidance for the identification of chemical effects on x‐ray or electron‐excited Auger electron spectra as well as for applications of these effects in chemical characterization of surface/interface layers of solids. In addition to elemental composition, information can be obtained on the chemical state and the surrounding local electronic structure of the atom with the initial core hole from the changes of Auger electron spectra upon the alteration of its local environment. The methods of identification and use of chemical effects on Auger electron spectra, as described in this Technical Report, are very important for accurate quantitative applications of Auger electron spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of AA2024‐T3 surface pretreatment on the physicochemical properties and the anticorrosion performance of poly(γ‐glycidoxypropyltrimethoxysilane) sol‐gel coating

This study investigated the dependence of the anticorrosion performance of a poly(γ‐glycidoxypropyltrimethoxysilane) (poly(γ‐GPTMS)) sol‐gel coating on AA2024‐T3 aluminum alloy surface state. Two different AA2024‐T3 surface pretreatment procedures were tested: a degreasing with acetone and a chemical multistep etching process (industrial chemical etching pretreatment). Poly(γ‐GPTMS) coatings were deposited onto both pretreated surfaces using the dip‐coating technique. Surfaces were characterized principally by scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared attenuated total reflectance, contact angles, and roughness measurements. Moreover, for the coated AA2024‐T3 surfaces, a pull‐off test was used to evaluate the poly(γ‐GPTMS) adhesion to the pretreated surface. Bare surface properties depended on the applied pretreatment. The chemically etched surface was the roughest and the most concentrated in hydroxyl groups. In addition, comparatively to the degreased surface, it has a more hydrophobic character. Poly(γ‐GPTMS) coating revealed an uneven nature and a poor adhesion once it was deposited onto the degreased surface. Coatings anticorrosion performances were evaluated using electrochemical impedance spectroscopy measurements (EIS). Electrochemical impedance spectroscopy data proved that the sol‐gel coating applied onto the chemically etched surface had better anticorrosion performance.     

Surface study of sintered alumina substrates using solution‐processed ZnO nanorods as a microscopic wettability indicator

Wettability and its distribution are crucial factors that indicate the surface conditions of substrates. We report a surface study of sintered alumina substrates using solution‐processed ZnO nanorods as a microscopic wettability indicator. The alumina substrates comprising of micrometer‐sized sintered grains were treated separately with ultraviolet/ozone (dry process) or ozone water (wet process), and their surface conditions were characterized by conventional surface analysis methods, such as water contact angle, X‐ray photoelectron spectroscopy and grazing angle attenuated total reflection Fourier transform infrared spectroscopy. The results showed that the alumina substrates treated with ultraviolet/ozone and ozone water had distinct clean surfaces compared to those without treatments, but no significant differences were noted between these two ozone‐based treatments. Then, as a wettability‐sensitive deposition technique, Pd‐catalyzed chemical deposition of ZnO nanorods was performed on the alumina substrates, which involved dip coating of Pd nanoparticles on the substrates in aqueous solutions, followed by the chemical solution growth of ZnO. Vertically aligned ZnO nanorods of ~85 nm in diameter were densely formed along a rough surface of the substrates. Morphological uniformity of the nanorods varied depending on the treatment condition; local surfaces with sufficient wettability provided uniform nanorods but those with insufficient wettability gave irregular nanorods, making the visualization of the microscopic surface wettability possible. Copyright © 2016 John Wiley & Sons, Ltd.     

AuN films – structure and chemical binding

AuN films were produced on 304 stainless steel using an arc‐pulsed – assisted plasma physical vapor deposition system. The deposition was performed using an Au target in a nitrogen atmosphere at different pressures. The films were characterized using x‐ray photoelectron spectroscopy and x‐ray diffraction. A 398.1‐eV binding energy was observed and assigned to gold nitride species. The x‐ray diffraction patterns displayed a crystallographic structure that corresponded to the Au‐fcc phase with broad diffraction lines. The observed widening of the Bragg diffraction lines (rocking curves) can be attributed to the presence of interstitial nitrogen atoms in the Au‐fcc structure. Copyright © 2015 John Wiley & Sons, Ltd.