Total Electron Yield X-ray Absorption Research Articles

Mn 2p and O 1s X-ray absorption spectroscopy of manganese oxides

Manganese oxides (MnOx) are used as electrode materials in many different energy storage applications such as batteries and supercapacitors. X-ray spectromicroscopy, using near edge X-ray absorption spectra (NEXAFS) for chemical speciation, is a powerful tool to study reduction and oxidation processes in such systems. High quality reference spectra are required for both qualitative identification and quantitative mapping of MnOx species. Here we present accurate, quantitative Mn 2p and O 1s NEXAFS spectra of MnO, MnSO4, Mn3O4, Mn2O3, α-MnO2, β-MnO2, and KMnO4, measured using both transmission and total electron yield X-ray absorption techniques. An example of the use of these reference spectra in a study of Zn/MnO2 batteries is given.

Quantitative and Fingerprint Analysis Method of Nitrogen in Graphitic Carbon Materials Using Total-Electron-Yield Soft X-ray Absorption Spectroscopy

To evaluate nitrogen in graphitic carbon materials, we propose a simple quantitative and fingerprint analysis method, which measures the total electron yield X-ray absorption spectra (TEY-XAS) of aromatic compounds possessing typical nitrogenated functional groups as standard samples, and fingerprint analysis is performed using the X-ray absorption near edge structure (XANES) in the N K and C K regions. The relationship between the atomic ratio of nitrogen to carbon (N/C) and the X-ray absorption intensity ratio of N K edge to C K edge (N Kσ*/C Kσ*) of standard samples yields a working curve to quantitatively analyze nitrogen. The successful application to carbon nitride films demonstrates that the proposed method is capable of quantitative and fingerprint analysis.

Unusual Co moment reduction in the NiCoO/Co exchange bias system

To answer the question on how the explicit mechanism of coupling in the antiferromagnetic alloy NiCoO is established when in close contact to a ferromagnetic Co layer, X-ray magnetic circular dichroism (XMCD) measurements have been performed. Precise XMCD spectra at the L 2 , 3 -edge of Ni as well as Co have been obtained at room temperature and at 80 K by measuring total electron yield X-ray absorption spectra. The Ni XMCD clearly shows the existence of free, rotatable magnetic Ni moments in the antiferromagnet. As for the Co, XMCD at room temperature shows an average magnetic moment comparable to bulk values. Cooling the sample to 80 K decreases the average Co moment by 10 % . This decrease is explained by a reduction of ferromagnetic cobalt moments related to antiferromagnetic coupling or pinning close to the interface.

Microstructure of organic–inorganic composite coatings studied by TEM and XANES

Chromate coatings on Zn or Zn alloy coated steel sheets often include silica for the aim to improve corrosion resistance. In the case of dry-in-place chromate coatings containing acrylic resin (hereafter referred to as an organic–inorganic composite coating), an addition of silica, however, did not show an improvement in corrosion resistance. The microstructures of the organic–inorganic composite coatings were observed by transmission electron microscopy (TEM) and the chemical states of Cr were investigated by the total electron yield X-ray absorption near edge structure (TEY-XANES) method. TEM samples were successfully prepared by dry ultramicrotomy preventing water-soluble components in the coatings fromdissolving out. TEY-XANES revealed the chemical states of components even in the organic matrix. Using these methods, it was found that the addition of silica changed just the morphology of the chromium compound in the organic–inorganic composite coating but not the chemical state of Cr. This is a reason for the addition of silica being not effective at improving corrosion resistance. The combination of dry ultramicrotomy-TEM and TEY-XANES spectroscopy was proven to be a powerful tool for characterizing organic–inorganic composite coatings.

Local structure around phosphorus atoms in nickel–phosphorus alloy films studied by total electron yield x‐ray absorption fine structure

AbstractNickel– phosphorus alloy films, deposited on titanium by electroless NiP plating, were studied by means of total electron yield (TEY) x‐ray absorption fine structure (XAFS) and x‐ray diffraction (XRD). XAFS spectra were analyzed by the discrete variational Xα (DV‐Xα) molecular orbital method and XAFS spectral simulation using photoelectron multiple scattering theory (FEFF8), in order to clarify the deposition mechanism of Ni3P from NiP alloy films under various heating conditions. As for the electroless NiP plating, the quasi‐intermetallic compounds of Ni3P were formed under as‐deposited conditions before the heat treatment. The samples obtained after the heat treatment were in the form of larger crystal grains of Ni3P structure. Copyright © 2001 John Wiley & Sons, Ltd.

Nanostructure of Giant Magnetoresistance Heterogeneous Alloys Ni0.20Ag0.80After Annealing

Heterogeneous alloys N 0.20 A g0.80 presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Ni K edge from as-deposited to annealed stages. Up to 150°C annealing, the Ni atoms are mainly in small poorly ordered agglomerates and the local Ni atomic environment is very stable and disordered. Up to 250°C annealing, some Ni atoms occupy substitutional sites in the Ag matrix and 40 to 50 % of the Ni nearest neighbors are Ag atoms. After annealing at 400°C during 10 mn, the nanostructures evolve towards larger, more compact and well ordered granules. The Ni-Ni distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicating that the small agglomerates are under strain in the Ag matrix.

Evolution of the Nanostructure of Giant Magnetoresistance Heterogeneous Alloys CoxAg1-x Upon Annealing

AbstractHeterogeneous alloys CoxAg1-x with atomic concentrations x=0.20 and 0.35, presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Co K edge after annealings at various temperatures. For both sample concentrations, the Co atoms are mainly in small filament agglomerates for the as-deposited and low temperature annealed samples (T<150°C). In this temperature range, the local Co atomic environment is very stable and disordered. A structural change has been detected by XANES and EXAFS analysis between the 250 and 400°C annealings. After a 400°C annealing during 10 min, the nanostructures evolve towards larger, more compact and well ordered granules. The Co-Co distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicating that the small filament-shaped agglomerates are under strain in the Ag matrix. The Debye-Waller factor of the Co0.35Ag0.65 samples decreases continously as the annealing temperature increases, as this factor drops suddenly after a 250°C annealing for the Co0.20Ag0.80 sample. The Co agglomeration is steadily larger for the Co0.35Ag0.65 sample than for the Co0.20Ag0.80 one. The Co-Ag contribution is negligible for the Co0.35Ag0.65 sample, as it represents approximately one third of the nearest neighbors for the Co0.20Ag0.80 sample from the as-deposit up to a 250°C annealing stage.