EFFECT OF THE ANNEALING TEMPERATURE ON THE ELECTRONIC AND ATOMIC STRUCTURES OF EXCHANGE-BIASED NiFe–FeMn BILAYERS

2002 ◽  
Vol 09 (01) ◽  
pp. 293-298 ◽  
Author(s):  
J. M. LEE ◽  
J. C. JAN ◽  
J. W. CHIOU ◽  
W. F. PONG ◽  
M.-H. TSAI ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Nearest Neighbor ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Atomic Structures ◽  
Bilayer Films ◽  
Fe And Mn ◽  
Fourier Transform Spectra ◽  
X Ray Absorption

In this study we measured the Fe, Mn, and Ni L2,3-edge X-ray absorption near-edge structure (XANES) and K-edge extended X-ray absorption fine structure (EXAFS) of the ferromagnetic (FM) NiFe and antiferromagnetic (AFM) FeMn bilayer films prepared with various annealing temperatures. The branching ratios of the white-line intensities in the Fe, Mn, and Ni L2,3-edges XANES spectra and consequently the magnetic properties of these exchange-biased FM NiFe - AFM FeMn bilayers are found to depend strongly on the annealing temperature. We find that the first peak in the Fe, Mn, and Ni K-edge EXAFS Fourier transform spectra are very similar, which suggests that the nearest-neighbor bond lengths among Fe, Mn, and Ni atoms are essentially the same in the NiFe–FeMn bilayers. However, the peaks at distances greater than ~ 3 Å appear to be sensitive to the annealing temperature especially for the Fe and Mn K-edge spectra, which suggests that annealing alters the atomic structures of the next-nearest-neighbor and more distant shells surrounding the Fe and Mn atoms in the NiFe–FeMn bilayers.

Fluorescence Extended X-Ray Absorption Fine Structure Study on Local Structures of Rare-Earth-Doped InGaGdN

2016 ◽  
Vol 1133 ◽  
pp. 429-433
Author(s):  
Siti Nooraya Mohd Tawil ◽  
Shuichi Emura ◽  
Daivasigamani Krishnamurthy ◽  
Hajime Asahi
Keyword(s):  
Fine Structure ◽  
Rare Earth ◽  
Nearest Neighbor ◽  
Structure Study ◽  
Edge Structure ◽  
X Ray ◽  
Local Structures ◽  
Absorption Fine ◽  
X Ray Absorption

Local structures around gadolinium atoms in rare-earth (RE)-doped InGaGdN thin films were studied by means of fluorescence extended X-ray absorption fine structure (EXAFS) measured at the Gd LIII-edges. The samples were doped with Gd in-situ during growth by plasma-assisted molecular beam epitaxy (PAMBE). Gd LIII-edge EXAFS signal from the GaGdN, GdN and Gd foil were also measured as reference. The X-ray absorption near edge structure (XANES) spectra around Gd LIII absorption edge of InGaGdN samples observed at room temperature indicated the enhancement of intensities with the increase of Gd composition. Further EXAFS analysis inferred that the Gd atoms in InGaN were surrounded by similar atomic shells as in the case of GaGdN with the evidence indicating majority of Gd atoms substituted into Ga sites of InGaGdN. A slight elongation of bond length for the 2nd nearest-neighbor (Gd–Ga) of sample with higher Gd concentration was also observed.

scholarly journals An X-ray absorption method for the identification of calcium phosphate species using peak height ratios

2013 ◽  
Vol 10 (11) ◽  
pp. 18723-18756 ◽  
Author(s):  
J. F. Oxmann
Keyword(s):  
Calcium Phosphate ◽  
Peak Height ◽  
Apatite Formation ◽  
Spectral Features ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Compound Libraries ◽  
Phosphate Species ◽  
X Ray Absorption

Abstract. X-ray absorption near edge structure (XANES) studies on calcium phosphate species (Ca-P) deal with marginal differences among subtle spectral features despite a hitherto missing systematic breakdown of these differences. Related fingerprinting approaches depend therefore on spectral libraries that are not validated against each other, incomplete and scattered among publications. This study compiled a comprehensive spectral library from published reference compound libraries in order to establish more clear-cut criteria for Ca-P determination by distinctive phosphorus K-edge XANES features. A specifically developed normalization method identified diagnostic spectral features within the compiled library, e.g. by uniform calculation of ratios between white-line and secondary peak heights. Post-processing of the spectra (n = 81) verified distinguishability among most but not all phases, which included hydroxylapatite (HAP), poorly crystalline HAP, amorphous HAP, fluorapatite, carbonate fluorapatite (CFAP), carbonate hydroxylapatite, β-tricalcium phosphate, octacalcium phosphate (OCP), brushite, monetite, monocalcium phosphate, amorphous calcium phosphate (ACP), anapaite, herderite, scholzite, messelite, whiteite and P on CaCO3. Particularly, peak height ratios significantly improved analyte specificity, e.g. by supplementary breakdown into OCP and ACP. The spectral analysis also revealed Ca-P standards that were rarely investigated or inappropriately synthesized, and thus provides a basis for standard selection and synthesis. The developed method and resulting breakdown by species were subsequently tested on Ca-P spectra from studies on bone and sediment. The test indicated that bone material likely comprises only poorly crystalline apatite, which implies direct nucleation of apatite in bone. This biological apatite formation is likely opposed to that of sedimentary apatite, which apparently forms by successive crystallization. Application of the method to μXANES spectra of sediment particles indicated authigenic apatite formation by an OCP precursor.

Tb L3-edge X-ray Absorption Near-edge Structure Spectroscopic Analysis of Terbium-doped Phosphor Compoundsfor Plasma Display Panel Applications

2002 ◽  
Vol 17 (1) ◽  
pp. 31-35 ◽  
Author(s):  
Yong Gyu Choi ◽  
Kee-Sun Sohn ◽  
Kyong Hon Kim ◽  
Hee Dong Park
Keyword(s):  
Spectroscopic Analysis ◽  
Green Emission ◽  
Concentration Quenching ◽  
Plasma Display Panel ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Line Absorption ◽  
Plasma Display ◽  
X Ray Absorption

We have analyzed Tb L3-edge x-ray absorption near-edge structure spectra of Tb-doped phosphor compounds for plasma display panel applications. Intensity and lifetime of the green emission from the Tb3+:5D4→7F5 transition were measured with respect to nominal terbium concentration in the host compounds, i.e., YBO3, YPO4,and Y4Al2O9, all of which were made through the solid-state reaction. Typical concentration quenching was evident on the fluorescence intensity and the fluorescing level lifetime in our samples. From the analyses of white line absorption peaks at TbL3-edge, it was verified that terbium is essentially trivalent in all the samples, even invery highly concentrated ones. Thus, this implies that the concentration quenching was not caused by presence of mixed-valent states of terbium. Instead, it is believed that anonradiative energy transfer route among Tb3+ ions might be responsible for thebehavior.

Stoichiometric Study of Iron Sulfide Prepared by Mechanochemical Reaction

2007 ◽  
Vol 561-565 ◽  
pp. 2099-2102 ◽  
Author(s):  
Chung Kwei Lin ◽  
Chin Yi Chen ◽  
Pee Yew Lee ◽  
Chih Chieh Chan
Keyword(s):  
Ball Milling ◽  
Nearest Neighbor ◽  
Iron Sulfide ◽  
Structural Evolution ◽  
High Energy ◽  
Mechanochemical Reaction ◽  
Iron Sulfides ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

In the present study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe50S50. A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The prepared powders were examined by conventional X-ray diffractometry and synchrotron X-ray absorption spectroscopy. The experimental results revealed that mechanochemical reactions occurred during the ball milling process for all the compositions. The Fe50S50 phase was obtained after ball milling for 20 h. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function (RDF) for iron decreased when iron sulfides formed. X-ray absorption near edge structure (XANES) of S K-edges distinguished better the structural evolution of these iron sulfides.

Effect of gamma irradiation on X-ray absorption and photoelectron spectroscopy of Nd-doped phosphate glass

2016 ◽  
Vol 23 (6) ◽  
pp. 1424-1432 ◽  
Author(s):  
V. N. Rai ◽  
Parasmani Rajput ◽  
S. N. Jha ◽  
D. Bhattacharyya ◽  
B. N. Raja Shekhar ◽  
...  
Keyword(s):  
Gamma Irradiation ◽  
Photoelectron Spectroscopy ◽  
Glass Matrix ◽  
Structural Changes ◽  
Phosphate Glasses ◽  
White Line ◽  
Edge Structure ◽  
Xps Spectra ◽  
X Ray ◽  
X Ray Absorption

X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) of Nd-doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of theL3-edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d5/2peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy-dispersive X-ray spectroscopy measurements. The ratio of non-bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.

scholarly journals Random Forest Machine Learning Models for Interpretable X-Ray Absorption Near-Edge Structure Spectrum-Property Relationships

2020 ◽  
Author(s):  
Steven Torrisi ◽  
Matthew Carbone ◽  
Brian Rohr ◽  
Joseph H. Montoya ◽  
Yang Ha ◽  
...  
Keyword(s):  
Machine Learning ◽  
Functional Materials ◽  
Learning Models ◽  
Linear Quadratic ◽  
White Line ◽  
Edge Structure ◽  
Line Energy ◽  
X Ray ◽  
X Ray Absorption ◽  
Machine Learning Models

X-ray absorption spectroscopy (XAS) produces a wealth of information about the local structure of materials, but interpretation of spectra often relies on easily accessible trends and prior assumptions about the structure. Recently, researchers have demonstrated that machine learning models can automate this process to predict the coordinating environments of absorbing atoms from their XAS spectra. However, machine learning models are often difficult to interpret, making it challenging to determine when they are valid and whether they are consistent with physical theories. In this work, we present three main advances to the data-driven analysis of XAS spectra: we demonstrate the efficacy of random forests in solving two new property determination tasks (predicting Bader charge and mean nearest neighbor distance), we show that multiscale featurization can elucidate the regions and trends in spectra that encode various local properties, and we address the effect of normalization on model interpretability. The multiscale featurization transforms the spectrum into a vector of polynomial-fit features, and is contrasted with the commonly-used "pointwise" featurization that directly uses the entire spectrum as input. We find that across thousands of transition metal oxide spectra, the relative importance of features describing the curvature of the spectrum can be localized to individual energy ranges, and we can separate the importance of constant, linear, quadratic, and cubic trends, as well as the white line energy. This work has the potential to assist rigorous theoretical interpretations, expedite experimental data collection, and automate analysis of XAS spectra, thus accelerating discovery of new functional materials.

Thermal Annealing Effect on Real Time Atomic Relocation of Iron-Cobalt Alloys Prepared by Electro-Deposition

2015 ◽  
Vol 1103 ◽  
pp. 69-75 ◽  
Author(s):  
Ketwadee Wetsuwan ◽  
Prathan Prachopchok ◽  
Theerasak Juagwon ◽  
Wanwisa Limphirat ◽  
Kritsanu Tivakornsasithorn ◽  
...  
Keyword(s):  
Real Time ◽  
Indium Tin Oxide ◽  
Annealing Temperature ◽  
Oxide Glass ◽  
Iron Sulfate ◽  
Electro Deposition ◽  
X Ray ◽  
Atomic Structures ◽  
X Ray Absorption ◽  
Co Alloys

Atomic structures of fabricated Fe-Co alloys were investigated real time by time resolved x-ray absorption spectroscopy (TRXAS) at annealing temperature of 400° C. The various compositions of Fe-Co alloy thin films were prepared by electro-deposition on indium-tin oxide glass substrate with iron sulfate and cobalt chloride electrolyte solutions. The current density of 80 A/m2 was used to deposit Fe-Co thin film with varying the ratio of Fe and Co ion concentrations. The Fe-Co alloys with boron nitride powders were mixed, grinded and pressed in the pallet form in order to insert into environmental controlled sample holder for TRXAS measurement. The samples were annealed under 20% oxygen and 80% nitrogen atmospheric by increasing the temperature up to 400° C and then remaining for an hour. The influence of annealing temperature can modify the atomic structures of Fe-Co alloys as indicated in the variation of extended x-ray absorption fine structure (EXAFS) peaks. Most of the EXAFS peaks followed the temperature profile i.e. increasing or decreasing during the temperature rising and then maintaining about constant values during holding the temperature at 400° C. By transforming the EXAFS peaks into scattering radius space, the modification of relative scattering amplitude from each nearest neighbor position indicated the atomic relocation during annealing the samples. Some of scattering patterns from Fe and Co oxides can be found and their amounts changed during rising the annealing temperature. In addition, the atomic relocations extracted from the Co absorption edge was very much smaller than those of Fe edge probably due to relative more stable of Co atomic positions for this range of annealing temperature.

Arsenic Speciation in Biological Samples Using XAS and Mixed Oxidation State Calibration Standards of Inorganic Arsenic

2009 ◽  
Vol 63 (8) ◽  
pp. 961-970 ◽  
Author(s):  
J. G. Parsons ◽  
M. L. Lopez ◽  
H. Castillo-Michel ◽  
J. R. Peralta-Videa ◽  
J. L. Gardea-Torresdey
Keyword(s):  
Limit Of Detection ◽  
Arsenic Speciation ◽  
Inorganic Arsenic ◽  
Energy Difference ◽  
Energy Separation ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Calibration Curves ◽  
X Ray Absorption

The speciation of elements without pre-edge features preformed with X-ray absorption near edge structure (XANES) can lead to problems when the energy difference between two species is small. The speciation of arsenic (As) in plant samples was investigated using the mixtures As2S3/As2O5, As2S3/As2O3, or As2O3/As2O5. The data showed that the energy separation (eV) between As2O5 and As2S3 was 5.8, between As2O3 and As2O5 was 3.6, and between As2S3 and As2O3 was 2.1. From the intensity of the white-line feature and the concentration of As species, calibration curves showing a limit of detection of approximately 10% were generated. In addition, an error of ±10% was determined for the linear combination–XANES (LC-XANES) fitting technique. The difference between the LC-XANES fittings and calculations from the calibration curves was <10%. The data also showed that the speciation of As in a sample can be determined using EXAFS (extended X-ray absorption fine structure). Finally, it was also shown that both EXAFS and XANES of the sample should be examined to determine the true speciation of an element. Even though there is a difference of 2 eV between As(III) bound to O and As(III) bound to S, in the EXAFS region the As(III)–S and As(III)–O ligands are clearly visible. However, distinction between the As(III)–O and As(V)–O ligands in the EXAFS spectra was not clearly visible in this study.

scholarly journals First Principles Approach to Extracting Chemical Information from X-Ray Absorption Near-Edge Spectra of Ga-Containing Materials

2021 ◽  
Author(s):  
Kyle Groden ◽  
FERNANDO D. VILA ◽  
Li Li ◽  
Simon Bare ◽  
Susannah Scott ◽  
...  
Keyword(s):  
First Principles ◽  
Chemical Information ◽  
Active Materials ◽  
White Line ◽  
Edge Structure ◽  
Coordination Environment ◽  
X Ray ◽  
Catalytically Active ◽  
Ligand Coordination ◽  
X Ray Absorption

The X-ray absorption near edge structure (XANES) can provide uniquely detailed information on the coordination environments of important Ga-containing materials with unknown structures, including catalytically-active materials. In this study, the Ga K-edge XANES was simulated using first principles-based methods for seven molecular Ga complexes, as well b-Ga2O3, in order to explore the chemical origins of the experimentally observed features. The theoretical spectra were computed using FEFF, CASTEP and StoBE, in order to assess the sensitivity of the results to the computational approach. While the XANES features depend on the Ga coordination environment, they are also sensitive to the electronegativity of the ligands and the symmetry at Ga. The white line position responds to changes in both the core state (due to differential screening) and the valence “p” states (arising from differences in ligand coordination).

Sign in / Sign up

Export Citation Format

Share Document