Fe 2p Core Level Research Articles

Iron oxide nanoparticles produced by the laser ablation technique and analyzed by x-ray photoelectron spectroscopy

The study of iron nanoparticles is one of the most researched areas in recent times due to the potential applications they have and because the study of iron by XPS is one of the most debated elements. In this work, we provide investigation data of iron oxide nanoparticles produced using the laser ablation technique, which were characterized using x-ray photoelectron spectroscopy. Survey spectra, C 1s, O 1s, and Fe 2p core levels spectra were acquired. Results showed the presence of Fe+3 and Fe+2 elements that constitute hematite and magnetite with differences in their concentrations depending on the fitting method. In addition, the presence of adventitious carbon and carbon from impurities was detected.

XPS analysis of graphitic carbon nitride functionalized with CoO and CoFe2O4

Materials based on graphitic carbon nitride (gCN) have drawn a great deal of attention as (photo)electrocatalysts triggering the oxygen evolution reaction (OER) in H2O splitting processes to yield hydrogen fuel. In this work, nonmonochromatized Mg Kα radiation (1253.6 eV) was used to acquire photoelectron spectroscopy data on gCN-containing composite systems supported on fluorine-doped tin oxide. The investigated materials were prepared via a straightforward decantation route to yield carbon nitride, followed by functionalization with low amounts of nanostructured co-catalysts (CoO, CoFe2O4) through radio frequency-sputtering, and final thermal treatment under an inert atmosphere. Structural and morphological analyses highlighted the formation of composite systems, in which the single constituents, featuring an intimate contact, maintained their chemical identity. This work proposes a data record including both survey scans and high-resolution spectra of C 1s, N 1s, O 1s, Co 2p, and Fe 2p core-levels for three representative specimens comprising bare and functionalized graphitic carbon nitride (gCN, gCN-CoO, and gCN-CoFe2O4). The obtained results, discussed in relation to the different chemical environments for the various elements, will be useful as a comparison for further studies in related fields.

XPS study of the thermal stability of passivated NiCrFeCoMo multi‐principal element alloy surfaces

X‐ray photoelectron spectroscopy analysis was applied to investigate the thermal stability under ultra‐high vacuum environment of the surface oxide film formed by electrochemical passivation of a newly designed Cr15Fe10Co5Ni60Mo10 (at.%) multi‐principal element alloy and providing the alloy superior localized corrosion resistance compared to conventional stainless steels and alloys. A spectral decomposition methodology involving the subtraction of Auger peaks overlapping the Fe 2p and Co 2p core level regions was applied for quantification of the oxide film composition and thickness. The results show that, at 100°C, the passive oxide film is mainly dehydrated and dehydroxylated. Obvious loss of Ni hydroxide and conversion of Mo (VI) to Mo (IV) species are observed at 200°C, with further reduction of Mo species to Mo (III) observed at 300°C. In this temperature range, the total cation quantity in the oxide film remains stable despite the compositional alteration. At 400°C, Cr (III) oxide forms at the expense of Fe and Mo oxides, resulting in an oxide film essentially consisting of chromium oxide. At 500°C, Cr (III) oxide is eliminated, making the passive film unstable at this temperature. Possible Cr oxide removal mechanisms are discussed.

Surface-to-bulk core level shift in CoFe2O4 thin films

In spite of the absence of significant segregation of either cobalt oxide or iron oxide, core level photoemission binding energy shifts tend to indicate that the surface is significantly different from the bulk for CoFe2O4(111) thin films grown on Al2O3(0001). CoFe2O4(111) thin films show a surface-to-bulk core level shift in both the Co 2p and Fe 2p core level photoemission spectra. Surface weighted components in the core level photoemission spectra of both Co 2p3/2 and Fe 2p3/2 can be distinguished from the bulk components, by angle-resolved x-ray photoemission spectroscopy, for CoFe2O4(111) thin films. The surface termination of CoFe2O4(111) contains both Co and Fe with no evidence of strong preferential surface termination of either an iron or cobalt oxide, except for CoFe2O4(111) in the thin film limit. With extensive annealing above room temperature, the cobalt oxide component of very thin CoFe2O4(111) films, grown on Al2O3 (0001), will lose oxygen.

Impact of high temperatures on aluminoceladonite studied by M\xf6ssbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopy

Mössbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopies were used to examine the effects of temperature on the structure of two aluminoceladonite samples. The process of oxidation of Fe2+ to Fe3+ ions started at about 350 °C for the sample richer in Al and at 300 °C for the sample somewhat lower Al-content. Mössbauer results show that this process may be associated with dehydroxylation or even initiate it. The first stage of dehydroxylation takes place at a temperature > 350 °C when the adjacent OH groups are replaced with a single residual oxygen atom. Up to ~500 °C, Fe ions do not migrate from cis-octahedra to trans-octahedra sites, but the coordination number of polyhedra changes from six to five. This temperature can be treated as the second stage of dehydroxylation. The temperature dependence on the integral intensity ratio between bands centered at ~590 and 705 cm−1 (I590/I705) clearly reflects the temperature at which six-coordinated polyhedra are transformed into five-coordinated polyhedra. X-ray photoelectron spectra obtained in the region of the Si2p, Al2p, Fe2p, K2p and O1s core levels, highlighted a route to identify the position of Si, Al, K and Fe cations in a structure of layered silicates with temperature. All the measurements show that the sample with a higher aluminum content and a lower iron content in octahedral sites starts to undergo a structural reorganization at a relatively higher temperature than the less aluminum-rich sample does. This suggests that iron may perform an important role in the initiation of the dehydroxylation of aluminoceladonites.

Structural characterization, dielectric, magnetic and optical properties of double perovskite Bi2FeMnO6 ceramics

Double perovskite Bi2FeMnO6 (BFMO) oxides are promising candidate for single-phase multiferroic system. However, up to date only a limited works are carried out to synthesize the BFMO ceramics, and most of them have the issues of impure phases. In this work, we report on the structural, dielectric, magnetic, and optical properties of single-phase BFMO ceramics synthesized by solid-state reaction method. The BFMO ceramics crystallized in a rhombohedral structure with R3c space group, and their grains exhibited polyhedron morphology with average size of 15.0 µm. X-ray energy dispersive spectroscopy revealed the ceramic grains with atomic ratio of Bi:Fe:Mn equal to 2.0:1.16:0.90. XPS spectra of Fe 2p and Mn 2p core levels confirm the mixed chemical valence states of Fe (Fe2+ and Fe3+) and Mn (Mn3+ and Mn4+) in the BFMO ceramics. O 1s XPS spectra reveal the oxygen existing in the forms of lattice oxygen and oxygen vacancies while bismuth is present as Bi3+. Dielectric measurements demonstrate that the BFMO ceramics have much high dielectric constant (in the order of 104) in the frequency below 102 Hz but decrease fast with increasing the frequency. The same phenomenon appeared for the dielectric loss. A dielectric relaxation behavior with activation energy of 0.34 eV was observed in the BFMO ceramics, which was due to the thermal motion of the oxygen vacancies. The BFMO ceramics exhibit antiferromagnetic nature but a weak ferromagnetic behavior at 2 K. Sharp cusp peaks were observed in the zero-field-cooling (ZFC) curves and bifurcations between the field-cooling (FC) and ZFC curves were observed. Both of them shifted to low temperature as increasing the external applied magnetic field, indicating a spin-glass like behavior in the system. UV–Vis absorption spectra demonstrated a broad absorption peak in the wavelength range of 300–800 nm and a direct optical band gap of ~1.23 eV for the BFMO ceramics. Such narrow optical band gap as well as the high dielectric constant at room temperature enable the BFMO ceramics to be promising candidate used for solar cells, sensors, bolometer and optoelectronic devices.

Electronic structures of MgO/Fe interfaces with perpendicular magnetization revealed by hard X-ray photoemission with an applied magnetic field

ABSTRACT We have developed hard X-ray photoelectron spectroscopy (HAXPES) under an applied magnetic field of 1 kOe to study the electronic and magnetic states related to the MgO/Fe interface-induced perpendicular magnetic anisotropy (PMA). In this work, we used MgO (2 nm)/Fe (1.5 and 20 nm)/MgO(001) structures to reveal the interface-induced electronic states of the Fe film. Perpendicular magnetization of the 1.5-nm-thick Fe film without extrinsic oxidation of the Fe film was detected by the Fe 2p core-level magnetic circular dichroism (MCD) in HAXPES under a magnetic field, and easy magnetization axis perpendicular to the film plane was confirmed by ex situ magnetic hysteresis measurements. The valence-band HAXPES spectrum of the 1.5-nm-thick Fe film revealed that the Fe 3d electronic states were strongly modified from the thick Fe film and a reference bulk Fe sample due to the lifting of degeneracy in the Fe 3d states near the MgO/Fe interface. We found that the tetragonal distortion of the Fe film by the MgO substrate also contributes to the lifting of degeneracy in the Fe 3d states and PMA, as well as the Fe 3d-O 2p hybridization at the MgO/Fe interface, by comparing the valence-band spectrum with density functional theory calculations for MgO/Fe multilayer structures. Thus, we can conclude that the Fe 3d-O 2p hybridization and tetragonal distortion of the Fe film play important roles in PMA at the MgO/Fe interface. HAXPES with in situ magnetization thus represents a powerful new method for studying spintronic structures.

Multi-electron Reduction Capacity and Multiple Binding Pockets in Metal-Organic Redox Assembly at Surfaces.

Metal-ligand complexation at surfaces utilizing redox-active ligands has been demonstrated to produce uniform single-site metals centers in regular coordination networks. Two key design considerations are the electron storage capacity of the ligand and the metal-coordinating pockets on the ligand. In an effort to move toward greater complexity in the systems, particularly dinuclear metal centers, we designed and synthesized tetraethyltetra-aza-anthraquinone, TAAQ, which has superior electron storage capabilities and four ligating pockets in a diverging geometry. Cyclic voltammetry studies of the free ligand demonstrate its ability to undergo up to a four-electron reduction. Solution-based studies with an analogous ligand, diethyldi-aza-anthraquinone, demonstrate these redox capabilities in a molecular environment. Surface studies conducted on the Au(111) surface demonstrate TAAQ's ability to complex with Fe. This complexation can be observed at different stoichiometric ratios of Fe:TAAQ as Fe 2p core level shifts in X-ray photoelectron spectroscopy. Scanning tunneling microscopy experiments confirmed the formation of metal-organic coordination structures. The striking feature of these structures is their irregularity, which indicates the presence of multiple local binding motifs. Density functional theory calculations confirm several energetically accessible Fe:TAAQ isomers, which accounts for the non-uniformity of the chains.

Soft X-ray photoemission study of Ba adsorption on the ceramic multiferroic BiFeO3

Electronic structure of the ceramic multiferroic BiFeO3 and ultrathin Ba/BiFeO3 interface was studied in situ using photoelectron spectroscopy with energies in the range of 120–900 eV. The photoemission from the Bi 4f, O 1s, Fe 2p, and Ba 4d core levels was studied. An effect of Ba adsorption is found to induce a significant change in all spectra that is originated from the strong interaction with the charge transfer between Fe, O, Bi surface atoms and Ba adatoms. The recharge between Fe3+↔ Fe2+ ions in surface region induced by Ba adsorption is found that provide enhancing the ferroelectric polarization gain.

Time-resolved electron spectroscopy for chemical analysis of photodissociation: Photoelectron spectra of Fe(CO)5, Fe(CO)4, and Fe(CO)3.

The prototypical photoinduced dissociation of Fe(CO)5 in the gas phase is used to test time-resolved x-ray photoelectron spectroscopy for studying photochemical reactions. Upon one-photon excitation at 266 nm, Fe(CO)5 successively dissociates to Fe(CO)4 and Fe(CO)3 along a pathway where both fragments retain the singlet multiplicity of Fe(CO)5. The x-ray free-electron laser FLASH is used to probe the reaction intermediates Fe(CO)4 and Fe(CO)3 with time-resolved valence and core-level photoelectron spectroscopy, and experimental results are interpreted with ab initio quantum chemical calculations. Changes in the valence photoelectron spectra are shown to reflect changes in the valence-orbital interactions upon Fe-CO dissociation, thereby validating fundamental theoretical concepts in Fe-CO bonding. Chemical shifts of CO 3σ inner-valence and Fe 3p core-level binding energies are shown to correlate with changes in the coordination number of the Fe center. We interpret this with coordination-dependent charge localization and core-hole screening based on calculated changes in electron densities upon core-hole creation in the final ionic states. This extends the established capabilities of steady-state electron spectroscopy for chemical analysis to time-resolved investigations. It could also serve as a benchmark for how charge and spin density changes in molecular dissociation and excited-state dynamics are expressed in valence and core-level photoelectron spectroscopy.

Surface modification of iron oxides by ion bombardment – Comparing depth profiling by HAXPES and Ar ion sputtering

Thin films of the iron oxide maghemite (γ-Fe2O3) and hematite (α-Fe2O3) grown on fluorine doped tin oxide (FTO) with pulsed chemical vapour deposition have been investigated with hard X-ray photoelectron spectroscopy. It is found that even low energy sputtering induces a reduction of the surface layer into FeO. Satellites in the Fe 2p core level spectra are used to determine the oxidation state of iron. Depth profiling with changing photon energy shows that the unsputtered films are homogeneous and that the information obtained from sputtering thus, in this instance, represents sputter damages to the sample.

X-ray diffraction and spectroscopic study of wiluite: implications for the vesuvianite-group nomenclature

Two wiluite samples from the Wiluy River, Yakutia, Russia have been investigated by means of single-crystal and powder X-ray diffraction, electron microprobe analysis, 1H, 27Al, 11B, and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (DSC/TGA), X-ray photoelectron spectroscopy (XPS) at the Si2p, Ca2p, Al2p, Mg1s, B1s and Fe2p core levels, 57Fe Mossbauer spectroscopy, infrared (IR) spectroscopy and optical measurements. The crystal structures have been refined in the P4/nnc space group [a = 15.7027(3), c = 11.7008(3) A, V = 2885.1(1) A3 for 1 and a = 15.6950(2), c = 11.6787(4) A, V = 2876.9(1) A3 for 2] to R 1 = 0.022 and R 1 = 0.021, respectively. In the crystal structure of wiluite, five-coordinated Y1 site is predominantly occupied by Mg. IR spectra of wiluite substantially different from those of vesuvianite, in particular, by the presence of additional bands in the range 1080‒1415 cm−1, which correspond to symmetric B‒O stretching vibrations of the BO 3 3− and BO 4 5− groups. According to the MAS NMR data, tetrahedrally coordinated T1 site is occupied by B3+ with minor amounts of Al3+. The general formula of wiluite can be written as follows (Z = 2): Ca19Mg(Al,Mg,Fe,Ti,Mn)12(B,Al,◻)5(Si2O7)4(SiO4)10(O,OH)9O2–3. The diversity of vesuvianite-group minerals is largely determined by the population of the Y1 sites. However, wiluite is characterized by the presence of additional T1 and T2 sites and should be considered as special among other vesuvianite-group minerals. The reasonability of subdivision of the wiluite subgroup within the vesuvianite group is discussed.

Characterization of LiFePO4/C composite and its thermal stability by Mössbauer and XPS spectroscopy

AbstractThe powders of the /C composite have been synthesized using the sol–gel method. The binding energies of the Fe 2p, P 2p, and O 1s core level the of /C surface were determined by X‐ray photoelectron spectroscopy (XPS). The deconvolution of the Fe 2p core level XPS is associated with the Fe2+ and Fe3+ valence states of the composite. Chemical composition and phase transitions were investigated using Mössbauer spectroscopy in the temperature interval of 10–600 K. Thermal decomposition of the composite was observed at 550 K.

Effect of Al and Fe doping in ZnO on magnetic and magneto-transport properties

The structural, magnetic and magneto-transport of undoped ZnO, Zn0.97Al0.03O, Zn0.95Fe0.05O and Zn0.92Al0.03Fe0.05O thin films grown on Si(100) substrate using pulsed laser deposition were investigated. The single phase nature of the films is confirmed by X-ray diffraction and Raman spectroscopy measurements. The possibility of Fe metal cluster in Fe doped/co-doped films is ruled out by Fe 2p core level photoelectron spectra. From O 1s core level spectra it is observed that oxygen vacancy is present in all the films. The undoped ZnO film shows magnetic ordering below ∼175K, whereas Fe doped/codoped samples show magnetic ordering even at 300K. The Al doped sample reveals paramagnetic behavior. The magneto-transport measurements suggest that the mobile carriers undergo exchange interaction with local magnetic moments.

Local electronic states of Fe4N films revealed by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L2,3 and N K-edges for Fe4N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe4N, we compared experimentally obtained XAS and XMCD spectra with those simulated by a combination of a first-principles calculation and Fermi's golden rule. We revealed that the shoulders observed at Fe L2,3-edges in the XAS and XMCD spectra were due to the electric dipole transition from the Fe 2p core-level to the hybridization state generated by σ* anti-bonding between the orbitals of N 2p at the body-centered site and Fe 3d on the face-centered (II) sites. Thus, the observed shoulders were attributed to the local electronic structure of Fe atoms at II sites. As to the N K-edge, the line shape of the obtained spectra was explained by the dipole transition from the N 1s core-level to the hybridization state formed by π* and σ* anti-bondings between the Fe 3d and N 2p orbitals. This hybridization plays an important role in featuring the electronic structures and physical properties of Fe4N.

Study of magnetic behavior in ball-milled nanocrystalline Fe-50 at.%Al alloy as a function of milling time

Ball milling technique has been extensively used to prepare different metastable states with nanocrystalline microstructures from intermetallic compounds. The present study was made on the identification of the changes in magnetic and electronic properties as a result of high-energy ball milling of Fe -50 at.% Al alloy samples. The phase formation and physical properties of the alloys were determined as a function of milling time by means of Mössbauer and X-ray photoelectron spectroscopy (XPS). The Mössbauer results show the formation of nanostructured body-centered cubic (BCC) FeAl alloy only after 5 h of mechanical milling and the same is also confirmed by Scanning electron microscope (SEM) and Transmission electron microscopy (TEM) studies. Mössbauer studies further confirm that there is magnetic behavior retention in the FeAl alloy samples even after 5 h of milling but magnetization decreases as the milling time increases. The reason for the same is due to the shocks and fracturing of the Al atoms embedded in the sites of Fe and as a result of which Fe – Fe nearest neighbors decreases. Secondly, with the increase in milling time, the particle size and the number density of equiatomic BCC Fe 50 Al 50 grains decrease while the volume of grain boundary containing a solid solution of BCC FeAl and concentration of Al in a solid solution of BCC FeAl at the grain boundary increases as a result of which magnetization decreases. The shift in the binding energy of Fe 2p and Al 2p core level towards higher binding energy also supports the alloy formation after milling.

SEM/EDX, XPS, and impedance spectroscopy of LiFePO<sub>4</sub> and LiFePO<sub>4</sub>/C ceramics

The powders of LiFePO4 compounds have been synthesized by the solid state reaction, and LiFePO4/C composites were sintered in argon gas. The ceramics of LiFePO4 were sintered in air. The surfaces of the ceramics were investigated by a scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX). The binding energies of the Fe 2p, P 2p, and O 1s core level of LiFePO4 ceramic and LiFePO4/C composite surfaces were determined by X-ray photoelectron spectroscopy (XPS). The deconvolutions of Fe 2p core level XPS are associated with Fe2+ and Fe3+ valence states of the ceramics. Impedance spectroscopy of the ceramics has been performed in the frequency range of 10 Hz to 3 GHz by low frequency and microwave impedance spectrometers. Two- and four-probe methods were used for measurements at low frequencies. The LiFePO4/C composite was investigated in nitrogen gas, and the measurements of LiFePO4 were conducted in air. The measurements of the electrical properties of the ceramics were carried out in the temperature interval of 300–500 K.

SEM/EDX, XPS, and impedance spectroscopy of LiFePO<sub>4</sub> and LiFePO<sub>4</sub>/C ceramics

The powders of LiFePO4 compounds have been synthesized by the solid state reaction, and LiFePO4/C composites were sintered in argon gas. The ceramics of LiFePO4 were sintered in air. The surfaces of the ceramics were investigated by a scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDX). The binding energies of the Fe 2p, P 2p, and O 1s core level of LiFePO4 ceramic and LiFePO4/C composite surfaces were determined by X-ray photoelectron spectroscopy (XPS). The deconvolutions of Fe 2p core level XPS are associated with Fe2+ and Fe3+ valence states of the ceramics. Impedance spectroscopy of the ceramics has been performed in the frequency range of 10 Hz to 3 GHz by low frequency and microwave impedance spectrometers. Two- and four-probe methods were used for measurements at low frequencies. The LiFePO4/C composite was investigated in nitrogen gas, and the measurements of LiFePO4 were conducted in air. The measurements of the electrical properties of the ceramics were carried out in the temperature interval of 300–500 K.

ChemInform Abstract: Iron(II) Spin Crossover Films on Au(111): Scanning Probe Microscopy and Photoelectron Spectroscopy

AbstractReview: 52 refs.

Importance of ligands in the electronic properties of FeTe0.6Se0.4

We investigate the electronic structure of FeTe0.6Se0.4 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Fe 2p core level and the valence band spectra exhibit signature of strong electron correlation in the electronic structure. The electronic states near the Fermi level reduces in intensity with the decrease in temperature in conformity with the insulating transport observed near 300 K. An insulator to metal transition around 150 K could be related to the spectral lineshape change in the vicinity of the Fermi level. The spectral features near Fermi level exhibit significant p orbital character due to the correlation induced Fe d spectral weight transfer. The experimental spectra reveal dominant temperature dependence of the spectral functions possessing large p-character. While the origin of the anomalous electronic properties in the normal phase could be revealed in the electronic structure of this material, these results emphasizes the importance of ligand states in the high temperature superconductors that is important to explore such materials for various applications.