Fe 2p Core Level Research Articles

Catalytic conversion of syngas to olefins over Mn–Fe catalysts

Abstract A series of MnO 2 –Fe 2 O 3 with various contents of Mn (0–40% atomic ratio) was synthesized by the co-precipitation method. XRD patterns indicate that the sharp and intense peaks are related to the excellent crystal quality of α-Fe 2 O 3 nanostructures. HR-TEM images showed that α-Fe 2 O 3 and MnO 2 , were partly in close contact and the lattice fringes exhibit the typical distances, i.e., α-Fe 2 O 3 (104) (2.7 A) and MnO 2 (310) (3.1 A). X-ray photoelectron spectroscopy (XPS) results of the Fe 2p core-level binding energy spectrum of the α-Fe 2 O 3 and Mn 2p, indicated the presence of Fe 3+ and Mn 4+ . The direct synthesis of olefins from syngas was carried out over the MnO 2 –Fe 2 O 3 catalysts under pressurized fixed-bed continuous flow conditions. The results showed that Mn–Fe catalyst had high catalytic activity and high olefins selectivity without the addition of any promoters at low pressure. It was found that the catalyst containing 20 at% Mn–Fe was an optimal catalyst for the conversion of synthesis gas to hydrocarbons especially light olefins. The maximum CO conversion rate was 15%, and the yield of olefins (totally about 23.77%) with a predominance of CH 4 (12.24%), and C 2 H 6 (2.80%) components. Mn–Fe catalyst can be regarded as a potential candidate for catalytic conversion of biomass-derived syngas to olefins.

Structural phase transition and magnetic properties of Er-doped BiFeO3 nanoparticles

The structural phase transition and local structural distortion of Er-doped BiFeO3 nanoparticles have been discussed in order to understand the variation of magnetic properties in this system. The X-ray diffraction patterns and X-ray absorption fine structure of these samples demonstrate that there is structural phase transition and no obvious local structural distortion with the increasing of doping concentration. Unfortunately, no ferromagnetic properties have been observed even at a lower temperature. And the X-ray absorption spectra of Fe 2p core level of these samples are totally same, especially the energy positions do not shift which means the consistent valence states of Fe ions.

Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

Ferromagnetic FexGe1−x with x = 2%–9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe3 to approximately FeGe2, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane [110] easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

Iron(ii) spin crossover films on Au(111): scanning probe microscopy and photoelectron spectroscopy

The growth of films of [H2B(pz)2]Fe(ii)(bpy) on Au(111) is characterized from the bilayer film to multilayer film regime. Scanning tunneling microscopy shows a transition from a well-ordered, uniform bilayer film to a poorly-ordered film at larger thicknesses. Previous local tunneling spectroscopy and conductance mapping in bilayer films permit the identification of coexisting molecular spin-states at all temperatures. New ultraviolet photoelectron spectroscopy is consistent with this picture and in agreement with the density of states calculated by density functional theory. In thicker films with a polycrystalline morphology, evidence for a more bulk-like change in spin composition as a function of temperature is obtained by observing the reduction in intensity of Fe 2p core level satellites in X-ray photoelectron spectra.

Magnetron-sputter epitaxy of β-FeSi2(220)/Si(111) and β-FeSi2(431)/Si(001) thin films at elevated temperatures

β-FeSi2 thin films have been grown on Si(111) and Si(001) substrates by magnetron-sputter epitaxy at 700 °C. On Si(111), the growth is consistent with the commonly observed orientation of [001]β-FeSi2(220)//[1-10]Si(111) having three variants, in-plane rotated 120° with respect to one another. However, on Si(001), under the same growth conditions, the growth is dominated by [-111]β-FeSi2(431)//[110]Si(001) with four variants, which is hitherto unknown for growing β-FeSi2. Photoelectron spectra reveal negligible differences in the valance-band and Fe2p core-level between β-FeSi2 grown on Si(111) and Si(001) but an apparent increased Si-oxidization on the surface of β-FeSi2/Si(001). This phenomenon is discussed and attributed to the Si-surface termination effect, which also suggests that the Si/Fe ratio on the surface of β-FeSi2(431)/Si(001) is larger than that on the surface of β-FeSi2(220)/Si(111).

Evaluation of residual iron in carbon nanotubes purified by acid treatments

A detailed analysis by X-ray photoelectron spectroscopy was carried out on multi-walled carbon nanotube (MWCNT) surfaces after non-oxidative and oxidative purification treatments in liquid-phase. The MWCNT were produced by pyrolysis of camphor and ferrocene, that provides a high yield but with high iron contamination (∼15%wt). The elimination and/or oxidation of iron nanoparticles were monitored by Fe2p and O1s core level. Oxygen-based functional groups attachment was also investigated by C1s fitting. The effectiveness of each treatment in iron removal was evaluated by thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS). The integrity of the MWCNT structure was verified by Raman spectroscopy (RS) and transmission electron microscopy (TEM). A purity degree higher than 98% was achieved only with non-oxidative treatments using sonification process.

Laser induced structural modification in Fe-Na-B glass samples investigated by advanced XPS technique

The effect of laser irradiation from Nd: YAG laser on the glass structure in sodium borate glass containing Fe2O3 has been investigated by X-ray photoelectron spectroscopy (XPS). Core level spectra Fe 2p, Na 1s, B 1s and O 1s have been recorded and analysed. The general behaviour of the spectra indicate a decrease in intensity of the Fe 2p core level peaks implying a gradual loss of Fe ions from the surface of the sample with a change in laser wavelength. The O 1s peak showed a slight narrowing with increase in laser wavelength. The O 1s spectra were all curved fitted with two contributions from bridging oxygen (BO) and non-bridging oxygen (NBO). A model was introduced to explain the correlation between the disappearance of Fe ion from the glass surface and the narrowing of the O 1s spectra with increase in laser wavelength.

Crystal chemistry, surface morphology and X-ray photoelectron spectroscopy of Fe-rich osumilite from Mt. Arci, Sardinia (Italy)

Microprobe analysis, single crystal X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray absorption spectroscopy were applied on Fe-rich osumilite from the volcanic massif of Mt. Arci, Sardinia, Italy. Osumilite belongs to the space group P6/mcc with unit cell parameters a = 10.1550(6), c = 14.306(1) A and chemical formula (K0.729)C (Na0.029)B (Si10.498 Al1.502)T1 (Al2.706 Fe 0.294 2+ )T2 (Mg0.735 Mn0.091 Fe 1.184 2+ )AO30. Structure refinement converged at R = 0.0201. Unit cell parameter a is related to octahedral edge length as well as to Fe2+ content, unlike the c parameter which does not seem to be affected by chemical composition. The determination of the amount of each element on the mineral surface, obtained through X-ray photoelectron spectroscopy high-resolution spectra in the region of the Si2p, Al2p, Mg1s and Fe2p core levels, suggests that Fe presents Fe2+ oxidation state and octahedral coordination. Two peaks at 103.1 and 100.6 eV can be related to Si4+ and Si1+ components, respectively, both in tetrahedral coordination. The binding energy of Al2p, at 74.5 eV, indicates that Al is mostly present in the distorted T2 site, whereas the Mg peak at 1,305.2 eV suggests that this cation is located at the octahedral site. X-ray absorption at the Fe L2,3-edges confirms that iron is present in the mineral structure, prevalently in the divalent state and at the A octahedral site.

TiN–Fe nanocomposite thin films deposited by reactive magnetron sputtering

TiN–Fe films with various iron concentrations were deposited on Si and NaCl single-crystal substrates by direct current reactive magnetron sputtering. The structure and chemical composition of the films were examined by x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray and x-ray photoelectron spectroscopy (XPS). The effects of Fe addition on the structural, mechanical and magnetic properties of TiN films were studied. XRD and HRTEM revealed for TiN–Fe a cubic B-1 structure while no sign of an iron phase was observed. It was found that the lattice parameter and the grain size decreased with an increase in the Fe/Ti atomic ratio. At Fe/Ti = 0.2, the XRD revealed a change in the preferential orientation from (1 1 1) to (2 0 0) with a tendency of line broadening as the iron concentration increased. The Fe 2p core level peak of XPS indicates that the greater part of Fe atoms in TiN–Fe films exists as free pure metallic iron while the lesser part was in the form of iron oxide. Film annealing at 500 and 600 °C led to iron precipitation of the α-Fe phase indicating that below 500 °C Fe–TiN, films can be considered as nanocomposites materials, as confirmed by nanoindentation measurements and HRTEM observations.

Oriented growth of Fe3O4 thin film on crystalline and amorphous substrates by pulsed laser deposition

We have deposited magnetite thin films using the pulsed laser deposition technique from a α-Fe2O3 target on different substrates (Si (1 1 1), GaAs (1 0 0), Al2O3 (0 0 1) and amorphous float glass (FG)) without any buffer layer at a substrate temperature of 450 °C. These films have been characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, ac magnetic susceptibility and four-probe resistivity. The XRD results of these films show highly (1 1 1) oriented growth and single phase nature of Fe3O4 films on all substrates. Fe 2p core level x-ray photoelectron spectra and Raman spectra reveal the formation of Fe3O4 throughout the thickness of the films. All films show a Verwey transition at or around 120 K. It is observed that the oriented growth of Fe3O4 films takes place along the [1 1 1] direction on these substrates, which have either a huge lattice mismatch or no matching at all (as in FG) with Fe3O4.

Photoemission study of ternary to penternary Fe-based metallic glasses: Chemical analysis of surface and bulk

Bulk metallic glasses consisting of Fe, Mo, Cr, C, B, and Er have been investigated by x-ray photoelectron spectroscopy, aimed to elucidate the local atomic structure of the amorphous phase. In order to examine the electronic properties of this class of material, photon energy dependent measurements in combination with argon-ion irradiation were employed to identify and separate surface and bulk contributions to the spectra. The core levels suggest the presence of a carbon-rich surface layer with oxidized boron and metals, and metal carbides and borides in the bulk. Exposure to molecular oxygen and annealing experiments probe the chemical reactivity of the material. Formation of boron oxides at comparably low temperatures (300°C) might have consequences for the stability of the amorphous phase. We observe variations in binding energy of the Fe 3p core level with respect to the alloy composition, which indicate changes in the chemical state of iron.

Investigation of quasicrystalline Al62.5Cu25Fe12.5 and crystalline β-Al50Cu33Fe17 alloys by X-ray photoelectron spectroscopy

The electronic spectra of the valence band and core levels of the surface of polygrain alloys with the icosahedral structure and the β-(CsCl)-type solid solution of Al50Cu33Fe17 were investigated by X-ray photoelectron spectroscopy (XPS). The obtained XPS spectra of the Al62.5Cu25Fe12.5 alloy, in comparison with those of the crystalline Al50Cu33Fe17 alloy demonstrate narrowing and a decrease in asymmetry of the Fe2p core level and a decrease in the electron state density N(EF) near the Fermi level, features expected for the poorly conducting icosahedral phase. The XPS data are compared with the estimates of N(EF) based on the low-temperature specific heat measurements.

Magnetic and structural properties of Fe ion-implanted GaN

The magnetic and structural properties of Fe ion-implanted GaN was investigated by various measurements. XRD results did not show any peaks associated with second phase formation. The magnetization curve at 5 K showed ferromagnetic behavior for 900 °C-annealed sample. In zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements, the irreversibility and a cusp-like behavior of the ZFC curve were observed for 900 °C-annealed sample. These behaviors are typically observed in superparamagnetic or spin glass phase. While the temperature dependence magnetization of 800 °C-annealed sample showed non-Brillouin-like curve and it is not exhibited ferromagnetic hysteresis at 5 K. In XPS measurement, the coexistence of metallic Fe (Fe 0) and Fe–N bond (Fe 2+ and Fe 3+) for Fe 2p core level spectra is observed in as-implanted sample. But 700–900 °C-annealed samples showed only Fe–N bond (Fe 2+ and Fe 3+) spectra. For Ga 3d core level spectra only Ga–N bonds showed for as implanted with 700–900 °C-annealed samples. From XPS results, it could be explained that magnetic property of our films originated from FeN structures.

Fibronectin adsorption on Fe–Cr alloy studied by XPS

AbstractImproved knowledge of the chemical composition of biomaterial surfaces and a better understanding of interactions between biomolecules and material surfaces will allow a more rational design of biomaterials. Surface characterisation of alloys before and after their interaction with proteins is an essential aspect of this approach. In this work, the interactions of fibronectin with stainless steel surfaces (Fe–17Cr alloy) were studied by X‐ray photoelectron spectroscopy (XPS). Different solution concentrations of fibronectin were tested (0, 8, 60, 120 and 240 µg ml−1) in interaction with the stainless steel sample. N 1s, C 1s, Cr 2p and Fe 2p core level spectra were systematically recorded and compared. The results indicate that fibronectin is adsorbed on the stainless steel surface. The alloy surface composition and oxide thickness are almost unchanged (Fe2O3—Cr2O3 + Cr(OH)3) in presence of the protein, whatever the protein solution concentration. The isotherm of fibronectin adsorption at 37 °C was measured. A saturation is clearly reached for solution concentrations greater than 60 µg ml−1. On the plateau, the equivalent protein thickness is 6.3 nm, corresponding to one fibronectin monolayer. Copyright © 2006 John Wiley & Sons, Ltd.

Magnetisation dynamics of Fe nanoclusters exchange-coupled to magnetic substrates

Synchrotron radiation was used to study exposed Fe nanoclusters with controlled sizes in the size range 140–270 atoms (1.5–1.8 nm) deposited in situ from a gas aggregation source on to magnetic vitrovac amorphous ribbons. Magnetic linear dichroism in the angular distribution (MLDAD) of the Fe 3p core level photoemission was used to show that the clusters are exchange-coupled to the substrate with an interface molecular field of about 20 T. The switching dynamics was studied on the nanosecond timescale by time-resolved spin-polarised photoemission. At low coverages, below the percolation threshold, when the film consists of separated islands the switching dynamics of the cluster islands is identical to the clean substrate. At around the percolation threshold, however, the data indicates that the magnetic reversal propagates faster in the cluster film than in the substrate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Static and dynamic magnetic behaviour of iron nanoclusters on magneticsubstrates

The static and dynamic magnetic behaviour of Fe nanoclusters with controlledsizes in the range 140–270 atoms (1.5–1.8 nm) deposited in situ froma gas aggregation source on magnetic vitrovac amorphous ribbons hasbeen studied using synchrotron radiation. The static magnetization ofthe cluster films in the exchange field of the substrates was measured asa function of coverage using magnetic linear dichroism in the angulardistribution (MLDAD) of the Fe 3p core level photoemission. The switchingdynamics were studied on the nanosecond timescale by time-resolvedspin-polarized photoemission. For a given particle size, the magnetization of theFe cluster film increases with coverage and saturates at a coverage ofabout 0.4 cluster monolayers. Modelling the growth of the magnetizationgives an effective exchange field at the interface of ∼20 T. Densecluster films with several cluster layers have an MLDAD signal at saturation that is∼5%higher than a molecular beam epitaxy (MBE)-grown film, indicating anenhanced spin moment even when clusters are in contact. Coating an exposedsub-monolayer cluster layer with Co increases the Fe MLDAD signal by 35%,indicating a substantially increased magnetic moment within the Fe clusters. Atlow coverages, below the percolation threshold, the switching dynamics of thesample remains the same as in the clean substrate. At around the percolationthreshold, however, a significant acceleration of the magnetic reversal is observedwith a fast component due to a reversal propagating through the cluster film.We show that, on average, each cluster switches in about 10 ns.

Oxygen structures on Fe(1 1 0)

The adsorption of oxygen on a Fe(1 1 0) single crystal has been studied by means of high resolution photoelectron spectroscopy (HRPES) and scanning tunneling microscopy (STM). Core level spectra were analyzed in detail on both clean and adsorbate covered surfaces. A shoulder on the high binding energy side of the Fe 2p core level indicates a structure comprising multiple components interpreted as an exchange split of the final state due to interaction between the 2p and 3d electrons. After adsorption of oxygen, (2×5), (2×2) and (3×1) reconstructions were observed with atomically resolved STM. The iron surface was further exposed to gradually higher doses of oxygen. Deconvolution of the O 1s HRPES spectra revealed two components separated approximately by 0.4 eV. The component at lower binding energy dominates at low coverage, while the high binding energy component increases in intensity with increasing O coverage. The formation of oxides was observed in the Fe 2p spectrum in the region between 708 and 710 eV. Further, well ordered iron oxides were grown by exposure to oxygen at 250 °C. The O 1s core level contained a single component with a binding energy similar to that of the high energy component in the just discussed O 1s spectrum. Low energy electron diffraction and STM images of this structure showed a large moiré pattern with a 22.1 A ̊ ×30.9 Å unit cell.

TRANSVERSE MAGNETO-OPTICAL KERR EFFECT IN THE SOFT X-RAY REGIME OF ULTRATHIN IRON FILMS AND ISLANDS ON W(110)

The transverse magneto-optical Kerr effect (T-MOKE) in the soft X-ray regime is used to investigate the magnetic properties of ultrathin epitaxial Fe(110) films and thermally created epitaxial Fe islands on W(110). The measurements have been carried out at the Fe 2p core levels with tunable, linearly polarized synchrotron radiation. Besides the chemical selectivity T-MOKE at core levels is characterized by a much larger sensitivity compared to the visible regime. We have analyzed the transition from thin films to a three-dimensional island system at a thickness of 4 ML and the magnetic behavior when increasing the iron coverage to 8 ML. The Fe island system is characterized by a rotation of the easy magnetization axis in this coverage regime.

Structure modulated LMDAD effects in BCC-Fe vs. RCP-Fe

The atomic-like behavior of the photoionization cross-section of core levels in solids is remarkably displayed in the observation of linear magnetic dichroism in the angular distribution of photoelectrons. Structure-related effects are clearly visible as modulations of the dichroism signal, induced by photoelectron diffraction, a fact that can be exploited to obtain information from magnetic surfaces. A systematic investigation of such effects has been carried out for Fe 2p and 3p core levels on the ALOISA beamline at ELETTRA. We present results for Fe(0 0 1) with a reference calibration for amorphous RCP-Fe grown on Fe 30Ni 50B 20, which provides the atomic-like standard, free from diffraction effects.

Element-specific magnetometry with photoelectron dichroism: FeCo and FeNi

We have investigated fcc Fe x Co 1− x and Fe x Ni 1− x alloys grown on Cu(1 0 0) with X-ray magnetic linear dichroism angular distributions in photoemission (XMLDAD). To achieve this end, a simple model has been developed, which accurately describes the experimental spectra and supports our application of XMLDAD as a form of elementally specific magnetometry. This model combines the simplicity and physical insight of a single-electron picture with multielectronic effects, via the utilization of “Doniach–Sunjic” lineshapes for each component within the Fe 3p multiplet. We will also briefly discuss the observed fine structure in the emission of the Fe 3p core level, which was previously predicted but lacking experimental confirmation. We have found different behavior for the dichroism of the Fe 3p level at high and low Fe concentrations upon alloying with Co, compared to alloying with Ni. These contrasting observations can be explained in part by the different behavior of the atomic volume. Both systems show also a change of the in-plane easy axis upon increasing the Fe content. For small concentrations the easy axis is along the {0 1 1} direction, which changes to the {0 0 1} direction at a higher Fe content. Interestingly the actual transition occurs in both instances at roughly the same electron/atom count.