Relation between 2p X-ray photoelectron and Kα X-ray emission spectra of manganese and iron oxides

The high resolution Mn and Fe Kα X-ray emission spectra (XES), and Mn and Fe 2p X-ray photoelectron spectra (XPS) for manganese and iron oxides were measured. The spectra were compared with those of [MnO₄]⁻, [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ ions. As the electronic structure of the latter compounds do not change with electron hole creation in the core levels, satellite peaks due to charge transfer are not observed in the 2p XPS spectra, and the peak profiles of metal 2p XPS and Kα XES are governed by the exchange splitting between 2p and valence electrons. The metal 2p XPS spectra of the oxides had satellite peaks, but the XES spectra had no satellites. FWHMs of the metal 2p_3/2 main peaks of the compounds being low spin states are smaller than those of metal Kα₁ XES spectra. However, FWHMs of Mn 2p_3/2 of the manganese oxide were nearly equal to those of Mn Kα₁ XES spectra, and those of Fe 2p_3/2 XPS spectra of the iron oxides are greater than those of Fe Kα₁ XES spectra.     

Fe,Co共掺杂ZnO薄膜结构及发光特性研究

采用溶胶凝胶法在玻璃衬底上制备了Fe,Co共掺Zn0.9FexCo0.1-xO(x=0,0.03,0.05,0.07)系列薄膜.通过扫描电镜(SEM)、X射线衍射(XRD)、X射线光电子谱(XPS)和光致发光(PL)谱对薄膜样品的表面形貌、晶体结构、成分和光学性能进行了研究.XRD结果表明所有ZnO薄膜样品都呈六方纤锌矿结构,在样品中没有观察到与Fe和Co相关的团簇,氧化物及其他杂相的衍射峰,表明共掺杂改善了Fe或Co在ZnO的分散性.XPS测试结果揭示样品中Co离子的价态为+2价;Fe离子的价态为+2价和+3价共存,但Fe相对浓度的增大导致Fe3+含量增加.所有样品的室温光致发光谱(PL)均观察到紫外发光峰和蓝光双峰,其中Fe,Co共掺ZnO薄膜的紫外发光峰较本征ZnO出现蓝移,蓝光双峰峰位没有变化,但发光强度有所减弱;而掺杂ZnO薄膜的绿光发光峰几乎消失.最后,结合微结构和成分分析对薄膜样品的发光机理进行了讨论.     

Sol-gel synthesis and dilute magnetism of nano MgO powder doped with Fe

Mg oxides doped with 1 % ⁵⁷Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe³⁺ in Mössbauer spectra although Fe³⁺ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe³⁺ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe³⁺ species are located at the core and shell of fine MgFe₂O₄ grains and diluted in MgO matrix.     

Core and valence level photoemission studies of iron oxide surfaces and the oxidation of iron

The core and valence level XPS spectra of Fe_xO (x ~ 0.90–0.95); Fe₂O₃ (α and γ); Fe₃O₄; and FeOOH have been studied under a variety of sample surface conditions. The oxides may be characterized by a combination of valence level differences and core-level effects (chemical shifts, multiplet splittings, and shake-up structure). Fe^II and Fe^III states are distinguishable, but octahedral and tetrahedral sites are not. The O 1 s BE cannot be used to distinghuish between the oxides since it has a nearly constant value. Fe 3d valence level structure spreads some 10 eV below E_F, much broader than suggested by previous UPS and photoelectron-spin-polarization (ESP) measurements for Fe_xO and Fe₃O₄. Fe surfaces (films, foils, (100) face) yield predominantly Fe^III species when exposed to high exposures of oxygen or air, though there is evidence for some Fe^II also. At low exposures the Fe^II/Fe^III ratio increases.     

Simultaneous regulation of photoabsorption and ferromagnetism of NaTaO3 by Fe doping

NaTa_1-xFe_xO₃ (0 ≤ x ≤ 0.40) nanocubes were synthesized by a relatively low temperature hydrothermal method, using Ta₂O₅, FeCl₃ and NaOH as the precursors. The UV–vis diffuse reflectance spectra showed that NaTa_1-xFe_xO₃ had significant visible-light-absorbing capability, and the absorption edge of NaTaO₃ shifted to longer wavelength with the increase of Fe dopants. Moreover, NaTa_1-xFe_xO₃ exhibited room-temperature ferromagnetism when Fe³⁺ occupied Ta⁵⁺ sites in NaTaO₃ crystal lattice. The ferromagnetism is mainly attributed to the superexchange interactions between doped Fe³⁺, rather than the contribution of oxygen vacancies caused by Fe doping. Therefore, Fe doping can simultaneously regulate the optical and magnetic properties of NaTaO₃ semiconductor, which will enable its potential applications in multifunctional optical-electronics and optical-spintronics devices.     

The iron oxidation state in Mg-Al-Fe mixed oxides derived from layered double hydroxides: An XPS study

Mixed oxides with large surface area and high thermal stability can be obtained by thermal treatment of the layered double hydroxides (LDH). Mg-Al-Fe mixed oxide samples with varying Mg/Al ratio and 5 mol.% of Fe were prepared in this way and the iron oxidation state (Fe_ox) in these compounds was studied by X-ray photoelectron spectroscopy (XPS), using a calibration based on the relation of Fe_ox to the splitting between the O 1s and Fe 2p_3/2 centroids. The XPS results confirm Fe³⁺ as a dominant oxidation state in the studied mixed oxides. A vacuum-induced reduction of iron in the Fe₂O₃ and Mg-Al-Fe oxide samples has been observed and an influence of the Mg:Al ratio on this effect in mixed oxides has been detected. The role of the local variations of the electron density distribution in the close neighbourhood of the surface oxygen atoms in the mixed oxides in the reduction processes is discussed.     

The charge states of iron in insulators implanted with57Co and57Fe

Single crystals of α-Al₂O₃ and LiNbO₃ were implanted with⁵⁷Co (dose: up to 2×10¹⁵ atoms/cm²) and with⁵⁷Fe (dose: 2×10¹⁵ atoms/cm²) ions. The Mössbauer spectra revealed the disordered atomic environment. Fe²⁺ and Fe³⁺ charge states were observed. The spectra were compared to the spectra of crystals doped with⁵⁷Co. It was remarkable that in the doped α-Al₂O₃ Fe³⁺ states with slow spin-spin relaxation have appeared. The CEMS study of the samples implanted with⁵⁷Fe resulted in Fe²⁺ ionic states indicating that a fraction of Co atoms can also be in Co²⁺ state.     

Iron-rich spinels from Brazilian soils

Tropical soils often contain high amounts of iron oxides. Hematite (αFe₂O₃) and goethite (αFeOOH) are the most widespread iron oxides, but magnetite (Fe₃O₄) and maghemite (γFe₂O₃) occur in magnetic pedons. A wide range of spinel compositions in the Fe₃O₄-γFe₂O₃ series has been identified in magnetic Brazilian soils. Isomorphic substitution of mainly Ti⁴⁺, Al³⁺ and Mg²⁺, but also of Cr³⁺ and Mn²⁺ and other minor elements for iron are related to changes in their structural stability and magnetic properties. Magnetic iron oxides of selected Brazilian pedodomains are discussed, distinguishing those produced from mafic rocks (tuffite, basalt), where primary magnetite transforms to maghemite, from those produced in non-mafic lithologies (such as steatite), where inherited magnetite may be exceptionally stable in the soil. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis profiles of oxide films on chrome steel by auger emission and x-ray photoelectron spectroscopies

Samples of steel from two different sources were examined. The materials had nominally the same bulk composition but different samples from each batch had been hardened under two slightly different conditions.The surface oxide films were analysed by both Auger emission spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) after a number of ion bombardments, and the variation in composition with depth was established. In general the outermost oxide layers were chromium deficient and XPS results suggested the presence of Fe₂O₃ at the surface, together with atmospheric contamination. After ion bombardment the proportion of chromium oxide increased and both iron metal and oxide (Fe₃O₄) were present. The amount of chromium oxide reached a maximum at the steel oxide interface and on further bombardment was replaced by chromium metal. AES and XPS results were in agreement qualitatively and also quantitatively after measurement with a curve analyser of the areas under the peaks of certain elements.The present investigation has shown that AES and XPS can give very similar analyses provided some simple corrections are applied. However, the use of the higher resolution of XPS can provide additional information which cannot be obtained by AES. Thus, using expanded XPS scans, together with suitable curve analysis techniques, it is relatively simple to separate signals from oxide and from free metal regions of the sample, and to study in detail the changes in composition of the oxide from the oxide-air to the oxide-metal interfaces.The study of the four steel samples in this manner has shown that there is a thin region rich in chromium oxide adjacent to the metal. The high level of chromium falls off fairly rapidly nearer the surface and appears to stabilize at a very low level. This is particularly obvious in the thicker oxides (PH), where there is a thick surface layer which is principally iron oxide. It would appear that under the conditions of the heat treatment given to the present samples the thickening of the oxide is due almost entirely to iron oxide. Other work has shown that the low temperature air-formed oxide on these steels is chromium rich and it is suggested that the thickening is due to diffusion of iron through the original film with little movement of the chromium.In view of the high chromium deficiency in the outer layers of the oxides examined it is apparent that the supposedly protective chromium oxide film on chrome steel is situated at the oxide-metal interface and not on the outer surface.The present investigation has shown the existence of two unreported iron satellites. One would appear to be associated with the mixed valence oxide Fe₃O₄ and another with the purely trivalent oxide Fe₂O₃. The satellites could be associated with a strong plasma loss mechanism, or be due to shake-up phenomena as in the case of copper and nickel oxides¹⁴As might be expected from the normal oxidation behaviour of iron, the present oxide films appear to consist of a thin layer of Fe₂O₃ overlying the main Fe₃O₄ oxide. The removal of this outermost Fe₂O₃ layer is rapid and is accompanied by the changes in the satellites mentioned above, together with changes in the position of the Fe 2p_{$\text{3}\text{2}$} oxide peak.In conclusion, it is clear that a detailed XPS examination can not only provide information on overall compositional changes, as can be obtained by AES, but can also provide a comprehensive picture of changes in oxide composition, including those due to oxides of one metal in different valency states.     

XANES investigations of interatomic interactions in multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32

The electronic structure and phase composition of amorphous multilayered nanostructures (Co₄₅Fe₄₅Zr₁₀/a-Si)₄₀ and (Co₄₅Fe₄₅Zr₁₀/SiO₂)₃₂ have been investigated by means of the X-ray absorption near-edge structure (XANES) technique, which is the most sensitive and useful in investigation of the chemical environment of elements in multicomponent nanostructures. The fact of interatomic interactions leading to the formation of composite “nanoferrite”-like FeO · Fe₂O₃ · ZrO₂(CoO) was established. Also it was shown that in the mentioned nanoferrite there is an exchange interaction which involves not only two- and three-charged ions of iron (Fe²⁺ and Fe³⁺) but also ions like Zr⁴⁺ and, partially, Co²⁺. The transformation of the thin structure of L _2,3-ranges for the iron component of multilayered nanostructures in XANES spectra reflects on the change of the ratio of di- and trivalent ions in iron oxides as a part of the composite “nanoferrite.”     

A polyhedron model for the spinel systems LI x Fe1−x CR2O4

Mössbauer spectra of the system Li⁺ _xFe²⁺ _1?2xFe³⁺ _x[Cr₂]O₄ measured at 150 K consist of one Fe(III) absorption and several Fe(II) doublets. An explanation was able by use of a statistical model of the Fe(II) environments.     

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg_0.8,Fe_0.2)₂Si₂O₆) and diopside (Ca(Mg_0.8Fe_0.2)Si₂O₆) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO₂ and olivines ((Mg,Fe)₂SiO₄); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M-O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO_2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites.The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t_2g and e_g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si-O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.     

Structure-property relationships in the R-type hexaferrites: Cation distributions and magnetic susceptibilities of MX2Fe4O11

The strong, and heretofore unexplained, dependence of the magnetic properties of the R-type hexaferrites MX₂Fe₄O₁₁ on heat treatment has been investigated by means of⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy at 297 K.⁵⁷Fe Mössbauer spectra of samples of BaTi₂Fe₄O₁₁, BaSn₂Fe₄O₁₁, and SrSn₂Fe₄O₁₁, annealed at several temperatures consist of three partially resolved quadrupole doublet patterns. The pattern with the very large quadrupole splitting, i.e. 1.3 mm s^–1 E _Q 1.7 mm s^–1, is readily assigned to the trigonal bipyramidal site, and exhibits no dependence of its parameters, including the relative intensity, on heat treatment. The remaining two patterns are assigned to Fe³⁺ ions on octahedral sites, and exhibit relative intensities that are strongly dependent on heat treatment. The¹¹⁹Sn spectrum of BaSn₂Fe₄O₁₁ is a broad, apparently single line that, with the exception of verifying the presence of tin as Sn⁴⁺, provides little insight into the details of the structure. The distributions of the cations over all the lattice sites have been deduced from the Mössbauer spectra and compared with the magnetic susceptibility data. It is concluded that the cation distributions of the Sn-containing phase are not strongly dependent on heat treatment, and the magnetic properties exhibit a similar insensitivity to heat treatment. The Ti analogs exhibit a strong dependence of cation distribution on heat treatment, which is reflected in widely varying magnetic ordering temperatures, a variation that is confirmed by the incipient magnetic hyperfine splitting despite the strong magnetic frustration in the R-type hexaferrites.     

Electron Paramagnetic Resonance and Mössbauer Studies of Fe3+ Ions in the Fe2O3 [dbnd] MoO3 System

The electron paramagnetic resonance (EPR) and Mössbauer spectra of ironmolybdenum mixed oxides system have been investigated. Both EPR and Mössbauer measurements revealed the formation of ferric molybdate, Fe₂ (MoO₄)₃ and the existence of two different Fe³⁺ species. The EPR spectra of Fe₂ (MoO₄)₃, show two resonance lines of Fe³⁺ ions indicating that a strong exchange interaction is dominates in pure iron molybdate. Mösbauer measurements revealed that the isomer shift (I. S) increases with increasing the iron content. A maximum of quadrupole splitting (Q. S) is observed at the stoichiometric concentration corresponding to the formation of Fe₂ (MoO₄)₃. The effect of a catalytaic dehydration process on the redox behaviour of Fe³⁺ located in iron molybdate frame work is investigated. Results indicate that the catalytaic dehydration of 2-proppanol over this catalyst reduces Fe³⁺ ions to Fe²⁺ leading to the formation of the inactive phase FeMoO₄. the essential role of oxygen, in the alcohol gas feed, in regeneration the activity of the catalysts was demonstrated.     

Determination of the recoilless-fraction for57Fe in Fe3O4 by the Mössbauer Faraday effect

We have observed the Mössbauer Faraday effect in nonstoichiometric Fe₃O₄ by using a Mössbauer polarimeter. Experimental results demonstrated that electronic hopping above the Verwey temperature between Fe²⁺?Fe³⁺ ions on the octahedral sites is a localized phenomenon only and the recoilless fractions of⁵⁷Fe nuclei in Fe_3?vO₄ (v=0.02) are 0.71 for A sites and 0.62 for B sites, respectively.     

Fe掺杂对溶胶凝胶法制备的ZnO: Ni薄膜结构及发光特性的影响

采用溶胶凝胶法在玻璃基片上制备了ZnO及Ni, Fe共掺杂的Zn_0.95-xNi_0.05Fe_xO (x=0, 0.005, 0.01, 0.03, 0.05) 薄膜. 通过扫描电镜(SEM) 和X射线衍射(XRD) 研究了薄膜样品的表面形貌和晶体结构. 结果表明所有样品都具有(002) 择优取向, Fe掺杂导致ZnO: Ni薄膜的晶体质量变差, 晶粒尺寸减小, 但适当的Fe掺杂有利于获得致密、 均匀的薄膜. XPS测试结果表明样品中Ni离子的价态为+2价, Fe离子的价态为+2价和+3价.室温光致发光(PL) 测量表明, 所有样品均观察到较强的紫外发光峰, 蓝光双峰和绿光发光峰. ZnO: Ni薄膜的发光强度可以通过Fe掺杂进行有效调节. 进而我们讨论了Ni, Fe共掺杂ZnO样品的发光机理.     

Mössbauer study of nano-TiO2 doped with Fe

A Mössbauer study of nano-TiO₂ doped with Fe is presented. The samples are prepared by sol-gel method, doping Fe by 5, 10 and 15 wt.%, respectively, which are measured with XRD, TEM and Raman spectra. Especially, Mössbauer spectra are emphasized in this study. The anatase phase is major in both doped and no-doped sample. The α-Fe₂O₃ phase is also in the doped samples. The grain size of doped sample is in 5–20 nm range, the major grains are about 13 nm. And the grain size of no-doped sample is about 8 nm. Studying Mössbauer spectra and Raman spectra, we concluded that in the doping process the Fe³⁺ ions entered anatase lattice and substituted Ti⁴⁺ ions. However, the amount of Fe ions in the site is limited to about 1.5 wt.%. It does not increase as the doping Fe increase. The more Fe doped, the more α-Fe₂O₃ formed. For comparing conveniently, it also can be described as (Ti_0.98Fe_0.02)O₂ by atomic percent.     

New interpretations of XPS spectra of nickel metal and oxides

A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d⁹4s² (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd⁹L and the unscreened cd⁸ final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)₂, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni²⁺ and Ni³⁺ simulate the main line and satellite structures for Ni(OH)₂ and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.     

Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.