Fe M2 Research Articles

Spin polarized electron dynamics enhance water splitting efficiency by yttrium iron garnet photoanodes: a new platform for spin selective photocatalysis.

This work presents a spectroscopic and photocatalytic comparison of water splitting using yttrium iron garnet (Y3Fe5O12, YIG) and hematite (α-Fe2O3) photoanodes. Despite similar electronic structures, YIG significantly outperforms widely studied hematite, displaying more than an order of magnitude increase in photocurrent density. Probing the charge and spin dynamics by ultrafast, surface-sensitive XUV spectroscopy reveals that the enhanced performance arises from (1) reduced polaron formation in YIG compared to hematite and (2) an intrinsic spin polarization of catalytic photocurrents in YIG. Ultrafast XUV measurements show a reduction in the formation of surface electron polarons compared to hematite due to site-dependent electron-phonon coupling. This leads to spin polarized photocurrents in YIG where efficient charge separation occurs on the Td sub-lattice compared to fast trapping and electron/hole pair recombination on the Oh sub-lattice. These lattice-dependent dynamics result in a long-lived spin aligned hole population at the YIG surface, which is directly observed using XUV magnetic circular dichroism. Comparison of the Fe M2,3 and O L1-edges show that spin aligned holes are hybridized between O 2p and Fe 3d valence band states, and these holes are responsible for highly efficient, spin selective water oxidation by YIG. Together, these results point to YIG as a new platform for highly efficient, spin selective photocatalysis.

Ligand redistribution reactions for the synthesis of heterobimetallic rare-earth metal complexes of Co(ii) and Fe(ii)

Ligand redistribution reactions led to the formation of heterobimetallic Y(iii)–M(ii) (M = Co, Fe) and homobimetallic M2 complexes.

Simplifying the Synthesis of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are porous, crystalline materials constructed from organic linkers and inorganic nodes that have attracted widespread interest due to their permanent porosity and highly modular structures. However, the large volumes of organic solvents and additives, long reaction times, and specialized equipment typically required to synthesize MOFs hinder their widespread adoption in both academia and industry. Recently, our lab has developed several user-friendly methods for the gram-scale (1-100 g) preparation of MOFs. Herein, we summarize our progress in the development of high-concentration solvothermal, mechanochemical, and ionothermal syntheses of MOFs, as well as in minimizing the amount of modulators required to prepare highly crystalline Zr-MOFs. To begin, we detail our work elucidating key features of acid modulation in Zr-MOFs to improve upon current dilute solvothermal syntheses. Choosing an optimal modulator maximizes the crystallinity and porosity of Zr-MOFs while minimizing the quantity of modulator needed, reducing the waste associated with MOF synthesis. By evaluating a range of modulators, we identify the pKa, size, and structural similarity of the modulator to the linker as controlling factors in modulating ability. In the following section, we describe two high-concentration solvothermal methods for the synthesis of Zr-MOFs and demonstrate their generality among a range of frameworks. We also target the M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd; dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) family of MOFs for high-concentration synthesis and introduce a two-step preparation of several variants that proceeds through a novel kinetic phase. The high-concentration methods we discuss produce MOFs on multi-gram scale with comparable properties to those prepared under traditional dilute solvothermal conditions. Next, to further curtail solvent waste and accelerate reaction times, we discuss the mechanochemical preparation of M2(dobdc) MOFs utilizing liquid amine additives in a planetary ball mill, which we also apply to the synthesis of two related salicylate frameworks. These samples exhibit comparable porosities to traditional dilute solvothermal samples but can be synthesized in just minutes, as opposed to days, and require under 1 mL of liquid additive to prepare ~0.5 g of material. In the following section, we discuss our efforts to avoid specialized equipment and eliminate solvent use entirely by employing ionothermal conditions to prepare a variety of azolate- and salicylate-based MOFs. Simply combining metal chloride (hydrate) salts with organic linkers at temperatures above the melting points of the salts affords high-quality framework materials. Further, ionothermal conditions enable the syntheses of two new Fe(III) M2(dobdc) derivatives that cannot be synthesized under normal solvothermal conditions. Last, as a demonstrative example, we discuss our efforts to synthesize 100 g of high-quality Mg2(dobdc) in a single batch using a high-concentration (1.0 M) hydrothermal synthesis. Our Account will be of significant interest to researchers aiming to prepare gram-scale quantities of MOFs for further study.

Intrinsic Photoexcited Charge Trapping from Small Polaron Formation in α-Fe2O3

Polaron formation and hopping is known to diminish carrier mobility in the ground state of metal oxide photocatalysts. Trap states, however, are usually cited as the cause of limited carrier mobility and short carrier lifetimes in the photoexcited state. We investigate how small polaron formation controls the ultrafast localization and trapping of photoexcited carriers in hematite (α-Fe2O3), potentially bridging these two pictures. Ultrafast transient extreme ultraviolet (XUV) spectroscopy of the Fe M2,3 edge measures a sub-5 fs shift in charge density from the oxygen to the iron atom following optical excitation. An energetic splitting of the Fe M2,3­ edge is then measured on a 100 fs timescale, with the kinetics of the splitting matching those typically associated with trap or mid-gap states in hematite. The splitting of the Fe M2,3 edge, however, is best reproduced by predictions for small polaron localization of the photoexcited carriers, and not the pre-edge absorption or bleach expected for mid-gap states. The polaron formation efficiency versus visible light excitation energy is measured to match the discrepancy between the photoconversion efficiency and visible light absorption of hematite. These results therefore suggest that small polaron formation is responsible for the intrinsic recombination and transport issues that currently limit hematite’s performance. In particular, the increased small polaron formation rate at near-band gap excitation may result in the decreased visible light photoconversion efficiency. Possible materials routes to overcoming small-polaron localization, as well as the role of small polarons in other metal oxide photocatalysts, will be discussed.

Bimetallic platinum group metal-free catalysts for high power generating microbial fuel cells

M1-M2-N-C bimetallic catalysts with M1 as Fe and Co and M2 as Fe, Co, Ni and Mn were synthesized and investigated as cathode catalysts for oxygen reduction reaction (ORR). The catalysts were prepared by Sacrificial Support Method in which silica was the template and aminoantipyrine (AAPyr) was the organic precursor. The electro-catalytic properties of these catalysts were investigated by using rotating ring disk (RRDE) electrode setup in neutral electrolyte. Fe-Mn-AAPyr outperformed Fe-AAPyr that showed higher performances compared to Fe-Co-AAPyr and Fe-Ni-AAPyr in terms of half-wave potential. In parallel, Fe-Co-AAPyr, Co-Mn-AAPyr and Co-Ni-AAPyr outperformed Co-AAPyr. The presence of Co within the catalyst contributed to high peroxide production not desired for efficient ORR. The catalytic capability of the catalysts integrated in air-breathing cathode was also verified. It was found that Co-based catalysts showed an improvement in performance by the addition of second metal compared to simple Co- AAPyr. Fe-based bimetallic materials didn't show improvement compared to Fe-AAPyr with the exception of Fe-Mn-AAPyr catalyst that had the highest performance recorded in this study with maximum power density of 221.8 ± 6.6 μWcm−2. Activated carbon (AC) was used as control and had the lowest performances in RRDE and achieved only 95.6 ± 5.8 μWcm−2 when tested in MFC.

Small Polaron Formation Leads to Intrinsic Photoexcited Charge Trapping in α-Fe2O3

The diminished carrier mobility in the ground-state of metal oxide photocatalysts is known to depend on polaron formation and hopping. Photo-excited dynamics and short carrier lifetimes, however, are usually associated with trap states. In this presentation, we investigate the role that small polaron formation plays in the ultrafast localization and trapping of photoexcited carriers in hematite (α-Fe2O3), potentially bridging these two pictures. Ultrafast transient extreme ultraviolet (XUV) spectroscopy on the Fe M2,3 edge measures a sub-5 fs shift in charge density from the oxygen to the iron atom following optical excitation. Small polaron localization of the photoexcited electrons begins on a 100 fs time scale, as measured by a splitting of the Fe M2,3 edge. The subsequent kinetics reproduce the lifetimes typically associated with trap or mid-gap states in hematite. The splitting of the Fe M2,3 edge, however, only matches predictions of polaron localization, and not the pre-edge absorption or bleach expected for mid-gap trap states. The measured polaron formation efficiency also matches the discrepancy between the incident photoconversion efficiency and the visible light absorption of hematite with varying excitation wavelength. These results suggest that sub-100 fs small polaron formation is responsible for the intrinsic recombination and transport issues that limit hematite’s performance, even when techniques such as nanostructuring or trap-state passivation are employed. The role of small-polaron localization in metal oxide photocatalysts, as well as possible materials routes to overcome this effect, will be discussed.

Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α-Fe2O3.

Small polaron formation is known to limit ground-state mobilities in metal oxide photocatalysts. However, the role of small polaron formation in the photoexcited state and how this affects the photoconversion efficiency has yet to be determined. Here, transient femtosecond extreme-ultraviolet measurements suggest that small polaron localization is responsible for the ultrafast trapping of photoexcited carriers in haematite (α-Fe2O3). Small polaron formation is evidenced by a sub-100 fs splitting of the Fe 3p core orbitals in the Fe M2,3 edge. The small polaron formation kinetics reproduces the triple-exponential relaxation frequently attributed to trap states. However, the measured spectral signature resembles only the spectral predictions of a small polaron and not the pre-edge features expected for mid-gap trap states. The small polaron formation probability, hopping radius and lifetime varies with excitation wavelength, decreasing with increasing energy in the t2g conduction band. The excitation-wavelength-dependent localization of carriers by small polaron formation is potentially a limiting factor in haematite's photoconversionefficiency.

Probing ultrafast changes of spin and charge density profiles with resonant XUV magnetic reflectivity at the free-electron laser FERMI.

We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q-resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Qz, we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film.

A CT-scan database for the facial soft tissue thickness of Taiwan adults

Facial reconstruction is a branch of forensic anthropology used to assist in the identification of skeletal remains. The majority of facial reconstruction techniques use facial soft tissue depth chart data to recreate facial tissue on a skull or a model of a skull through the use of modeling clay. This study relied on 193 subjects selected from the Taiwanese population on the basis of age and gender to determine the average values of 32 landmarks, include midline and bilateral measures, by means of CT scans. The mean age of the subjects was 46.9±16.4 years, with a mean age of 43.8±16.6 for males and 49.9±15.8 for females respectively. There were 16 landmarks with statistically significant differences between male and female subjects, namely S, G, N, Na, Ph, Sd and Id in the midline portion, FE, LO, ZA and Sub M2 in the bilateral-right and left portion, and IM point in the bilateral-left portion (abbreviations adapted from Karen T. Taylor's work). The mean soft tissue depth was greater in males than in females, and there was significant difference between the right and left sides of the face in Za point. This study's findings were compared with those of Bulut et al.

Lipid Nanotube Encapsulating Method for Two- and Three-Dimensional Transmission Electron Microscopy Analyses of Cage-Shaped Proteins

A novel, sample-fixation technique for transmission electron microscopy (TEM) is proposed. We encapsulated various samples in one-dimensional hollow cylinders of a glycolipid nanotube (LNT) and found it to be highly stable, flexible, and reproducible. The cylindrical shape of the LNT allows us to observe nanomaterials consistently even when the samples are rotated around the tube axis. This is critical in improving TEM computed tomography (CT), which suffers from the loss of the electron beam at high tilting angles because of the increased effective thickness of the supporting film. This technique makes it possible to reconstruct three-dimensional images from weak-signal TEM images. In this work, we examined two types of cage-shaped proteins, ferritin, and DNA-binding protein from starved cells (Dps). We reconstructed three-dimensional images of Fe cores from zero-loss images or from electron energy-loss spectroscopy (EELS) mapping images obtained with the Fe M2,3 edge. We also applied negative staining and vitreous ice embedding (VIE). These results show the potential of the LNT encapsulation technique.

Order and anti-order in olivine II: Thermodynamic analysis and crystal-chemical modelling

The equilibrium order/anti-order behaviour in olivine Fe 0.48 Mg 0.52 [SiO 4 ] is analysed in terms of the Thompson (1969, 1970) model for the Gibbs energy due to ordering, G ord , \[G^{ord} \frac{1}{2}{\Delta}G^{0}_{exch} Q {-} TS^{ord}_{conf}.\] ΔG 0 exch = ΔH 0 exch − TΔS 0 exch relates to the exchange reaction Fe M2 Mg M1 ↔ Fe M1 Mg M2 . Since for the investigated olivine both ΔH 0 exch and ΔS 0 exch are positive (ΔH 0 exch = 1.2 kJ/mol, ΔS 0 exch = 3.7 J/mol K), an ordered Fe 2+ ,Mg configuration is favoured by the enthalpic part of ΔG 0 exch whereas the vibrational entropic part favours anti-ordering. As a result, at low temperatures, where ΔH 0 exch > TΔS 0 exch , Fe 2+ prefers M2. Since, however, the energy TΔS 0 exch steadily increases with increasing temperature it promotes Fe 2+ into M1 and full disorder is attained at a crossover temperature T co where ΔH 0 exch = T co ΔS 0 exch . Above T co , TΔS 0 exch becomes progressively larger than ΔH 0 exch and stimulates further fractionating of Fe 2+ into M1 corresponding to increasing anti-order. The unusual phenomenon of anti-order increasing at increasing temperatures is due to ΔH 0 exch being relatively small in FeMg olivine compared to the temperature proportional energy TΔS 0 exch . In other AB olivines (A, B = Mn, Fe, Co, Ni, Mg) the exchange enthalpies are much larger, between 9 and 20 kJ/mol, so that they dominate ΔG 0 exch to a degree that precludes a crossover from ordered to anti-ordered states up to the melting point. The exchange enthalpies reported for MnMg, FeMg, CoMg, NiMg and MnFe olivines can be rationalized in terms of cation radius (r) and electronegativity (χ) ratios of the A and B cations. In a novel approach, both radii and electronegativities have been derived from topological analyses of the procrystal electron density distributions of pure M 2 [SiO 4 ] olivines (M = Mn, Fe, Co, Ni, Mg) yielding a very satisfactory description by \[{\Delta}H^{0}_{exch} 252.6({\pm}6.1) [r(A)/r(B) {-} 1] {-} 75.8({\pm}1.9) [{\chi}(A)/{\chi}(B) {-} 1].\] Accordingly, the small value of ΔH 0 exch found for FeMg olivine is a consequence of opposite radius and electronegativity contributions which almost cancel. In MnFe olivine, although both contributions are small, they cooperate resulting in a moderate value of ΔH 0 exch . In MnMg olivine, it is the radius ratio that dominates, contrary to CoMg and NiMg olivine where the electronegativity ratios control ΔH 0 exch . Consequently, Mn prefers M2, and Co and Ni segregate into M1. ΔS 0 exch can be split into vibrational, ΔS 0,vib exch , and electronic exchange entropies, ΔS 0,el exch . Describing the first in terms of a new octahedral distortion parameter, D f , and estimating the second from the Boltzmann distribution of the 3d-electrons, ΔS 0 exch can be satisfactorily modelled by \[{\Delta}S^{0}_{exch} 35.76({\pm} 0.34) {\{}[D_{f} (A)^{M1} + D_{f} (B)^{M2}]/[D_{f} (B)^{M1} + D_{f} (A)^{M2}] {-} 1{\}} + {\Delta}S^{0,el}_{exch}\] The resulting lnK D = −(ΔH 0 exch − T ΔS 0 exch )/RT allows, for the first time and to the best of our knowledge, an exclusively electron density based description of the experimentally observed temperature variations of the site occupancies in AB olivines. This modelling of lnK D allows also for predicting the temperature variation of equilibrium cation distributions in AB olivines not investigated so far.

Studies of positron trapping at quantum-dot-like particles on metal surfaces

The decrease of the Fe M2,3 VV positron annihilation induced Auger signal intensity and the enhancement of the Cu one with enrichment of the Cu content of the Fe–Cu alloy is explained by theoretical calculations as being due to trapping of positrons in the regions of Cu nanoparticles embedded in the top atomic layers of Fe.

Ordering kinetics of Mg-Fe2+exchange in a Wo43En46Fs11augite

The kinetics of Fe 2+ -Mg exchange between the M1 and M2 sites (Fe M2 2+ + Mg M1 = Fe 2+ M1 + Mg M2 ) were followed by ordering experiments in an augitic clinopyroxene (Ca 0.841 Na 0.019 Mg 0.888 Fe 2+ 0.151 Ti 0.011 Al 0.028 Cr 0.003 Fe 3+ 0.054 Mn 0.006 )(Si 1.914 Al 0.086 ) from a dike on Alicudi (Aeolian Islands, Italy). The same single crystal was annealed in silica tubes in an iron-wüstite buffered Ar atmosphere, at 700, 750, 800, 850, and 950 °C, followed by quenching after each thermal treatment, and was used for the collection of X-ray diffraction data and for microprobe analysis. Kinetic constants (K) for each isotherm were calculated from the distribution coefficient K D [= (Fe 2+ /Mg) M1 /(Fe 2+ /Mg) M2 ] measured during a series of experiments carried out by increasing annealing times until exchange equilibrium was achieved. Calculations of K were performed using the Ginzburg-Landau equation, the kinetic model of Mueller, and the mathematical formulation proposed by Sha and Chappell (1996) to check the responses of various kinetic models for a Ca-rich pyroxene on the same data set. The activation energy of the Fe 2+ -Mg exchange spans a narrow range, yielding values of 200 (±28) kJ/mol, independent of the method used to calculate K.

Microanalysis of Fe 3+ /ΣFe in oxide and silicate minerals by investigation of electron energy-loss near-edge structures (ELNES) at the Fe M 2,3 edge

The Fe M2,3-edge spectra of solid solutions of garnets (almandine-skiagite Fe3(Al1–xFex)2[SiO4]3 and andradite-skiagite (Fe1–xCax)3Fe2[SiO4]3), pyroxenes (acmite-hedenbergite (Ca1–xNax)(Fe2+1−xFe3+x)Si2O6), and spinels (magnetite-hercynite Fe(Al1–xFex)2O4) have been measured using the technique of parallel electron energy-loss spectroscopy (EELS) conducted in a transmission electron microscope (TEM). The Fe M2,3 electron energy-loss near-edge structures (ELNES) of the minerals exhibit a characteristic peak located at 4.2 eV and 2.2 eV for trivalent and divalent iron, respectively, prior to the main maximum at about 57 eV. The intensity and energy of the pre-edge feature varies depending on Fe3+/ΣFe. We demonstrate a new quantitative method to extract the ferrous/ferric ratio in minerals. A systematic relationship between Fe3+/ΣFe and the integral intensity ratio of the main maximum and the pre-edge peak of the Fe M2,3 edge is observed. Since the partial cross sections of the Fe M2,3 edges are some orders of magnitude higher than those of the Fe L2,3 edges, the Fe M2,3 edges are interesting for valence-specific imaging of Fe. The possibility of iron valence-specific imaging is illustrated by Fe M2,3-ELNES investigations with high lateral resolution from a sample of ilmenite containing hematite exsolution lamellae that shows different edge shapes consistent with variations in the Fe3+/ΣFe ratio over distances on the order of 100 nm.

The Chemistry of η3-Vinylcarbene Complexes

Abstract The chemistry of η3-vinylcarbene transition-metal complexes is reviewed. The η3-vinylcarbene complexes are prepared by 1) the alkylation of (η3-acryloyl)tricarbonylferrate, 2) the treatment of cyclopropenes with [Fe2(CO)9], 3) the insertion of acetylenes into a carbene–metal double bond, 4) the reaction of acetylene with [ReCl3(Me5C5)]2, 5) the reaction of carbyne complexes with allyl bromides, and 6) the thermal decarbonylation of (η1-vinylcarbene)pentacarbonylchromium. The structures of the complexes, which were determined by X-ray analyses, are represented by the hybrid of the resonance structures (A) and (B). The contribution of the two structures was very sensitive to the respective MLn fragments. The vinylcarbene complex, [Fe(η3-vinylcarbene)(CO)3] (1), is a parent complex of a series of various complexes. The carbene carbons of the reported Fischer-type η3-vinylcarbene complexes are electrophilic. Carbonylation of the η3-vinylcarbene complexes gives η4-vinylketene complexes. Treatment of the η3-vinylcarbene(carbonyl)irons with an excess of tertiary phosphines or bidentate amines gives ferracyclopentenones. Reaction of 1 with isocyanides gives the first example of the η4-vinylketenimine complex. Treatment of 1 with diazomethane gives (η4-1,3-butadiene)tricarbonyliron. The complex 1 with a methoxycarbonyl group on the 3-position reacts with carbon monoxide to give a η4-pyrone complex, which thermally rearranges to its isomer. The rearrangement was deduced to proceed via a η4-methoxyfuran complex. The complex 1 reacts with hydride to give a η3-allyl complex. Reaction of (η3-2-trifluoromethylvinylcarbene)tricarbonyliron with K[BH(s-Bu)3] or phenyllithium gives (η4-difluorotrimethylenemethane)tricarbonyliron, leaving a fluoride ion. η3-Vinylcarbene complexes react with acetylenes to give η4-cyclopentadiene metal complexes. The reaction proceeds via a metallacyclohexadiene. The complex 1 reacts with an unsaturated metal complex M2Ln to give a binuclear vinylcarbene complex or (η3 : η1-allyl)(Fe–M2). Reaction of 1 with Ru(CO)3(COD) provides a method for selective preparation of (η3 : η1-allyl)(Fe–Ru), which reacts with acetylenes to give [Fe(η4-ruthenacyclohexadiene)(CO)3]. Formation of a η3-vinylcarbene complex by the reaction of a carbene complex with acetylene, and subsequent carbonylation of this complex, is the essential pathway of the Dötz reaction.

Magnetic linear dichroism effects in reflection spectroscopy: A case study at the Fe M2,3 edge

Magneto-optical measurements are strongly dependent on the polarization of the radiation as well as the interaction geometry of the light with respect to the relative orientation and direction of the magnetization M. We performed magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements around the Fe M2,3 transition by measuring the difference between the reflected intensities of right and left circular polarized light (MCD) and the difference between the reflected intensities for opposite magnetization directions (MLD). From the angular variations of the MCD measurements we extracted the dielectric tensor ε(ω) which was then used as an input parameter to calculate the magneto-optical response of Fe in reflection MLD spectra. The experimental data around the M2,3 edge show good agreement with model calculations.

Magnetic circular versus linear dichroism effects: A case study at the Fe M2,3 edge (abstract)

Magneto-optical measurements are strongly dependent on the polarization of the radiation as well as the interaction geometry of the light with respect to the relative orientation and direction of the magnetization M. In an effort to identify the different angular and spectral contributions and to select the preferred experimental setup for magneto-optical measurements, we performed magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements around the Fe M2,3 transition. The MCD experiments were performed by measuring the difference between the reflected intensities of left and right circularly polarized soft x-ray radiation. While for the MCD experiments, the magnetization was kept constant, it was modulated between M+ and M− for the MLD spectra. We used a quadruple reflection polarizer that was tuned to act as a λ/4 phase shifter for the MCD measurements and as a linear polarizer for the MLD experiments. The experiments confirm our model calculations for longitudinal and polar MCD and transverse MLD using a previous determined energy-dependent dielectric tensor ε(ω). The outcome of our experiments has consequences for most MCD experiments performed with Pcirc<1 in combination with mixed geometry. Such a configuration could severely alter the quantitative MCD analysis due to the strong MLD contribution.

A new type of magnetic linear dichroism at Fe and Co M2,3 edges

We have found a new type of magnetic linear dichroism in photoyield spectra at the Fe and Co M2,3 edges. Spectra excited by p-polarized light at oblique incidence show cross section dependence on the sign of the magnetization. The experimental geometry is the same as that of the transverse magneto-optic Kerr effect (T-MOKE). The dichroism is enhanced when the light impinges on the sample towards grazing incidence. The T-MOKE at the Co M edge also measured simultaneously. The new type of dichroism can be applied for imaging of magnetic domains of surfaces by a photoelectron microscopy.

A new type of magnetic linear dichroism at Fe and Co M2,3 edges

We have found a new type of magnetic linear dichroism in photoyield spectra at the Fe and Co M 2,3 edges. Spectra excited by p-polarized light at oblique incidence show cross section dependence on the sign of the magnetization. The experimental geometry is the same as that of the transverse magneto-optic Kerr effect (T-MOKE). The dichroism is enhanced when the light impinges on the sample towards grazing incidence. The T-MOKE at the Co M edge also measured simultaneously. The new type of dichroism can be applied for imaging of magnetic domains of surfaces by a photoelectron microscopy.

Factor analysis of Fe M2,3 VV spectra of oxidizing iron: The role of the background in the emergence of ghost components

AbstractThe influence of the (correction for the) background in AES spectra on the results of factor analysis (FA) was investigated. To this purpose a set of experimental spectra for the Fe M2,3VV transition, obtained on the oxidation of pure iron, and sets of look‐alike simulated spectra, using a linear combination of two elastic components superimposed on background components, were analysed with FA after different types of treatment of the spectra prior to FA, e.g. differentiation or removal of a particular type of background. In the sets of simulated spectra the roles of a background due to the secondary electron cascade and that due to the inelastically scattered electrons were investigated separately. It was observed that for both types of backgrounds additional principal components with respect to the two elastic components arise, irrespective of the considered treatment of the spectra prior to FA. Results obtained for the experimental set and for the simulated sets with a background originating from the secondary electron cascade were very similar. In the simulated spectra, the origin of the additional components could be identified unambiguously as (an inadequate correction for) the background due to the secondary electron cascade. It is likely that the same origin applies to the additional (third) component emerging on FA of the set of experimental Fe M2,3 VV spectra.