Ir Substrate Research Articles

Energy surface and lifetime of magnetic skyrmions

The stability of skyrmions in various environments is estimated by analyzing the multidimensional surface describing the energy of the system as a function of the directions of the magnetic moments in the system. The energy is given by a Heisenberg-like Hamiltonian including terms representing Dzyaloshinskii-Moriya interaction, anisotropy energy and interaction with an external magnetic field. Local minima on this surface correspond to the ferromagnetic and skyrmion states. Minimum energy paths (MEP) between the minima are calculated using the geodesic nudged elastic band method. The maximum energy along an MEP corresponds to a first order saddle point on the energy surface and gives an estimate of the activation energy for the magnetic transition, such as creation and annihilation of a skyrmion. The pre-exponential factor in the Arrhenius law for the rate, the so-called attempt frequency, is estimated within harmonic transition state theory where the eigenvalues of the Hessian at the saddle point and the local minima are used to characterize the shape of the energy surface. For some degrees of freedom, so-called “zero modes”, the energy of the system remains invariant. They need to be treated separately and give rise to temperature dependence of the attempt frequency. As an example application of this general theory, the lifetime of a skyrmion in a track of finite width for a PdFe overlayer on a Ir(1 1 1) substrate is calculated as a function of track width and external magnetic field. Also, the effect of non-magnetic impurities is studied. Various MEPs for annihilation inside a track, via the boundary of a track and at an impurity are presented. The attempt frequency as well as the activation energy has been calculated for each mechanism to estimate the transition rate as a function of temperature.

Probing the hydrogen adsorption affinity of Pt and Ir by surface interrogation scanning electrochemical microscopy (SI-SECM)

Scanning electrochemical microscopy in the surface interrogation mode (SI-SECM) has been used to probe the strength of metal-adsorbed H bonds at Pt and Ir. The generally accepted view is that this technique can only give meaningful results for similar probe and substrate electrode dimensions. However, it is shown that SI-SECM can also provide valuable information for H adsorption even when the substrate is much larger than the microelectrode probe (of 500 and 25μm diameter respectively), for properly chosen substrate and mediator combinations that minimize the tip currents under substrate open circuit potential conditions. Linear sweep voltammetry at a microelectrode positioned at a very small probe–substrate distance (2.5μm) showed remarkable positive feedback in the presence of an oxidizable mediator (TMPD) when a full or partial H monolayer was electrochemically pre-formed on the Pt or Ir substrate. The magnitude and shapes of chronoamperometric responses at the tip were interpreted in terms of variation of H coverage with time and changes in the open circuit potential of the substrate. The higher affinity of Ir than Pt for adsorbed H has been used to validate the approach.

Co film stretching induced by lattice mismatch and annealing: The role of Graphene

Thin Co films intercalated between a Graphene capping layer and the Ir(111) surface are of interest for spintronics applications due to their peculiar magnetic properties and to their chemical stability. The structure, and then the magnetic properties, of the Co films depend on the intercalation process which is strongly influenced by the temperature, total amount of Cobalt and quality of the capping Graphene layer. In order to identify and disentangle the effects of these contributions, we report on the structural characterisation of four Co films as a function of thickness, annealing temperature, and Graphene capping. From the structural point of view, the deposition of Co on a hot Ir substrate mimics quite well the intercalation process proving the validity of the colander model describing the Graphene role during the process.

Electrocrystallization of iridium on the graphite, rhenium and iridium electrode from the NaCl-KCl-CsCl-IrCl3 molten salts

Mechanism and kinetics of iridium (Ir) electrocrystallization on the graphite, rhenium (Re) and Ir electrode was investigated in the NaCl-KCl-CsCl melts containing 0.5mol/L IrCl3 at 570°C. It found that the 3D spherical Ir nucleuses on graphite electrodes were grown from the laminated structure of graphite. There were two kinds of Ir nucleus were observed on the Re electrodes, 3D hemispherical particles and 2D layers. Ir nucleuses on its intrinsic substrates were 3D hemispherical particles growing directly from the original Ir grains. The results suggested that nucleation of Ir on graphite electrodes was an 3D island growth process (Volmer-Weber growth mode) under diffusion-controlling, and that on the Re electrodes followed the so-called Stranski-Krastanov growth mode, namely 3D Ir particles deposited on the pre-deposited 2D Ir layers. Nucleation of Ir on its intrinsic substrates was also a 3D process. The best non-linear fitting results of current transients showed that both initial nucleus density N0 and nucleation rate A of Ir particles on the three electrodes increased with the applied over-potential. Nucleation of Ir particles on its intrinsic substrates had the highest initial nucleus density and nucleation rate. Taking the nucleus density and bond strength into consideration, Ir substrate was the best choice for electrodeposition of Ir coating following by the Re substrate.

Tailoring noncollinear magnetism by misfit dislocation lines

The large epitaxial stress induced by the misfit between a triple atomic layer Fe film and an Ir(111) substrate is relieved by the formation of a dense dislocation line network. Spin-polarized scanning tunneling microscopy (SP-STM) investigations show that the strain is locally varying within the Fe film and that this variation affects the magnetic state of the system. Two types of dislocation line regions can be distinguished and both exhibit spin spirals with strain-dependent periods (ranging from 3 nm to 10 nm). Using a simple micromagnetic model, we attribute the changes of the period of the spin spirals to variations of the effective exchange coupling in the magnetic film. This assumption is supported by the observed dependence of the saturation magnetic field on the spin spiral period. Moreover, magnetic skyrmions appear in an external magnetic field only in one type of dislocation line area, which we impute to the different pinning properties of the dislocation lines.

Highly Enhanced Oxygen Reduction Reaction Activity and Electrochemical Stability of Pt/Ir(111) Bimetallic Surfaces

We demonstrate highly enhanced ORR activity and electrochemical stability of Pt/Ir(111) model core-shell catalysts prepared by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV). Reflection high-energy electron diffraction patterns for the surfaces show that Pt grew epitaxially on the clean Ir(111) substrate and the corresponding scanning tunneling microscope images collected in UHV reveal atomically flat terraces with 50–80nm widths at a substrate temperature of 673K. In contrast, the corresponding surfaces prepared at a substrate temperature of 303K show island-like topmost surface structures. The two-monolayer (ML)-thick Pt grown on Ir(111) (Pt2ML/Ir(111)) surfaces, prepared at substrate temperatures of 303K and 673K, show ca. 6 and 24 times higher ORR activities than clean Pt(111), respectively. The anomalous activity enhancement for the latter surface prepared at 673K is probably caused by homogeneous surface strain acting on the Pt shells that is derived from the 2.2% lattice mismatch between the Pt and Ir. The preparation-temperature–dependent ORR activity suggests that the activity can be dominated by the topmost surface and interface structures of the Pt shell–Ir(111) bimetallic system. Furthermore, while the initial ORR activity of pristine surfaces decreases with increasing Pt shell thickness, the stability during room temperature potential cycling between 0.6 and 1.0V in a 0.1M HClO4 solution was greatly enhanced above three ML thickness; the Pt4ML/Ir(111) surface prepared at 673K retained 6.5 times higher ORR activity than Pt(111), even after 5000 potential cycles. The ORR activity and electrochemical stabilities for the Pt/Ir(111) bimetallic surfaces are the highest among the MBE-prepared Pt/M(111) (M=Ir, Pd, Au) systems reported to date. The results obtained in this study show that Pt/Ir core–shell nanostructures are potential candidates for highly active and durable ORR catalysts.

Oxygen Reduction Reaction Activity and Durability for Model Pt Shell Layers on Ir(111) Prepared by Molecular Beam Epitaxy

Introduction The core-shell type nanostructure, that is composed of ultra-thin Pt coating on other transition metal nanoparticles have attracted much attention from the viewpoints of cathode electrode catalysts in polymer electrolyte fuel cell (PEFC). Compressive strain of the Pt-shells induced by lattice mismatch and direct electronic interaction between the Pt shell and core elements influences electronic properties of the Pt shell layers and, thereby, contributing to enhanced oxygen reduction reaction (ORR) activity [1]. However, because of operating conditions of PEFC, i.e., low pH, high positive potentials, ORR activity of the core-shell catalysts decline through dissolution of core elements and rearrangements of surface Pt atoms. Considering standard electrode potentials, iridium is stable among the transition metals and Pt-shell/Ir-core nanoparticles might be stable under the PEFC operating conditions. However, at present, relationship between Pt-Ir bimetallic surface structures and ORR properties has been less reported [2]. In this study, we prepared well-defined Pt/Ir(111) bimetallic surfaces by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV) and studied the ORR activity and durability. Experimental Ir(111) single crystal substrate was cleaned by Ar+ sputtering and annealing at 1273 K in UHV. Various-monolayers(ML)-thick Pt was deposited onto the clean Ir(111) substrate by an electron beam evaporation method at the substrate temperature of 673K. The resulting surface structures were verified by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) in UHV. The UHV-fabricated samples were transferred to electrochemical evaluation systems set in a N2-purged glove box without air exposure. CV and LSV measurements were conducted in N2-purged and O2-saturated 0.1 M HClO4, respectively. The ORR activity was evaluated from j k values at 0.9 V vs. RHE by using the Koutecky-Levich equation. EC degradation of the Pt/Ir(111) surface was evaluated by applying potential cycles between 0.6 V (3s) and 1.0 V (3s) vs. RHE in the O2-saturated solution at room temperature. Results and Discussion Fig. 1 (a) summarizes CV curves of the MBE-prepared nML-thick Pt/Ir(111) (n=1-4: Pt n ML/Ir(111)) and clean Pt(111). All CV curves of the Pt nML/Ir(111) show symmetrical peaks similar to the clean Pt(111) (so-called butterfly peak) in the region of OH adsorption and desorption (0.6-1.0 V), accompanied with remarkable decrease in hydrogen adsorption and desorption charges (0.05-0.35 V). The CV features are typical for highly-ORR-active Pt-based bimetallic surfaces reported to date, suggesting that the topmost surfaces comprise pure Pt(111) lattice. Fig. 1 (b) presents changes in j k during potential cycles loading between 0.6 and 1.0 V. Initial ORR activity enhancement factors for the 2ML, 3ML and 4ML-thick Pt shell layers can be estimated to be ×24, ×12 and ×8, respectively compared with the clean Pt(111). Because Ir lattice constant is smaller than Pt, the Ir(111) substrate should induce compressive surface strain on the Pt-shell. As a result, the ORR activity is enhanced. Furthermore, because compressive strain of the Pt shell layers should be relaxed with increasing the Pt shell layer thickness, the initial activity enhancement factors decreased with increasing the thickness. After the 5000 potential cycles loading, the enhancement factors for the Pt2ML/Ir(111) decreased to ×2 vs. clean Pt(111) indicating that compressive surface strain is easily released by the potential cycle loading. In contrast, particularly, the initial activity of the 4ML-Pt-shell remains nearly unchanged even after the 5000 cycles loading: the activity is the highest among the other well-defined Pt-M(111) bimetallic systems, e.g., Pt/Pd(111) [3], Pt-skin surfaces of Pt-Ni(111) [4] and Pt-Co(111) [5], reported in our laboratory. The results can be explained by 3D migration of the surface Pt atoms during the potential cycle loading and by release in compressive strain in Pt shell. Therefore, the results suggest that Pt-Ir bimetallic system can be expected to be applied to ORR catalysts for practical use. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan and Grant- in Aid for young scientists (B) from the Japan society for the promotion of science (N. T.).

Symmetry breaking in spin spirals and skyrmions by in-plane and canted magnetic fields

The influence of in-plane and canted magnetic fields on spin spirals and skyrmions in atomic bilayer islands of palladium and iron on an Ir(111) substrate is investigated by scanning tunneling microscopy at low temperatures. It is shown that the spin spiral propagation direction is determined by the island’s border which can be explained by equilibrium state calculations on a triangular lattice. We find a different response of spin spirals to in-plane magnetic fields for a propagation direction parallel to the applied field as compared to perpendicular, which originates from their cycloidal nature. As a result, the spin spiral propagation direction may be reorientated by in-plane fields. Furthermore, it is demonstrated that also skyrmions are distorted in canted fields which allows to determine the sense of magnetization rotation as enforced by the interfacial Dzyaloshinskii–Moriya interaction.

Towards functionalization of graphene: in situ study of the nucleation of copper-phtalocyanine on graphene

Molecular films present an elegant way for the uniform functionalization or doping of graphene. Here, we present an in situ study on the initial growth of copper phthalocyanine (CuPc) on epitaxial graphene on Ir(111). We followed the growth up to a closed monolayer with low energy electron microscopy and selected area electron diffraction (μLEED). The molecules coexist on graphene in a disordered phase without long-range order and an ordered crystalline phase. The local topography of the graphene substrate plays an important role in the nucleation process of the crystalline phase. Graphene flakes on Ir(111) feature regions that are under more tensile stress than others. We observe that the CuPc molecules form ordered domains initially on those graphene regions that are closest to the fully relaxed lattice. We attribute this effect to a stronger influence of the underlying Ir(111) substrate for molecules adsorbed on those relaxed regions.

Anatomy and Giant Enhancement of the Perpendicular Magnetic Anisotropy of Cobalt-Graphene Heterostructures.

We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co films by graphene coating from both first-principles and experiments. Our calculations show that graphene can dramatically boost the surface anisotropy of Co films up to twice the value of its pristine counterpart and can extend the out-of-plane effective anisotropy up to unprecedented thickness of 25 Å. These findings are supported by our experiments on graphene coating on Co films grown on Ir substrate. Furthermore, we report layer-resolved and orbital-hybridization-resolved anisotropy analysis, which help understanding of the physical mechanisms of PMA and more practically can help design structures with giant PMA. As an example, we propose superexchange stabilized Co-graphene heterostructures with a robust constant effective PMA and linearly increasing interfacial anisotropy as a function of film thickness. These findings point toward possibilities to engineer graphene/ferromagnetic metal heterostructures with giant magnetic anisotropy more than 20-times larger compared to conventional multilayers, which constitutes a hallmark for future graphene and traditional spintronic technologies.

Wafer bowing control of free-standing heteroepitaxial diamond (100) films grown on Ir(100) substrates via patterned nucleation growth

The potential of patterned nucleation growth (PNG) technique to control the wafer bowing of free-standing heteroepitaxial diamond films was investigated. The heteroepitaxial diamond (100) films were grown on an Ir(100) substrate via PNG technique with different patterns of nucleation regions (NRs), which were dot-arrays with 8 or 13μm pitch aligned to <100> or <110> direction of the Ir(100) substrate. The wafer bows and the local stress distributions of the free-standing films were measured using a confocal micro-Raman spectrometer. For each NR pattern, the stress evolutions within the early stage of diamond growth were also studied together with a scanning electron microscopic observation of the coalescing diamond particles. These investigations revealed that the NR pattern, in terms of pitch and direction of dot-array, strongly affects the compressive stress on the nucleation side of the diamond film and dominantly contributes to the elastic deformation of the free-standing film. This indicates that the PNG technique with an appropriate NR pattern is a promising solution to fabricate free-standing heteroepitaxial diamond films with extremely small bows.

Electrochemical impedance studies of IrO 2 catalysts for oxygen evolution

Abstract IrO 2 electrodes used as oxygen evolving anodes were studied by electrochemical impedance spectroscopy (EIS) to establish criteria for the assessment of their electroactive surface area and their intrinsic catalytic activity. Two types of IrO 2 -coated electrodes were used: anodically grown oxides on an Ir substrate and commercially available IrO 2 nanoparticles, dispersed in a Nafion® polymer electrolyte layer on a glassy carbon substrate. EIS data indicate that both formulations behave as porous electrodes and their response can be described by variants of the classic transmission line model both at potentials outside and within the oxygen evolution reaction (OER) potential range; however, in the latter case, useful parameters could also be obtained by the use of common Randles models. An alternative approach to obtain capacitance values (free from the assumptions and geometric formulations of a model) has been based on plots of − 1/(ωZ Im ) vs. Z re that acquire or approach a limiting total capacitance value C t at low or intermediate frequencies; the latter scales well with the charge associated with IrO 2 surface electrochemistry and with oxide layer thickness or oxide particle loading. C t can be taken as a measure of the catalyst electroactive surface area and the product R ct C t (where R ct is the OER charge transfer/polarization resistance) as the appropriate parameter to characterise the catalyst intrinsic catalytic activity. C t can also be used to correct direct current vs. electrode potential OER data for electroactive surface area effects.

Large-scale transfer and characterization of macroscopic periodically nano-rippled graphene

Nano-rippled graphene, a structurally modified graphene, presents a novel material with a large range of possible applications including sensors, electrodes, coatings, optoelectronics, spintronics and straintronics. In this work we have synthesized macroscopic single layer graphene with well-defined uniaxial periodic modulation on a stepped Ir(332) substrate and transferred it to a dielectric support. The applied fast transfer process does not damage the Ir crystal which can be repeatedly used for graphene synthesis. Upon transfer, a millimeter sized graphene flake with a uniform periodic nano-ripple structure is obtained, which exhibits a macroscopically measurable uniaxial strain. The periodic one dimensional arrangement of graphene ripples was confirmed by atomic force microscopy and polarized Raman measurements. An important feature of this system is that the graphene lattice is rotated in several different, well-defined orientations with respect to the direction of the ripple induced uniaxial strain. Moreover, geometry of the ripples can be modified by changing the graphene synthesis parameters.

Layered structure and related magnetic properties for annealed Fe/Ir(111) ultrathin films

After annealing treatments for fcc-Fe/Ir(111) below 600 K, the surface layers remain pseudomorphic. The Ir(111) substrate plays an important role on the expanded Fe lattice. At temperatures between 750 and 800 K, the surface composition shows a stable state and a c(2 × 4) structure is observed. We discover a layered structure composed of some Fe atoms on the top of a Fe0.5Ir0.5 interfacial alloy supported on the Ir(111) substrate. The competition between the negative formation heat of Fe0.5Ir0.5 and surface free energy of Fe causes the formation of layered structure. The existence of ferromagnetic dead layer coincides with the formation of fcc-Fe for ultrathin Fe on Fe0.5Ir0.5/Ir(111). For Fe films thicker than three monolayers, the linear increase of the Kerr intensity versus the Fe coverage is related to the growing of bcc-Fe on the surface where the Fe layer is incoherent to the underlying Fe0.5Ir0.5/Ir(111). These results emphasize the importance of the substrate induced strain and layered structure of Fe/Fe0.5Ir0.5/Ir(111) on the magnetic properties and provide valuable information for future applications.

Influence of the local atom configuration on a hexagonal skyrmion lattice.

Spin-resolved scanning tunneling microscopy is used to reveal a commensurate hexagonal nanoskyrmion lattice in the hcp stacked Fe monolayer on Ir(111). The exact nature of the spin configuration is due to magnetic interactions between the Fe atoms and the Ir substrate, either originating from polarization effects, or due to a three-site hopping mechanism of the Dzyaloshinsky-Moriya interaction leading to a canting of the Dzyaloshinsky-Moriya vector with respect to the interface.

Dexamethasone downregulates caveolin-1 causing muscle atrophy via inhibited insulin signaling.

Glucocorticoids play a major role in the development of muscle atrophy in various medical conditions, such as cancer, burn injury, and sepsis, by inhibiting insulin signaling. In this study, we report a new pathway in which glucocorticoids reduce the levels of upstream insulin signaling components by downregulating the transcription of the gene encoding caveolin-1 (CAV1), a scaffolding protein present in the caveolar membrane. Treatment with the glucocorticoid dexamethasone (DEX) decreased CAV1 protein and Cav1 mRNA expression, with a concomitant reduction in insulin receptor alpha (IRα) and IR substrate 1 (IRS1) levels in C2C12 myotubes. On the basis of the results of promoter analysis using deletion mutants and site-directed mutagenesis a negative glucocorticoid-response element in the regulatory region of the Cav1 gene was identified, confirming that Cav1 is a glucocorticoid-target gene. Cav1 knockdown using siRNA decreased the protein levels of IRα and IRS1, and overexpression of Cav1 prevented the DEX-induced decrease in IRα and IRS1 proteins, demonstrating a causal role of Cav1 in the inhibition of insulin signaling. Moreover, injection of adenovirus expressing Cav1 into the gastrocnemius muscle of mice prevented DEX-induced atrophy. These results indicate that CAV1 is a critical regulator of muscle homeostasis, linking glucocorticoid signaling to the insulin signaling pathway, thereby providing a novel target for the prevention of glucocorticoid-induced muscle atrophy.

Scanning tunneling microscopy study of in-plane graphene-hexagonal boron nitride heterostructures

In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a research focus of graphene due to its predicted fascinating properties such as bandgap opening and magnetism, which hence has ignited the attempt of experimentally growing such in-plane two-dimensional (2D) hybrid materials. Many previous researches demonstrated the synthesis of such heterostructures on Cu foils via chemical vapor deposition (CVD) process. The obtained 2D hybrid materials would offer a possibility for fabricating atomically thin electronic devices. However, many fundamental issues are still unclear, including the in-plane atomic continuity, the edge type, and the electronic properties at the boundary of hybridized h-BN and graphene domain. To clarify these issues, we report the syntheses of h-BN-G monolayer heterostructures on strongly coupled Rh(111) substrate and weakly coupled Ir(111) substrate via a two-step growth process in an ultrahigh vacuum (UHV) system, respectively. With the aid of scanning tunneling microscopy (STM), it is revealed that graphene and h-BN could be linked together seamlessly on an atomic scale at the linking boundaries. More importantly, we find that the atomically sharp zigzag-type boundaries dominate the patching interface between graphene and h-BN as demonstrated by atomic-scale STM images. To understand the physical origin of the atomic linking of the h-BN-G heterostructures, we also perform density functional theory (DFT) calculations, including geometry optimizations and binding energy calculations for different kinds of linking interfaces. The calculated results reconfirm that graphene prefers to grow on the h-BN domain edges and form zigzag linking boundaries. Besides the atomic structures on the linking interfaces, the electronic characteristics are also of particular importance. It is worth noting that the substrates coupled strongly with graphene by π-d orbital hybridization (such as Rh(111) and Ru(0001)), lead to downward shift of graphene π-bands away from the Fermi level, or decay of the intrinsic electronic structure of graphene. In this regard, the influence of h-BN on the electronic property of graphene is hard to identify on such h-BN-G heterostructures. The weakly coupled Ir(111) is chosen to be a perfect substrate to investigate the interface electronic properties of h-BN-G heterostructure due to the absence of substrate electronic doping effect. Scanning tunneling spectroscopy studies indicate that the graphene and h-BN tend to exhibit their own intrinsic electronic features near the linking boundaries on Ir(111). Therefore, the present work offers a deep insight into the h-BN-G boundary structures and the effect of adlayer-substrate coupling both geometrically and electronically.

Quasi-Freestanding Monolayer Heterostructure of Graphene and Hexagonal Boron Nitride on Ir(111) with a Zigzag Boundary

In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a focus of graphene research owing to its tunable bandgap and intriguing properties. We report herein the synthesis of a quasi-freestanding h-BN-G monolayer heterostructure on a weakly coupled Ir(111) substrate, where graphene and h-BN possess distinctly different heights and surface corrugations. An atomically sharp zigzag type boundary has been found to dominate the patching interface between graphene and h-BN, as evidenced by high-resolution Scanning tunneling microscopy investigation as well as density functional theory calculation. Scanning tunneling spectroscopy studies indicate that the graphene and h-BN tend to exhibit their own intrinsic electronic features near the patching boundary. The present work offers a deep insight into the h-BN-graphene boundary structures both geometrically and electronically together with the effect of adlayer-substrate coupling.

Postexercise Improvement in Insulin-Stimulated Glucose Uptake Occurs Concomitant With Greater AS160 Phosphorylation in Muscle From Normal and Insulin-Resistant Rats

Earlier research on rats with normal insulin sensitivity demonstrated that acute exercise increased insulin-stimulated glucose uptake (GU) concomitant with greater phosphorylation of Akt substrate of 160 kDa (pAS160). Because mechanisms for exercise effects on GU in insulin-resistant muscle are unknown, our primary objective was to assess insulin-stimulated GU, proximal insulin signaling (insulin receptor [IR] tyrosine phosphorylation, IR substrate 1–phosphatidylinositol-3-kinase, and Akt phosphorylation and activity), and pAS160 in muscles from acutely exercised (one session) and sedentary rats fed either chow (low-fat diet [LFD]; normal insulin sensitivity) or a high-fat diet (HFD; for 2 weeks, insulin-resistant). At 3 h postexercise (3hPEX), isolated epitrochlearis muscles were used for insulin-stimulated GU and insulin signaling measurements. Although exercise did not enhance proximal signaling in either group, insulin-stimulated GU at 3hPEX exceeded respective sedentary control subjects (Sedentary) in both diet groups. Furthermore, insulin-stimulated GU for LFD-3hPEX was greater than HFD-3hPEX values. For HFD-3hPEX muscles, pAS160 exceeded HFD-Sedentary, but in muscle from LFD-3hPEX rats, pAS160 was greater still than HFD-3hPEX values. These results implicated pAS160 as a potential determinant of the exercise-induced elevation in insulin-stimulated GU for each diet group and also revealed pAS160 as a possible mediator of greater postexercise GU of insulin-stimulated muscles from the insulin-sensitive versus insulin-resistant group.

Magnetic properties and magnon excitations in Fe(001) films grown on Ir(001)

We present a comprehensive study of magnetic properties and high wave-vector magnon excitations in epitaxial Fe(001) films grown on Ir(001) substrate. The magnetic properties are investigated by magneto-optical Kerr effect for various thicknesses of Fe film from 4 up to 27 monolayers. The magnon dispersion relation is obtained by means of spin-polarized electron energy loss spectroscopy. By comparing the experimental and theoretical results, we comment on the effect of the strain induced tetragonal distortion in the Fe film and the electronic hybridizations between the film and the substrate on the exchange interaction and magnon dispersion relation. The thickness-dependent measurements show that the magnon dispersion relation does not change significantly while changing the film thickness in the regime, where the film is uniformly strained. In addition, the measurements are also performed on thicker Fe films, where the films are relaxed into a bulklike structure. The magnon energies close to the zone boundary differ from the ones measured on thick Fe(110) films on W(110). However, the magnon dispersion relation measured for both systems can be well described within the Heisenberg model by using the same effective exchange parameters.