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Suche nach „[L.] [Piraux]“ hat 78 Publikationen gefunden
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    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    B. Rana, M. Mátéfi-Tempfli, M. Agrawal, A. Barman, R. Hicken, U.A.S. Al-Jarah, O. Dmytriiev, Gangmei P., L. Piraux, V. Kruglyak, Stefan Mátéfi-Tempfli, B. Mahato

    Static and dynamic magnetic properties of densely packed magnetic nanowire arrays

    Physical Review B, vol. 87, no. 17

    2013

    DOI: 10.1103/PhysRevB.87.174429

    Abstract anzeigen

    The static and dynamic magnetic properties of magnetic nanowire arrays with high packing density (>0.4) and wire diameter much greater than the exchange length have been studied by static and time-resolved magneto-optical Kerr effect measurements and micromagnetic simulations. The nanowires were formed by electrodeposition within a nanoporous template such that their symmetry axes lay normal to the plane of the substrate. A quantitative and systematic investigation has been made of the static and dynamic properties of the array, which lie between the limiting cases of a single wire and a continuous ferromagnetic thin film. In particular, the competition between anisotropies associated with the shape of the individual nanowires and that of the array as a whole has been studied. Measured and simulated hysteresis loops are largely anhysteretic with zero remanence, and the micromagnetic configuration is such that the net magnetization vanishes in directions orthogonal to the applied field. Simulations of the remanent state reveal antiferromagnetic alignment of the magnetization in adjacent nanowires and the formation of vortex flux closure structures at the ends of each nanowire. The excitation spectra obtained from experiment and micromagnetic simulations are in qualitative agreement for magnetic fields applied both parallel and perpendicular to the axes of the nanowires. For the field parallel to the nanowire axes, there is also good quantitative agreement between experiment and simulation. The resonant frequencies are initially found to decrease as the applied field is increased from remanence. This is the result of a change of mode profile within the plane of the array from nonuniform to uniform as the ground state evolves with increasing applied field. Quantitative differences between experimental and simulated spectra are observed when the field is applied perpendicular to the nanowire axes. The dependence of the magnetic excitation spectra upon the array packing density is explored, and dispersion curves for spin waves propagating within the array parallel to the nanowire axis are presented. Finally, a tunneling of end modes through the middle region of the nanowires was observed. The tunneling is more efficient for wires forming densely packed arrays, as a result of the extended penetration of the dynamic demagnetizing fields into the middle of the wires and due to the lowering of the tunneling barrier by the static demagnetizing field of the array.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    A. Radu, L. Piraux, Stefan Mátéfi-Tempfli, V. Antohe

    Circuit Modeling on Polyaniline Functionalized Nanowire-Templated Micro-Interdigital Capacitors for pH Sensing

    IEEE Transactions on Nanotechnology, vol. 10, no. 6, pp. 1314-1320

    2011

    Abstract anzeigen

    This study presents an improved alternative current (ac) circuit modeling of a highly sensitive capacitive pH-sensing element based on polyaniline (PANI) functionalized nanowire-templated micro-interdigited electrodes (NWs μIDEs). While electrical resonance measurements deal with a total equivalent capacity, comparative investigations show a good agreement with the fitting parameters of the corresponding model. A physical interpretation of the model is discussed to help in understanding the detection mechanism and a possible methodology to be used for further integration of the subsequent device is suggested.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, L. Piraux, A. Vlad, S. Melinte, Stefan Mátéfi-Tempfli

    Vertical nanowire architectures: Statistical processing of porous templates towards discrete nanochannel integration

    Small, vol. 6, no. 18, pp. 1974-1980

    2010

    DOI: 10.1002/smll.201000723

    Abstract anzeigen

    Nanowires and statistics: A statistical process for reading ultradense arrays of nanostructured materials is presented (see image). The experimental realization is achieved through selective nanowire growth using porous alumina templates. The statistical patterning approach is found to provide rigorous selection rules for measuring well‐defined numbers of nanowires located into nanoporous templates, and provides a conceptual framework for the fabrication of nanowire‐based crossbar latches.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, L. Piraux, A. Vlad, Stefan Mátéfi-Tempfli, V. Antohe

    Nanowires and nanostructures fabrication using template methods: A step forward to real devices combining electrochemical synthesis with lithographic techniques

    Journal of Materials Science: Materials in Electronics, vol. 20, no. 1, pp. 249-254

    2009

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, S. Michotte, J. Vanacken, X. Hallet, L. Piraux, Stefan Mátéfi-Tempfli

    Artificial pinning centers using the barrier layer of ordered nanoporous alumina templates

    Journal of Physics: Conference Series, vol. 153, no. 1

    2009

    DOI: 10.1088/1742-6596/153/1/012013

    Abstract anzeigen

    The barrier layer of self-ordered anodized aluminium oxide, which is grown from an aluminium foil, has been revealed by a selective chemical etching of the remaining aluminium. The surface obtained in this way consists of a triangular lattice of bumps with 100nm spacing, and heights of approximately 50nm. Using this surface as a template for controlling the pinning in thin superconducting films, superconducting Nb was deposited with different thicknesses and under different deposition angles. The evaporation under a 30° angle shows an asymmetric pinning potential composed of two triangular lattices having different pinning strengths. Matching effects are observed up to 1T. Matching effects are also maintained at relatively low temperature.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, S. Michotte, J. Vanacken, X. Hallet, L. Piraux, Stefan Mátéfi-Tempfli

    Quasi-hexagonal vortex pinning lattice using anodized aluminum oxide nanotemplates.

    Small, vol. 5, no. 21, pp. 2413-2416

    2009

    Abstract anzeigen

    The bottom barrier layer of well‐ordered nanoporous alumina membranes reveals a previously unexploited nanostructured template surface consisting of a triangular lattice of hemispherical nanoscale bumps. Quasi‐hexagonal vortex‐pinning lattice arrays are created in superconducting Nb films deposited onto this template (see image). Matching effects are preserved at higher magnetic fields and lower temperatures when compared to holes on the top face.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, S. Michotte, J. Vanacken, X. Hallet, L. Piraux, Stefan Mátéfi-Tempfli

    High field matching effects in NbN induced by a dense ferromagnetic nanowires array grown in a nanoporous alumina template

    Applied Physics Letters, vol. 95, no. 25

    2009

    DOI: 10.1063/1.3276557

    Abstract anzeigen

    Dense arrays of ordered ferromagnetic nanowires have been used to create periodic magnetic pinning centers in thin superconducting NbN films. The nanowires were electrodeposited in a highly ordered porous alumina membrane and the thin NbN film was deposited on top of the perpendicularly oriented magnetic nanowires. Matching effects have been observed up to 2.5 T (11th matching field) and are maintained at low temperature. An appreciable enhancement of the superconducting properties is observed. At low fields, a hysteretic behavior in the magnetoresistance is found, directly related to the magnetization processes of arrays of interacting single domain ferromagnetic nanowires.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    A. Crahay, N. Reckinger, V. Bayot, M. Mátéfi-Tempfli, B. Olbrechts, L. Piraux, A. Vlad, S. Faniel, S. Melinte, Stefan Mátéfi-Tempfli, V. Antohe

    Nanowire-decorated Microscale Metallic Electrodes

    Small, vol. 4, no. 5, pp. 557-560

    2008

    DOI: 10.1002/smll.200700724

    Abstract anzeigen

    One of the challenging aspects of science and technology on ananometer-scale is the precise three-dimensional control ofnano-objects. Scanning probe microscopy manipulation,magnetic- or electric-field alignment and lithography-basedtechniques are only a few of the techniques that have beenreported so far.[1]Nevertheless, most of these techniques arestill being developed and their integration for devicefabrication represents a real challenge for the scientificcommunity. Within this context, nanowires and nanotubesare of great interest because they lie between the macroscopicand atomic scales. The ability to fabricate and manipulate suchobjects in a reliable manner on a large scale will foster their usein electronic, photonic, and sensing applications.[2]Template-based methods have been successfully used for nanowirefabrication as they allow the realization of complex organic/inorganic nanostructures.[3]To date, nanoporous anodicalumina oxide (AAO) made by the electrochemical oxidationof aluminum has been extensively used because it provides agood platform for the development of various nanostructures.This interest originates from the fact that AAO membranes,having a high density of nanopores (up to 1012cm2), are easilyproduced over large areas with variable thicknesses.[4]More-over, a good chemical and mechanical stability combined withinteresting electrical properties make AAO membranes goodcandidates for nanowire fabrication. However, the use of suchnanostructures as passive or active components in emergingelectronic devices requires smartly engineered arrays ofnanowires with well defined position and pitch.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, W. Vinckx, S. Michotte, J. Vanacken, L. Piraux, Stefan Mátéfi-Tempfli, Ye X.

    Vortex pinning in superconductors laterally modulated by nanoscale self-assembled arrays

    Physica C: Superconductivity and its Applications, vol. 468, no. 7-10, pp. 585-588

    2008

    DOI: 10.1016/j.physc.2007.11.070

    Abstract anzeigen

    Being the exponent of the so-called “bottom-up” approach, self-assembled structures are now-a-days attracting a lot of attention in the fields of science and technology. In this work, we show that nanoscale self-assembled arrays used as templates can provide periodic modulation in superconducting thin films by studying their vortex pinning properties. In this work advantage was made of the fact that self-organized assemblies of identical units such as colloidal crystals and anodic aluminum oxide provide extended periodic topographic surfaces. By directly growing Nb on top of these self-assembled arrays, the templating effect was exploited in order to achieve triangular and honeycomb arrays of pinning centers in thin superconducting films. We show experimentally that periodic matching is achieved in both systems at magnetic fields, well above those present in lithographically prepared pinning arrays (up to 1 T!). Furthermore, we demonstrate in the case of anodic aluminum oxide that the presence of porous antidots in Nb not only provides strongly increased critical currents but also conserves matching at temperatures well below the critical temperature. The studies conducted on these systems indicate that the method of template growth might be considered as a viable alternative for the incorporation of periodic pinning arrays in superconducting applications of today and the future.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V.-A. Antohe, P. Bertrand, S. Yunus, M. Mátéfi-Tempfli, A. Radu, A. Attout, L. Piraux, Stefan Mátéfi-Tempfli

    A versatile method to grow localized arrays of nanowires for highly sensitive capacitive devices

    Journal of Optoelectronics and Advanced Materials, vol. 10, no. 11, pp. 2936-2941

    2008

    Abstract anzeigen

    We propose a new approach to increase the detection efficiency of the capacitive sensing devices, by growing vertically aligned nanowires arrays, localized and confined on small interdigited electrodes structures. The metallic tracks are made using optical lithography, and the nanowires are realized by electrochemical synthesis in nanoporous materials (i.e. supported alumina templates). By controlling the preparation conditions, both their positions and pitches can be easily tuned, as well as their geometrical design (i.e. diameters between 5 – 350 nm and lengths between 150 nm – 10 μm). Based on these considerations, a capacitive sensor structure with high active surface is sensitized with polyaniline, for pH detection. Reported data show that the sensitivity of the sensor is substantially improved by using nanowires arrays.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, V. Cros, C. Deranlot, Guillemet R., Bouzehouane K., L. Piraux, T. Blon, Stefan Mátéfi-Tempfli, Fusil S.

    Spin momentum transfer effects observed in electrodeposited Co/Cu/Co nanowires

    Journal of Applied Physics, vol. 102, no. 10

    2007

    DOI: 10.1063/1.2812677

    Abstract anzeigen

    Spin-transfer torque effects are reported in nanowires consisting in Co/Cu/Co trilayers electrodeposited on an anodic alumina template. Using a nanolithography process based on electrically controlled nanoindentation of the alumina template, we are able to investigate the spin transport properties of single nanowires at room temperature. For small applied magnetic fields, we have measured resistance changes above a critical direct-current (dc) injected current that corresponds to the change in resistance observed in the magnetoresistance curves at low current. We conclude that magnetic reversals are driven by a spin-polarized current. The critical current densities needed for the magnetization reversals are in the 107 A/cm2 range and the dependence of the critical currents with the applied field is consistent with the spin-transfer mechanism. For large applied magnetic fields, the differential resistance exhibits some peaks that we attribute to the onset of high-frequency excitations of the free-layer magnetization. According to the high density of electrodeposited nanowires in alumina templates, our results are promising for synchronized spin-transfer oscillators.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, W. Vinckx, S. Michotte, J. Vanacken, L. Piraux, X. Ye, Stefan Mátéfi-Tempfli

    High field matching effects in superconducting Nb porous arrays catalyzed from anodic alumina templates

    Physica C: Superconductivity and its Applications, vol. 459, no. 1-2, pp. 5-10

    2007

    DOI: 10.1016/j.physc.2007.04.194

    Abstract anzeigen

    Vortex pinning in a superconducting Nb thin film deposited on an anodically grown alumina template is investigated. Anodic oxidation of aluminium layers permits under specific conditions the formation of highly ordered porous alumina, a membrane-like structure consisting of triangular arrays of parallel pores. Its pore diameter and interpore distance are set by careful tuning of the anodization parameters. A superconducting Nb thin film is deposited directly onto the alumina film. The porous alumina acts as a template and it allows Nb to form a periodic pinning array during its growth. Pinning force vs. field measurements derived from magnetization measurements, show matching effects in fields up to 1 T. We demonstrate that the anodic alumina template with 50 nm interpore spacing provides enhanced vortex pinning in a large field and temperature range.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, V. Cros, C. Deranlot, Guillemet R., Bouzehouane K., L. Piraux, T. Blon, Stefan Mátéfi-Tempfli, Fusil S.

    Spin momentum transfer effects observed in electrodeposited Co/Cu/Co nanowires

    Virtual Journal of Nanoscale Science & Technology (NanoUnion)

    2007

    Abstract anzeigen

    Spin-transfer torque effects are reported in nanowires consisting in Co/Cu/Co trilayers electrodeposited on an anodic alumina template. Using a nanolithography process based on electrically controlled nanoindentation of the alumina template, we are able to investigate the spin transport properties of single nanowires at room temperature. For small applied magnetic fields, we have measured resistance changes above a critical direct-current (dc) injected current that corresponds to the change in resistance observed in the magnetoresistance curves at low current. We conclude that magnetic reversals are driven by a spin-polarized current. The critical current densities needed for the magnetization reversals are in the 107 A/cm2 range and the dependence of the critical currents with the applied field is consistent with the spin-transfer mechanism. For large applied magnetic fields, the differential resistance exhibits some peaks that we attribute to the onset of high-frequency excitations of the free-layer magnetization. According to the high density of electrodeposited nanowires in alumina templates, our results are promising for synchronized spin-transfer oscillators.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Bayot, M. Mátéfi-Tempfli, L. Piraux, A. Vlad, S. Faniel, S. Melinte, Stefan Mátéfi-Tempfli

    Controlled growth of single nanowires within a supported alumina template

    Nanotechnology, vol. 17, no. 19, pp. 4873-4876

    2006

    DOI: 10.1088/0957-4484/17/19/016

    Abstract anzeigen

    A simple technique for fabricating single nanowires with well-defined position is presented. The process implies the use of a silicon nitride mask for selective electrochemical growth of the nanowires in a porous alumina template. We show that this method allows the realization of complex nanowire patterns as well as arrays of single nanowires with a precise position and spacing.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    V. Moshchalkov, M. Mátéfi-Tempfli, W. Vinckx, S. Michotte, J. Vanacken, L. Piraux, Stefan Mátéfi-Tempfli

    Vortex pinning in superconducting Nb thin films deposited on nanoporous alumina templates

    European Physical Journal B: Condensed Matter and Complex Systems, vol. 53, no. 2, pp. 199-203

    2006

    DOI: 10.1140/epjb/e2006-00358-7

    Abstract anzeigen

    We present a study of magnetization and transport properties of superconducting Nb thin films deposited on nanoporous aluminium oxide templates. Periodic oscillations in the critical temperature vs. field, matching effects in fields up to 700 mT and strongly enhanced critical currents were observed. These fields are considerably higher than those typical for periodic pinning arrays made by lithographic techniques, which reflects the benefits of nanostructuring superconductors by using self-organized growth. This method provides a periodic pinning potential with sub-100 nm spacing between the pinning centers, which enhances vortex pinning in broad field and temperature ranges.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    B. Sulik, S. Biri, M. Mátéfi-Tempfli, Z. Juhász, N. Stolterfoht, L. Piraux, Gy Vikor, J. Pálinkás, Stefan Mátéfi-Tempfli, I. Iván, F. Gáll, E. Fekete

    Guided transmission of slow Ne6+ ions through the nanochannels of highly ordered anodic alumina

    Nanotechnology, vol. 17, no. 15, pp. 3915-3919

    2006

    DOI: 10.1088/0957-4484/17/15/050

    Abstract anzeigen

    A highly ordered hexagonally close-packed nanochannels array was prepared using the self-ordering phenomena during a two-step anodization process of a high purity aluminium foil. The anodized aluminium oxide, with pore diameters of about 280 nm and interpore distances of about 450 nm was prepared as a suspended membrane of about 15 µm thickness on the aluminium frame to which it belongs. The Al2O3 capillaries were bombarded with 3 keV Ne6+ ions. The first results unambiguously show the existence of ion guiding observed at 5° and 7.5° tilt angles of the capillaries compared to the beam direction. To the best of our knowledge, such ion guiding effects of slow ions through hexagonally ordered nanochannels in alumina has not been reported previously.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    P. Smet, S. Michotte, P. Lommens, D. Poleman, L. Piraux, Z. Hens, Stefan Mátéfi-Tempfli, de Mello Donega, C., A. Meijerink

    Photoluminescence properties of Co2+-doped ZnO nanocrystals

    Journal of Luminescence, vol. 118, no. 2, pp. 245-250

    2006

    DOI: 10.1016/j.jlumin.2005.08.020

    Abstract anzeigen

    We performed photoluminescence experiments on colloidal, Co2+-doped ZnO nanocrystals in order to study the electronic properties of Co2+ in a ZnO host. Room temperature measurements showed, next to the ZnO exciton and trap emission, an additional emission related to the Co2+ dopant. The spectral position and width of this emission does not depend on particle size or Co2+ concentration. At 8 K, a series of ZnO bulk phonon replicas appear on the Co2+-emission band. We conclude that Co2+ ions are strongly localized in the ZnO host, making the formation of a Co2+d-band unlikely. Magnetic measurements revealed a paramagnetic behaviour.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, L. Vila, S. Michotte, L. Piraux, M. Darques, Stefan Mátéfi-Tempfli, A. Encinas, F. Elhoussine

    Magnetic and superconducting nanowires

    Journal of Nanoscience and Nanotechnology, vol. 5, no. 3, pp. 372-389

    2005

    DOI: 10.1166/jnn.2005.062

    Abstract anzeigen

    This article is focused on the use of electrodeposition and of various nanoporous templates for the fabrication of metallic nanowires made from single metals (Ni, Co, Pb, Sn), alloys (NiFe, CoFe, CoPt), and multilayers (Co/Cu, NiFe/Cu). An overview is given of our recent studies performed on both magnetic and superconducting nanowires. Using different approaches entailing measurements on both single wires and arrays, numerous interesting physical properties have been identified in relation to the nanoscopic dimensions of these materials. Finally, various novel applications of the nanowires are also discussed.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, L. Piraux, K. Yu-Zhang, Stefan Mátéfi-Tempfli, J. Mallet

    Electrodeposited L10 CoxPt1-x nanowires

    Journal of Physics D: Applied Physics, vol. 38, no. 6, pp. 909-914

    2005

    DOI: 10.1088/0022-3727/38/6/020

    Abstract anzeigen

    Arrays of face-centred cubic (fcc) CoxPt1 − x (0.45 < x < 0.55) nanowires were electrodeposited into thin film nanoporous alumina supported on a Si substrate. The heat treatment under specific conditions was then carried out in order to transform the fcc phase into the face-centred tetragonal or L10 ordered phase. The influence of both the phase transition and the temperature on the magnetic properties of CoxPt1−x nanowires has been studied. Coercive fields higher than 1 T (10 kOe) have been obtained at room temperature with ordered nanowires, 80 nm in diameter.

    NachhaltigEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    M. Mátéfi-Tempfli, V. Cros, S. Michotte, K. Bouzehouane, C. Deranlot, J.-M. George, L. Piraux, L. Pereira, S. Fusil, C. Saul, Stefan Mátéfi-Tempfli

    Nanolithography based contacting method for electrical measurements on single template synthesized nanowires

    Nanotechnology, vol. 16, no. 12, pp. 2936-2940

    2005

    DOI: 10.1088/0957-4484/16/12/036

    Abstract anzeigen

    A reliable method enabling electrical measurements on single nanowires prepared by electrodeposition in an alumina template is described. This technique is based on electrically controlled nanoindentation of a thin insulating resist deposited on the top face of the template filled by the nanowires. We show that this method is very flexible, allowing us to electrically address single nanowires of controlled length down to 100 nm and of desired composition. Using this approach, current densities as large as 109 A cm−2 were successfully injected through a point contact on a single magnetic multilayered nanowire. This demonstrates that the technique is very promising for the exploration of electrical spin injection in magnetic nanostructures.