Maria-Rita Mátéfi-Tempfli

Electrodeposited L1(0) CoxPt1-x nanowires

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 L1(0) 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.

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

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 mu m 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 degrees and 7.5 degrees 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.

Functionalization of magnetic nanowires by charged biopolymers.

We report on a facile method for the preparation of biocompatible and bioactive magnetic nanowires. The method consists of the direct deposition of polysaccharides by layer-by-layer (LbL) assembly onto a brush of metallic nanowires obtained by electrodeposition of the metal within the nanopores of an alumina template supported on a silicon wafer. Carboxymethylpullulan (CMP) and chitosan (CHI) multilayers were grown on brushes of Ni nanowires; subsequent grafting of an enzyme was performed by conjugating free amine side groups of chitosan with carboxylic groups of the enzyme. The nanowires are finally released by a gentle ultrasonic treatment. Transmission electron microscopy, electron energy-dispersive loss spectroscopy, and x-ray photoelectron spectroscopy indicate the formation of an homogeneous coating onto the nickel nanowires when one, two, or three CMP/CHI bilayers are deposited. This easy and efficient route to the biochemical functionalization of magnetic nanowires could find widespread use for the preparation of a broad range of nanowires with tailored surface properties.

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

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 10(9) 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.

Low-energy electron transmission through high aspect ratio Al2O3 nanocapillaries

Electron transmission through insulating Al2O3 nanocapillaries of different diameters (40 and 270 nm) and 15 mu m length has been investigated for low-energy electrons (2-120 eV). The total intensity of transmitted current weakly depends on the incident electron energy and tilt angle defined with respect to the capillary axis. On the other hand, the intensity of elastically transmitted electrons significantly varies with the alteration of electron energy and tilt angle. In addition, we measured an energy distribution of electrons transmitted both in the straightforward direction and at large tilt angle. The measured spectra show that inelastic processes dominate and, in particular, a large amount of low-energy electrons. These low-energy electrons can be either inelastically scattered projectiles or secondary electrons emitted within the capillaries. Furthermore, a change of the tilt angle appears to influence significantly only the intensity of the elastic transmission. The present results suggest a more complex nature of low-energy electron transport through insulating nanocapillaries than proposed for positive ions. Copyright (C) EPLA, 2009

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

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 10(7) A/cm(2) 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. (c) 2007 American Institute of Physics.

Nanochannel alignment analysis by scanning transmission ion microscopy

In this paper a study on the ion transmission ratio of a nanoporous alumina sample is presented. The sample was investigated by scanning transmission ion microscopy (STIM) with different beam sizes. The hexagonally close-packed Al(2)O(3) nanocapillary array, realized as a suspended membrane of 15 microm thickness, had pore diameters of approximately 215 nm and spacing of approximately 450 nm. When the proton beam size was limited to a single domain, a peak transmission ratio of 19% was observed as is expected from the geometry (approximately 19-20%). This result points out an almost perfectly parallel alignment of the capillaries within one domain. However, for larger beam scanning areas (sampling multiple domains) the transmission ratio was reduced to 5%. The STIM analysis over an area larger than the typical domain size revealed an overall capillary angular spread of approximately 2 degrees.

High magnetic field matching effects in NbN films induced by template grown dense ferromagnetic nanowires arrays

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

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

The interest in the template-based synthesis of nanomaterials and nanostructures is continuously increasing due to the advantageous features offered by the templates and the ease of processing a large number of nanostructures in parallel. In recent years, nanoporous anodic aluminum oxide (AAO) has been intensively studied and used for that purpose. [1] At present, it is considered one of the most promising templates [2] mainly because of its unique features, which include easily tunable geometrical parameters, mild preparation conditions, and resistance to high temperatures. AAO, whichisatypicalself-orderednanopore-arraymaterialformed by the electrochemical oxidation of Al in acidic solutions, is an excellent starting host material for the fabrication of various nanomaterials and nanostructures. It possesses a hexagonally packed arrangement of nanoscale-sized straight blind holes aligned perpendicular to the surface. The voids of the nanoscale-channeled structure are typically filled with various materials and heterostructures using electrochemical or chemical vapor deposition methods after the elimination of the oxide barrier layer that closes the bottom ends of the holes. While this barrier layer is typically considered undesirable and eliminated, herein we emphasize that the surface of this layer possesses an ordered array of hemispheres that can also be used as a very interesting template. We describe the advantages of the ordered bumpy surface for creating artificial superconducting pinning centers in Nb films deposited on it.

Carpet of nanowires on flexible silicone substrate

Here we show that by applying pulsed anodization conditions we successfully create nanoporous alumina templates supported on polydimethylsiloxane, a flexible silicone elastomer. Moreover, we show that by using this template with nanopores ending on a conducting underlayer, high density nanowires array can be simply grown by direct dc-electrodeposition on the top of the silicone rubber. The method presented opens up new ways for applications based on nanostructures supported on flexible substrates. We highlight advantages of high density nanowires arrays supported on silicone for use as nerve stimulating electrodes, sensors and bio-sensors.