A. Cortés

Silver nanowire arrays electrochemically grown into nanoporous anodic alumina templates

Silver nanowire arrays with high aspect ratios have been prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide template. The nucleation and growth processes are intensively studied by current versus time transients. Scanning electron microscopy results show that the nanowires have a highly anisotropic structure with diameters and lengths of 170?nm and 58??m, respectively, which coincide with the dimensions of the template used. Structural characterization using x-ray diffraction shows that the Ag nanowires are highly crystalline, and those obtained at higher overpotentials present a very strong [220] preferred crystallographic orientation. The optical properties of the silver nanowires embedded in the alumina template show a clear edge close to 320?nm, that is an expected value for a silver?alumina composite material.

Angular dependence of magnetic properties in Ni nanowire arrays

The angular dependence of the remanence and coercivity of Ni nanowire arrays produced inside the pores of anodic alumina membranes has been studied. By comparing our analytical calculations with our measurements, we conclude that the magnetization reversal in this array is driven by means of the nucleation and propagation of a transverse wall. A simple model based on an adapted Stoner–Wohlfarth model is used to explain the angular dependence of the coercivity.

Geometry dependence of coercivity in Ni nanowire arrays.

Magnetic properties of arrays of nanowires produced inside the pores of anodic alumina membranes have been studied by means of vibrating sample magnetometer techniques. In these systems the length of the wires strongly influences the coercivity of the array. A simple model for the coercivity as a function of the geometry is presented which exhibits good agreement with experimental results. Magnetostatic interactions between the wires are responsible for a decrease of the coercive field.

Magnetic Characterization of Nanowire Arrays Using First Order Reversal Curves

Arrays of Ni nanowires have been studied by means of first order reversal curves (FORC) diagrams. The dependence of the coercivity of the arrays as a function of the length of the nanowires has been experimentally investigated. We have shown that the FORC diagrams provide detailed information about the distribution of interactions and coercivities and allowed us to observe the reversible component of magnetization. Our results are in good agreement with analytical calculations obtained by means of a simple model.

Magnetic properties of arrays of nanowires: Anisotropy, interactions, and reversal modes

Arrays of Co and Ni nanowires of different lengths have been prepared by electrodeposition into nanopores of alumina membranes. The dependence of the coercivity of the arrays as a function of temperature and measurement angle of the nanowires has been measured. A simple model is presented in order to explain the behavior of the magnetic properties as a function of the angle of measurement. The analytical calculations show that while for Ni nanowires demagnetization reversal in the array is driven by means of the nucleation and propagation of a transverse wall, in Co arrays the reversal mode changes from curling to coherent when the angle of measurements changes.

CVD SYNTHESIS OF GRAPHENE FROM ACETYLENE CATALYZED BY A REDUCED CuO THIN FILM DEPOSITED ON SiO2 SUBSTRATES

Few-layer graphene was grown by Chemical Vapor Deposition on a CuO thin film pre-deposited by sputtering on SiO2/Si substrates using acetylene as the carbon source. After evaporation of metal, graphene lies directly in contact with the SiO2 dielectric layer. Raman spectroscopy was used to confirm the presence of a single and/or few-layers of graphene. This procedure does not requiring any post processing to transfer the thin film onto a dielectric substrate or the use of ultra-high vacuum during synthesis.

Capacitance of a highly ordered array of nanocapacitors: Model and microscopy

This manuscript describes briefly the process used to build an ordered porous array in an anodic aluminum oxide (AAO) membrane, filled with multiwall carbon nanotubes (MWCNTs). The MWCNTs were grown directly inside the membrane through chemical vapor deposition (CVD). The role of the CNTs is to provide narrow metal electrodes contact with a dielectric surface barrier, hence, forming a capacitor. This procedure allows the construction of an array of 1010 parallel nano-spherical capacitors/cm2. A central part of this contribution is the use of physical parameters obtained from processing transmission electron microscopy (TEM) images, to predict the specific capacitance of the AAOs arrays. Electrical parameters were obtained by solving Laplace’s equation through finite element methods (FEMs).

Magnetic Properties of Cobalt Nanowire Arrays

Arrays of Co nanowires with different lengths and diameters have been prepared by electrodeposition into nanopores of alumina and polycarbonate membranes. The dependence of the coercivity and remanence of the arrays as a function of the length, the electrodeposition potential, and the electrolytic bath pH of the nanowires has been experimentally investigated through hysteresis curves performed in a VSM (vibrating sample magnetometer) and a SQUID (superconducting quantum interference device).

PHOTOELECTROCHEMICAL CHARACTERIZATION OF NATURAL COPPER SULPHIDE ELECTRODES IN ALKALINE MEDIA: EFFECT OF XANTHATE ADSORPTION

A photoelectrochemical approach is utilized for studying the processes that take place on copper sulfide mineral surfaces in alkaline solutions, either in absence or presence of potassium ethyl - xanthate. It is found that photoresponses are closely related to the mineral stoichiometric composition which also determines its semiconducting or metallic character. It appears that in the potential interval where xanthate anions can be adsorbed, surface composition and reactivity are closely linked