Electrochemical Impedance Investigation of Anodic Alumina Barrier Layer

International audienceIn the present work, well ordered nanoporous anodic aluminum oxides (AAO) have been prepared on aluminum by a two step anodization process in 0.5 M oxalic acid at various potentials. We report the properties and semiconducting characteristics of the porous alumina barrier layers by electrochemical impedance spectroscopy analysis (EIS). EIS is considered to be a highly sensitive and non-destructive technique that allows determining barrier oxide layer characteristics. Aluminum oxide barrier is considered as a semiconductor which acts as a p-n heterojunction at anodizing voltages up to 20 V. The alumina barrier layer structure consists of a hole transport inner layer and an electron transport outer layer. Doping densities, flatband potential as well as space charge layer thickness are discussed in correlation with anodizing potential. Barrier layer thicknesses measurements obtained by EIS were compared with those obtained after EIS measurements by direct scanning electron microscopy observations

Electrodeposition of equiatomic FeNi and FeCo nanowires: Structural and magnetic properties

International audienceIn the present work, equiatomic FeNi and FeCo magnetic nanowires (NWs) have been electrodeposited in Anodic Aluminum Oxide (AAO) membranes with 70 nm pore size. The role of the electroactive species Ni2+ and Co2+ on the anomalous codeposition behavior in thin films and nanowires has been discussed and compared. Field Emission Gun-Scanning Electron Microscope (FEG-SEM), X-ray diffraction (XRD) and Vibrating Sample Magnetometer (VSM) were used to evaluate the morphology, composition, crystalline structure and magnetic properties of the materials. SEM-FEG analysis showed very homogeneous NWs lengths for both FeNi and FeCo NWs, Energy dispersive X-ray spectroscopy (EDS) analysis revealed a stable composition along the FeCo NWs and a change in composition along the FeNi NWs. The XRD patterns indicate the predominance of the bcc structure for both alloys. Except for additional peaks of fcc phase found on FeNi alloy, the same crystalline bcc structure is observed after annealing treatment of 300 °C during 20 h. TEM analysis confirmed the ordered character of the bcc FeCo alloy. The hysteresis loops show an easy magnetization direction parallel to the wires due to the predominance of the shape anisotropy. The coercive field (Hc) of FeNi NWs increases with the length of the wires while that of FeCo NWs decreases. The annealing treatment doesn’t affect the magnetic properties of FeNi NWs, whereas a remarkable increase in the coercivity of the FeCo NWs is observed

Morphological, physicochemical and magnetic characterization of electrodeposited Mn-Bi and Mn-Bi/Bi thin films on Cu Substrate

International audienceMn-Bi thin films were electroplated on Cu (111) substrates in an acidic chloride bath. In order to determine the deposition potential of each element, cyclic voltammetry using a rotating disk electrode was performed. Two types of thin films were obtained using two deposition mode: the first one called thin Mn-Bi layers by using a single applied potential and the second one called Mn-Bi/Bi bilayers by using a double pulse potential. Annealing treatments at 300 °C for 1 hour under vacuum condition were carried out in order to cause an interdiffusion between manganese and bismuth. The morphological and crystalline structure of the various deposits was investigated by scanning electron microscopy with field effect (SEM-FEG) and by X-ray diffraction analysis (XRD). Magnetic characterizations were also made using a superconducting quantum interference device (SQUID) magnetometer.The morphological and the structural properties of the thin layers and the bilayers are completely different, indicating that the growth process changes according to the plating mode. After annealing a mixed MnBiCu phase with a coercivity of 300 Oe and 400 Oe was observed on the thin layers and the bilayers respectivel