Optical characterization of transparent nickel oxide films deposited by DC current reactive sputtering

International audienceIn this paper, we characterize high transparency p-type semiconducting NiO thin films deposited by Direct Current Reactive Magnetron Sputtering from a pure Ni target in a mixture of oxygen and argon gases on Corning glass/SnO2:F substrates at different oxygen contents ranging from 0% at 30%. The influence of the O2/Ar ratio and thickness on transmittance has been examined using ultraviolet-visible spectroscopy. The results show that whatever the oxygen proportion into the discharge, the nickel oxide films exhibit a polycrystalline structure. At low oxygen content, the preferential orientation is (111), for stoichiometric films the XRD diagram is powder-like whereas the preferential orientation is (200) for higher oxygen content. For low and high oxygen content, the transmittance is low. Thanks to plasma method and its ability to tune the oxygen content in the discharge and therefore the film composition, we have been able to explore carefully the intermediate zone and obtain transparent films. The optical absorption coefficient α has been calculated from the transmittance and the variation of (αhν)2 versus the photon energy (hν) for nickel oxide is presented. The optical band gap energy has been evaluated and varies from 3.2 to 3.8 eV

Electrodes based on nano-tree-like vanadium nitride and carbon nanotubes for micro-supercapacitors

International audienceVanadium nitride (VN) was deposited by DC-sputtering on a vertically aligned carbon nanotube (CNTs) template for the purpose of nano-structuration. This led to the fabrication of hierarchically composite electrodes consisting of porous and nanostructured VN grown on vertically aligned CNTs in a nano-tree-like configuration for micro-supercapacitor application. The electrodes show excellent performance with an areal capacitance as high as 37.5 mF cm−2 at a scan rate of 2 mV s−1 in a 0.5 M K2SO4 mild electrolyte solution. Furthermore, the capacitance decay was only 15% after 20,000 consecutive cycles. Moreover, the capacitance was found to increase with VN deposit thickness. The X-ray photoelectron spectroscopy analyses of the electrodes before and after cycling suggest that the oxide layers that form at the VN surface is the responsible for the redox energy storage in this material. Such electrodes can compete with other transition metal nitride based electrodes for micro-supercapacitors. © 201

AlN film thickness effect on photoluminescence properties of AlN/carbon nanotubes shell/core nanostructures for deep ultra-violet optoelectronic devices

International audienceAluminum nitride (AlN) nanostructures are very attractive in various optoelectronic applications such as deep ultraviolet light emitting devices. The fabrication of these AlN nanostructures with good crystalline quality and compatibility in line with other micro-fabrication processes has significant importance for practical applications. AlN films of different thickness values were deposited via DC reactive magnetron sputtering over vertically aligned multiwalled carbon nanotube (CNTs) arrays to obtAln AlN/CNTs vertically-aligned shell/core nanostructure assembly. Such hybrid nanostructures were characterized using scanning electron microscope, transmission electron microscope, X-ray diffraction, Raman spectroscopy and time-resolved photoluminescence spectroscope (TR-PL) techniques. The results indicated that AlN/CNTs have a nanorods structure morphology with good AlN crystalline quality. The PL measurements revealed a maximum increase in the luminescent intensity of the exciton band in case of AlN/CNTs with 600 nm thick AlN layer, which is many orders of magnitude higher than that of AlN film produced over silicon substrate. It is anticipated that synergistic effects of CNTs and AlN through an increase in the specific surface area and oxygen-induced defects cause enhancement in the photoluminescence properties, making these hybrid nanostructures a promising candidate for optoelectronic applications