INSIGHT INTO NANOPARTICLE CHARGING MECHANISM IN NONPOLAR SOLVENTS TO CONTROL THE FORMATION OF PT NANOPARTICLE MONOLAYERS BY ELECTROPHORETIC DEPOSITION

Electrophoretic deposition of nanoparticles is considered to be one of the convenient methods for preparation of ordered nanoparticle monolayers. By using a nonpolar suspension of nanoparticles, we can (a) limit the current between the electrodes; (b) reduce the changes in the composition and conductivity of the medium due to the generation of charged species near the electrodes; and (c) suppress electrochemical reactions at the electrodes. One of the important questions about understanding the principle mechanisms of electrophoretic deposition is to identify the origin of electric charge in nonpolar suspension from which the nanoparticles are deposited. We developed a simple model of nanoparticle charging and we explained how the amount of the charge carried by nanoparticles can affect the quality of deposited monolayers. For electrophoretic deposition, we used silicon substrates as electrodes and Pt nanoparticles in water-AOT-isooctane reverse micellar system as a suspension. We used the centrifugation of Pt in combination with DLS measurements for controlling the charge carried by nanoparticles. Prepared nanoparticle monolayers were analyzed by AFM, SEM and electrical measurements. Please click Additional Files below to see the full abstract

Hydrogen sensors based on electrophoretically deposited Pd nanoparticles onto InP

Electrophoretic deposition of palladium nanoparticles prepared by the reverse micelle technique onto InP substrates is addressed. We demonstrate that the substrate pre-deposition treatment and the deposition conditions can extensively influence the morphology of the deposited palladium nanoparticle films. Schottky diodes based on these films show notably high values of the barrier height and of the rectification ratio giving evidence of a small degree of the Fermi level pinning. Moreover, electrical characteristics of these diodes are exceptionally sensitive to the exposure to gas mixtures with small hydrogen content

Chemical composition of nanoporous layer formed by electrochemical etching of p-type GaAs

Abstract : We have performed a detailed characterization study of electrochemically etched p-type GaAs in a hydrofluoric acid-based electrolyte. The samples were investigated and characterized through cathodoluminescence (CL), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that after electrochemical etching, the porous layer showed a major decrease in the CL intensity and a change in chemical composition and in the crystalline phase. Contrary to previous reports on p-GaAs porosification, which stated that the formed layer is composed of porous GaAs, we report evidence that the porous layer is in fact mainly constituted of porous As2O3. Finally, a qualitative model is proposed to explain the porous As2O3 layer formation on p-GaAs substrate

Optical and electrical characterization of CuO/ZnO heterojunctions

CuO/ZnO p-n heterojunctions are fabricated on ZnO nanorod arrays by sputtering of metallic Cu thin films and by their subsequent thermal annealing at 400 °C. Structural, morphological, and optical properties of both copper oxide nanocrystalline films and zinc oxide nanorod arrays are discussed with the emphasis on the electrical junction properties investigated by current–voltage and impedance spectroscopy measurements. Electrical characteristics of these junctions are sensitive to gas mixtures with a low hydrogen concentration and show fast response and recovery time. The copper oxide/zinc oxide heterojunctions are shown to be more efficient to hydrogen detection at room temperature in comparison with the resistivity sensors based on zinc or copper oxides