Electrical, photoelectrical and morphological properties of ZnO nanofiber networks grown on SiO2 and on Si nanowires

Abstract

ZnO nanofibre networks (NFNs) were grown by vapour transport method on Si-based substrates. One type of substrate was SiO 2 thermally grown on Si and another consisted of a Si wafer onto which Si nanowires (NWs) had been grown having Au nanoparticles catalysts. The ZnO-NFN morphology was observed by scanning electron microscopy on samples grown at 600 °C and 720 °C substrate temperature, while an focused ion beam was used to study the ZnO NFN/Si NWs/Si and ZnO NFN/SiO 2 interfaces. Photoluminescence, electrical conductance and photoconductance of ZnO-NFN was studied for the sample grown on SiO 2 . The photoluminescence spectra show strong peaks due to exciton recombination and lattice defects. The ZnO-NFN presents quasi-persistent photoconductivity effects and ohmic I-V characteristics which become nonlinear and hysteretic as the applied voltage is increased. The electrical conductance as a function of temperature can be described by a modified three dimensional variable hopping model with nanometer-ranged typical hopping distances.

ZnO nanowire sensitization with Ru polypyridyl complexes: charge-transfer probed by spectral and relaxation photocurrent measurements

“…This is similar to the behavior observed on ZnO NW samples under conditions where atmospheric air has been removed from the ZnO NW walls, and it is related to the role of atmospheric adsorbates as electron traps [53]. When the illumination is interrupted, the current for the three cases decreases very slowly, showing a quasi-persistent behavior that is wellknown for ZnO [21]. In is interesting to note that the relaxation curve for the sample sensitized with RuL2 presents much faster relaxation than the data for the other samples ( Fig.…”

“…In contrast, for FeL3, RuL2 and RuL3, bands corresponding to (C N) of non-anchored nitrile groups appear at the same value as for the free complexes ( = 2240 cm -1 ), indicating that (as may be expected) only one nitrile group coordinates to the semiconductor surface while the other (RuL2) or other two (RuL3 and FeL3) remain uncoordinated. The spectrum for the unsensitized ZnO NW sample is dominated by a band in the visible peaked at about nm and is due to transitions involving deep defect states in the ZnO bandgap [20], [21]. The RuL1, RuL2 and RuL3-sensitized samples exhibit a band in the visible as well, however redshifted and less intense than the band for the reference sample.…”

“…The ZnO NWs are preferentially oriented perpendicular to the substrate with wide angular dispersion, and are about 1 µm long and 60 nm thick. These NWs grow after the formation of a thin, porous ZnO layer, which is expected for these growth conditions [20][21][22] [2]. After soaking the samples with the complexes [Fig.…”

“…The ZnO nanowires (NWs) were fabricated through a vapor transport method, under controlled ultra-high purity Ar and O 2 flows on Au-nanocluster covered, electrically insulating SiO 2 /Si substrates, as described in [20][21][22][1], [2]. The source-to-substrate distance within the tube furnace (25 cm) and the O 2 flow rate (3 sccm) were chosen to produce a dense interconnected ZnO NWs network with electrical resistance in the 10 2 M range [21]. The source temperature was 1100ºC and the Ar flow rate was 125 sccm.…”

ZnO Nanostructures Synthesized by Vapor Transport and Liquid Phase Synthesis Techniques: Growth and Properties

“…C) The carbothermal reaction, with or without O 2 [8][9][10][11][12] , where solid ZnO and graphite powders are mixed to react at high temperature (between 800°C and 1100°C) to reduce the ZnO into Zn and ZnO x (x<1) cluster vapors, with the formation of CO/CO 2 as a byproduct. Vapors rich in Zn then condense on the substrate and react with O atoms to form the ZnO nanocrystals, while most of the CO/CO 2 molecules (due to their great stability) are essentially removed by the pumping system 13,14 .…”