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In this review, we briefly describe work devoted in recent years towards the effective control of morphology, structure and optical properties of ZnO nanostructures, with particular focus on cost effective and simple methods for ZnO nanowires (NWs) fabrication. For the vapor transport technique, we describe in detail mechanisms for growth precursors generation, their transport in inert and forming gas, as well as their reactions on different pretreated substrates and corresponding growth mechanisms. As for low temperature synthesis methods, three techniques are outlined: sol-gel, solvothermal and electrophoretic deposition, with emphasis on effective morphology, structure and optical properties control. In this context, we discuss recent attempts to understand the role of solvent and alkaline agents used during solvothermal synthesis of ZnO nanostructures on their morphology and photoluminescence properties. Recent success of electrophoretic deposition of ZnO nanoparticles on pre-patterned silicon substrates in the form of NWs and NW bunches is highlighted over many previous attempts to fabricate ZnO NWs with inconvenient sacrificial templates. Finally, we present a critical discussion on the current understanding of passivation mechanisms of ZnO NW surfaces by MgO shells.

Powders of ZnO and ZnO:M (M = Al3+ and Sr2+) with 1 and 4% of M nominal content were synthetized by a hydrothermal method in a diethanolamine (DEA) medium. The samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), micro-Raman and photoluminescence (PL). The powder particles were spherical with average radius decreasing from 1 μm down to 70 nm with increasing Al3+ nominal content but nearly independent on the Sr2+ nominal content. The XRD and micro-Raman results indicate that both Al3+ and Sr2+ mostly incorporated substitutionally into the ZnO lattice, giving rise to compressive and tensile strain, respectively, as a result of ionic radii differences. The PL spectra for ZnO:Al exhibit a dopant-induced contribution at ∼3.1 eV, which is not observed for ZnO:Sr, due to radiative transitions involving trapping of photocarriers at theoretically expected substitutional Al3+ donor states or at Zn interstitial defects. Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina Fil: Soliz, Tania. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina Fil: Gutierrez, Jorge Andrés. Universidad del Quindío. Facultad de Ciencias Básicas y Tecnológicas; Colombia Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina Fil: Figueroa, Carlos. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Laboratorio de Física del Sólido; Argentina

Heteroleptic ruthenium (II) complexes were used for sensitizing ZnO surfaces in organic solar cells (OSCs) as mediators with photoactive layers. The complexes [Ru(4,4′-X2-bpy)(Mebpy-CN)2]2+ (with X = −CH3, −OCH3 and −N(CH3)2; bpy = 2,2′-bipyridine; Mebpy-CN = 4-methyl-2,2′-bipyridine-4′-carbonitrile) were synthesized and studied by analytical and spectroscopical techniques. Spectroscopic, photophysical, and electrochemical properties were tuned by changing the electron-donating ability of the -X substituents at the 4,4′-positions of the bpy ring and rationalized by quantum mechanical calculations. These complexes were attached through nitrile groups to ZnO as interfacial layer in an OSC device with a PBDB-T:ITIC photoactive layer. This modified inorganic electron transport layer generates enhancement in photoconversion of the solar cells, reaching up to a 23% increase with respect to the unsensitized OSCs. The introduction of these dyes suppresses some degradative reactions of the nonfullerene acceptor due to the photocatalytic activity of zinc oxide, which was maintained stable for about 11 months. Improving OSC efficiencies and stabilities can thus be achieved by a judicious combination of new inorganic and organic materials., The authors thank CONICET (Grant PIP-2015-098), FONCyT (Grant PICT-2016-0553), and UNT (Grant PIUNT 26D/620) for financial support. F.F.S. thanks CONICET for a graduate fellowship. N.C.V., M.T., D.C., F.E.M.V., M.C., and N.E.K. are Members of the Research Career (CONICET). J.P.J. and M.C.Q. acknowledge financial support from the Spanish Ministry Science and Innovation through the “Severo Ochoa” Program for Centers of Excellence in R&D SEV-2015-0496 (FUNMAT) and CEX2019-000917-S (FUNFUTURE) and PGC2018-095411-B-I00 (RAINBOW) projects. This project received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 713673. J.P.J. received financial support through the “la Caixa” INPhINIT Fellowship Grant for Doctoral studies at Spanish Research Centers of Excellence (Grant code: LCF/BQ/IN17/ 11620035), “la Caixa” Banking Foundation (ID100010434), Barcelona, Spain.

Powders composed of ZnO sub-microspheres were obtained in two stages: solvothermal synthesis and thermal annealing at 125, 300, 450 or 600oC in atmospheric conditions. The synthesis was carried out with methanol as solvent, zinc acetate dihydrate as Zn2+ source and ammonia chloride as complexing agent. The as-grown and annealed samples were studied through photoluminescence, microRaman and reflectance spectroscopies, scanning electron microscopy and X-ray diffraction (XRD). After the solvothermal synthesis stage, a white precipitate was obtained composed of a flower-like multiphase assembly of layers identified mainly as a layered basic zinc salts (LBZS) and Zn(NH3)2Cl2. After the annealing treatments, the LBZS and Zn(NH3)2Cl2 transformed into ZnO, while the powder morphology changed from the layered flower-like to polycrystalline ZnO spherical particles with sub-micrometer diameters. With increasing annealing temperature, the ZnO spheres size remained unchanged, while the mean crystallite size and wurtzite lattice parameters decreased as a result of tensile stress relaxation. Concomitantly, a blueshift of the defect-related ZnO emission was observed. The combined analysis of emission, vibrational and reflectance spectra and XRD suggests that the annealing treatments result in the formation of ZnO crystallites with oxygen vacancies and oxygen vacancy-zinc interstitial complexes whose densities increase as the annealing temperature increases. The results and analysis reported in this work contribute to the understanding of growth mechanisms relevant for the tailoring of ZnO powder properties through solvothermal synthesis in non-aqueous media.

Self-supported membranes consisting of entangled 2 to 6 μm long ZnO nanowires (NWs) on graphite with excellent UV emission were fabricated by a vapor transport technique at high temperature in a tubular furnace. The NWs grew on catalyst-free graphite flakes that had been mechanically compacted within an alumina boat crucible (the “substrate crucible”). The self-supported ZnO NW/graphite membrane detached spontaneously from the graphite substrate during the cooling stage after NW growth. The inversion of the substrate crucible orientation to an upside down position (usually used by our group for rigid substrates) resulted in strong reductions of the UV/visible emission ratio; by a factor of ~20 for NWs grown on compacted graphite and of ~1000 for NWs grown on Au-catalyzed Si wafers. Simulations of the transport fluid dynamics within the synthesis tube demonstrate that the substrate holder shape and substrate position within the holder play crucial roles in the reduction of precursor velocities, which is likely a key factor for achieving the long entangled NWs with enhanced UV/visible emission ratios that conform the self-supported ZnO NW/graphite membranes. Fil: Tosi, Ezequiel. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina

Zn1−xNixO thin films (nominal x = 0, 0.01, 0.02, 0.04, 0.1 and 0.2) were synthesized on silicon substrates through a sol-gel/dip-coating technique. Samples were studied by X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, Rutherford backscattering spectrometry and depth-profiling X-ray photoelectron spectroscopy. The results from X-ray diffraction show growth in the wurtzite crystal structure for all samples, with cubic NiO being detected as a secondary phase for x = 0.2. While for x = 0 (pure ZnO) no texture is present, for 0 ≤ x ≤ 0.1 strong preferential crystallization along the c-axis is observed. A tendency for Ni diffusion towards the film/Si substrate interface was observed. The formation of substitutional ZnxNi1−xO solid solution for 0.01 ≤ x ≤ 0.04 is suggested by the results. Photoluminescence spectra exhibit strong near band edge UV emission and suppression of deep defect-related emission in the visible upon Ni+2 incorporation into the ZnO lattice. As in pure ZnO, the UV emission in ZnNiO at room temperature is dominated by the first two phonon replica of the excitonic emission, however the LO phonon energy (ħωLO) is reduced by up to ∼15 meV inthe 0 ≤ x ≤ 0.04 range. Due to this reduction of ħωLO, the exciton-phonon coupling increases, in consistency with a corresponding expected increase of the Fröhlich coupling constant with decreasing ħωLO. Fil: Marín Ramírez, Oscar Alonso. Nanoproject – LAFISO, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina Fil: Alastuey, Patricio. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina. Nanoproject – LNPD, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina Fil: Tosi, Ezequiel. Nanoproject – LAFISO, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina Fil: Orive, Joseba. Laboratorio de Materiales Funcionales a Nanoescala, Departamento de Ingeniería Química, Biotecnología y Materiales, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile; Chile Fil: Mosquera, Edgar. Departamento de Física, Universidad del Valle, Cali; Colombia Fil: Zampieri, Guillermo. Instituto Balseiro, Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Suarez, Sergio. Instituto Balseiro, Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Comedi, David Mario. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina. Nanoproject – LAFISO, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina Fil: Tirado, Monica Cecilia. Nanoproject - LNPD, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina

The photoluminescence from solid-state ZnO nanoparticles (NPs) assemblies was studied as a function of the number on NPs in the assembly. With increasing number of NPs, the UV emission band broadened and redshifted, while the UV/visible emission rate ratio decreased. Furthermore, while samples with few NPs displayed a typical linear dependence for the UV emission rate as a function of the excitation power, samples with large number of deposited NPs showed unusual non-linear, nonmonotonic dependences with maxima at intermediate excitation powers. Also, for samples with large number of NPs, the UV band became broader as the excitation power was increased. These unusual results can be understood by considering the interplay between photon self-absorption effects, interface trap states between NPs and illumination power dependent potential barriers at NP/NP interfaces. The exposure of samples with large number of NPs to ethanol vapor during the photoluminescence measurements resulted in partial removal of the non-monotonic behavior of the UV emission rate dependence on excitation power.

To date, EPD obtained ZnO one-dimensional nanostructures have been achieved by depositing ZnO nanoparticles through a sacrificial anodic alumina membrane or promoted by the presence of pre-deposited Au nanoclusters on the substrate. In the present work, we explored using boron (p-type)-doped crystalline Si (100) substrates with different conductivities. We found the conditions for the direct self-assembly of one-dimensional ZnO nanorod bunches, in a novel and easy way, at room temperature. A colloidal dispersion of ≈5 nm-sized ZnO nanoparticles in 2-propanol was used. The results showed differences in the morphology of ZnO nanostructures depending on the Si substrate conductivity used. XRD patterns indicated that ZnO nanorods were preferentially formed in (002) direction corresponding to c-axis orientation in the wurtzite structure. Photoluminescence measurements revealed the presence of quantum confined excitons and high emission intensity in the visible range. Photoluminescence spectra showed that emission was dominated by the ZnO nanoparticles that form the nanostructures and not by the morphology or size of the nanostructures themselves. The results presented in this work expand the EPD technique applications to form nanorod nanostructures in a single step.

ZnO films were synthesized on SiO2/Si substrates through the sol-gel technique using diethanolamine as chelating agent and annealed in ArþO2 atmospheres with different O2 flow-rates in the 10–100 sccm range. Samples were studied by scanning electron microscopy and X-ray diffraction, evidencing a nanostructured morphology with a preferential orientation along the (0 0 2) direction (c-axis orientation), which is uncommon when diethanolamine is used as the chelating agent. The room temperature photoluminescence spectra show strong UV emissions at around 375 and 384 nm from near band-edge transitions and phonon replica, and a broad defect-related band extending from the visible to near infrared (∼500–800 nm). The analysis of the defect-related emission band and its various components as a function of the O2 flow-rate is discussed in terms of contributions from specific luminescent point defect centers established during annealing. Fil: Marin, Oscar. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; Chile. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Budini, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Mosquera, Edgar. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; Chile Fil: Figueroa, Carlos. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Nanocrystalline ZnO films were grown on silicon substrate by hydrothermal synthesis at 125 °C, using diethanolamine as stabilizer. A powder containing ZnO spheres, with diameters between 100 to 200 nm and formed by aggregation of ZnO nanoparticles, was also obtained as a secondary reaction product. The samples were studied by scanning electron microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. The effects of the [diethanolamine]/[Zn+2] molar ratio on morphological, structural and optical properties were studied, as well as the effect of laser illumination (=325 nm) and annealing treatment on photoluminescence properties. The film samples exhibited a compact columnar structure, with thickness between 180 to 210 nm, which were not strongly affected by the diethanolamine concentration. The X-ray diffraction patterns from the films evidenced preferred orientation along the c-axis of the ZnO wurzite structure; while the nanospheres did not show any preferential crystalline direction. The PL spectra from the films showed large initial UV emission and a weak defect band centered in the yellow. A PL evolution while the samples were UV illuminated, attributed to oxygen vacancy generation following the photoinduced equilibration of metastable structures, was observed. Fil: Gonzalez, Vanessa. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina. NanoProject - LNPD, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina Fil: Marín Ramírez, Oscar Alonso. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina. NanoProject - LAFISO, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina Fil: Tirado, Monica Cecilia. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina. NanoProject - LNPD, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina Fil: Comedi, David Mario. NanoProject - LAFISO, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán; Argentina. Instituto de Física del Noroeste Argentino, INFINOA (CONICET-UNT); Argentina

Dye-sensitized ZnO nanowire (NW) electrodes were fabricated using Ru polypyridyl complexes that use nitrile instead of carboxylic group as anchoring unit to the NW surfaces. The complexes formula is [Ru(bpy)3−x(Mebpy-CN)x]2+ (x = 1−3, bpy = 2,2'-bipyridine, Mebpy-CN = 4-methyl-2,2'-bipyridine-4'-carbonitrile). The ZnO NWs were grown by a vapor transport method on insulating SiO2/Si substrates. The sensitized ZnO NW electrodes were studied by electron microscopy, Raman and PL spectroscopies, and spectral and relaxation photocurrent measurements. The Raman spectra confirm that the complexes were effectively anchored to the ZnO NWs through one of the pendant nitrile groups of the bipyridyl ligands. The nanostructured morphology of the NW electrodes was maintained so that their light trapping characteristics were preserved. The Ru complexes were found to be excellent sensitizers of the ZnO NWs, improving by orders of magnitude their photocurrent in the visible region. The Fe-based complex of formula [Fe(Mebpy-CN)3](PF6)2 was also tested; however it did not show any sensitizing effect. An order of magnitude shortening of the persistent photocurrent relaxation times (after the illumination is interrupted) was found to occur upon successful sensitization of the ZnO NWs with the Ru complexes. This effect is interpreted in terms of hole traps at ~1 eV above the ZnO valence band edge, which are lowered by ~50–60 meV in the soaked samples due to screening of the trap centers provided by the extra photoexcited charge carriers transferred from the sensitizing complex to the NWs. Fil: Vega, Nadia Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Instituto de Física del Noroeste Argentino, INFINOA. Universidad Nacional de Tucumán, Facultad de Ciencias Exactas y Tecnología, Argentina; Argentina Fil: Mecchia Ortiz, Juan Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Instituto de Física del Noroeste Argentino, INFINOA. Universidad Nacional de Tucumán, Facultad de Ciencias Exactas y Tecnología, Argentina; Argentina; Argentina Fil: Katz, Néstor Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Instituto de Física del Noroeste Argentino, INFINOA. Universidad Nacional de Tucumán, Facultad de Ciencias Exactas y Tecnología, Argentina; Argentina; Argentina

Nanomaterials based on ZnO have been used to build glucose sensors due to its high isoelectric point, which is important when a protein like Glucose Oxidase (GOx) is attached to a surface. It also creates a biologically friendly environment to preserve the activity of the enzyme. In this work we study the electrical transport properties of ZnO thin films (TFs) and single crystals (SC) in contact with different solutions by using impedance spectroscopy. We have found that the composition of the liquid, by means of the charge of the ions, produces strong changes in the transport properties of the TF. The enzyme GOx and phosphate buffer solutions have the major effect in the conduction through the films, which can be explained by the entrapment of carriers at the grain boundaries of the TFs. These results can help to design a new concept in glucose biosensing. Fil: Sappia, Luciano David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentina Fil: Trujillo, Ricardo Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentina Fil: Lorite, Israel. University of Leipzig; Alemania Fil: Madrid, Rossana Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentina Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina Fil: Esquinazi, Pablo. University of Leipzig; Alemania

We report white light emission under UV excitation from porous silicon (PS) samples annealed at different temperatures and surrounding atmospheres. The photoluminescence (PL) spectra show a broad emission from ultraviolet to near infrared. Annealed PS samples were studied by photoluminescence, FTIR and EPR spectroscopies. The PL spectra were found to include three main components centered at the violet, green and infrared. The FTIR experiments suggest the formation of a system composed by silicon nanocrystals embedded in a nonstoichiometric silicon oxide matrix (nc-Si/SiOx). The EPR measurements reveal the existence of the well-know Pb0 (g~2.007) and Pb1 (g~2.004) centres, and of a signal at g~1.9997. The combined PL, FTIR and EPR results suggest that violet and green emissions come from oxygen-excess defects in SiOx while the infrared emission is related to defects located at Si/SiOx interfaces. Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Gennaro, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Koropecki, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Comedi, David Mario. Universidad Catolica de la Plata. Facultad de Ciencias Exactas y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

ZnO nanocones were grown on porous silicon (PS) by vapor transport at different temperatures and O2 flow rates without metal nanocatalysts. The ZnO/PS heterostructures were studied by electron microscopy, and by photoluminescence and electron resonance (EPR) spectroscopies. Samples emitted strong white PL, opening potential application for white light illumination. The photoluminescence spectra were found to include five main components centered at 1.84, 2.06, 2.30, 2.48 and 3.31 eV. The components at 2.48 and 2.06 eV were related to oxygen vacancies in ZnO, that at 2.3 eV to Zn vacancies and the one at 1.84 eV to the PS substrate. The low excitonic emission intensity at 3.31 eV and the observed rough ZnO nanocone morphology suggest the presence of surface trap states. EPR shows a g ∼ 2.006 line attributed to Zn divacancies. The absence of the g = 1.96 line, attributed to conduction band electrons, suggests strong carrier depletion. Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Grinblat, Gustavo Sergio. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Gennaro, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Koropecki, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The room temperature photoluminescence from ZnO/MgO core/shell nanowires (NWs) grown by a simple two-step vapor transport method was studied for various MgO shell widths (w). Two distinct effects induced by the MgO shell were clearly identified. The first one, related to the ZnO/MgO interface formation, is evidenced by strong enhancements of the zero-phonon and first phonon replica of the excitonic emission, which are accompanied by a total suppression of its second phonon replica. This effect can be explained by the reduction of the band bending within the ZnO NW core that follows the removal of atmospheric adsorbates and associated surface traps during the MgO growth process on one hand, and a reduced exciton-phonon coupling as a result of the mechanical stabilization of the outermost ZnO NW monolayers by the MgO shell on the other hand. The second effect is the gradual increase of the excitonic emission and decrease in the defect related emission by up to two and one orders of magnitude, respectively, when w is increased in the ∼3-17 nm range. Uniaxial strain build-up within the ZnO NW core with increasing w, as detected by x-ray diffraction measurements, and photocarrier tunneling escape from the ZnO core through the MgO shell enabled by defect-states are proposed as possible mechanisms involved in this effect. These findings are expected to be of key significance for the efficient design and fabrication of ZnO/MgO NW heterostructures and devices. Fil: Vega, Nadia Celeste. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad de Chile; Chile Fil: Tosi, Ezequiel. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Grinblat, G.. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Mosquera, E.. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas. Departamento de Geología; Chile Fil: Moreno, M. S.. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina

Stable immobilization and homogenous distribution of ZnO nanostructures on solid substrates can play a fundamental role in developing nanostructured biosensing devices. In this work we studied how phosphonic acid-terminated self-assembled monolayers (SAMP of 1) can enhance the electrocatalytic behaviour of ZnO nanoparticles (NPs) immobilized on gold surface. It is well known that alkanethiols can form uniform and conformal monolayers on gold through the thiol group and it has already been shown that ZnO surface can be modified by organophosphonates. Here we focus on the application of this chemistry as a tool for the fabrication of designed architectures of ZnO nanostructures on gold electrodes. Successful surface modification was verified by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Our results indicate the formation of highly stable arrays of ZnO nanoparticles. As a proof of concept, the novel electrodes developed were tested in electrochemical assays for the detection of the transgenic protein neomycin phosphotransferase II (NPTII), showing enhanced electrocatalytic stability in immunosensor applications. The target protein could be detected down to nanomolar level by using the difference in charge transfer resistance (ΔRct) recorded in impedance spectroscopy measurements.

The present work reports the self-assembled growth of ZnO nanowires on silicon substrate with nanometer sized Au clusters using electrophoretic deposition technique at room temperature without a sacrificial template. A colloidal suspension of ≈5 nm sized ZnO nanoparticles dispersed in 2-propanol was used (nanoparticle bandgap of 3.47 eV as determined from absorbance measurements). The results show that the Au nanoclusters on the silicon substrate induce the self-assembly of the ZnO nanoparticles into vertically aligned ZnO nanowires. This effect is tentatively explained as being due to increased electric field intensities near the Au nanoclusters during the electrophoretic deposition. Photoluminescence measurements reveal the presence of quantum confined excitons and a relatively low concentration of deep defects in the nanowires. The electric field guided growth of semiconductor nanostructures at room temperature has great industrial potential as it minimizes production costs and enables the use of substrate materials not withstanding high temperatures. Fil: Sandoval, Claudia. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Propiedades Dielectricas; Argentina Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Real, Silvina. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Propiedades Dielectricas; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Propiedades Dielectricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We present a glucose biosensor based on ZnO nanowire self-sustained films grown on compacted graphite flakes by the vapor transport method. Nanowire/graphite films were fragmented in water, filtered to form a colloidal suspension, subsequently functionalized with glucose oxidase and finally transferred to a metal electrode (Pt). The obtained devices were evaluated using scanning electron microscopy, energy-dispersive x-ray spectroscopy, cyclic voltammetry and chronoamperometry. The electrochemical responses of the devices were determined in buffer solutions with successive glucose aggregates using a tripolar electrode system. The nanostructured biosensors showed excellent analytical performance, with linear response to glucose concentrations, high sensitivity of up to ≈17 μA cm-2 mM-1 in the 0.03-1.52 mM glucose concentration range, relatively low Michaelis-Menten constant, excellent reproducibility and a fast response. The detection limits are more than an order of magnitude lower than those achievable in commercial biosensors for glucose control, which is promising for the development of glucose monitoring methods that do not require blood extraction from potentially diabetic patients. The strong detection enhancements provided by the functionalized nanostructures are much larger than the electrode surface-area increase and are discussed in terms of the physical and chemical mechanisms involved in the detection and transduction processes. Fil: Gallay, Pablo. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tosi, Ezequiel. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Madrid, Rossana Elena. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina

We combine X-ray absorption, electron spin resonance and Raman spectroscopies, X-ray diffraction and photoluminescence (PL) techniques to determine the structure and luminescence mechanisms in Si nanoclusters (Si-ncls) embedded within Si oxides at various intermediate formation stages. The Si-ncls/oxide systems are fabricated by thermally annealing plasma-enhanced chemical vapor deposited Si-rich Si-oxide films. The structural and chemical orders in the amorphous oxide matrix, the Si-ncls amorphous and crystalline volume fractions and sizes, the dangling bond density and PL spectra and decay rates are followed closely as a function of the annealing temperature. The results can be interpreted by a crystalline core/amorphous shell model for the Sincls. The important role of the shell, often ignored in the literature, is discussed. As the Si-ncls crystalline cores grow at the expense of thinning amorphous shells, the PL undergoes a transition from a regime dominated by disorder-induced effects to a situation where quantum confinement prevails. Fil: Borrero Gonzalez, Luis Jose. Universidade de São Paulo; Brasil Fil: Nunes, L. A. O.. Universidade de São Paulo; Brasil Fil: Guimaraes, F. E. G.. Universidade de São Paulo; Brasil Fil: Wojcik, J.. McMaster University; Canadá Fil: Mascher, P.. McMaster University; Canadá Fil: Gennaro, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán; Argentina

The polarization resistance and capacitance of platinum black electrodes in contact with aqueous NaCl solutions was investigated. A series of measurements were made at 25±0.1 °C in the 10 Hz to 10 MHz range using a HP 4192A Impedance Analyzer. The measurement cell has flat parallel platinum electrodes 15 mm in diameter, with a continuously variable spacing from 0.5 to 9 mm. They were platinized prior to each measurement. The electrolyte solution conductivities were in the 0.004–0.6 S m−1 range. The data were analyzed using an equivalent circuit consisting in a constant phase element in series with a parallel connection of a resistance and another constant phase element. The characteristic parameters of the model are presented as a function of the electrolyte solution conductivity.

The main difficulties related to low-frequency dielectric measurements of liquid conducting samples using impedance analyzers such as the HP 4192 A or HP 4284 A are presented and discussed. These include the small value of the phase angle and the electrode polarization impedance. We propose ways to overcome these difficulties in terms of cell design, choice of instrument settings, choice of electrode material, connection of the cell to the instrument. We also propose a new calibration method that allows a differential measurement of the dielectric properties with far higher precision than possible using the standard short–open calibration.

The dielectric properties of aqueous suspensions of unilamelar phospholipid vesicles were measured over a broad frequency range extending from 1 kHz to 1 GHz. The low-frequency measurements (1 kHz to 10 MHz) were performed at Tucuman using a HP 4192 A Impedance Analyzer with a variable spacing cell and Short-Open-Load calibration. The high-frequency spectra (1 MHz to 1 GHz) were obtained at Gottingen using a HP 8753 A Network Analyzer with a reflection cut-off measuring cell. The vesicles were prepared using different concentration mixtures of non-ionic and ionic phospholipids: 1,2 Dimyristoyl-sn-Glycero-3 Phosphocholine and L-α-Phosphatidyl-DL-Glycerol-Dimyristoyl (Na-Salt). Their mean diameter had the value of 116 nm, obtained by means of multiple extrusions. They were suspended in either tridistilled water or an aqueous NaCl solution. The dielectric spectra were described and interpreted using existing theoretical models (for the counterion polarization and the membrane charging together with the Maxwell–Wagner dispersion processes) with the ζ potential as the only adjustable parameter.

Unexpectedly, the Fano resonance caused by the interference of continuum electron excitations with the longitudinal optical (LO) phonons was observed in random porous Si by Raman scattering. The analysis of the experimental data shows that the electron states trapped at the SiSiO2 interface dominate in the observed Raman scattering. The gap energy associated with the interface states was determined. Copyright © 2011 John Wiley & Sons, Ltd.

To neutralise the influence of the surface of ZnO nanowires for photonics and optoelectronic applications, we have covered them with insulating MgO film and individually contacted them for electrical characterisation. We show that such a metal-insulator-semiconductor-type nanodevice exhibits a high diode ideality factor of 3.4 below 1 V. MgO shell passivates ZnO surface states and provides confining barriers to electrons and holes within the ZnO core, favouring excitonic ultraviolet radiative recombination, while suppressing defect-related luminescence in the visible and improving electrical conductivity. The results indicate the potential use of ZnO/MgO nanowires as a convenient building block for nano-optoelectronic devices. Fil: Grinblat, Gustavo Sergio. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bern, Francis. University of Leipzig; Alemania Fil: Barzola Quiquia, José. University of Leipzig; Alemania Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Esquinazi, Pablo. University of Leipzig; Alemania

Tunable second harmonic (SH) polaritons have been efficiently generated in ZnO nanocombs, when the material is excited close to half of the band-gap. The nonlinear signal couples to the nanocavity modes, and, as a result, Fabry-Pérot resonances with high Q factors of about 500 are detected. Due to the low effective volume of the confined modes, matter-light interaction is very much enhanced. This effect lowers the velocity of the SH polariton in the material by 50 times, and increases the SH confinement inside the nanocavity due to this higher refractive index. We also show that the SH phase-matching condition is achieved through LO-phonon mediation. Finally, birrefringence of the crystal produces a strong SH intensity dependence on the input polarization, with a high polarization contrast, which could be used as a mechanism for light switching in the nanoscale. Fil: Capeluto, Maria Gabriela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires; Argentina Fil: Grinblat, Gustavo Sergio. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Propiedades Dielectricas; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentina Fil: Bragas, Andrea Veronica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires; Argentina

ZnO/MgO (core/shell) nanowires (NWs) grown by a two-step vapour transport method under different MgO shell growth conditions are examined by x-ray diffraction, photoluminescence (PL) excitation and temperature (10–300 K) dependent PL. The excitonic-to-defect PL ratio is increased by more than two orders of magnitude in the core/shell as compared to bare ZnO NWs. Concomitantly, a strong depression of the PL thermal quenching, most particularly for the visible part of the PL spectrum, occurs. Using a semi-quantitative model, results are interpreted as a strong radiative to non-radiative lifetime ratio reduction due to defect passivation at the ZnO NW walls and photocarrier confinement within the ZnO core by the MgO shell. These beneficial effects are, however, significantly weakened when metal interdiffusion across the core/shell interface is favoured during the shell growth. Non-radiative recombination lifetime in the sample with sharp core/shell interface is described by a single activation energy of 15 meV (bound exciton release). For interdiffused cases and bare ZnO an additional activation energy of 60 meV (free exciton breakup) is observed. Fil: Grinblat, Gustavo Sergio. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Borrero González, L. J.. Universidade de Sao Paulo; Brasil Fil: Nunes, L. A. O.. Universidade de Sao Paulo; Brasil Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucuman. Facultad de Ciencias Exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Propiedades Dielectricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We report in this work the synthesis and spectroscopic, electrochemical, spectroelectrochemical, and photophysical characterization of a novel series of ruthenium polypyridyl complexes with 4-methyl-2,2′-bipyridine-4′- carbonitrile (Mebpy-CN) as an auxiliary ligand of general formula [Ru(bpy) 3-x(Mebpy-CN)x](PF6)2 (x = 1-3) (with bpy = 2,2′-bipyridine). A significant increase in the lifetime and quantum yield of emission of the lowest 3MLCT excited state is disclosed when going from x = 1 to x = 3, evidencing an improvement of the photosensitizing properties with respect to [Ru(bpy)3](PF 6)2. Furthermore, quenching by molecular oxygen of 3MLCT excited states of the three complexes produced singlet molecular oxygen (1O2) with quantum yield values higher than that of [Ru(bpy)3]2+ in CH3CN. The structure of the complex with x = 1 has been determined by X-ray diffraction. The photoconductivity of ZnO nanowires covered with this same complex is increased by an order of magnitude, pointing to its feasibility as a component of a DSSC. A new dinuclear complex with Mebpy-CN as a bridging ligand has also been prepared and characterized by physicochemical techniques. The derived mixed-valent species of formula [(bpy)2RuII(Mebpy-CN) RuIII(NH3)5]5+ displays a considerable metal-metal electronic coupling due to the delocalization effect of a nitrile group in the 4′ position of the bpy ring. © 2013 American Chemical Society. Fil: Mecchia Ortiz, Juan Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Vega, Nadia Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología; Argentina Fil: Romero, Isabel. Universidad de Girona; España Fil: Fontrodona, Xavier. Universidad de Girona; España Fil: Parella, Teodor. Universitat Autònoma de Barcelona; España Fil: Moran Vieyra, Faustino Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; Argentina Fil: Borsarelli, Claudio Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; Argentina Fil: Katz, Néstor Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina

ZnO nanofibre networks (NFNs) were grown by vapour transport method on Si-based substrates. One type of substrate was SiO2 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/SiO2 interfaces. Photoluminescence, electrical conductance and photoconductance of ZnO-NFN was studied for the sample grown on SiO2. 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. Fil: Vega, Nadia Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina Fil: Rodriguez, Andres. Universidad Politécnica de Madrid; España Fil: Rodriguez, Tomás. Universidad Politécnica de Madrid; España Fil: Hughes, Gareth M.. University of Oxford; Reino Unido Fil: Grovenor, Chris R. M.. University of Oxford; Reino Unido Fil: Audebert, Fernando Enrique. University Of Oxford; Reino Unido. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Vertically aligned ZnO nanowires (NWs) were grown on Au-nanocluster-seeded amorphous SiO(2) films by the advective transport and deposition of Zn vapours obtained from the carbothermal reaction of graphite and ZnO powders. Both the NW volume and visible-to-UV photoluminescence ratio were found to be strong functions of, and hence could be tailored by, the (ZnO+C) source-SiO(2) substrate distance. We observe C flakes on the ZnO NWs/SiO(2) substrates which exhibit short NWs that developed on both sides. The SiO(2) and C substrates/NW interfaces were studied in detail to determine growth mechanisms. NWs on Au-seeded SiO(2) were promoted by a rough ZnO seed layer whose formation was catalysed by the Au clusters. In contrast, NWs grew without any seed on C. A correlation comprising three orders of magnitude between the visible-to-UV photoluminescence intensity ratio and the NW volume is found, which results from a characteristic Zn partial pressure profile that fixes both O deficiency defect concentration and growth rate.

GaAs nanowires were passivated by AlInP shells grown by the Au-assisted vapor-liquid-solid method in a gas source molecular beam epitaxy system. Transmission electron microscopy confirmed a core-shell GaAs-AlInP structure. Current-voltage measurements on ensemble nanowires indicated improved carrier transport properties in the passivated nanowires as compared to their unpassivated counterpart. Similarly, individual nanowires showed improved photoluminescence intensity upon passivation. A detailed model is presented to quantify the observed improvements in nanowire conduction and luminescence in terms of a reduction in surface charge trap density and surface recombination velocity upon passivation. The model includes the effects of high-level injection, bulk recombination, and surface recombination. The model can be used as a tool for assessing various passivation methods. © 2012 American Institute of Physics. Fil: Chia, A. C. E.. Mc Master University; Canadá Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Li, Y.. McGill University; Canadá Fil: Zhao, S.. McGill University; Canadá Fil: Mi, Z.. McGill University; Canadá Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Lapierre, R. R.. Mc Master University; Canadá

Vertically aligned GaAs nanowire (NW) bundles grown by gas-source molecular beam epitaxy on an n-doped GaAs substrate by a metal catalysis method and embedded in an insulating matrix (SU8-2) were studied by impedance spectroscopy. The DC current-voltage characteristics measured between Au dot contacts to the NW tips and the substrate exhibited Schottky behavior. A detailed analysis of the impedance data measured in reverse bias conditions is presented, which enables the elimination of the stray capacitance due to the insulating matrix, and the separation of the different contributions to the total admittance from the metal/NW Schottky interface and from the NW region beyond the barrier region. The observed NW conductances and capacitances are shown to be consistent with rough estimates based on the GaAs conductivity and permittivity data and the NW dimensions, and the NW conductance increases as a power law of the frequency. Possible charge transport mechanisms to explain this result are discussed. Fil: Tirado, Monica Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Laboratorio de Propiedades Dieléctricas; Argentina Fil: Comedi, David Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Sólido; Argentina Fil: LaPierre, Ray R.. Mc Master University; Canadá

GaAs nanowire (NW)-based p-n photovoltaic devices, with two distinct p and n spatial distributions and where Te was the n-dopant, have been studied by impedance spectroscopy in the 10(3)-10(7) Hz frequency range and the - 1.5-1.5 V bias range. For a large n-core/p-shell overlap region within NWs in a coaxial geometry, the p-n junction properties (DC rectification and p-n depletion capacitance) are found to prevail. The impedance data at low bias for both NW devices show large frequency dispersions with relaxation frequencies that are compatible with carrier re-emission times from traps due to GaAs surface states. An increasing conductance with increasing frequency for low bias is observed, suggesting hopping transport through localized states. For large bias the conductance increases exponentially with bias and is frequency independent, indicating conduction through extended states in this regime.

The impedance polarization behavior of the platinum black electrodes in contact with different concentrations of colloidal suspensions of polystyrene particles was investigated. All measurements were performed at 25±0.1° C, in the frequency range of 10 Hz to 10 MHz, using an HP 4192 A impedance analyzer and an acrylic cell with flat 15‐mm‐diameter electrodes and variable spacing ranging from 0.5 to 10 mm. The volume concentrations of the colloidal suspensions were in the 5% to 38% range. The polarization resistance and reactance of the electrodes were analyzed to determine their dependence on the concentration and conductivity of the colloidal suspension and on the frequency of the applied field.

Dielectric properties of four suspensions of spherical polystyrene particles were measured at 25 ◦ C over a broad frequency range extending from 100 Hz to 10 MHz, using a HP 4192 A Impedance Analyzer. The instrument was coupled to a cell with parallel platinum black electrodes and variable spacing, and the quadrupole calibration method was used. The aqueous electrolyte solutions were prepared using equal concentrations of NaCl, KCl, NaAc, or KAc, so that the calculated Debye screening length and Zeta potential remained constant, while the conductivity changed. The polystyrene particles used (Interfacial Dynamics Corp., surfactant-free white sulfate latex) have a diameter of 1 micron and a surface charge density that is independent of the pH. The dielectric spectra were described using the Nettelblad–Niklasson expression combined with a Debye type high-frequency term and analyzed using the Shilov–Dukhin theory and numerical results. The theoretical prediction that the low-frequency dispersion parameters are determined by the co-ion diffusion coefficient was experimentally confirmed. This also allowed to justify an alternative definition of the characteristic time of the low-frequency dispersion. On the contrary, the prediction that the high-frequency dispersion parameters are determined by the diffusion coefficient of counterions could not be confirmed, possibly due to experimental problems. However, the ζ -potential values deduced from high-frequency data were compatible with values deduced from electrophoretic mobility measurements. Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Grosse, Constantino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina

A careful analysis of the main factors that affect the low-frequency dielectric measurements of conducting liquid samples is carried out. The influence of the type of the measurement cell, the calibration method, and the type of the instrument used, on the spectra obtained using the variable electrode spacing technique, is investigated. Permittivity and conductivity measurements in the 10 Hz to 10 MHz range are reported for low (sigma approximately 0.01 S/m) and high (sigma approximately 0.7 S/m) conductivity samples, both electrolyte solutions and polystyrene particle suspensions. Two measurement cells are evaluated: one made of glass currently used at Granada and the other made of acrylic currently used at Tucumán. Two calibration methods, the classical Short/Open correction and the quadrupolar technique (similar to the Short/Open/Load correction), are contrasted, and two impedance analyzers, the HP 4284 A and the HP 4192 A, are compared. Copyright 2000 Academic Press.

The dielectric properties of suspensions of spherical polystyrene particles with radii of 34 and 50 nm, in aqueous electrolyte solutions were measured in the frequency range of 10 kHz to 30 GHz using HP 4192A impedance and 8753A network analyzers, and double path interferometers. The samples were prepared from the stock suspensions with a high particle concentration (volume fraction of 0.4), which were used either unchanged or diluted with increasing amounts of water down to a concentration of 0.05. The permittivity and total loss spectra showed three well-defined relaxation regions, which could successfully be interpreted using an existing model [Grosse, C., J. Phys. Chem. 92, 3905 (1988)] (corrected by including a term of counterion diffusion on the particle surface). A model spectral function was fitted to the data using seven free parameters: the static conductivity of the electrolyte solution, three parameters associated with the relaxation of the electrolyte solution, and just three parameters for the description of both the counterion and the Maxwell-Wagner relaxations. For different particle concentrations, the values of the surface conductivity (obtained from the Maxwell-Wagner parameters) remained essentially constant, while the low-frequency relaxation parameters exhibited very good agreement with theoretical predictions in Delgado, A. V., Arroyo, F. J., Gonzales-Caballero, F., Shilov, V. N., and Borkovskaya, Yu. B., Colloids Surf. A, in press. Copyright 1998 Academic Press.

Fabrication, current-voltage characterization and analytical modeling of an AlInP-passivated GaAs nanowire (NW) ensemble device are presented. During fabrication, sonication was used as a novel and crucial step to ensure effective contacting of the NWs. Current-voltage characteristics of the passivated NW devices were fitted using an analytical surface depletion and transport model which improves upon established models by implementing a non-uniform density of GaAs surface states across the bandgap and including a NW diameter distribution. Scanning electron microscopy, capacitance-voltage characterization and secondary ion mass spectrometry were used to fix key parameters in the model. A 43% decrease in surface state density was achieved upon passivation, corresponding to an impressive four order of magnitude increase in the effective carrier concentration of the NWs. Moreover, the thickest NWs in the ensemble were found to dictate the device characteristics, which is a behavior that should be common to all ensemble NW devices with a distribution in radius. As final confirmation of effective passivation, time-resolved photoluminescence measurements showed a 25x improvement in carrier lifetime upon passivation. The fabrication and passivation methods used can be easily implemented into future optoelectronic applications. Fil: Chia, A. C. E.. Mc Master University; Canadá Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucuman. Facultad de Cs.exactas y Tecnologia. Departamento de Fisica. Departamento de Nanomateriales y Prop. Dielectricas; Argentina Fil: Thouin, F.. University Of Montreal; Canadá Fil: Leonelli, R.. University Of Montreal; Canadá Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentina Fil: Lapierre, R. R.. Mc Master University; Canadá

Hierarchical ZnO nanostructures (such as nanowires, nanocombs and nanohedgehogs) were grown by means of a vapor-phase transport technique in a tubular furnace. Silicon based substrates were used, over which Au nanoclusters were deposited as growth catalyzers. We study the two-photon absorption induced photoluminescence (TPPL) from the various ZnO nanoobjects grown using a micrometer sized polarised laser beam as the excitation source. The UV region of the TPPL spectra contains various peaks whose different patterns depend on the type of nanostructure and its orientation with respect to the incident polarization. We identify the peaks in the TPPL spectra, which are found to be dominated by free exciton emission and their phonon replicas. For the nanocomb, however, Fabry-Perot modes originating from optical multiple reflections within the comb's teeth are demonstrated.

Synchrotron x-ray absorption spectroscopy (XAS) and electron spin resonance (ESR) experiments were performed to determine, in combination with Raman spectroscopy and x-ray diffraction (XRD) data from previous reports, the structure and paramagnetic defect status of Si-nanoclusters (ncls) at various intermediate formation stages in Si-rich Si oxide films having different Si concentrations (y = 0.36-0.42 in Si(y)O(1-y)), fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition and isochronally (2 h) annealed at various temperatures (T(a) = 900-1100 °C) under either Ar or (Ar + 5%H(2)) atmospheres. The corresponding emission properties were studied by stationary and time dependent photoluminescence (PL) spectroscopy in correlation with the structural and defect properties. To explain the experimental data, we propose crystallization by nucleation within already existing amorphous Si-ncls as the mechanism for the formation of the Si nanocrystals in the oxide matrix. The cluster-size dependent partial crystallization of Si-ncls at intermediate T(a) can be qualitatively understood in terms of a 'crystalline core-amorphous shell' Si-ncl model. The amorphous shell, which is invisible in most diffraction and electron microscopy experiments, is found to have an important impact on light emission. As the crystalline core grows at the expense of a thinning amorphous shell with increasing T(a), the PL undergoes a transition from a regime dominated by disorder-induced effects to a situation where quantum confinement of excitons prevails.