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Optical properties of ZnO-CdTe electrochemically prepared on a core-shell nanostructure (NS) were studied. Numerical simulations based on effective medium approximation give higher absorption than ZnO-CdS samples and a sensitive dependence on CdTe content. The absorption edges for deep black samples found by transmittance (T(λ)) and diffuse reflectance (Rdiff(λ)) measurements were at 1.33eV and 1.55eV, respectively. A split-off band edge was also found by Rdiff(λ) at ∼2.5eV. The red shift observed in T(λ), previously observed in ZnO-CdS, and may confirm the enhancement of sub-bandgap absorption due to the NS nature of samples.

The microstructural, morphological, optical and water-adsorption properties of nanocrystalline ZnO thin films and ZnO nanowires were studied and compared. The ZnO thin films were obtained by a sol-gel process, while the ZnO nanowires were electrochemically grown onto a ZnO sol-gel spin-coated seed layer. Thin films and nanowire samples were deposited onto crystalline quartz substrates covered by an Au electrode, able to be used in a quartz crystal microbalance. X-ray diffraction measurements reveal in both cases a typical diffraction pattern of ZnO wurtzite structure. Scanning electron microscopic images of nanowire samples show the presence of nanowires with hexagonal sections, with diameters ranging from 30 to 90. nm. Optical characterization reveals a bandgap energy of 3.29. eV for the nanowires and 3.35. eV for the thin films. A quartz crystal microbalance placed in a vacuum chamber was used to quantify the amount and kinetics of water adsorption onto the samples. Nanowire samples, which have higher surface areas than the thin films, adsorb significantly more water. Fil: Broitman, E.. Linköping University; Suecia Fil: Bojorge, Claudia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina Fil: Elhordoy, F.. Universidad de la República; Uruguay Fil: Kent, V. R.. Universidad de la República; Uruguay Fil: Zanini Gadioli, G.. Universidade Estadual de Campinas; Brasil Fil: Marotti, R. E.. Universidad de la República; Uruguay Fil: Canepa, Horacio Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina Fil: Dalchiele, E. A.. Universidad de la República; Uruguay

In this study, we examined the synthesis of Prussian blue onto p-Si(100). The Prussian blue formation was carried out by means of the deposition of a Fe film and then its dissolution in presence of potassium hexacyanoferrate(II). In the first stage, a study by cyclic voltammetry was carried out, and then, using the potential step method, the corresponding nucleation and growth mechanism were determined. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy was carried out. The results are consistent with a 3D progressive nucleation with diffusion-controlled growth. Finally, this research is oriented to construct electrochemical storage devices which can be in situ loaded by the photovoltaic action of the semiconductor base material doped silicon.

ublica, Montevideo, Uruguay The effects of bath temperature on the electrodeposition of zinc oxide (ZnO) thin films from zinc perchlorate and molecular oxygen, dissolved in dimethylsulfoxide, are reported. The obtained films were highly compact and homogeneous. Scanning electron microscopy images showed that they were formed by nanometric crystallites whose sizes are dependent on bath temperature. Inversely dependence was found between the band-gap (Eg) of the semiconductor with estimated diameters (D) of the crystallites, which corresponds well with quantum confinement effects.

The direct template-free synthesis and characterization of CdO nanorods (NRs) obtained through electrochemical reduction process of molecular oxygen (O 2 ) in a dimethylsulfoxide solution containing CdCl 2 are reported. X-ray diffraction characterization of the NRs shows that the CdO phase was obtained without the presence of any other secondary phases. In agreement with the aspect ratio of a typical nanorod structure, CdO NRs presented average diameters of ca . 170 nm and average lengths of ca . 920 nm. Current results also demonstrate that the employed electrochemical synthesis route favors the growth of NRs with a preferred crystallographic orientation along the [200] axis direction. The synthesized CdO NRs exhibited a n-type semiconductor character with a donor carrier concentration of N D = 4.3 × 10 19 cm − 3 .

The electrochemical deposition of ZnO nanowires (NW) was optimized by growing onto a previously deposited seed layer. The ZnO seed layer was prepared by a sol―gel process from different precursor solutions and deposited onto FTO/glass by spin coating. Afterwards, NW were electrochemically grown onto those seed layers. The electrolyte was an aqueous solution of the Zn +2 precursor (1 mM zinc acetate) and a supporting electrolyte (0.1 M sodium acetate), saturated with bubbling oxygen. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmittance. The XRD measurements show typical diffraction pattern of ZnO wurtzite structure. The SEM micrographs show the presence of smooth NW with hexagonal sections with diameters ranging from 40 to 250 nm. The optical transmittance reveals the presence of ZnO with bandgap energy between 3.23 and 3.29 eV. These spectra show a monotonically increasing transmittance from the UV into the red part of the spectrum. This feature may be originated in the dispersion of light at the NW and can be used to enhance below-gap absorption.

The influence of electrodeposition potential, pH, composition and temperature of the electrolytic bath on the structure of cobalt nanowires arrays electrodeposited into anodic aluminum oxide (AAO) porous membranes is reported. XRD, SEM, and TEM analysis were employed to characterize structural (crystal phase, crystallographic texture, and grain size), and morphological nanowire properties. It was confirmed that at pH 2 the electrodeposition potential has not influence on the preferred crystallographic orientation of the electrochemically grown Co nanowires. At pH 4 the electrodeposition potential controls the growth of cobalt nanowires along some preferential crystallographic planes. The electrolytic pH bath modulates the fcc or hcp phase exhibited by the cobalt nanowires. Single crystalline nanowires with a hcp phase strongly oriented along the (2021) crystallographic plane were obtained at pH 4 and at -1.1 V (vs. Ag/AgCl), a result not previously reported. High electrolytic bath temperatures contributed to improve the single crystalline character of the cobalt nanowires. The presence of chloride anion in the electrolytic bath also influenced on the structural properties of the resulting cobalt nanowires, improving their crystallinity. The optical reflectance of the samples shows a structure in the UV-blue region that can be assigned to the two-dimensional morphology arising in the shape of the almost parallel nanowires. Magnetic measurements showed that different electrodeposition potentials and electrolytic bath pH lead to different magnetic anisotropies on the nanowire array samples.

In this study we examined the rhenium electrodeposition process onto p-Si(100) from acidic media. The study was carried out by means of cyclic voltammetry and the potential-steps method from which the corresponding nucleation and growth mechanism were determined. Both methods were performed under illumination using a solar simulator for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy. An energetic characterization through capacitance measurements (Mott–Schottky plots and parallel capacitance) of the p-Si/NO3− and p-Si/Re/NO3− interfaces was done. The photoelectrochemical reduction of nitrate ions, PERN, on the different p-Si/Re electrode systems synthesized was studied. An overpotential decrease of 0.3 V and a photocurrent increase for the PERN on p-Si(100)/Re electrode systems compared with p-Si(100) and metallic Re was found. Finally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy. A brief analysis from this technique was done. According to these results, the p-Si/Re electrode system could be a potential photoelectrocatalyst for the PERN.

This paper examines the influence of electrodeposition potential, pore size, pH, composition, and temperature of the electrolytic bath on the structure of nickel nanowires arrays electrodeposited into anodic alumina oxide porous membranes. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy analysis were employed to characterize the structural and morphological properties of the nanowires. Results show that the electrodeposition potential controls the growth of nickel nanowires along some preferential crystallographic planes. At -0.90 V (vs. Ag/AgCl) single crystalline nanowires with a strong (111) orientation were obtained. High temperatures and a moderately acid pH solution contributed to improve the single crystalline character of nanowires. The presence of chloride ions produced polycrystalline nanowires at low temperature and single crystalline nanowires at high temperature. The influence of the electrodeposition potential in their magnetic anisotropies is also reported.

The electrochemical reduction of O2 in a dimethyl sulfoxide DMSO solution onto a glassy carbon substrate at 423 K has been studied. Electrochemical potentiodynamic studies show that the reduction process is controlled by O2 diffusion and reveal a two-step mechanism. The first one corresponds to an electrochemical step which gives the superoxide ion that, in a second chemical step, forms the peroxide ions through a disproportion reaction. The proposed mechanism can be used for the formation of semiconductor CdO thin films. Here, results for CdO film formation, obtained in a direct way without the presence of CdOH2 The metal oxides and peroxides are materials of great interest in current research. This is because, while some of them have low conductance, many others usually called TCOs for transparent con- ducting oxides can exhibit high electrical conductivity and optical transparency and can be grown efficiently as thin films. Moreover, they are extensively used for a variety of applications such as pho- tovoltaic solar cells, 1 phototransistors, 2 photodiodes, 3 and gas sensors. 4 Different methods can be used for their synthesis. 5-10 A common preparation method of these materials is the chemical bath deposition CBD 11,12 in an aqueous solution. However, this tech- nique has the disadvantage of forming deposits that include, besides the desired metal-oxide phase, the presence of metallic hydroxides, which implies the need for a postdeposition thermal treatment. 13 Alternatively, the electrodeposition of these materials can be carried out in an organic solution starting from the electrochemical reduc- tion of molecular oxygen. In fact, the electrochemical reduction of O2 in aprotic solvents has been known since 1965. 14-18 These studies have included the effect of the solvent as well as the employed metallic substrate. 19 However, an adequate comprehension of the oxygen reduction mechanism at high temperature is of great impor- tance when dealing with the formation of metallic oxide or peroxide thin films by electrochemical methods. concentration was obtained by a cathodic pulse developed at 0.75 V onto a GC electrode in an O2-saturated DMSO solution. The concentration of O2 was calculated from the difference between the total charge and the capacitive charge, both obtained by the integra- tion of i/t responses in the O2/LiCl/DMSO and LiCl/DMSO solu- tions, respectively. Considering a two-electron mechanism, the mo- lecular oxygen concentration was 0.48 mM at 423 K. The potentiodynamic studies as well as the film deposition experiments were made in darkness using a conventional three-electrode electro- chemical cell connected to an Autolab PGSTAT30 potentiostat. The GC electrode was mechanically polished with 0.03 m alumina, washed with deionized water, and afterward dried by an argon flow. A platinum wire separated from the GC by a glass frit was used as a counter electrode and a Ag/AgClsat electrode was used as a refer- ence one E Ag/AgClsat 0 = + 0.192 V vs normal hydrogen electrode. For the CdO synthesis, the films were prepared at 423 K by a cathodic pulse developed at 1.00 V on glass electrodes covered with SnO2:F fluorine-doped tin oxide, FTO from 20 mM CdCl2 Aldrich 99.9% and 0.10 M LiCl in the O2-saturated DMSO solu- tion. The oxygen content was adjusted according to the same proce- dure indicated previously. The properties of the CdO films were studied by X-ray diffraction XRD spectroscopy with a Philips PW3710 diffractometer using Cu K radiation. The morphology and topology of the films were obtained by scanning electron mi- croscopy SEM using a JEOL JSM-5900LV instrument and atomic force microscopy AFM Digital Instruments NanoScope IIIA series employed in the "tapping" mode at a scan rate of 10.0 m/s, re- spectively. The effect of the thermal treatment on the optical prop- erties of the CdO films was obtained at room temperature by a Shimadzu UV-160A double-beam spectrophotometer using a clean FTO glass as a reference. For this, the films were annealed at 623 K for 2 h under oxygen flux in a Lindberg/Blue M Tube Furnace.

Nanocrystalline zinc oxide films have been obtained by the sol-gel process. The films were deposited from precursor solutions by dip-coating on quartz substrates, and subsequently transformed into nanocrystalline pure or aluminium-doped ZnO films after a thermal treatment. The film microstructure and composition characterization was studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical properties were studied by transmittance spectroscopy. The water adsorption energy was measured by temperature programmed desorption (TPD) in the range 90-700 K. The optical transmittance in the UV region gives bandgap energy values of 3.27 eV for undoped samples, and higher than 3.30 eV for the Al-doped ones. The increase in bandgap energy in Al-doped samples may be explained by band-filling effects. The band edge absorption coefficient increases monotonically for the Al-doped samples but has a shoulder for the undoped ones, which may be assigned to room-temperature excitonic absorption. Fil: Marotti, R. E.. Universidad de la República; Uruguay Fil: Bojorge, Claudia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; Argentina. Repsol-YPF; Argentina Fil: Broitman, E.. Carnegie Mellon University; Estados Unidos Fil: Canepa, Horacio Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas. Centro de Investigaciones en Sólidos; Argentina. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas; Argentina Fil: Badán, J. A.. Universidad de la República; Uruguay Fil: Dalchiele, E. A.. Universidad de la República; Uruguay Fil: Gellman, A. J.. Carnegie Mellon University; Estados Unidos

Detailed information about the electrochemical and physicochemical phenomena associated with copper nanowire growth within the nanosized pores of polycarbonate track-etched membranes (PCM) was in situ obtained by electrochemical impedance spectroscopy. From an equivalent circuit that reproduces the ac-impedance results, it was found that the charge-transfer resistances associated with the Cu 2+ → Cu + and Cu + → Cu° electrochemical processes presented low and high values, respectively. It was also possible to observe the change from a diffusional growth process inside the pores (first stages) to a growth process in solution (film formation onto PCM).

Highly crystallographically-oriented single-crystalline copper nanowire arrays were electrochemically deposited into nanoporous commercial alumina templates. A gold/copper backward contact was needed in the template, while the nanowires were grown from a 0.5 M CuSO4·5H2O solution adjusted to pH=1. The kinetics of the growing process is studied by means of current vs. time curves. The pore filling is between 80 to 90%. The structure and morphology of the wires are studied by XRD, SEM and TEM. The wires have an average diameter of 150 nm corresponding to the pore diameter of the template, with the cubic face-centered copper structure. This structure is highly oriented along the [100] direction parallel to the wire axis. The preferential growing along this direction was not previously found in the literature, which may have interesting applications when such direction is required.

CdS thin films were deposited by chemical bath deposition onto glass substrates from chemical bath containing cadmium sulfate, thiourea and ammonia at pH=10.5. The temperature of the bath was maintained at either 75°C or 85°C and under mill stirring. After that the samples were annealed in air at 450°C. Analysis of the as-deposited thin films by energy dispersive X-ray analysis showed that almost all samples have a stoichiometric composition. The morphology of CdS films has been investigated by atomic force microscopy. The structural properties were determined by XRD and a cubic zincblende phase was present in all of the as-grown samples. Evidence of a wurtzite phase appeared after annealing. Grain sizes between 85 and 205 A were determined from the XRD diffraction peak broadening. The sizes increase with both bath temperature and annealing. The optical properties were studied measuring the transmittance spectra. The room-temperature bandgap energies for each sample were determined from the transmittance by two different methods: extrapolating absorption coefficient and first derivative peak position. The bandgap energy varies from 2.48 to 2.35 eV following closely the quantum confinement dependence of energy against crystallite radius. This shows that the absorption edges of these samples are determined primarily by the grain sizes.

In present work we report the one step electrodeposition of ZnX (X = Se y Te) thin films in acid solution. In order to establish the appropriate conditions for the electrodeposition, a voltammetric and photovoltammetric study on different substrates was previously performed. The films were analyzed by different techniques (SEM, EDS, XRD and optical reflectance). The composition of the ZnTe films was very close to the stoichiometric one, instead, ZnSe films presented a selenium excess that can be eliminated with a proper annealing. Optical reflectance characterization of ZnSe and ZnTe samples grown on titanium gave direct band gaps values of 2.64 eV and 2.27 eV, respectively, in agreement with those reported in the bibliography. El presente trabajo describe la síntesis y la caracterización de películas delgadas de ZnX (X = Se y Te) obtenidas por electrodeposición a potencial constante en medio ácido. Previamente, se realizó un estudio voltamétrico y fotovoltamétrico sobre diferentes substratos conductores los que permitieron determinar las mejores condiciones para la electro obtención de estos compuestos. Las películas delgadas de ZnSe y de ZnTe fueron analizadas por diferentes técnicas (SEM, EDS, XRD y medidas ópticas). Las películas de ZnTe presentaron una composición muy cercana a la estequiometrica, en tanto que las de ZnSe presentaron un exceso de Se el cual puede ser eliminado por un adecuado tratamiento térmico. La caracterización óptica de ambos semiconductores depositados sobre titanio arrojó valores de ancho de banda prohibida de transición directa de 2,64 eV para ZnSe y 2,27 eV para ZnTe, muy cercanos a los aceptados en bibliografía.

ZnO/CdS core/shell nanorod arrays were fabricated by a two-step method. Single-crystalline ZnO nanorod arrays were first electrochemically grown on SnO2:F (FTO) glass substrates. Then, CdS nanocrystals were deposited onto the ZnO nanorods, using the successive ion layer adsorption and reaction (SILAR) technique, to form core/shell nanocable architectures. Structural, morphological and optical properties of the nanorod heterojunctions were investigated. The results indicate that CdS single-crystalline domains with a mean diameter of about 7 nm are uniformly and conformally covered on the surface of the single-crystalline ZnO nanorods. ZnO absorption with a bandgap energy value of 3.30 ± 0.02 eV is present in all optical transmittance spectra. Another absorption edge close to 500 nm corresponding to CdS with bandgap energy values between 2.43 and 2.59 eV is observed. The dispersion in this value may originate in quantum confinement inside the nanocrystalline material. The appearance of both edges corresponds with the separation of ZnO and CdS phases and reveals the absorption increase due to CdS sensitizer. The photovoltaic performance of the resulting ZnO/CdS core/shell nanorod arrays has been investigated as solar cell photoanodes in a photoelectrochemical cell under white illumination. In comparison with bare ZnO nanorod arrays, a 13-fold enhancement in photoactivity was observed using the ZnO/CdS coaxial heterostructures. (Some figures may appear in colour only in the online journal)

Single-crystalline n-type silicon nanowire (n-SiNW) arrays have been synthesized by electroless metal deposition on a silicon wafer chip in an ionic Ag/HF solution through selective etching. The photoelectrochemical properties of the SiNW arrays were studied (under 40 mW cm -2 white illumination conditions) in an aqueous electrolyte [with Fe(CN) 4- 6 /Fe(CN) 3- 6 redox couple] and compared to those of its untreated bare polished Si sample counterpart (n-Si). The open-circuit photovoltage was lower, on average, for SiNWs array photoelectrodes, while short-circuit current density, fill factor, and overall energy conversion efficiency of the SiNWs array photoelectrodes were generally superior to those of the n-Si junction devices.