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In this work, the influence of the electrochemical insertion of different alkali ions, e.g., lithium, sodium, and potassium, on the electrochromic properties of copper(II) hexacyanoferrate(III) (CuHCF) was addressed. CuHCF was electrochemically synthesized on FTO substrates, and a nucleation and growth analysis was shown that follows a 3D progressive nucleation with diffusion-controlled growth, which was confirmed by SEM analysis. The spectroelectrochemical study demonstrated that spectral changes were centered into three regions: a green band (506 nm) associated with a charge transfer (FeIII → CuII), a violet band (413 nm) associated with d-d orbital transition for Cu+2 ions, and an ultraviolet band (354 nm) associated with a ligand-metal charge transfer (CN-→ FeIII). This electronic transfer, along with the calculated electrochromic efficiency averages, indicates a relationship between the ionic radius of insertion ions and the deformation generated in CuHCF. An increase in the ionic radius decreases the interatomic charge transfer, which produces a low electrochromic efficiency.

The influence of the incorporation of a nanostructured ZnO layer on the carrier recombination and dynamics of chalcopyrite solar cells was studied. Intensity-modulated photocurrent and photovoltage spectroscopy (IMPS and IMVS, respectively) were used for the charge carrier dynamics characterization of two ZnO/In2S3/CuInS2-based solar cells. The charge carrier dynamics on a cell with a ZnO nanorod (ZnO-NR) layer was compared with a similar sample without the nanostructured layer. The IMPS and IMVS responses were measured at different continuous light intensities, and a multitrapping behavior was observed. Higher recombination and transport times were obtained for the cell including the NR layer. Moreover, an enhancement in the charge carrier collection efficiency was observed for the cell with the NR additional layer. The increased surface-to-volume ratio of the NR layer and the passivation of defects in the ZnO/In2S3 interface could be associated with the observed charge dynamics enhancement.

Transparent conductive oxide electrodes and specifically SnO2:F/glass are widely employed substrates in the preparation of optoelectronic devices. This study deals with the surface effect of commercially SnO2:F/glass electrodes on the properties of ZnO nanowires grown onto them by using an electrochemical method. Four types of commercially SnO2:F/glass with sheet resistances in the range of 7–15 Ω cm−2 and roughness from 9 to 39 nm were used. The deposition process of ZnO nanowires was performed with zero, one, and two ZnO seed layers, respectively. The seed layer was grown from an ethanolic solution of zinc acetate as a Zn2+ precursor, and further, a thermal treatment was performed. The formation of the nanomaterial was carried out by using the potentiostatic method at − 1 V and until reaching a total charge of − 1.5 C at a temperature of 75 °C. Different densities of nanowires were obtained for each case, with diameters ranging from 30 to 400 nm. The SnO2:F/glass roughness affects the diameter and alignment of the ZnO nanowires. Measurements of diffusive spectra in the optical range, as well as the determination of polarization properties, show that the seed layer deposition is indispensable to obtain optimal optical quality. The findings here discussed constitute another critical factor to be considered in the synthesis of well-aligned nanowires.

The optical properties of ZnO nanorod (NR) arrays were investigated by optical total transmittance (TT) and diffuse reflectance (DR) spectroscopy in the visible region. The NRs were grown electrochemically in a three-electrode cell over a glass/fluorine-doped tin oxide (FTO) substrate. The mean length, radius, and density of NR samples were characterized by scanning electron microscopy. The results were correlated with the observed optical properties. Since light scattering for these NR arrays is highly dependent on their morphology, therefore, a model for light scattering based in the Mie theory for cylinders was implemented to understand the observed spectra. The mean scattering and extinction cross sections were calculated from the morphology of the samples. They were used to fit the DR spectra. From the fittings, the TT spectra of the samples could be calculated. A good agreement with the experimental results was obtained. This indicates that the implemented model represents well the observed scattering phenomena.

P-type CuSCN nanorods (NRs) grown on CuSCN seed layers were obtained with modulated diameters through an electrochemical procedure. Their morphological, structural, optical, electrochemical and photoelectrochemical features were studied in depth. Morphology of samples can be tuned from a near vertically and dense 1D nanostructure to a quasi 2D film according the value of the SCN – /Cu 2+ molar ratio ( r ) present in the electrochemical bath. Raman studies confirmed the nature of CuSCN in its beta phase. For low r values CuSCN NRs presented high preferential orientation along the c-axis and high optical scattering at low wavelengths which lead to both low haze and high integrated diffuse reflectance. Band gap values were also affected by the r value thus experiencing a redshift, probably related to both quantum confinement and light dispersion. Electrochemical and photoelectrochemical measurements confirmed the p-type behavior of samples together with the enhancement of their surface at low r values. This knowledge opens new and more objective perspectives in the real use of CuSCN nanostructures in photovoltaics.

Cu2ZnSnS4 (CZTS) thin films were prepared by thermal sulfurization of co-electrodeposited CuZnSn (CZT) metal precursors. Electrodeposition times between 10 and 40 min were used to study the influence of this parameter on the composition, structure, thickness, and morphology of the sulfurized films. CZT precursors and CZTS films were characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and Raman spectroscopy. The morphologies were evaluated by electronic microscopy. The electrodeposition time was found to influence the chemical composition of the metal precursor, especially the Cu and Sn content. Furthermore, XRD results showed the formation of Cu5Zn8, while Sn seemed to be present in an amorphous state. A cauliflower-like morphology was observed in the precursors, especially at long deposition times, which can be related to an electrodeposition mechanism controlled by mass transfer. A significant increase of the film thickness was observed after sulfurization. The morphology changed to round particles and presented a bi-layered structure with an internal compact layer of nanometer size particles and an external layer formed by micrometer-size particles. Raman spectroscopy, XRD, and EDS measurements confirmed the formation of crystalline CZTS after sulfurization. In addition, a disperse Cu2S secondary phase co-existed in the film. Increasing the precursor deposition time increased the amount of secondary phases in the film after sulfurization. Direct energy gap values close to 1.5 eV were estimated for CZTS films using transmittance spectra in the infrared region. CZTS films obtained with short electrodeposition times are promising as absorbers in kesterite thin films solar cells. Fil: Valdes, Matias Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Di Iorio, Yesica Dolores. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Castañeda, K.. Universidad del Quindio; Colombia Fil: Marotti, R.E.. Universidad de la República; Uruguay Fil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

The dynamics of carrier recombination and transport of two CuInS2 superstrate solar cells was studied by intensity modulated photovoltage and photocurrent spectroscopy (IMVS and IMPS respectively). For the analysis of the resulting data two different approaches were implemented. In the first approach, the typically used analysis in Dye Sensitized Solar Cells (DSSC) was adapted to obtain the characteristic times of the processes involved. The second approach was based on the fittings of both the IMVS and IMPS data to the solution of the continuity equation. These fittings allow the calculation of different dynamic parameters of the cells. Moreover, consistency between the obtained parameters was observed, in good agreement with the typical analysis for DSSC. The resulting dynamics was associated with the presence and distribution of defect states among the samples. Moreover, from the performed analysis, a relation between the results and the post-treatment applied to the solar cells could be established. The difference in the dynamics of the cells is mainly observed in the difference between the electron lifetimes of both solar cells. Fil: Pereyra, Carlos J.. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Uruguay Fil: Di Iorio, Yesica Dolores. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Marotti Priero, Ricardo Enrique. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Uruguay

In this study, the electrodeposition of a composition-graded stacked CdS x Se (1–x) multilayer film is a matter which is reported for the first time. The electrodeposition was carried out using CdSO 4 , Na 2 S 2 O 3 and SeO 2 as precursors in an acid solution. Previously, an exhaustive electrochemical study was carried out in order to establish the best condition for the electrodeposition of this structure. In order to confirm the feasibility of the method proposed, CdS x Se (1–x) single-layer films of different composition were electrodeposited and characterized. The electrodeposition of the composition-graded stacked layer arrangement was potentiostatically performed through successive electrodeposition steps in a unique electrolytic solution in which its Se content is gradually increases. The characterization of both, single-layer films and multilayer structure was performed using different techniques, confirming the formation of an alloy between CdS and CdSe. Furthermore, the multilayer structure composition gradually changes from pure CdS to a rich selenium CdS x Se (1–x) compound as the electrolytic solution composition increases its SeO 2 , forming a depth bandgap graded material.

Changes in the polarization state of light due to its interaction (reflection and transmission) with samples of CuSCN nanorod and ZnO nanowire arrays are analyzed and compared following a recently proposed technique (Valente et al., 2019). The determination of the degree of polarization and measurements of diffusive light are used to investigate the influence of the morphology of nanorods and nanowires on the optical properties. It is shown that the CuSCN nanorods are better than ZnO nanowires to preserve polarization, although the degree of polarization decreases with the lengths for both materials. It is shown that the degree of polarization correlate with the diffusive light, which allow an estimation of the large scale uniformity of the samples. However, it is also shown that the loss of polarization quality can be present even in absence of diffusion, which indicates that the interferometric effect on the nanoscale should be an important cause of the depolarizing effect.

This study addresses the synthesis and characterization of iron(III) hexacyanoferrate(II) (Prussian blue, PB) deposited on a semiconductor hematite electrode (α-Fe2O3). The formation of the Prussian blue/hematite interface was carried out by cyclic voltammetry. The modified electrode was morphologically characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), structurally by x-ray diffraction (XRD), and photoelectrochemically by cyclic voltammetry under polychromatic illumination. The structure of the electrode system shows a cauliflower type morphology, with the typical PB structure. The electrochemical characterization indicates an increase of the currents of the low- and high-spin iron systems of PB when the system is illuminated, indicating that photogenerated charge carriers are involved.

The Optical Properties of ZnO Nanorods (NR) sensitized with different semiconductors in Core-Shell nanostructures were studied, comparing them with those of bare ZnO NR. Experimental measurements of Transmittance and Diffuse Reflectance show an increased light absorption at the solar spectrum and the appearances of new absorption edges (AE). The measurements are compared with numerical simulations based on Bruggeman Effective Medium Approximation. An increased absorption with the sensitizer content is observed. For similar changes in filling fractions, CdTe presents higher changes in absorption than CdS. Shifts in the AE are observed experimentally (e.g. between 2.34 eV and 2.66 eV for CdS). These shifts cannot be assigned to sensitizer content or confinement effects. A similar behaviour is observed for CdTe in which the AE measured by transmittance is between 1.31 eV and 1.36 eV, while the one obtained from Kubelka-Munk analysis of reflectance is, for the same samples, 1.57 eV and 1.49 eV, respectively. Moreover, the split-off AE is also observed at 2.55 eV and 2.28 eV. The observed large red-shifts could be associated with an enhancement of the subbandgap absorption due to an increase in the light free path at the core-shell nanostructure.

This study shows the results obtained in the direct electrodeposition of CuFeO 2 thin films from a DMSO based solution. First, a detailed electrochemical study was carried out in order to determinate the best condition for the CuFeO 2 electrodeposition. The films were obtained potentiostatically from a 0.01 M CuCl 2 + 0.005 M Fe(ClO 4 ) 3 + 0.1 M LiClO 4 solution in the presence of molecular oxygen at 50 °C onto FTO/glass substrates. In all cases, the time of electrodeposition was 1000 s. The grown films presented a yellow-reddish color and exhibit an homogeneous aspect. Analyses of composition carried out through EDS, shown that a stoichiometric composition (atomic relation Cu:Fe = 1:1) is obtained at a potential of –0.6 V. However, as-grown films analyzed through XRD experiences did not evidence the presence of CuFeO 2 compound presumably because it is amorphous. An annealing treatment at 650° C for 30 minutes in an argon atmosphere was necessary to transform the solid phase of the as grown films in crystalline CuFeO 2 . Furthermore, the presence of CuFeO 2 has been confirmed through XPS analyses. UV-vis analyzes shown a ladder-like appearance due to the presence of several absorption edges from the IR to the UV spectrum region. The most clearly determined were a direct-like edge at the IR: E g (IR) = 1.64 eV. However, several absorption edges in the visible (E g dir (vis) = 2.35 eV, and E g ind (vis) = 2.03 eV) and UV beginning (E g ind (UV) = 3.37 eV) spectrum region also were observed.

Optical properties of Si nanowire (SiNW) arrays prepared on p-doped Si(111) and Si(100) substrates were studied. SiNWs were synthesized by self-assembly electroless metal deposition nanoelectrochemistry in an ionic silver HF solution through selective etching. Total reflectance (Rt) and total diffuse reflectance (Rdt) of SiNWs change drastically in comparison to polished Si. To understand these changes, diffuse reflectance (Rd) with polarized incident light was studied. For samples prepared on Si(111), the wave length integrated Rd (wIRd) shows maxima at certain angles of incidence θ, regardless of the incident light polarization. For samples prepared on Si(100), wIRd increases with θ and depends on incident light polarization. Also, Rd spectra show structures due to interference effects. Therefore, SiNWs prepared on Si(100) can be considered as thin films whose refractive index depends on light polarization. Moreover, Rdt of SiNWs prepared on Si(111) can be modeled as an ensemble of diffuse reflectors.

Silver nanoparticles have been grown onto crystalline silicon substrates. Three soft-solution one-step processing techniques have been assayed: electroless metal deposition (EMD), electrodeposition (ED) and spray pyrolysis (SP). The shapes exhibited by the silver nanoparticles prepared by EMD and ED are hemispherical, while the shapes of those prepared by SP (for long processing times) are similar to disks of aspect ratio 0.5 approximately. Integrated total reflectance spectra and integrated diffuse reflectance spectra shows distinctive features due to the electronic structure of silicon. Specular reflectance spectra of samples (except those grown by SP with long processing times) show a dip, corresponding to a surface plasmon resonance. Simulations, considering granular composite media were made. The simulated spectra confirm the presence of the spectral dip. Surface plasmon resonance show shifts with the angle of incidence. For samples prepared by ED, the tendency is the same as the one of the model, indicating that there is not much coupling between nanoparticles.

The changes in the polarization state of light due to transmission through ZnO nanowires grown upon FTO substrate is analyzed. It is shown that the inhomogeneities on a nanometric scale induce non trivial changes on the polarization state of light, that turns perfect polarized light into partially polarized light. Correlations are found between the morphology of the NW arrays and the degree of polarization of the transmitted light. It is shown that as the nanowires become longer, the light polarization is more disturbed, while the increase of the nanowire density helps to preserve light polarization.

Nanostructured zinc oxide thin films were spin coated on conductive glass substrates via a sol-gel based technique using zinc acetate dihydrate as precursor. The pH of the alkalis used as catalytic agents in the hydrolysis step is shown to have a strong effect on the structural and morphological properties of the deposited ZnO. The size of the particles was observed by Transmission Electron Microscopy (TEM), while Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) and Atomic Force Microscopy (AFM), were used to analyze the morphology of the films. X-ray iffraction (XRD) and Raman spectra provided evidence of crystal growth together with an increase in the crystalline degree of the hexagonal wurtzite structure after annealing. The bandgap energy was estimated by Tauc´s method and found to decrease after annealing, which is attributed to an increase in the crystallite size and to the presence of less defect sites. A good correlation between crystallite size and absorption edges was found. The photoluminescence spectra of as-deposited samples depend on the nature and pH values of catalytic agent used, and reveal the presence of a broad visible emission attributed to a variety of intrinsic defects. Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Fil: Pereyra, C.J.. Universidad de la República. Facultad de Ingenieria. Instituto de Física. Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales; Uruguay; Fil: Mhlongo, G.H.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica; Fil: Dhlamini, M.S.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica; University of South Africa. Department of Physics; Sudafrica; Fil: Hillie, K.T.. Council for Scientific and Industrial Research. National Centre for Nano-Structured Materials; Sudafrica; University of the Free State. Department of Physics; Sudafrica; Fil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina; Fil: Marotti, R.E.. Universidad de la Republica. Facultad de Ingenieria. Instituto de Fisica y CINQUIFIMA; Uruguay

Reflectance of selective surfaces is numerically simulated from a continuous atomic concentration profile and then compared with experimental data, from a solar selective surface for solar thermal applications. The propagation of electromagnetic radiation is solved by using finite differences equation. Several theoretical models for optical properties of composite materials are compared and a proper mixing procedure is achieved. Results from Bruggeman effective medium theory are verified by comparison with experimental data. These data was obtained from Ni electrochemically impregnated into nanoporous alumina anodized onto an aluminum substrate. Concentration profile was measured using X-ray Photoelectron Spectroscopy. The procedure allows deducing measured reflectance from a very detailed model of the surface in depth, which uses three materials at the same time. This model could be used as a layout for a general three constituents mix for improving properties of solar thermal surfaces.

alaga, Spain CdS quantum dots (QDs) decorated ZnO nanorod (NR) arrays were fabricated by a two-step method. The first step consisted in electrochemical growth of single-crystalline ZnO NR arrays, followed by the novel spin-coating assisted SILAR method for decorating the ZnO NRs with CdS QDs. Structural, morphological and optical characterization of CdS QDs/ZnO NR arrays were done. ZnO NRs had a single crystal wurtzite structure growing along the c-axis. The decorated CdS QDs had a quasi-spherical shape with a mean diameter of about 5 nm. The increase of CdS content produces an increase in the visible part of the absorption spectrum. Bandgap energy values for ZnO between 3.26‐3.29 eV were obtained. For CdS the measured absorption edge values are between 2.35‐2.65 eV (decreasing with the number of coating cycles). Numerical simulations based on effective medium approximation were done to verify these features. The Urbach tail parameter in CdS absorption edge is between 44‐52 meV. The photovoltaic

As-grown and chloride-doped ZnO nanopillars were electrodeposited onto bareFTO/glass and ZnO-compact layer/FTO/glass substrates. To analyse the effect of the presence of chloride ions in the electrolytic bath, NH4Cl was progressively added up to 0.02 mol L-1. As preliminary examination, the morphology of ZnO nanostructures was analysed by SEM micrographs and chlorine incorporation was detected by EDS. Then, a detailed analysis comprising structural, electrical, optical and defect properties was constructed using XRD, electrical resistance measurements and UV-Vis-IR spectroscopy. As the chlorine concentration in the film increases, XRD reveals a displacement of diffracted planes due to macrostrain of the ZnO lattice and the electrical resistance diminishes. Also, the UV optical absorption edge shifts to higher energies due to Moss-Burstein effect which corresponds to electron densities in the order of 1 to 6 x 1019 cm-3, and the infrared spectra reveal the presence of free electrons, allowing a moreprecise determination of the free electron densities. Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Gau, D. L. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Uruguay Fil: Dalchiele, E.A. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Uruguay Fil: Vazquez, Marcela Vivian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Marotti, R.E. Universidad de la Republica. Facultad de Ingeniería. Departamento de Física; Uruguay

Single-crystalline p-type silicon nanowire (SiNW) arrays have been formed by electroless metal deposition on a silicon wafer piece in an ionic Ag/fluorhydric acid (HF) solution through selective etching. They display mechanical properties that are different from those of both bulk silicon and single SiNWs. As any practical application of these materials is likely to involve a large number of nanowires in close proximity to each other, it is necessary to understand the mechanical properties of SiNW arrays. In this work, as a first step to characterize their mechanical properties, the buckling instabilities of the surfaces formed by vertically aligned SiNWs have been studied by nanoindentation tests.

ZnO nanowire arrays were grown by potentiostatic cathodic electrodeposition on aluminum anodic oxide template (AAO) from dimethyl sulfoxide (DMSO) solutions containing zinc chloride and molecular oxygen as precursors. The nanowires presented high aspect ratio and exhibited a very high crystallinity with a wurtzite crystal structure with preferential orientation along the (0001) crystallographic axis. Chronoamperometric experiments were performed on gold bulk electrodes in order to model this preferential mode growth of ZnO nanowires, which has not been previously reported for similar precursors in DMSO solution. The analysis of the corresponding chronoamperograms revealed that chloride ions influence the oxide nucleation and growth mechanism. It was found that in the absence of KCl as a supporting electrolyte, the data fitted an instantaneous three-dimensional diffusion-controlled (IN-3D)diff nucleation and growth mechanism (NGM). The presence of KCl, instead favored a progressive three-dimensional (PN-3D)diff NGM. With these results, a model for the more complex nanowire’s growth inside the pores of the AAO template is proposed.

In this study, we examined the characterization of Prussian blue deposited onto p-Si(100). A cyclic voltammetry analysis was carried out under illumination showing quasi-reversibility responses of high and low-spin iron centres in the deposit. Optical measurements were done, where XRD analysis allowed to determine crystallinity while EDS analysis indicated that there is influence in the number of cycles on the film composition. Reflectance measurements confirm the coloration observed in the films. However a Kubelka–Munk analysis demonstrates the presence of blue greenish coloration which is an indication of a mix between Prussian blue and Berlin green films. 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..

We examined the reduction reaction of nitrate ions on different electrode systems: silicon monocrystalline (n-type and p-type), porous silicon, and silicon modified by electrodeposited metallic rhenium. In a first stage, voltammetric analysis in different HF media was performed. With this technique it was possible to establish the different processes associated to porous silicon formation. The morphology of the porous silicon was studied using AFM. Voltammetric analysis was then performed using different silicon substrates. This was then used to study the electrochemical reduction reaction of nitrate ions. A decrease in the overpotential of the reaction was observed, with a consequent increase in current density when the silicon electrodes were modified by electrodeposited rhenium. Finally, an analysis of the reaction products from the nitrate electroreduction was carried out using photoelectrolysis at controlled potential.

Selective surfaces for solar to thermal conversion were studied for understanding the main parameters affecting selectivity. For this purpose samples of Ni inclusions into nanoporous anodized aluminum were electrochemically prepared. Their optical reflectance from 200 nm to 17 μm was measured showing a step-like behavior and several interference fringes. Different models were used to interpret this behavior varying several of the involved parameters. The composition of Ni/alumina film is the first cause for selectivity. Interference effects occurring in this film strengthen the step-like behavior of the reflectance spectra and therefore, the selectivity.

In the present work, n-type silicon nanowire (n-SiNW) arrays have been synthesized by self-assembly electroless metal deposition (EMD) nanoelectrochemistry. The synthesized n-SiNW arrays have been submitted to scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and optical studies. Initial probes of the solar device conversion properties and the photovoltaic parameters such as short-circuit current, open-circuit potential, and fill factor of the n-SiNW arrays have been explored using a liquid-junction in a photoelectrochemical (PEC) system under white light. Moreover, a direct comparison between the PEC performance of a polished n-Si(100) and the synthesized n-SiNW array photoelectrodes has been done. The PEC performance was significantly enhanced on the n-SiNWs photoelectrodes compared with that on polished n-Si(100).

The present work comparatively studies the optical properties of CdO against CdSe samples potentiostatically electrodeposited onto fluorine-doped tin oxide/glasses (FTO). The films were prepared by electrochemical reduction processes in dimethyl sulfoxide (DMSO) solution. The optical properties are studied by transmittance measurements and diffuse reflectance spectra (DRS). Structural properties of the films were also studied by X-ray diffraction spectroscopy (XRD). For CdSe the direct bandgap energy obtained from both transmittance measurements and first derivative peak position of the DRS is 1.69 ± 0.01 eV. In the case of CdO both direct and indirect gaps were found. Careful deconvolution of the spectra allows assigning the direct bandgap energy at 2.52 eV. A first indirect bandgap appears at 2.03 eV, while it is possible to have a second one at 0.46 eV.

In this study we examined the rhenium photoelectroless deposition process onto p-Si(1 0 0) from HF solutions. In the first stage an energetic characterization through capacitance measurements (Mott–Schottky plots) of the p-Si/HF interface was done. Before the rhenium photoelectroless deposition process, a voltammetric and photovoltammetric analysis of p-Si in ReO 4 - / HF solutions was done. In this study, a decrease of the rhenium deposition charge was observed as a function of the increased HF concentration. This behavior was attributed to competition with the silicon dissolution process when an increased HF concentration was present in the electrolytic bath. A morphologic analysis was completed by means of atomic force microscopy (AFM) for the rhenium deposits obtained by photoelectroless process at different HF concentrations and different deposition times. X-ray photoelectron spectroscopy (XPS) technique was utilized to characterize the rhenium deposits, and it was concluded that the films formed by the photoelectroless process were metallic rhenium with only the uppermost atomic layer containing rhenium oxide species. The hydrogen evolution reaction (HER) on the different p-Si/Re electrode systems synthesized was studied. For the HER on p-Si(1 0 0)/Re electrode systems an overpotential decrease of 0.2 V and a photocurrent increase between one and two orders of magnitude, compared with p-Si(1 0 0) and metallic Re, was found. Additionally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy (IMPS). 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 HER.

The red photoluminescence (PL) band (peaked between 610 and 640 nm) from electrochemically deposited ZnO thin films is studied. The absorption coefficient is obtained from diffuse reflectance measurements. The absorption band edge depends on deposition conditions. The PL peak follows the shift of the band edge. A similar correlation appears when cooling down to 20 K. This suggests that PL is due to a transition from an intrinsic shallow state to an intrinsic deep state. Comparing against ZnO samples showing green PL, the shallow nature of the state is confirmed.

In this work, results on the study of the influence of silver nanowire dimensions on the crystallinity and structural properties are presented. Silver nanowire arrays with high aspect ratios were prepared in the hollow structures of nanoporous templates using potentiostatic electrodeposition. Two types of material were employed as a template: commercial porous anodic aluminum oxide (with a mean pore diameter of 180 nm) and track-etched polycarbonate membranes (with a mean pore diameter of 15, 30 and 80 nm). Characterization of the silver nanowires has been done by EDS, XRD, TEM and electron diffraction. The degree of preferred crystallographic orientation (along the (1 1 1), (2 0 0) or (2 2 0) crystallographic planes) and the crystallite size of the silver nanowires as a function of template pore diameter are given and discussed.

The optical properties of metallic nanowires (NW) grown in a dielectric template are investigated. The metallic NW of copper or of silver were grown into the nanoporous structure of commercially available alumina membranes. The optical reflectance of the metallodielectric samples prepared at different conditions are compared to each other and to unfilled alumina membranes. A simple model based on the Bruggeman approximation can be used to understand the results and to compare them to the bulk material.

The optical properties of nanoporous alumina (Al2O3) prepared by electrochemical anodization of aluminum foils are studied. The samples show an ordered array of nanometric sized pores. Their reflectance spectra show an absorption edge in the UV that shifts into the visible with anodization temperature. A strong photoluminescence (PL) in the blue-green spectral range is also shown. The PL spectra shift in the same direction as the reflectance. The PL spectra were also measured at low temperatures. The results are best interpreted assigning the PL to oxygen vacancies. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Zinc oxide thin films were grown by potentiostatic electrodeposition at different bath temperatures (62–89 °C, and −1 V vs. SCE) from a 0.1 M Zn(NO 3 ) 2 solution. X-ray diffraction (XRD) shows there is crystallite size enlargement as bath temperature increases. The band gap energy values, determined from optical reflectance spectra, are between 3.2 and 3.3 eV, decreasing when the bath temperature increases. A quantum size effect is deduced from the correlation between the band gap energy and the crystallite size.

Silver nanowire arrays with high aspect ratios have been prepared using potentiostatic electrodeposition within the confined nanochannels of a commercial porous anodic aluminium oxide template. The nucleation and growth processes are intensively studied by current versus time transients. Scanning electron microscopy results show that the nanowires have a highly anisotropic structure with diameters and lengths of 170?nm and 58??m, respectively, which coincide with the dimensions of the template used. Structural characterization using x-ray diffraction shows that the Ag nanowires are highly crystalline, and those obtained at higher overpotentials present a very strong [220] preferred crystallographic orientation. The optical properties of the silver nanowires embedded in the alumina template show a clear edge close to 320?nm, that is an expected value for a silver?alumina composite material.

Indium doped ZnO thin films were obtained by co-electrodeposition (precursor and dopant) from aqueous solution. XRD analysis showed typical patterns of the hexagonal ZnO structure for both doped and undoped films. No diffraction peaks of any other structure such as In2O3 or In(OH)3 were found. The incorporation of In into the ZnO film was verified by both EDS and XPS measurements. The bandgap energy of the films varied from 3.27 eV to 3.42 eV, increasing with the In concentration in the solution. This dependence was stronger for the less cathodic potentials. The incorporation of In into the film occurs as both, an In donor state in the ZnO grains and as an amorphous In2O3 at the grain boundaries. D 2005 Elsevier B.V. All rights reserved.

Nickel oxide (NiO) thin films were prepared onto ITO/glass substrates by spin-coating, dipping and electrochemically. Studies of the morphological and structural properties of the films were done by atomic force microscopy (AFM). Photoelectrochemical and optical experiments were carried out in order to characterize the semiconductor properties of the nanostructured NiO thin films. The experiments were also done for Eosin B- and Erythrosin J-sensitized nanostructured NiO films, with the aim to visualize their potential application as photocatodes in tandem dye-sensitized solar cells (TDSSC). The NiO grown by dipping was the one presenting the best morphological properties. The photoelectrochemical results for all the bare NiO, NiO–Eosin B and NiO–Erythrosin J/electrolyte (I2/I−) systems showed a p-type behavior. An enhancement in the photocurrent has been observed for the systems sensitized with the dyes. For the NiO/Erythrosin J system the enhancement of the current under illumination in comparison to the dark current was about 200%.

ZnO thin films were electrochemically deposited onto opaque and transparent substrates (copper and ITO). The electrolyte consisted of a 0.1 M Zn(NO 3 ) 2 solution with the initial pH adjusted to 6.0, different electrodeposition potentials from E =−700 to −1200 mV (saturated calomel electrode, SCE). The resulting samples have the structural, chemical and morphological properties of hexagonal ZnO, with thickness varying from less than 1 μm to almost 30 μm. The bandgap energy varies inversely with film thickness, ranging from less than 3.1 to 3.4 eV. The bandgap also depends on the electrodeposition potential. This result allows to adjust the desired absorption edge within a 30 nm wide region in the UV.

Fil: Berruet, Mariana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

In this study, ZnO thin films have been deposited onto monocrystalline n-type Si(1 0 0) by electrodeposition at different applied potentials. XRD shows a preferential orientation (0 0 0 2) that increases when the applied cathodic potential increases. The XPS analysis presents a Zn/O composition close to stoichiometric. SEM micrographs show a compact structure withlocalized platelets witha grain size of about 10 mm. However, crystallite size determined by the Scherrer method shows a size close to 2.50 � 10 � 2 mm, then the grains can be considered as clusters of crystallites. Optical measurements were made on samples deposited on ITO/glass through the same procedures giving a band gap of 3.3 eV in agreement withth e reported values for ZnO at room temperature. r 2001 Elsevier Science B.V. All rights reserved.

The solar absorptance αs of nanostructured selective surface (NSS) for solar thermal energy is improved. The NSS are prepared by AC electrochemical impregnation of metal inclusions (MI) into porous anodized aluminum oxide (AAO). The dependence of the NSS performance with composition depth profile and MI is studied by numeric simulations based in a gradient index model and effective medium theory. The results are compared with experimental NSS prepared varying three control parameters and MI (Ni, Cu, Ag). The αs is improved to > 85% (keeping thermal emittance εT relatively low) for Ni MI, mainly by increasing MI content. Increasing AAO thickness or MI molecular weight (for a given experimental composition profile) also improves the performance. For Ag the αs was further improved to 90%.