Papers by Eduardo Cartagena
The direct template-free synthesis and characterization of CdO nanorods (NRs) obtained through el... more 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 .
In this work morphological, structural and photoelectrochemical properties of n-type α-Fe 2 O 3 (... more In this work morphological, structural and photoelectrochemical properties of n-type α-Fe 2 O 3 (hematite) thin films synthetized by means of two different electrochemical procedures: potential cycling electrodeposition (PC) and potential pulsed electrodeposition (PP) have been studied. The X-ray diffraction measurements showed that the films obtained after a thermal treatment at 520°C present a nanocrystalline character. Scanning electron microscopy allowed finding that hematite films obtained by PP technique exhibit nanostructured morphology. The electrochemical and capacitance (Mott-Schottky and parallel capacitance) measurements showed that when in the PC and PP procedures the anodic limit E λ,A is being made more anodic, a decrease of the majority carriers concentration (N D ) and the surface states number has been observed. The photovoltammetry measurements indicated that the hematite films formed with the PP technique present a photocurrent one order of magnitude higher than the ones exhibited by the iron oxide films formed by PC. For instance, PP hematite films exhibit photovoltaic conversion efficiencies of 0.96% which are 2.5 times higher than the corresponding to the PC ones (0.38%). The maximum incident photon-to-current efficiency measured at λ = 370 and 600 nm was observed for hematite films grown by the PP procedure. By means of the photocurrent transient technique a decrease in the recombination process for those samples synthesized by PP was observed. The results obtained are discussed considering the influence of the anodic limit of the potential employed during the preparation of the iron oxyhydroxide (β-FeOOH) precursor film, all of this related to a decrease of the oxygen defects in this material and to a decrease of Fe(II) amount that is formed during the electrodeposition process.
Nickel oxide (NiO) thin films were prepared onto ITO/glass substrates by spin-coating, dipping an... more 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 (I 2 /I À ) 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%. D
The present work comparatively studies the optical properties of CdO against CdSe samples potenti... more 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.
Rhenium thin films were prepared by electrodeposition from an aqueous solution containing 0.1 M N... more Rhenium thin films were prepared by electrodeposition from an aqueous solution containing 0.1 M Na 2 SO 4 +H 2 SO 4 , pH 2 in presence of y mM HReO 4 . As substrates polycrystalline gold ( y=0.75 mM HReO 4 ) and monocrystalline n-Si(100) ( y=40 mM HReO 4 ) were used. The electrochemical growth of rhenium was studied by cyclic voltammetry and electrochemical quartz microbalance on gold electrodes. The results found in the potential region before the hydrogen evolution reaction (her) showed that ReO 3 , ReO 2 and Re 2 O 3 with different hydration grades can be formed. In the potential region where the her is occurring, either on gold or n-Si(100) the electrodeposition of metallic rhenium takes place. On both substrates, rhenium films were formed by electrolysis at constant potential and X-ray photoelectron spectroscopy technique was used to characterise these deposits. It was concluded that the electrodeposited films were of metallic rhenium and only the uppermost atomic layer contained rhenium oxide species. D
In this study we examined the rhenium electrodeposition process onto p-Si(100) from acidic media.... more 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, diffusioncontrolled 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/NO 3 − and p-Si/Re/NO 3 − interfaces was done.
A new copolymer derived from 2,7-carbazole with thiophene is reported. This copolymer was obtaine... more A new copolymer derived from 2,7-carbazole with thiophene is reported. This copolymer was obtained through the synthesis of 2,7-dibromo-N-methyl carbazole and 2-bromothiophene using a Kumada-type reaction to bond both rings and using two different kinds of Pd catalysts, [Pd(OAc) 2 ] and [Pd(PPh 3 ) 4 ], with significant differences in their yields. The trimer that was obtained was subsequently electropolymerized using cyclic voltammetry, and the photoelectrochemical properties were determined. Polymerization using electrochemistry showed that the trimer contains two types of possible bonds for the formation of the macromolecule, which led to the formation of two distinctly different materials. The obtained materials exhibit promising photoelectric responses suggesting that they both can be explored in the designing of photovoltaic cells.
The influence of the processing parameters on the synthesis of low-density polyethylene (LDPE)/or... more The influence of the processing parameters on the synthesis of low-density polyethylene (LDPE)/organically modified montmorillonite (OMM) nanocomposite films was studied using experimental design. Intercalation in the nanocomposites was analysed using X-ray diffraction and verified using atomic force microscopy. Four direct melt processing parameters were studied to obtain surface maps of intercalation in the nanocomposites: concentration of OMM (clay-%), concentration of Polybond 3149 (compatibilizer-%), mixing temperature (T mix ) and mixing time. An ANOVA validated the polynomial function, and intercalation maps from response surface methodology (RSM) were obtained. The clay-% parameter had the most significant effect, and T mix showed no significant effect on intercalation (p < 0.05). A strong synergic interaction between clay-% and compatibilizer-% was observed, which is not possible to detect using univariate experiments. RSM provides a powerful tool for choosing the best processing conditions that lead to formulations with the highest intercalations by considering the main factors and their interactions.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. Th... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
Pure and 10% Pt-loaded tungsten oxide thin films have been successfully prepared by direct UV irr... more Pure and 10% Pt-loaded tungsten oxide thin films have been successfully prepared by direct UV irradiation of bis(b-diketonate)dioxotungsten(VI) and Pt(II) precursor complexes spin-coated on Si(1 0 0) substrates. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500°C. The results of XRD and AFM analysis showed that the as-photodeposited films are amorphous and have a rougher surface than thermally treated films. Post-annealing of the films in air at 500°C transforms the oxides to a monoclinic WO 3 phase. Gas sensing tests reveal that annealed 10% Pt/WO 3 films exhibit a better response than unloaded WO 3 films towards 20 ppm carbon monoxide at an operating temperature of 350°C. The sensors also posses fast response and recovery characteristics.
In this study, we examined the characterization of Prussian blue deposited onto p-Si(100). A cycl... more 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 quasireversibility 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. .
Indium (III) oxide (In 2 O 3 ) thin films have been obtained after heat treatment of In(OH) 3 pre... more Indium (III) oxide (In 2 O 3 ) thin films have been obtained after heat treatment of In(OH) 3 precursor layers grown by a potential cycling electrodeposition (PCED) method from a dimethylsulfoxide (DMSO) based electrolytic solution onto fluorine-doped tin oxide (FTO) coated glass substrates. X-ray diffraction (XRD) measurements indicate the formation of a polycrystalline In 2 O 3 phase with a cubic structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed a smooth morphology of the In 2 O 3 thin films after an optimized heat treatment had been developed. The surface composition and chemical state of the semiconductor films was established by X-ray photoelectron spectroscopy analysis. The nature of the semiconductor material, flat band potential and donor density were determined from Mott-Schottky plots. This study reveals that the In 2 O 3 films exhibited n-type conductivity with an average donor density of 2.2 Â 10 17 cm À3 . The optical characteristics were determined through transmittance spectra. The direct and indirect band gap values obtained are according to the accepted values for the In 2 O 3 films of 2.83 and 3.54 eV for the indirect and direct band gap values.
In this study we examined the influence of the illumination intensity and the presence of poly(et... more In this study we examined the influence of the illumination intensity and the presence of poly(ethylene oxide) (PEO) as an additive for the process of copper electrodeposition onto p-Si(100). The study was carried out by means of cyclic voltammetry (CV) and the potential step method from which the corresponding nucleation and growth mechanism (NGM) were determined. Both methods were performed under illumination for the electron's photogeneration. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy (AFM) was carried out. In the first stage, Mott-Schottky measurements were taken to characterize the energetic of the semiconductor/electrolyte interface. The CV results indicated that the presence of PEO inhibits the electrochemical reaction of oxide formation on the surface of the semiconductor. This allows a decrease in the overpotential associated with the electrodeposition process. The analysis of the j/t transients shows that in the absence of additive the NGM corresponds to progressive 3D diffusional controlled (PN3D DIFF ), while in the presence of PEO the NGM corresponds to instantaneous 3D diffusional controlled (IN3D DIFF ). In both cases analysis by the AFM technique was performed and confirmed these mechanisms. The morphologic analysis by this technique led us to the conclusion that the deposits made in the presence of additive are more homogeneous.
In this study, we examined the influence of illumination and the presence of poly(ethylene oxide)... more In this study, we examined the influence of illumination and the presence of poly(ethylene oxide) (PEO) as an additive for the copper electrodeposition process onto n-Si(100). The study was carried out by means of cyclic voltammetry (CV) and the potential steps method, from which the corresponding nucleation and growth mechanism (NGM) were determined. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy (AFM) was carried out. In a first stage, Mott-Schottky measurements so as to characterize the energetics of the semiconductor/electrolyte interface were made. Also, parallel capacity measurements were carried out in order to determine the surface state density of the substrate. It was found that when PEO concentration is increased, the number of these surface states decreases. The CV results indicated that the presence of PEO inhibits the photoelectrochemical reaction of oxide formation on the surface of the semiconductor. This allows a decrease in the overpotential associated with the electrodeposition process. The analysis of the j/t transients shows that the NGM corresponds to progressive three-dimensional (3D) diffusional controlled (PN3D Diff ), which was confirmed by the AFM technique. Neither illumination nor the presence of PEO changes the mechanisms. Their influence is in that they diminish the size of the nuclei and the speed with which these are formed, which produces a more homogeneous electrodeposit.
Prussian blue (PB) can be deposited from colloidal solutions (5.4×10 −3 mol PB L −1 , 0.01 mol L ... more Prussian blue (PB) can be deposited from colloidal solutions (5.4×10 −3 mol PB L −1 , 0.01 mol L −1 KNO 3 ) on glassy carbon, either by potential cycling or potentiostatically, provided that the deposition potential is more positive than −0.2 V vs. Hg/Hg 2 Cl 2 . Depending on the deposition potential, the PB particles form either a single layer of Everitt's salt, of PB, or multilayers of Berlin green. Also depending on the electrode potential, the deposition was accompanied by currents which were either only of capacitive nature, or represent the sum of capacitive and faradaic currents. The currents were always limited by the diffusion of the colloidal particles to the electrode surface, i.e., they obeyed the Cottrell equation. The PB layers were characterized by in situ atomic force microscopy.
Amorphous non-stoichiometric molybdenum oxide thin films have been successfully prepared by direc... more Amorphous non-stoichiometric molybdenum oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of molybdenum dioxo tropolonate complexes on Si(100) substrates. Photodeposited films were characterized by X-ray photoelectron spectroscopy (XPS) and the surface morphology examined by Atomic Force Microscopy (AFM). It was found that as-photodeposited films are uniform with rms surface roughness of 231 nm and contain non-stoichiometric oxides (MoO 3 − x ). The results of XRD analysis showed that postannealing of the films in air at 350°C transforms the sub-oxides to α-MoO 3 phase with a much smoother surface morphology (rms = 164 nm). Both, the as-photodeposited and annealed MoO 3 − x films exhibit good optical quality with transparency in the visible region better than 80%. Gas sensing tests reveal that annealed MoO 3 − x films exhibit a better response than as-deposited films towards 50 ppm ammonia at an operating temperature of 350°C.
The electrochemical synthesis of auto-organized TiO 2 arrays generated by Ti anodization in diffe... more The electrochemical synthesis of auto-organized TiO 2 arrays generated by Ti anodization in different nonaqueous electrolytes was analyzed. Propylene carbonatebased electrolytes seem to be good electrolytic media for the controlled growth of titania nanotube structures. Scanning electron microscopy (SEM) analysis indicated that, depending on the media employed in the synthesis of the TiO 2 nanotubes, different aspect ratios (length/diameter) could be obtained. Impedance analysis using the passive pit model gave the electrical properties of the layers during the different stages of nanotubes formation. Mott-Schottky analysis and the impedance results showed that the TiO 2 nanotubes layers were n-type semiconductors with highly defective walls on top of a resistive barrier layer. Photoelectrochemical measurements showed that tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbed onto the TiO 2 nanotube arrays, which could be employed as an efficient photosensitizer for solar-energy conversion by TCPP-sensitized nanotubular TiO 2 electrodes.
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Papers by Eduardo Cartagena