Education
University of Bucharest, Faculty of Chemistry (Department of Physical Chemistry). Licence in Chemistry-1981.
• Doctoral degree in Chemistry, University Politehnica of Bucharest-1996, for studies on electrochemistry of conducting polymers.
Awards
Romanian Academy prize Stefan Procopiu/2004
Expertize
Semiconductor electrochemistry, photoelectrochemistry, nanostructured materials
Patents
1. Printer for the deposition of ultra-thin layers with different physico-chemical properties
Patent number: RO 132082/2019
Inventors: M. Iliescu, M. Lazar, I. Pintilie, L. Vladareanu, T. Necsoiu, V. Stancu, A.G. Tomulescu, C. Stan Besleaga, M. Sima, L. Leonat, E.M. Stanciu, B. Comanescu, V.A. Enuica
2. Method for producing a thermoelectric material
Patent number: RO 12753/2014
Inventors: Marian Sima, Anca Cojocaru, Mariana Sima
3. Zinc/polyaniline compact secondary electric cell
Patent number: RO 114206-B1/1999
Inventors: Marian Sima, Teodor Visan, Mariana Sima
4. Method for drying of sodium iodide
Patent number: RO 91709/1986
Inventor: Marian Sima
Publications
1. WO3 layer sensitized with BiVO4 and MIL-101(Fe) as photoanode for photoelectrochemical water oxidation
Authors:
Sima, M; Vasile, E; Preda, N; Matei, E; Sima, A; Negrila, C
Published: OCT 2023, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 181, 111472, DOI: 10.1016/j.jpcs.2023.111472
Thick tungsten oxide layers were prepared electrophoretically in order to be used as photoanodes in photoelectrochemical water oxidation applications. The highest photocurrent density was obtained for a WO3 layer with thickness of similar to 900 nm. Additionally, WO3/BiVO4 and WO3/BiVO4/MIL-101(Fe) heterojunctions have been fabricated using WO3 layer as substrate. WO3/BiVO4 shows an increased value of the electrochemical active surface area indicating that more sites of this photoanode are activated through the formation of the heterojunction. The small V5+ signals observed in the V 2p XPS spectra of these heterojunctions were attributed to the substitution of V5+ atoms with W6+ atoms on the surface of BiVO4. Excessive W doping of the BiVO4 film determined the decrease of the photoelectrochemical performance of WO3/BiVO4 photoanode. The significant improvement of the photoconversion efficiency of the sample decorated with MIL-101(Fe) indicated that this cocatalyst provides sites more efficiently in the photoelectrochemical process. This performance was correlated with the reduced value of the charge transfer resistance at electrode/electrolyte interface obtained from electrochemical impedance spectroscopy investigation.
2. Water oxidation at photoanodes based on hematite films and nanowire arrays
Authors:
Sima, M; Matei, E; Vasile, E; Sima, A; Preda, N; Logofatu, C
Published: APR 30 2021, THIN SOLID FILMS, 724, DOI: 10.1016/j.tsf.2021.138626
In this paper we report the results of a photoelectrochemical study performed on photoanodes based on hematite nanowire arrays and films prepared on fluoride-doped tin oxide coated glass (FTO) and FTO/TiO2 substrates, respectively by hydrothermal and spray pyrolysis methods. The hematite nanowires grown on FTO/TiO2 substrate are more stable mechanically, longer (1 ?m) and their density on substrate is higher. Hematite film obtained on FTO substrate has a thickness of 92 nm covering uniformly the substrate. X-ray photoelectron spectroscopy measurements showed that hematite samples synthesized on FTO/TiO2 substrate have lower content of oxygen vacancies. The photoelectrochemical performances of the prepared photoanodes are in close connection with the presence or absence of the TiO2 underlayer, with oxygen vacancies content and with their morphological characteristics. Electrochemical impedace spectroscopy was used to investigate the charge transfer kinetics at electrode/electrolyte interface and Mott-Schottky analysis was performed to estimate the flatband potential and the carrier density. TiO2 underlayer led to the formation of defects on the samples surface which induced a positive shift of the flatband potentials compared to that of the bare hematite film. The results showed that the best density photocurrent was obtained with a photoanode of hematite nanowires grown on FTO/TiO2 substrate.
3. Effect of ferroelectric poling on the photoelectrochemical activity of hematite-BaTiO3 nanowire arrays
Authors:
Sima, M; Vasile, E; Preda, N; Sima, A; Matei, E; Logofatu, C
Published: OCT 22 2021, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 46, 36244, DOI: 10.1016/j.ijhydene.2021.08.152
Ferroelectric alpha-Fe2O3/BaTiO3 photoanodes (hematite/BT) were fabricated on FTO and FTO/TiO2 substrates using a hydrothermal process and spin coating along with thermal treatments. The prepared hematite nanowires had length under 1 mu m and the BT film was about 18 nm thick. SEM, TEM and XPS investigations prove the formation of alpha-Fe2O3/BaTiO3 heterojunction structure. The ferroelectric poling of hematite/BT heterojunction was conducted both in propylene carbonate and in air. The photoelectrochemical performance of hematite/BT photoanodes is strongly influenced by the direction of ferroelectric polarization. The positive poling of the hematite/BT prepared on FTO/TiO2 substrate produces a 40.4% photocurrent density enhancement, in comparison with not poled version of the sample. Electrochemical impedance spectroscopy measurements provided usefull information regarding the effect of ferroelectric polarization on the charge transfer kinetics at the photoanode/electrolyte interface. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
4. TiO2/Fe2O3 photoanodes for solar water oxidation prepared via electrodeposition of amorphous precursors
Authors:
Vasile, E; Sima, M; Sima, A; Logofatu, C
Published: JAN 2020, MATERIALS RESEARCH BULLETIN, 121, DOI: 10.1016/j.materresbull.2019.110623
Hematite-titania thin films with various ratios of Ti/Fe have been prepared on FTO substrate via cathodic and anodic deposition of amorphous Ti oxyhydroxide gel (TiOx) and iron oxyhydroxide (FeOOH) films, respectively followed by annealing processes. TiOx underlayer behaved as a template for FeOOH electrodeposition. The photocatalytic behavior of the photoanodes based on the prepared structures was studied. An increased photocurrent density was obtained without anodic shifting of the photocurrent onset potential. Mott-Schottky studies showed that Ti contributes little to donor density in hematite-titania photoanodes prepared by this technique. The impedance measurements suggest that both separation and transfer of charge carriers are promoted in these hematite-titania photoanodes. For comparative studies, hematite-titania photoanodes have been prepared from TiOx and FeOOH precursors formed by spin-coating technique and anodic deposition method, respectively. The photoelectrochemical performance of these photoanodes in the presence of cobalt-phosphate catalyst was also evaluated.
5. PHOTOELECTROCHEMICAL WATER OXIDATION ON HEMATITE FILMS IN NEUTRAL AND ALKALINE ELECTROLYTES
Authors:
Vasile, E; Sima, M; Sima, A
Published: JUL-SEP 2020, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 15, 706, DOI:
Nanostructured hematite prepared via anodic deposition has been studied as photoanode in neutral and alkaline electrolytes. The morphology of the nanostructures was characterized by SEM, XRD analysis was performed to verify the phase of the films, absorption coefficient and band gap were determined from spectrophotometric measurements and the atomic concentration of Sn in hematite film was estimated from XPS measurements. EIS measurements and photocurrent responses showed the different behavior of hematite photoanode in alkaline and neutral electrolytes. The alkaline medium favors the chemisorption of the water molecules on hematite photoanode, contributing to the diminishing of the charge transfer resistance.
6. Graphitic carbon nitride based photoanodes prepared by spray coating method
Authors:
Sima, M; Vasile, E; Sima, A; Preda, N; Logofatu, C
Published: SEP 20 2019, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 44, 24440, DOI: 10.1016/j.ijhydene.2019.07.243
Controlled deposition of g-C3N4 films, used as photoelectrodes in PEC water splitting is still considered a challenge. In this paper, nanosheets of g-C3N4 were deposited on FTO and FTO/TiO2 substrates via spray coating method. This method allows the preparation of g-C3N4 films with a better exposure of nanosheet edges to the solution and light, favoring the photocatalytic process. The morphology, chemical composition and optical properties of these films were investigated, their behavior as photoanodes in photoelectrochemical water splitting being also evaluated. The results evidenced the formation of g-C3N4 films with an enhanced visible light absorption and improved photocatalytic activity. The interaction of these films with TiO2 substrate consists in the insertion of nitrogen species in the TiO2 lattice. A significant increase in bulk donor densities value correlated with a longer lifetime of photogenerated electrons was observed for TiO2/g-C3N4 photoanode. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
7. INVESTIGATION OF THE PHOTOELECTROCHEMICAL BEHAVIOR OF NANOCARBON/MESOPOROUS TiO2 FILMS
Authors:
Sima, M; Vasile, E; Sima, A
Published: OCT-DEC 2019, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 14, 941, DOI:
In this work, we report the influence of nanocarbon deposited on mesoporous TiO2 by spray method on photoelectrochemical performance of the formed photoanodes. Scanning electron microscopy and transmission electron microscopy images confirmed presence of carbon nanoparticles on the surface of anatase TiO2 films. Nanocarbon decorated TiO2 photoanodes were characterized by electrochemical impedance spectroscopy and Mott-Schottky analysis. Charge recombination process was evaluated by measurement of open-circuit voltage decay after interruption the illumination Only a small enhancement of photoelectrochemical performance of these photoanodes was observed. It was attributed to increasing of charge carrier density as a result of nanocarbon deposition on TiO2 film.
8. Piezoelectric ferromagnetic BNT-BT0.08/CoFe2O4 coaxial core-shell composite nanotubes for nanoelectronic devices
Authors:
Cernea, M; Vasile, BS; Surdu, VA; Trusca, R; Sima, M; Craciun, F; Galassi, C
Published: JUL 5 2018, JOURNAL OF ALLOYS AND COMPOUNDS, 752, 388, DOI: 10.1016/j.jallcom.2018.04.146
In this paper we report on a novel 1-D piezoelectric/ferroelectric nanostructure. Composites of piezoelectric (0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) abbreviated as BNT-BT0.08) and ferromagnetic (CoFe2O4) nanotubes were assembled and studied in order to envisage new multifunctional applications. Using a polycarbonate membrane template and sols precursors of BNT-BT(0.08 )and CoFe2O4, heterostructured BNT-BT0.08/CoFe2O4 core-shell composite nanotubes were created. Selective methods such as SEM, TEM, AFM, PFM and MFM were used for the characterization of the as-prepared hybrid piezoelectric/ferromagnetic coaxial nanotubes structure. This composite shows two crystalline phases: rhombohedral BNT-BT0.08 and cubicCoFe(2)O(4). The piezoelectric and ferromagnetic properties have been characterized. Piezo force microscopy (PFM) images evidenced ferroelectric domains with opposite polarity due to lead free piezoelectric BNT-BT0.08 outer tube. Magnetic force microscopy (MFM) images evidenced magnetic domains attributed to the CoFe2O4 inner tube. Magnetic hysteresis curves demonstrate a weak ferromagnetic behavior, accompanied by a linear variation of the magnetization at higher magnetic fields, especially at room temperature. From dielectric measurements, high tunability values reaching about 70% at 0.5 kHz and E = 80 kV/cm have been obtained. An effective dielectric constant epsilon(r) = 32 has been measured. The results obtained from this work provide a base for the design of tubular multi-layered materials with novel functionalities and applications in various multifunctional electronic devices such as actuators, transducers, and energy storage microsystems. (C) 2018 Elsevier B.V. All rights reserved.
9. Investigation of the interactions of PVDF shell films with Ni core submicron wires and AAO matrix
Authors:
Sima, M; Baibarac, M; Vasile, E; Sima, M; Schinteie, GA; Kuncser, V
Published: SEP 15 2018, PHYSICA B-CONDENSED MATTER, 545, 509, DOI: 10.1016/j.physb.2018.07.015
Arrays of Ni submicron wires surrounded by poly (vinylidene fluoride) (PVDF) submicron tubes were prepared via solution-processed polymer and Ni electrodeposition into anodic aluminum oxide template. The PVDF solution was filtered in vacuum through the template and the resulting dried structure was used for the electrodeposition of Ni wires. The obtained core-shell submicron wire structure consists of a metallic magnetic nanowire core of about 50 mu m in length and about 300 nm diameter surrounded by a polymer tube shell with thickness less than 10 nm. The specific ferroelectric beta-phase of the polymer was obtained whereas the magnetic behavior of the Ni-cores was proven to be specific to an array of ferromagnetic Ni cylindrical wires (about 0.62 mu(B)/Ni atom) with magnetization reversal mechanisms dominated by dipolar interactions and domain wall displacements. No significant differences of the magnetization reversal mechanism were observed in case of Ni submicron wires surrounded by PVDF tubes and similar Ni wires without PVDF shell, suggesting that magneto-coupling effects in such systems might be observed only by measuring the perturbation of the electric state of the polymer shell under a magnetic excitation of the Ni cores.
10. Photoanode for solar water oxidation based on titania and hematite films
Authors:
Sima, M; Vasile, E; Sima, A
Published: JUL 31 2018, THIN SOLID FILMS, 658, 11, DOI: 10.1016/j.tsf.2018.05.019
Nanostructured hematite (alpha-Fe2O3) film deposited on mesoporous titania (TiO2) underlayer was described as a photoanode for photoelectrochemical water splitting. Mesoporous TiO2 layers were prepared by spin coating a paste on conductive fluorine-doped tin oxide glass followed by an annealing process. Hematite film was prepared after electrochemical and annealing processes. The TiO2/Fe2O3 photoanodes achieve photocurrent densities up to 0.5 mA/cm(2) at 1.23 V versus reversible hydrogen electrode. This value is greater than that for photocurrent density obtained with pristine hematite photoanode. Impedance measurements showed that prepared heterostructure TiO2/Fe2O3 contributes to diminution of electron-hole recombination process.
11. Lead acetate film as precursor for two-step deposition of CH3NH3PbI3
Authors:
Sima, M; Vasile, E; Sima, M
Published: MAY 2017, MATERIALS RESEARCH BULLETIN, 89, 96, DOI: 10.1016/j.materresbull.2017.01.031
This paper relates to a method for the preparation of lead acetate film and its use as precursor for twostep solution deposition of CH3NH3PbI3 perovskite film. For the preparation of perovskite film, lead acetate was used both in the form of trihydrate and dehydrated. The effects of lead acetate trihydrate dehydration on the structure of the resulted perovskite films were studied. The prepared perovskite films which consist of cuboid grains, show high surface coverage both on FTO and TiO2 substrates. XRD measurements have not revealed the presence of the PbI2 contaminant in perovskite film. Solvent vapor annealing method was employed to prepare perovskite film that contains lead iodide. Using impedance spectroscopy measurements, we further evaluated the influence of the prepared perovskite films on the performance of the photovoltaic devices. (C) 2017 Elsevier Ltd. All rights reserved.
12. PHOTOACTIVITY OF HEMATITE ELECTRODE PREPARED VIA ANODIC ELECTRODEPOSITION ON FTO AND FTO/TiO2 SUBSTRATES
Authors:
Sima, M; Vasile, E; Sima, MA
Published: JUL-SEP 2017, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 12, 758, DOI:
The hematite films were prepared via anodic electrodeposition on FTO and FTO/mesoporous TiO2 substrates. The hematite photoanodes were characterized by X-ray diffraction and scanning electron microscopy. The performance of the prepared hematite photoanodes was assessed based on photocurrent-voltage curves and electrochemical impedance spectra. The modification of the hematite surface with nickel oxide nanoparticles improved the performance of the hematite photoanode while phosphorous doped hematite photoanode shows poor photoactivity. The onset of water oxidation photocurrent was cathodically shifted for hematite photoanodes prepared on FTO/TiO2 substrate.
13. Anodic deposition of nanostructured hematite film using agarose gel as template. Application in water splitting
Authors:
Sima, M; Vasile, E; Sima, A; Logofatu, C
Published: DEC 20 2017, ELECTROCHIMICA ACTA, 258, 1462, DOI: 10.1016/j.electacta.2017.12.013
The present study shows the results obtained in anodic electrodeposition of hematite precursor films in agarose gel template and photoelectrochemical characterization of the prepared hematite films. The peak current in cyclic voltammetry increases after each scan of the potential between -0.1 and 1.3 V for FTO electrode covered with a film of agarose gel in 0.1 M iron sulfate solution. The hematite samples with different thicknesses were prepared using template electrodeposition and annealing in air. The obtained nanostructured films were characterized by field emission scanning electron microscopy, X-ray diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The results show that a synergistic improvement of photocurrent density (1.14 mAcm(-2) at 1.23 V vs RHE) is induced by Sn-doping and slight surface modification of hematite with thin and discontinuous NiO film. The results indicate that thicker hematite films and hematite films strongly modified with NiO nanostructures show a reduced photoactivity. (C) 2017 Elsevier Ltd. All rights reserved.
14. Iodine Migration and Degradation of Perovskite Solar Cells Enhanced by Metallic Electrodes
Authors:
Besleaga, C; Abramiuc, LE; Stancu, V; Tomulescu, AG; Sima, M; Trinca, L; Plugaru, N; Pintilie, L; Nemnes, GA; Iliescu, M; Svavarsson, HG; Manolescu, A; Pintilie, I
Published: DEC 15 2016, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 7, 5175, DOI: 10.1021/acs.jpclett.6b02375
We monitored the evolution in time of pinhole-free structures based on FTO/TiO2/CH3NH3PbI2.6Cl0.4 layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 degrees C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 degrees C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I- from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I- negative space charge accumulated at the perovskite-OMeTAD interface.
15. Fabrication and Raman scattering of a core-shell structure based on Mn doped ZnO and barium titanate
Authors:
Sima, M; Baibarac, M; Vasile, E; Sima, M; Mihut, L
Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 1062, DOI: 10.1016/j.apsusc.2015.07.191
A combination of chemical and thermal annealing techniques was used to prepare an array of ZnO/Zn1-xMNxO/BaTiO3 nanorods. ZnO nanorod arrays were obtained by hydrothermal-electrochemical processes. The precursors for Zn1-xMnxO and BaTiO3, prepared by sol-gel technique were deposited by spin coating on the surface of ZnO nanorods. Each deposition stage was accompanied by thermal treatment stages. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and photoluminescence spectroscopy reveal the presence of a film of Zn1-xMnxO with wurtzite structure on the surface of ZnO nanorods. Transmission electron microscopy images demonstrate that a layer of BaTiO3 is deposited on the surface of each ZnO/Zn1-xMnxO core shell nanorod. BaTiO3 film onto the ZnO/Zn1-xMnxO core shell nanorods is also evidenced in Raman scattering by broadening of the Raman band situated in the spectral range 500-750 cm(-1). (C) 2015 Elsevier B.V. All rights reserved.
16. Organic-inorganic solar cell based on ZnO nanorod arrays
Authors:
Sima, M; Vasile, E; Sima, M
Published: SEP-OCT 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1313, DOI:
In this study, we communicate an investigation on perovskite solar cell based on ZnO nanorod array and spiro OMeTAD film as electron and hole selective contacts. It was found that large thickness or small electrical conduction of the Li doped spiro OMeTAD layer and recombination processes at the interfaces contributed to the reduced efficiency of the solar cell.
17. Optical properties of Mn doped ZnO films and wires synthesized by thermal oxidation of ZnMn alloy
Authors:
Sima, M; Mihut, L; Vasile, E; Sima, M; Logofatu, C
Published: SEP 1 2015, THIN SOLID FILMS, 590, 147, DOI: 10.1016/j.tsf.2015.07.072
Mn doped ZnO films and wires, having different manganese concentrations were synthesized by thermal oxidation of the corresponding ZnMn alloy films and wires electrodeposited on a gold substrate. Structural and optical properties were addressed with scanning electron microscopy, X-ray diffraction (XRD), Raman scattering and photoluminescence (PL). To estimate the manganese concentration in Mn doped ZnO films, X-ray photoelectron spectroscopy was used. XRD patterns indicate that the incorporation of Mn2+ ions into the Zn2+ site of ZnO lattice takes place. Quenching of the ZnO PL appears due to Mn2+ ions in the ZnO lattice. Moreover, a significant decrease in the green emission of ZnO is reported in the case of the Mn doped ZnO wire array with a Mn concentration of 1.45%. The wurtzite ZnO has a total of 12 phonon modes, namely, one longitudinal acoustic (LA), two transverse acoustic (TA), three longitudinal optical (LO), and six transverse optical branches. Compared to the undoped ZnO, a gradual up-shift of the Raman lines assigned to the 2LA and A(1) (LO) vibrational modes, from 482 and 567 cm(-1) to 532 and 580 cm(-1), respectively, takes place for the Mn doped ZnO films having a Mn concentration between 2 and 15%. Additionally, in the case of the Mn doped ZnO films with 7 and 15% Mn concentration, Raman spectra show the appearance and increase in the relative intensity of the ZnO Raman line assigned to the TA + LO vibrational mode in the 600-750 cm(-1) spectral range. For the Mn-doped ZnO wires, the presence of the Raman line peaking at 527 cm(-1) confirms the insertion of Mn2+ ions in ZnO lattice. (C) 2015 Elsevier B.V. All rights reserved.
18. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays
Authors:
Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L
Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062
A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
19. Electrochemical Studies on the Growth Process of the Zinc Oxide Films from Nitrate Solutions
The cathodic deposition of zinc oxide film on Pt from an aqueous solution containing 0.05 M Zn(NO3)(2) was investigated using linear sweep voltammetry and electrochemical impedance spectroscopy. The film formation is an electroprecipitation process due to reduction of nitrate ion on the surface of working electrode in the presence of Zn2+ ions. A morphology of ZnO with hexagonal platelets was observed. The standard electromotive force of the cell reaction was calculated for both NO3/NO2 process and overall deposition process. Linear voltammograms and visual observations showed that polarizing the electrode at higher negative potentials than -1.1 V, the parallel reduction of zinc ion to zinc metal occurs together with reduction of nitrate ion to hydroxide ion; as a consequence, a partial amorphous state of ZnO film was recorded on SEM micrographs. Experimental impedance data and data calculated by fitting with an equivalent circuit showed that the ZnO formation involves an adsorption of complexed zinc ions on Pt electrode, before the charge transfer.
20. Investigation on the electrodeposition of Pt-(Bi,Sb)(2)Te-3 nanocomposite as film and wires
Authors:
Sima, M; Vasile, E; Buda, M; Sima, M
Published: MAY 1 2014, ELECTROCHIMICA ACTA, 127, 214, DOI: 10.1016/j.electacta.2014.02.032
In this work we have investigated the electrochemical processes by which Pt nanoparticles were included in (Bi,Sb)(2)Te-3 films and submicrometer wires. Solutions containing ions of Bi3+, HTeO2+ and Sb3+ as well as Pt nanoparticles or [PtCl6](2-) ions were used for this study. For comparison, a solution with the same composition in Bi3+, HTeO2+ and Sb3+ ions was used to study the electrodeposition process of (Bi,Sb)(2)Te-3 films and submicrometer wires. Linear and cyclic voltammetry was employed in experiments to find the influences of addition to electrodeposition bath of Pt nanoparticles or [PtCl6](2-) ions on deposition process of (Bi,Sb)(2)Te-3 film. Pt-(Bi,Sb)(2)Te-3 nanocomposites has been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDX) to determine structural, morphological and compositional properties. Two mechanisms for Pt nanoparticles embedding in (Bi,Sb)(2)Te-3 films and wires have been proposed. (c) 2014 Elsevier Ltd. All rights reserved.
21. PHOTOANODE FOR DYE-SENSITIZED SOLAR CELL BASED ON ELECTROPHORETICALLY DEPOSITED ZnO LAYER
Authors:
Sima, M; Vasile, E; Sima, A
Published: APR-JUN 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 763, DOI:
Electrophoretic deposition (EPD) method is employed to obtain a thick ZnO layer on a ZnO nanorod array prepared in a hydrothermal-electrochemical process. ZnO nanorods have the role to improve the mechanical stability and adherence of ZnO layer deposited by electrophoretic technique. D149 dye is used as sensitizer for ZnO semiconductor. The thus prepared ZnO layer is used for the photoanode of dye-sensitized solar cell (DSC). Performance parameters were extracted from standard current-voltage characteristic (I-V) and charge transfer phenomena occurring at ZnO/dye/electrolyte was evaluated by electrochemical impedance spectroscopy (EIS).
22. ZnO films and nanorod/shell arrays electrodeposited on PET-ITO electrodes
Authors:
Sima, M; Vasile, E; Sima, M
Published: APR 2013, MATERIALS RESEARCH BULLETIN, 48, 1586, DOI: 10.1016/j.materresbull.2012.12.045
In this work, ZnO films, nanorod and nanorod/shell arrays were synthesized on the surface of PET-ITO electrodes by electrochemical methods. ZnO films with high optical transmittance were prepared from a zinc nitrate solution using a pulsed current technique with a reduced pulse time (3 s). The X-ray diffraction pattern of ZnO film deposited on PET-ITO electrode showed that it has a polycrystalline structure with preferred orientations in the directions [0 0 2] and [1 03]. ZnO nanorods were synthesized on electrochemical seeded substrate in an aqueous solution containing zinc nitrate and hexamethylenetetramine. In order to increase the stability of PET-ITO electrode to electrochemical and chemical stresses during ZnO nanorods deposition the surface of the electrode was treated with a 17 wt% NH4F aqueous solution. Electrochemical stability of PET-ITO electrode was evaluated in a solution containing nitrate ions and hexamethylenetetramine. ZnO nanorod/shell arrays were fabricated using eosin Y as nanostructuring agent. Photoluminescence spectra of ZnO nanorod and ZnO nanorod/shell arrays prepared on the surface of PET-ITO electrode were discussed comparatively. By employing the 1.5 mu m-length ZnO nanorod/shell array covered with a Cu2O film a photovoltaic device was fabricated on the PET-ITO substrate. (C) 2012 Elsevier Ltd. All rights reserved.
23. Luminescent Eosin Y-SiO2 hybrid nano and microrods prepared by sol-gel template method
Authors:
Secu, M; Secu, CE; Sima, M; Negrea, RF; Bartha, C; Dinescu, M; Damian, V
Published: NOV 2013, JOURNAL OF LUMINESCENCE, 143, 92, DOI: 10.1016/j.jlumin.2013.04.043
Sol-gel chemistry within the pores of a polycarbonate template membrane was used for the preparation of Eosin Y-SiO2 hybrid nano- and microrods, using tetraethylorthosilicate [TEOS, Si(OC2H5)(4)] as the precursor in the presence of trifluoroacetic acid (TFA) catalyst. The ethanolic solution of Eosin-Y was added to the silica sal to trap dye molecules inside the SiO2 gel network during the gelation. Structural and morphological characterization using scanning electron microscopy (SEM) and luminescence microscopy have shown the formation of rods with 200 nm and 1.2 mu m diameter and about 30 mu m length, exhibiting luminescence properties. Spectroscopic characterization has shown that the luminescence is due to Eosin-Y molecule in the xerogel porous network, surrounded by a solvation shell given mainly by the water. (C) 2013 Elsevier B.V. All rights reserved.
24. ELECTRODEPOSITION AND ANODIZING OF ZnMn ALLOY SUBMICRON WIRES
Authors:
Sima, M; Sima, M
Published: JUL-SEP 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 882, DOI:
The study of the electrodeposition and anodic oxidation processes of ZnMn alloy submicron wires is reported; ZnMn wire arrays were electrodeposited using a pulse current technique and an aqueous solution containing 0.2 mol dm(-3) Zn(II)-EDTA + 0.2 mol dm(-3) MnSO4 + 0.6 mol dm(-3) sodium citrate. The obtained alloy was anodized at a current constant density, in a methoxyethanol solution containing sodium hydroxide and in an aqueous potassium zincate solution. Photoluminescence spectra and SEM images showed the presence of the oxide layer on the surface of the anodized ZnMn wires.
25. Electrochemical Investigation of the Deposition/Dissolution of Selenium in Choline Chloride with Urea or Ethylene Glycol Ionic Liquids
The electrochemical behaviour of Se(IV) ion on Pt electrode in ionic liquids containing choline chloride - urea and choline chloride - ethylene glycol eutectics (1:2 mole ratio) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in open air conditions. Cyclic voltammograms showed a cathodic peak of selenium massive deposition preceeded by one or more waves corresponding to UPD processes. It is followed by another cathodic peak of Se(II) anion formation. It was found a diffusion control of reduction process and, therefore, the value of the diffusion coefficient of Se(IV) ion in ChCl-urea ionic liquid at 60 degrees C was calculated. EIS spectra as Nyquist and Bode plots confirm the potential range for bulk selenium deposition and formation of thin selenium films.
26. Preparation of nanostructured ZnO nanorods in a hydrothermal-electrochemical process
Authors:
Sima, M; Vasile, E; Sima, M
Published: MAY 1 2012, THIN SOLID FILMS, 520, 4636, DOI: 10.1016/j.tsf.2011.10.116
An array of ZnO nanorods, each nanorod being covered with a shell of porous ZnO was prepared in two steps by hydrothermal-electrochemical processes. The growth of ZnO nanorods was achieved in a zinc nitrate and hexamethylenetetramine aqueous solution on fluorine-doped tin oxide film. The porous ZnO shell was grown from a similar solution in the presence of eosin Y as nanostructuring agent. A dye-sensitized solar cell was assembled using as photoanode an eosin Y sensitized ZnO nanorod/shell layer. (C) 2011 Elsevier B.V. All rights reserved.
27. Sol-gel template synthesis of luminescent glass-ceramic rods
Authors:
Secu, M; Secu, CE; Sima, M
Published: APR 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0772-1
We report an original way to prepare luminescent glass-ceramic microrods containing Eu3+ doped BaF2 nanocrystals by sol-gel chemistry within the pores of a polycarbonate template membrane. Structural characterization by scanning electron microscopy and X-ray diffraction has shown the formation of glass-ceramic microrods with 0.8-m diameter of and 10 mu m length in which BaF2 nanocrystals of about 30 nm size are embedded. Photoluminescence measurements have indicated the incorporation of Eu3+ ions inside the BaF2 nanocrystals in a broad range of sites with low coordination symmetry. The comparison made with the bulk glass-ceramic indicated an influence of the dimensional constraints imposed by the membrane pores during xerogel formation and subsequent glass ceramization.
28. Preparation of graphene and its application in dye-sensitized solar cells
Authors:
Sima, M; Enculescu, I; Sima, A
Published: MAR 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 418, DOI:
Graphene sheets were prepared using electrochemical and chemical steps followed graphite electrochemical oxidation, graphite chemical oxidation, ultrasound expholiation and chemical reduction of carbon material. Films of graphene were electrophoretically deposited from aqueous dispersion on FTO electrode. These films were tested as cathode for a dye-sensitized solar cell. The morphology of the prepared products was imaged by scanning electron microscopy; the intermediate compound, graphene oxide was characterized by IR spectroscopy.
29. Electrochemical Growth of Eosin Y/Manganese Doped ZnO as Hybrid Films and Nanowires
Authors:
Sima, M; Visan, T; Matei, E; Ungureanu, F; Enculescu, I; Sima, M
Published: 2011, ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS, 225, 339, DOI: 10.1524/zpch.2011.0042
The electrodeposition process of Eosin Y/ZnO:Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at -1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO:Mn nanowires electrodeposited at -1.1 V/SCE.
30. Study of electrodeposition of (Bi,Sb)(2)Te-3 nanowires by voltammetric methods and electrochemical impedance spectroscopy
Authors:
Sima, M; Vasile, E; Sima, M
Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1602, DOI:
Nanostructured thermoelectric semiconductors are a promising material to convert waste heat to electricity for energy regeneration due to improvement of Seebeck coefficient and thermal conductivity reducing. Among various thermoelectric materials, bismuth telluride based alloys are the most used in the fabrication of TE devices. The processes associated with the electrodeposition of (Bi,Sb)(2)Te-3 nanowires and films are reported along with an analysis of the composition, morphology and structure of resulting materials. Electrochemical behavior was examined using cyclic and linear voltammetry and electrochemical impedance spectroscopy techniques.
31. ELECTRICAL PROPERTIES OF (Zn,Cu)O:Mn SUBMICRON WIRES
Authors:
Ion, L; Antohe, S; Sima, A; Sima, M
Published: OCT-DEC 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1700, DOI:
Arrays of multisegment Pd/(Zn,Cu)O:Mn/Pd submicron wires have been grown electrochemically into the pores of nuclear track polycarbonate membranes. Their transport properties were investigated, by measuring current-voltage (I-V) characteristics in a temperature range from 300 K down to 40 K. I-V characteristics of Pd/(Zn,Cu)O:Mn/Pd wires exhibited a symmetric, non-linear shape on applied bias voltage ranging from -20 V to +20V. The ohmic region corresponds to polarization voltage under 3.5V. Comparatively, I-V characteristics of Pd/ZnO/Pd array of wires with diameter about 500 nm are linear in the entire range of applied voltages (-20 V to +20V).
32. A new ZnO photoanode for dye-sensitized solar cell
Authors:
Sima, M; Secu, M; Sima, M; Vasile, E
Published: SEP 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1328, DOI:
The present work reports the preparation of nanostructured ZnO nanorods in a hydrothermal-electrochemical process and preliminary attempt to fabricate a dye-sensitized solar cell using this material as photoanode. Synthesis of ZnO nanorods in solutions with and without eosin Y dye, used as nanostructuring agent, was studied. ZnO nanorod arrays were characterized by photoluminescence spectroscopy, scanning electron microscopy and X-ray diffraction analysis. Fabricated dye-sensitized solar cell comprised a photoanode prepared with nanostructured ZnO nanorods and eosin Y dye, a platinum counter electrode and an electrolyte consisting of 0.5M KI + 0.03M I-2 in acetonitrile/ethylene carbonate (v/v=1/4). Performance parameters of dye-sensitized solar cell were extracted from standard current-voltage characteristic.
33. Semiconductor Hybrid Structure: Nanowires Embedded in a Matrix from the Same Material
Authors:
Sima, M; Vasile, E; Sima, M; Matei, E
Published: 2010, SEMICONDUCTORS, METAL OXIDES, AND COMPOSITES: METALLIZATION AND ELECTRODEPOSITION OF THIN FILMS AND NANOSTRUCTURES, 25, 161, DOI: 10.1149/1.3318514
Hybrid systems obtained by incorporation of a nanostructurated material into a matrix from the same thermoelectric (TE) material are predicted to show an increased TE efficiency compared to classical bulk materials. The authors have synthesized Bi1.95Te2.7Se0.35 submicron wires by electrodeposition into a polycarbonate membrane; after polymer membrane dissolution, the wire array supported on a metallic film was electrochemically embedded in a Bi2Te2.65Se0.35 film in order to prepare a hybrid structure. Wires and hybrid structure were analyzed by scanning electron microscopy (SEM), energy X-ray spectrometry (EDX) and X-ray diffraction (XRD).
34. Growth and Characterization of ZnO:Mn Submicron Wires via Electrodeposition from Nitrate-Lactic Acid Solution
Authors:
Sima, M; Grecu, MN; Sima, M; Enculescu, I
Published: 2010, SEMICONDUCTORS, METAL OXIDES, AND COMPOSITES: METALLIZATION AND ELECTRODEPOSITION OF THIN FILMS AND NANOSTRUCTURES, 25, 171, DOI: 10.1149/1.3318515
Electrodeposition of manganese doped ZnO wires into polycarbonate membranes from an aqueous solution containing Zn(NO3)(2), Mn(NO3)(2) and lactic acid was investigated using linear sweep voltammetry and electrochemical impedance spectroscopy (EIS). The equivalent electrical circuits used for fitting experimental results were similar to those for characterization of metal/polymer coating systems. The precipitation of metal oxides in the pores of membrane used as template was observed at potentials between -0.9 and -1.15V/SCE. Morphology of the ZnO: Mn submicron wires arrays was observed by scanning electron microscopy and the Mn content of the obtained samples was measured by X-ray analysis. The submicron wires prepared at a potential of -1.1V/SCE have a composition expressed by the formula Zn0.97Mn0.03.
35. Optical properties of CdS electrodeposited nanowires
Authors:
Matei, E; Preda, N; Enculescu, M; Sima, M; Sima, M; Enculescu, I
Published: OCT 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1022, DOI:
Electrochemical deposition was performed in order to prepare CdS nanowires. The method employed for preparation of such high aspect ratio nanostructures was template replication. Ion track polycarbonate membranes were used as templates. The nanowires were studied by scanning electron microscopy (morphology characterization), energy dispersive X ray analysis (composition) and optical spectroscopy. Optical reflection spectroscopy was performed in order to determine the band gap value while photoluminescence spectroscopy was used for getting information regarding the point defects in the material.
36. Electrochemically deposited thermoelectric Bi(2)(Se,Te)(3) nanowires
Authors:
Sima, M; Vasile, E; Sima, M
Published: JUN 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 542, DOI:
The processes associated with the electrodeposition of thermoelectric Bi(2)(Se,Te)(3) nanowires are reported along with an analysis of the composition, morphology and structure of resulting material. Electrochemical behavior was examined using cyclic and linear voltarnmetry techniques. Energy dispersive X-ray spectrometry (EDX) indicates that the composition of self-standing Bi(2)(Se, Te)(3) wires can be controlled by the electrodeposition method. The composition of Bi(2)(Se,Te)(3) Wires prepared at a potential of -0.01V vs SCE is close to Bi(2)Te(27)Se(0.3). The structure and morphology of Bi(2)(Se,Te)(3) nanowires were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).
37. Submicron wires with nanosized grain structure
Authors:
Sima, M; Ion, L; Antohe, S; Vasile, E
Published: DEC 2009, SUPERLATTICES AND MICROSTRUCTURES, 46, 839, DOI: 10.1016/j.spmi.2009.09.010
Recent results have shown that size-effects in nanostructured materials may enable much more efficient thermoelectric devices. In this paper, the electrochemical preparation of Bi(1.95)Te(2.7)Se(0.35) and Bi(2.15)Te(2.55)Se(0.3) submicron wires arrays with nanosized grain structure is reported. X-ray diffraction (XRD) analysis has indicated the presence of nanosized crystallites in the structure of the wires; high resolution transmission electron microscopy (HRTEM) investigations have confirmed the formation of crystallites with geometrical dimensions of 5-14 nm and random orientations in the structure of these wires. These wires were further analyzed by field emission scanning electron microscopy (FESEM). The measurement of the transport properties showed that a highly degenerate semiconductor with a large thermopower (-125 mu V K(-1) at 300 K) and a low resistivity was obtained. (C) 2009 Elsevier Ltd. All rights reserved.
38. Photoluminescence and thermoluminescence of ZnO nano-needle arrays and films
Authors:
Secu, CE; Sima, M
Published: APR 2009, OPTICAL MATERIALS, 31, 880, DOI: 10.1016/j.optmat.2008.10.025
ZnO nano-needle arrays and films have been prepared by anodic etching of ZnO foil at constant current in potassium zincate solution and sodium hydroxide alcoholic solution, respectively. Photoluminescence (PL) spectra recorded on ZnO nano-needles have shown a broad band at 585 nm due to the native oxygen defects incorporated during the synthesis processes; in a ZnO film-type sample this band is replaced by another one at 432 nm. Thermoluminescence (TL) glow curves recorded on ZnO nano-needle arrays have shown a broad peak at about 360 degrees C similar to that observed in ZnO polycrystalline powder. A very strong TL peak at about 325 degrees C superimposed on a broad one has been observed in a ZnO film-type sample. TL recorded on ZnO nano-needles has tentatively been attributed to the recombination of charge carriers released from the surface states associated with oxygen defects, mainly interstitial oxygen ion centres; the TL mechanism is supported by a recovery effect of the PL and TL after storage in air. (C) 2008 Elsevier B.V. All rights reserved.
39. Transport properties of electrodeposited ZnO nanowires
Authors:
Tazlaoanu, C; Ion, L; Enculescu, I; Sima, M; Enculescu, M; Matei, E; Neumann, R; Bazavan, R; Bazavan, D; Antohe, S
Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2507, DOI: 10.1016/j.physe.2007.07.013
ZnO nanowires were electrodeposited by using a template approach. Ion track polycarbonate foils (30 mu m thick) were used as templates. Current-voltage (I-V) characteristics were recorded in the temperature range 40-300 K. I-V characteristics show a symmetric, non-linear shape, at temperatures greater than 240 K and voltages greater than 15 V. At lower temperatures, linear characteristics were recorded for the voltage range used. The temperature dependence of the electrical resistance is activated, with activation energy of 0.42 eV at temperatures greater than 240 K. (C) 2007 Elsevier B.V. All rights reserved.
40. Influence of polyvinylpyrolidone as an additive in electrochemical preparation of ZnO nanowires and nanostructured thin films
Authors:
Enculescu, I; Matei, E; Sima, M; Enculescu, M; Sima, M; Ghica, C
Published: MAR-APR 2008, SURFACE AND INTERFACE ANALYSIS, 40, 560, DOI: 10.1002/sia.2749
Preparation of ZnO in different nano-morphological forms became a hot topic during the last few years. This tendency was motivated by the wide field of potential applications ranging from optics to electronics and spintronics. In the present work, we deal with the preparation of ZnO nanowires and nanostructured thin films using electrochemical deposition. ZnO nanowires were grown using the template approach, namely by replicating the nanopores of polycarbonate ion track membranes. The method yields uniform arrays of nanowires with the morphology controlled by the shape and size of the templates pores. Adding polyvinylpyrolidone as an additive in the growth bath became a necessity due to the fact that polycarbonate ion track membranes are usually hydrophobic and thus filling of the nanopores with the growth electrolyte is rather difficult. In order to better understand the influence of the additive on the electrochemical deposition of such nanostructures, similar experiments were performed for the deposition of ZnO thin films. Scanning electron microscopy, X-ray diffraction and optical spectroscopy measurements were performed for characterization of the deposited structures. Copyright (c) 2008 John Wiley & Sons, Ltd.
41. PbSe nanowires grown by the template method
Authors:
Sima, M; Enculescu, I; Sima, M
Published: 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 70, DOI:
PbSe nanowires were prepared using the template method. Polycarbonate ion track membranes with pore sizes ranging between 50 nm and 1.5 mu m were used as templates. The deposition of PbSe in the pores of the template was performed electrochemically. The influence of the deposition potential and membrane porosity on the morphology and composition of the prepared nanowires was studied. The composition of the wires has been determined by EDX measurements for different potentials. Scanning electron microscopy revealed the morphology of the deposited nanowires. X ray diffraction has been used for structural measurements.
42. Preparation and Properties of Cobalt Doped ZnO Nanowires
Authors:
Enculescu, I; Matei, E; Sima, M; Neumann, R; Granville, S; Ansermet, JP
Published: NOV 2008, IEEE TRANSACTIONS ON MAGNETICS, 44, 2680, DOI: 10.1109/TMAG.2008.2003242
The template method was used for preparing Zn1-xCoxO nanowires with x ranging from 0.01 to 0.05. Thus, electrochemical deposition was employed for filling up the pores of polycarbonate ion track nanoporous membranes with the desired material. The method allows a good control over the morphology and composition of the deposited nanowires, as evidenced by scanning electron microscopy (SEM) and energy dispersive X ray analysis (EDX). Measurements of the magnetic properties showed a paramagnetic behavior of the nanowire arrays for the whole set of temperatures and Co concentrations.
43. Electrical properties of electrodeposited CdS nanowires
Authors:
Ghenescu, M; Ion, L; Enculescu, I; Tazlaoanu, C; Antohe, VA; Sima, M; Enculescu, M; Matei, E; Neumann, R; Ghenescu, O; Covlea, V; Antohe, S
Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2488, DOI: 10.1016/j.physe.2007.09.188
A template method was used to obtain cadmium sulfide (CdS) nanowires. Polymer ion tracks foils (30 mu m tick) were used as templates, after etching with solutions containing NaOH and methanol. CdS nanowires were electrochemically grown in the resulting pores. The nanowires were contacted by sputtering a gold layer on top of the membrane, and the electrical properties were recorded in the temperature range 40-300K. An activated electrical resistance was observed, with activation energy of 0.27eV at temperatures larger than 180 K. I-V characteristics show a symmetric, non-linear shape, in the voltage range used in this experiment. (C) 2007 Elsevier B.V. All rights reserved.
44. Luminescence and EPR study of ZnO : Mn : Cu nanowire array
Authors:
Sima, M; Enculescu, I; Grecu, MN; Secu, M; Sima, M; Matei, E; Vasile, V
Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2498, DOI: 10.1016/j.physe.2007.08.075
We report on photoluminescence studies on manganese and copper-doped ZnO nanowire array prepared by template method. The ZnO:Mn:Cu semiconductor grown using the electrochemical technique was characterized by electron paramagnetic resonance (EPR) and optical reflection measurements. Morphology and the structure were observed by SEM and X-ray diffraction. The photoluminescence of this system was correlated with manganese and copper concentration in the ZnO matrix. (C) 2007 Elsevier B.V. All rights reserved.
45. Nickel nanotubes prepared by electroless deposition in ion track templates
Authors:
Enculescu, I; Sima, M; Enculescu, M; Matei, E; Molares, MET; Cornelius, T
Published: MAR 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 136, DOI:
Nickel nano- and micro- tubes were prepared by electroless deposition in ion track template membranes. By choosing the appropriate etching conditions membranes with cylindrical or conical pores were obtained allowing the preparation of cylindrical or conical tubules. The activation of the membranes was a two step process. The bath used for deposition was an acidic one. Typically for acidic bath deposition, by energy dispersive X ray analysis, a phosphorous content of up to 10 % was found in the deposit.
46. EIS studies of electrodeposition process of manganese and copper doped ZnO wires
Authors:
Sima, M; Enculescu, I; Sima, M; Vasile, E; Visan, T
Published: MAR-APR 2008, SURFACE AND INTERFACE ANALYSIS, 40, 565, DOI: 10.1002/sia.2721
Electrodeposition of manganese- and copper-doped ZnO wires into polycarbonate membranes, from an aqueous solution containing 0.05 mol dm(-3) Zn(NO3)(2)+ 0.01 mol dm(-3) Mn(NO3)(2)+ 0.0005 mol dm(-3) Cu(NO3)(2)+ 0.0075 mol dm(-3) lactic acid, pH = 4.7 was investigated using linear sweep voltammetry and electrochemical impedance spectroscopy (EIS). The equivalent electrical circuits for fitting experimental results were similar to those for characterization of metal/polymer coating systems. impedance data and voltarnmetric curves showed that an increase of local pH due to reduction process of nitrate ions induces the co-precipitations of metal ions in the proximity of electrode as oxides. Copyright (c) 2008 John Wiley & Sons, Ltd.
47. Preparation of metallic nanowires with magnetic properties using the template method
Authors:
Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R
Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:
Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.
48. Influence of geometrical properties on light emission of ZnO nanowires
Authors:
Enculescu, I; Sima, M; Enculescu, M; Enache, M; Vasile, V; Neumann, R
Published: SEP 2007, OPTICAL MATERIALS, 30, 75, DOI: 10.1016/j.optmat.2007.01.002
The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70 degrees C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties. (c) 2007 Elsevier B.V. All rights reserved.
49. Micro and nanorods of alkali halides grown in polymer templates
Authors:
Enculescu, M; Enculescu, I; Sima, M; Neumann, R; Trautmann, C
Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1563, DOI:
Porous membranes containing cylindrical pores with diameters ranging from a few tens of nanometers to a few tens of micrometers were prepared by using the ion track technique. Swift heavy ions (e.g. Au with 11.4 MeV/nucleon specific energy) were used for creating the ion tracks in polycarbonate foils. Etching was performed using an aqueous solution of NaOH containing methanol. The growth of the alkali-halides micro- and nanorods was performed by evaporation from a saturated solution. The rods were imaged using scanning electron microscopy. The method opens up the possibility of growing nanostructures with applications as nanolaser media or nanoscintillators.
50. Deposition and properties of CdTe nanowires prepared by template replication
Authors:
Enculescu, I; Sima, M; Enculescu, M; Enache, M; Ion, L; Antohe, S; Neumann, R
Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1611, DOI: 10.1002/pssb.200675109
We used the template method to prepare CdTe wires with diameters ranging from 80 nm to 1 mu m. As templates we used polycarbonate and polyethilene tereplitalate ion track membranes and as the method of filling the pores of such membranes we employed electrochemical deposition. The conditions (i.e. bath composition and deposition potential) necessary to obtain the stoichiometric composition of the semiconductor were found. Scanning and transmission electron microscopy were employed for morphological characterization of the nano and microwires. Energy dispersive X-ray analysis was employed for determining the Cd/Te ratio. Selected area electron diffraction was employed for structural measurements. Reflection spectroscopy measurements were performed on nanowire arrays for determining the band gap of the deposited nanostructures. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
51. ZnO : Mn : Cu nanowires prepared by template method
Authors:
Sima, M; Enculescu, I; Sima, M; Enache, M; Vasile, E; Ansermet, JP
Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1527, DOI: 10.1002/pssb.200675126
Manganese and copper doped ZnO films and nanowire arrays were prepared by cathodic electrodeposition from aqueous solution. The electrochemical process was examined by linear voltammetry and the morphology and the composition of obtained semiconductor were observed by SEM and EDX measurements. Optical absorption spectra indicated the presence of copper in ZnO: Mn: Cu nanowire arrays as Cu2+ ions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
52. Semiconductor nanowires obtained by template method
Authors:
Sima, M; Enculescu, I; Sima, M; Vasile, E
Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1554, DOI:
One-dimensional structures having uniform diameters were prepared by electrochemical deposition using polycarbonate membranes as templates. Lead chalcogenides and ZnO tubes and rods growth processes were presented comparatively. The tendency of PbTe and PbSe semiconductors to grow as tubes both in membrane micro and nanopores was explained based on the absorption of lead ions on the pore wall.
53. Investigation by electrochemical impedance spectroscopy of electrodeposition of zinc-oxide microwires using nitrate bv template method
Authors:
Sima, M; Manea, AC; Sima, M; Visan, T
Comparative experiments regarding electrodeposition of zinc oxide either as films on Pt and Au substrates or as microwires grown in microporous polycarbonate membranes were carried out using nitrate aqueous solutions as electrolyte. Linear sweep voltammetry and electrochemical impedance spectroscopy together with SEM and XRD techniques were used for investigation. The equivalent electrical circuits for fitting experimental results were similar to those for characterisation of metal/polymer coating systems.
54. Growth of ZnO micro and nanowires using the template method
Authors:
Sima, M; Enculescu, I; Vasile, E
Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 828, DOI:
The electrochemical deposition in ion track nanoporous membranes was employed for ZnO micro and nanowires preparation. A ZnNO3 bath was employed for the deposition, performed at -800 mV (vs. SCE) and at temperatures around 90 degrees C. Scanning and transmission electron microscopy were used to characterize the wires from a morphological point of view. Electron and X-ray diffraction were employed for the characterization of materials from the point of view of structure. The technique allowed the fabrication of nanowire arrays with good morphological and structural quality.
55. Absorption and photoluminescence properties of Cds : Mn2+: Cu+ nanostructures
Authors:
Sima, M; Enculescu, I; Ghiordanescu, V; Mihut, L
Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1955, DOI:
A layer of doped CdS nanocrystals was deposited on the surfaces of nanopores of polyethyleneterephtalate (PET) membranes. Optical absorption measurements were used to determine the bandgaps of the nanocrystals; CdS:Mn2+ and CdS:Mn2+:Cu+ show a blue and red shift, respectively, relative to the band gap of nanostructurated CdS. Photoluminescence spectra of the doped and undoped CdS samples exhibit wide bands covering the visible spectrum range.
56. Photoluminescence of manganese- and copper-doped CdS nanowires
Authors:
Ghiordanescu, V; Sima, M; Enculescu, I; Grecu, MN; Mihut, L; Secu, M; Neumann, R
Published: FEB 2005, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202, 454, DOI: 10.1002/pssa.200406927
Arrays of US: Mn2+ : Cu+ micro- and nanowires grown in polycarbonate ion-track templates exhibit photoluminescence in the spectral domain ranging from 500 to 800 mn at room temperature. A comparison with similar US and CdS:Mn2+ wire arrays is presented. The individual contributions to the emission spectra of Cu+ and Mn2+ ions in the US matrix are explained using their energy level schemes. Also SEM, EDX and EPR data are given or these wires. (c) 2005 WILEY-VCH Verlag GmbH A Co. KGaA, Weinheim.
57. Manganese and copper doped CdS nanowire arrays preparation
Authors:
Sima, M; Enculescu, I; Ioncea, A; Visan, T; Trautmann, C
Published: DEC 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 1198, DOI:
Manganese and copper doped CdS nanowires were obtained by the template technique in a two step process. In the first step metallic alloy CdMnCu nano and microwires were electrodeposited in ion track membranes with pore diameters in the range 150 nm-2 mum. In the following step the resulted nanowires were anodized in a sodium sulphide alkaline solution. Electron microscopy results show participation of the whole metallic wire in the anodization process; manganese and copper doped CdS wires are obtained The composition of micro and nanowires was determined by energy dispersive X-ray analysis.
58. The electrodeposition of semiconductor nanowires with thermoelectric properties using "template" method
A binary telluride (CdTe) as well as a ternary telluride (PbSeTe) were electrodeposited in the pores of a track-etched polycarbonate membrane, resulting nanowires and nanotubes. Either acid or alkaline solutions were used for preparing CdTe compound, whereas the ternary PbSe1-xTex compound was deposited from an acid solution, only. The investigation of electrode mechanisms was performed by cyclic voltammetry. The nanostructures were visualized using scanning electron microscopy (SEM).
59. Electrochemical deposition of PBSe1-xTex nanorod arrays using ion track etched membranes as template
Authors:
Sima, M; Enculescu, I; Visan, T; Spohr, R; Trautmann, C
Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 418, 755, DOI: 10.1080/15421400490478885
Lead chalcogenides (PbS, PbSe, PbTe) are narrow band gap semiconductors which have been studied in the field of IR detection and thermoelectric devices. The template method is a general approach for synthesizing nanomaterials within the pores of membranes. The membranes employed contain cylindrical pores with monodisperse diameters, and corresponding cylindrical nanostructures are obtained. The aim of the present study was to prepare PbSe1-xTex nanorod arrays using electrodeposition. The process was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The resulted PbSe1-xTex nanostructures were characterized using scanning electron microscopy (SEM) as well as energy dispersive X-ray analysis (EDAX).
60. Electrodeposition of CdTe nanorods in ion track membranes
Authors:
Sima, M; Enculescu, I; Trautmann, C; Neumann, R
Published: MAR 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 125, DOI:
CdTe nanowires were electrodeposited in ion track membranes with pore diameters in the range 100-2000 nm. Acidic and basic baths were tested for obtaining materials with good stoichiometry. The cyclic voltammograms were compared for the case of deposition on a carbon rotating disc and on the porous membrane substrates, the differences being attributed to the additional resistance induced by the pores. For larger pores a tendency of growing hollow structures was observed.
61. Electrosynthesis and properties of some substituted polyanilines in phosphate buffer
Authors:
Sima, M; Buda, M; Vasile, E; Visan, T
Published: JAN-FEB 2002, REVUE ROUMAINE DE CHIMIE, 47, 193, DOI:
The electropolymerizations of 2-aminohippuric acid methyl ester and 2-aminobenzoic acid methyl ester monomers in phosphate buffer (pH = 6.5) were studied. The formation of thin films at the platinum electrode surface is observed as main product and the electrosynthesis process of the two substituted polyanilines shows the voltammetric characteristics of the polyaniline film electrosynthesis. The necessary charge to deposit 0.05 mum poly(2-aminohippuric acid methyl ester) or poly(2-aminobenzoic acid methyl ester) films is about 60 mC/cm(2). The polymer films were investigated by electrochemical impedance spectroscopy. On the basis of the obtained results we propose the equivalent circuit for these polymer films.
62. Bi2-xSbxTe3 thick thermoelectric films obtained by electrodeposition from hydrochloric acid solutions
Authors:
Nedelcu, M; Sima, M; Manea, AS; Lazarescu, MF; Ghita, RV; Craciunoiu, F; Visan, T
Published: MAR 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 106, DOI:
A method to produce composition modulated Bi2-xSbxTe3 alloys by electrodeposition has been developed. The electrolyte, which consists in a HCl 6M (pH = 0) aqueous solution, allows for the co-deposition of bismuth, antimony and tellurium to be accomplished at room temperature on glassy carbon, platinum or nickel electrode. The composition of the films, their crystal structures and morphology were studied as function of electrochemical parameters and bath composition. It is shown that the electrodeposits are monophasic and exhibit a polycrystalline state. The electrical resistivity was of the order of 7-10 mOmegacm, whereas the electrodeposition rate value was 30-50 mum/h for the films with good thermoelectric properties.
63. Optical properties of polyaniline/CdS nanocrystals composite film
Authors:
Ghiordanescu, V; Sima, M; Nedelcu, M; Giubelan, M
Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 93, DOI:
The optical spectra of CdS nanocrystals embedded in polyaniline matrix have been studied. The presence of surface states is revealed both in absorption and emission spectra. The polymer matrix determines a shift of the absorption edge of CdS nanocrystals, towards higher energies.
64. Visible light emission from Cd1-xMnxS nanocrystals
Authors:
Ghiordanescu, V; Sima, M; Grecu, MN; Mihut, L
Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 524, DOI:
The luminescence spectra of some Cd1-xMnxS nanocrystals have been measured at room and liquid nitrogen temperature. The Mn2+ ions give rise to a broad emission band centered at about 580 nm, between the emission bands of CdS host.
65. PbSe1-xTex thick thermoelectric films obtained by electrochemical deposition from aqueous solutions
Authors:
Nedelcu, M; Sima, M; Visan, T; Pascu, T
Published: 2001, TWENTIETH INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS, 330, DOI: 10.1109/ICT.2001.979898
This work describes the study of PbSe1-xTex film electrodeposition on glassy carbon and ITO electrodes in acid solutions (0.1 M HNO3), using cyclic voltammetry and rotating-disk techniques. Electrochemical impedance spectroscopy study of PbSe1-xTex film in 0.1M HNO3 were also presented.
66. Bi2-xSbxTe3 thick thermoelectric films obtained by electrodeposition from hydrochloric acid solutions.
Authors:
Nedelcu, M; Sima, M; Visan, T; Pascu, T; Franga, I; Craciunoiu, F
Published: 2001, TWENTIETH INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS, 326, DOI: 10.1109/ICT.2001.979897
A method to produce composition modulated Bi2-xSbxTe3 alloys by electrodeposition has been developed. The electrolyte, which consists in a HCl 6M (pH = 0) aqueous solution, allows the codeposition of bismuth, antimony and tellurium to be accomplished at room temperature on glassy carbon, platinum or nickel electrode. The composition of the films. their crystal structures and morphology were studied as function of electrochemical parameters and bath composition. It is shown that the electrodeposits are monophasic and exhibit a polycrystalline state. The electrical resistivity was of the order of 7-10 mOmegacm, whereas the electrodeposition rate value was 30-50 mum/h for the films with good thermoelectric properties.
67. PbSe1-xTex thick thermoelectric films obtained by electrochemical deposition from aqueous solutions
Authors:
Nedelcu, M; Sima, M; Stoica, T; Manea, AS; Lazarescu, MF; Visan, T
Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 914, DOI:
It is presented a study of PbSe1-xTex thick films electrodeposition on glassy carbon and ITO electrodes in acid solutions (0.1M HNO3), using cyclic voltammetry and rotating-disk techniques. Electrochemical impedance spectroscopy study of PbSe1-xTex film in 0.1M HNO3 is reported.
68. Magneto-thermoelectric alloys obtained by electrodeposition
Authors:
Nedelcu, M; Sima, M; Aldica, G; Apostol, E
Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 720, DOI:
When a magnetic field is applied on a narrow gap semiconductor with high hole mobility, a substantial rise in the figure of merit can be observed due to Ethinghausen effect. The most important proof of this effect was achieved by using Bi-Sb alloys. The present paper is devoted to performance of the electrochemical synthesis of Bi-Sb alloys from acid aqueous solutions and to the investigations of physico-chemical. properties of these alloys. Thick films of Bi-Sb alloy were electrodeposited from both chloride and perchlorate solutions. The electro-deposited films obtained from perclorate solutions are thicker, more compact and more uniform. The Bi/Sb ratio in the solution bulk was found to be approximately the same to the Bi/Sb ratio in the electrodeposited alloy. The Hall effect was measured by a home-made apparatus. The range of the magnetic field (B) determined by a standard induction coil was 0.05-1 T. Carrier concentration, n is 10(18) cm(-3) and increases slow in the choosen magnetic range.
69. Characterization of perchlorate or sulphate doped polyaniline films by electrochemical impedance spectroscopy
Authors:
Visan, T; Sima, M; Buda, M; Marin, G
Published: MAY 1999, REVUE ROUMAINE DE CHIMIE, 44, 517, DOI:
Cyclic voltammetry and impedance spectroscopy were used for study of polyaniline in acid solutions. Impedance spectra were presented both as Bode diagrams and Nyquist representations. The capacitive charging behaviour and anion (ClO4-, HSO4-) insertion/elimination reaction of the polymer film were discussed on the basis of a simplified Randles circuit model. The examined scanning electron micrographs have also shown that the nature of dopant anion changes the film morphology.
70. A comparative study of zinc-polyaniline electrochemical cells having sulfate and chloride electrolytes
Authors:
Sima, M; Visan, T; Buda, M
Published: AUG 1995, JOURNAL OF POWER SOURCES, 56, 136, DOI: 10.1016/0378-7753(95)80024-B
Polyaniline (PANI) films were investigated at 20 degrees C as the positive electrodes for Zn/PANI secondary cells containing either 1 M ZnCl2, 0.5 M NH4Cl or 1 M ZnSO4, 0.18 M (NH4)(2)SO4 electrolytes, respectively, at pH=4.5, Cyclic voltammograms showed similar behaviour for the thin PANI films as those in highly acid media. From the discharge curves specific capacities were calculated of 127-130 Ah kg(-1) for the Zn/PANI, Cl- cell and 82-107 Ah kg(-1) for the Zn/PANI, SO42- cell. Charging limit values of 1.48 V for the Zn/PANI, Cl- cell and 1.52 V for the Zn/PANI SO42- cell were obtained in order to prevent the electrochemical inactivation of the polymer. After 20 to 30 cycles the capacity of both cells decreases rapidly and then levels off. The self-discharge process is important only in the first approximately 80 h, after which the open-circuit voltage remains constant. Zn/PANI, Cl- cell showed better electrical characteristics for use as a secondary system.
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