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Dr. Camelia FLORICA

Scientific Researcher III

Laboratory of Functional Nanostructures

camelia[DOT]florica[AT]infim[DOT]ro

Publications

1. Nanohybrid Composites Based on TiO2 and Single-Walled Carbon Nanohorns as Promising Catalysts for Photodegradation of Amoxicillin
Authors: Cercel, R; Androne, A; Florica, CS; Lorinczi, A; Serbschi, C; Baibarac, M

Published: OCT 2023, MOLECULES, 28, 6958, DOI: 10.3390/molecules28196958

In this work, applications of nanohybrid composites based on titanium dioxide (TiO2) with anatase crystallin phase and single-walled carbon nanohorns (SWCNHs) as promising catalysts for the photodegradation of amoxicillin (AMOX) are reported. In this order, TiO2/SWCNH composites were prepared by the solid-state interaction of the two chemical compounds. The increase in the SWCNH concentration in the TiO2/SWCNH composite mass, from 1 wt.% to 5 wt.% and 10 wt.% induces (i) a change in the relative intensity ratio of the Raman lines located at 145 and 1595 cm(-1), which are attributed to the E-g(1) vibrational mode of TiO2 and the graphitic structure of SWCNHs; and (ii) a gradual increase in the IR band absorbance at 1735 cm(-1) because of the formation of new carboxylic groups on the SWCNHs' surface. The best photocatalytic properties were obtained for the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.%, when approx. 92.4% of AMOX removal was achieved after 90 min of UV irradiation. The TiO2/SWCNH composite is a more efficient catalyst in AMOX photodegradation than TiO2 as a consequence of the SWCNHs' presence, which acts as a capture agent for the photogenerated electrons of TiO2 hindering the electron-hole recombination. The high stability of the TiO2/SWCNH composite with a SWCNH concentration of 5 wt.% is proved by the reusing of the catalyst in six photodegradation cycles of the 98.5 mu M AMOX solution, when the efficiency decreases from 92.4% up to 78%.
2. Self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors
Authors: Costas, A; Florica, C; Preda, N; Besleaga, C; Kuncser, A; Enculescu, I

Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6834, DOI: 10.1038/s41598-022-10879-5

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.
3. New Aspects Concerning the Ampicillin Photodegradation
Authors: Cercel, R; Paraschiv, M; Florica, CS; Daescu, M; Udrescu, A; Ciobanu, RC; Schreiner, C; Baibarac, M

Published: APR 2022, PHARMACEUTICALS, 15, 415, DOI: 10.3390/ph15040415

New aspects concerning the photodegradation (PD) of ampicillin are reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. The exposure of ampicillin in the absence (AM) and in the presence of the excipient (AMP) to UV light leads to an intensity diminution of the photoluminescence excitation (PLE) and photoluminescence (PL) spectra and the emergence of a new IR band at 3450 cm(-1). The photoluminescence studies demonstrate that the AM PD is amplified in the presence of excipients and an alkaline medium. In this last case, the PD process of AM involves the emergence of new compounds, whose presence is highlighted by: (i) the emergence of the isosbestic point at 300 nm in the UV-VIS spectra; (ii) a change in the ratio between the absorbance of IR bands situated in the spectral ranges 1200-1660 and 3250-3450 cm(-1); and (iii) a change in the ratio between the intensities of the Raman lines localized in the spectral ranges 1050-1800 and 2750-3100 cm(-1). A chemical mechanism of the PD processes of AM in an alkaline medium is proposed.
4. Photodetecting properties of single CuO-ZnO core-shell nanowires with p-n radial heterojunction
Authors: Costas, A; Florica, C; Preda, N; Kuncser, A; Enculescu, I

Published: OCT 29 2020, SCIENTIFIC REPORTS, 10, DOI: 10.1038/s41598-020-74963-4

CuO-ZnO core-shell radial heterojunction nanowire arrays were obtained by a simple route which implies two cost-effective methods: thermal oxidation in air for preparing CuO nanowire arrays, acting as a p-type core and RF magnetron sputtering for coating the surface of the CuO nanowires with a ZnO thin film, acting as a n-type shell. The morphological, structural, optical and compositional properties of the CuO-ZnO core-shell nanowire arrays were investigated. In order to analyse the electrical and photoelectrical properties of the metal oxide nanowires, single CuO and CuO-ZnO core-shell nanowires were contacted by employing electron beam lithography (EBL) and focused ion beam induced deposition (FIBID). The photoelectrical properties emphasize that the p-n radial heterojunction diodes based on single CuO-ZnO core-shell nanowires behave as photodetectors, evidencing a time-depending photoresponse under illumination at 520 nm and 405 nm wavelengths. The performance of the photodetector device was evaluated by assessing its key parameters: responsivity, external quantum efficiency and detectivity. The results highlighted that the obtained CuO-ZnO core-shell nanowires are emerging as potential building blocks for a next generation of photodetector devices.
5. Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes
Authors: Locovei, C; Filipoiu, N; Kuncser, A; Stanciu, AE; Antohe, S; Florica, CF; Costas, A; Enculescu, I; Piraux, L; Kuncser, V; Antohe, VA

Published: DEC 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10122444

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures' electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.
6. Laser Processed Antimicrobial Nanocomposite Based on Polyaniline Grafted Lignin Loaded with Gentamicin-Functionalized Magnetite
Authors: Visan, AI; Popescu-Pelin, G; Gherasim, O; Grumezescu, V; Socol, M; Zgura, I; Florica, C; Popescu, RC; Savu, D; Holban, AM; Cristescu, R; Matei, CE; Socol, G

Published: FEB 2019, POLYMERS, 11, DOI: 10.3390/polym11020283

Composite thin coatings of conductive polymer (polyaniline grafted lignin, PANI-LIG) embedded with aminoglycoside Gentamicin sulfate (GS) or magnetite nanoparticles loaded with GS (Fe3O4@GS) were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. The aim was to obtain such nanostructured coatings for titanium-based biomedical surfaces, which would induce multi-functional properties to implantable devices, such as the controlled release of the therapeutically active substance under the action of a magnetic and/or electric field. Thus, the unaltered laser transfer of the initial biomaterials was reported, and the deposited thin coatings exhibited an appropriate nanostructured surface, suitable for bone-related applications. The laser processing of PANI-LIG materials had a meaningful impact on the composites' wettability, since the contact angle values corresponding to the composite laser processed materials decreased in comparison with pristine conductive polymer coatings, indicating more hydrophilic surfaces. The corrosion resistant structures exhibited significant antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans strains. In vitro cytotoxicity studies demonstrated that the PANI-LIG-modified titanium substrates can allow growth of bone-like cells. These results encourage further assessment of this type of biomaterial for their application in controlled drug release at implantation sites by external activation.
7. Core-shell nanowire arrays based on ZnO and CuxO for water stable photocatalysts
Authors: Florica, C; Costas, A; Preda, N; Beregoi, M; Kuncser, A; Apostol, N; Popa, C; Socol, G; Diculescu, V; Enculescu, I

Published: NOV 21 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-53873-0

Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.
8. Radial heterojunction based on single ZnO-CuxO core-shell nanowire for photodetector applications
Authors: Costas, A; Florica, C; Preda, N; Apostol, N; Kuncser, A; Nitescu, A; Enculescu, I

Published: APR 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-42060-w

ZnO-CuxO core-shell radial heterojunction nanowire arrays were fabricated by a straightforward approach which combine two simple, cost effective and large-scale preparation methods: (i) thermal oxidation in air of a zinc foil for obtaining ZnO nanowire arrays and (ii) radio frequency magnetron sputtering for covering the surface of the ZnO nanowires with a CuxO thin film. The structural, compositional, morphological and optical properties of the high aspect ratio ZnO-CuxO core-shell nanowire arrays were investigated. Individual ZnO-CuxO core-shell nanowires were contacted with Pt electrodes by means of electron beam lithography technique, diode behaviour being demonstrated. Further it was found that these n-p radial heterojunction diodes based on single ZnO-CuxO nanowires exhibit a change in the current under UV light illumination and therefore behaving as photodetectors.
9. Magnetism and magnetoresistance of single Ni-Cu alloy nanowires
Authors: Costas, A; Florica, C; Matei, E; Toimil-Molares, ME; Stavarache, I; Kuncser, A; Kuncser, V; Enculescu, I

Published: AUG 30 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 2355, DOI: 10.3762/bjnano.9.219

Arrays of magnetic Ni-Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithography was used for contacting single nanowires in order to investigate their galvano-magnetic properties. The results of the magnetoresistance measurements made on single Ni-Cu alloy nanowires of different compositions have been reported and discussed in detail. A direct methodology for transforming the magnetoresistance data into the corresponding magnetic hysteresis loops was proposed, opening new possibilities for an easy magnetic investigation of single magnetic nanowires in the peculiar cases of Stoner-Wohlfarth-like magnetization reversal mechanisms. The magnetic parameters of single Ni-Cu nanowires of different Ni content have been estimated and discussed by the interpretation of the as derived magnetic hysteresis loops via micromagnetic modeling. It has been theoretically proven that the proposed methodology can be applied over a large range of nanowire diameters if the measurement geometry is suitably chosen.
10. Organic heterostructures obtained on ZnO/Ag/ZnO electrode
Authors: Socol, M; Preda, N; Breazu, C; Florica, C; Costas, A; Istrate, CM; Stanculescu, A; Girtan, M; Gherendi, F

Published: AUG 2018, VACUUM, 154, 370, DOI: 10.1016/j.vacuum.2018.05.039

This work is focused on the use of multilayer transparent conductive electrode (TCE) based on ZnO/Ag/ZnO in the fabrication of the organic heterostructures. The ZnO/Ag/ZnO obtained combining sputtering/thermal evaporation/sputtering techniques is featured by a good optical transmittance, a low electrical resistivity and a reduced roughness. All these characteristics recommend it as a viable alternative to indium tin oxide (ITO) for different applications. The organic materials, N,N' - diphenyl N,N' - bis (1 - aphthyl) 1,1' - biphenyl 4,4' - diamine (alpha-NPD), 5,12-Dihydro-5-12-dimethylquino [2,3-b]acridine-7,14dione (DMQA) and 4,7 diphenyl-1,10-phenanthroline (BPhen) were deposited by vacuum thermal evaporation (VTE) method, the properties of the obtained layers being investigated by FTIR, UV-VIS and PL) spectroscopy. The I-V characteristic (recorded in dark) of the organic heterostructure fabricated on the ZnO/Ag/ZriO electrode shows diode behavior, revealing its potential applications in the organic light emitting devices (OLED).
11. IZO deposited by PLD on flexible substrate for organic heterostructures
Authors: Socol, M; Preda, N; Stanculescu, A; Breazu, C; Florica, C; Rasoga, O; Stanculescu, F; Socol, G

Published: MAY 2017, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 123, DOI: 10.1007/s00339-017-0992-4

In: ZnO (IZO) thin films were deposited on flexible plastic substrates by pulsed laser deposition (PLD) method. The obtained layers present adequate optical and electrical properties competitive with those based on indium tin oxide (ITO). The figure of merit (9 X 10(-3) Omega(-1)) calculated for IZO layers demonstrates that high quality coatings can be prepared by this deposition technique. A thermal annealing (150 degrees C for 1 h) or an oxygen plasma etching (6 mbar for 10 min.) were applied to the IZO layers to evaluate the influence of these treatments on the properties of the transparent coatings. Using vacuum evaporation, organic heterostructures based on cooper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) were deposited on the untreated and treated IZO layers. The optical and electrical properties of the heterostructures were investigated by UVVis, FTIR and current-voltage (I-V) measurements. For the heterostructure fabricated on IZO treated in oxygen plasma, an improvement in the current value with at least one order of magnitude was evidenced in the I-V characteristics recorded in dark conditions. Also, an increase in the current value for the heterostructure deposited on untreated IZO layer can be achieved by adding an organic layer such as tris-8-hydroxyquinoline aluminium (Alq(3)).
12. Laser deposition of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) - lysozyme microspheres based coatings with anti-microbial properties
Authors: Grumezescu, V; Holban, AM; Sima, LE; Chiritoiu, MB; Chiritoiu, GN; Grumezescu, AM; Ivan, L; Safciuc, F; Antohe, F; Florica, C; Luculescu, CR; Chifiriuc, MC; Socol, G

Published: APR 15 2017, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 521, 195, DOI: 10.1016/j.ijpharm.2017.01.069

The purpose of this study was to obtain, characterize and evaluate the cytotoxicity and antimicrobial activity of coatings based on poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) -Lysozyme (P(3HB3HV)/ Lys) and P(3HB-3HV) -Polyethylene glycol -Lysozyme (P(3HB-3HV)/PEG/Lys) spheres prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique, in order to obtain functional and improved Ti-based implants. Morphological investigation of the coatings by Infrared Microscopy (IRM) and SEM revealed that the average diameter of P(3HB-3HV)/Lys spheres is around 2 mm and unlike the drop cast samples, IRM recorded on MAPLE films revealed a good distribution of monitored functional groups on the entire scanned surface. The biological evaluation of MAPLE structured surfaces revealed an improved biocompatibility with respect to osteoblasts and endothelial cells as compared with Ti substrates and an enhanced anti-biofilm effect against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) tested strains. Thus, we propose that the fabricated P(3HB-3HV)/PEG/Lys and P(3HB-3HV)/Lys microspheres may be efficiently used as a matrix for controlled local drug delivery, with practical applications in developing improved medical surfaces for the reduction of implant-associated infections. (C) 2017 Elsevier B. V. All rights reserved.
13. Antimicrobial polycaprolactone/polyethylene glycol embedded lysozyme coatings of Ti implants for osteoblast functional properties in tissue engineering
Authors: Visan, A; Cristescu, R; Stefan, N; Miroiu, M; Nita, C; Socol, M; Florica, C; Rasoga, O; Zgura, I; Sima, LE; Chiritoiu, M; Chifiriuc, MC; Holban, AM; Mihailescu, IN; Socol, G

Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 243, DOI: 10.1016/j.apsusc.2016.11.129

In this study, coatings based on lysozyme embedded into a matrix of polyethylene glycol (PEG) and polycaprolactone (PCL) were fabricated by two different methods (Matrix Assisted Pulsed Laser Evaporation -MAPLE and Dip Coating) for obtaining antimicrobial coatings envisaged for long term medical applications. Coatings with different PEG: PCL compositions (3: 1; 1: 1; 1: 3) were synthesized in order to evaluate the antimicrobial activity of lysozyme embedded into the polymeric matrix. The main surface features, such as roughness and wettability, with impact on the microbial adhesion as well as on the eukaryote cell function were measured. The obtained composite coatings exhibited a significant antibacterial activity against Escherichia coli, Bacillus subtilis, Enterococcus faecalis and Staphylococcus aureus strains. As well, specific blended coatings showed appropriate viability, good spreading and normal cell morphology of SaOs2 human osteoblasts and mesenchymal stem cells (MSCs). These investigations highlight the suitability of biodegradable composites as implant coatings for decreasing the risk of bacterial contamination associated with prosthetic procedures. (C) 2016 Elsevier B.V. All rights reserved.
14. Organic heterostructures deposited by MAPLE on AZO substrate
Authors: Socol, M; Preda, N; Stanculescu, A; Breazu, C; Florica, C; Stanculescu, F; Iftimie, S; Girtan, M; Popescu-Pelin, G; Socol, G

Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 203, DOI: 10.1016/j.apsusc.2017.02.260

Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence (PL) and current-voltage (I-V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode. (C) 2017 Elsevier B.V. All rights reserved.
15. ZnO nanowires grown directly on zinc foils by thermal oxidation in air: Wetting and water adhesion properties
Authors: Florica, C; Preda, N; Costas, A; Zgura, I; Enculescu, I

Published: MAY 1 2016, MATERIALS LETTERS, 170, 159, DOI: 10.1016/j.matlet.2016.02.035

Large scale ZnO nanowire arrays were grown directly on zinc foils using the thermal oxidation in air method. The X-ray diffraction and reflectance investigations confirm that the as-grown nanowires properties are typical for ZnO having a hexagonal wurtzite crystalline structure and band-gap values between 3.2 and 3.3 eV. The scanning electron microscopy images prove that the density and the dimensions (diameter and length) of the ZnO nanowires can be tuned by controlling the oxidation temperature. Wettability studies reveal in the case of Zn foils a hydrophilic behavior with high water droplet adhesion which is transformed into a superhydrophobic one with low water droplet adhesion after the foils' surfaces are covered with ZnO nanowires. Obtaining functional surfaces with such interesting wetting properties using a simple, inexpensive and highly reproducible thermal oxidation in air technique is very attractive for anticorrosion coatings and self-cleaning applications. (C) 2016 Elsevier B.V. All rights reserved.
16. POLYESTER FABRICS COVERED WITH AMORPHOUS TITANIUM DIOXIDE LAYERS: COMBINING WETTABILITY MEASUREMENTS AND PHOTOINDUCED HYDROPHILICITY TO ASSESS THEIR SURFACE PROPERTIES
Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Cotorobai, VF; Ganea, CP

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 269, DOI:

Wettability properties of thin TiO2 amorphous layers obtained by sputtering or sol-gel onto polyester textile materials were investigated. Contact angle (CA) measurements by the sessile drop method were used to evaluate these properties. Comparison was performed with coated samples of related poly(lactic acid) material. The samples coated by sol gel have CAs a few degrees higher than those coated by sputtering. Wetting properties were conversely changed under alternate darkness/illumination conditions. Photoinduced hydrophilicity was observed even for these amorphous coating particles, being higher for sputtered samples than for sol gel ones.
17. High performance FETs based on ZnO nanowires synthesized by low cost methods
Authors: Florica, C; Costas, A; Kuncser, A; Preda, N; Enculescu, I

Published: NOV 25 2016, NANOTECHNOLOGY, 27, DOI: 10.1088/0957-4484/27/47/475303

Single ZnO nanowires prepared by wet and dry methods are used as channels in high performance back-gated field effect transistors working in low power operation mode, with on-off ratios up to 10(5) and mobilities up to 167 cm(2) V-1 s(-1). The nanowires' properties, generated by the growth techniques, influence the parameters of the transistors, therefore a throughout comparison is made.
18. Electrical properties of templateless electrodeposited ZnO nanowires
Authors: Matei, E; Costas, A; Florica, C; Enculescu, M; Pintilie, I; Pintilie, L; Enculescu, I

Published: FEB 2016, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 42, 372, DOI: 10.1016/j.mssp.2015.11.007

Electrochemical deposition allows the preparation of ZnO nanostructures with precisely controlled morphology and properties, by finely tuning the process parameters. ZnO nanowires were deposited onto gold substrates by electrodeposition from a low concentration zinc nitrate bath Photolithography was employed for patterning interdigitated electrode systems onto silicon/silicon dioxide substrates and ZnO electrodeposition lead to wires connected to each other by bridging neighboring interdigits allowing electronic transport characterization. Optical measurements, i.e. reflection and photoluminescence spectroscopy, were performed and the results were correlated to electronic transport data. We found that we deal with a system for which one can apply a model of space charge limited currents with different traps energy distribution as a consequence of electrodeposition rate. Current versus temperature measurements show different behavior for lower and higher range of temperatures. Such nanowires, fabricated and contacted in a straightforward way, allow a wide area of applications ranging from conductometric bio- or chemo-sensors to optoelectronic devices. (C) 2015 Elsevier Ltd. All rights reserved.
19. Electrical properties of single CdTe nanowires
Authors: Matei, E; Florica, C; Costas, A; Toimil-Molares, ME; Enculescu, I

Published: FEB 12 2015, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 450, DOI: 10.3762/bjnano.6.45

Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were performed on these individual nanowires. The influence of a bottom gate was investigated and it was found that surface passivation leads to improved transport properties.
20. ELECTROSPRAYING OF ZnO MICROSTRUCTURES FOR ELECTRICAL CONTACTING
Authors: Costas, A; Florica, C; Evanghelidis, A; Enculescu, M; Preda, N; Enculescu, I

Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1188, DOI:

ZnO complex microstructures were deposited onto interdigitated metallic electrodes by electrospraying. Simple methods, such as wet chemical precipitation and optical lithography, were used for the synthesis of flower-like and snowflake-like ZnO structures and for the preparation of interdigitated metallic electrodes, respectively. The electrosprayed ZnO particles preserve the structural, optical and morphological properties of the chemically synthesized ZnO powders. During the electrospraying process, the ZnO microstructures form bridges between the interdigitated metallic electrodes leading to electrical contacting. Changes in the electron transport through the ZnO microstructures are evidenced by their exposure to ammonia or their passivation with poly(methyl methacrylate). Merging such easy-scalable and low-cost techniques, devices based on electrosprayed complex ZnO structures can be designed.
21. Electrical properties of single CuO nanowires for device fabrication: Diodes and field effect transistors
Authors: Florica, C; Costas, A; Boni, AG; Negrea, R; Ion, L; Preda, N; Pintilie, L; Enculescu, I

Published: JUN 1 2015, APPLIED PHYSICS LETTERS, 106, DOI: 10.1063/1.4921914

High aspect ratio CuO nanowires are synthesized by a simple and scalable method, thermal oxidation in air. The structural, morphological, optical, and electrical properties of the semiconducting nanowires were studied. Au-Ti/CuO nanowire and Pt/CuO nanowire electrical contacts were investigated. A dominant Schottky mechanism was evidenced in the Au-Ti/CuO nanowire junction and an ohmic behavior was observed for the Pt/CuO nanowire junction. The Pt/CuO nanowire/Pt structure allows the measurements of the intrinsic transport properties of the single CuO nanowires. It was found that an activation mechanism describes the behavior at higher temperatures, while a nearest neighbor hopping transport mechanism is characteristic at low temperatures. This was also confirmed by four-probe resistivity measurements on the single CuO nanowires. By changing the metal/semiconductor interface, devices such as Schottky diodes and field effect transistors based on single CuO p-type nanowire semiconductor channel are obtained. These devices are suitable for being used in various electronic circuits where their size related properties can be exploited. (c) 2015 AIP Publishing LLC.
22. Titanium dioxide layer deposited at low temperature upon polyester fabrics
Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Ganea, CP; Negrila, CC; Diamandescu, L

Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1063, DOI:

TiO2 deposition by sputtering or sol-gel techniques was applied onto less thermal stable polyester textiles and onto a related poly(lactic acid) material. The temperature of deposition and of the further treatment was low enough as allowed by the support nature. Structural and spectroscopic characterization of the raw and coated samples has been performed. TiO2 coated particles are amorphous as indicated by X-ray diffraction and scanning electron microscopy. Sputtered layers consist in aggregates randomly distributed on the substrate while the sol gel layers show a uniform coverage of nanoparticles having a mosaic-like structure. The morphology of the sputtered layers depends on the deposition pressure as well. The loading degree estimated on the basis of the thermogravimetric data is rather low (ca. 2%), but the fabric properties are much influenced by the deposition. Photocatalytic activity also present on the coated surfaces was evaluated in the methylene blue degradation. TiO2 layer is quite adherent as checked by an ultra-sonication method.
23. Correlation of optical reflectivity with numerical calculations for a two-dimensional photonic crystal designed in Ge
Authors: Husanu, MA; Popescu, DG; Ganea, CP; Anghel, I; Florica, C

Published: DEC 10 2015, EUROPEAN PHYSICAL JOURNAL D, 69, DOI: 10.1140/epjd/e2015-60478-7

A two dimensional photonic crystal (2DPhC) with triangular symmetry is investigated using optical reflectivity measurements and numerical calculations. The system has been obtained by direct laser writing, using a pulsed laser (lambda = 775 nm), perforating an In-doped Ge wafer. A lattice of holes with well-defined symmetry has been designed. Analyzing the spectral signature of PBGs recorded experimentaly with finite difference time domain theoretical calculations one was able to prove the relation between the geometric parameters (hole format, lattice constant) of the system and its ability to trap and guide the radiation in specific energy range. It was shown that at low frequency and telecommunication ranges of transvelsal electric modes photonic band gap occur. This structure may have potential aplications in designing photonic devices with applications in energy storage and conversion as potential alternative to Si-based technology.
24. Zinc oxide electroless deposition on electrospun PMMA fiber mats
Authors: Preda, N; Evanghelidis, A; Enculescu, M; Florica, C; Enculescu, I

Published: JAN 1 2015, MATERIALS LETTERS, 138, 242, DOI: 10.1016/j.matlet.2014.10.021

ZnO crystallites were grown by electroless deposition on poly(methyl methacrylate) (PMMA) fiber mats prepared by an electrospinning technique. The electroless deposition involves three steps: sensitization, activation and deposition, which were performed by subsequently dipping the PMMA fiber mats in the appropriate solutions. After the deposition the PMMA fibers are uniformly coated with ZnO prisms which show hexagonal wurtzite structure and optical signatures (band-gap value and emission bands) typical for this semiconductor. By combining electroless deposition and electrospinning, different semiconductor coated polymer fibers can be obtained for a wide range of applications. Both methods are appropriate for large scale production, being scalable, cheap, efficient and suitable for large-area covering techniques. (C) 2014 Elsevier B.V. All rights reserved.
25. DEPOSITION OF TITANIUM DIOXIDE LAYERS UPON POLYESTER TEXTILE MATERIALS: CHECKING THE ADHERENCE BY ULTRA-SONICATION
Authors: Zgura, I; Frunza, S; Enculescu, M; Florica, C; Cotorobai, F

Published: 2015, ROMANIAN JOURNAL OF PHYSICS, 60, 494, DOI:

An important parameter of deposited thin films is their adhesion to the substrate materials, we focused on the adhesion of TiO2 layer by sol-gel or sputtering onto textile substrate as checked by an ultra-sonication method. The characterization-made prior and after the tests have shown a good adherence of the nanoparticles, despite the low deposition temperature.
26. Surface topography to reflectivity mapping in two-dimensional photonic crystals designed in germanium
Authors: Husanu, MA; Ganea, CP; Anghel, I; Florica, C; Rasoga, O; Popescu, DG

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 1191, DOI: 10.1016/j.apsusc.2015.07.218

Light confinement in a two dimensional photonic crystal (2D PhC) with hexagonal symmetry is studied using infra-red reflectance spectromicroscopy and numerical calculations. The structure has been realized by laser ablation, using a pulsed laser (lambda = 775 nm), perforating an In-doped Ge wafer and creating a lattice of holes with well-defined symmetry. Correlating the spectral signature of the photonic gaps recorded experimentally with the results obtained in the finite difference time domain and finite difference frequency domain calculations, we established the relationship between the geometric parameters of the structure (lattice constants, shape of the hole) and its efficiency in trapping and guiding the radiation in a well-defined frequency range. Besides the gap in the low energy range of transversal electric modes, a second one is identified in the telecommunication range, originating in the localization of the leaky modes within the radiation continuum. The emerging picture is of a device with promising characteristics as an alternative to Si-based technology in photonic device fabrication with special emphasize in energy storage and conversion. (C) 2015 Elsevier B.V. All rights reserved.
27. Metallic Nanowires and Nanotubes Prepared by Template Replication
Authors: Matei, E; Enculescu, M; Preda, N; Florica, C; Costas, A; Busuioc, C; Molares, MET; Kuncser, V; Enculescu, I

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 165, DOI: 10.1007/978-3-662-44479-5_6

Low dimensional nanostructures represent a hot scientific field nowadays due mainly to the tremendous potential for applications. Low dimensions open the possibilities for both ultra-miniaturization and increase in functionality. Numerous procedures were developed for fabricating such nanostructures. Template replication represents a highly effective method in fabricating metallic nanowires and nanotubes. The approach is characterized by the excellent control in obtaining nano objects with the desired shape and dimensions. A large variety of templates are available ranging from viruses and proteins to nanoporous membranes fabricated by using swift heavy ion accelerators. In the following chapter the main steps involved in employing the method for fabricating metalic nanowires and nanotubes by replicating ion track nanoporous membranes were described. The steps include here membrane fabrication and replication and involve track etching and electrochemical metal deposition. The influence of the process parameters on the properties of the nanoobjects prepared by this approach was reviewed. It was found that simple experimental parameters can be chosen in such a way that the functionality of the nanowires or nanotubes can be finely tuned.
28. Field Effect Transistor with Electrodeposited ZnO Nanowire Channel
Authors: Florica, C; Matei, E; Costas, A; Molares, MET; Enculescu, I

Published: AUG 10 2014, ELECTROCHIMICA ACTA, 137, 297, DOI: 10.1016/j.electacta.2014.05.124

ZnO nanowires were prepared by electrochemical deposition in polycarbonate ion track templates. After the deposition process the polymer templates were dissolved in dichloromethane and the nanowires were harvested by ultrasonication in isopropyl. A droplet of nanowire suspension was placed on a Si/SiO2 substrate patterned with interdigitated electrodes. By means of electron beam lithography single nanowires were selected and provided with electrical contacts. We found that in order to obtain reliable electrical contacts and typical field effect characteristics the electrode deposition process needs to be adapted to the 3 D shape of the wires and that annealing and passivation treatments are necessary. (C) 2014 Elsevier Ltd. All rights reserved.
29. INFLUENCE OF PREPARATION STEPS ON THE PROPERTIES OF ELECTROSPUN ZnO FIBERS
Authors: Busuioc, C; Evanghelidis, A; Florica, C; Enculescu, I

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1578, DOI:

ZnO nanofibers were obtained by calcination of electrospun Zn(Ac)(2)center dot 2H(2)O/PMMA composite fibers and characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. The thermal treatment led to polymer burning and polycrystalline hexagonal ZnO phase formation. The average fiber diameters range between 450 and 600 nm before calcination and 200 - 300 nm after calcination. PL investigation revealed a strong dependence of ZnO fibers emission band on the calcination temperature. Furthermore, electrical contacts were fabricated by photolithography and electric characteristics were measured.
30. DEPENDENCE ON THE DYE'S TYPE AND CONCENTRATION OF THE EMISSIVE PROPERTIES OF ELECTROSPUN DYE-DOPED BEADED NANOFIBERS
Authors: Enculescu, M; Evanghelidis, A; Busuioc, C; Florica, C; Costas, A; Oancea, M; Preda, N; Matei, E; Enculescu, I

Published: APR-JUN 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 816, DOI:

Luminescent polymer fibers were obtained by electrospinning solutions of 8% (in ethanol) polyvinylpyrrolidone (PVP) doped with three different dyes (coumarin 6, rhodamine 6G and sulforhodamine 101). Using the same parameters for the electrospinning process, nanofibers with diameters between 200 and 800 nm and different sizes and distributions of the beads were obtained as proven by scanning electron microscopy (SEM). We assessed the dependence of their emissive properties (intensity and wavelength) on the type of dye using photoluminescence (PL) spectra for the same concentration of the dopand dye (10(-3)M). Moreover, employing 4 different concentrations for coumarin 6 and rhodamine 6G (from 10(-3) to 10(-6) M) we evaluated the dependence with the concentration of the dye on the emissive properties of the electrospun dye-doped PVP nanofibers.
31. Superhydrophobic ZnO networks with high water adhesion
Authors: Florica, C; Preda, N; Enculescu, M; Zgura, I; Socol, M; Enculescu, I

Published: AUG 8 2014, NANOSCALE RESEARCH LETTERS, 9, DOI: 10.1186/1556-276X-9-385

ZnO structures were deposited using a simple chemical bath deposition technique onto interdigitated electrodes fabricated by a conventional photolithography method on SiO2/Si substrates. The X-ray diffraction studies show that the ZnO samples have a hexagonal wurtzite crystalline structure. The scanning electron microscopy observations prove that the substrates are uniformly covered by ZnO networks formed by monodisperse rods. The ZnO rod average diameter and length were tuned by controlling reactants' concentration and reaction time. Optical spectroscopy measurements demonstrate that all the samples display bandgap values and emission bands typical for ZnO. The electrical measurements reveal percolating networks which are highly sensitive when the samples are exposed to ammonia vapors, a variation in their resistance with the exposure time being evidenced. Other important characteristics are that the ZnO rod networks exhibit superhydrophobicity, with water contact angles exceeding 150 degrees and a high water droplet adhesion. Reproducible, easily scalable, and low-cost chemical bath deposition and photolithography techniques could provide a facile approach to fabricate such ZnO networks and devices based on them for a wide range of applications where multifunctionality, i.e., sensing and superhydrophobicity, properties are required.
32. Zinc Oxide and Polysaccharides: Promising Candidates for Functional Nanomaterials
Authors: Preda, N; Enculescu, M; Zgura, I; Socol, M; Florica, C; Evanghelidis, A; Matei, E; Enculescu, I

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 136, DOI: 10.1007/978-3-662-44479-5_5

Recently, ZnO and natural polysaccharides have received more and more attention as interesting components for designing complex functional nanomaterials, key elements being their high occurrence and low-cost. In this chapter are presented possibilities for tailoring the ZnO properties by using polysaccharides in the synthesis process as well as reports on the functionalization of cellulose-based natural fabrics with ZnO. In both cases, in the preparation step were used only simple and scalable wet chemical methods. The resulting materials with suitable characteristics, e.g. dependence of the ZnO nanostructures optical properties on their morphology or high-UV blocking and superhydrophobicity for ZnO-functionalized fabrics, can find applications in domains where such qualities are required.
33. Micropatterned ZnO rod arrays prepared by Au-catalyzed electroless deposition
Authors: Florica, C; Preda, N; Enculescu, M; Enculescu, I

Published: JUL 2014, PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 8, 652, DOI: 10.1002/pssr.201409089

Micropatterned ZnO was synthesized by an electroless deposition process using Au stripes as catalytic surfaces. The Au-patterned electrodes were prepared on SiO2/Si wafers using photolithography. The site-selective deposition of patterned ZnO hexagonal rod arrays is confirmed by scanning electron microscopy. The ZnO micropatterned surface revealed a conversion of wettability from hydrophilic to super-hydrophobic depending on the deposition reaction parameters. The electrical measurements carried out at room temperature before and after exposure to ammonia vapors of the patterned ZnO arrays show a resistance variation with exposure time. Highly reproducible, easy scalable and low-cost, photolithography and electroless deposition techniques could provide a facile approach to fabricate functionalized micropatterns, for a wide range of applications. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
34. MORPHOLOGY-CONTROLLED SYNTHESIS OF ZnO STRUCTURES BY A SIMPLE WET CHEMICAL METHOD
Authors: Preda, N; Enculescu, M; Florica, C; Costas, A; Evanghelidis, A; Matei, E; Enculescu, I

Published: OCT-DEC 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1600, DOI:

Zinc oxide particles were synthesized by a simple wet chemical method. Using zinc nitrate and various precipitating agents, like KOH, NaOH and (CH2)(6)N-4, particles with different morphologies were obtained. Also, the addition of a structure-directing agent, like gum arabic - a highly branched biopolymer, leads to a decrease in the ZnO particles size (for KOH and NaOH) and to a dramatical change of the ZnO particle shape in the case of (CH2)(6)N-4. The X-ray diffraction analysis showed that all obtained samples are of wurtzite structure. The reflectance and photoluminescence spectra have been used to investigate the optical properties of the ZnO structures. The morphologies observed by scanning electron microscopy reveal snowflake-like, flower-like, star-like and double-raspberry-like structures. A possible formation mechanism for ZnO micro/nanostructures with different morphologies was proposed. The biopolymer-assisted crystallization method could provide a facile approach to synthesize other desired compounds with controllable morphology.
35. Transparent indium zinc oxide thin films used in photovoltaic cells based on polymer blends
Authors: Besleaga, C; Ion, L; Ghenescu, V; Socol, G; Radu, A; Arghir, I; Florica, C; Antohe, S

Published: SEP 1 2012, THIN SOLID FILMS, 520, 6806, DOI: 10.1016/j.tsf.2012.07.030

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.
36. Study of thiols deposition on GaAs
Authors: Ghita, RV; Cotirlan, C; Ungureanu, F; Florica, C; Negrila, CC

Published: JAN-FEB 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, 244, DOI:

A genuine GaAs surface is covered with a relatively thick layer (similar to nm) of native oxide pinning the Surface Fermi level within the band gap of semiconductor. The method presented in this work is related to sulfur passivation by treating n-GaAs in different solutions of alkane thiols. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs(100) face, that are putted in evidence by scanning electron microscopy (SEM) images and second harmonic generation (SHG) analysis. Using X-ray photoelectron spectroscopy (XPS) is presented a detailed analysis of XPS data at the surface of thiols on GaAs together with the presence of the covalent bond As-S. The electric characteristics of the AuGeNi/Thiol/GaAs structure are presented in I (V) curves recorded in the region of small currents.
37. PRODUCTION AND CHARACTERIZATION OF CdTe WIRE ARRAYS FOR HYBRID INORGANIC/ORGANIC PHOTOVOLTAIC CELLS
Authors: Florica, C; Arghir, I; Ion, L; Enculescu, I; Antohe, VA; Radu, A; Radu, M; Chisulescu, G; Dina, N; Antohe, S

Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 27, DOI:

A new approach for obtaining hybrid inorganic/organic photovoltaic structures, based on CdTe nanowires and organic dye films is reported. The wire arrays of CdTe (10(6) wires/cm(2)) were electrochemically grown using a template method. Ion track polycarbonate foils (30 micrometer thick) were used as templates and the growth conditions for obtaining good quality and stoichiometric CdTe nanowires were identified. After dissolving the polycarbonate template, a CdTe thin film (300 nm) has been deposited by thermal vacuum evaporation onto the wire array before the deposition of ZnPc film as organic absorber. Finally a ZnO thin film was deposited by Electron Pulsed Deposition on ZnPc, working as TCO top electrode. The structural, morphological, electrical and optical properties of each component layer are investigated. Typical parameters of the prepared photovoltaic structures are determined. The external quantum efficiency of the Au/wire array CdTe/CdTe(300 nm)/ZnPc/ZnO structures was significantly increased, with respect to that of Au/wire arrays CdTe/ZnPc/ZnO structures.
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