Publications

Electro-optical devices that work in a similar fashion as PDLCs (polymer-dispersed liquid crystals), produced from cellulose acetate (CA) electrospun fibers deposited onto indium tin oxide coated glass and a nematic liquid crystal (E7), were studied. CA and the CA/liquid crystal composite were characterized by multiple investigation techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the dielectric loss with the Havriliak-Negami functions. To determine the electrical characteristics of the studied samples, impedance measurements results were treated using the Cole-Cole diagram and the three-element equivalent model.

We explored in-gap states (IGSs) in perovskite oxide heterojunction films. We report that IGSs in these films play a crucial role in determining the formation and properties of interfacial two-dimensional electron gas (2DEG). We report that electron trapping by IGSs opposes charge transfer from the film to the interface. The IGS in films yielded insulating interfaces with polar discontinuity and explained low interface carrier density of conducting interfaces. An ion trapping model was proposed to explain the physics of the IGSs and some experimental findings, such as the unexpected formation of 2DEG at the initially insulating LaCrO3/SrTiO3 interface and the influence of substitution layers on 2DEG.

Un-doped ZnO (UDZO) and Li-doped ZnO (LZO) polycrystalline thin films were grown on platinized silicon by pulsed laser deposition (PLD). The electrical properties were investigated on as-grown and annealed UDZO and LZO films with capacitor configuration, using top and bottom platinum electrodes. In the case of the as-grown films it was found that the introduction of Li increases the resistivity of ZnO and induces butterfly shape in the C-V characteristic, suggesting ferroelectric-like behavior in LZO films. The properties of LZO samples does not significantly changes after thermal annealing while the properties of UDZO samples show significant changes upon annealing, manifested in a butterfly shape of the C-V characteristic and resistive-like switching. However, the butterfly shape disappears if long delay time is used in the C-V measurement, the characteristic remaining non-linear. Pyroelectric signal could be measured only on annealed films. Comparing the UDZO results with those obtained in the case of Li: ZnO, it was found that the pyroelectric properties are considerably enhanced by Li doping, leading to pyroelectric signal with about one order of magnitude larger at low modulation frequencies than for un-doped samples. Although the results of this study hint towards a ferroelectric-like behavior of Li doped ZnO, the presence of real ferroelectricity in this material remains controversial. (C) 2017 Elsevier B.V. All rights reserved.

Hydroxyapatite-starch composites solidify rapidly via jellification, making them suitable candidates for robocasting. However, many aspects related to hydroxyapatite powder characteristics, hydroxyapatite-starch interaction, and composites composition and properties need to be aligned with robocasting requirements to achieve a notable improvement in the functionality of printed scaffolds intended for bone regeneration. This article presents a preliminary evaluation of hydroxyapatite-starch microcomposites. Thermal analysis of the starting powders was performed for predicting composites' behavior during heat-induced densification. Also, morphology, mechanical properties, and hydroxyapatite-starch interaction were evaluated for the jellified composites and the porous bodies obtained after conventional sintering, for different starch additions, and for ceramic particle size distributions. The results indicate that starch could be used for hydroxyapatite consolidation in limited quantities, whereas the composites shall be processed under controlled temperature. Due to a different mechanical behavior induced by particle size and geometry, a wide particle size distribution of hydroxyapatite powder is recommended for further robocasting ink development.

Nowadays, the advances materials science have created the possibility of using nanomaterials as adsorbents in environmental technologies. This study is focused on the evaluation of C-HAp powders capacity in lead ions removal from contaminated solutions. The C-HAp powders after removal of lead (Pb2+) ions from contaminated water were characterized by X-Ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-ray analysis (EDX). The presence of lead in the hydroxyapatite powders after removal experiments was observed in the XPS general spectrum and also in the EDX spectra. In addition, the AAS studies revealed that the C-HAp powders possess a high affinity towards lead ions with an effective removal rate of 80% for an initial lead concentration of 20 mg.L-1.

The paper is focused on the investigation of the properties of some organic heterostructures deposited on patterned AZO electrodes. In the first step, 2D patterned arrays based on commercially photoresist were fabricated on glass substrates using nanoimprint litography. Next, on these periodic nanostructures, the transparent AZO layers were deposited by pulsed laser deposition. Further, heterostructures consisting in organic thin films such as 4,7 diphenyl-1,10-phenanthroline (BPhen) (electron transport layer), N,N'-di(1-naftalenil)-N,N'-diafenil-(1,1'-bifenil)-4,4'-diamina (alpha-NPD) (hole transport layer) and arylenevinylene oligomers (3,3-bis (N-hexylcarbazole)vinylbenzene (P13) and 1,4-bis [4-(N,N-diphenylamino)phenylvinyl] benzene (P78)) were obtained by matrix assisted pulsed laser evaporation. The fabricated multilayer organic structures have been investigated from optical (UV-VIS spectroscopy), morphological (scanning electron microscopy and atomic force microscopy) and electrical (I-V characteristics) point of view. An improvement in the current value recorded on the samples prepared on nanostructured electrode was recorded. The results evidence the possibility to integrate these heterostructures in organic electronic devices.

MoO2-Fe2O3 nanoparticle system was successfully synthesized by mechanochemical activation of MoO2 and alpha-Fe2O3 equimolar mixtures for 0-12 hours of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale. X-ray powder diffraction (XRD), Mossbauer spectroscopy and magnetic measurements were used to study the phase evolution of MoO2-Fe2O3 nanoparticle system under the mechanochemical activation process. The Mossbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextet and a doublet upon duration of the milling process with molybdenum dioxide. Recoilless fraction was determined using our dual absorber method and was found to decrease with increasing ball milling time. Magnetic measurements recorded at 5 and 300 K in an applied magnetic field of 50,000 Oe showed the magnetic properties in the antiferromagnetic and canted ferromagnetic states. The Morin transformation was evidenced by zero-field cooling-field cooling (ZFC-FC) measurements in 200 Oe and the transformation characteristic temperatures were shifted to lower values.

Iron oxide-dextran nanoparticle suspensions (IOD-NPsS) have attracted attention for their considerable applications in various biomedical area such as cosmetics, water remediation, hyperthermia, drug delivery or magnetic resonance imaging (MRI) contrast enhancement. In these research we report the antimicrobial studies on iron oxide-dextran colloidal suspension against prokaryotic cells such as Escherichia coli (E. coli). The ultrasound studies and dynamic light scattering (DLS) of iron oxide-dextran nanoparticle suspensions. According colloidal studies of the iron oxide suspension, the nanoparticles was in dispersed state.

The present research is focused on the synthesis, structural and morphological characterization and antimicrobial evaluation of silver doped hydroxyapatite (AgHAp) in water. The preliminary ultrasonic characterizations of the AgHAp in water synthesized by an adapted co-precipitation method are also presented. X-ray diffraction result showed that silver ions were substituted in the hydroxyapatite structure. The lattice parameters increased when the silver substitution increased. The morphology of AgHAp were evaluated by Scanning Electron Microscopy (SEM). By EDX analysis the constituents elements of hydroxyapatite were detected in all analyzed samples. The silver was also found in the samples with x(Ag) = 0.5 and 0.2. The colloidal properties of the resulted AgHAp (x(Ag) = 0.0, 0.05 and 0.2) in water were analyzed by Dynamic Light Scattering (DLS) and zeta potential. On the other hand, the novelty of our research consists of preliminary ultrasonic measurements (US) conducted on AgHAp in water. Furthermore, the antimicrobial activity of AgHAp was evaluated and a decrease in the number of surviving cells was established.