National Institute Of Materials Physics - Romania

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5714 articles found

2111. Laser Emission from Diode-Pumped Nd:YAG Cladding Waveguides Obtained by Direct Writing with a Femtosecond-Laser Beam

Authors: Salamu, G; Voicu, F; Jipa, F; Zamfirescu, M; Dascalu, T; Pavel, N

Published: 2014, LASER SOURCES AND APPLICATIONS II, 9135, DOI: 10.1117/12.2052250

Cladding waveguides have been realized in Nd:YAG by direct writing with a femtosecond-laser beam. A classical method that inscribes many tracks around the waveguide circumference with step-by-step translations of the laser medium, and a new technique in which the laser medium is moved on a helical trajectory and that delivers waveguides with well-defined walls were employed. Laser emission on the 1.06 mu m F-4(3/2)-> I-4(11/2) transition and at 1.3 mu m on the F-4(3/2)-> I-4(13/2) line was obtained under the pump with a fiber-coupled diode laser. Thus, laser pulses at 1.06 mu m with energy of 1.3 mJ for the pump at 807 nm with pulses of 12.5-mJ energy were recorded from a circular waveguide of 100-mu m diameter that was inscribed in a 5-mm long, 0.7-at.% Nd: YAG single crystal by the classical translation technique. A similar waveguide that was realized in a 5-mm long, 1.1-at.% Nd: YAG ceramic increased the 1.06-mu m laser pulse energy to 2.15 mJ for the pump pulses of 13.1-mJ energy. Furthermore, a circular waveguide of 100-mu m diameter that was inscribed in the Nd: YAG ceramic by the helical-movement method yielded pulses at 1.06 mu m with increased maximum energy of 3.2 mJ; the overall optical-to-optical efficiency was 0.24, and the laser operated with a slope efficiency of 0.29. The same device outputted laser pulses at 1.3 mu m with energy of 1.15 mJ.

2112. Self-organization and Size Effects in Amorphous Silicon

Authors: Popescu, M; Sava, F; Velea, A

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 45, DOI: 10.1007/978-3-662-44479-5_2

Self-organization and size effects in amorphous silicon have been investigated by modelling of the structure at nanoscale. The size effect related to the disorder in silicon is treated by the free energy balance in nanometric clusters using valence force field theory. The computed structural and energetical parameters of three continuous random network (CRN) models of amorphous silicon with 2,052, 156 and 155 atoms are compared with the experimental values. In order to show the importance of the interfaces between different a-Si clusters, two networks of 200 and 205 atoms were modelled separately and then linked using an amorphous and a crystalline interface. Also the voids in the a-Si clusters are investigated.

2113. COVALENT FUNCTIONALIZATION OF SINGLE WALLED CARBON NANOTUBES WITH DOXORUBICIN FOR CONTROLLED DRUG DELIVERY SYSTEMS

Authors: Ciobotaru, CC; Damian, CM; Polosan, S; Matei, E; Iovu, H

Published: JAN-MAR 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 422, DOI:

The objective of this study was to obtain nanocomposites based on SWCNTs functionalized with carboxyl groups and doxorubicin (DOX) as a chemotherapeutic drug through covalent bonds formed by carboxyl groups from SWCNTs and amino groups from DOX. The formation of these nanocomposites was proved by using different characterization methods like Fourier transform Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). Also thermogravimetrical analysis was employed to study the thermal behavior of our nanocomposites. X-ray diffraction and Raman spectroscopy revealed that the surface was modified by the covalent bonding of DOX to SWCNTs. The in vitro drug release was studied by using UV-VIS Spectroscopy.

2114. 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.

2115. Band Bending at Ferroelectric Surfaces and Interfaces Investigated by X-ray Photoelectron Spectroscopy

Authors: Apostol, NG

Published: 2014, TIM 2013 PHYSICS CONFERENCE, 1634, 88, DOI: 10.1063/1.4903018

This work reports on the use of X-ray photoelectron spectroscopy to quantify band bending at ferroelectric free surfaces and at their interfaces with metals. Surfaces exhibiting out-of-plane ferroelectric polarization are characterized by a band bending, due to the formation of a dipole layer at the surface, composed by the uncompensated polarization charges (due to ionic displacement) and to the depolarization charge sheet of opposite sign, composed by mobile charge carriers, which migrate near surface, owing to the depolarization electric field. To this surface band bending due to out-of-plane polarization states, metal-semiconductor Schottky barriers must be considered additionally when ferroelectrics are covered by metal layers. It is found that the net band bending is not always an algebraic sum of the two effects discussed above, since sometimes the metal is able to provide additional charge carriers, which are able to fully compensate the surface charge of the ferroelectric, up to the vanishing of the ferroelectric band bending. The two cases which will be discussed in more detail are Au and Cu deposited by molecular beam epitaxy on PbZr0.2Ti0.8O3(001) single crystal thin layers, prepared by pulsed laser deposition. Gold forms unconnected nanoparticles, and their effect on the band bending is the apparition of a Schottky band bending additional to the band bending due to the out-of-plane polarization. Copper, starting with a given thickness, forms continuous metal layers connected to the ground of the system, and provide electrons in sufficient quantity to compensate the band bending due to the out-of-plane polarization.

2116. Charge storage properties of HfO2/Ge-HfO2/SiO2 trilayer structures

Authors: Palade, C; Slav, A; Lepadatu, AM; Teodorescu, VS; Ciurea, ML

Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 62, DOI:

We report on the charge storage properties of trilayer structures consisting in sputtered gate HfO2/co-sputtered Ge-HfO2 layer/rapid thermal tunneling SiO2 oxide. Investigations of transmission electron microscopy and X-ray diffraction evidence the formation of HfO2 with mixed structure of monoclinic and tetragonal in the annealed structures. Capacitance-voltage (C-V) characteristics were measured on Al/HfO2/Ge-HfO2/SiO2/Si/Al metal-oxide-semiconductor capacitors based on as-deposited and annealed structures. Large C-V hysteresis is observed for the as-deposited structures and is controlled by traps present in oxide and interface. The annealing yields a C-V hysteresis with smaller memory window being due to injected charges in Ge nanocrystals.

2117. ZnS and ZnO Semiconductor Nanoparticles Doped with Mn2+ Ions. Size Effects Investigated by EPR Spectroscopy

Authors: Stefan, M; Nistor, SV; Ghica, D

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 27, DOI: 10.1007/978-3-662-44479-5_1

Electron paramagnetic resonance (EPR) spectroscopy has been extensively employed to investigate the presence, localization, distribution and interaction with the host crystalline lattice of the paramagnetic point defects (intrinsic defects and transition metal ions) in semiconductors. The retrieval of such information for nanostructured semiconductors is considerably more difficult, due to the high disorder level in such systems, reflected in broad, featureless EPR spectra. We show here how, with proper adjustments of the EPR experiments and accurate numerical analysis of the resulting spectra, it was possible to obtain more accurate information regarding the localization and structure of various Mn2+ centers in ZnS and ZnO semiconductor nanoparticles (NPs). This lead to the observation and investigation of size related effects such as the presence of the extended lattice defect assisted incorporation of impurities in small (similar to 3 nm) cubic ZnS NPs, the dominant size induced lattice disorder observed for ZnO NPs, independent of the synthesis procedures, or the three steps decomposition of the epsilon-Zn(OH)(2) disordered shell of ZnS NPs with formation of new oxy-hydrated zinc compounds. These effects can be used to synthesize semiconductor nanoparticles with controlled size distribution, doping level and functionalized surfaces for specific technological applications.

2118. Trapping centers in heavy ion irradiated silicon

Authors: Palade, C; Lazanu, S; Ciurea, ML

Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 128, DOI:

Low fluence heavy ions incident on high resistivity Si produce lattice defects which act as trapping centers, and produce also an important local field of strain. The strain field intensity increases with the increase of the difference in atomic size and mass between the ion and the Si atom host. We investigate the correlation between the change of trapping parameters and the strain field. The strain field produced by Bi ions in Si is two times more intense than in Si irradiated with I ions, and effects the Gaussian broadening of trapping levels and the temperature dependence of cross sections.

2119. POLYESTER FABRICS COVERED WITH ZNO PARTICLES: PARTICLE INTERACTION WITH THE SURFACE SHOWN BY DIELECTRIC PROPERTIES

Authors: Ganea, CP; Frunza, L; Zgura, I; Preda, N; Matei, E; Frunza, S

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1503, DOI:

Polyester fabrics modified with ZnO particles by electroless deposition were investigated by broadband dielectric spectroscopy in a parallel capacitor between 10(-2) and 10(7) Hz in a temperature interval from ca. 123 to 473 K. Textile samples were routinely characterized for the structure and interaction of the ZnO particles with the fiber surface. Since a textile fabric material is a mixture of air and fibers, the parameters taken into consideration should be called as effective ones. The deposition of ZnO particles lead to complex dielectric spectra and to the temperature dependence of the decomposed peaks following Arrhenius law.

2120. Toxicity Evaluation following Intratracheal Instillation of Iron Oxide in a Silica Matrix in Rats

Authors: Prodan, AM; Ciobanu, CS; Popa, CL; Iconaru, SL; Predoi, D

Published: 2014, BIOMED RESEARCH INTERNATIONAL, 2014, DOI: 10.1155/2014/134260

Iron oxide-silica nanoparticles (IOSi-NPs) were prepared from a mixture of ferrous chloride tetrahydrate and ferric chloride hexahydrate dropped into a silica xerogel composite. The structure and morphology of the synthesized maghemite nanoparticles into the silica xerogel were analysed by X-ray diffraction measurements, scanning electron microscopy equipped with an energy dispersive X-ray spectrometer, and transmission electron microscopy. The results of the EDAX analysis indicated that the embedded particles were iron oxide nanoparticles. The particle size of IOSi-NPs calculated from the XRD analysis was estimated at around 12.5 nm. The average size deduced from the particle size distribution is 13.7 +/- 0.6 nm, which is in good agreement with XRDanalysis. The biocompatibility of IOSi-NPs was assessed by cell viability and cytoskeleton analysis. Histopathology analysis was performed after 24 hours and 7 days, respectively, from the intratracheal instillation of a solution containing 0.5, 2.5, or 5mg/ kg IOSi-NPs. The pathological micrographs of lungs derived from rats collected after the intratracheal instillation with a solution containing 0.5mg/kg and 2.5mg/ kg IOSi-NPs show that the lung has preserved the architecture of the control specimen with no significant differences. However, even at concentrations of 5mg/ kg, the effect of IOSi-NPS on the lungs was markedly reduced at 7 days post treatment.