Publications

The use of amorphous and transparent oxides is a key for the development of new thin film transistors and displays. Recently, indium zinc oxide (IZO) was shown to exhibit high transparency in the visible range, low resistivity, and high mobility. Since the properties and the cost of these films depend on the In/(In + Zn) values, the measurement of this ratio is paramount for future developments and applications. We report on accurate analysis of the elemental composition of IZO thin films synthesized using a Combinatorial Pulsed Laser Deposition technique. The monitoring of the thin films elemental composition by Laser-Induced Breakdown Spectroscopy was chosen in view of further in situ and real-time technological developments and process control during IZO fabrication. Our analytical approach is based on plasma modeling, the recorded spectra being then compared to the spectral radiance computed for plasmas in local thermal equilibrium. The cation fractions measured were compared to values obtained by complementary measurements using energy dispersive X-ray spectroscopy and Rutherford backscattering spectrometry. Spectroscopic ellipsometry assisted the scientific discussion. A good agreement between methods was found, independently of the relative fraction of indium and zinc that varied from about 65 to 90 and 35 to 10 at%, respectively, and the measurement uncertainties associated to each analytical method.

This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) technique of organic bulk heterojunctions made from the mixture of a star-shaped arylenevinylene compound, 4,4',4aEuro(3)-tris[(4'-diphenylamino)styryl] triphenylamine as donor and fullerene derivative, [6, 6]-phenyl C61 butyric acid butyl ester, as acceptor, in the weight ratio 1:2. The mixed layer has been characterized by spectroscopic (UV-Vis, Fourier transform infrared) and microscopic (AFM) methods, and the effects of the deposition conditions (number of pulses) and of a buffer layer of poly(aniline-co-aniline propane sulfonic acid) or poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) have been analyzed. The study of the electrical properties has revealed a typical solar cell behavior for the heterostructure glass/ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/4,4',4aEuro(3)-tris[(4'-diphenylamino)styryl] triphenylamine: [6, 6]-phenyl C61 butyric acid butyl ester/Al, confirming that MAPLE could be an adequate method for the preparation of active layer based on bulk heterojunction for solar cells.

Silver nanoparticles were obtained by picosecond laser ablation in water at 1064 nm, using focusing geometry to design the particles' size. The position of the target surface with respect to the focal point strongly influences the NPs' size: above and in the focus it is up to 20 nm and below focus <= 150 nm. Generated particles have a spherical shape. The solutions were further employed on human cells and the tests showed a deteriorating effect on DNA.

In order to study the effect of spark plasma sintering (SPS) technique synthesis SiC-MgB2 on the phase formation, the MgB2 and SiC-MgB2 bulks were fabricated with mixed powders by various SPS synthesis routes. The phase formation processes were investigated with the aid of X-ray diffraction analysis, TEM investigations and sintering theories. The solid-solid reaction between Mg and B powders formed MgB2 at low temperature. As the sintering temperature increases, the reactions of molten Mg with B form MgB2, and simultaneously, the molten Mg promotes the decomposition of SiC and nuclei of Mg2Si may form on the surface of SiC grains; the nascent MgB2 incorporates the carbon into lattice, hereby enhancing the SiC decomposition. The experimental results are in good agreement with the assumed chemical reaction.

The pyroelectric signal generated by an epitaxial Pb(Zr0.2Ti0.8)O-3 film can be enhanced by continuous illumination with ultraviolet (UV) light. The measured signal increases more than 2 times at low modulation frequencies of the incident infrared (IR) radiation (similar to 10 Hz) and at wavelengths where the short-circuit photocurrent presents the maximum value (similar to 280-300 nm). The tentative explanation is that the changes in polarization induced by the temperature variation under modulated IR illumination are generating a variable internal electric field, able to collect the photogenerated carriers produced under continuous UV illumination leading to an additional signal in phase with the pyroelectric one. This finding could be exploited for designing pyroelectric detectors with enhanced characteristics by combining both UV and IR responses. (C) 2014 AIP Publishing LLC.

Depressed cladding waveguides have been realized in Nd:YVO4 employing direct writing technique with a femtosecond-laser beam. It was shown that the output performances of such laser devices are improved by the reduction of the quantum defect between the pump wavelength and the laser wavelength. Thus, under the classical pump at 808 nm (i.e. into the F-4(5/2) level), a 100-mu m diameter circular waveguide inscribed in a 0.7-at.% Nd:YVO4 outputted 1.06-mu m laser pulses with 3.0-mJ energy, at 0.30 optical efficiency and slope efficiency of 0.32. The pump at 880 nm (i.e. directly into the F-4(3/2) emitting level) increased the pulse energy at 3.8 mJ and improved both optical efficiency and slope efficiency at 0.36 and 0.39, respectively. The same waveguide yielded continuous-wave 1.5-W output power at 1.06 mu m under the pump at 880 nm. Laser emission at 1.34 mu m was also improved using the pump into the F-4(3/2) emitting level of Nd:YVO4. (C)2014 Optical Society of America

The photocatalytic performance of magnetron-sputtered titanium dioxide (TiO2) coatings of different thickness in anatase crystalline structure deposited on aluminium 1050 alloy substrates was investigated using a combination of photo-electrochemistry, methylene blue decomposition, and microscopic and spectroscopic methods, such as high resolution scanning and transmission electron microscopy, atomic force microscopy and ellipsometry. The reaction resistance was measured by AC impedance, while photocurrent measurements were carried out using the zero resistance ammetry (ZRA) method. The results showed that the TiO2 grains grow in dipyramidal columns having a linear increase in surface area with increased coating thickness. The refractive index values indicate also an evolutionary growth. The refractive index values obtained for the thin coatings on aluminium substrate were well below the values reported for monocrystalline anatase. The photocatalytic performance increased with increased coating thickness, though more rapidly over a range of 100-500 nm thickness. The dielectric constant also increased linearly with coating thickness. (C) 2014 Elsevier B.V. All rights reserved.

Si/SiO2 quantum dots (QDs) are novel particles with unique physicochemical properties that promote them as potential candidates for biomedical applications. Although their interaction with human cells has been poorly investigated, oxidative stress appears to be the main factor involved in the cytotoxicity of these nanoparticles. In this study, we show for the first time the influence of Si/SiO2 QDs on cellular redox homeostasis and glutathione distribution in human lung fibroblasts. The nanoparticles morphology, composition and structure have been investigated using high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. MRC-5 cells (human lung fibroblasts) were incubated with various concentrations of Si/SiO2 QDs ranging between 25 and 200 mu g/mL for up to 72 h. The results of the MTT and sulforhodamine B assays showed that exposure to QDs led to a time-dependent decrease in cell viability and biomass. The increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels together with the lower glutathione content suggested that the cellular redox homeostasis was altered. Regarding GSH distribution, the first two days of treatment resulted in a localization of GSH mainly in the cytoplasm, while at longer incubation time the nuclear/cytoplasmic ratio indicated a nuclear localization. These modifications of cell redox state also affected the redox status of proteins, which was demonstrated by the accumulation of oxidized proteins and actin S-glutathionylation. In addition, the externalization of phosphatidylserine provided evidence that apoptosis might be responsible for cell death, but necrosis was also revealed. Our results suggest that Si/SiO2 quantum dots exerted cytotoxicity on MRC-5 cells by disturbing cellular homeostasis which had an effect upon protein redox status. (C) 2014 Elsevier Ireland Ltd. All rights reserved.

We study an array of dissipative tunnel-coupled cavities, each interacting with an incoherently pumped two-level emitter. For cavities in the lasing regime, we find correlations between the light fields of distant cavities, despite the dissipation and the incoherent nature of the pumping mechanism. These correlations decay faster than any power of the distance for arrays in any dimension but become increasingly long ranged with increasing photon tunneling between adjacent cavities. The interaction-dominated and the tunneling-dominated regimes show markedly different scaling of the correlation length which always remains finite due to the finite photon trapping time. We propose a series of observables to characterize the spontaneous buildup of collective coherence in the system.