Publications

The glycerol iron oxide nanoparticles (GIO-NPs) were obtained by an adapted coprecipitation method. The X-ray diffraction (XRD) studies demonstrate that GIO-NPs were indexed into the spinel cubic lattice with a lattice parameter of 0.835 nm. The refinement of XRD spectra indicated that no other phases except maghemite were detected. The adsorption of glycerol on iron oxide nanoparticles was investigated by Fourier transform infrared (FTIR) spectroscopy. On the other hand, this work implicated the use of GIO-NPs in antibacterial studies. The results indicate that, in the case of P.aeruginosa 1397 biofilms, at concentrations from 0.01 mg/mL to 0.625 mg/mL, the glycerol iron oxide inhibits the ability of this strain to develop biofilms on the inert substratum.

This paper presents a detailed transmission electron microscopy (TEM) study of GeSiO films with Ge nanoparticles. The films with 2.5 mu m thickness were deposited by magnetron sputtering and subsequently annealed in H-2 at 2 atm and 500 degrees C for 2 h for nanostructuring. After H-2 annealing, the majority of the resulted Ge nanoparticles are amorphous, less than 5 nm in size, forming a uniform network in the film volume. Big Ge nanoparticles with sizes between 20 and 50 nm are also formed. Some of them are identified to be crystallized in the (Ge-III/ST12) tetragonal phase. The high resolution TEM observation induces the amorphysation of the Ge tetragonal phase, followed by the crystallization of the amorphous Ge phase in the cubic diamond structure (Ge-I), as an effect of electron irradiation. A secondary annealing performed in N-2 at 800 degrees C and 1 atm for 2 h induces formation of faceted cubic Ge nanoparticles distributed in the SiO2 matrix.

The ceramics of Nb5+, Zr4+ or Eu3+ doped BaZn1/3Ta2/3O3 complex perovskite oxide were obtained by the conventional solid-state reaction method, being sintered in air, at temperatures between 1400 and 1600 degrees C, for 2 h. X-ray diffraction, scanning electron microscopy and dielectric measurements were used for the compositional, structural, morphological and dielectric characterization. All BaZn1/3Ta2/3O3 ceramics present single-phase compositions after removing the surface layer in which zinc volatilization occurred. Furthermore, the 1:2 ordering of zinc and tantalum cations on the octahedral positions of the perovskite structure was observed for all sintering temperatures. The microstructure of BaZn1/3Ta2/3O3 ceramics is strongly influenced by the dopant type, in terms of grains size and shape. The dielectric constant varies between 16.9 and 31.5. BaZn1/3Ta2/3O3 resonator doped with 1.00 % Nb2O5 and sintered at 1600 degrees C, 2 h, exhibits the highest value for the quality factor, Qxf similar to 157 THz at 10 GHz.

Laser pulses at 1.06 mu m with 2.5-mJ energy and 3.1-MW peak power have been obtained from a composite, all-polycrystalline ceramics, passively Q-switched 1.1-at.% Nd:YAG/Cr4+:YAG laser that was quasi-continuous-wave pumped with diode lasers. Single-pass frequency doubling with LiB3O5 nonlinear crystal at room temperature yielded green laser pulses at 532 nm with energy of 0.36-mJ and 0.45-MW peak power; the infrared-to-green conversion efficiency was 0.27.

In this work, anomalous discontinuities observed in Capacitance-Voltage (C-V) characteristics on non-nitridated n-4H-SiC/SiO2 capacitors at low temperature are addressed. The appearance of abrupt capacitance minima, always at the same gate voltages (4V and 8V) and independent on probe frequency, led us to consider a resonant electron tunneling process from neutral donor states present at the SiC/SiO2 interface into two well defined energy levels in the oxide layer. Results of numerical simulations based on this model describe quantitatively the experimentally observed discontinuities at 4V and 8V and provide strong evidence for the presence resonant tunneling.

In physics of non crystalline materials there are many challenging problems. This article offers the explanation of the some phenomena in the disordered semiconductors, first of all in chalcogenide glasses on the fundamentyals of the barrier-cluster-heating model. This model assumes that an amorphous semiconductor consists of nanoregions (clusters), separated from each other by potential barriers. Barrier-cluster-heating model allows to explain many phenomena observed in chalcogenide glasses. In this article the mechanism of the appearance weak absorption tail (second exponential tails) of optical absorption in chalcogenide glasses is explained.

Silver-doped hydroxyapatite (Ag:HAp) was obtained by coprecipitation method. Transmission electron microscopy (TEM), infrared, and Raman analysis confirmed the development of Ag:HAp with good crystal structure. Transmission electron microscopy analysis showed an uniform ellipsoidal morphology with particles from 5 nm to 15 nm. The main vibrational bands characteristic to HAp were identified. The bands assigned to phosphate vibrational group were highlighted in infrared and Raman spectra. The most intense peak Raman spectrum is the narrow band observed at 960 cm(-1). In this article Ag:Hap-NPs were also evaluated for their antimicrobial activities against gram-positive, gram-negative, and fungal strains. The specific antimicrobial activity revealed by the qualitative assay demonstrates that our compounds are interacting differently with the microbial targets.

Quantum well solar cells with p-i-n structure are presented. The physical processes in multiple quantum well solar cells, the materials commonly used for photovoltaic applications, and technological aspects are analyzed. The quantum confinement effect produces resonant energy levels located in the valence and conduction bands of well layers. In addition, it produces energy quantum confinement levels located in the energy band gap of both well and barrier layers. The absorption on both resonant and quantum confinement levels leads to an extension of the internal quantum efficiency in near infrared domain. Several structures with different absorbers from 3-5 and 4 groups are described and discussed. Various technological and design solutions, such as multiple quantum well solar cells with graded band gap, with tandem configurations, with strain-balanced structure, and strain-balanced structure improved with nanoparticles deposited atop are analyzed. The cell parameters are discussed and related to the materials and technology.

Ce 3d X-ray photoelectron spectroscopy (XPS) spectra is characterized by the presence of "shake-up" and "shake-down" satellites, which complicate the analysis of the XPS data and especially the identification of different ionization states. The present paper proposes a new model for interpreting the 3d XPS lines of cerium oxide (CeO2). This model supposes 6 pairs of doublets with spin-orbit splitting, three corresponding of trivalent cerium and three corresponding of tetravalent cerium. The three components used for each ionization state correspond to the "shake-down" process, to the "parent" (Koopman) line, and to the "shake-up" line, in order of increasing binding energy. From the time dependence of Ce 3d and C 1s XPS spectra, a model for the contamination process is derived and also the length of the alkyl chains of the hydrocarbons may be estimated. The present analysis allowed a more accurate computation of the Ce 3d atomic sensitivity factor (ASF), in accord with the values found for other rare earths elements.

A genuine GaAs surface is covered with a layer (similar to few nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. In this work is presented a study of GaAs surface passivation by sulfur compounds inorganic and organic (alkane thiols), a method that combines both chemical and electronic passivation. 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 surface, a compound putted into evidence by scanning electron microscopy (SEM) images, photoluminescence analysis, second harmonic generation (SHG) measurement and Raman spectroscopy. Using X-ray photoelectron spectroscopy (XPS) it is putted into evidence the presence of covalent bonds Ga-S and AsS as a result of chemical interaction with sulf ions. Electrical characteristic of AuGeNi/thiol/GaAs structure is presented in I (V) recorded in the region of small currents.