Publications

The structure and electronic properties of the system resulted by epitaxial growth of a single atomic Au layer on a heated Ge(001) surface featured by (2 x 1) reconstruction are studied. The deposition at similar to 750 K results in a well-ordered Au surface featured by ripples separated by four times the theoretical distance between two neighboring Au atoms. As revealed by valence-band photoemission studies, the Au/Ge(001) system has metallic character. Correlating X-ray photoelectron spectroscopy results with first-principles calculations we derive the implications on the covalent bonding of Au on the Ge dimer surface. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The cryogenic detectors in the form of bolometers are presently used for different applications, in particular for very rare or hypothetical events associated with new forms of matter, specifically related to searches for dark matter. In the detection of particles with a semiconductor as target and detector, usually two signals are measured: ionization and heat. The amplification of the thermal signal is obtained with the prescriptions from the Luke-Neganov effect. The energy deposited in the semiconductor lattice as stable defects in the form of Frenkel pairs at cryogenic temperatures, following the interaction of a dark matter particle, is evaluated and consequences for measured quantities are discussed. This contribution is included in the energy balance of the Luke effect. Applying the present model to germanium and silicon, we found that for the same incident weakly interacting massive particle the energy deposited in defects in germanium is about twice the value for silicon. (C) 2013 Elsevier B.V. All rights reserved.

The specific topology of the line-centered square lattice (known also as the Lieb lattice) induces remarkable spectral properties such as the macroscopically degenerated zero-energy flat band, the Dirac cone in the low-energy spectrum, and the peculiar Hofstadter-type spectrum in a magnetic field. We study here the properties of the finite Lieb lattice with periodic and vanishing boundary conditions. We investigate the behavior of the flat band induced by disorder and external magnetic and electric fields. We show that in the confined Lieb plaquette threaded by a perpendicular magnetic flux there are edge states with nontrivial behavior. The specific class of twisted edge states, which have alternating chirality, are sensitive to disorder and do not support integer quantum Hall effect (IQHE), but contribute to the longitudinal resistance. The symmetry of the transmittance matrix in the energy range where these states are located is revealed. The diamagnetic moments of the bulk and edge states in the Dirac-Landau domain, and also of the flat states in crossed magnetic and electric fields are shown. DOI: 10.1103/PhysRevB.87.125428

The impact of non-resonant background emitters in semiconductor quantum-dot microcavity lasers is addressed within theoretical investigations based on the solution of the von Neumann equation. Off-resonant coupling between emitter resonances and the cavity mode is enabled via phonons, which are included in the von Neumann dynamics by an effective Lindblad contribution. The results show enhanced coherent emission from non-resonantly coupled quantum dots, while the frequently used phenomenological cavity feeding mechanism only enhances the thermal component of the emission.

Ex situ spark plasma sintering was used to obtain dense MgB2 co-doped with SiC and Te. The composition (MgB2) + (SiC)(0.025) + Te-0.01 shows critical current densities J(c)(20 K, 5 T) of 3.5 x 10(2) A cm(-2) and J(c)(5 K, 9 T) of 2 x 10(3) A cm(-2). These values are higher than for pristine samples or those separately doped with Te or SiC. They are also comparable at high fields and temperatures with the best reported values for the co-doped MgB2 bulks produced by conventional in situ methods. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Over the last decade, field emission miniature x-ray tubes emerged as cutting-edge applications of nanotechnology, possessing massive potential for use in various important fields, including that of precision medical therapy. The article essentially presents a review of such new devices reported in the literature. Additional discussions on the necessity of stabilizing the electron beam that generates x-rays are also included, and a simple technique for minimizing the current fluctuations is described. It is also pointed out that further miniaturization of field emission x-ray sources may need new concepts in designing the tube in shapes acting as "self focusing" structures for the electron beams.

Surface- and bulk-phosphated ceria catalysts were prepared and studied in propane oxidative dehydrogenation (ODH) at 823 and 873K. The catalysts were characterized by N2 adsorption at 77K, XRD, TEM, and diffuse reflectance IR Fourier transform (DRIFT), Raman, X-ray photoelectron (XPS), and energy dispersive X-ray (EDX) spectroscopies. Both series of catalysts presented an increase in the ODH selectivity with respect to pure ceria mainly at the expense of total oxidation selectivity. Thus, the selectivity to propene was approximately 74% with surface-phosphated catalysts and 62% with bulk-phosphated catalysts. For the surface-phosphated samples, P is confined to the surface and subsurface regions of the ceria particles, whereas P is also dispersed in the bulk of the oxide in the bulk-phosphated samples. Finally, all the characterization techniques led us to the conclusion that Ce4+ cations that interact with P are responsible for the observed increase in the ODH.

Monodisperse core-shell hybrid nanoparticles based on cobalt ferrite (CoFe2O4) particles coated with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) biopolymers were obtained employing a two-step procedure: the CoFe2O4 of 21 nm mean particle size were first synthesized by coprecipitation method assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The FTIR spectra also indicated the interaction between the cobalt ferrite particles and the two polymers were used as bio-compatible coatings. Transmission electron microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses revealed the formation of approximately 22 nm CoFe2O4-PVP and CoFe2O4-PEG hybrid nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids on Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica serovar typhimurium bacteria and Candida scotti yeast it was clear that no significant toxic activity was obtained. Moreover, all the prepared nanohybrids and their components possess antioxidant activity. (C) 2012 Elsevier B.V. All rights reserved.

The correlation of the lattice disorder with the nanocrystal average size, in ZnO nanocrystals synthesized by several different methods, has been quantitatively monitored by line shape analysis of the multifrequency electron paramagnetic resonance (EPR) spectra of low concentrations of substitutional Mn2+ probing ions. The observed correlation between the line broadening parameter of the spectrum and the average ZnO nanocrystals size, independent of the synthesis procedure of the ZnO nanocrystals, demonstrates the dominance of the size related strain/disorder. On the basis of this result, a new method for determining the average ZnO nanocrystal size from the quantitative analysis of the EPR spectra of the Mn2+ probes was derived. The nanocrystallization of the disordered ZnO formed by the thermal decomposition of hydrozincite was monitored using this procedure. The observed ZnO nanocrystallite growth kinetics at lower temperatures was described by a structural relaxation mechanism consisting of the local ordering by rearrangements of the atoms in the interfaces/grain boundaries, with a growth activation energy of similar to 23 kJ/mol. When the nanostructured ZnO was more than 75% crystallized, another growth mechanism of the nanocrystals was found to occur, driven by the reduction of the total grain boundary energy.

We report on the fabrication of magnetite/salicylic acid/silica shell/antibiotics (Fe3O4/SA/SiO2/ATB) thin films by matrix-assisted pulsed laser evaporation (MAPLE) to inert substrates. Fe3O4-based powder have been synthesized and investigated by XRD and TEM. All thin films were studied by FTIR, SEM and in vitro biological assays using Staphylococcus aureus and Pseudomonas aeruginosa reference strains, as well as eukaryotic HEp-2 cells. The influence of the obtained nanosystems on the microbial biofilm development as well as their biocompatibility has been assessed. For optimum deposition conditions, we obtained uniform adherent films with the composition identical with the raw materials. Fe3O4/SA/SiO2/ATB thin films had an inhibitory activity on the ability of microbial strains to initiate and develop mature biofilms, in a strain-and antibiotic-dependent manner. These magnetite silica thin films are promising candidates for the development of novel materials designed for the inhibition of medical biofilms formed by different pathogenic agents on common substrates, frequently implicated in the etiology of chronic and hard to treat infections.