National Institute Of Materials Physics - Romania

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5781 articles found

2391. SATELLITES IN Ce 3d X-RAY PHOTOELECTRON SPECTROSCOPY OF CERIA

Authors: Radutoiu, N; Teodorescu, CM

Published: OCT-DEC 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1549, DOI:

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.

2392. ON THE PASSIVATION OF GaAs SURFACE BY SULFIDE COMPOUNDS

Authors: Ghita, RV; Negrila, CC; Cotirlan, C; Logofatu, C

Published: JUL-SEP 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1344, DOI:

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.

2393. Multi-Component Oxide Thin Films and Heterostructures for Electronics: Growth Principles

Authors: Endo, K; Ikenaga, N; Badica, P

Published: 2013, ADAPTIVE, ACTIVE AND MULTIFUNCTIONAL SMART MATERIALS SYSTEMS, 77, +, DOI: 10.4028/www.scientific.net/AST.77.209

In the last years oxide materials for electronics show significant progress. However, many details regarding technology control of the properties have to be solved. For electronics, thin films and heterestructures are important taking advantage of integration and synergetic concepts leading to new types of devices and functionalities. It is notable that, while fabrication of new devices and materials showing new phenomena are booming, the growth principles and concepts are somehow developing slowly within this general trend. This is because in many cases, growth of materials is very personalized. Understanding of the bi-directional relationship between the general and particular principles deserves attention. The immediate benefit is that knowledge on growth for one material can be transferred to another one. In our work we have analyzed such relationships for some oxide multicomponent perovskites. Materials used in our examples are Bi-Sr-Ca-Cu-O and YBa2Cu3O7, (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Presented thin films or heterostructures are with c-axis and non-c-axis orientations and based on these examples we discuss some of the growth principles.

2394. EFFECT OF STRESS ON TRAPPING PHENOMENA IN SILICON: FROM SINGLE CRYSTAL TO NANOSTRUCTURES

Authors: Ciurea, ML

Published: 2013, ROMANIAN REPORTS IN PHYSICS, 65, 856, DOI:

In this article, we present and discuss how the stress influences the trapping phenomena in both the bulk Si and nanostructures based on Si. For this, we use single crystal Si irradiated with 28 MeV iodine ions of fluence (5 +/- 0.5) x 10(11) ions/cm(2) and 2D Si based nanostructures of (nc-Si/CaF2)(50) multilayers. The method of thermally stimulated discharge currents without bias was employed to investigate the trapping phenomena and the modeling of the discharge current curves was carried out. In the case of irradiated Si, we have modeled the discharge currents considering six trapping levels and a supplementary stress electric field independent of temperature superposed on the frozen-in electric field produced by the charged traps at low temperature. The stress electric field is due to the stopped iodine ions which are heavier than those of Si host. Six traps are evidenced and their parameters are calculated. In the (nc-Si/CaF2)(50) multilayer structures, we experimentally evidenced traps which produce in the discharge current maxima with two shapes. Three maxima have normal shape and the others five maxima are narrow and sharp looking like spikes. We modeled the discharge current curves taking for the concentration a power temperature dependence law, and for the cross section a Gaussian temperature dependence.

2395. Conduction mechanism versus annealing in SiO2 films with Ge nanoparticles

Authors: Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML

Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 34, DOI:

This paper analyses and discusses the effect of Ge/Si atomic ratio and annealing temperature on the conduction mechanisms governing the electrical behavior of Ge-SiO2 films containing Ge nanoparticles embedded in amorphous SiO2 matrix. For this, the experimental conductance-temperature curves are modeled in correlation with the microstructure findings for two types of films. One type of films has a lower Ge/Si ratio of 0.73 and was obtained by magnetron sputtering followed by annealing in H-2, at 500 degrees C, while the second one has a higher ratio of 1.86 and was obtained also by sputtering, but was annealed in N-2, at 800 degrees C. Both types of films show an electrical behavior with a T-1/4 conductance dependence on temperature, typical for hopping mechanism.

2396. Surface free energy of smooth and dehydroxylated fused quartz from contact angle measurements using some particular organics as probe liquids

Authors: Zgura, I; Moldovan, R; Negrila, CC; Frunza, S; Cotorobai, VF; Frunza, L

Published: JUL-AUG 2013, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 15, 634, DOI:

The dispersion and the polar independent contributions to the surface free energy in the case of fused quartz plates were evaluated by contact angle measurements against a series of liquids like water, glycerol, ethylene glycol, dimethyl sulfoxide and a nematic mixture NP5 of azoxybenzene type compounds. The smooth fused quartz plates were thermally pretreated at 240 degrees C and 1000 degrees C to decrease the number of surface hydroxyl groups; their surface was characterized by X-ray photoelectron spectroscopy. The contact angle data were further processed applying either the approach of Owens-Wendt with geometric mean or the Wu's approach of harmonic mean of nonpolar and polar interactions. The liquids were chosen thus to fulfill Della Volpe and Siboni's criterion namely that these have the condition number of system matrix low enough. The values obtained for the components of surface free energy were discussed in comparison with the results obtained in literature for crystalline quartz or for other silica forms as bulk or films. The study has shown a decrease of the polar component of the surface tension by increase of the pretreatment temperature.

2397. Hydroxyapatite thin films synthesized by Pulsed Laser Deposition onto titanium mesh implants for cranioplasty applications

Authors: Duta, L; Stan, GE; Popescu, AC; Socol, G; Miroiu, FM; Mihailescu, IN; Ianculescu, A; Poeata, I; Chiriac, A

Published: 2013, ROMOPTO 2012: TENTH CONFERENCE ON OPTICS: MICRO- TO NANOPHOTONICS III, 8882, DOI: 10.1117/12.2032338

We report on the synthesis of advanced nanostructured hydroxyapatite (HA) thin films onto 3D titanium (Ti) mesh substrates by Pulsed Laser Deposition method. Morphological and structural investigations as well as pull-out tests proved the stoichiometric transfer of crystalline HA films along with their good adherence. In vivo tests were performed on 12 patients (six with simple Ti mesh, six with Ti mesh biofunctionalized with HA). The tomodensitometry analysis of the cranial control scans evidenced the process of osseogenesis. For four patients with implanted HA/Ti mesh structures, the modification of the value obtained on Hounsfield scale was observed at the level of implant, proving the progress of osseointegration. We conclude that the structures exhibit excellent bonding strength and functionality, and are suitable for neurosurgical applications.

2398. Polymer photonic crystal band-gap modulation using PbS quantum dots

Authors: Diacon, A; Rusen, E; Mocanu, A; Nistor, LC

Published: 2013, JOURNAL OF MATERIALS CHEMISTRY C, 1, 4357, DOI: 10.1039/c3tc30172a

This study aims to present the manufacture of polymer photonic crystals (PCs) and the study of the influence of PbS quantum dots on their optical properties. Monodisperse latexes resulting from the polymerization of styrene and acrylic acid were obtained by a soap-free emulsion copolymerization process and their optical response was modified using PbS high refractive index nanoparticles. A stop-band modulation was achieved by controlling the nanoparticles concentration that resulted in the altering of the self-assembly process. Thus, at low PbS concentrations, a blue-shift of the band-gap was registered, whereas at high concentrations, a red-shift was measured. The hybrid materials were investigated by DLS, SEM, HRTEM, UV-VIS and XRD analyses.

2399. PARAMAGNETIC POINT DEFECTS IN PURE AND C-13 AND O-17 IMPLANTED SILICON FOR HIGH ENERGY PARTICLE DETECTORS

Authors: Nistor, SV; Ghica, D; Pintilie, I; Manaila, E

Published: 2013, ROMANIAN REPORTS IN PHYSICS, 65, 819, DOI:

The presence and structure of paramagnetic point defects in C-13 and O-17 implanted ultrapure Si single-crystal material, two impurities which seem to play a major role in the detectors performance degradation and radiation resistance enhancement, respectively, are reported before and after irradiation with 6 MeV electrons. The investigation, performed by Q-band electron spin resonance spectroscopy in the 300 - 10 K temperature range, included also reference ultrapure and O-16 doped single-crystal Si-platelets. It resulted in the observation of points defects associated with lattice defects as dangling bonds and impurities.

2400. SINGLE CRYSTAL ZnO NANOWIRE LUMINESCENCE SHIFTING BY NANOSTRUCTURED ZnO LAYERS

Authors: Marcu, A; Enculescu, I; Vizireanu, S; Birjega, R; Porosnicu, C

Published: APR-JUN 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 605, DOI:

Single crystal ZnO nanowires grown by pulsed laser deposition (PLD) and vapour-liquid-solid (VLS) technique respectively, were in-situ and ex-situ covered with additional ZnO shell layers. Luminescence investigation revealed significant luminescence spectra shift from UV to blue emission band of the obtained structures while changing the deposited shell layer film thickness. But with no monotone variation with the deposited film thicknesses. While the luminescence changes are generally considered as being determined by the ratio between core emission lines intensity and shell 'defects' lines intensity, the strongest changes in the photoluminescence spectra were obtained in our experiments for the nanometer order shell layer thicknesses. The comparison between luminescence results and luminescence studies on 50 nm ZnO nanoparticles clusterization, together with HRTEM investigations of the ZnO shell layer suggest that the nanoparticle-nanowire interface, respectively the coupling between the ZnO single crystal core and ZnO nanostructured shell layer, might play a significant role in the luminescence spectra changes.