National Institute Of Materials Physics - Romania

Publications

5714 articles found

2151. Giant pyroelectric coefficient determined from the frequency dependence of the pyroelectric signal generated by epitaxial Pb(Zr0.2Ti0.8)O-3 layers grown on single crystal SrTiO3 substrates

Authors: Botea, M; Iuga, A; Pintilie, L

Published: DEC 2 2013, APPLIED PHYSICS LETTERS, 103, DOI: 10.1063/1.4838035

Epitaxial Pb(Zr0.2Ti0.8)O-3 layers of good structural quality were grown on single crystal SrTiO3 substrates. The pyroelectric coefficient was estimated from the signal generated by the ferroelectric film working as a pyroelectric detector in the voltage mode, without pre-poling procedure. The obtained value is as high as 1.9 x 10(-3) C/m(2) K. The large value is attributed to the presence of 90 degrees ferroelectric domains and to the compressive misfit strain, leading to an enhanced ferroelectric polarization. (C) 2013 AIP Publishing LLC.

2152. Challenges for silicon pixel sensors at the European XFEL

Authors: Klanner, R; Becker, J; Fretwurst, E; Pintilie, I; Pohlsen, T; Schwandt, J; Zhang, JG

Published: DEC 1 2013, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 730, 7, DOI: 10.1016/j.nima.2013.05.166

A systematic experimental study of the main challenges for silicon-pixel sensors at the European XFEL is presented. The high instantaneous density of X-rays and the high repetition rate of the XFEL pulses result in signal distortions due to the plasma effect and in severe radiation damage. The main parameters of X-ray-radiation damage have been determined and their impacton p(+)n sensors is investigated. These studies form the basis of the optimized design of a pixel-sensor for experimentation at the European XFEL. (C) 2013 Elsevier B.V. All rights reserved.

2153. Radiation damage in n-type silicon diodes after electron irradiation with energies between 1.5 MeV and 15 MeV

Authors: Radu, R; Fretwurst, E; Klanner, R; Lindstroem, G; Pintilie, I

Published: DEC 1 2013, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 730, 90, DOI: 10.1016/j.nima.2013.04.080

Radiation damage in silicon, caused by the creation of point and cluster defects due to energetic charged hadrons and neutrons, results in a serious degradation of silicon-sensor performance and limits their lifetime. So far not all the defects are understood. The work presented here focuses on the study of radiation damage by electrons of different kinetic energies, from 1.5 MeV to 15 MeV, in order to study the differences between point- and cluster-related defects. The introduction rate of vacancy-related point defects and of so-called clustered regions was investigated as a function of electron energy. It is shown that the ratio between cluster dominated and point defect formation increases with increasing electron energy. 1.5 MeV electrons create only point defects, and the formation of cluster defects starts already at 3.5 MeV. To study the defect kinetics, isothermal annealing at 80 degrees C and isochronal annealing measurements were performed. (C) 2013 Elsevier B.V. All rights reserved.

2154. Enhancement of Superconductivity in Quenched alpha-FeSe Flakes

Authors: Zhao, PH; Yan, W; Han, YL; Shen, SC; Aldica, G; Sandu, V; Badica, P; Nie, JC

Published: DEC 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 3353, DOI: 10.1007/s10948-013-2194-4

Tetragonal alpha-FeSe flakes were fabricated by a simple method. Enhancement of superconductivity was observed in the quenched samples. The properties were characterized by X-ray diffraction, a superconductivity quantum interference device, and physical property measurement system. It is interesting that the superconducting transition temperature of the quenched samples is about 2 K higher than that of unquenched samples, but after reannealed, the enhancement of superconductivity disappeared. The reduction of the c/a ratio might be responsible for the enhancement of superconductivity in the quenched FeSe flakes.

2155. Influence of a hydrophobin underlayer on the structuring and antimicrobial properties of ZnO films

Authors: Popescu, AC; Stan, GE; Duta, L; Dorcioman, G; Iordache, O; Dumitrescu, I; Pasuk, I; Mihailescu, IN

Published: DEC 2013, JOURNAL OF MATERIALS SCIENCE, 48, 8336, DOI: 10.1007/s10853-013-7646-5

Adhesion to substrate and antimicrobial efficiency of pulsed laser-deposited ZnO nanostructures were significantly increased by interposing a buffer nano-layer of hydrophobin. The hydrophobin interlayer increased by eight times the ZnO film resilience to wash in water, while in alkaline or acidic artificial sweat, it increased by 2 and 1.2 times, respectively, as compared to textiles covered with ZnO films only. Hydrophobin boosted the biocide effect of ZnO nanostructured films in case of Candida albicans and mold mix inoculum cultures by 50 and 30 %, respectively. An interpretation of these phenomena is advanced based upon the results of the structural investigations.

2156. InN Based Water Condensation Sensors on Glass and Flexible Plastic Substrates

Authors: Dumitru, V; Costea, S; Brezeanu, M; Stan, GE; Besleaga, C; Galca, AC; Ionescu, G; Ionescu, O

Published: DEC 2013, SENSORS, 13, 16949, DOI: 10.3390/s131216940

2157. Multi-layer haemocompatible diamond-like carbon coatings obtained by combined radio frequency plasma enhanced chemical vapor deposition and magnetron sputtering

Authors: Popa, AC; Stan, GE; Husanu, MA; Pasuk, I; Popescu, ID; Popescu, AC; Mihailescu, IN

Published: DEC 2013, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 24, 2707, DOI: 10.1007/s10856-013-5026-y

Radio-frequency Plasma Enhanced Chemical Vapour Deposition (in different methane dilutions) was used to synthesize adherent and haemocompatible diamond-like carbon (DLC) films on medical grade titanium substrates. The improvement of the adherence has been achieved by interposing a functional buffer layer with graded composition TixTiC1-x (x = 0-1) synthesized by magnetron co-sputtering. Bonding strength values of up to similar to 67 MPa have been measured by pull-out tests. Films with different sp(3)/sp(2) ratio have been obtained by changing the methane concentration in the deposition chamber. Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed for the physical-chemical characterization of the samples. The highest concentration of sp(3)-C (similar to 87 %), corresponding to a lower DLC surface energy (28.7 mJ/m(2) ), was deposited in a pure methane atmosphere. The biological response of the DLC films was assayed by a state-of-the-art biological analysis method (surface enhanced laser desorption/ionization-time of flight mass spectroscopy), in conjunction with other dedicated testing techniques: Western blot and partial thromboplastin time. The data support a cause-effect relationship between sp(3)-C content, surface energy and coagulation time, as well as between platelet-surface adherence properties and protein adsorption profiles.

2158. Increased Diffusion Coefficient of Polymeric Nanocomposite Layer for Gas Sensing Applications

Authors: Nicolae, I; Viespe, C; Serban, N; Negrila, CC; Teodorescu, VS; Trupina, L

Published: DEC 2013, SENSOR LETTERS, 11, 2332, DOI: 10.1166/sl.2013.3083

A high-performance polymeric nanostructured sensing layer for a surface acoustic wave sensor, deposited using a modified matrix assisted pulsed laser evaporation direct write technique, exhibited improved performance in terms of response time and frequency deviation. In the present work, we assessed the factors and mechanisms that account for the layer's increased sensing capabilities. The increase in the sensing performance was attributed to an increased diffusion constant, due to greater molecular mobility of polymeric chains caused by the nanoparticles embedded in the polymer matrix.

2159. Combined influence of Coulomb interaction and polarons on the carrier dynamics in InGaAs quantum dots

Authors: Steinhoff, A; Kurtze, H; Gartner, P; Florian, M; Reuter, D; Wieck, AD; Bayer, M; Jahnke, F

Published: NOV 22 2013, PHYSICAL REVIEW B, 88, DOI: 10.1103/PhysRevB.88.205309

Experimental results for the carrier capture and relaxation dynamics in self-organized semiconductor quantum dots are analyzed using a microscopic theory. Time-resolved differential transmission changes of the quantum-dot transitions after ultrafast optical excitation of the barrier states are studied in a wide range of carrier temperatures and excitation densities. The measurements can be explained by quantum-dot polaron scattering and their excitation-dependent renormalization due to additional Coulomb scattering processes. Results of configuration-picture and single-particle-picture descriptions, both with nonperturbative transition rates, show good agreement with the experiments while Boltzmann scattering rates lead to a different excitation density and temperature dependence.

2160. Band bending at free Pb(Zr,Ti)O-3 surfaces analyzed spectroscopy by X-ray photoelectron

Authors: Apostol, NG; Stoflea, LE; Lungu, GA; Tache, CA; Popescu, DG; Pintilie, L; Teodorescu, CM

Published: NOV 20 2013, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 178, DOI: 10.1016/j.mseb.2013.02.007

This paper analyses in detail the core levels evolution of Pb(Zr,Ti)O-3, i.e. Pb 4f, Zr 3d, Ti 2p, O 1s in various conditions: absolutely freshly prepared sample, sample stored under air, and the effects of in vacuum annealing. The aim of the study is to quantify separately the chemical reactivity at the surface and the band bending effects due to the ferroelectric polarization. It is found that freshly prepared samples present mostly inwards (down arrow) polarization. This phenomenon is mostly revealed by the Ti 2p and O 1s spectra, manifested as a distinct component with 1.8 eV lower binding energy in the O 1s binding energy and by 1.1 eV in the Ti 2p binding energy. Sample aging under air suppresses the inwards polarization, and most signal comes from surfaces not presenting ferroelectric permanent polarization perpendicular to the sample surface. This process conducts also to the formation of Pb(CO3)(2) on the surface. Annealing to temperatures up to 400 degrees C stabilizes a surface composed by a main part of surface without polarization perpendicular to the surface, and with some areas presenting outwards (up arrow) polarization. These areas have, most probably, different terminations, the polarized area being (Ti,Zr)O-2 terminated. (C) 2013 Elsevier B.V. All rights reserved.