National Institute Of Materials Physics - Romania

Publications

5975 articles found

4241. Spin magnetoconductance in the mesoscopic spin-interferometer

Authors: Aldea, A; Tolea, M; Zittartz, J

Published: JUL 2005, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 28, 202, DOI: 10.1016/j.physe.2005.03.013

We investigate the properties of the electron spin-transmission through an Aharonov-Bohm interferometer with an embedded two-dimensional (2D) multilevel quantum dot containing magnetic impurities. A suitable formalism is developed. The amplitude and the phase of the flip- and non-flip-transmittances are calculated numerically as function of the magnetic field. The effects induced by the exchange interaction and those arising from the 2D character of the dot are shown. (c) 2005 Elsevier B.V. All rights reserved.

4242. Morphology and shape evolution of the copper monosulfide nanocrystallites with the reaction time

Authors: Simonescu, CM; Teodorescu, VS; Brezeanu, M; Melinescu, A

Published: JUN 2005, REVISTA DE CHIMIE, 56, 614, DOI:

Copper monosulfide nanocrystallites have been obtained by reaction between copper acetate and sodium thiosulphate (1:4) at 90 +/- 5 degrees C. The powder was studied by X ray diffraction, IR spectrometry and TEM - transmission electron microscopy and electron diffraction. The copper monosulfide crystallites have been obtained in spherical or discoidal "nodules" which are bonded in much bigger aggregates. The dimensions of the copper monosulfide crystallites are small (10 to 15 nm) near the nucleation center (indicated by an arrow) and bigger at the edges of the spherical nodule (60 to 80 nm). The evolution of the morphology and the shape of the crystallite aggregate with the reaction time allows to propose a nucleation and a crystal growth mechanism for this system.

4243. Electron affinity changes induced by gaseous species present in the sourrounding atmosphere

Authors: Tomescu, A; Roescu, R

Published: JUN 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1532, DOI:

A simultaneous evaluation of variation in electrical resistance and work function was carried out in order to calculate electron affinity changes induced by appearance of surface dipoles at sensor interface triggered by exposure to different gas species, respectively CO, CH4 and H2O.

4244. Preparation of stacked structures based on HTS by MOCVD: growth problems of c-axis and non c-axis BiSrCaCuO/Bi4Ti3O12 heterostructures

Authors: Endo, K; Badica, P

Published: JUN 2005, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 15, 3069, DOI: 10.1109/TASC.2005.848741

Several articles report two-layer c-axis heterostructures of Bi4Ti3O12 on BiSrCaCuO. However in some applications, or for integration purposes, multi-layer geometries composed of alternating c-axis or non c-axis thin films might be useful. From this perspective we investigated growth of c-axis and non c-axis BiSrCaCuO on Bi4Ti3O12 structures. The paper mainly focuses on evaluation of the structures from the growth, stability/interdiffusion, uniformity/morphology points of view based on structural and microstructural data.

4245. Transport through a quantum ring, dot, and barrier embedded in a nanowire in magnetic field

Authors: Gudmundsson, V; Lin, YY; Tang, CS; Moldoveanu, V; Bardarson, JH; Manolescu, A

Published: JUN 2005, PHYSICAL REVIEW B, 71, DOI: 10.1103/PhysRevB.71.235302

We investigate the transport through a quantum ring, a dot, and a barrier embedded in a nanowire in a homogeneous perpendicular magnetic field. To be able to treat scattering potentials of finite extent in a magnetic field we use a mixed momentum-coordinate representation to obtain an integral equation for the multiband scattering matrix. For a large embedded quantum ring we are able to obtain Aharonov-Bohm type of oscillations with superimposed narrow resonances caused by interaction with quasibound states in the ring. We also employ the scattering matrix approach to calculate the conductance through a semiextended barrier or well in the wire. The numerical implementations we resort to in order to describe the cases of weak and intermediate magnetic field allow us to produce high resolution maps of the "near field" scattering wave functions, which are used to shed light on the underlying scattering processes.

4246. Investigations by X-ray topography of quartz and langasite resonators

Authors: Mateescu, I; Capelle, B; Detaint, J; Johnson, G; Tsoi, E; Bran, C

Published: JUN 2005, JOURNAL DE PHYSIQUE IV, 126, 6, DOI: 10.1051/jp4:2005126001

This paper presents the results of the X-ray topography investigations of mass-loading influence on electrical parameters of AT-cut quartz resonators and Y-cut langasite resonators. This study reveals that the mass-loading effect on electrical parameters of Y-cut langasite resonators is smaller than in the case of AT-cut quartz resonators. The results of the X-ray topography investigations are in good agreement with electrical measurements.

4247. Magnetically modulated microwave absorption investigation of Bi1.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox/(LiF)(y) superconducting system

Authors: Velter-Stefanescu, M; Duliu, OG; Mihalache, V

Published: JUN 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1561, DOI:

The effect of LiF content on the 2223 phase of the high temperature superconducting system Bi1.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox/(LiF)(y) (y = 0.02 to 0.15) was investigated by means of magnetically modulated microwave absorption (MAMMA). The experimental results confirmed a two fold increase of the superconducting phase content together with a slight rise (around 2 %) of the critical temperature for y=0.07. At the same time, for y between 0.05 and 0.12 the -Delta T-c(mw)/Delta B ratio was practically constant and equal to (18.5 +/- 1.5) KT-1, a typical value for 2223 superconducting phase.

4248. Correlated photon-pair emission from a charged single quantum dot - art. no. 235308

Authors: Ulrich, SM; Benyoucef, M; Michler, P; Baer, N; Gartner, P; Jahnke, F; Schwab, M; Kurtze, H; Bayer, M; Fafard, S; Wasilewski, Z; Forchel, A

Published: JUN 2005, PHYSICAL REVIEW B, 71, DOI: 10.1103/PhysRevB.71.235328

The optical creation and recombination of charged biexciton and trion complexes in an (In,Ga)As/GaAs quantum dot is investigated by microphotoluminescence spectroscopy. Under the condition of quasiresonant pulsed excitation into the p shell we find nearly background-free photoluminescence from single quantum dots where multiple-photon (> 1) emission is fully suppressed. This reflects almost perfect triggered single-photon emission. Photon cross-correlation measurements demonstrate the temporally correlated decay of charged biexciton and trion states. Our calculations provide strong evidence for radiative decay from the excited trion state, thus indicating a long-lived p-electron spin configuration.

4249. Raman spectra of AsxSe100-x glasses doped with metals

Authors: Iovu, MS; Kamitsos, EI; Varsamis, CPE; Boolchand, P; Popescu, M

Published: JUN 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1221, DOI:

Chalcogenide glasses in the system AsxSe100=x, as well as As40Se60 and As50Se50 glasses doped with metals (Bi, Ge, Cd, Ag, Sn, Mn, Dy and Sm) were investigated by Raman spectroscopy. The Raman spectra of AsxSe100-x with 0 <= x <= 10 suggest that the majority building units are Se chains and See closed rings. At higher As contents, new structural units are formed from As and Se atoms. The Raman profiles for x > 50 are characterized by the presence of strong narrow bands indicating the high ordering in the structure of these glassy materials. The doped samples with small amounts of metals, 0.1 - 1.0 at.%, do not show appreciable changes in their short-range order structure, with the exception of the 0.5 at.% Dy-doped sample. For the sample As50Se50+7.5 at.% Sn, there is direct evidence for the formation of new Sn-based structural units, such as Sn(Se-1/2)(4) tetrahedra.

4250. Micro-structure and magnetic properties of Fe-Cu nanocomposites for anisotropic permanent magnets

Authors: Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Jianu, A; Kappel, W; Codescu, M; Patroi, E; Pasuk, I; Bulinski, M; Filoti, G

Published: MAY 31 2005, JOURNAL OF ALLOYS AND COMPOUNDS, 395, 6, DOI: 10.1016/j.jallcom.2004.11.059

Melt spun ribbons of FexCu100-x were obtained by different procedures, in order to maximize the dispersion of the Fe atoms in the Cu matrix. Subsequent thermal and mechanical treatments were used for a controlled crystallization process of the soft magnetic phase. A detailed analysis of structural aspects and crystallization dynamics and their relation with the magnetic behavior of the Fe-Cu ribbons has been obtained via Mossbauer spectroscopy, X-ray diffraction (XRD) and magnetic measurements. In order to obtain composite permanent magnets with shape anisotropy, the optimal conditions and the suitable processing were established. © 2004 Elsevier B.V. All rights reserved.