NIMP| Roxana RADU, Author at NIMP

Publications

1. Magnetoelectric properties of CoFe2O4/BNT-BT0.08 biphasic nanocomposites, with 0-3 connectivity, prepared by sol-gel method

Authors: Cernea, M; Radu, R; Amorín, H; Vasile, BS; Surdu, VA; Trusca, R; Gavrila, R; Galassi, C

Published: AUG 15 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 952, 170041, DOI: 10.1016/j.jallcom.2023.170041

Motivated by the goal of developing ultralow power, smart and multifunctional nano (micro) electronic devices, research has shown unwavering interest in synthesis methods, architectures and interphase connectivity of composites containing magnetostrictive and piezoelectric phases, known as magnetoelectric (ME) materials. Herein we report on CoFe2O4/0.92Bi0.5Na0.5TiO3-0.08BaTiO3 biphasic ME composites, obtained by sol-gel chemistry, by mixing the precursor sols of the two phases into one precursor sol and further transforming it into gel, with the goal of obtaining homogeneous nanocomposites with magnetoelectric properties. The structural properties, the temperature dependance of dielectric properties, the magnetic and magnetoelectric properties of these biphasic mixtures, with various molar ratios CoFe2O4/ BNT-BT0.08 = 0.5:1, 1:1 and 1.5:1, are investigated. It is observed that the amount of CoFe2O4 and the synthesis in situ of these composites influences their macroscopic properties showing a high difficulty of carrying out an efficient poling resulting in small piezoelectric and magnetoelectric response. It was concluded that the synthesis procedure, the type of architecture and the interphase connectivity are of outmost importance for magnetoelectric properties based on lead-free materials. (c) 2023 Published by Elsevier B.V.

2. Dielectric, piezoelectric and magnetic behavior of CoFe2O4/BNT-BT0.08 monolayer thin films composites

Authors: Cernea, M; Radu, R; Craciun, F; Gavrila, R; Surdu, VA; Trusca, R; Mihalache, V

Published: AUG 2022, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 282, 115770, DOI: 10.1016/j.mseb.2022.115770

We report in this paper on the monolayer composites thin films that have the magnetic spinel CoFe2O4 and the piezoelectric perovskite BNT-BT0.08 as constituent phases. Composite thin films of CoFe2O4 and BNT-BT0.08, with molar ratios of 0.5:1, 1:1 and 1.5:1, have been deposited by spin coating method from a sol precursor, mixture type, of CoFe2O4 and BNT-BT0.08. The monolayer thin films, deposited on Si/SiO2/TiO2/Pt substrate, were characterized using selected methods, such as: X-ray diffraction, scanning electron microscopy, atomic force microscopy/piezoelectric force microscopy, dielectric spectroscopy, and vibrating sample magnetometer. X-ray diffraction demonstrated the two phases: cubic CoFe2O4 and rhombohedral BNT-BT0.08. Furthermore, the Si/ SiO2/TiO2/Pt/BNT-BT0.08/CoFe2O4 monolayers show a simultaneous enhancement of both the magnetization and coercivity with the increase of the magnetic phase, accompanied by a decrease of the dielectric constant. The obtained results reveal that the investigated monolayer structures present superior properties compared to those of bilayer composites.

3. Structural, electrical properties and photoluminescence analyses of the terbium doped barium titanate

Authors: Cernea, M; Secu, M; Radu, R; Ganea, P; Surdu, VA; Trusca, R; Vasile, ET; Secu, EC

Published: OCT 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 878, DOI: 10.1016/j.jallcom.2021.160380

Multifunctional materials integrating optical and electric properties into a composite or into a doped single-phase material have attracted much attention from scientists for future optoelectronic devices. In this work, polycrystalline Ba1-xTbxTiO3, x = 0.00, 0.01 and 0.05 materials were synthesized by hydrothermal route and their photoluminescence and dielectric properties were studied. The as-prepared powders showed a microstructure consisting of grains with the shape of cube; and average particle size ranging from 75 nm to 150 nm. The investigated temperature dependence of dielectric permittivity of Ba1-xTbxTiO3 ceramics revealed a decrease of the Curie temperature (Tc) with increasing terbium content, and a more pronounced degree of diffuseness of phase transition. The resistivity at room temperature was discussed in terms of positive temperature coefficient of resistance (PTRC) effect. UV-vis reflectance spectra of Ba1-xTbxTiO3 samples showed a decrease of the band gap energy with the increase of Tb amount, due to the band-gap narrowing effect. The photoluminescence spectra recorded for Tb doped BaTiO3 materials, at 80 K, evidenced the typical f-f luminescence lines of the Tb3+ accompanied the broad luminescence band at about 425 nm due to self-trapped exciton recombination. These results demonstrated that the terbium enhances the dielectric properties and photoluminescence simultaneously, being suitable for electronic applications. (C) 2021 Elsevier B.V. All rights reserved.

4. Lead-Free BNT-BT0.08/CoFe2O4 Core-Shell Nanostructures with Potential Multifunctional Applications

Authors: Cernea, M; Radu, R; Amorin, H; Greculeasa, SG; Vasile, BS; Surdu, VA; Ganea, P; Trusca, R; Hattab, M; Galassi, C

Published: APR 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10040672

Herein we report on novel multiferroic core shell nanostructures of cobalt ferrite (CoFe2O4) bismuth, sodium titanate doped with barium titanate (BNT-BT0.08), prepared by a two step wet chemical procedure, using the sol gel technique. The fraction of CoFe2O4 was varied from 1:0.5 to 1:1.5 = BNT-BT0.08/CoFe2O4 (molar ratio). X-ray diffraction confirmed the presence of both the spinel CoFe2O4 and the perovskite Bi0.5Na0.5TiO3 phases. Scanning electron microscopy analysis indicated that the diameter of the core shell nanoparticles was between 15 and 40 nm. Transmission electron microscopy data showed two phase composite nanostructures consisting of a BNT-BT0.08 core surrounded by a CoFe2O4 shell with an average thickness of 4-7 nm. Cole-Cole plots reveal the presence of grains and grain boundary effects in the BNT-BT0.08/CoFe2O4 composite. Moreover, the values of the dc conductivity were found to increase with the amount of CoFe2O4 semiconductive phase. Both X-ray photoelectron spectroscopy (XPS) and Mossbauer measurements have shown no change in the valence of the Fe3+, Co2+, Bi3+ and Ti4+ cations. This study provides a detailed insight into the magnetoelectric coupling of the multiferroic BNT-BT0.08/CoFe2O4 core shell composite potentially suitable for magnetoelectric applications.

5. Magnetic properties of BaNi x Fe 12-x O 19 (x=0.0-1.0) hexaferrites, synthesized by citrate -gel auto -combustion and sintered by conventional and spark plasma methods

Authors: Cernea, M; Greculeasa, SG; Radu, R; Aldica, G; Ganea, P; Surdu, VA; Tanasa, ET; Cioangher, M; Iacob, N; Costescu, RM

Published: AUG 5 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 831, DOI:

6. Ferroelectric Field Effect Transistors Based on PZT and IGZO

Authors: Besleaga, C; Radu, R; Balescu, LM; Stancu, V; Costas, A; Dumitru, V; Stan, G; Pintilie, L

Published: 2019, IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY, 7, 275, DOI: 10.1109/JEDS.2019.2895367

Ferroelectric field effect transistors (FeFETs) based on lead zirconate titanate (PZT) ferroelectric material and amorphous-indium-gallium-zinc oxide (a-IGZO) were developed and characterized. The PZT material was processed by a sol-gel method and then used as ferroelectric gate. The a-IGZO thin films, having the role of channel semiconductor, were deposited by radio-frequency magnetron sputtering, at a temperature of similar to 50 degrees C. Characteristics of a typical field effect transistor with SiO2 gate insulator, grown on highly doped silicon, and of the PZT-based FeFET were compared. It was proven that the FeFETs had promising performances in terms of I-on/I-off ratio (i.e., 10(6)) and IDS retention behavior.

7. Kinetics of cluster-related defects in silicon sensors irradiated with monoenergetic electrons

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

Published: APR 28 2018, JOURNAL OF APPLIED PHYSICS, 123, DOI: 10.1063/1.5011372

This work focuses on the kinetic mechanisms responsible for the annealing behavior of radiation cluster-related defects with impact on the electrical performance of silicon sensors. Such sensors were manufactured on high resistivity n-type standard float-zone (STFZ) and oxygen enriched float-zone (DOFZ) material and had been irradiated with mono-energetic electrons of 3.5 MeV energy and fluences of 3 x 10(14) cm(-2) and 6 x 10(14) cm (-2). After irradiation, the samples were subjected either to isochronal or isothermal heat treatments in the temperature range from 80 degrees C to 300 degrees C. The specific investigated defects are a group of three deep acceptors [H(116 K), H(140 K), and H(152 K)] with energy levels in the lower half of the band gap and a shallow donor E(30 K) with a level at 0.1 eV below the conduction band. The stability and kinetics of these defects at high temperatures are discussed on the basis of the extracted activation energies and frequency factors. The annealing of the H defects takes place similarly in both types of materials, suggesting a migration rather than a dissociation mechanism. On the contrary, the E(30 K) defect shows a very different annealing behavior, being stable in STFZ even at 300 degrees C, but annealing-out quickly in DOFZ material at temperatures higher than 200 degrees C, with a high frequency factor of the order of 10(13) s(-1). Such a behavior rules out a dissociation process, and the different annealing behavior is suggested to be related to a bistable behavior of the defect. Published by AIP Publishing.

8. Study of point-and cluster-defects in radiation-damaged silicon

Authors: Donegani, EM; Fretwurst, E; Garutti, E; Klanner, R; Lindstroem, G; Pintilie, I; Radu, R; Schwandt, J

Published: AUG 1 2018, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 898, 23, DOI: 10.1016/j.nima.2018.04.051

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 10(14) cm(-2) and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280 degrees C, are presented. A method based on SRH (Shockley-Read-Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, Delta E-a is extracted from the TSC data. For the VOt (vacancy-oxygen interstitial) defect Delta E-a = 0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the Delta E-a values for different defects are determined after annealing at 80 degrees C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value Delta E-a = 0 is found, whereas for the electron energies of 6-27 MeV Delta E-a > 0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The Delta E-a values determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

9. Properties of perovskite ferroelectrics deposited on F doped SnO2 electrodes and the prospect of their integration into perovskite solar cells

Authors: Pintilie, I; Stancu, V; Tomulescu, A; Radu, R; Stan, CB; Trinca, L; Pintilie, L

Published: DEC 5 2017, MATERIALS & DESIGN, 135, 121, DOI: 10.1016/j.matdes.2017.09.013

The integration of ferroelectrics in perovskite solar cells is proposed as possible way to enhance charge collection efficiency. First results on solar cellmanufactured with PbTiO3 (PTO) instead of TiO2 have shown negligible values for the power conversion efficiency (PCE). This is explained by the high serial resistance of sol-gel deposited PTO on F:SnO2 electrodes (FTO). Although PTO layer has remnant polarization of 22 mu C/cm(2), the high potential barrier (0.25 +/- 0.05 eV) at the FTO/PTO interface and lowcarriermobility (10(-8) cm(2) V-1 s(-1)) compared to TiO2 leads to high serial resistance. Better results were obtained with thinner PTO layers grown by pulsed laser deposition, with PCE values up to 0.6%. Further enhancement was obtained by replacing PTO with BaTiO3 (BTO), with PCE value reaching about 0.8% after poling the cell with +3 V. The most important finding was that the magnitude of the short circuit current increases with the amplitude of the poling voltage while the value of the open-circuit voltage remains about the same, around 0.9 V. This is explained through more efficient collection of the charges generated under illumination in the absorber layer due to the polarization that is present in the ferroelectric film. (C) 2017 Elsevier Ltd. All rights reserved.

10. TEMPERATURE INFLUENCE ON THE CAPACITANCE-VOLTAGE HYSTERESIS OF TRANSPARENT a-IGZO/PZT/FTO MFS-HETEROSTRUCTURE

Authors: Trinca, LM; Besleaga, C; Stancu, V; Radu, R; Iuga, A; Boni, AG; Galca, AC; Pintilie, L

Published: 2017, ROMANIAN REPORTS IN PHYSICS, 69, DOI:

Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.

11. On the growth of conductive aluminum doped zinc oxide on 001 strontium titanate single crystals

Authors: Trinca, LM; Galca, AC; Aldica, G; Radu, R; Mercioniu, I; Pintilie, L

Published: FEB 28 2016, APPLIED SURFACE SCIENCE, 364, 370, DOI: 10.1016/j.apsusc.2015.12.106

Aluminum doped zinc oxide (AZO) thin films were obtained by pulsed laser deposition on (001) SrTiO3 (STO) on a range of substrate temperatures during ablation between 300 degrees C and 600 degrees C. A hexagonal system lying on a cubic one should be difficult to be obtained in epitaxial form. The geometrical selection of the AZO growth on (001) STO is not giving a unique preferential orientation. Two orientations, c-axis (along [001]) and 110, have been observed experimentally with different ratios at different substrate temperature. Discussions are made with respect to the temperature dependence of lattice mismatch between the two cases and the cubic surface of the substrate, and to the substrate surface morphology and terminating atomic layer composition. The 110 AZO is the main phase at deposition temperature of 550 degrees C, while for other substrate temperatures the 001 is the preferential orientation. The conductive character of 110 AZO thin film have been inferred from both ellipsometry spectra and current-voltage measurements. Excepting the samples deposited at 300 degrees C, the lowest resistivity is recorded for the samples with 110 AZO as the main phase. (C) 2015 Elsevier B.V. All rights reserved.

12. Investigation of point and extended defects in electron irradiated silicon-Dependence on the particle energy

Authors: Radu, R; Pintilie, I; Nistor, LC; Fretwurst, E; Lindstroem, G; Makarenko, LF

Published: APR 28 2015, JOURNAL OF APPLIED PHYSICS, 117, DOI: 10.1063/1.4918924

This work is focusing on generation, time evolution, and impact on the electrical performance of silicon diodes impaired by radiation induced active defects. n-type silicon diodes had been irradiated with electrons ranging from 1.5 MeV to 27 MeV. It is shown that the formation of small clusters starts already after irradiation with high fluence of 1.5 MeV electrons. An increase of the introduction rates of both point defects and small clusters with increasing energy is seen, showing saturation for electron energies above similar to 15 MeV. The changes in the leakage current at low irradiation fluence-values proved to be determined by the change in the configuration of the tri-vacancy (V-3). Similar to V-3, other cluster related defects are showing bistability indicating that they might be associated with larger vacancy clusters. The change of the space charge density with irradiation and with annealing time after irradiation is fully described by accounting for the radiation induced trapping centers. High resolution electron microscopy investigations correlated with the annealing experiments revealed changes in the spatial structure of the defects. Furthermore, it is shown that while the generation of point defects is well described by the classical Non Ionizing Energy Loss (NIEL), the formation of small defect clusters is better described by the "effective NIEL" using results from molecular dynamics simulations. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

13. BiFeO3 doped-BNT-BT0.08 piezoelectric and magnetic nanowires, derived from sol-gel precursor

Authors: Cernea, M; Trupina, L; Vasile, B; Bartha, C; Radu, R; Chirila, C; Teodorescu, A

Published: JAN 10 2014, JOURNAL OF NANOPARTICLE RESEARCH, 16, DOI: 10.1007/s11051-013-2231-z

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, doped with 5 mol %BiFeO3 (BNT-BT-BFO) nanowires was prepared from its corresponding precursor sol. A polycarbonate membrane with the thickness of 30 mu m and the pore diameter of 100 nm was used as template. Nanowires with average diameter of similar to 80 nm and different lengths of a few microns were prepared from BNT-BT-BFO precursor sol with similar to 0.03 M concentration. Ferroelectric and piezoelectric characterizations of BNT-BT-BFO nanowires were performed using AFM-PFM equipment. The HR-TEM micrograph of nanocrystals, SAED patterns, and XRD pattern indicated that BNT-BT-BFO nanowires crystallized on the lattice of rhombohedral (Na0.5Bi0.5TiO3) phase. The BNT-BT-BFO nanowires showed a significant piezoelectric response, suggesting a good piezoelectric behavior. The saturation magnetization of the nanowires, measured at room temperature and at 5 kOe magnetic field, was Ms = 0.061 emu/g. A saturated ferromagnetic hysteresis loop has been also obtained.

14. Magnetic properties of BaxSr1-xFe12O19 (x=0.05-0.35) ferrites prepared by different methods

Authors: Cernea, M; Sandu, SG; Galassi, C; Radu, R; Kuncser, V

Published: JUN 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 561, 128, DOI: 10.1016/j.jallcom.2013.01.081

Hexagonal ferrites BaxSr1-xFe12O19 (x = 0.05, 0.15, 0.25, 0.35) were prepared by sol-gel and conventional solid state reaction techniques. Their magnetic properties, investigated by magnetometry and Mossbauer spectroscopy, were discussed in correlation to structural aspects. Whereas the hexaferrites obtained by sol-gel are almost single phase, the ones prepared by the conventional solid state reaction technique present a low amount of BaFe2O4 as secondary phase. All samples show a relative high coercive field and remanent magnetization, as specific features for permanent magnet behavior. The five Fe3+ sites of the specific elemental cell have been revealed and their relative occupancy has been derived from the Mossbauer spectra. The analyzed samples show a sensitivity of the magnetic properties (magnetic moment and anisotropy) with respect to the occupancy of the different Fe sites. (C) 2013 Elsevier B. V. All rights reserved.

15. 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.

16. Ferroelectric and dielectric multilayer heterostructures based on KTa0.65Nb0.35O3 and Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y grown by pulsed laser deposition and chemical solution deposition for high frequency tunable devices

Authors: Le Febvrier, A; Deputier, S; Bouquet, V; Demange, V; Ollivier, S; Galca, AC; Dragoi, C; Radu, R; Pintilie, L; Guilloux-Viry, M

Published: MAY 1 2012, THIN SOLID FILMS, 520, 4567, DOI: 10.1016/j.tsf.2011.10.142

Epitaxial growth of Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (BZN) thin films was achieved on (100)(pc) LaAlO3 substrate by pulsed laser deposition (PLD) and by chemical solution deposition based on Pechini process. Effect of bismuth and zinc deficiency on the BZN thin films obtained by PLD was discussed, in relation with the starting target composition. Dielectric permittivity and bandgap values were determined from electrical and spectroscopic ellipsometry measurements performed on randomly oriented films grown on Pt/Si substrate. BZN thin films obtained by PLD exhibit, at 100 kHz, a dielectric constant of epsilon(r) = 203 and quite low dielectric losses of tan delta = 5 x 10(-2). Epitaxial ferroelectric - dielectric KTa0.65Nb0.35O3 (KTN) -Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (KTN on BZN and BZN on KIN) bilayers were obtained by PLD on (100)(pc) LaAlO3 with the insertion of a suitable buffer layer of KNbO3 in the case of KTN on BZN. Such multilayer heterostructures with an epitaxial growth control of each layer are promising candidates for potential integration in microwave devices. (C) 2011 Elsevier B.V. All rights reserved.

17. Silicon detectors for the sLHC

Authors: Affolder, A; Aleev, A; Allport, PP; Andricek, L; Artuso, M; Balbuena, JP; Barabash, L; Barber, T; Barcz, A; Bassignana, D; Bates, R; Battaglia, M; Beimforde, M; Bemardini, J; Betancourt, C; Bilei, GM; Bisello, D; Blue, A; Bohm, J; Bolla, G; Borgia, A; Borrello, L; Bortoletto, D; Boscardin, M; Bosma, MJ; Bowcock, TJV; Breindl, M; Broz, J; Bruzzi, M; Brzozowski, A; Buhmann, P; Buttar, C; Campabadal, F; Candelori, A; Casse, G; Charron, S; Chren, D; Cihangir, S; Cindro, V; Collins, P; Gil, EC; Costinoaia, CA; Creanza, D; Cristobal, C; Dalla Betta, GF; de Boer, W; De Palma, M; Demina, R; Dierlamm, A; Diez, S; Dobos, D; Doherty, F; Kittelmann, ID; Dolezal, Z; Dolgolenko, A; Dragoi, C; Driewer, A; Dutta, S; Eckstein, D; Eklund, L; Eremin, I; Eremin, V; Erfle, J; Fadeeva, N; Fahrer, M; Fiori, F; Fleta, C; Focardi, E; Forshaw, D; Fretwurst, E; Frey, M; Bates, AG; Gallrapp, C; Garcia, C; Gaubas, E; Genest, MH; Giolo, K; Glaser, M; Goessling, C; Golubev, A; Gorelov, I; Gregoire, G; Gregori, P; Grigoriev, E; Grillo, AA; Grinstein, S; Groza, A; Guskov, J; Hansen, TE; Harkonen, J; Hartjes, FG; Hartmann, F; Hoeferkamp, M; Horisberger, R; Houdayer, A; Hynds, D; Ilyashenko, I; Junkes, A; Kadys, A; Kaminski, P; Karpenko, A; Kaska, K; Kazuchits, N; Kazukauskas, V; Kharchuk, A; Khivrich, V; Kierstead, J; Klanner, R; Klingenberg, R; Kodys, P; Koffeman, E; Kohler, M; Kohout, Z; Korjenevski, S; Korolkov, I; Kozlowski, R; Kozubal, M; Kramberger, G; Kuhn, S; Kuleshov, S; Kuznetsov, A; Kwan, S; La Rosa, A; Lacasta, C; Lange, J; Lassila-Perini, K; Lastovetsky, V; Lazanu, I; Lazanu, S; Lebel, C; Lefeuvre, G; Lemaitre, V; Leroy, C; Li, Z; Lindstrom, G; Litovchenko, A; Litovchenko, P; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Macraighne, A; Maenpaa, T; Makarenko, LF; Mandic, I; Maneuski, D; Manna, N; Marco, R; Garcia, SII; Marunko, S; Masek, P; Mathieson, K; Matysek, M; Mekki, J; Messineo, A; Metcalfe, J; Mikestikova, M; Mikuz, M; Militaru, O; Minano, M; Miyamoto, J; Moll, M; Monokhov, E; Mori, R; Moser, HG; Muenstermann, D; Sanchez, FJM; Naletko, A; Nisius, R; Oshea, V; Pacifico, N; Pantano, D; Parkes, C; Parzefall, U; Passeri, D; Pawlowski, M; Pellegrini, G; Pernegger, H; Petasecca, M; Piemonte, C; Pignatel, GU; Pintilie, I; Pintilie, L; Piotrzkowski, K; Placekett, R; Pohlsen, T; Polivtsev, L; Popule, J; Pospisil, S; Preiss, J; Radicci, V; Radu, R; Raf, JM; Rando, R; Richter, R; Roeder, R; Roger, R; Rogozhkin, S; Rohe, T; Ronchin, S; Rott, C; Roy, A; Rummler, A; Ruzin, A; Sadrozinski, HFW; Sakalauskas, S; Samadashvili, N; Scaringella, M; Schumm, B; Seidel, S; Seiden, A; Shipsey, I; Sibille, J; Sicho, P; Slavicek, T; Solar, M; Soldevila-Serrano, U; Son, S; Sopko, V; Sopko, B; Spencer, N; Spiegel, L; Srivastava, A; Steinbrueck, G; Stewart, G; Stolze, D; Storasta, J; Surma, B; Svensson, BG; Tan, P; Tomasek, M; Toms, K; Tsiskaridze, S; Tsvetkov, A; Tuboltsev, Y; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Ullan, M; Vaitkus, JV; van Beuzekom, M; Verbitskaya, E; Alvarez, IV; Visser, J; Vossebeld, J; Vrba, V; Walz, M; Weigell, P; Wiik, L; Wilhelm, I; Wunstorf, R; Zaluzhny, A; Zavrtanik, M; Zelazko, J; Zen, M; Zhukov, V; Zontar, D; Zorzi, N

Published: DEC 1 2011, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 658, 16, DOI: 10.1016/j.nima.2011.04.045

In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages. (C) 2011 Elsevier B.V. All rights reserved.

18. Dielectric and Ferroelectric Characterization of Ba0.95Tm0.05TiO3 Ceramics Derived from Sol to Gel

Authors: Cernea, M; Vasile, BS; Ganea, P; Radu, R; Mihalache, V; Husanu, A

Published: MAR 2011, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 741, DOI: 10.1111/j.1551-2916.2010.04179.x

Barium titanate (BaTiO3) has been doped in situ with 5 mol% thulium by a sol-gel method. The as-prepared gel powder consists of nanosized grains (20-30 nm) and crystallizes on the cubic BaTiO3 lattice, at 700 degrees C. Ba0.95Tm0.05TiO3 ceramics derived from this powder have tetragonal perovskite structure and contain a small amount of Tm2Ti2O7 pyrochlore phase. These ceramics exhibit dielectric constants of 4282-3240 and dielectric loss (tan delta) of 0.1077-0.0161 at Curie temperature T-c=132 degrees C and at 10 Hz-100 kHz, respectively. For a drive voltage of 400 V, the hysteresis loop recorded at the frequency of 100 Hz shows a remnant polarization (P-r) value of 76 mu C/cm2 and a coercive field (E-c) of 124 V and for 1 kHz a remnant polarization (P-r) value of 58 mu C/cm2 and a coercive field (E-c) of 116 V.

19. Ba(Ti1-xSnx)O-3 (x=0.13) nanomaterials produced by low-temperature aqueous synthesis

Authors: Cernea, M; Trusca, R; Radu, R; Valsangiacom, C

Published: OCT 13 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 9937, DOI: 10.1016/j.jallcom.2011.07.101

BaTi0.87Sn0.13O3 (BTS13) nanopowder was prepared by low-temperature aqueous synthesis (LTAS) method. The evolution of the structure and microstructure of the precursor precipitate, heated at temperatures up to 1000 degrees C was studied by TGA, FT-IR, SEM and XRD techniques. The dried precipitate showed a microstructure consisting of nano-sized grains (similar to 40 nm) with great tendency to agglomeration. BaTi0.87Sn0.13O3 single phase was obtained at 800 degrees C. The ceramics prepared from as-obtained BTS13 powders (60-70 nm) show good dielectric and ferroelectric characteristics. The dielectric constant was about 4800 and the dielectric loss (tan delta) was 0.229 at 1 kHz and at the Curie temperature (31 degrees C). The remanent polarization (P-r) and the coercive field (E-C) of Ba0.97Ho0.03TiO3 ceramics, at 1 kHz, were P-r = 13 mu C/cm(2) and E-C = 0.89 kV/cm. The ferroelectric parameters E-C and P-r decrease with increasing frequency in the domain 100 Hz to 10 kHz. (C) 2011 Elsevier B.V. All rights reserved.

20. Application of spark plasma sintering to processing of dense Ba(Ti1-xSnx)O-3 (x=0.13) ceramic

Authors: Aldica, G; Cernea, M; Radu, R; Trusca, R

Published: AUG 27 2010, JOURNAL OF ALLOYS AND COMPOUNDS, 505, 277, DOI: 10.1016/j.jallcom.2010.06.044

Short time spark plasma sintering at 1200 degrees C for 10 min and under a uniaxial pressure of 95 MPa followed by annealing at 1100 degrees C for 5 h is proposed for synthesis of high density (99%) Ba(Ti0.87Sn0.13)O-3 ceramic. Starting powder of 450 nm was obtained by co-precipitation, while the average grain size in the sintered ceramic was of 580 nm. X-ray diffraction analysis of the as prepared Ba(Ti0.87Sn0.13)O-3 samples indicated the presence of single phase BaTi0.87Sn0.13O3 developed in the BaTiO3 cubic structure. Samples have high relative dielectric constant of 5680 and low dissipation factor (tan delta = 0.009) at Curie temperature of 57 degrees C and 1 kHz, good tunability and ferroelectric properties. Remarkable is that these results are from some points of view different than for the conventionally processed samples with similar stoichiometry. Some ideas in this regard are presented and this suggests that SPS can be useful for expanded possibilities in the control of the properties. (C) 2010 Elsevier B.V. All rights reserved.

21. Temperature induced change in the hysteretic behavior of the capacitance-voltage characteristics of Pt-ZnO-Pb(Zr0.2Ti0.8)O-3-Pt heterostructures

Authors: Pintilie, L; Dragoi, C; Radu, R; Costinoaia, A; Stancu, V; Pintilie, I

Published: JAN 4 2010, APPLIED PHYSICS LETTERS, 96, DOI: 10.1063/1.3284659

Pt-ZnO-Pb(Zr0.2Ti0.8)O-3-Pt (PZT-ZnO) heterostructures were fabricated by using a sol-gel process. Capacitance-voltage measurements performed on a wide temperature range (20-450 K) have revealed the presence of a hysteresis that undergo a change of direction from clockwise at temperatures below 350 K to counter-clockwise at higher temperatures. In the first case, the hysteresis is produced by charge injection, similar to the case of classical metal-oxide-semiconductor capacitors. In the last case, the hysteresis is the fingerprint of polarization reversal, as reported for metal-ferroelectric-semiconductor (MFS) structures based on n-Si. The memory window at 450 K is about 6 V. This result suggests that PZT-ZnO MFS heterostructures can be used for memory devices working at elevated temperatures, in which the ZnO plays the role of the semiconductor.

22. Sol-gel synthesis and characterization of BaTiO3-doped (Bi0.5Na0.5)TiO3 piezoelectric ceramics

Authors: Cernea, M; Andronescu, E; Radu, R; FochiB, F; Galassi, C

Published: FEB 4 2010, JOURNAL OF ALLOYS AND COMPOUNDS, 490, 694, DOI: 10.1016/j.jallcom.2009.10.140

(Bi0.5Na0.5)TiO3 doped with 8 mol% BaTiO3 (BNT-BT0.08) powder was prepared by an acetate-alkoxide sol-gel method. The evolution of the structure and microstructure of the precursor gel, heated at various temperatures as well as, the piezoelectric and ferroelectric properties of BNT-BT0.08 ceramics were studied. Nanopowder of BNT-BT0.08 with average particles size of 30 nm and, crystallized on the perovskitic structure of (Bi0.5Na0.5)TiO3, were obtained from the precursor gel by heating at 600 degrees C, 3 h in air. The ceramics of composition 0.92(Bi0.5Na10.5)TiO3-0.08BaTiO(3), manufactured from the as-prepared nanostructured powder, present good dielectric properties (epsilon(r,max) = 4000-4500, tan delta = 0.02-0.03) and high mechanical quality factor (Q(m) similar to 500). (C) 2009 Elsevier B.V. All rights reserved.

23. Electrical investigations of holmium-doped BaTiO3 derived from sol-gel combustion

Authors: Cernea, M; Galassi, C; Vasile, BS; Ganea, P; Radu, R; Ghita, G

Published: JUN 2010, JOURNAL OF MATERIALS RESEARCH, 25, 1063, DOI: 10.1557/JMR.2010.0149

Holmium-doped BaTiO3 with composition Ba0.97Ho0.03TiO3 was prepared by sol-gel combustion method. A molar ratio of citrate/nitrate (CA/NO3- = 1.3) was used to prepare nanopowders of (Ba,Ho)TiO3. The structure and microstructure of (Ba,Ho)TiO3 powders and ceramics were investigated. The ceramics exhibit a dielectric constant of about 4400 and dielectric loss (tan delta = 0.267) at 10 Hz, and at the Curie temperature (T-c = 132 degrees C). The remanent polarization and the coercive field of Ba0.97Ho0.03TiO3 ceramics, at 1 kHz, were P-r = 6 mu C/cm(2) and E-C = 0.75 kV/cm. The dielectric and ferroelectric behavior of the holmium-doped BaTiO3 is influenced by the amphoteric character of Ho3+ ions.

Dr. Roxana RADU

Scientific Researcher III