National Institute Of Materials Physics - Romania

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838 articles found

811. Electrical and optical characterization of PbTiO3/Si heterostructures for applications in optoelectronics

Authors: Dragoi, V; Pintilie, L; Pintilie, I; Petre, D; Boerasu, I; Alexe, M

Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 851, DOI: 10.1117/12.312674

The ferroelectric/semiconductor heterostructures were fabricated by sol-gel deposition of lead titanate (PT) thin films on a single-crystalline p-type Si wafers. The ETT films were crystallyzed by a conventional thermal annealing for 30 min at temperatures ranging from 575 degrees C to 675 degrees C. Current-voltage and capacitance-voltage characteristics show a hysteresis which can be due to the spontaneous polarization of PbTiO3. The current-voltage characteristics exhibit a diode behaviour while the capacitance-voltage exhibits a large memory window, up to 3.5 V, for the films annealed at 600-650 degrees C. At the illumination with modulated light, a.c. photovoltage was detected on a broad range of wavelengths (0.35+4 mu m) for all samples. The spectral distribution of the photoelectric signal in the UV-Vis-IR domain shows two local maxima. A model is proposed to explain the observed experimental results.

812. A model of the metallic surface-emitting second harmonic generator

Authors: Popa, A; Lazarescu, MF; Dabu, R; Stratan, A

Published: SEP 1997, IEEE JOURNAL OF QUANTUM ELECTRONICS, 33, 1480, DOI: 10.1109/3.622625

We present an accurate calculation of the intensity of the second harmonic radiation generated by the reflection of the incident radiation from a metal surface, This radiation is due to two currents, The first current results from the rapid variation of the normal component of the oscillating electric field in the vicinity of the surface and depends on both conduction and bound electrons, The second one results from the action of the Lorentz force on conduction electrons, We show that if the adiabatic and the Thomas-Fermi assumptions are considered, then an accurate calculation of these currents is possible and leads to a simple relation of the intensity of the second harmonic radiation.

813. Indirect enhancement of PbS photoconductivity by ferroelectric field effect in a PbS/PbTiO3/Si heterostructure

Authors: Pintilie, I; Pintilie, L; Dragoi, V; Petre, D; Botila, T

Published: AUG 25 1997, APPLIED PHYSICS LETTERS, 71, 1106, DOI: 10.1063/1.119740

A lead sulphide/lead titanate/silicon (PbS/PbTiO3/Si) heterostructure was manufactured by successive deposition of PbTiO3 and PbS thin film on a single crystalline, p-type Si substrate. Chemical methods were used for deposition. A three electrode configuration was used to control the photoconductivity of PbS thin film by field effect, through the ferroelectric PbTiO3 thin film. The spectral distribution of the photoconductive signal shows two maxima, situated at 1.1 and 2.45 mu m. It was found that the photoconductive signal at 1 mu m varies of about eight times when the voltage applied on the Si substrate is varied between -1 and +1 V. At 2 mu m the photoconductive signal is almost independent of the applied voltage on the Si substrate. The observed results are explained considering a ferroelectric field effect by which the photogenerated carriers in Si influence the photoconductive signal in the PbS thin film. (C) 1997 American Institute of Physics.

814. Enhancement of the photoconductive properties of PbS films deposited on ferroelectric substrates

Authors: Pintilie, I; Pintilie, L; Pentia, E; Petre, D

Published: FEB 1997, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 44, 296, DOI: 10.1016/S0921-5107(96)01729-1

PbS films were chemically deposited on poled and unpoled ferroelectric ceramic substrates and on glass. The sensitivity of the PbS thin films and the concentration of trapping centers inside these films depend on the nature of the substrate and, in the case of poled ferroelectric substrates, depend on the polarity of the ferroelectric polarization as well. A considerable enhancement of the photoconductive signal at liquid nitrogen temperature was found in the case of PbS films deposited on the positive face of a poled ferroelectric substrate. (C) 1997 Elsevier Science S.A.

815. Equivalent circuit analysis of a PbS/ferroelectric heterostructure

Authors: Pintilie, L; Pintilie, I; Botila, T; Petre, D; Licea, I

Published: FEB 1997, INFRARED PHYSICS & TECHNOLOGY, 38, 58, DOI: 10.1016/S1350-4495(96)00026-6

The frequency characteristic of the transverse photoelectric signal of a three electroded PbS/ferroelectric heterostructure is analyzed in this paper. The ferroelectric material is a lead titanate-zirconate ceramic obtained by hot pressing. It was found that the frequency characteristic of this signal is similar to a high-pass filter and depends on the properties of the ferroelectric substrates on which the PbS film was deposited, An equivalent circuit was proposed comparing the studied heterostructure with a metal-oxide semiconductor (MOS) structure. The circuit elements were determined fitting the obtained formula for the output signal with the experimental data. Some of the circuit elements were determined experimentally using various measuring techniques. It was found that the experimentally determined values are close to the theoretically determined values. The studied heterostructure can be changed into a band-pass filter adding some external circuit elements such as resistors and capacitors.

816. Growth and properties of CdS thin films deposited from aqueous solutions, using different cadmium salts

Authors: Pintilie, L; Pentia, E; Pintilie, I; Petre, D

Published: FEB 1997, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 44, 406, DOI: 10.1016/S0921-5107(96)01728-X

Cadmium sulphide (CdS) thin films were deposited on glass substrates using the homogeneous precipitation technique and different cadmium salts. The structure of the films was analysed using scanning electron microscopy (SEM). Thermally stimulated current (TSC) measurements had revealed the existence of several trapping levels in as deposited and annealed films. The activation energy of these traps was determined from TSC measurements. The following values were found for CdS films deposited from cadmium acetate: E-1 = 0.3 eV; E-2 = 0.45 eV, E-3 = 0.51 eV. For CdS films deposited from cadmium chloride several trapping levels were found with the activation energies between 0.04 and 0.33 eV. A considerable enhancement of photoconduction after annealing in air was found. The experimental results were explained considering a sensitizing process due to the chemisorbtion of the oxygen. (C) 1997 Elsevier Science S.A.

817. Temperature dependence of the pyroelectric voltage in a 2-2 connectivity pyroelectric bimorph

Authors: Pintilie, L; Pintilie, I

Published: 1997, FERROELECTRICS, 200, 235, DOI: 10.1080/00150199708008608

Parallel and series pyroelectric bimorph structures, with 2-2 connectivity, are theoretically analysed to obtain the electric fields inside the two component phases. The proposed model takes into consideration the possibility of an electrical interaction between the two phases. It is demonstrated that the value of the internal electric field, due to the pyroelectric charge generated during heating of the bimorph structure, is considerably different than the case where each of the two phases is heated separately. It is shown that the value and the orientation of the electric fields inside the two phases of the bimorph depend on the value of the pyroelectric coefficients and dielectric constants of the two phases. The most interesting result is obtained in the case of the series bimorph, where the orientation of the electric field inside the phase with a lower pyroelectric coefficent is opposite to the orientation of spontaneous polarisation of this phase.

818. Thermally stimulated currents in PbTiO3 thin films

Authors: Pintilie, L; Alexe, M; Pintilie, I; Boierasu, I

Published: 1997, FERROELECTRICS, 201, 223, DOI: 10.1080/00150199708228371

Using the Thermally Stimulated Current (TSC) method, the activation energy of trapping levels in sol-gel deposited lead titanate films was determined. Four levels were found in films annealed at 550 degrees C and 600 degrees C. Their activation energies are: E-1 = 0.23 eV, E-2 = 0.30 eV, E-3 = 0.34 eV and E-4 = 0.40 eV. For the films annealed at 650 degrees C only one level (E-2) was observed. It was found that the TSC magnitude decreases if the same sample is subjected to several cycles of cooling and heating between 100 K and 373 K in vacuum. This suggests a ''healing'' of the traps, probably due to the desorption of some gaseous species from the surface of the ferroelectric thin film.

819. Properties and stability of ferrite materials for magnetic temperature transducers

Authors: Tanasoiu, C; Miclea, C; Dimitriu, E

Published: DEC 1 1996, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 41, 303, DOI: 10.1016/S0921-5107(96)01663-7

Magnetic materials in the CuZnTi ferrite system with the chemical composition Cu1-xZnxTiyFe2-yO4, with 0.5 less than or equal to x less than or equal to 0.62 and 0 less than or equal to y less than or equal to 0.05 were investigated as a function of sintering temperature and time and cooling speed in order to see the influence of these factors upon the Curie temperature and the permeability behaviour around the Curie point. The quality of the magnetic temperature transducers made from such materials is directly connected with the value of the slope of the mu(T) curve. The higher the slope the more sensitive will be the transducer. Slopes as high as 50%degrees C-1 were obtained by a proper cooling of the samples. this value bring the highest reported so far for such materials. The results are discussed in terms of the ionic distribution of the Cu, Zn and Ti ions over the tetrahedral and octahedral sites of the spinel lattice. The materials proved to be stable in time if the temperature does not exceed 200 degrees C, but higher temperatures may induce irreversible change in the material structure due to cation migration and electron transfer from copper ions to iron ions.

820. Interface charge modulation in lead sulphide-ferroelectric ceramic heterostructures

Authors: Pintilie, I; Pintilie, L; Pentia, E; Botila, T; Ofrim, D

Published: OCT 1996, INFRARED PHYSICS & TECHNOLOGY, 37, 665, DOI: 10.1016/S1350-4495(96)00004-7

An anomalous high signal was observed across lead sulphide-ferroelectric ceramic heterostructures illuminated at room temperature with light having wavelengths between 0.8 and 3.1 mu m. The frequency characteristic of this signal is similar to a high-pass filter and depends on the value of the load resistance in series with the lead sulphide thin film, This signal is only two to three times smaller than the usual photoconductive signal generated by the lead sulphide thin film. Its nature is not pyroelectric because of its frequency dependence. The interface charge released from the PbS-ferroelectric interface during polarization reversal was integrated and a hysteresis loop was obtained. Electrons and hole concentrations were evaluated from this curve. The values obtained are: 4.4 x 10(16) cm(-3) for holes and 3.4 x 10(16) cm(-3) for electrons.