Papers by Cristina Dragoi
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011
was submitted under my name for the RD50 speaker's bureau. The actual speaker remains to be chose... more was submitted under my name for the RD50 speaker's bureau. The actual speaker remains to be chosen by the speaker's bureau in due time]
Structural and electrical properties of NBT–BT0.08 ceramic prepared by the pyrosol method
Ceramics International, 2013
Abstract [(Bi 0.5 Na 0.5 )TiO 3 ] 0.92 –[BaTiO 3 ] 0.08 lead free piezoelectric materials were pr... more Abstract [(Bi 0.5 Na 0.5 )TiO 3 ] 0.92 –[BaTiO 3 ] 0.08 lead free piezoelectric materials were prepared by the pyrosol method. The as-obtained powder shows spherical grains of various sizes, composed of crystallites of about 10 nm. NBT–BT 0.08 ceramic obtained at 700 °C show rhombohedral NBT as the main phase and traces of hexagonal Bi 2 O 3 as secondary phase. The ceramics prepared from this powder and sintered at 1000 and 1100 °C are single phase with good dielectric and ferroelectric properties.
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
Thin Solid Films, 2012
Epitaxial growth of Bi1.5-xZn0.92-yNb1.5O6.92–1.5x-y (BZN) thin films was achieved on (100)pc LaA... more 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
Pizeoelectric epitaxial sol-gel Pb(Zr<inf>0.52</inf>Ti<inf>0.48</inf>)O<inf>3</inf> film on Si(001)
Proceedings of ISAF-ECAPD-PFM 2012, 2012
ABSTRACT Epitaxial Pb(Zr0.52Ti0.48)O-3 (PZT) thin film has been successfully integrated on Si(001... more ABSTRACT Epitaxial Pb(Zr0.52Ti0.48)O-3 (PZT) thin film has been successfully integrated on Si(001) substrate by sol-gel method. SrTiO3 (STO) layer deposited on Si by Molecular Beam Epitaxy (MBE) acts as a template layer in this study to avoid the formation of amorphous SiO2, and allows the chemical compatibility for further epitaxial growth. For bottom electrode, SrRuO3 (SRO) layer grown by Pulsed Laser Deposition (PLD) on STO/Si was used. Epitaxial single crystalline growth of PZT film after Rapid Thermal Annealing (RTA) at 650 C was evidenced by X-Ray Diffraction (XRD). The following relationship in the heterostructure was deduced: [110] PZT (001) // [110] SRO (001) // [110] STO (001) // [100] Si (001). A clear piezoelectric response of the film was observed by Piezoresponse Force Microscope (PFM). Moreover, the structural STO quality was proved to have a major impact on the electrical properties of PZT films.
Interface controlled photovoltaic effect in epitaxial Pb(Zr,Ti)O3 films with tetragonal structure
Journal of Applied Physics, 2011
ABSTRACT It is shown that the short-circuit photocurrent measured under illumination in Pb(Zr,Ti)... more ABSTRACT It is shown that the short-circuit photocurrent measured under illumination in Pb(Zr,Ti)O3 epitaxial films is strongly dependent on the metal used as the top electrode. The magnitude of the photocurrent varies by more than 2 orders of magnitude from Pt (largest signal) to Al (smallest signal). The differences are for both directions of polarization. The imprint is also dependent on the top metal electrode, with a direct effect on the shape of the spectral distribution. The results support the hypothesis that the origin of the photovoltaic effect in ferroelectric thin films is different from that of the anomalous photovoltaic effect observed in bulk ceramics and single crystals.
Applied Physics Letters, 2009
The leakage current in epitaxial BiFeO 3 capacitors with bottom SrRuO 3 and top Pt electrodes, gr... more The leakage current in epitaxial BiFeO 3 capacitors with bottom SrRuO 3 and top Pt electrodes, grown by pulsed laser deposition on SrTiO 3 ͑100͒, SrTiO 3 ͑110͒, and SrTiO 3 ͑111͒ substrates, is investigated by current-voltage ͑I-V͒ measurements in the 100-300 K temperature range. It is found that the leakage current is interface-limited and strongly dependent on the orientation of the substrate. The potential barriers at the electrode interfaces are estimated to about 0.6, 0.77, and 0.93 eV for the ͑100͒, ͑110͒, and ͑111͒ orientations, respectively.
Thin Solid Films, 2011
The results of the electric and magnetic measurements performed on PbZr 0.2 Ti 0.8 O 3-BiFeO 3 sy... more The results of the electric and magnetic measurements performed on PbZr 0.2 Ti 0.8 O 3-BiFeO 3 symmetric structures, deposited on Pt/Si wafers, were compared for different number of layers in order to analyse the effect of interfaces over the macroscopic properties. It was found that the shape and magnitude of the capacitance-voltage characteristic, as well as the shape and parameters of the ferroelectric and magnetic hysteresis, depend on the number of interfaces in the intended multilayer structure. A temperature induced gradual transition from a magnetically disordered spin glass like phase of low temperature to an uncompensated antiferromagnetic phase at room temperature takes place in the BiFeO 3 films, under low applied magnetic fields. A partial ferromagnetic like order can be obtained at low temperatures by increasing the field. The observed changes in the electric and magnetic behaviour of the systems were related to an increased degree of disorder for electric dipoles and magnetic moments, due to the increased number of layers and crystallization treatments.
Applied Surface Science, 2011
The difficulties in synthesizing phase pure BaTiO 3 doped-(Na 0.5 Bi 0.5 )TiO 3 are known. In thi... more The difficulties in synthesizing phase pure BaTiO 3 doped-(Na 0.5 Bi 0.5 )TiO 3 are known. In this work, we reporting the optimized pulsed laser deposition (PLD) conditions for obtaining pure phase 0.92(Na 0.5 Bi 0.5 )TiO 3 -0.08BaTiO 3 , (BNT-BT 0.08 ), thin films. Dielectric, ferroelectric and piezoelectric properties of BNT-BT 0.08 , thin films deposited by PLD on Pt/TiO 2 /SiO 2 /Si substrates are investigated in this paper. Perovskite structure of BNT-BT 0.08 thin films with random orientation of nanocrystallites has been obtained by deposition at 600 • C. The relative dielectric constant and loss tangent at 100 kHz, of BNT-BT 0.08 thin film with 530 nm thickness, were 820 and 0.13, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 22 C/cm 2 and a coercive field of 120 kV/cm. The piezoresponse force microscopy (PFM) data showed that most of the grains seem to be constituted of single ferroelectric domain. The as-deposited BNT-BT 0.08 thin film is ferroelectric at the nanoscale level and piezoelectric.
Ferroelectric multilayers
physica status solidi (a), 2012
High quality pulsed laser deposited lead zirconate titanate (PZT) films are obtained by pulsed la... more High quality pulsed laser deposited lead zirconate titanate (PZT) films are obtained by pulsed laser deposition on SrRuO 3 (111) single crystal layers and characterized by X-ray photoelectron spectroscopy (XPS), to determine the surface composition. It is found that a minor amount of Pb forms PbO 2 at the surface and also some Pb is included into the contamination layer, in form of a Pb(CO 3 ) 2 layer of about 1 nm thickness, occupying about one quarter of the PZT surface. The stoichiometry of the outermost 4-5 nm layers yielded as PbZr 0.25 Ti 0.80 O 2.5 , which suggest the formation of an oxygen depleted, Brownmillerite-like layer at the surface, of at least 5 nm thickness.
Journal of Materials Science, 2011
0.89(Na 0.5 Bi 0.5 )TiO 3 -0.11BaTiO 3 , (BNT-BT 0.11 ) thin film was fabricated by sol-gel/spin ... more 0.89(Na 0.5 Bi 0.5 )TiO 3 -0.11BaTiO 3 , (BNT-BT 0.11 ) thin film was fabricated by sol-gel/spin coating process, on platinized silicon wafer. Perovskite structure with random orientation of crystallites has been obtained at 700°C. Piezoelectric activity of BNT-BT 0.11 thin film was detected using piezoresponse force microscopy (PFM). Effective piezoelectric coefficient d 33eff of such film, recorded at 5 V applied dc voltage, was *29 pm/V, which is similar to other BNT-BT x thin films. The complex refractive index and dielectric function of BNT-BT 0.11 thin films were also investigated. The high leakage current density significantly influences the dielectric, ferroelectric, and piezoelectric properties of the BNT-BT 0.11 films.
Structural and piezoelectric characteristics of BNT–BT0.05 thin films processed by sol–gel technique
Journal of Alloys and Compounds, 2012
Polycrystalline ferroelectric lead-free (Bi0. 5Na0. 5) 0.95 Ba0. 05TiO3 (BNT–NT0. 05) thin films ... more Polycrystalline ferroelectric lead-free (Bi0. 5Na0. 5) 0.95 Ba0. 05TiO3 (BNT–NT0. 05) thin films have been deposited on Pt/TiO2/SiO2/Si substrates by an optimized sol–gel/spin-coating process. The film thermal treated at 700° C is dense and well crystallized in the ...
Quantification of lipophilic vitamins in clinical or biological samples is very important from th... more Quantification of lipophilic vitamins in clinical or biological samples is very important from the medical, epidemiological and informational points of view. Adequate dietary intake of nutrients such as vitamin A (retinol) and vitamin E (tocopherol) is essential for normal ...
Applied Surface Science, 2011
The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural an... more The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance.
Applied Physics Letters, 2010
Pt-ZnO-Pb͑Zr 0.2 Ti 0.8 ͒O 3 -Pt ͑PZT-ZnO͒ heterostructures were fabricated by using a sol-gel pr... more Pt-ZnO-Pb͑Zr 0.2 Ti 0.8 ͒O 3 -Pt ͑PZT-ZnO͒ heterostructures were fabricated by using a sol-gel process. Capacitance-voltage measurements performed on a wide temperature range ͑20-450 K͒ 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 ͑MFS͒ 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.
Evaluation of serum osteocalcin in elderly patients with type-2 diabetes mellitus
…, 2009
Osteocalcin, the second most abundant protein in bone tissue after collagen, is secreted by osteo... more Osteocalcin, the second most abundant protein in bone tissue after collagen, is secreted by osteoblasts and thought to participate in mineralization and calcium ion homeostasis. In addition to its use as biomarker in ostoporosis, experimental studies on mice published in Cell ...
Journal of Materials Science, 2012
Thin films with the composition [(Bi 0.5 Na 0.5 )-TiO 3 ] 0.92 -[BaTiO 3 ] 0.08 (hereafter BNT-BT... more Thin films with the composition [(Bi 0.5 Na 0.5 )-TiO 3 ] 0.92 -[BaTiO 3 ] 0.08 (hereafter BNT-BT 0.08 ) were deposited on Pt-Si by spin-coating from a stable sol precursor. The BNT-BT 0.08 film, crystallized on the Bi 0.5 Na 0.5 TiO 3 rhombohedral lattice, was obtained after annealing the film-gel at 700°C. The films have a smooth surface (Rms = 2.76 nm) and grains with ferroelectric domains. The film showed a bandgap of 3.25 eV and a refractive index of 2.20 at a wavelength of 630 nm. The dielectric characteristics of BNT-BT 0.08 thin films were measured at room temperature and 10 kHz the dielectric constant (e r ) was 243 and the loss tangent (tand) was 0.38. The remnant polarization (P r ) was 0.87 lC/cm 2 and the coercive field (E c ) was 220 kV/cm at 10 kHz and room temperature. The current density was approximately 2.7 9 10 -5 A/cm 2 at low electric fields (100 kV/cm). BNT-BT 0.08 thin films shown piezoelectric properties (d 33eff = 100 pm/V) comparable to those of PZT thin films.
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Papers by Cristina Dragoi