1,721,044 research outputs found
The effect of bottom electrode on the ferroelectric property of RF-magnetron sputtered BaTiO3 thin films
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Microwave dielectric properties of ferroelectric BaTiO3 thin film
No full textThe dielectric properties of c-axis epitaxial BaTiO3 thin film on LaAlO3 are investigated at frequencies of 0.5-30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 gm wide and spaced 2 mum apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 mum. The capacitance of epitaxial BaTiO3 films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO3 film with a finger length of 80 mum due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/omegaCR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO3 film has a tunability [defined as k(V) = [C(0) - C(V)]C(0)] of 1.5% at 15 V, a loss tangent of less than or equal to0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO3 film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO3 capacitor, the tetragonality (c/a) of epitaxial BaTiO3 film and design of interdigital capacitor should be modified.This work was supported by grant no. R01-2000-00226 from the basic research program of the Korea Science & Engineering Foundation. It was also supported by the Brain Korea 21 project in 2003 and the Ministry of Science and Technology (M1010500066-01H2006400)
Photovoltaic effect of Sn2P2S6 ferroelectric crystal and ceramics
No full textTo investigate the photovoltaic effect in Sn2P2S6 ferroelectrics, Sn2P2S6 crystal and ceramic sample that had a high relative density of 95% and a grain size of below I [Lm were fabricated. The steady-state photovoltaic currents under infrared light illumination on both Sn2P2S6 crystal and ceramic sample were observed for the first time. The photovoltaic currents i(pw) on Sn2P2S6 ceramic sample and crystal were 5 and 25 nA/cm, respectively. The difference in the magnitude of the photovoltaic current resulted from the difference in the remanent polarization P-r between the crystal and the ceramic sample. The values of the photovoltaic field E-pv determined from I-V curve for Sn2P2S6 ceramic sample and crystal were 0.2 and 6 V/cm, respectively; these values were several orders lower than that observed on the perovskite-type ferroelectric ceramics. The photovoltaic fields observed in this study were discussed with the conductivity of the crystal and the ceramic sample, in consideration of the figure of merit for the photostriction.This work is partially supported by the Brain Korea 21 project in 2001
Pollycation gene delivery systems: escape from endosomes to cytosol
No full textClinical success of gene therapy based on oligonucleoticles (ODNs), ribozymes, RNA and DNA will be greatly dependent on the availability of effective delivery systems. Polycations have gained increasing attention as a non-viral gene delivery vector in the past decades. Significant progress has been made in understanding complex formation between polycations and nucleic acids, entry of the complex into the cells and subsequent entry into the nucleus. Sophisticated molecular architectures of cationic polymers have made the vectors more stable and less susceptible to binding by enzymes or proteins. Incorporation of specific ligands to polycations has resulted in more cell-specific uptake by receptor-mediated mechanisms. However, there are still other barriers limiting the transfection efficiency of polycation gene delivery systems. There is a consensus that polycation-DNA complexes (polyplexes) enter cells via the endocytotic pathway. It is not clearly understood, however, how the polyplexes escape (if they do) from endosomes, how DNA is released from the polyplexes or how the released DNA is expressed. The primary focus of this article is to review various polycation gene delivery systems, which are designed to translocate DNA from endosomes into cytosol. Many polycation gene delivery systems have tried to mimic the mechanisms that viruses use for the endosomal escape. Polycation gene delivery systems are usually coupled with synthetic amphipathic peptides mimicking viral fusogenic peptides, histidine-based gene delivery systems for pH-responsive endosomal escape, polycations with intrinsic endosomolytic activity by the proton sponge mechanism and polyanions to mimic the anionic amphiphilic pepticles
Diffuse dielectric anomaly in ferroelectric materials
No full textIt has not been clear whether the diffuse dielectric anomaly by Debye-type dielectric relaxation is extrinsic or intrinsic in origin although it has been frequently found in ferroelectric materials regardless of their structures and ferroelectric properties. We experimentally investigated the extrinsic nature of the diffuse dielectric anomaly in ferroelectric oxides and sulfide such as BaTiO3, Pb0.9La0.1TiO3, and SnP2S6. The advanced fitting method using the modified Debye relaxation equation was introduced in order to explain the temperature dependent behavior of the diffuse dielectric anomaly. It was confirmed that the diffuse dielectric anomaly was a competitive phenomenon between the dielectric relaxation and the electrical conduction of the relaxing species. It was also proved that the activation energy of the dielectric relaxation should be always higher than the conductivity activation energy of the relaxing species in the diffuse dielectric anomaly.This work was supported by grant no. R01-2000-00226 from the basic research program of the Korea Science & Engineering Foundation. It was also supported by the Brain Korea 21 project in 2003 and the Ministry of Science and Technology (M1010500066-01H2006400)
Self-assembled Nanoparticle of Poly(amino acid)s with alpha-helices and Targeted system for cancer therapy
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