Giant Piezoelectricity on Si for Hyperactive MEMS Baek, S. H.; Park, J.; Kim, D. M. ...
Science (American Association for the Advancement of Science),
11/2011, Letnik:
334, Številka:
6058
Journal Article
Recenzirano
Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been ...constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(MG 1/3 Nb 2/3 )O₃-PbTiO₃ (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO₃ template layer with superior piezoelectric coefficients (e 31,f = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.
Non-volatile memory devices are so named because they retain information when power is interrupted; thus they are important computer components. In this context, there has been considerable recent ...interest in developing non-volatile memories that use ferroelectric thin films-'ferroelectric random access memories', or FRAMs-in which information is stored in the polarization state of the ferroelectric material. To realize a practical FRAM, the thin films should satisfy the following criteria: compatibility with existing dynamic random access memory technologies, large remnant polarization (Pr) and reliable polarization-cycling characteristics. Early work focused on lead zirconate titanate (PZT) but, when films of this material were grown on metal electrodes, they generally suffered from a reduction of Pr ('fatigue') with polarity switching. Strontium bismuth tantalate (SBT) and related oxides have been proposed to overcome the fatigue problem, but such materials have other shortcomings, such as a high deposition temperature. Here we show that lanthanum-substituted bismuth titanate thin films provide a promising alternative for FRAM applications. The films are fatigue-free on metal electrodes, they can be deposited at temperatures of ∼650 °C and their values of Pr are larger than those of the SBT films.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. ...This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We investigated the emission properties of Eu ion-doped ABaPO4 (ABaPO4:Eu, A = Li, Na, and K) in which the valence state of the Eu ions was controlled by annealing in various ambients, gamma-ray ...(γ-ray) irradiation, and hydrogen ion (H+) implantation. We synthesized the ABaPO4:Eu samples by solid-state reaction in air. The as-synthesized samples showed sharp red emission near 600 nm, which originated from Eu3+ ions. Interestingly, annealing under H2 ambient changed the valence state of the Eu ions from 3+ to 2+, which was indicated by the disappearance of the red emission and concurrent emergence of strong blue emission. After subsequent annealing in O2 atmosphere, the red emission of Eu3+ was recovered. The reversible switching between the 2+ and 3+ states was found to be repeatable by alternating H2 and O2 annealing. The valence state was also changed from 3+ to 2+ by H+ implantation and γ-ray irradiation of the as-synthesized samples, possibly owing to the formation of oxygen vacancies. Our results suggest that the luminescence color of the ABaPO4:Eu phosphors can be controlled within a range from red to blue by simple annealing in various ambients.
•Both Eu2+ and Eu3+ luminescences were investigated in ABaPO4 (A = Li, Na, and K).•The valence states of Eu ions changed reversibly through the H2- and O2-ambient post-annealing.•The valence states of Eu ions could be changed by gamma-ray irradiation and H+-implantation.•The color of Eu ion doped ABaPO4 phosphors can be tuned easily in a range from red to blue by post-treatments.
This is an executive summary of the 2019 update of the 2004 guidelines and levels of care for PICU. Since previous guidelines, there has been a tremendous transformation of Pediatric Critical Care ...Medicine with advancements in pediatric cardiovascular medicine, transplant, neurology, trauma, and oncology as well as improvements of care in general PICUs. This has led to the evolution of resources and training in the provision of care through the PICU. Outcome and quality research related to admission, transfer, and discharge criteria as well as literature regarding PICU levels of care to include volume, staffing, and structure were reviewed and included in this statement as appropriate. Consequently, the purposes of this significant update are to address the transformation of the field and codify a revised set of guidelines that will enable hospitals, institutions, and individuals in developing the appropriate PICU for their community needs. The target audiences of the practice statement and guidance are broad and include critical care professionals; pediatricians; pediatric subspecialists; pediatric surgeons; pediatric surgical subspecialists; pediatric imaging physicians; and other members of the patient care team such as nurses, therapists, dieticians, pharmacists, social workers, care coordinators, and hospital administrators who make daily administrative and clinical decisions in all PICU levels of care.
We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase TiO2 thin film, using the magnetic circular dichroism (MCD) at the Co L(2,3) absorption edges. The ...magnetic moment was observed to be approximately 0.1 micro(B)/Co in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at approximately 400 degrees C, the MCD signal increases, and the moment reaches up to approximately 1.55 micro(B)/Co, which is approximately 90% of the moment in Co metal. In the latter case, the cluster size was observed to be 20-60 nm.
At present, the incidence of acute myocardial infarction is increasing year by year, and it has become one of the diseases with the highest mortality rate in humans. Myocardial ischemia-reperfusion ...injury (MIRI) is a major problem in the treatment of myocardial infarction, but clinically there is no effective way to treat MIRI. This study used Cystatin C (Cys C) to treat cardiomyocytes and rats to investigate the effect of Cys C on MIRI.
We used H2O2 to induce rat cardiomyocytes (H9c2 cells) injury and stimulated the cells with Cys C. Cell counting kit 8 (CCK8) assay was used to determine the optimal concentration of H2O2 and Cys C to stimulate H9c2 cells. We determined the effects of Cys C on oxidative stress and apoptosis levels in H9c2 cells by measuring the activity of dehydrogenase (LDH), superoxide dismutase (SOD) and malondialdehyde (MDA), and the expression of apoptosis-related molecules (caspase3/8/9, Bax and Bcl-2). Changes in the activity of the NF-κB signaling pathway in H9c2 cells were also detected. In addition, we made rat MIRI models by ligating the coronary arteries and used Cys C to treat rats to verify the effect of Cys C on MIRI.
According to the results of the CCK8 assay, 1000 μM of H2O2 and 15 μM of Cys C were used to stimulate H9c2 cells. Cys C alleviated H2O2-induced H9c2 cell injury, manifested as a decrease in LDH and MDA activity and an increase in SOD activity. Cys C also reduced the apoptosis level in H9c2 cells. The activity of NF-κB signaling pathway in injured H9c2 cells was increased, and stimulation of Cys C could inhibit the NF-κB signaling pathway in H9c2 cells. The application of Cys C in MIRI rats also verified its therapeutic effect on MIRI.
Cys C reduced the oxidative stress and apoptosis levels of cardiomyocytes by inhibiting the activity of NF-κB signaling pathway in cardiomyocytes, thereby reducing cardiomyocyte injury and treating MIRI.
We report a significant enhancement of the upper critical field Hc2 of different MgB2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities ...rho, we show a clear trend of an increase in Hc2 as rho increases. One particular high resistivity film had a zero-temperature Hc2(0) well above the Hc2 values of competing non-cuprate superconductors such as Nb3Sn and Nb-Ti. Our high-field transport measurements give record values T and T for high resistivity films and T for untextured bulk polycrystals. The highest Hc2 film also exhibits a significant upward curvature of Hc2(T) and a temperature dependence of the anisotropy parameter opposite to that of single crystals: gamma(T) decreases as the temperature decreases, from to . This remarkable Hc2 enhancement and its anomalous temperature dependence are a consequence of the two-gap superconductivity in MgB2, which offers special opportunities for further Hc2 increases by tuning of the impurity scattering by selective alloying on Mg and B sites. Our experimental results can be explained by a theory of two-gap superconductivity in the dirty limit. The very high values of Hc2(T) observed suggest that MgB2 can be made into a versatile, competitive high-field superconductor.
The trapping currents and the macroscopic polarization–depolarization currents were observed together for a series of on-off switching of O2 plasma-treated and UV-treated poly-4-vinylphenol (PVP) ...dielectrics mixed with methylated poly (melamine-co-formaldehyde) (MMF).
Initially, both O2 plasma and UV created trap states on the PVP surface; however, prolonged O2 plasma or UV promoted cross-linking of the PVP (MMF 40wt.%) dielectric, and reduced the macroscopic polarization. Filtering of PVP solutions was also helpful in reducing the polarization.
The slowly decreasing currents were ascribed to the trapping and buildup of charged-traps at the interface of PVP and the electrode, and this impedes the injection of further charges from the contacts.
The macroscopic depolarization was found to be reduced with increased cross-linking. It is suggested that the macroscopic polarization–depolarization currents may possibly be related to free ions from the remnant hydroxyl groups inside the leakage channels.
•O2 plasma and UV treatment of poly-4-vinylphenol dielectric induces trapping currents.•Buildup of charged-traps at the interface impedes injection of further charges.•Macroscopic polarization can be reduced by filtering, O2 plasma, and UV treatments.•Macroscopic polarization may be related to free ions inside the leakage channels.
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