Synthesis and characterization of multiferroic thin films

Multiferroic materials and multiferroic materials systems which simultaneously exhibit ferroelectricity and magnetism have attracted great attention because of their exotic physical properties and their potential applications which utilize coupling of magnetism and ferroelectricity. The goal of this thesis was to study multiferroic materials systems in thin film and multilayer forms in order to explore the possibility of fabricating room temperature thin film devices. In particular, we have focused on two types of multiferroic materials systems: 1) intrinsic multiferroic/magnetoelectric thin film materials and 2) magnetostrictive/ piezoelectric bilayer systems for investigation of the strain-mediated magnetoelectric (ME) effect. BiFeO3 is an intrinsic multiferroic which displays ferroelectricity and antiferromagnetism at room temperature, and thus of strong interest for ambient device applications. In this thesis, we have extensively investigated the role of microstructure on the properties of BiFeO3 thin films. We studied multiphase formation in Bi-Fe-O thin films, and found that formation of secondary phases such as α-Fe2O3, γ-Fe2O3, and Fe3O4 increased overall saturation magnetization and released the misfit strain of the BiFeO3 grains in the films. We have studied several aspects of the ME effect which are directly relevant to possible novel device applications. Electric field tunable spintronic devices using the ME effect have been proposed. In one such device configuration, the desired effect is electric field tuning of giant magnetoresistance or tunnel magnetoresistance through control of exchange bias via the ME effect. We have investigated the feasibility of such a device using exchange-biased Co/Pt multilayers on Cr2O3 thin films. The strain-mediated ME effect at the interface of magnetostrictive/ piezoelectric bilayers has been widely used to demonstrate magnetic field detection with extremely high sensitivity. Although the overall mechanism of such an effect is known, the details of the bilayer interfaces and how they affect the coupling is not understood. In order to directly observe the strain-mediated ME coupling effect, we fabricated bilayer thin film structures and performed in-situ dynamic observation of magnetic domains while an electric-field was being applied using Lorentz transmission electron microscopy. Electric-field induced motion of magnetic domain boundaries in the magnetostrictive layer was observed for the first time

Prediction of abundance of arthropods according to climate change scenario RCP 4.5 and 8.5 in South Korea

AbstractAbundance and diversity of arthropods were projected according to climate warming in South Korea. The taxa highly linked with temperature were selected for the projection. The values of abundance and richness were estimated using the mean values of abundance and richness in each temperature range. Temperature changes were based on the RCP (Representative Concentration Pathway) 4.5 and RCP 8.5, and the abundance and richness during two periods (2011 -2015, 2056 -2065) were projected. From these projected results, change of other common taxa (> 1% occurrence) were qualitatively predicted (i.e., decrease or increase). The projections showed that 45 of a total of 73 taxa will increase, 6 will change a little and 24 will decrease: the number of taxa that were expected to increase was two times more than the number of taxa that were expected to decrease. However, the overall abundance and diversity of arthropods were expected to decline as the temperature rises

Antidiabetic Effect of Fresh Nopal ( Opuntia ficus-indica

The objective of the present study was to evaluate α-glucosidase inhibitory and antidiabetic effects of Nopal water extract (NPWE) and Nopal dry power (NADP) in low-dose streptozotocin- (STZ-) induced diabetic rats fed a high-fat diet (HFD). The type 2 diabetic rat model was induced by HFD and low-dose STZ. The rats were divided into four groups as follows: (1) nondiabetic rats fed a regular diet (RD-Control); (2) low-dose STZ-induced diabetic rats fed HFD (HF-STZ-Control); (3) low-dose STZ-induced diabetic rats fed HFD and supplemented with NPWE (100 mg/kg body weight, HF-STZ-NPWE); and (4) low-dose STZ-induced diabetic rats fed HFD and supplemented with comparison medication (rosiglitazone, 10 mg/kg, body weight, HF-STZ-Rosiglitazone). In results, NPWE and NADP had IC50 values of 67.33 and 86.68 μg/mL, both of which exhibit inhibitory activities but lower than that of acarbose (38.05 μg/mL) while NPWE group significantly decreased blood glucose levels compared to control and NPDP group on glucose tolerance in the high-fat diet fed rats model (P<0.05). Also, the blood glucose levels of HR-STZ-NPWE group were significantly lower (P<0.05) than HR-STZ-Control group on low-dose STZ-induced diabetic rats fed HFD. Based on these findings, we suggested that NPWE could be considered for the prevention and/or treatment of blood glucose and a potential use as a dietary supplement

Optical Spectroscopy of Supernova Remnants in M81 and M82

We present spectroscopy of 28 SNR candidates as well as one H II region in M81, and two SNR candidates in M82. Twenty six out of the M81 candidates turn out to be genuine SNRs, and two in M82 may be shocked condensations in the galactic outflow or SNRs. The distribution of [N II]/H{\alpha} ratios of M81 SNRs is bimodal. M81 SNRs are divided into two groups in the spectral line ratio diagrams: an [O III]-strong group and an [O III]-weak group. The latter have larger sizes, and may have faster shock velocity. [N II]/H{\alpha} ratios of the SNRs show a strong correlation with [S II]/H{\alpha} ratios. They show a clear radial gradient in [N II]/H{\alpha} and [S II]/H{\alpha} ratios: dLog ([N II]/H{\alpha})/dLog R = -0.018 {\pm} 0.008 dex/kpc and dLog ([S II]/H{\alpha})/dLog R = -0.016 {\pm} 0.008 dex/kpc where R is a deprojected galactocentric distance. We estimate the nitrogen and oxygen abundance of the SNRs from the comparison with shock-ionization models. We obtain a value for the nitrogen radial gradient, dLog(N/H)/dLogR = -0.023 {\pm} 0.009 dex/kpc, and little evidence for the gradient in oxygen. This nitrogen abundance shows a few times flatter gradient than those of the planetary nebulae and H II regions. We find that five SNRs are matched with X-ray sources. Their X-ray hardness colors are consistent with thermal SNRs.Comment: 19 pages, 24 figures, 5 tables, ApJ accepte

Microfluidic Biosensor Based on Microwave Substrate-Integrated Waveguide Cavity Resonator

A microfluidic biosensor is proposed using a microwave substrate-integrated waveguide (SIW) cavity resonator. The main objectives of this noninvasive biosensor are to detect and analyze biomaterial using tiny liquid volumes (3 μL). The sensing mechanism of our proposed biosensor relies on the dielectric perturbation phenomenon of biomaterial under test, which causes a change in resonance frequency and return loss (amplitude). First, an SIW cavity is realized on a Rogers RT/Duroid 5870 substrate. Then, a microwell made from polydimethylsiloxane (PDMS) material is loaded on the SIW cavity to observe the perturbation phenomenon. The microwell is filled with phosphate-buffered saline (PBS) solution (reference biological medium). To demonstrate the sensing behavior, the fibroblast (FB) cells from the lungs of a human male subject are analyzed and one-port S-parameters are measured. The resonance frequency of the structure with FB cells is observed to be 13.48 GHz. The reproducibility and repeatability of our proposed biosensor are successfully demonstrated through full-wave simulations and measurements. The resonance frequency of the FB-loaded microwell showed a shift of 170 MHz and 20 MHz, when compared to those of empty and PBS-loaded microwells. Its analytical limit of detection is 213 cells/μL. Our proposed biosensor is noncontact and reliable. Furthermore, it is miniaturized, inexpensive, and fabricated using simple- and easy-design processes

Reliable and cost effective design of intermetallic Ni2Si nanowires and direct characterization of its mechanical properties

We report that a single crystal Ni2 Si nanowire (NW) of intermetallic compound can be reliably designed using simple three-step processes: casting a ternary Cu-Ni-Si alloy, nucleate and growth of Ni2 Si NWs as embedded in the alloy matrix via designing discontinuous precipitation (DP) of Ni2 Si nanoparticles and thermal aging, and finally chemical etching to decouple the Ni2 Si NWs from the alloy matrix. By direct application of uniaxial tensile tests to the Ni2 Si NW we characterize its mechanical properties, which were rarely reported in previous literatures. Using integrated studies of first principles density functional theory (DFT) calculations, high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX) we accurately validate the experimental measurements. Our results indicate that our simple three-step method enables to design brittle Ni2 Si NW with high tensile strength of 3.0 GPa and elastic modulus of 60.6GPa. We propose that the systematic methodology pursued in this paper significantly contributes to opening innovative processes to design various kinds of low dimensional nanomaterials leading to advancement of frontiers in nanotechnology and related industry sectors.1