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Magnetotransport Irreversibility in Single Crystalline La0.18Pr0.40Ca0.42MnO3 Thin Films
No full textMagnetotransport irreversibility in single crystalline La0.18Pr0.40Ca0.42MnO3 thin films is probed with respect to intrinsic electronic phase separation (IEPS). Temperature-dependent magnetization and resistivity measurements show that (i) the high temperature non-hysteretic regime is dominated by the antiferromagnetic insulator (AFMI) and the charge ordered (CO) phases; (ii) at intermediate temperatures hysteretic regime is akin to a spin liquid; and (iii) the glass transition occurs at temperature T-g below which the spin liquid freezes. The suppression of the ferromagnetic and insulator-metal transitions (T-C and T-IM) during cooling confirms supercooled magnetic liquid. Magnetic field-dependent resistivity (rho-H) measured during cooling and warming highlights the differences in the spin-ordered structures through (i) reversible behavior at T T-IM (warming). The present study demonstrates that the scaling of area between the isothermal cooling and warming cycle rho-H curves with temperature mimics the rho-T behavior and hence also reflects the insulator-metal transition. The observed irreversibility and the area scaling in the different spin regimes have been explained in terms of the intrinsic electronic phase separation
Magnetocaloric effect and piezoresponse of engineered ferroelectric-ferromagnetic heterostructures
No full textThis study reports the magnetocaloric effect (MCE) and piezoresponse of integrated ferroelectric-ferromagnetic heterostructures of PbZr0.52Ti0.48O3 (PZT) (5 nm)/Bi-Sr-Ca-Cu-2-O-x (BSCCO) (5 nm)/La0.67Sr0.33MnO3 (LSMO) (40 nm)/MgO (0 01). Magnetic and pizoresponse behavior of the heterostructures are found to be governed by magneto-electric coupling and induced lattice strains. In addition, a maximum MCE is studied using Maxwell equations from both Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization data. Maximum MCE entropy change (vertical bar Delta s vertical bar) of 42.6 mJkg(-1)K(-1) (at 258 K) and 41.7 mJkg(-1)K(-1) (at 269 K) are found corresponding to FC and ZFC data, respectively. The variation in maximum entropy change and corresponding temperatures for FC and ZFC data revealed that the application of a magnetic field can significantly contribute towards tuning of the MCE. Interestingly, these multilayered structures are found to sustain MCE over a broad temperature range, which makes them attractive for improved solid-state energy conversion devices
Mesoporous strontium ferrite/polythiophene composite: Influence of enwrappment on structural, thermal, and electromagnetic interference shielding
No full textStrontium ferrite (SrFe12O19) and Strontium ferrite enwrapped polythiophene (SrF/PT) composites have been synthesized via sol-gel and in-situ emulsion polymerization techniques for the first time. The structural, morphological, magnetic, dielectric, and electromagnetic interference (EMI) shielding performances of these composites have been investigated. The composite possessing SrF:PT = 2:1 (SrF/PT-21) composition showed maximum shielding effectiveness (SE) of -31.64 dB at 15.73 GHz for 1 mm thick sample in the Ku-band (12.4-18 GHz) region, which is found to be higher than all composites and pristine SrFe12O19. This behavior is mainly attributed to the high dielectric and magnetic losses occurred within the material. The enwrapping of mesoporous SrFe12O19 nanoparticles by conducting PT further eased the electron transportation within the composite network that offered the greater impedance match for electromagnetic wave. Therefore, the composite may act as a promising microwave absorber with a lightweight, high thermal stability, and excellent SE ability for a broad frequency range
Measurement of Benzo(a)pyrene in PM10 Collected in New Delhi
Get PDFPolyaromatic hydrocarbons (PAH) are the compound which consists of multiple benzene rings bonded in straight, groups or angular forms. They are also found in atmospheric aerosols. In the atmosphere, they can be emitted primarily as a result of incomplete combustion of natural sources (fossil fuels, forest fires, smoke etc.) or anthropogenic sources (coal burning, vehicular emissions, smoke, etc.) or secondarily by atmospheric processes. Depending on the anthropogenic sources, PAHs may occur in significant concentration in urban and industrial ambient air, i.e., bounded with particulate matter (PM). A particle whose aerodynamic diameter is <= 10 mu m is called PM10. Benzo(a)pyrene (BaP) is among the most toxic and carcinogenic PAHs. Both PM10 and BaP are among the 12 criteria pollutants listed in Indian National Ambient Air Quality Standards (NAAQS). In this paper, BaP concentration in PM10 collected in a representative site of New Delhi was studied during the year 2014-2015. The average concentration of BaP is varied from 0.04 to 25.7 ng m(-3). The uncertainty components in measurements were also estimated along with statistical analysis. The most significant uncertainty component is the purity of the BaP standard which has the highest uncertainty contribution as 77%
Barium ferrite nanoparticles: a highly effective EMI shielding material
No full textElectromagnetic interference (EMI) is one of the main causes for the failure of electronic devices working in close vicinity of EM field induced by the neighboring electronic device. Therefore, we report a facile synthesis of barium ferrite (BaFe12O19) nanoparticles via sol-gel technique for efficient EMI shielding application. These nanoparticles were annealed at 400 degrees C, 700 degrees C, and 850 degrees C to investigate the effect of temperature on shielding efficiency and morphology of BaFe12O19 nanoparticles. The structure, morphology, phase purity, magnetism, and shielding effectiveness were analyzed using Fourier-transform infrared (FT-IR) spectroscopy, x-ray diffraction (XRD), electron microscopy (SEM and TEM), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. These studies suggest that BaFe12O19 nanoparticles annealed at 850 degrees C exhibit crystalline pure phase hexagonal structure with the high magnetic moment (31.32 emu g(-1)) and coercivity (2.7 kOe). The total shielding effectiveness of the same was found to be -17.57 dB at 11.58 GHz, which is much higher than those of earlier reported studies
Biophysical Characterization and Drug Delivery Potential of Exosomes from Human Wharton's Jelly-Derived Mesenchymal Stem Cells
No full textCell-derived exosomes (30-200 nm) as biological "nanocarriers" have attracted a great deal of interest for therapeutic applications due to their ability to internalize in in vivo biological systems (i.e., cells). Although they can be harvested from various sources including stem cells, yet an appropriate isolation and characterization protocol to obtain "pure" exosomal population is needed. For potential clinical applications, understanding the functional ability of exosomes and their purity, that is, free from microvesicles, apoptotic bodies, and protein aggregates, is a pre-requisite. To achieve high purity and yield of exosomes from human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs) in the size range of 30-200 nm, we have performed and compared three isolation procedures: ultracentrifugation (UC), sucrose cushion (SC), and commercially available reagent (CR). The isolated exosomes were characterized using nanoparticle tracking analysis (NTA), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). Furthermore, to understand the therapeutic potential of the hWJ-MSC-derived exosomes (hWJ-ME) to target pancreatic tumor cells, the internalization efficacy has been evaluated on the MiaPaCa-2 cell lines using confocal microscopy and flow cytometry. The NTA results showed sucrose cushion to be an optimal method for exosome isolation with high purity (86.8%), as compared to UC (40.5%; p = 0.050) and CR (38%; p = 0.050). Optical analysis by FESEM and AFM revealed that SC-isolated exosomes presented a spherical morphology, whereas UC- and CR-isolated exosomes exhibited an uneven morphology. Furthermore, the data from confocal images and flow cytometry showed that hWJ-ME were internalized by MiaPaCa-2, demonstrating the feasibility of exosomes as a "potential nanocarrier". Thus, our study suggests that a combination of NTA (yield), AFM (dimensions), and FESEM (morphology and topography) could provide sensitive biophysical characterization of hWJ-ME. In the future, enriched exosomes could be used as a delivery vehicle to transport target-specific drugs or gene-silencing constructs to tumors
Controlled inter-state switching between quantized conductance states in resistive devices for multilevel memory
Get PDFA detailed understanding of quantization conductance (QC), the correlation with resistive switching phenomena and controlled manipulation of quantized states is crucial for realizing atomic-scale multilevel memory elements. Here, we demonstrate highly stable and reproducible quantized conductance states (QC-states) in Al/niobium oxide/Pt resistive switching devices. Three levels of control over the QC-states, required for multilevel quantized state memories, like, switching ON to different quantized states, switching OFF from quantized states, and controlled inter-state switching among one QC state to another has been demonstrated by imposing limiting conditions of stop-voltage and current compliance. The well-defined multiple QC states along with a working principle for switching among various states show promise for implementation of multilevel memory devices
Correlation of donor-acceptor pair emission on the performance of GaN-based UV photodetector
No full textHigh responsivity UV photodetector has been realized by fabricating single crystalline epitaxial GaN-based devices grown on silicon substrate by using molecular beam epitaxy system. The influence of trap states existing within the forbidden gap on GaN-based optoelectronic devices has been investigated. The quality and performance of the fabricated GaN based UV photodetector with distinct AlN buffer layer grown at low and high substrate temperature are substantiated. A detailed analysis reveals that high temperature buffer can yield improved crystalline quality of GaN with similar morphological properties as compared to buffer layer grown at low temperature. However, the distinct buffer layer influence the optical properties as the photoluminescence analysis explains that both the films possess superior band-to-band edge emission where GaN grown with high temperature AlN buffer consists of dominant acceptor defect states in comparison to GaN with low temperature AlN buffer layer. The existence of acceptor states has been accredited by the presence of Ga vacancy related states in the band gap. The fabricated devices yield high photoresponsivity of 2.1 and 1.5 A/W at 1 V from GaN films bearing low and high accepter defect states which explain a clear correlation of device performance with trap states within the band-gap region
Electrical properties of Strontium Barium Niobate (Sr0.6Ba0.4Nb2O6) thin films deposited by pulsed laser deposition technique
No full textGrowth of Sr0.6Ba0.4Nb2O6 (SBN60) thin films on Pt-Si substrate has been carried out using Pulsed Laser Deposition (PLD) technique by varying the oxygen pressure from 1.33 x 10(-3) mbar to 26.67 x 10(-3) mbar and at a fixed substrate temperature of 800 degrees C. The crystalline behavior of as-deposited films was studied using X-ray diffraction technique indicating the preferential growth along c-axis. The Metal-Ferroelectric-Metal (MFM) structure was used to measure the current-voltage (I-V) and dielectric properties of as-prepared SBN thin film. A large value of dielectric constant of about 503 at 1 MHz was obtained for SBN60 thin film with good ferroelectric polarization-hysteresis loop (P-r = 5.32 mu C/cm(2) and P-max = 9.86 mu C/cm(2). A high value of total stored energy density 4.60 J/cm(2) with an efficiency of 17% efficiently contributes towards its potential application in non-volatile memory devices
Electron transport and ultrafast spectroscopic studies of new methanofullerenes bearing a heteroatom in the exohedral chain
No full textFullerene derivatives (C60 and C70) have been widely used in excitonic solar cells due to their exceptional electron accepting properties and low reorganization energies. In recent years, a wide variety of fullerene-based n-type materials have been developed, showing tremendous potential in the field of organic photovoltaics. However, only a few studies have been performed on heteroatom bearing methanofullerenes and their opto-electronic properties for use as n-type organic semiconductor materials. In the present study, we report the synthesis of two mono-substituted methanofullerene derivatives, i.e., C60-Th (Product 1) and C60-TPA (Product 2), with a heteroatom (S and N, respectively) in the exohedral chain attached via an ethylene linker to the cyclopropane ring, and a comprehensive study of their photophysical and electrochemical properties. The methanofullerene derivatives have been synthesized using an amine-assisted cycloaddition (AACA) reaction method. The structures of the synthesized products were established via different spectroscopic techniques. Reasonable quenching efficiencies were observed with respect to the fluorescence emission in mixtures with the donor polymer P3HT using both methanofullerenes. The electron transport properties were evaluated through fabricating electron-only devices, and 10 and 6 times higher mobilities were found compared to PC61BM for Products 1 and 2, respectively. Finally, the charge transfer properties were evaluated in mixtures with P3HT via transient absorption spectroscopy to study the ultrafast charge separation and formation of long-lived charge-separated states. The study suggests that both the products show excellent electron transport properties and the formation of longer-lived charge-separated states in mixtures with the donor polymer for use as n-type materials for organic solar cells