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  • 1
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    Far-forward collective scattering measurements by FIR polarimeter-interferometer on J-TEXT tokamak (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-08-04
    Description: The multi-channel three-wave polarimeter-interferometer system on J-TEXT tokamak has been exploited to measure far-forward collective scattering from electron density fluctuations. The diagnostic utilizes far infrared lasers operated at 432 μ m with 17-channel vertical chords (3 cm chord spacing), covering the entire cross section of plasma. Scattering laser power is measured using a high-sensitivity Schottky planar diode mixer which can also detect polarimetric and interferometric phase simultaneously. The system provides a line-integrated measurement of density fluctuations with maximum measurable wave number: k ⊥ max ≤ 2 cm −1 and time response up to 350 kHz. Feasibility of the diagnostic has been tested, showing higher sensitivity to detect fluctuation than interferometric measurement. Capability of providing spatial-resolved information of fluctuation has also been demonstrated in preliminary experimental applications.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Electric field control of magnetization in Cu2O/porous anodic alumina hybrid structures at room temperature (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-04-06
    Description: Cu 2 O nanoporous films are deposited on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. This paper focuses on voltage driven magnetization switching in Cu 2 O/PAA (CP) composite films prepared by DC-reactive magnetron sputtering. By applying a dc electric field, the magnetization of the CP composite films can be controlled in a reversible and reproducible way and shows an analogous on-off behavior. The magnitude of the change in the magnetization was about 75 emu/cm 3 as the electric field was switched on and off. Resistive switching behavior was also observed in as-prepared CP composite films. Further analysis indicated that the formation/rupture of conducting filaments composed of oxygen vacancies is likely responsible for the changes in the magnetization as well as in the resistivity. Such reversible change of magnetization controlled by an electric field at room temperature may have applications in spintronics and power efficient data storage technologies.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 3
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    Ultralow-frequency Raman system down to 10 cm−1 with longpass edge filters and its application to the interface coupling in t(2+2)LGs (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-05-28
    Description: Ultralow-frequency (ULF) Raman spectroscopy becomes increasingly important in the area of two-dimensional (2D) layered materials; however, such measurement usually requires expensive and nonstandard equipment. Here, the measurement of ULF Raman signal down to 10 cm −1 has been realized with high throughput by combining a kind of longpass edge filters with a single monochromator, which are verified by the Raman spectrum of L-cystine using three laser excitations. Fine adjustment of the angle of incident laser beam from normal of the longpass edge filters and selection of polarization geometry are demonstrated how to probe ULF Raman signal with high signal-to-noise. Davydov splitting of the shear mode in twisted (2+2) layer graphenes (t(2+2)LG) has been observed by such system in both exfoliated and transferred samples. We provide a direct evidence of twist-angle dependent softening of the shear coupling in t(2+2)LG, while the layer-breathing coupling at twisted interfaces is found to be almost identical to that in bulk graphite. This suggests that the exfoliation and transferring techniques are enough good to make a good 2D heterostructures to demonstrate potential device application. This Raman system will be potentially applied to the research field of ULF Raman spectroscopy.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 4
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    Influence of coherent optical phonon on ultrafast energy relaxation (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-08-14
    Description: Ultrafast energy relaxation process in Bi 2 Te 3 thin films is studied using a collinear two color pump-probe technique. The coherent optical phonon is enhanced and destroyed by changing the separation times of double pump pulses. The non-oscillatory component of the reflectivity trace after the second pump pulse shows a distinct difference with and without the presence of coherent optical phonons, thus providing a direct evidence of the effect of optical phonon on the hot carrier relaxation process. The deduced characteristic times are systematically smaller when coherent optical phonons are involved in the energy transfer process. Comparatively, the conventional relaxation process is relatively slow, which is explained by the screening effect of the incoherent optical phonon. This work suggests that the energy relaxation can be manipulated through the excitation of coherent optical phonons.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 5
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    Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI4 (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-10-28
    Description: The pressure-induced amorphization and subsequent recrystallization of SnI 4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119 Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI 4 under ambient conditions. Although high pressure structures of SnI 4 were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 6
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    Effects of solution volume on hydrogen production by pulsed spark discharge in ethanol solution (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-15
    Description: Hydrogen production from ethanol solution (ethanol/water) by pulsed spark discharge was optimized by varying the volume of ethanol solution (liquid volume). Hydrogen yield was initially increased and then decreased with the increase in solution volume, which achieved 1.5 l/min with a solution volume of 500 ml. The characteristics of pulsed spark discharge were studied in this work; the results showed that the intensity of peak current, the rate of current rise, and energy efficiency of hydrogen production can be changed by varying the volume of ethanol solution. Meanwhile, the mechanism analysis of hydrogen production was accomplished by monitoring the process of hydrogen production and the state of free radicals. The analysis showed that decreasing the retention time of gas production and properly increasing the volume of ethanol solution can enhance the hydrogen yield. Through this research, a high-yield and large-scale method of hydrogen production can be achieved, which is more suitable for industrial application.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Giant exchange bias in Mn2FeGa with hexagonal structure (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-23
    Description: In this study, we present the experimental observation that polycrystalline Mn 2+x Fe 1−x Ga (x = −0.2, 0, 0.2, 0.4) compounds can be synthesized to be D0 19 -type (Ni 3 Sn-type) hexagonal structure with space group P63/mmc. A giant exchange bias field up to 1.32 kOe was achieved in hexagonal Mn 2 FeGa alloy at 5 K. A cluster glass state is confirmed by ac susceptibility measurement under different driving frequencies. Interestingly, robust horizontal and vertical shifts in magnetic hysteresis loop were simultaneously observed at 5 K under high cooling field up to 90 kOe. The large exchange bias is originated from the large exchange anisotropy between cluster glass phase and ferrimagnetic matrix. The vertical shift is thought to be attributed to the incomplete reversal of frozen cluster spins.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 8
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    Effects of interlayer screening and temperature on dielectric functions of graphene by first-principles (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-07-22
    Description: The dielectric functions of few-layer graphene and the related temperature dependence are investigated from the atomic scale using first-principles calculations. Compared with ellipsometry experiments in the spectral range of 190–2500 nm, the normalized optical constants of mono-layer graphene demonstrate good agreement and further validate first-principles calculations. To interpret dielectric function of mono-layer graphene, the electronic band structure and density of states are analyzed. By comparing dielectric functions of mono-, bi-, and tri-layer graphene, it shows that interlayer screening strengthens intraband transition and greatly enhances the absorption peak located around 1 eV. The strengthened optical absorption is intrinsically caused by the increasing electron states near the Fermi level. To investigate temperature effect, the first-principles calculations and lattice dynamics are combined. The lattice vibration enhances parallel optical absorption peak around 1 eV and induces redshift. Moreover, it is observed that the van der Waals force plays a key role in keeping the interlayer distance stable during dynamics simulations.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 9
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    Effect of L12 ordering in antiferromagnetic Ir-Mn epitaxial layer on exchange bias of FePd films (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-29
    Description: Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures ( T s  = 300–700 °C), were investigated using magnetron sputtering. L 1 2 ordering was revealed for the 30 nm-thick IrMn epitaxial (001) films with T s  ≥ 400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing T s from 400 to 700 °C monotonically increases the ordering parameter of L 1 2 phases from 0.17 to 0.81. An in-plane exchange bias field ( H eb ) of 22 Oe is obtained in a 10 nm-thick FePd film that is deposited on the disordered IrMn films. As the L 1 2 ordering of the IrMn layers increases, the H eb gradually decreases to 0 Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing T s cannot be the main cause of the decrease in H eb due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A 1 to the L 1 2 phase was correlated with the evolution of H eb .
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 10
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    Bias tuning charge-releasing leading to negative differential resistance in amorphous gallium oxide/Nb:SrTiO3 heterostructure (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-12-31
    Description: Negative differential resistance (NDR) and bipolar resistive switching (RS) phenomena were observed in Au/Ga 2 O 3−x /Nb:SrTiO 3 /Au heterostructures fabricated by growing amorphous gallium oxide thin films on 0.7%Nb-doped SrTiO 3 substrates using pulsed laser deposition technique. The RS behavior is reproducible and stable without the forming process. The NDR phenomenon happened during the course of RS from low resistance state to high resistance state and was dependent much on the applied forward bias. The bias dependent charge releasing from oxygen vacancies was considered to contribute to the NDR behavior. The results show that there is a very close relationship between NDR and RS.
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    Electronic ISSN: 1077-3118
    Topics: Physics
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