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In the context of KSTAR plasma research, the discovery of the fast ion regulated enhanced mode is noteworthy due to its remarkable ability to maintain ion temperatures exceeding up to 10 keV for a few tens of seconds, avoid impurity accumulation, and keep low loop voltages. This new plasma operating scenario is achieved in a diverted configuration plasma by avoiding the H-mode transitions with sufficient additional power for the transition. Keeping the density low is the primary method for the avoidance. Additionally, adjustments to other parameters (plasma shape, neutral beam injection, and toroidal magnetic field) associated with the H-mode threshold power are applied to inhibit the transition process. This paper includes an experimental analysis and discussion of these findings. [ABSTRACT FROM AUTHOR]

Direct fabrication of electroactive shape memory polymer composites (eSMPCs) into complex non-planar geometries is highly desirable to enable remotely deployable, form-functional structures. However, traditional processes such as injection molding, casting, and extrusion limit the producible geometries to planar ribbons, wires, or tubes and the design of deployment modes to flattening-out/self-folding motions. To achieve low-voltage eSMPCs with a complex geometry, we report a direct fabrication strategy of bespoked-geometry eSMPCs via a two-stage sequential cure-and-foam technique for a new type of porous eSMPC, functionalized with 3D graphene nanofoam monolith (3DC). In our method, we resolved the difficulty in shaping fragile 3DC, and thus, various complex shape transforms (curved, helical, and wavy) can be intuitively designed via direct sculpting. Our method can be compatible with kirigami techniques for the design of hierarchical and combinatorial shape-change structures. 3DC not only serves as an intrinsic heater but, during synthesis, its cell walls also act as a confinement framework for architecting porosity within 3DC-eSMPCs, which can be actuated with low-voltage (7.5 V, <2 W). The herein reported 3DC-eSMPC and its synthesis strategy represent a new method and material to fabricate low-voltage deployables of bespoked shapes, capable of low-voltage actuation. [ABSTRACT FROM AUTHOR]

We investigate the relationship between the excess volume and undercoolability of Zr-Ti and Zr-Hf alloy liquids by using electrostatic levitation. Unlike in the case of Zr-Hf alloy liquids in which sizes of the constituent atoms are matched, a remarkable increase of undercoolability and negative excess volumes are observed in Zr-Ti alloy liquids as a function of their compositional ratios. In this work, size mismatch entropies for the liquids were obtained by calculating their hard sphere diameters, number densities, and packing fractions. We also show that the size mismatch entropy, which arises from the differences in atomic sizes of the constituent elements, plays an important role in determining the stabilities of metallic liquids. [ABSTRACT FROM AUTHOR]

This work utilizes low-energy sputtering to incorporate the generated nitrogen plasma into an epitaxial 1.4 nm Co film on the surface of a ZnO(002) substrate. In this method, ultrathin Co–N amorphous films were formed. Interestingly, Co is key to the formation of Co–N films. Without the deposition of Co on the ZnO(002), nitride films cannot be formed. Observations of the surface composition of the Co–N films after the firing of a N+ ion beam onto it demonstrated that the surface concentration of Co reduced at the same rate as the reduction in the concentration of N upon successive sputtering. Theoretical calculations based on the Auger peak-to-peak amplitudes established that the composition of the amorphous Co–N thin films may be Co3N2. [ABSTRACT FROM AUTHOR]

CoFe–MgO–CoFe magnetic tunnel junctions (MTJs) were fabricated by means of ion beam sputtering of MgO as well as subsequent thin films on CoFe. We demonstrated that when a submonolayer of Mg was deposited on the CoFe layer prior to the deposition of MgO, profound improvement in the performance of the CoFe–Mg–MgO–CoFe MTJ was achieved compared to that without the Mg layer. ac impedance measurement indicated that the interfacial Mg layer resulted in fivefold increase in the magnetoresistance ratio from 0.76% for MTJs without it to 4% for that with it. Complex-capacitance (CC) spectra of MTJs showed that the contribution in the relaxation frequency by textured MgO increased. This indicated that the submonolayer Mg improved the texture of the subsequently deposited MgO. Bias-dependent complex-impedance (CI) spectra reveal that interfacial defects were also suppressed due to the submonolayer of Mg. Results obtained from x-ray reflectivity and transmission electronic microscopy were also consistent with those of CI and CC. [ABSTRACT FROM AUTHOR]

The dc magnetron co-sputtering technique was used in fabricating amorphous carbon films containing magnetic Fe[sub 3]C nanograins. A composite target of a 2-in.-diam graphite disk plus several pieces of iron rods, 2 mm in diameter and 4 mm in length, were used. The films containing pure Fe[sub 3]C grains could be obtained only in proper sputtering conditions. Films containing only grains of Fe[sub 3]C phase were subjected to postdeposition annealing at temperatures of 250 to 600 °C for 60 and 90 min, respectively. Auger electron spectroscopy was used to determine the atomic concentration and its fluctuations. The microstructure and phases of grains were determined by high-resolution transmission electron microscopy (HRTEM) and selected area diffraction patterns. Very good crystallinity appeared at T[sub a] ≥ 250 °C. From the HRTEM image, lattice spacings of 6.7 Å-corresponding to Fe[sub 3]C (001) planes—and 4.3 Å—corresponding to Fe[sub 3]C (100) planes—were observed. Higher annealing temperature and larger annealing time caused an increase of grain size. The largest grain (18 nm) was obtained at T[sub a] = 550 °C. [ABSTRACT FROM AUTHOR]

Immiscible flows that involve radial displacements of shear-thinning or shear-thickening fluids by a Newtonian fluid in a homogeneous porous medium are modeled numerically. The interfacial instabilities are tracked in time for different values of the rheological parameters, namely, the Deborah number (De) and the power-law index (n), and are characterized through the effective number of fingers and the finger area density. The results of the study reveal that the effects of these two parameters on the instability are not monotonic, and it is found that the flow is least unstable for some critical value of either De or n. The dependence of these critical values, in particular, on the mobility ratio (M) and capillary number (Ca) is analyzed. It is found that when all other parameters are fixed, the critical Deborah number (Dec) increases as the power-law index increases in shear-thinning fluids or decreases in shear-thickening ones. Similarly, the critical power-law index (nc) increases with increasing (decreasing) Deborah number in shear-thinning (shear-thickening) flows. Furthermore, both critical parameters are found to vary monotonically with the mobility ratio, with the dependence most noticeable at small values of M. Their variation with the capillary number is however nonmonotonic reaching an extremum at an intermediate value of Ca. An examination of the rate of shear strain at the interface reveals that it consistently shows the smoothest variation and the smallest average value at the critical parameter. [ABSTRACT FROM AUTHOR]

Provides information on a study that investigated the light-emission characteristics of a white-light-emitting electroluminescent device with a doubly doped ZnS:Pr,Ce,F phosphor layer. Details on the specimen preparation; Results and discussion; Conclusion.

Presents a study which obtained x-ray diffraction patterns of zinc sulfide:manganese (ZnS:Mn) powder and thin film to investigate the formation of the cubic and the hexagonal phases of the host material as a function of Mn concentration. Experimental procedures; Analysis and discussion; Conclusions.

Presents a study that observed the decrease of the number of effective emission centers Mn&sup2+; in the aged ZnS:Mn electroluminescence devices. Experimental procedure; Experimental results; Conclusion.

Presents a study which investigated the fluorescence emission and excitation spectra of white-light emitting strontium sulphur: praseodymium, fluoride thin film electroluminescent devices. Experimental methods; Results and discussion; Analysis of the hyperfine structure of an isolated manganese&sup2+; ion.

Presents a study that investigated the silicon implantation efficiency, the silicon depth profile and the vacancy formation for silicon-implanted gallium arsenide crystals. Background on the implantation of impurity atoms in semiconductor materials; Discussion on the incident angle dependence of the implantation depth of the silicon ions and the vacancies of gallium and arsenic.

Presents a study which investigated the defect levels in silicon ion-implanted gallium arsenide semiconductors with a thermally stimulated current (TSC) technique. Sample preparation and experimental details; Information on TSC; Results and discussion.

Focuses on a study which examined the reactive ion etching of aluminum oxide in carbon hydrogen fluoride[sub3] and sulphur fluoride[sub6] generated by electron cyclotron resonance in conjunction with in situ ellipsometric measurement for thickness variation. Information on reactive ion etching; Chemical sputtering of aluminum oxide; Measurement of threshold ion energy.

Rather strong third- and fifth-order four-wave mixing (FWM) signals from a 500 μm thick undoped GaAs anda 350 μm thick undoped InP in detuning ranges of 80–170 meV below the band gap are observed. The spectrally resolved (SR) FWM signals for both samples far below the band gap are blue-shifted significantly with respect to the spectrum of the excitation laser pulse for negative time delays, whereas they are red-shifted for positive time delays. The temporal and spectral shapes of the FWM signals for both samples far below the band gap are nearly consistent with those of the excitation laser pulse but are remarkably different from the excitonic properties. The shifts of SR-FWM signals far below the band gap are interpreted as due to the instantaneously created virtual states by the temporal overlap of the excitation laser pulses. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the surface structure and other properties of porous silicon using atomic force microscopy. Methodology; Analysis of the photoluminescence of the samples; Examination of the Raman scattering of the samples.

The dichotomy of photoinduced quasiparticle dynamics in the anisotropic high Tc superconductors (YBa2Cu3O7) is revealed by using the orientation-resolved femtosecond reflection spectroscopy in the specially designed thin films. The transient reflectivity ΔR/R along the ab diagonal and b axis are totally different in the slow relaxation process which relates to the opening of the superconducting gap. In addition, the distribution of the temperature evolution of ΔR/R on the CuO2 planes of YBa2Cu3O7 may indicate the d-wave symmetry of the superconducting gap in high Tc superconductors. [ABSTRACT FROM AUTHOR]

By applying a critical bias field instead of conventional surface treatments, the electron emission properties of screen-printed nanotubes were investigated through scanning electron microscopy and emission current-voltage characteristics. After the surface treatment, at the bias field of 2.5 V/μm, the electron emission current density with good uniform emission sites reached the value of 2.13 mA/cm2, which was 400 times higher than that of the untreated sample, and the turn-on voltage decreased markedly from 700 to 460 V. In addition, the enhancement of the alignment of carbon nanotubes to the vertical direction was observed, resulting in an increase in the field-enhancement factor. [ABSTRACT FROM AUTHOR]

Magnetron dc cosputtering of a composite target of graphite disk plus iron rods was used in manufacturing carbon films with Fe[SUB3]C nanograin inclusions. Both temperature- and field-dependent magnetizations, M(T) and M(H), were measured for samples of various carbon concentrations (from 37% to 85%). M(T) were measured in both conditions of zero-field cooling and a field cooling at H = 100 Oe. Experimental results of χ(T), obtained from M(T), of zero-field cooling, were theoretically fitted by using Wolhfarth's model of noninteracting particles with log-normal distribution function of particle size. [ABSTRACT FROM AUTHOR]

We report the growth of high quality topological insulator Bi2Se3 thin films on a single layer, transitional metal dichalcogenide MoS2 film via van der Waals epitaxy in a planar geometry. In stark contrast to the reported growth of using 3-D crystalline substrates such as Al2O3(0001), Bi2Se3 thin films grown on a 2-D template made of single layer MoS2 showed excellent crystallinity starting immediately from the growth of the first quintuple layer. Excellent crystallinity of Bi2Se3 thin films is attained, with the increased size of the triangular shaped Bi2Se3 domains and 2–3 times enhancement in mobility, along with the observation of Shubnikov–de Haas oscillations in the magnetoresistance. Our approach of adopting a van der Waals type template may be extended to the thin film growth of other low dimensional layered materials. [ABSTRACT FROM AUTHOR]

Studies the anisotropic and giant magnetoresistance (GMR) in cobalt and copper epitaxial multilayers. Difference between GMR and anisotropic MR; Details on the experiment; Discussion on the results of the study.

Provides information on a study that used the mechanical resonance frequency method in measuring Young's moduli for thin films and substrate. Experimental procedure; Results and discussion on the study; Conclusion.

Provides information on a study which investigated the magnetic relaxation phenomenon by using the pulse method for an alloy with nanoscale grain structure. Relationship between the microstructure and the magnitude of magnetic aftereffect in the nanocrystalline state; Change in the jumping field defined by the magnetic field; Features of Fe based nanocrystalline materials.

Investigates a gallium arsenide delta-doped tunneling diode. Potential applications of GaAs delta-doped structure with both two-dimensional electron concentration and electron mobility enhancement; Details on the experiment; Discussion on the results of the experiment.

Presents a study which investigated the superconducting and magnetic properties of radical barium[sub2]copper[sub3]oxygen[sub7-x] compounds using direct current electrical resistivity and alternating current magnetic susceptibility techniques. Sample preparation; X-ray diffraction properties of the compounds; Conclusions.

Instead of detecting electrical signals for diagnosing cardiac abnormalities, a promising alternative is to detect the magnetic signals generated from cardiac electrical currents. The system utilizing 64 low-transition-temperature superconducting quantum interference devices was tested to detect the time-dependent magnetocardiac signals that are spatially distributed over the heart. To achieve efficient acquisition and analysis, we propose a method to detect two-dimensionally, the T wave propagation of electromagnetic signals of beating hearts. In addition to characterizing the propagating behaviors, the differences between normal hearts and those with coronary artery disease were investigated. [ABSTRACT FROM AUTHOR]

In this work, the authors used a superconducting quantum interference device (SQUID) magnetocardiography (MCG) system consisted of 64-channel low-transition-temperature SQUID gradiometers to detect the MCG signals of hepercholesterolemic rabbits. In addition, the MCG signals were recorded before and after the injection of magnetic nanoparticles into the rabbits’ ear veins to investigate the effects of magnetic nanoparticles on the MCG signals. These MCG data were compared to those of normal rabbits to reveal the feasibility for early detection of the electromagnetic changes induced by hypercholesterolemia using MCG with the assistance of magnetic nanoparticle injection. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL), photoluminescence, and transmission electron microscopy have been used to study the light-emitting and structural properties of (1&1bar;02) sapphire implanted with 30-key Si ions and subsequently annealed at temperatures up to 1100°C. This procedure creates oriented Si crystallites with diameters in the range 4-5 nm together with extended defects parallel to the (0001) planes of (1&1bar;02) Al2O3. Several CL hands found in Si--implanted Al2O3(Al2O3:Si-) before and/or after annealing are compared with those from O- and Al--implanted samples. These and related experiments, including annealing temperature and implant dose dependence, suggest that a yellow CL band (2.16 eV/574 nm) from annealed Al2O3:Si- is nanocrystal related, while others are defect related. [ABSTRACT FROM AUTHOR]

Highly efficient extraction of photoluminescence is observed from two-dimensional photonic crystal slabs employing InGaAs quantum dots as active material. The introduction of quantum dots reduces diffusion of carriers and thereby suppresses the surface recombination at the air-hole sidewalls of the photonic crystal. Around the normalized frequency of 0.7, over thirty-fold enhancement of the photoluminescence extraction is achieved at 78 K, indicating strong coupling to leaky modes of the free-standing photonic crystal slab. In addition, when the photoluminescence spectra overlaps with a photonic band gap, enhanced light extraction originating from the photonic band gap is observed experimentally. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nonlinear refractive index changes in 299 Å multiple quantum well GaAs were obtained directly by measuring Fabry–Perot transmission peak shifts. These changes crosscheck those obtained by Kramers–Kronig transformations of the nonlinear absorption under identical pumping conditions. High intensities saturate the exciton, so that nonlinear refractive index changes are dominated by nonresonant contributions. Thermal refractive index changes were also measured directly. [ABSTRACT FROM AUTHOR]

The effectiveness of surface recombination in speeding up the relaxation of a GaAs étalon is reported. Various thickness (1.5, 0.5, 0.3, 0.13 μm) bulk GaAs windowless samples were fabricated and tested as optical logic gates. Times for complete recovery of transmission lie between 400 and 30 ps. The response shows a roughly linear increase in speed as the sample thickness decreases, consistent with surface recombination being the dominant relaxation mechanism. A very fast cycle time of 70 ps is demonstrated using a 0.3-μm-thick windowless GaAs étalon as an all-optical logic device. Proton-bombarded samples show slower recovery and poorer contrast, and they require more gating energy. [ABSTRACT FROM AUTHOR]

We report the first parallel operation of GaAs optical logic elements and bistable devices. Arrays up to 2×4 in size were operated using a picosecond pump and probe technique, while in the bistable mode we achieved uniform response in two spots. Crosstalk due to carrier diffusion became noticeable at separations of typically ∼20–30 μm in the bistable devices. Pulsed operation at 82 MHz allowed separations down to ∼10 μm limited only by diffraction. Efficient heat sinking in the pulsed array resulted in negligible heating even when continually operated for many minutes. All experiments were performed at room temperature. [ABSTRACT FROM AUTHOR]