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The laser ablation and subsequent shock generation in solid targets plays an important role in a variety of research topics from equation of state models for materials to inertial confinement fusion. One of the long-standing issues is the knowledge of ablation depth in the picosecond time regime. We report on a direct technique for determining the ablation depth in aluminum using x-ray diffraction data from Linac Coherent Light Source at the Stanford Linear Accelerator Center. This technique gives a direct measurement of the shock wave propagation in the bulk target, enabling an ability to discern early timescale physics from late timescale effects not available in postmortem analysis. We find that the ablation depths only vary by 0.2 μm across three orders of magnitude of laser intensity, while the pressure increased by a factor of 10 following a square root dependence on laser pulse energy. We further observe that the ablation depth in this intensity range ( 10 11 – 1 0 13 W / cm 2 in intensity , corresponding to 0.8 – 80 J / cm 2 in fluence) cannot be modeled by a universal scaling law, given the complexity of the mechanisms governing laser ablation in this intensity regime. [ABSTRACT FROM AUTHOR]

Shock–bubble interactions (SBIs) are important across a wide range of physical systems. In inertial confinement fusion, interactions between laser-driven shocks and micro-voids in both ablators and foam targets generate instabilities that are a major obstacle in achieving ignition. Experiments imaging the collapse of such voids at high energy densities (HED) are constrained by spatial and temporal resolution, making simulations a vital tool in understanding these systems. In this study, we benchmark several radiation and thermal transport models in the xRAGE hydrodynamic code against experimental images of a collapsing mesoscale void during the passage of a 300 GPa shock. We also quantitatively examine the role of transport physics in the evolution of the SBI. This allows us to understand the dynamics of the interaction at timescales shorter than experimental imaging framerates. We find that all radiation models examined reproduce empirical shock velocities within experimental error. Radiation transport is found to reduce shock pressures by providing an additional energy pathway in the ablation region, but this effect is small (∼1% of total shock pressure). Employing a flux-limited Spitzer model for heat conduction, we find that flux limiters between 0.03 and 0.10 produce agreement with experimental velocities, suggesting that the system is well-within the Spitzer regime. Higher heat conduction is found to lower temperatures in the ablated plasma and to prevent secondary shocks at the ablation front, resulting in weaker primary shocks. Finally, we confirm that the SBI-driven instabilities observed in the HED regime are baroclinically driven, as in the low energy case. [ABSTRACT FROM AUTHOR]

The kinetic theory for the microinstabilities of a cylindrical plasma, produced by the cylindrical azimuthally symmetric (azimuthal mode number m 0 = 0) helicon wave, based on the Vlasov–Poisson system of equations, is developed. The derived linear integral equation for the Fourier–Bessel transform of the electrostatic potential is the basic equation for the investigations of the parametric and the current-driven instabilities of the radially inhomogeneous cylindrical plasma in the radially inhomogeneous helicon wave. The short-wavelength solution of this equation for the electrostatic potential is derived in the form of the functional equation, which includes an infinite number of its satellites at a frequency separation equal to the helicon wave frequency. The analytical solution is derived for the high-frequency kinetic ion-acoustic instability of the cylindrical helicon plasma, driven by the coupled effect of the electron diamagnetic drift and of the steady azimuthal rotation of electrons relative to the ions with a radially inhomogeneous angular velocity. [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 theory of the nonmodal ion-acoustic instability in the skin layer of the inductively coupled plasma is developed. This instability has a time-dependent growth rate and is driven by the current formed in the skin layer by the accelerated motion of electrons relative to ions under the action of the ponderomotive force. We found that the development of the ion-acoustic turbulence (IAT) in the skin layer and the scattering of electrons by IAT are primary channels of the nonlinear absorption of the RF energy in the skin layer. [ABSTRACT FROM AUTHOR]

Microtransfer printing is a versatile process for retrieving, transferring, and placing nanomembranes of various materials on a diverse set of substrates. The process relies on the ability to preferentially propagate a crack along specific interfaces at different stages in the process. Here, we report a mechanics-based model that examines the factors that determine which interface a crack will propagate along in microtransfer printing with a soft elastomer stamp. The model is described and validated through comparison to experimental measurements. The effects of various factors, including interface toughness, stamp geometry, flaw sizes at the interfaces, and nanomembrane thickness, on the effectiveness of transfer printing are investigated using a fracture-mechanics framework and finite element modeling. The modeling results agree with experimental measurements in which the effects of interface toughness and nanomembranes thickness on the transfer printing yield were examined. The models presented can be used to guide the design of transfer printing processes. [ABSTRACT FROM AUTHOR]

This research proposes a novel intravascular helical magnetic millirobot (IHMM) that can conduct various functional motions such as helical navigating, unclogging, object delivery, and object collecting motions, simply actuated by a precession rotating magnetic field (PRMF). The proposed IHMM is composed of a helical body with a tapered drilling tip attached to the front head. Since it is composed of two identical halves of a cone hinged to two separate pin joints, the drilling tip can also act as a magnetically actuated gripper to deliver objects to a target area or collect debris after unclogging motions. This research established a simplified equation to maneuver the IHMM's different mechanical motions in a straightforward manner. Then, it conducted various experiments demonstrating various functional motions of the IHMM to show the validity of the proposed mechanism. [ABSTRACT FROM AUTHOR]

In pump–probe experiments with an X-ray Free Electron Laser (XFEL) and a high-power optical laser, spatial overlap of the two beams must be ensured to probe a pumped area with the x-ray beam. A beam monitoring diagnostic is particularly important in short-pulse laser experiments where a tightly focused beam is required to achieve a relativistic laser intensity for generation of energetic particles. Here, we report the demonstration of on-shot beam pointing measurements of an XFEL and a terawatt class femtosecond laser using 2D monochromatic Kα imaging at the Matter in Extreme Conditions end-station of the Linac Coherent Light Source. A thin solid titanium foil was irradiated by a 25-TW laser for fast electron isochoric heating, while a 7.0 keV XFEL beam was used to probe the laser-heated region. Using a spherical crystal imager (SCI), the beam overlap was examined by measuring 4.51 keV Kα x rays produced by laser-accelerated fast electrons and the x-ray beam. Measurements were made for XFEL-only at various focus lens positions, laser-only, and two-beam shots. Successful beam overlapping was observed on ∼58% of all two-beam shots for 10 μm thick samples. It is found that large spatial offsets of laser-induced Kα spots are attributed to imprecise target positioning rather than shot-to-shot laser pointing variations. By applying the Kα measurements to x-ray Thomson scattering measurements, we found an optimum x-ray beam spot size that maximizes scattering signals. Monochromatic x-ray imaging with the SCI could be used as an on-shot beam pointing monitor for XFEL-laser or multiple short-pulse laser experiments. [ABSTRACT FROM AUTHOR]

Compared with the traditional sinusoidal voltage source, a short rising nanosecond voltage source can generate a high electron current for a short rising time. This paper investigates how the nanopulse parameters such as the voltage amplitude, pulse duration, and repetition frequency affect the radical generation and the plasma bullet propagation in an atmospheric pressure helium plasma jet. An intensified charge-coupled device was used to observe the bullet propagation in the nanosecond gate mode. The plasma bullet's propagation speed is mainly affected by the applied voltage and externally biased electrodes rather than the pulse duration or the driving frequency. In contrast, optical emission spectroscopy diagnostics estimate that the radical density inside the atmospheric pressure plasma jet mainly increases with the repetition frequency. At the same time, the population of high-energy electrons can be controlled with the unipolar voltage amplitude. Thus, unipolar nanosecond pulses make it possible to control the emitting charges and the generated radicals independently. [ABSTRACT FROM AUTHOR]

The drift-Alfvén instabilities of the sheared flow along the magnetic field of a finite beta (1>β≫me/mi) plasma with comparable inhomogeneous ion temperature and homogeneous electron temperature are examined by the numerical analysis of the derived linear dispersion equation. Accounting for the electromagnetic ion kinetic response, which has been neglected in conventional discussions of the drift-Alfvén instabilities of a steady plasma, a new kinetic drift-Alfvén instability has been found. It develops in a plasma shear flow due to the coupled action of the ion temperature gradient, the flow velocity shear, and the inverse ion Landau damping. [ABSTRACT FROM AUTHOR]

The stability theory of the inductively coupled plasma (ICP) is developed for the case when the electron quiver velocity in RF wave is of the order of or is larger than the electron thermal velocity. The theory predicts the existence of the instabilities of the ICP which are driven by the current formed in the skin layer by the accelerated motion of electrons relative to ions under the action of the ponderomotive force. [ABSTRACT FROM AUTHOR]

Different magnetic navigation systems (MNSs) have been investigated for the wireless manipulation of biomedical magnetic robots. Here we propose a novel MNS simply composed of a triad of electromagnetic coils (TEC) that can effectively manipulate a magnetic robot in two-dimensional (2D) environments. We derived a constraint equation of the TEC's input currents in order to manipulate the magnetic robot's 2D aligning and propelling motions in a controlled manner. We also examined the TEC's ability to manipulate those motions by simulating the TEC's magnetic field and the corresponding magnetic force in terms of several newly defined dimensionless variables. We then constructed the proposed TEC and demonstrated several controlled 2D motions of a magnetic robot to show the validity of the proposed system and the robot manipulation method. [ABSTRACT FROM AUTHOR]

The article examines material liquid structure when compressed to 84(19) gigapascals (GPa). It reports on the radial distribution function and liquid structure function of tin that undergoes shock compression using femtosecond x-ray diffraction to study liquid diffuse scattering signals.It comments that the structural evolution of the liquid tin under increasing pressure mimicked the evolution of the solid phase and evolved into a simple liquid structure with a coordination number around 12.

The authors report on the growth mechanism of ZnO homoepitaxy at the low-temperature range of 500 °C, which is unavailable to obtain high-quality ZnO films in heteroepitaxy. One typical set of ZnO films were grown on (0001) ZnO substrates by molecular-beam epitaxy: a standard structure without buffer and two buffered structures with high-temperature (HT) homobuffer and low-temperature (LT) homobuffer. As a result, the LT homobuffered structure had the outstanding material properties: the surface roughness is 0.9 nm, the full width at half maximum of x-ray rocking curve is 13 arcsec, and the emission linewidth of donor-bound excitons is 2.4 meV. In terms of the theoretical interpretation of the experimentally obtained electron mobilities, it was found that the LT homobuffered structure suffers less from the dislocation scattering and the ionized-impurity scattering compared to the HT homobuffered structure. It is proposed that, in the ZnO low-temperature homoepitaxy, the LT homobuffer plays a key role in inducing the complete termination of dislocations in the homointerface and suppressing the outdiffusion of contaminants and point defects on the ZnO surface, which results in the formation of smooth wetting layer on the homointerface. [ABSTRACT FROM AUTHOR]

We report on the crystallinity, N incorporation efficiency, optical properties, and electrical properties of N and Te codoped ZnO films grown by plasma-assisted molecular-beam epitaxy. Te improves the surface morphology and roughness of ZnO films in terms of both streak reflection high energy electron diffraction pattern and atomic force microscopy observations. Also, N and Te codoping is helpful to improve the crystallinity and N incorporation efficiency simultaneously. We found that; (a) narrower x-ray linewidth and higher N concentration were obtained by codoping. (b) Nitrogen related emission lines including donor-acceptor pair and acceptor-bound exciton dominantly emerged in photoluminescence spectra. (c) Codoping enhanced the carrier compensation of native donors in ZnO films and suppressed the dislocation scattering. As a consequence, we concluded that N and Te codoping is very effective for the growth of reliable p-type ZnO films which fulfill the controversial requirements; high N concentration and high crystallinity, simultaneously. [ABSTRACT FROM AUTHOR]

The interfacial reaction of hafnium-silicate [(HfO2)x(SiO2)1-x, x=0.5,0.7] thin films grown on Ge(001) by atomic layer deposition was investigated using x-ray photoelectron spectroscopy and medium energy ion scattering spectroscopy. According to the peak changes in Hf 4f and Ge 3d, the Hf-silicate film reacted with the oxidized Ge surface forming Hf-germanate at the interface. The formation of Hf-germanate induced band bending of the Ge substrate at the interface and decreased band gap to 5.1 eV, which was lower than that of GeO2 (5.6 eV). In particular, the interfacial reaction was dependent on the amount of SiO2 in the Hf-silicate film, which resulted in more decrement in the band gap in the film with a high SiO2 fraction. [ABSTRACT FROM AUTHOR]

A homogeneous crystalline Sm2Ti2O7 (ST) phase was formed in films grown at temperatures ranging between 100 and 200 °C and subsequently annealed at 900 °C. The ST film had a large dielectric constant of 58, which is similar to that of ST ceramics. The leakage current density of the ST film was low and the Poole-Frenkel emission was suggested as being the leakage current mechanism. The ST film had a negative quadratic voltage coefficient of capacitance (VCC), possibly due to the dipolar relaxation. The 100-nm-thick ST film had a high capacitance density of 5.2 fF/μm2 with a low leakage current density of 1.34 nA/cm2 at 2 V. Its quadratic and linear VCCs were -99.5 ppm/V2 and 11 ppm/V, respectively, with a low temperature coefficient of capacitance of 135 ppm/°C at 100 kHz. These results confirmed the potential for the ST film to be used as a high performance metal-insulator-metal capacitor. [ABSTRACT FROM AUTHOR]

We report the emission properties of various InGaN/GaN quantum wells. The photoluminescence of In[sub x]Ga[sub 1-x]N/GaN (x > 20%) quantum wells under varying external bias voltages has been investigated. A redshift of the photoluminescence peak position and decrease of photoluminescence peak intensity with an increase in voltage were observed regardless of the direction of external bias applied. For the sample in which the quantum dot-like region is abundant in quantum well layers, the peak position and intensity were not influenced much by the externally applied bias voltage. The results show that the origin of strong emission from InGaN/GaN quantum wells can be attributed to exciton localization in the quantum dot-like region and they are consistent with those of high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Plasma-induced damage of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) has been studied in terms of forward turn-on and reverse breakdown voltages, together with etch rate and surface morphology. The physical degradation of sidewall along with rough surface morphology of n-GaN caused by increased ion scattering induced the deterioration of the forward and reverse voltages. The forward turn-on voltage was relatively independent of the pressure up to 20 mTorr. The reverse breakdown voltage showed the worst degradation at 75% Cl[sub 2] mainly because of a sidewall contamination. It was found that the turn-on voltage is sensitive to the surface roughness of the etched n-GaN and the breakdown voltage is strongly affected by the sidewall contamination. Annealing under nitrogen after the mesa etching improved the electrical properties of the InGaN/GaN MQW LEDs. [ABSTRACT FROM AUTHOR]

Mg-doped p-type GaN epilayers grown by metalorganic chemical vapor deposition exhibit two different types of photoluminescence (PL) characteristics depending on Mg doping rate; the existence of critical Mg concentration is found where both electrical and optical characteristics show an abrupt change in their behavior. In samples with relatively low Mg concentration, a band edge emission, a peak associated with shallow donor-acceptor pair recombination, and a 2.8 eV blue band emission appear in the PL spectrum. Intensities of all three PL peaks decrease with increasing annealing temperature; the blue band quenches most rapidly. In contrast, in samples grown with high ratio of Mg/Ga flow rate, only a strong blue emission band is observed and the intensity of the blue band increases with the annealing temperature suggesting a different origin from the blue band of lightly doped samples. From the annealing temperature dependence of the blue band intensity, we speculate that the emission mechanism of the blue band in relatively lightly Mg-doped GaN epilayers involves Mg-related deep level complexes such as substitutional/interstitial Mg-related complexes. On the other hand, a model involving a formation of pyramidal defects and the presence of Mg-rich inclusions which modifies the dominant optical transition can be a possible explanation for the origin of the blue band in heavily doped ones. [ABSTRACT FROM AUTHOR]

Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells were investigated by using photoluminescence, transmission electron microscopy, optical microscopy, and high resolution x-ray diffraction. The In[sub x]Ga[sub 1-x]N/GaN (x>0.2) quantum wells used in this study were grown on c-plane sapphire by using metalorganic chemical vapor deposition. The interruption was carried out by closing the group-III metalorganic sources before and after the growths of the InGaN quantum well layers. The transmission electron microscopy images show that with increasing interruption time, the quantum-dot-like regions and well thickness decreased due to indium reevaporation or the thermal etching effect. As a result the photoluminescence peak position was blueshifted and the intensity was reduced. Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. The sizes and the number of V defects did not differ with the interruption time. The interruption time is not directly related to the formation of defects. The V defect originates at threading dislocations and inversion domain boundaries due to higher misfit strain. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Deep-level defect-related optical properties of undoped n-type GaN grown by metalorganic chemical vapor deposition are investigated using photoluminescence (PL), optical absorption (OA), photoconductivity (PC), and persistent photoconductivity (PPC) measurements. From the temperature dependence of the PL and OA, we find that the yellow luminescence (YL) is due to shallow-to-deep donor recombination. PL, PC, and PPC results manifest a strong correlation in properties related to deep levels. Samples which emit YL exhibit a PC peak at 1.9 eV due to the photoionization of deep levels as well as to the persistent photoconductivity effect, whereas samples with no YL have no PC peak in the forbidden gap and no PPC at any photon energy, suggesting a common origin. Furthermore, two types of PPC behavior were observed depending on the sample quality: typical stretched exponential decay in relatively thick samples and photocurrent quenching and a subsequent reduction of the dark current in thin samples. An explanation of the latter phenomenon based on photoinduced metastable electron traps in a highly defective layer near the interface is suggested from the temporal behavior of the PC. These traps seem to disappear slowly after the illuminating light is turned off. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The kinetic theory for the instabilities driven by the Hall current with a sheared current velocity, which has the method of the shearing modes or the so-called nonmodal approach as its foundation, is developed. The developed theory predicts that in the Hall plasma with the inhomogeneous electric field, the separate spatial Fourier mode of the perturbations is determined in the frame convected with one of the plasma components. Because of the different shearing of the ion and electron flows in the Hall plasma, this mode is perceived by the second component as the Doppler-shifted continuously sheared mode with time-dependent wave numbers. Due to this effect, the interaction of the plasma components forms the nonmodal time-dependent process, which should be investigated as the initial value problem. The developed approach is applied to the solutions of the linear initial value problems for the hydrodynamic modified two-stream instability and the kinetic ion-sound instability of the plasma with a sheared Hall current with a uniform velocity shear. These solutions reveal that the uniform part of the current velocity is responsible for the modal evolution of the instability, whereas the current velocity shear is the source of the development of the nonmodal instability with exponent growing with time as ∼ (t − t 0) 3 . [ABSTRACT FROM AUTHOR]

The electromagnetic (EM) ion cyclotron (IC) instability of a plasma with parallel sheared current is investigated analytically with numerical solutions. This instability is the electromagnetic counterpart of the electrostatic current-driven ion cyclotron instability, which is renowned as the Drummond-Rosenbluth (DR) instability. Considered is the case with the current velocity shearing rate less than the ion cyclotron frequency, which corresponds to the tokamak and space plasmas. We found two new EM DR instabilities: the modified EM DR instability by the current shear and the subcritical EM DR instability which develops above the upper and below the lower critical velocities of the EM DR instability driven by the uniform current, respectively. The modified EM DR instability by the current shear develops due to the inverse electron Landau damping, whereas the subcritical EM DR instability develops due to the coupled effect of the IC damping and the current shear jointly with the inverse electron Landau damping. We also found the shear-flow-driven EM IC instability of the current-free sheared flow which develops by virtue of the coupled action of the IC damping and flow velocity shear. [ABSTRACT FROM AUTHOR]

X-ray free electron laser (XFEL) sources have revolutionized our capability to study ultrafast material behavior. Using an XFEL, we revisit the structural dynamics of shock compressed bismuth, resolving the transition sequence on shock release in unprecedented details. Unlike previous studies that found the phase-transition sequence on shock release to largely adhere to the equilibrium phase diagram (i.e., Bi-V → Bi-III → Bi-II → Bi-I), our results clearly reveal previously unseen, non-equilibrium behavior at these conditions. On pressure release from the Bi-V phase at 5 GPa, the Bi-III phase is not formed but rather a new metastable form of Bi. This new phase transforms into the Bi-II phase which in turn transforms into a phase of Bi which is not observed on compression. We determine this phase to be isostructural with β-Sn and recover it to ambient pressure where it exists for 20 ns before transforming back to the Bi-I phase. The structural relationship between the tetragonal β-Sn phase and the Bi-II phase (from which it forms) is discussed. Our results show the effect that rapid compression rates can have on the phase selection in a transforming material and show great promise for recovering high-pressure polymorphs with novel material properties in the future. [ABSTRACT FROM AUTHOR]

We present measurements of the plasmon shift in shock-compressed matter as a function of momentum transfer beyond the Fermi wavevector using an X-ray Free Electron Laser. We eliminate the elastically scattered signal retaining only the inelastic plasmon signal. Our plasmon dispersion agrees with both the random phase approximation (RPA) and static Local Field Corrections (sLFC) for an electron gas at both zero and finite temperature. Further, we find the inclusion of electron-ion collisions through the Born-Mermin Approximation (BMA) to have no effect. Whilst we cannot distinguish between RPA and sLFC within our error bars, our data suggest that dynamic effects should be included for LFC and provide a route forward for higher resolution future measurements. [ABSTRACT FROM AUTHOR]

Presents a study which measured the electrical conductivity and Hall coefficient of the n-indium antimonide as functions of temperature. Discussion on the scattering mechanisms involved in the study; Details of the impurity phenomena; Results related to band gaps.

Focuses on a study that investigated the conversion acceptor and its contribution to hole scattering in annealed gallium arsenide. Details of the experiment; Analysis; Results and discussion.

Examines the temperature induced blue shift of the intersubband absorption peak in GaAs/Al0.3Ga0.7As multiple quantum wells. Calculation as a function of well thickness; Domination of the blue shift by the barrier height; Importance of exchange interactions for well thickness; Reduction of the photocurrent spectrum.

Provides information on the photoluminescence of aluminum-gallium-arsenic heterostructures in the presence of high magnetic fields. Effect of magnetic fields on the interficial roughness; Residual impurities in ultra-pure materials; Distribution of the substitutional carbon impurities in discrete atomic layers near the interface.

Examines the substrate temperature effects on the preparation of yttrium-barium-copper oxide superconducting films on strontium-titanium oxide. Use of laser ablation in depositing superconducting thin films in a substrate; Experimental details; Result of the study.

The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p→3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d3) and that Ni ions are formally divalent (3d8). Mn and Ni 2p→3d RPES shows that the occupied Mn 3d3 (t2g3↑) states are sharp and located around 2 eV below EF, while the occupied Ni 3d8 (t2g3↑t2g3↓eg2↑) states are broader than the Mn 3d states and they extend from EF to ∼5 eV below EF. [ABSTRACT FROM AUTHOR]

Electronic structures of FeCr2X4 (X=S and Se) have been investigated by employing soft-x-ray absorption spectroscopy and soft-x-ray magnetic circular dichroism (XMCD). It is found that FeCr2S4 and FeCr2Se4 have similar electronic structures. The valence states of Cr and Fe ions are nearly trivalent (Cr3+) and divalent (Fe2+), respectively. The Fe 3d states are strongly hybridized to the X p states. The Fe and Cr 2p XMCD study provides evidence for the antiparallel alignment between Cr and Fe spins and the strong hybridization between the Fe 3d and X p electrons. [ABSTRACT FROM AUTHOR]

The electronic structures of SrMn1-xFexO3 (0≤x≤1) have been investigated by using photoemission spectroscopy (PES) and soft x-ray absorption spectroscopy (XAS). Mn ions in SrMnO3 are found to be in the nearly tetravalent (Mn4+) states, but with a small mixture of the Mn2+ configuration. With increasing x in SrMn1-xFexO3, Mn ions remain in the 4+ states. Fe ions in SrMn1-xFexO3 are also in the nearly tetravalent (Fe4+) states for the whole range of x. Valence-band PES reveals that the occupied Mn t2g3 states are located about 2.5 eV below EF, while the occupied Fe t2g3eg1 states are broader than the Mn 3d occupied states, and are located between 3 and 6 eV below EF. The large overlap between Fe 3d and the O 2p states is found in SrFeO3, reflecting the strong hybridization between the Fe 3d states and the O 2p states, in agreement with the metallic nature of SrFeO3. [ABSTRACT FROM AUTHOR]

Temperature-dependent magnetization M(T), resistivity ρ(T), and specific heat Cp(T) were measured for single crystalline YbB4. M(T) showed a large anisotropy, that is M∥(T)>M⊥(T), for fields parallel and perpendicular, respectively, to the c axis. While M∥(T) followed Curie-Weiss behavior with slight crystalline electric field splittings, M⊥(T) showed a typical temperature dependence of intermediate valence (IV) fluctuation, which implies that YbB4 is a rare compound with two-dimensional IV fluctuation. ρ(T) followed ρ0+AT2 below Tcoh≈5 K, indicating a low-temperature Fermi liquid state of YbB4. In addition, anomalies were also found at ≈Tcoh in M(T), ρ(T), and Cp(T). [ABSTRACT FROM AUTHOR]

The electronic structures of SrMn1-xFexO3 (0≤x≤1) have been investigated by using photoemission spectroscopy (PES) and soft x-ray absorption spectroscopy (XAS). Mn ions in SrMnO3 are found to be in the nearly tetravalent (Mn4+) states, but with a small mixture of the Mn2+ configuration. With increasing x in SrMn1-xFexO3, Mn ions remain in the 4+ states. Fe ions in SrMn1-xFexO3 are also in the nearly tetravalent (Fe4+) states for the whole range of x. Valence-band PES reveals that the occupied Mn t2g3 states are located about 2.5 eV below EF, while the occupied Fe t2g3eg1 states are broader than the Mn 3d occupied states, and are located between 3 and 6 eV below EF. The large overlap between Fe 3d and the O 2p states is found in SrFeO3, reflecting the strong hybridization between the Fe 3d states and the O 2p states, in agreement with the metallic nature of SrFeO3. [ABSTRACT FROM AUTHOR]

The influence of multi-line pulsed excitation of target isotopes within the method of selective laser assisted retarded condensation (SILARC) on the efficiency of boron isotopes separation is investigated. In pulsed mode simultaneous excitation of all four isotopologues 11 B 35 C l n 37 C l 3 − n is possible. In order to study it, a new formula for multi-line excitation rate is derived. The total number of photons absorbed by target isotopologues for proposed physical parametrization of the laser pulse is compared with continuous wave excitation case, corresponding to the minimal level of laser intensity, required to excite all four isotopologues. It is found that irradiation efficiency of the pulsed mode is 20.59 times smaller than for CW-mode one. Influence of multi-pass cavity on the efficiency of excitation has been also considered. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate simultaneous phase-contrast imaging (PCI) and X-ray diffraction from shock compressed matter at the Matter in Extreme Conditions endstation, at the Linac Coherent Light Source (LCLS). We utilize the chromaticity from compound refractive X-ray lenses to focus the 24.6 keV 3rd order undulator harmonic of the LCLS to a spot size of 5 μm on target to perform X-ray diffraction. Simultaneous PCI from the 8.2 keV fundamental X-ray beam is used to visualize and measure the transient properties of the shock wave over a 500 μm field of view. Furthermore, we demonstrate the ability to extend the reciprocal space measurements by 5 Å−1, relative to the fundamental X-ray energy, by utilizing X-ray diffraction from the 3rd harmonic of the LCLS. [ABSTRACT FROM AUTHOR]

Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606–611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa. [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]

Refractive-index dispersion for the TlInGaAs quaternary alloys, grown on (100) InP substrates by gas-source molecular-beam epitaxy, has been measured at temperatures from 290 to 350 K in the photon-energy range of 1.2–2.0 eV by using spectroscopic ellipsometry. The temperature coefficient of the refractive-index decreases with increasing Tl composition. The result corresponds to the already reported reduced temperature dependence of the band-gap energy for the TlInGaAs because of the alloy of semiconductor InGaAs and semimetal TlAs. The result also agrees with the recently reported small temperature-variation of the lasing-wavelength for the TlInGaAs/InP laser diodes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this study, the effects of CoCrPtTa and CoCrPtB magnetic intermediate layers (ILs) on the magnetic properties and read/write performance of CoCrPt/soft magnetic layer perpendicular recording media were investigated. Even though the perpendicular coercivity of the media with these ILs was reduced by 500 Oe, these media still showed a low exchange slope of 1.4 and a large negative nucleation field of about -1000 Oe. Additionally, the reduced grain size of the media with these IL was observed by transmission electron microscopy. From the read/write test, these media with ILs showed improved performance of 3-5 dB higher signal-to-noise ratio and overwrite ratio (OW) compared to the media without ILs. These enhancements could be attributed to the reduction of grain size of the magnetic layer and weakening of the intergranular interaction between grains by insertion of the IL. [ABSTRACT FROM AUTHOR]

In this work, magnetic properties and thermal stability of antiferromagnetically coupled AFC medium with a CrMo spacer layer instead of the conventional Ru spacer layer were studied. It was found that a reduction of M[SUBr]/M[SUBs] could also be obtained in the AFC medium with a CrMo spacer layer due to the antiferromagnetic coupling, similar to the conventional AFC medium with a Ru spacer layer. Thermal stability ratio, K[SUBU]V/k[SUBB]T for the proposed medium was slightly smaller than that of the conventional AFC medium with a Ru spacer layer, but larger than that of a single magnetic layer medium. By a comparison of the switching field distribution and ΔM of the AFC medium with those of the conventional AFC medium, it is conjectured that the intergranular exchange coupling decreases when a CrMo is used as a spacer layer. [ABSTRACT FROM AUTHOR]

This paper presents results of finite element analysis of induction heating problems considering temperature dependence of material characteristics. In this analysis, we have used the three dimensional finite element method in order to correctly express the induction heating coil's shapes and to make clear its effects on temperature distributions. The heat conducting problem and the eddy current problem are coupled and solved by using step-by-step calculations. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) in PbWO[sub 4] single crystals doped with Pr[sup 3+], Sm[sup 3+], and Er[sup 3+] ion, which were grown by the Czochralski method, was studied. By investigating the PL for incident radiation with wavelength of 325 nm (He-Cd Laser), the energy levels of the PL centers were found: The PL levels in the Pr doped single crystal are [sup 3]P[sub 0] and [sup 1]D[sub 2], that in the Sm-doped one is [sup 4]G[sub 5/2], and those in the Er doped one are [sup 2]H[sub 11/2], [sup 4]S[sub 3/2], and [sup 4]F[sub 9/2]. In conclusion, the characteristics of these single crystals are governed solely by those of the rare-earth dopants, not by the lead tungstate. [ABSTRACT FROM AUTHOR]

We study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibility of the method. We present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system. [ABSTRACT FROM AUTHOR]