Here, we report the generation of MeV alpha-particles from H-11B fusion initiated by laser-accelerated boron ions. Boron ions with maximum energy of 6 MeV and fluence of 109/MeV/sr@5 MeV were generated from 60 nm-thick self-supporting boron nanofoils irradiated by 1 J femtosecond pulses at an intensity of 1019 W/cm2. By bombarding secondary hydrogenous targets with the boron ions, 3 × 105/sr alpha-particles from H-11B fusion were registered, which is consistent with the theoretical yield calculated from the measured boron energy spectra. Our results demonstrated an alternative way toward ultrashort MeV alpha-particle sources employing compact femtosecond lasers. The ion acceleration and product measurement scheme are referential for the studies on the ion stopping power and cross section of the H-11B reaction in solid or plasma.

The Richtmyer–Meshkov instability of a helium layer surrounded by air is studied in a semi-annular convergent shock tube by high-speed schlieren photography. The gas layer is generated by an improved soap film technique such that its boundary shapes and thickness are precisely controlled. It is observed that the inner interface of the shocked light gas layer remains nearly undisturbed during the experimental time, even after the reshock, which is distinct from its counterpart in the heavy gas layer. This can be ascribed to the faster decay of the perturbation amplitude of the transmitted shock in the helium layer and Rayleigh–Taylor stabilization on the inner surface (light/heavy) during flow deceleration. The outer interface first experiences ‘accelerated’ phase inversion owing to geometric convergence, and later suffers a continuous deformation. Compared with a sole heavy/light interface, the wave influence (interface coupling) inhibits (promotes) growth of instability of the outer interface.

The evolution of an $\text{SF}_{6}$ layer surrounded by air is experimentally studied in a semi-annular convergent shock tube by high-speed schlieren photography. The gas layer with a sinusoidal outer interface and a circular inner interface is realized by the soap-film technique such that the initial condition is well controlled. Results show that the thicker the gas layer, the weaker the interface–coupling effect and the slower the evolution of the outer interface. Induced by the distorted transmitted shock and the interface coupling, the inner interface exhibits a slow perturbation growth which can be largely suppressed by reducing the layer thickness. After the reshock, the inner perturbation increases linearly at a growth rate independent of the initial layer thickness as well as of the outer perturbation amplitude and wavelength, and the growth rate can be well predicted by the model of Mikaelian (Physica D, vol. 36, 1989, pp. 343–357) with an empirical coefficient of 0.31. After the linear stage, the growth rate decreases continuously, and finally the perturbation freezes at a constant amplitude caused by the successive stagnation of spikes and bubbles. The convergent geometry constraint as well as the very weak compressibility at late stages are responsible for this instability freeze-out.

In order to suppress the failure of preserving positivity of density or pressure, a positivity-preserving limiter technique coupled with h-adaptive Runge-Kutta discontinuous Galerkin (RKDG) method is developed in this paper. Such a method is implemented to simulate flows with the large Mach number, strong shock/obstacle interactions and shock diffractions. The Cartesian grid with ghost cell immersed boundary method for arbitrarily complex geometries is also presented. This approach directly uses the cell solution polynomial of DG finite element space as the interpolation formula. The method is validated by the well documented test examples involving unsteady compressible flows through complex bodies over a large Mach numbers. The numerical results demonstrate the robustness and the versatility of the proposed approach.

Diffraction data of calcite were collected using a conventional Bragg–Brentano diffractometer, which is a convenient, low-cost, and highly popular in-house instrument, and its crystal structure was refined by the Rietveld method. This paper shows how one treats preferred orientation and how different refinement strategies affect the accuracy of the result.

Fast linear transformer driver (FLTD) has some advantages in repetitive operation compared with traditional pulsed power generators. However, different types of gas switches applied in the field of pulsed power technology in recent years cannot reach the requirements of repetitive operation of FLTD. Therefore, the capability of repetitive operation of a multigap gas switch has been investigated in a circuit similar to the basic discharge loop named as brick in this paper. The switch has been triggered more than 2000 times and the distribution of delay time and switch jitter are analyzed and reported. Also, the self-breakdown voltages of the switch during different segments of the triggered breakdown experiment have been tested. The experimental results indicate that the delay time obeys the Gauss distribution and the jitter of 2000 times of discharge is about 2.3 ns.

Asymmetric PCRAM structure with the upper contact opening at an offset to the bottom contact opening allowed us to improve the thermal distribution within the phase change layer and lower the reset current to 50% that of a conventional symmetrical structure. In terms of endurance, asymmetric cell lasted for 1.1 × 108 cycles which is at least 10X higher than the conventional symmetrical cell. These results were based on Ge2Sb2Te5 as the phase change material.

In this paper, we used nitrogen doped Ge2Sb2Te5 [1] instead and the thickness of this phase change layer was 100 nm. During the sputtering of Ge2Sb2Te5, the Argon gas flow rate was fixed at 15 sccm while nitrogen flow rates of 0, 3, 4.5 and 6 sccm were introduced each time. Thus N2/Ar gas ratio of 0, 0.2, 0.3 and 0.4 were obtained respectively. After fabrication, the cell endurance of Asymmetric PCRAM cells incorporating Ge2Sb2Te5 doped with varying concentrations of nitrogen was tested. During testing, the PCRAM was repeatedly Reset/Set and the resistances of the two states were recorded at every 100k cycles. The cell was considered to be functioning well when its Reset/Set resistance ratio was greater than 10. From experiments, N-doped asymmetric cell with N2/Ar gas ratio of 0.2 lasted 2.4 × 1010 cycles which is 1000 times that of a conventional symmetrical PCRAM cells. The N2 doping concentration was also shown to be optimized when the N2/Ar gas ratio was fixed at 0.2. Higher doping concentrations with N2/Ar gas ratio of 0.3 and 0.4 decreased the cell endurance to 8.8 × 108 and 7.6 × 108 cycles respectively. Excessive doped nitrogen atoms might have degraded the phase change material, causing breakdown to occur sooner.

N-doped conventional symmetrical PCRAM was also fabricated and its overwrite cycles were measured only up to 1.2 × 109. With better thermal confinement, asymmetric PCRAM has proved to be better in endurance too. The above results were based on asymmetric PCRAM cells with 1 µm offset.

[1] H. Horii et al, “A Novel Cell Technology Using N-doped GeSbTe Films For Phase Change RAM”, p. 177-178, VLSI Tech. 2003

Switched phase change material in Phase Change Random Access Memory (PCRAM) is confined within a solid surrounding. As a result of mechanical properties and microstructure differences between the crystalline and the amorphous phases, strains and stresses are generated and may degrade the performance of PCRAM devices. This paper investigated the crystallization-induced stress in phase change Ge2Sb2Te5 (GST) nano film. The electric-thermal and thermo-mechanical simulation results show that the increases of both of the Young's modulus and Coefficient of Thermal Expansion (CTE) are responsible for the stress generation upon crystallization. The XRD studies correlate the strains and stresses with the lattice deformation in crystalline GST films.

Three-dimensional finite element method (FEM) is used to solve the thermal strain-stress fields of phase-change random access memory (PCRAM) cells. Simulation results show that thermal stress concentrates at the interfaces between electrodes and phase change layer and it is significantly larger than that within the phase change layer. It has been found that the peak thermal stress is linearly related to the voltage of electrical pulse in the reset process but once amorphous state is produced in the cell, a nonlinear relationship between thermal stress and electrical power exists. This paper reported the change of thermal stress during set process. It was found that the stress decreases significantly due to the amorphous active region during set processes.

H2NiTi4O10/TiO2 intercalated compound was fabricated by successive intercalation reactions of H2NiTi4O10 with n-C6H13NH2/C2H5OH mixed solution and acid TiO2 sol, followed by irradiating with a high-pressure mercury lamp. H2NiTi4O10, a layered perovskite type compound with TiO2-loading, exhibited a high activity for decomposition of methyl orange under UV and visible light irradiation. The experimental results showed that methyl orange was degraded with the decomposition ratio of 59.0 % by using H2NiTi4O10/TiO2 as photocatalyst under visible light ( > 420 nm) irradiation for 24 h. The H2NiTi4O10/TiO2 possessed higher photocatalytic activity than those commercial titania powder (Degussa P-25) which showed the decomposition ratio just only 24% under same condition.

The patterned nc-Si/a-SiNx:H superlattices were fabricated by using laser interference crystallization method and investigated with atomic force microscope (AFM), micro-Raman spectroscope, cross-section transmission electron microscope (TEM) and high resolution electron microscope (HREM). We found that after laser irradiation, self-assembled Si nanocrystallites (nc-Si) are formed within the initial a-Si:H sublayers, moreover, in the plane parallel to the surface of the films, these nc-Si orderly distribute in the certain regions with the same periodicity of 2.0 µm as phase shifting mask grating. Based on the structural analyses, the crystallization mechanism and the origin of the self-assembled phenomena are briefly discussed.

Transmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurements were applied to study the correlation between the microstructure and physical properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. When the density of the threading dislocation (TD) increases about one order of magnitude, the yellow luminescence (YL) intensity is strengthened from negligible to two orders of magnitude higher than the band edge emission intensity. The full width of half maximum (FWHM) of the GaN (0002) peak of the XRD rocking curve was widened from 11 min to 15 min, and in Raman spectra, the width of E2 mode is broadened from 5 cm−1 to 7 cm−1. A “zippers” structure at the interface of GaN/sapphire was observed by high-resolution electron microscope (HREM). Furthermore the origins of TD and relationship between physical properties and microstructures combining the growth conditions are discussed.

A novel sol-gel-hydrothermal process for preparation of highly oriented thin films of Pb(Zr0.52Ti0.48)O3 is reported. Pb(Zr0.52Ti0.48)O3 thin films with fully (111) orientation were successfully prepared on platinized silicon substrates at low temperature (100–200 °C) by combining a conventional sol-gel process and hydrothermal method, i.e., sol-gel-hydrothermal technique. The x-ray rocking curve for the (111) reflection as measured by a high-resolution four-crystal diffractrometer showed a narrow full width at half-maximum value of 0.20° for the as-prepared films. A dense, pinhole-free, and uniform surface morphology was observed from atomic force microscopy images of the films. The low leakage current density of the prepared films was also found.

X-ray scattering and transmission electron microscopy (TEM) have been used to study short-range order in Al1−xlnxAs thin films grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370°C and 400°C are characterized. The first exhibits simultaneous triple-period-A and CuPt-A short-range order with a rather short correlation range of about 2.4 nm normal to the (111) planes. Within these (individual) planes the concentration, however, is uniform over a considerably greater distance – about 6 to 9 nm – leading to a highly anisotropic scattering. This observation of triple-period short-range ordering in a sample that exhibits 2×1 surface reconstruction during growth is unexpected. We also report on the first observation of the coexistence of triple-period-A and CuPt-B short-range order. The diffuse scattering exhibits significant intensity anomalies that we attribute to atomic displacements associated with the short-range order. The second sample exhibits CuPt-B short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. This sample also exhibits intensity anomalies that must be associated with atomic displacements. The first sample contains a high density of twin lamellae, while both samples contain high densities of stacking faults leading to additional narrow streaking along symmetry-allowed 〈111〉 directions. These growth faults most likely arise from the relatively low growth temperatures.

Transmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurements were applied to study the correlation between the microstructure and physical properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. When the density of the threading dislocation (TD) increases about one order of magnitude, the yellow luminescence (YL) intensity is strengthened from negligible to two orders of magnitude higher than the band edge emission intensity. The full width of half maximum (FWHM) of the GaN (0002) peak of the XRD rocking curve was widened from 11 min to 15 min, and in Raman spectra, the width of E2 mode is broadened from 5 cm-1 to 7 cm-1. A “zippers” structure at the interface of GaN/sapphire was observed by high-resolution electron microscope (HREM). Furthermore the origins of TD and relationship between physical properties and microstructures combining the growth conditions are discussed.

A new silicon material, silicon-on-defect-layer (SODL), has been measured by secondary ion mass spectrometry (SIMS) and spreading resistivity (SR) measurements. SIMS data show that the buried defect-layer in SODL consists of silicon oxide due to the gettering of intrinsic oxygen by proton-implanted damage. Furthermore, SODL procedure makes a silicon wafer contain much fewer oxygen in surface-layer on the defect-layer, resulting in a purfied surface-layer. Measurements of SR indicate that the surface-layer of n-type silicon wafer was converted to p-type silicon after SODL procedure. A metal oxide semiconductor (MOS) device with a value of the electron mobility in the inversion mode of 714 cm2/(V s) was fabricated on SODL material. Like isolation function of a well in a complementary MOS (CMOS) device, the p-n junction in SODL material could play a role of isolation between the surface-layer and bulk. In addition, by reducing the implantation energy, SODL technology for making p-n junction, in which built-in field separates light-generated electrons and holes, is a candidate to make cheap solar cells by using low-quality low-cost silicon.