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We used thermal oxidization at various temperatures to prepare NiO/Pr-Ir for use in resistance random access memory (ReRAM) samples. In-situ transmission electron microscopy (TEM) was used to investigate the forming process of these ReRAM samples, where a needle-shaped top electrode of Pt-Ir was attached to the NiO/Pt-Ir ReRAM layer. The forming voltage initializing the NiO layer increased at an oxidization temperature of between 200 and 400 °C. In this process, conductive bridges, which are thought to be conductive filaments of a ReRAM, appeared, and their sizes showed a correlation with the injection power. It was as small as about 300 nm2 when the injection power was 10-6 W. Energy dispersive X-ray spectroscopy was used to analyze the bridge, and it was experimentally confirmed that the oxygen content of the bridge was lower than that of the initial NiO layer. However, these bridges in the low resistance state did not show further ReRAM switching to the high resistance state inside of a TEM instrument. To check the reason of this result, we investigated samples outside of the TEM instrument, which had similar geometry to that of TEM specimens. They showed the ReRAM switching in air ambient but not in vacuum. Combining these results inside and outside of the TEM instrument, it can be concluded that the existence of oxygen around the conductive filament plays an important role. This supports the filament redox model on the ReRAM operation. [ABSTRACT FROM AUTHOR]

Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the 'forming process' required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30-40 nm. This finding supports the 'breakdown' type forming in the so-called 'filament model' of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated. [ABSTRACT FROM AUTHOR]

The dependences of the observed maximum proton energy on laser fluence, and the type and thickness of the target material were studied. The maximum proton energy depended on the laser fluence rather than on the laser intensity for laser pulses with energies between 40 and 430 mJ and pulse durations between 55 and 400 fs. The maximum proton energy increased as the product of target thickness and target mass density decreased. When a polyimide tape target of 7.5 μm thickness was irradiated, the observed maximum proton energy and flux, counted as the number of etched tracks with a solid angle of 0.25 sr, were 3.3±0.1 MeV and 4×106/MeV/shot, respectively. For efficient proton acceleration when a wide ion emission angle is acceptable, polyimide was suitable for the tape target because it contains much hydrogen, and furthermore, it has a low mass density and a high tensile strength. [ABSTRACT FROM AUTHOR]

Investigates the native defect related inhomogeneity in characteristics of gallium arsenide (GaAs) field-effect transistors fabricated on annealed dislocation-free substrates. Substrate characteristics affecting the uniformity in the threshold voltage of field-effect transistors; Method used to make the undoped semi-insulating GaAs crystals grow; Ionized defects that could affect the electrical properties.

We evaluate the simplified method using the Lambert-Beer law to measure the temperature of bremsstrahlung photon generated by an ultraintense laser. Analytical values are compared to the results of the Monte Carlo calculation of GEANT4 and they agreed very well on the condition of the appropriate distance between the attenuator and the detector. We performed the experiment to measure the temperature of bremsstrahlung x-ray emitted from a metal target irradiated by a Ti:sapphire laser with 76 mJ, 72 fs, 2.2 × 1018 W/cm2. For a Cu target of 30 μm thick, the photon temperature was reasonably determined to be 0.18 MeV, which is in good agreement with previous studies. [ABSTRACT FROM AUTHOR]

Long, about a half of microsecond, nonuniform corona UV burst is observed after a femtosecond-laser-filament plasma appears nearby an electrode biased (positively or negatively) slightly higher than the corona discharge threshold and well-isolated from the natural streamer discharge. A bright UV emission area moving outwards, over a 20 cm distance, with the velocity of 0.6% of the speed of light and tearing from the filament plasma in the case of the negative voltage is observed. In the case of positive voltage, a bright, bouncing UV cone is formed at around 4 cm far from the filaments exposing the appearance of a leader. Both phenomena could be explained upon supposing the formation of runaway electrons in the vicinity of the filament plasma and electrode. [ABSTRACT FROM AUTHOR]

Fast protons are observed by a newly developed online time-of-flight spectrometer, which provides shot-to-shot proton-energy distributions immediately after the irradiation of a laser pulse having an intensity of ∼1018 W/cm2 onto a 5-μm-thick copper foil. The maximum proton energy is found to increase when the intensity of a fs prepulse arriving 9 ns before the main pulse increases from 1014 to 1015 W/cm2. Interferometric measurement indicates that the preformed-plasma expansion at the front surface is smaller than 15 μm, which corresponds to the spatial resolution of the diagnostics. This sharp gradient of the plasma has the beneficial effect of increasing the absorption efficiency of the main-pulse energy, resulting in the increase in the proton energy. This is supported by the result that the x-ray intensity from the laser plasma clearly increases with the prepulse intensity. [ABSTRACT FROM AUTHOR]

The production of energetic protons using a polyimide tape of 7.5 μm thickness was carried out with laser pulses of 30 mJ energy and 80 fs duration. A deformable mirror system with a genetic algorithm (GA) was developed to optimize the laser-focusing spot. The fitness values used in the GA were measured from the focusing intensities under the low-gain condition of the power amplifier, or from x-ray in situ signals emitted from the target. Although we obtained a diffraction-limited size of 2 μm (full width at half maximum) using the former value, a precise compensation using the latter value was essential to accelerate protons whose flux was 106/MeV/shot to a maximum energy of 1.1±0.3 MeV with laser pulses of only 30 mJ energy since a laser spot that is too tight may be sensitive to wave-front distortion caused by residual thermal lenses of the power amplifier. [ABSTRACT FROM AUTHOR]

A thin tape target driver for laser ion acceleration was developed. The driver can move a copper tape of 5 μm thickness with a positioning reproducibility of less than 30 μm (peak to valley), which is sufficient for a laser irradiation target. Using this tape target and laser pulses of energy 350 mJ and duration 60 fs, protons of energies of over 1 MeV were accelerated in the forward direction. [ABSTRACT FROM AUTHOR]

This paper presents an original method to measure the phase transition and macroscopic density fluctuation of supercritical carbon dioxide using a resonant microcantilever beam. There is a significant reduction of the resonant frequency near the phase transition point where the density and viscosity of carbon dioxide exhibit large variations, while the vibration amplitude of the micromechanical resonator displayed a large shift up due to generation of microscopic density fluctuation. The average length of the density fluctuation of supercritical fluid could be calculated from this large shift of the vibration amplitude and the value is in the range of millimeter. [ABSTRACT FROM AUTHOR]

For multiple laser pulse experiments, it is necessary to split a laser pulse. In order to split a short laser pulse without stretching the pulse width, the laser pulse should not pass through thick materials. For this reason, a pellicle beam splitter (BS) and/or a mirror with a hole are required as a BS for the short laser pulse. The focusing qualities of the laser pulse after passing through the pellicle BS and the mirror with a hole are the same as without the BS’s. The laser pulse quality reflected by the BSs should be considered for the laser pulse. A pellicle BS is a thin foil, so, it is weak against vibrations. One should be careful about airflows and isolation from vibration sources. The spot size of the reflected laser pulse is consistent with the size reflected by a normal mirror. The energy loss is about 10% compared with a normal mirror. A mirror with a hole is strong against external vibrations. The reflected laser pulse has a doughnut shape. The reflected laser pulse is interfered due to the shape. In order to cleanly focus the laser pulse, the inside size of the doughnut should be smaller than a half size of the outside portion of the doughnut. [ABSTRACT FROM AUTHOR]

By irradiating subpicosecond laser onto an iron plate, a nanofibrous structure consisting of iron nanoparticles with diameters less than 12 nm was produced. The nanofibrous structure was found to be three-dimensional fractal, and its fractal dimension measured from field-emission scanning electron microscopy images conserved the same fractal dimension of 1.73 in the wide-scale range from 30 nm to 60 μm, and the smallest fractal structure was less than 10 nm. The growth of this fractal is related to the cluster-cluster aggregation model, and it suggests that the fractal structure grew by the attachment of clusters consisting of nanoparticles. [ABSTRACT FROM AUTHOR]

It has been determined that the incorporation of carbon into GaAs crystals grown by the liquid encapsulated Czochralski method occurs as the result of a reaction between the GaAs melt and gaseous oxides of carbon, rather than carbon particles. The incorporation occurs during growth as well as during synthesis. The incorporation of carbon was particularly large when a commercially available large puller was used because of the greater number of carbon components in the hot zone which act as sources. Crystals with a low carbon concentration of 1×1015 cm-3 have been successfully grown by employing pyrolytic boron nitride coated graphite components in the large puller. [ABSTRACT FROM AUTHOR]

The direct synthesis and growth of InP have been successfully performed by the newly developed liquid P encapsulated Czochralski technique. We have developed a way to use liquid P both as a source element for the synthesis instead of P gas, and also as an ‘‘encapsulant’’ for the Czochralski growth instead of B2O3. The existence of two distinct layers, liquid P and molten InP, has been discovered during the process. Grown single crystals showed a carrier concentration of as low as 5×1015 cm-3. [ABSTRACT FROM AUTHOR]

We have measured the effective dynamic viscosity of molten GaAs and InSb as a function of axial magnetic field by the oscillating vessel method. Effective viscosity of these semiconductor melts is observed to increase with the axial magnetic field intensity in the range of 0 to 5 kG. [ABSTRACT FROM AUTHOR]

A method of electron energy control was studied in an inductively coupled plasma that employed a multimode antenna, for high performance in device fabrication plasma processes. The electron energy was reduced by changing the azimuthal mode of a one-turn antenna from m=0 to 2 with no notable change in electron density. Langmuir probe measurements showed that the electron energy reduction was more pronounced in the higher modes and at lower pressures. The antenna size was also a critical parameter. These results were confirmed by optical emission spectroscopy. It was found to be essential for the energy control that the distance between the induction-field reverse points is shorter than the electron free path. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]