Search

Micro- and nanoscale structures on a material surface formed by femotosecond laser processing have greatly changed its optical characteristics. In this work, the coloring of Al surface has been realized with scanning focused femtosecond laser beam on the Al surface. We further apply femtosecond laser filamentation to form micro- and nano-structures on a spherical Al surface, resulting in a black appearance of the spherical Al. This work opens ways to fabricate strong light-trapping micro- and nano-structure on a non-planar surface without the complexity of a 4-axis sample control. [ABSTRACT FROM PUBLISHER]

Simulation results show how cathode-side filaments may trigger a thermal runaway at the end of a reverse-recovery period of diodes turned off with extremely high current rates. The mechanism is not essentially affected by the edge termination if an appropriate design is chosen. While multiple avalanche-induced filaments may appear during the reverse-recovery period, at the end of the turn-off phase a single “winning” filament carries the total current. This can result in a local melting of the diode. The appearance of a cathode-side filament by itself does not necessarily lead to the diode destruction. However, a high thermal carrier generation rate can result in an uncontrollable increase of the current density in a single filament connecting the anode and the cathode contact. It is shown t hat the reverse-recovery charge as a function of the dc-link voltage shows a characteristic super-linear increase below the critical value dc-link voltage at which the diode current increases uncontrollably. [ABSTRACT FROM PUBLISHER]

Employment of H- ion sources for the LANSCE accelerator systems goes back about 20 years, to the construction of the Proton Storage Ring (PSR). The standard ion source consists of a filament driven multi-cusp discharge vessel with a biased converter electrode for negative-ion production and an 80-kV extraction system feeding into a 670-kV electrostatic pre-accelerator. The source typically delivers 18 mA pulsed beam current into the pre-accelerator column and reaches up to 35 days between services at 60 Hz pulse repetition rate. Recent development efforts with this source have been dedicated to improved filament material, improved cesium oven geometry and operating the source at elevated temperatures. A second line of development focuses on filament-less devices driven by a helicon discharge. Performance data obtained with the standard source as well as key results for the helicon experiments are given in this paper; the helicon work is discussed in a separate paper in much greater detail. [ABSTRACT FROM AUTHOR]

Cathode units of high power radio-frequency tubes are conventionally used in electron injectors with high repetition rate. This cathode utilization results in disturbance of the temperature regime of the cathode surface because of cutting the anode, which is “thermal mirror” in the tube. Estimations made in this work show an essential lowering of the emitter temperature for both porous metal and oxide cathodes without anodes. It shows that the oxide cathode utilization results in a significant thermal gradient in the oxide layer. [ABSTRACT FROM PUBLISHER]

An improvement in the switching performance is reported in a CMOS compatible Al/Ti/TiOx/HfOx/Pt memory cell, due to oxygen-rich HfOx layer insertion in simple metal-insulator-metal sandwich structure. TiOx and HfOx embedded in resistive-switching random access memory (RRAM) stack is one of the promising candidates for low power (>2V) bipolar resistive switching memory application. From I-V characteristics, trap-controlled space charge limited current (TC-SCLC) conduction mechanism is found to be the most suitable mechanism signifying the dominant current conduction in all the bias regions and resistance states. This device has shown good uniformity and data retention of >104 s at 85 ­C with a high resistance ratio of >102. [ABSTRACT FROM AUTHOR]

Improvement in the resistive switching characteristics using TiN bottom electrode on TaOx/W structure as compared to W electrode is reported. The thickness of TaOx layer is confirmed by high-resolution TEM image. The memory device with TiN electrode has shown formation-free repeatable bipolar resistive switching with resistance ratio of >30. Besides, improved resistive switching performance in terms of lower operation current (50 vs. 300 μΑ), longer read endurance (>105 cycles), 85 °C data retention of > 104 seconds and device yield of >90% is also achieved for TiN electrode. The TiN/TaOx interface is playing a key role in controlling the oxygen vacancy defects which in turn control the formation/dissolution of conducting filament. [ABSTRACT FROM PUBLISHER]

In this paper we analyzed the evolution of the active region AR09767 and other two active regions (AR09771 and AR09780) located in its neighborhood, as well as the evolution of the filament associated with our principal active region. Concomitantly, we studied the principal events of AR09767 such as flares and CME. We extrapolate the 3D coronal magnetic field configuration from the photospheric one in order to understand the magnetic field evolution and reconnections during these erupting events. [ABSTRACT FROM AUTHOR]