Nanoweb Formation: 2D Self‐Assembly of Semiconductor Gallium Oxide Nanowires/Nanotubes

This paper reports a method to produce networks of crystalline gallium oxide comprised of one‐dimensional (1D) nanostructures. Because of the unique arrangement of wires, these crystalline networks are termed as ‘nanowebs’. Nanowebs are of great technological interest since they contain wire densities of the order of 10⁹ cm^–2. A possible mechanism for the fast self‐assembly of crystalline metal oxide nanowires involves multiple nucleation and coalescence via oxidation–reduction reactions at the molecular level. The preferential growth of nanowires parallel to the substrate enabled them to coalesce into regular polygonal networks. The individual segments of the polygonal network consist of both nanowires and nanotubules of β‐gallium oxide. Individual wire properties contribute to a nanoweb’s overall capacity and the implications for devices based on nanowebs are expected to be enormous.     

QoS provisioning in cellular networks based on mobility prediction techniques

In cellular networks, QoS degradation or forced termination may occur when there are insufficient resources to accommodate handoff requests. One solution is to predict the trajectory of mobile terminals so as to perform resource reservations in advance. With the vision that future mobile devices are likely to be equipped with reasonably accurate positioning capability, we investigate how this new feature may be used for mobility predictions. We propose a mobility prediction technique that incorporates road topology information, and describe its use for dynamic resource reservation. Simulation results are presented to demonstrate the improvement in reservation efficiency compared with several other schemes.     

Formation of C49-TiSi2 in flash memories: a nucleation controlled phenomenon?

The formation of Ti silicides has been examined in flash memories with 0.25 μm linewidth by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It has been observed that, after the first rapid thermal process and the selective metal etch, there is no silicide on the source and on a majority of drain contacts while C49-TiSi₂ is found on the gate. A pre-amorphisation implant increases drastically the formation of C49-TiSi₂ in the drain zone while modifications of annealing conditions have little impact. These results indicate that the formation of C49-TiSi₂ is most likely controlled by nucleation and that this nucleation is sensitive to both the width and the length of the reaction zone. The formation of a Ti rich silicide may play an important role in this nucleation by decreasing the driving force for the formation of C49-TiSi₂. Curiously enough, the formation of C49-TiSi₂ appears thus as a major concern for the salicide process in flash memories.     

High‐Performance,Monolithic Polyaniline Electrochemical Actuators

New polyaniline (PANI) asymmetric membranes were fabricated using a phase‐inversion technique with hexane as the coagulation bath. These membranes exhibit a dense structure with macrovoids distributed asymmetrically throughout the cross‐section. A stress–strain study demonstrated that the Young's modulus (1.421 GPa) and strain at break (7.6 %) of the new PANI asymmetric membranes prepared from hexane are approximately 12 and 4 times higher, respectively, than the values reported previously for the PANI integrally skinned asymmetric membranes (ISAMs) (123 MPa Young's modulus and 1.8 % strain at break). Furthermore, monolithic electrochemical actuators based on a single PANI asymmetric membrane were constructed, and a bending movement of up to 20 Hz was experimentally recorded in a hydrochloric acid aqueous solution. A lifetime of over 329 500 cycles was determined for these actuators at a ± 2° angular displacement (5 Hz). The lifetime is limited by a bending fatigue that creates a transversal crack on the PANI membrane at the air–water interface. Control over the actuator movement is also manifested by the linear dependences of the bending angle on the charge and of the angular velocity on the current. These relationships are independent of both the kind of applied electric signal and the frequency used.     

Origin of the threshold voltage instability in SiO/sub 2//HfO/sub 2/ dual layer gate dielectrics

The magnitude of the V/sub T/ instability in conventional MOSFETs and MOS capacitors with SiO/sub 2//HfO/sub 2/ dual-layer gate dielectrics is shown to depend strongly on the details of the measurement sequence used. By applying time-resolved measurements (capacitance-time traces and charge-pumping measurements), it is demonstrated that this behavior is caused by the fast charging and discharging of preexisting defects near the SiO/sub 2//HfO/sub 2/ interface and in the bulk of the HfO/sub 2/ layer. Based on these results, a simple defect model is proposed that can explain the complex behavior of the V/sub T/ instability in terms of structural defects as follows. 1) A defect band in the HfO/sub 2/ layer is located in energy above the Si conduction band edge. 2) The defect band shifts rapidly in energy with respect to the Fermi level in the Si substrate as the gate bias is varied. 3) The rapid energy shifts allows for efficient charging and discharging of the defects near the SiO/sub 2//HfO/sub 2/ interface by tunneling.     

Effects of Light, Oxygen, and pH on the Absorbance of 2,2-Diphenyl-1-picrylhydrazyl

ABSTRACT: The absorbance of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at 517 nm in methanol and acetone decreased by 20 and 35% for 120 min at 25 °C under light, respectively; in the dark it did not change significantly for 150 min. Decomposition of DPPH under 21% oxygen after 90 min under light was significantly higher than that under 1% oxygen. Absorbance of DPPH in pH 4 buffer solution in methanol, and in pH 10 buffer solution in acetone, decreased by 55 and 80%, respectively, under light for 120 min. The evaluation of antioxidant activity by the changes of DPPH absorbance should be carefully interpreted since the absorbance of DPPH at 517 nm is decreased by light, oxygen, pH, and type of solvent in addition to the antioxidant.     

An analytical method for the calculation of static characteristicsof linear step motors for control rod drives in nuclear reactors

An analytical method for calculating static characteristics of linear dc step motors (LSM) is described. These multiphase passive-armature motors are now being developed for control rod drives (CRD) in large nuclear reactors. The static characteristics of such LSM is defined by the variation of electromagnetic force with armature displacement and it determines motor performance in its standing and dynamic modes of operation. The proposed analytical technique for calculating this characteristic is based on the permeance analysis method applied to phase magnetic circuits of LSM. Reluctances of various parts of phase magnetic circuit is calculated analytically by assuming probable flux paths and by taking into account complex nature of magnetic field distribution in it. For given armature positions stator and armature iron saturations are taken into account by an efficient iterative algorithm which gives fast convergence. The method is validated by comparing theoretical results with experimental ones which shows satisfactory agreement for small stator currents and weak iron saturation     

Long-wavelength infrared photoinduced switching of a resonanttunneling diode using the intersubband transition

Voltage switching induced by long-wavelength infrared light from a CO₂ laser was observed using a double-barrier resonant tunneling diode (RTD) biased in the bistable region and the intersubband transition (IT) between the quantum confined states. Possible optoelectronic and all-optical switching applications involving hysteresis are proposed and discussed     

Rotative quadrature phase-shift keying

A rotative quadrature phase-shift keying (RQPSK) modulation scheme is proposed. By rotating the QPSK signal constellation by pi /2 either clockwise or anticlockwise during a symbol duration, the conventional QPSK scheme can be modified to transmit 3 bits per symbol to achieve both power and bandwidth efficiency.<>