Light-induced resistive switching in silicon-based metal–insulator–semiconductor structures

We have studied light-induced resistive switching in metal–insulator–semiconductor structures based on silicon covered with a tunneling-thin SiO₂ layer and nanometer-thick layer of antimony. The role of an insulator was played by yttria-stabilized zirconia.

     

The forming process in resistive-memory elements based on metal-insulator-semiconductor structures

Using as an example metal-insulator-semiconductor structures based on GaAs with stabilized (by yttrium oxide) zirconium dioxide, which show the effect of resistive-switching random-access memory, the possibility is considered of controlling phenomena associated with the forming process in the insulator and on the insulator-semiconductor interface, as well as in the semiconductor, by measuring the response of the semiconductor.     

Formation of intermetallic phases during mechanical alloying and annealing of Cr + 20 wt % al mixtures

We have studied phase-formation processes in mixtures of Cr and Al (20 wt %) powders in the course of mechanical alloying (MA) and the phase transformations of the samples during subsequent annealing at temperatures of up to 800°C. The resultant x-ray amorphous intermetallic phases were identified by a differential dissolution method, which allows one to follow the formation of x-ray amorphous and partially crystallized phases. During MA of Cr + Al mixtures, the first to form is x-ray amorphous Cr₄Al, which then converts to partially crystallized Cr₂Al through reaction with aluminum. The peritectoid decomposition of Cr₄Al during heating of the MA samples is accompanied by heat release at 330–350°C. Heating to 420°C leads to the formation of Cr₅Al₈. At 800°C, Cr₅Al₈ reacts with Cr to form Cr₂Al.     

The development of catalysts for dehydrogenation of lower C3-C4 paraffins using the products of gibbsite thermal activation

A standardized approach to the preparation of alumina-chromia catalysts for dehydrogenation of lower C₃-C₄ paraffins is discussed. The approach is based on the use of initial products prepared by thermochemical activation (TCA) of gibbsite in an industrial flow-type flash reactor and the centrifugal thermal activation (CTA) on the CEFLAR? unit. Catalytic characteristics in reactions of dehydrogenation of propane and butanes in fluidized and fixed beds of microspherical and granulated catalyst samples are better than those of domestic commercial catalysts and are highly competitive with the best imported catalysts.     

Catalytic activity of powder and monolith perovskites in methane combustion

Honeycomb monolith perovskite catalysts were prepared from ultradispersed powders of mixed oxides of rare-earth metals (La–Ce or Dy–Y) and transition metals (Ni, Fe, Mn) by mechanochemical methods. A plasmochemical method was used to obtain La–Ni containing monoliths. The catalytic activity of powders and monoliths was compared in the catalytic combustion of methane. The intrinsic catalytic properties of the active components (apparent kinetic constant and energy of activation) were not significantly affected by the manufacturing procedure of monoliths in a large range of temperatures. Best performance was exhibited by La–Ni oxides containing monoliths which possess the highest pore volume and fraction of macropores.     

Electronic,chemisorption and catalytic properties of Pd overlayers on Ru(100) probed by CO and O2 adsorption and reaction

We have employed UHV surface sensitive techniques together with CO and oxygen adsorption and reaction to link the chemical, electronic and structural properties of ultra-thin Pd films vapour-deposited on Ru(100). At low Pd coverage the properties of the Pd overlayer are considerably modified relative to the bulk-like properties exhibited by thick Pd films. A Pd coverage of 6 ML seems to mark a critical transition to bulk-like Pd behaviour. The strongest modifications in the Pd overlayer occur for coverages up to 2 ML and are exemplified by a reduction in the CO desorption temperature, a low DOS at Fermi level,E _f, and a lower activity toward CO oxidation.     

Compact ultrahigh-frequency antenna designs for low-cost passive radio frequency identification transponders

Compact planar antennas for low-cost radio frequency identification (RFID) passive transponders are disclosed. The proposed ultrahigh-frequency antenna takes advantage of its unique topology to assure conjugate matching with essentially complex impedance of the electronic chip directly embedded into the radiator. Rectenna design issues are also emphasised. An original method to characterise IC chips and antennas as taken in its entirety of transponders is presented. The characterisation of the chip takes into account the impact of connecting antennas to the rectifier by flip-chip bonding process. The proposed experimental method allows finding chip impedance exactly as it seen by antennas. Refined rectifier circuitry effectively overcomes dependence of transponder performances on the type deviation of the connected antennas. Very good antenna performance is predicted theoretically and validated experimentally over an operating bandwidth of actual RFID systems.     

Small-signal field effect in GaAs/InAs quantum-dot heterostructures

InAs quantum dots (QDs), incorporated into the space-charge region of an epitaxial n-GaAs film at different distances (5?C300 nm) from the surface, decrease the potential barrier for the electrons located in n-GaAs. For tunnel-thin coating layers this decrease is related to tunneling through QD energy levels. For thick layers this decrease is caused by negative charging of the QDlevels and defects located near QDs. The decrease in the barrier increases the efficiency of electron capture by surface states and shifts the frequency dispersion of mobility under the field effect, related to this capture, toward higher frequencies. When QDs are incorporated near the barrier??s base, they manifest themselves in the relaxation of the small-signal field effect. Some parameters of the QD levels are determined. Defect formation is revealed in the layers adjacent to QDs.     

Admittance spectroscopy of ring diode InGaAs/InAlAs/InP quantum-well structures

The admittance of ring planar diode Au/InGaAs/InP and Au/InGaAs/InAlAs heteronanostructures on i-InP has been studied. The structures are constituted by a silicon ??-doped layer and an InGaAs quantum well (QW) in InP or InAlAs epitaxial layers. An analysis of the capacitance-voltage and conductance-voltage characteristics yielded distribution profiles of the electron concentration and mobility in the vicinity of the QW and ??-doped layer. It is shown that lowering the temperature leads to an increase in the electron concentration and mobility in the QW.