Nanocomposites of polyaniline (PANI) and the semiconducting metal sulfides CdS and Cu 2 S were prepared from the respective metal trifluoromethanesulfonates co-dissolved in N-methylpyrrolidone. Metal sulfide particles with typical diameters of 1-2 nm formed in situ upon addition of Li 2 S; the nanocomposites were subsequently isolated by co-precipitation. UV/VIS absorption spectra suggest that the PANI-CdS nanocomposites are stable in the air, while PANI was found to degrade in the presence of Cu 2 S. Appreciable photovoltaic effects were measured on multilayer devices based on Al/nanocomposite/Cd 12x Zn x O and Al/ nanocomposite/C 60 /Cd 12x Zn x O. In the absence of the C 60 layer, both open circuit photovoltage (U oc ) and short circuit photocurrent (I sc ) were found to increase substantially with increasing CdS content, while in the presence of a C 60 layer, more complex behavior was observed. ExperimentalMaterials PANI in its emeraldine base form was obtained from Neste Oy Chemicals. C 60 (content 99%) was received from the Kurchatov Institute Physical Chemistry Synthesis Group. Cadmium hydroxide hydrate [Cd(OH) 2 ?xH 2 O], trifluoromethanesulfonic acid, copper(II) trifluoromethanesulfonate [Cu(CF 3 SO 3 ) 2 ], and lithium sulfide were purchased from Aldrich Chemical Co. or Fluka, and N-methylpyrrolidone (NMP) was obtained from

We report measurements of very large output intensities corresponding to a gain larger than 10 5 for a single pass free-electron laser operating in the self-amplified spontaneous emission (SASE) mode at 12 mm. We also report the observation and analysis of intensity fluctuations of the SASE radiation intensity in the high-gain regime. The results are compared with theoretical predictions and simulations. [S0031-9007 (98)07403-1]

Energy gain of trapped electrons in excess of 20 MeV has been demonstrated in an inverse-free-electron-laser (IFEL) accelerator experiment. A 14.5 MeV electron beam is copropagated with a 400 GW CO2 laser beam in a 50 cm long undulator strongly tapered in period and field amplitude. The Rayleigh range of the laser, approximately 1.8 cm, is much shorter than the undulator length yielding a diffraction-dominated interaction. Experimental results on the dependence of the acceleration on injection energy, laser focus position, and laser power are discussed. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.

We report measurements of large gain for a single pass free-electron laser operating in self-amplified spontaneous emission (SASE) at 16 mm starting from noise. We also report the first observation and analysis of intensity fluctuations of the SASE radiation intensity in the high gain regime. The results are compared with theoretical predictions and simulations. [S0031-9007(97)04953-3]

An electronic bistability has been observed in a two-dimensional spatially ordered array of 10 nm quantum dots self-assembled by electrodepositing CdS in nanoporous anodic alumite film. The current–voltage characteristic of the array shows switching between two stable conductance states, which can be controlled by an external bias. The bistability is observed when current flows laterally between two contacts on the top surface of the array, and also when current flows vertically between a top contact and the bottom (conducting) substrate. If the system is left in one conductance state, it remains there for at least 180 h and possibly much longer, until switched to the other state by an external bias. Such an effect may find applications in inexpensive, ultradense nonvolatile static random access memory.

The application of gas sensors in breath analysis is an important trend in the early diagnostics of different diseases including lung cancer, ulcers, and enteric infection. However, traditional methods of synthesis of metal oxide gas-sensing materials for semiconductor sensors based on wet sol-gel processes give relatively high sensitivity of the gas sensor to changing humidity. The sol-gel process leading to the formation of superficial hydroxyl groups on oxide particles is responsible for the strong response of the sensing material to this factor. In our work, we investigated the possibility to synthesize metal oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in gas phase by spark discharge, enabling the reduction of the hydroxyl concentration on the surface and allowing the production of tin dioxide powder with specific surface area of about 40 m2/g after annealing at 610 °C. The drop in sensor resistance does not exceed 20% when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is a factor of 8 with very short response time of about 1 s. The sensor response was tested in mixtures of air with hydrogen, which is the marker of enteric infections and the marker of early stage fire, and in a mixture of air with lactate (marker of stomach cancer) and ammonia gas (marker of Helicobacter pylori, responsible for stomach ulcers).

This paper describes the magnetic behaviour of polymer nanocomposites containing nanoparticles (∽10 nm) of maghemite γ‐Fe2O3 and magnetite Fe3O4 in a polyvinyl alcohol matrix. The compositions were synthesised using an original method of in situ preparation, the reaction of oxide formation taking place inside the polymer matrix itself. It is the one‐domain‐per‐particle nature of magnetism in the given polymer nanocomposites that was found to be responsible for such a distinctive feature as superparamagnetism detected using Mössbauer spectroscopy and magnetisation measurements. A giant negative magnetoresistance was found in the highly filled compositions. As far as we know, this is the first time that this effect has been observed in polymer composites based on ferrite nanoparticles. Copyright © 1999 John Wiley & Sons, Ltd.

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