Antenna Devices Research Articles

Zeolite Microcrystals as Hosts for Supramolecular Organization of Dye Molecules

Zeolite microcrystals can act as host for supramolecular organization of molecules, complexes, clusters, and quantum-size particles. They allow the design of precise and reversible functionalities. Techniques for arranging zeolite microcrystals of good quality and narrow size distribution as dense monograin layers on different substrates can be used to realize specific properties. The chemical reactivity between the intercalated molecules offers possibilities for in situ synthesis of molecular chains, clusters, and quantum-size particles, which might not be accessible otherwise. In some cases, guest-host reactivity must be considered. The reactivity of intercalated compounds with (small) molecules penetrating from the outside is an option for changing the composition of a material, i.e., molecules intercalated as monomers in a first step can be linked to form chains. New electronic structures are accessible either by specific geometrical arrangements made possible by the structure of the host and/or by explicitly involving its electronic properties. Some systems meet the conditions necessary for the occurrence of intrazeolite charge transport (ionic and electronic), realized by the guests in their ground state and in electronically excited states under high-vacuum conditions or in the presence of a solvent, depending on the composition and the structure of the material. In this article, we focus on organic dye molecules in the one-dimensional channels of zeolites with a hexagonal framework. This system consists of supramolecularly organized dye molecules. It is shown to provide fascinating possibilities for building an artificial antenna device which consists of highly concentrated monomeric dye molecules of up to 0.4M with a large Förster energy-transfer radius and a high luminescence quantum yield in an ideal geometrical arrangement of optimal size. Extremely fast electronic excitation-energy transport has been demonstrated by us in oxonine- and pyronine-dye-loaded zeolite L microcrystals. Many other highly organized dye-zeolite materials can be prepared, and they are expected to show a wide variety of challenging properties. We report on methods to distinguish between dye molecules which are inside of a microcrystal and those adsorbed on its outer surface, and we explain a demonstration experiment illustrating the intercalation of thionine into zeolite L and the thus resulting improved chemical stability of this dye.

At the time he made the first photographs on paper: Did Henry Fox Talbot oxidize water to oxygen with sunlight?

Photocatalytic water oxidation to O 2 takes place at the solid/water phase boundary of an appropriately prepared thin AgCl layer in the presence of a small excess of Ag +. This water oxidation reaction shows self-sensitization: as the reaction proceeds, the sensitivity is extended from the near-UV—visible towards the red range. This means that new photo active colour centres are formed upon near UV illumination composed of reduced silver species. The quantum yield per redox equivalent for O 2 evolution upon illumination with near UV light (340–390 nm) is ∼0.8 and it is the same upon illumination with blue light (420–480 nm). In the green range it is ∼0.5. We discuss parameters controlling these reactions. Some of our observations parallel those made by Henry Fox Talbot 160 years ago when he made his first “photogenic drawings” on silver chloride containing paper. Zeolite microcrystals are investigated as hosts for supramolecular organization of clusters, complexes and molecules. They offer possibilities to design precise and reversible functionalities which have the potential to become useful in a solar energy conversion system because in favourable cases very stable materials have been obtained. The possibility to arrange zeolite microcrystals of good quality and narrow size distribution as dense monograin layers on different types of substrates allows the discovery of specific properties. In the present context, three functionalities are of special importance: intrazeolite ion transport, intrazeolite charge transport and intrazeolite excitation energy transport. All of them have been clearly demonstrated experimentally although there are still some controversies going on. The zeolite acts as a host in each case mentioned. It is not actively involved in the corresponding processes, but provides the necessary geometrical and chemical environment. Favourable conditions for finding an efficient antenna device are a high concentration of monomeric dye molecules with a large Förster energy transfer radius, high luminescence quantum yield and ideal geometrical arrangement of the chromophores, as well as an optimal size of the device. Very interesting supramolecular devices can be realized by enclosing dyes inside a microporous material such that the volume of the cages and channels is able to uptake monomers only, but not aggregates.

Degraded noise characteristics of submicrometer area field effect transistors subjected to plasma etching and Fowler–Nordheim stress

The effects of reactive ion etching (RIE) and Fowler–Nordheim (FN) gate current stresses upon both the 1/fγ and random telegraph signal (RTS) noise characteristics of submicrometer gate area metal oxide semiconductor field-effect transistors has been analyzed. While control devices exhibit the Lorentzian noise spectra and discrete switching behavior attributable to single oxide defects, the first layer metal antenna devices exhibit degraded RTSs and near ideal 1/f noise characteristics. An evolution of this 1/f behavior has been reproduced in control devices by subjecting them to a series of UV illuminated FN gate current stresses. Results of this study suggest that multiple oxide traps with a distribution in time constants are generated during RIE and that the amount of oxide degradation generated during plasma etching may be more substantial than that produced during plasma ashing.

Linear hydrophonic antenna and electronic device to remove right/left ambiguity, associated with this antenna

A linear hydrophonic antenna with an associated portside/starboard ambiguity removing device comprises three streamers placed in an equilateral triangle, with a center distance of the order of a third of the wave length which corresponds to the center frequency received. The density of the median streamer is notably greater than the common density of the other two streamers. Channels are formed in a standard way, and the received signals are phase shifted then added up so that the directivity associated with each channel shows a zero, either at portside or at starboard, the direction of which remains fixed despite the roll.

A parametric-excitation-integrated-ferrite antenna

A new type of ferrite antenna with fairly high sensitivity has been studied and experimental results are presented. Although ferrite antennas have long been used as one of the typical antennas of small size, it seems that the remarkable increase of the sensitivity of the ferrite antennas depends upon dimensions and performance of ferrite material, and improvement of those factors is not expected so easily at the present state of the art. One solution for this problem may be the application of the integration technique, that is combining an antenna and active devices in a unified structure with an inseparable form. To form an active device within an antenna, parametric excitation is incorporated into a ferrite antenna structure, and the principle of power transfer between signals, which follows Manley-Rowe's relation, is applied to it for obtaining an active gain within the antenna itself. The permeability variation of the ferrite material is effectively utilized to produce an active function from a passive antenna system. Results show about 5 to 10 dB gain depending upon the pumping power interims of S/N over the conventional passive ferrite antenna having the same size as that of the active antenna.