Semiconductor Laser or Light Emitting Diodes, (LEDs) as active elements of optical switches or spatial routing devices are widely used in integrated optical circuitry. Electro-optic, magneto-optic, mechanical or other methods are applied for that purpose. The present paper deals with a novel effect, which appears in the light field of a. c. driven luminescence emitters in Fabry-Perot structure under electrical excitation depending on time (a.c.), characterized because the light band emitted on the side face of the device moves up and down due to the finite diffusion velocity of the injected excess minority carriers. The combination of such emitter with a portioned detector element, allows spatial routing between these two detector segments. Particular emphasis is laid on a theoretical treatment of light propagation inside the emitter bulk which finally allows the construction of the light field intensity on the side face of the Fabry-Perot body, necessary to prove the proposed effect.

Láseres semiconductores o diodos fotoluminiscentes (LEDs) como elementos activos en switches ópticos o dispositivos de ruteo espacial son ampliamente usados en circuitos ópticos integrados. Para tal fin se aplica métodos basados en electro-óptica, magneto-óptica, mecánica, y algunos otros . En este trabajo se presenta un efecto novedoso, que aparece en el campo de radiación de diodos fotoluminiscentes en estructura Fabry-Perot bajo excitación eléctrica dependiendo en tiempo (a. c.), caracterizado por que la cinta de la luz emitida sobre la cara lateral del dispositivo se mueve hacia arriba y abajo debido a la velocidad de difusión finita de los portadores minoritarios inyectados. La combinación de tal emisor con un elemento detector partido permite el ruteo de la señal de luz entre estos dos segmentos del detector. Se pone particular énfasis en el tratamiento teórico de la propagación de luz dentro del volumen del emisor, que finalmente nos permite la construcción de la intensidad del campo de luz en las caras laterales del cuerpo Fabry-Perot, necesario para la comprobación del efecto propuesto.

Silicon-based microelectronics has been following the integration prognosis of MOORE's Law during the past decades and possibly will do so for another decade or two. Physical, technological and also financial limits in the foreseeable future will slow down the continued expansion of this branch of microelectronics and instead will force a new technological approach based on molecular-scale electronics (MOLETRONICS). New tools are needed to allow molecular device manufacturing and nanoscale engineering with high precision and productivity. One group of methods with the potential for use in such a manufacturing process is based on a.c. electrokinetics effects, which are described and discussed in this paper.

La microelectrónica en base a silicio ha seguido la prognosis de integración según la ley de MOORE durante las décadas pasadas, y posiblemente continuará así por otra década más. Límites físicos, tecnológicos y también financieros en el futuro cercano reducirán la razón de expansión de esta rama microelectrónica, y en su lugar generará una aproximación tecnológica novedosa, que se basa sobre la electrónica a escala molecular (MOLETRÓNICA). Se requieren nuevas herramientas, que permitan la fabricación de dispositivos moleculares y la ingeniería a escala nanométrica con alta precisión y productividad. Un grupo de métodos con el potencial de ser usado en tal proceso de fabricación se basa en efectos electrocinéticos en campos eléctricos alternos, que en el presente trabajo se describe y discute.

Electro-rotation can be used to determine the dielectric properties of cells, as well as to observe dynamic changes in both dielectric and morphological properties. Suspended biological cells and particles respond to alternating-field polarization by moving, deforming or rotating. While in linearly polarized alternating fields the particles are oriented along their axis of highest polarizability, in circularly polarized fields the axis of lowest polarizability aligns perpendicular to the plane of field rotation. Ellipsoidal models for cells are frequently applied, which include, beside sphere-shaped cells, also the limiting cases of rods and disks. Human erythrocyte cells, due to their particular shape, hardly resemble an ellipsoid. The additional effect of rouleaux formation with different numbers of aggregations suggests a model of circular cylinders of variable length. In the present study, the induced dipole moment of short cylinders was calculated and applied to rouleaux of human erythrocytes, which move freely in a suspending conductive medium under the effect of a rotating external field. Electro-rotation torque spectra are calculated for such aggregations of different length. Both the maximum rotation speeds and the peak frequencies of the torque are found to depend clearly on the size of the rouleaux. While the rotation speed grows with rouleaux length, the field frequency nup is lowest for the largest cell aggregations where the torque shows a maximum.

Amorphous and relaxed epitaxial GeSi films are prepared by Ge-implantation into Si(111) wafers of both 60 keV and 200 keV energetic Ge+-ions with appropriate dose, followed by post-implantation thermal annealing, comprising a single final annealing at a temperature of 900 °C. The implantation dose was varied between 10(14) and 10(17) atoms cm-2. Rutherford backscattering (RBS) and channeling analysis was applied in order to explore the formation of a single crystalline Si-Ge compound layer, both prior and after the thermal treatment. The depth and the thickness of the implanted layer, as well as their molar composition and crystalline quality was determined, and it was found that a single crystalline Si-Ge alloy layer was created, with both depth and mole fraction depending on the ion energy and the ion dose.

The polarization of particles or biological cells is commonly investigated by measuring the impedance of suspensions or by a variety of single particle methods, that exploit different force effects. For biological cells the most striking frequency-dependent changes in polariz-ability result from structural (Maxwell-Wagner) polarization phenomena. Explicit solutions of the Laplace equation are available only for objects with finite surfaces of the second degree. Thus, dielectric models consider the structural properties of cells by assuming spherical or ellipsoidal geometries, since only in very few cases is the effective local field Ei(r) in the presence of a dielectric object known. This concerns dielectric bodies of special shape, which are exposed to a special electric field E0(r). In the present paper an approximation procedure is presented for the general case, allowing to calculate the depolarization field Ei(r), which is generated in the presence of an arbitrarily shaped dielectric object, introduced into a field space. Contrary to recent numerical methods (finite element technique), which require extensive computer resources due to the unavailability of analytical solutions, the here presented approach results in closed analytical expressions. The applicability of the method is demonstrated for a non-ellipsoidal cylindrical dielectric by measuring its dipole moment in a microwave field. The accordance with the calculated results is found to be one order of magnitude better than it would be in the commonly practiced procedure, where the cylinder is substituted by a spheroid of the same axis relation.

La polarización de partículas o celdas biológicas se estudia comúnmente a través de la medición de la impedancia de suspensiones, o bien por una variedad de métodos de partículas sencillas, que se basan en efectos diferentes de fuerza. Para celdas biológicas, los cambios en la polarización más notables dependiendo de la frecuencia, resultan de fenómenos estructurados de polarización (Efecto Maxwell-Wagner). Modelos dieléctricos consideran las propiedades estructurales de celdas suponiendo geometrías esféricas o elipsoidales, puesto que sólo en muy pocos casos se conoce el campo efectivo local Ei(r) en presencia de un objeto dieléctrico. Esto se refiere a cuerpos dieléctricos de forma especial, que están expuestos a un campo eléctrico especial E0(r). En el presente trabajo se muestra un procedimiento de aproximación para el caso general que permite el cálculo del campo local Ei(r) generado en presencia de un objeto dieléctrico de forma arbitraria, introducido en el espacio de campo. La aplicabilidad del método es demostrada para un cilindro dieléctrico no-elipsoidal a través de la medición de su momento dipolar en un campo de microondas. La correspondencia con los resultados calculados se encuentra un orden de magnitud mejor que en el procedimiento común de aproximar el cilindro por un esferoide con las mismas relaciones axiales.