Energy and forces in boundary value problems of electrostatics are considered. It is well known that when boundary conditions can be simulated by electrical images, care must be taken in evaluating forces from energy. In this article, it is shown how the energy has to be corrected, in the general case, in order to be used as a force potential. Physical meaning of this correction is analyzed.
Electrical conductivity anisotropy of n-type indium selenide samples doped with different concentrations of tin is studied between 30 and 300 K. The anisotropy ratio is found to depend exponentially on the inverse temperature, the activation energy E , and the pre-exponential factor varying with free carrier concentration. This behaviour is explained by the existence of potential wells created by planar aggregates of ionized donor impurities screened by free electrons. A simple model in which the depth of these potential wells is calculated as a function of temperature, charge density in the planar defects, and electron concentration, gives account of the measured activation energies, but does not explain the high value of the anisotropy ratio. The existence of strictly two-dimensional electrons bound to planar defects not contributing to the electrical conduction across the layers is proposed to explain this result.Es wird die Anisotropie der elektrischen Leitfahigkeit von n-leitenden Indiumselenidproben, die mit verschiedenen Konzentrationen von Zinn dotiert sind, zwischen 30 and 300 K untersucht. Es wird gefunden, daS das Anisotropieverhaltnia exponentiell von der inversen Temperatur abhangt, wobei die Aktivierungsenergie K und der exponentielle Vorfaktor mit der Konzentration freier Ladungstriiger variiert. Dieses Verhalten wird mit der Existenz von Potentialmulden erkliirt, die durch ebene Assoziate von ionisierten Donator-Storstellen erzeugt werden, die durch freie Elektronen abgcschirmt werden. Ein einfaches Modell, mit dem die Tiefe dieser Potentialniipfe als Funktion der Temperatur, Ladungsdichte in den planaren Defekten und Elektronenkonzentration berechnet wird, erklllrt die gemessenen Aktivierungsenergien, jedoch nicht den hohen Wert des Anisotropieverh<nisses. Die Existenz von strikt zweidimensionalen Elektronen, die an planare Defekte gebunden sind und nicht zur elektrischen Leitfahigkeit durch die Schichten hindurch beitragen, wird zur Erklarung dieses Ergebnisses vorgeschlagen. l )
The fields of the reflected and refracted waves produced when a plane electromagnetic wave impinges on a plane boundary are related to the incident fields by means of a tensorial transformation. This procedure allows a unified treatment of external, internal, and total internal reflection and is suitable for general problems involving transformations of electromagnetic waves. As an application, the transmitted fields for total internal reflection of a bounded electromagnetic beam are obtained.
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