Core/Shell PbSe/PbS QDs TiO2 Heterojunction Solar Cell

Quasi type‐II PbSe/PbS quantum dots (QDs) are employed in a solid state high efficiency QD/TiO₂ heterojunction solar cell. The QDs are deposited using layer‐by‐layer deposition on a half‐micrometer‐thick anatase TiO₂ nanosheet film with (001) exposed facets. Theoretical calculations show that the carriers in PbSe/PbS quasi type‐II QDs are delocalized over the entire core/shell structure, which results in better QD film conductivity compared to PbSe QDs. Moreover, PbS shell permits better stability and facile electron injection from the QDs to the TiO₂ nanosheets. To complete the electrical circuit of the solar cell, a Au film is evaporated as a back contact on top of the QDs. This PbSe/PbS QD/TiO₂ heterojunction solar cell produces a light to electric power conversion efficiency (η) of 4% with short circuit photocurrent (J_sc) of 17.3 mA/cm². This report demonstrates highly efficient core/shell near infrared QDs in a QD/TiO₂ heterojunction solar cell.     

Computational fractal geometry with WFA

We define two measures of “fractalness” of gray-tone images: the degree of self-similarity and the gray-tone fractal dimension as a generalization of Minkovski dimension of compact sets. We show how to compute both these measures from the WFA-representation of a gray-tone image. Since we have developed a WFA-inference algorithm which computes a good approximation of any gray-tone image we can compute a close approximation of both our measures of fractalness for any gray-tone image. Received: 15 November 1994 / 6 October 1995     

The Shockley-like equations for the carrier densities and the current flows in materials with a nonuniform composition

The basic equations for the current and carrier densities in materials with a nonuniform band structure are reviewed. These equations are then recast into forms containing the effective intrinsic carrier density n_ie and the intrinsic level E_i. The carrier densities formally attain the standard forms as given by Shockley; however, these forms must be interpreted with care. In particular, n_ie is not a constant and the intrinsic level E_i does not have the profile of the electrostatic potential energy t-eφ. The current densities are also recast into Shockley-like forms; extra terms arise over and above the conventional results.     

l2 projection in bounded-error estimation

The problem of parameter estimation from bounded-error data is considered. In particular, the possibilities of using an l₂ projection (least squares) procedure are explored. Exact as well as approximate (polytopic) outer-bounding solutions are proposed. the main properties and difficulties in implementation of the l₂ projection procedures are discussed and illustrated. Since these methods appear to be computationally cumbersome when the number of measurements is large, a simpler (rectangular) characterization of the solution set, as a result of natural interval calculations, is proposed and discussed.     

Some effects of menu characteristics and user personality on performance with menu-driven interfaces

User performance with menu-based systems was studied. Three experiments concerning the effects of menu structure, menu breadth, menu system depth, several support facilities and user personality characteristics on user performance, measured in terms of search time and accuracy, are reported. The main findings are that performance is affected by menu structure, the depth of the menu system, the presence of escape facilities, the structure of the alternatives within the menu, some methods of informative support and certain personality characteristics. Some expensive support facilities are found to have no effect. The results are discussed in relation to problems of menu interface design.     

Uranyl prepared by the internal gelation. Part I. The determination of the gelation regions in uranyl nitrate systems

In the present paper preparation conditions for the formation of various types of uranyl gel, using the internal gelation route, are described. Various types of the gel can be prepared differing in their physico-mechanical properties. The research parameters were selected with respect to practical preparation conditions. The results of the paper represent an attempt to investigate systematically some of the basic chemistry problems of the gel process.     

Dielectric relaxation in calcium titanate-containing ceramics prepared by plasma spraying

The relative permittivity and loss factor frequency dependence in a weak electric field of plasma sprayed perovskite and ilminite polycrystalline ceramic materials—pure synthetic calcium titanate, as well as magnesium titanate—calcium titanate mixture, were studied. It was observed that plasma-sprayed titanates exhibit a strong relaxation of permittivity and loss factor decrease when they are measured in an as-sprayed state. The frequency dependence of the earlier properties is influenced by chemical composition and spraying parameters, but the relaxation character in general is preserved in all cases. The volume resistivity of the samples in an as-sprayed as well as subsequently annealed state was studied also. Several aspects of the structural features of plasma deposits and their possible influence on dielectric properties are discussed.