Nanoparticulate metals and semiconductors that have atomic arrangements at the interface of molecular clusters and "infinite" solid-state arrays of atoms have distinctive properties determined by the extent of confinement of highly delocalized valence electrons. At this interface, the total number of atoms and the geometrical disposition of each atom can be used to significantly modify the electronic and photonic response of the medium. In addition to teh novel inherent physical properties of the quantum-confined moieties, their "packaging" into nanocomposite bulk materials can be used to define the confinement surface states and environment, intercluster interactions, the quantum-confinement geometry, and the effective charge-carrier density of the bulk. Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.

https://science.sciencemag.org/content/sci/247/4943/669.full.pdf

Quantum confinement and host/guest chemistry: probing a new dimension.

Phase relations and structures of solids at high pressures

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.

Mobilization of Selenite by Ralstonia metallidurans CH34

Mittels Drehkristall- und WEISSENBERG-Aufnahmen werden die Abmessungen der Elementarzelle und die Ebenenstatistik bestimmt. Die monokline Zelle mit der wahrscheinlichen Raumgruppe P 21/m besitzt folgende Gitterkonstanten: 






Die rontgenographische Dichte ist ∥r = 5,70 gcm−3. In der Zelle sind 2 Formeleinheiten ZrSe3 enthalten. An Hand von PATTERSON- und FOURIER-Projektionen werden die Koordinaten der Atome ermittelt: 






. Zirkontriselenid bildet ein Schichtengitter, das leicht zu Verzwillingungen neigt. Die Struktur wird eingehend beschrieben. Eine Moglichkeit des Entstehens der Zwillinge wird diskutiert.



The unit cell of ZrSe3 and the statistics of the reflections are determined by rotation and WEISSENBERG photographs. The monoclinic cell with the probable symmetry group P 21/m has the following lattice constants: a = 5.41, b = 3.77, c = 9.45; β = 97.5°. The density is ∥r = 5.70 gcm−3. There are 2 formula units of ZrSe3 within the cell. The atomic parameters are determined by two-dimensional PATTERSON and FOURIER syntheses (data see „Inhaltsubersicht”).



ZrSe3 forms a layer lattice. Twins are easily created. The structure and possibility of building twins are discussed.

Die Struktur des Zirkontriselenids ZrSe3

The vapor compositions of SrSe, CdSe, HgSe, hexagonal selenium, α‐monoclinic selenium, and some mixed sulfur—selenium crystals have been studied by mass‐spectrometric analysis. Dissociation energies of Se2 (71.2±2 kcal/mole) and SrSe (59.1±3 kcal/mole) were obtained. The heats and free energies of formation of the various Sen molecular species detected in the vapor are also given. There is no significant difference between the vaporization behavior of the two Se allotropes. Mixed sulfur—selenium molecules form very slowly at room temperature, but they form more readily at higher temperature, and quenching to room temperature retains the mixed configurations.

Equilibrium Composition of Selenium Vapor; the Thermodynamics of the Vaporization of HgSe, CdSe, and SrSe

The crystal structure of β selenium

The crystal structure of beta-selenium Locality: synthetic Note: structure known as beta phase Note: cell parameters taken from Acta Crystallographica 5 (1952) 236-246

J. D. McCullough

Papers

The crystal structure of β selenium

The crystal structure of beta-selenium Locality: synthetic Note: structure known as beta phase Note: cell parameters taken from Acta Crystallographica 5 (1952) 236-246