John R. Ireland

Noncovalent functionalization of DNA-wrapped single-walled carbon nanotubes with platinum-based DNA cross-linkers.

A method for noncovalent functionalization of DNA-wrapped single-walled carbon nanotubes (SWNTs) using platinum-based DNA cross-linkers is investigated. In particular, cisplatin and potassium tetrachloroplatinate are shown to bind to DNA that encapsulates SWNTs in aqueous solution. The bound platinum salt can then be reduced to decorate the DNA-encapsulated SWNTs with platinum nanoparticles. The resulting SWNT/DNA/Pt hybrids are investigated by optical absorption spectroscopy, circular dichroism spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The unique combination of catalytic activity of nanoscale platinum, biological functionality of DNA, and optoelectronic properties of SWNTs suggests a myriad of applications including fuel cells, catalysts, biosensors, and electrochemical devices.

new ternary aluminides grown from aluminum flux

Abstract A series of ternary aluminide intermetallics with a new structure type were formed from the reaction of gold and rare-earth metals in aluminum flux. The REAu3Al7 structure was obtained with all rare earths RE with the exception of La and Eu. These materials crystallize in the rhombohedral space group R-3c, with unit cell parameters a=8.0922(6) A and c=21.066(2) A for PrAu3Al7 as an example. The variation in cell edges with rare-earth size is regular with the exception of the Yb analogue. The possible mixed valency indicated by this result was confirmed by magnetic susceptibility measurements. Density functional theory-based band structure calculations on YbAu3Al7 indicate the ytterbium f-orbitals are located just below the Fermi level, further supporting the mixed valence description of this material.

Synthesis, crystal structure and thermoelectric properties of β-K 2Bi 8Se 13 solid solutions

Solid solution series of the type K 2 Bi 8-x Sb x Se 13 , K 2-x Rb x Bi 8 Se 13 as well as K 2 Bi 8 Se 13-x S x were prepared and the distribution of the atoms (Bi/Sb, K/Rb and Se/S) on different crystallographic sites, the band gaps and their thermoelectric properties were studied. The distribution Se/S appears to be more uniform than the distribution of the Sb and Rb atoms in the β-K 2 Bi 8 Se 13 structure that shows preference in specific sites in the lattice. Band gap is mainly affected by Sb and S substitution. Seebeck coefficient measurements showed n-type character for of all Se/S members. In the Bi/Sb series an enhancement of p-type character was observed. The thermoelectric performance as well as preliminary high temperature measurements suggest the potential of these materials for high temperature applications.

Syntheses, crystal structures, and physical properties of La 5Cu6O4S7 and La5Cu 6.33O4S7

Single crystal and bulk powder samples of the quaternary lanthanum copper oxysulfides La5Cu6.33O4S7 and La5Cu6O4S7 have been prepared by means of high-temperature sealed-tube reactions and spark plasma sintering, respectively. In the structure of La 5Cu6.33O4S7, Cu atoms tie together the fluorite-like (2)infinity[La5O4S(5+)] and antifluorite-like (2) infinity[Cu6S6(5-)] layers of La5Cu6O4S7. The optical band gap, E g, of 2.0 eV was deduced from both diffuse reflectance spectra on a bulk sample of La5Cu6O4S7 and for the (010) crystal face of a La 5Cu6.33O4S7 single crystal. Transport measurements at 298 K on a bulk sample of La 5Cu 6O 4S 7 indicated p-type metallic electrical conduction with sigma electrical =2.18 S cm(-1), whereas measurements on a La 5Cu6.33O4S7 single crystal led to sigma electrical =4.5 10(-3) S cm(-1) along [100] and to semiconducting behavior. In going from La 5Cu6O4S7 to La5Cu6.33O4S7, the disruption of the (2)infinity[Cu6S6(5-)] layer and the decrease in the overall Cu(2+)(3d(9)) concentration lead to a significant decrease in the electrical conductivity.

Syntheses, Crystal Structures, and Physical Properties of La5Cu6O4S7and La5Cu6.33O4S7

Single crystal and bulk powder samples of the quaternary lanthanum copper oxysulfides La5Cu6.33O4S7 and La5Cu6O4S7 have been prepared by means of high-temperature sealed-tube reactions and spark plasma sintering, respectively. In the structure of La 5Cu6.33O4S7, Cu atoms tie together the fluorite-like (2)infinity[La5O4S(5+)] and antifluorite-like (2) infinity[Cu6S6(5-)] layers of La5Cu6O4S7. The optical band gap, E g, of 2.0 eV was deduced from both diffuse reflectance spectra on a bulk sample of La5Cu6O4S7 and for the (010) crystal face of a La 5Cu6.33O4S7 single crystal. Transport measurements at 298 K on a bulk sample of La 5Cu 6O 4S 7 indicated p-type metallic electrical conduction with sigma electrical =2.18 S cm(-1), whereas measurements on a La 5Cu6.33O4S7 single crystal led to sigma electrical =4.5 10(-3) S cm(-1) along [100] and to semiconducting behavior. In going from La 5Cu6O4S7 to La5Cu6.33O4S7, the disruption of the (2)infinity[Cu6S6(5-)] layer and the decrease in the overall Cu(2+)(3d(9)) concentration lead to a significant decrease in the electrical conductivity.

Syntheses, crystal structures, and physical properties of La 5 Cu 6 O 4 S 7 and La 5 Cu 6.33 O 4 S 7

Single crystal and bulk powder samples of the quaternary lanthanum copper oxysulfides La5Cu6.33O4S7 and La5Cu6O4S7 have been prepared by means of high-temperature sealed-tube reactions and spark plasma sintering, respectively. In the structure of La 5Cu6.33O4S7, Cu atoms tie together the fluorite-like (2)infinity[La5O4S(5+)] and antifluorite-like (2) infinity[Cu6S6(5-)] layers of La5Cu6O4S7. The optical band gap, E g, of 2.0 eV was deduced from both diffuse reflectance spectra on a bulk sample of La5Cu6O4S7 and for the (010) crystal face of a La 5Cu6.33O4S7 single crystal. Transport measurements at 298 K on a bulk sample of La 5Cu 6O 4S 7 indicated p-type metallic electrical conduction with sigma electrical =2.18 S cm(-1), whereas measurements on a La 5Cu6.33O4S7 single crystal led to sigma electrical =4.5 10(-3) S cm(-1) along [100] and to semiconducting behavior. In going from La 5Cu6O4S7 to La5Cu6.33O4S7, the disruption of the (2)infinity[Cu6S6(5-)] layer and the decrease in the overall Cu(2+)(3d(9)) concentration lead to a significant decrease in the electrical conductivity.

New Low-melting Cadmium Precursors for the Detailed Study of Texture Effects in MOCVD Derived CdO Thin-Films

from SciFinder

Initial assessment of the thermoelectric properties for the mixed system K2-xRbxBi8Se13

In previous studies we have investigated the thermoelectric properties of undoped and doped compositions of β-K2Bi8Se13. The attempt to substitute Rb for K resulted in a different structure type, but with potentially useful thermal properties. In this paper the results of measuring the thermoelectric properties of small crystalline samples for K2-xRbxBi8Se13 solid solutions are reported for the compositional ranges with 0 ≤ x ≤ 1 and with 1.8 ≤ x ≤ 2. The presence of rubidium provides a significant improvement in the thermopower but has much less of an effect on the electrical conductivity. The combined results are reflected in the power factor behavior as a function of temperature.

Transport properties of the doped thermoelectric material /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/

The synthesis, physicochemical, spectroscopic, and structural characterization of the compounds /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/, K/sub 2/Sb/sub 8/Se/sub 13/, K/sub 2.5/Bi/sub 8.5/Se/sub 14/, and K/sub 2.5/Sb/sub 8.5/Se/sub 14/ have been previously reported and show promising properties for thermoelectric applications. While /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/ is isostructural with K/sub 2/Bi/sub 7/S/sub 13/, the isostructural K/sub 2.5/Bi/sub 8.5/Se/sub 13/ and K/sub 2.5/Sb/sub 8.5/Se/sub 14/ are different but have similar structural features to /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/. Compared with /spl alpha/-K/sub 2/Bi/sub 3/Se/sub 13/, which has a room temperature electrical conductivity of 2 S/cm and a Seebeck coefficient ranging from -210 to -260 /spl mu/V/K, /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/ shows excellent electrical conductivity values at room temperature while maintaining high Seebeck coefficients. In this work the doping of the homologous compound /spl beta/-K/sub 2/Bi/sub 8/Se/sub 13/ was explored by employing varying concentrations of different dopants. Where possible, transport measurements were carried out on both single crystal and polycrystalline ingot material. From these data the trends in the key parameters were identified for optimizing the power factor and figure of merit.