Solution-phase, triangular ag nanotriangles fabricated by nanosphere lithography

A novel method to produce solution-phase triangular silver nanoparticles is presented. Ag nanoparticles are prepared by nanosphere lithography and are subsequently released into solution. The resulting nanoparticles are asymmetrically functionalized to produce either single isolated nanoparticles or dimer pairs. The structural and optical properties of Ag nanoparticles have been characterized. Mie theory and the Discrete Dipole Approximation method (DDA) have been used to model and interpret the optical properties of the released Ag nanoparticles.     

Transparent conducting oxides: texture and microstructure effects on charge carrier mobility in MOCVD-derived CdO thin films grown with a thermally stable, low-melting precursor

A series of low-melting, thermally stable cadmium metal-organic chemical vapor deposition (MOCVD) precursors have been synthesized, structurally and spectroscopically characterized, and implemented in growth of highly conductive and transparent CdO thin films. One member of the series, bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(N,N-diethyl-N',N'-dimethyl-ethylenediamine)cadmium(II), Cd(hfa)(2)()(N,N-DE-N',N'-DMEDA), represents a particularly significant improvement over previously available Cd precursors, owing to the low melting point and robust thermal stability. High-quality CdO films were grown by MOCVD on glass and single-crystal MgO(100) between 300 and 412 degrees C. Film growth parameters and substrate surface have large effects on microstructure and electron carrier transport properties. Enhanced mobilities observed for highly biaxially textured films grown on MgO(100) vs glass are attributed, on the basis of DC charge transport and microstructure analysis, to a reduction in neutral impurity scattering and/or to a more densely packed grain microstructure. Although single-grained films grown on MgO(100) exhibit greater mobilities than analogues with discrete approximately 100 nm grains and similar texture, this effect is attributed, on the basis of charge transport and Hall effect measurements as well as optical reflectivity analysis, to differences in carrier concentration rather than to reduced grain boundary scattering. Unprecedented conductivities and mobilities as high as 11,000 S/cm and 307 cm(2)/V.s, respectively, are obtained for epitaxial single-grained films (X-ray diffraction parameters: fwhm(omega) = 0.30 degrees, fwhm(phi) = 0.27 degrees ) grown in situ on MgO(100) at a relatively low temperature (400 degrees C).     

Encapsulating bis(beta-ketoiminato) polyethers. Volatile, fluorine-free barium precursors for metal-organic chemical vapor deposition

The synthesis, characterization, and incorporation in volatile metal-organic chemical vapor deposition (MOCVD) precursors of a new class of linked beta-ketoiminate-polyether-beta-ketoiminate ligands is presented. These ligands are designed to encapsulate alkaline-earth cations having low charges and large ionic radii. Barium complexes having the general formula Ba[(RCOCHC(R')N)2(R")] (R = tert-butyl or CF3; R' = tert-butyl, methyl, or CF3; R" = -(CH2CH2O)4CH2CH2- or -(CH2CH2O)5CH2CH2)-) were prepared and characterized by 1H and 13C NMR spectroscopy, elemental analysis, and mass spectrometry. Single-crystal X-ray diffraction analysis of 2,2,5,25,28,28-hexamethyl-9,12,15,18,21-pentaoxa-4,25-diene-6,24- diimino-3,27-pentacosadionatobarium(II) reveals a monomeric, nine-coordinate, tricapped trigonal prismatic coordination geometry. Single-crystal X-ray structural analysis of 1,1,1,24,24,24-hexafluoro-4,21-ditrifluoromethyl-8,11,14,17- tetraoxa-3,21-diene-5,20-diimino-2,23-tetracosadionatobarium(II).2DMSO reveals a monomeric, ten-coordinate, distorted tetracapped trigonal prismatic coordination geometry. Volatility data are presented for these barium complexes, demonstrating viability as MOCVD precursors. In addition, it is demonstrated that thin epitaxial films of BaTiO3 can be grown on (001) MgO by low-pressure MOCVD techniques using one of these barium complexes and Ti(dipivaloylmethanate)2(isopropoxide)2 as precursors.     

Structure of the first parallel DNA quadruplex-drug complex

The first crystal structure of a drug (daunomycin) bound to a parallel-stranded intermolecular telomeric G4 quadruplex (d(TGGGGT)4) has been determined to high resolution. A planar assemblage of three daunomycin molecules stacks onto the 5' end of the G4 column, with the daunosamine substituents occupying three of the four quadruplex grooves. The surface area of the terminal G-quartet in this parallel DNA quadruplex, presently occupied by three daunomycins, is sufficiently large that it could easily accommodate other potential telomerase inhibitors such as substituted porphyrins or telomestatin.     

High electron mobility in solution-cast and vapor-deposited phenacyl-quaterthiophene-based field-effect transistors: toward N-type polythiophenes

New carbonyl-functionalized quaterthiophenes, 5,5' '-diperfluorophenylcarbonyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DFCO-4T], 5,5' '-diphenyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DPCO-4T], and a polymer having the same basic motif as DFCO-4T, poly{1,4-bis[(3'-n-octyl-2,2'-dithiophene)carbonyl]-2,3,5,6-tetrafluorobenzene} [P(COFCO-4T)], have been synthesized, characterized, and the crystal structures of the molecules determined. Field-effect transistors fabricated with vapor-deposited and solution-cast films of DFCO-4T exhibit very high Ion:Ioff current ratios (up to 108) and electron mobilities up to approximately 0.51 and approximately 0.25 cm2.V-1.s-1, respectively. Solution-cast blends of P(COFCO-4T) and DFCO-4T (1:1 weight ratio) exhibit an electron mobility of approximately 0.01 cm2.V-1.s-1 (Ion:Ioff = 104).     

Growth and properties of particulate Fe films vapor deposited in UHV on planar alumina substrates

An integrated experimental approach was used to prepare and characterize well-defined particulate deposits of Fe on a variety of planar Al₂O₃ supports. The Fe particles were vapor deposited in UHV on in-situ cleaned and characterized amorphous and single crystal alumina supports at controlled substrate temperatures and deposition rates. Integrated support and deposit properties were monitored in-situ by AES, XPS, and LEED; particle number densities and sizes were monitored by standard TEM. It was found thata) metal exposure is an insufficient and often misleading measure of particle size when the support surface properties are unknown or poorly controlled,b) judicious combination of depostion temperature and impingement flux lead to size- and number density-controlled particulate deposits of good thermal stability, which can be improved by annealing. Preliminary results of XPS and of CO-TPD and H₂-TPD measurements exhibiting particle size effects are also reported.