Plasticity in pentacene thin films

We have investigated the structure, defects and plasticity of thermally evaporated thin films of the organic molecular semiconductor pentacene using X-ray Diffraction (XRD), Optical microscopy (OM), Transmission Electron Microscopy (TEM), Electron Diffraction (ED), and High Resolution Electron Microscopy (HREM). Using XRD the degree of (001) texturing present in the as-grown films was characterized. The nature of pentacene plasticity and deformation-induced molecular alignment was investigated using rubbing and scratching techniques, as well as nanoindentation. Rubbing of the bulk powder produced thin oriented films, and a deformation length scale dependence was seen. Under stress pentacene crystals initially fail by cracking, until they reach a critical size of about one micron, when they tend to plastically deform into thin sheets. Alignment of thermally evaporated films was achieved under a controlled load scratch, and the degree of molecular orientation inside the scratched region was directly imaged using HREM. Finally, using nanoindentation we measured pentacene's plastic hardness to be 0.25 GPa at a loading rate 0.05 mN/s. A loading rate dependence of the hardness and stiffness was measured, with thin films behaving harder and stiffer at faster indentation rates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44778/1/10853_2004_Article_5277106.pd

Defect-mediated curvature and twisting in polymer crystals

Crystalline polymer solids almost inevitably exhibit defects due to chain ends, chain folding and the limited molecular mobility. The defects result in local (dislocations, grain boundaries) or global (bending, twisting) distortions of the molecular symmetry with pronounced implications on materials properties. Depending on the localization of the deformation, continuous molecular distortions or chain scission are expected, resulting in distinct differences for the mechanical (crack formation) and optoelectronic properties (charge transport and delocalization), which become especially important in the light of the recent extraordinary developments in molecular electronics. Further studies of defect structure and properties in polymers are expected to result in an increasingly sophisticated understanding of the microstructure and microstructural evolution during processing necessary to control and optimize the nano- and micrometerscale structure of organic materials. Copyright © 2000 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35029/1/322_ftp.pd

ФОРМИРОВАНИЕ ПРОЕКТИВНОГО ПОКРЫТИЯ ГАЗОННОГО ТРАВОСТОЯ ПРИ ПРИМЕНЕНИИ МИНЕРАЛЬНЫХ И КРЕМНИЙСОДЕРЖАЩИХ УДОБРЕНИЙ

Silicon containing fertilizer “Siliplant” and mineral fertilizers are established to influence ornamental traits of lawn herbage. Increased projective covering of lawn herbage – meadow grass and red fes-cue – is marked with the preparation “Siliplant” and mineral fertilizers applied, particularly with their joint application. In the first and second years of research in dry and excessively humid vegetation periods the optimal results were obtained through the joint treatment with mineral fertilizers and the preparation “Siliplant”: the projective covering increased in the year of sowing by averaged 27.5 % in meadow grass and 25 % in red fescue versus the control, in the second year the covering went up by averaged 19.7 and 8.44 %, respectively. Mineral fertilizers applied increased the projective covering in the year of sowing on average by 22.5 % in meadow grass and by 20 % in red fescue, in the second year they did by 14.7 % and 6.25 %, respectively. The treatment with the silicon-containing preparation “Siliplant” increased the projective covering in the year of sowing by averaged 15 % in meadow grass and by 7.5 % in red fescue; in the second vegetation period the averaged effect of the treatment was by 6.58 and 1.51 % higher, respectively.Установлено влияние кремнийсодержащего удобрения «Силиплант» и минеральных удобрений на декоративные качества газонного травостоя. Отмечено увеличение проективного покрытия газонных травостоев мятлика лугового и овсяницы красной при применении препарата «Силиплант» и минеральных удобрений, особенно при их совместном использовании. В  первый и второй годы исследований при засушливом и избыточно влажном вегетационном периоде оптимальные результаты получены при применении минеральных удобрений совместно с препаратом «Силиплант»: проективное покрытие увеличивалось в год посева в среднем на 27,5% у мятлика лугового и на 25% у овсяницы красной по отношению к контролю, во второй год – на 19,7 и 8,44% соответственно. Применение минеральных удобрений увеличивало проективное покрытие в год посева в среднем на 22,5% у мятлика лугового и на 20% у овсяницы красной, во второй год на 14,7 и 6,25% соответственно. Применение кремнийсодержащего препарата «Силиплант» увеличивало проективное покрытие в год посева в среднем на 15% у мятлика лугового и на 7,5% у овсяницы красной; во втором вегетационном периоде на 6,58 и на 1,51% соответственно

A Prokaryotic Membrane Sculpting BAR Domain Protein

Bin/Amphiphysin/RVS (BAR) domain proteins belong to a superfamily of coiled-coil proteins influencing membrane curvature in eukaryotes and are associated with vesicle biogenesis, vesicle-mediated protein trafficking, and intracellular signaling. Here we report the first prokaryotic BAR domain protein, BdpA, from Shewanella oneidensis MR-1, known to produce redox-active membrane vesicles and micrometer-scale outer membrane extensions (OMEs). BdpA is required for uniform size distribution of membrane vesicles and scaffolding OMEs into a consistent diameter and curvature. Cryogenic transmission electron microscopy reveals a strain lacking BdpA produces lobed, disordered OMEs rather than membrane tubes produced by the wild type strain. Overexpression of BdpA promotes OME formation during conditions where they are less common. Heterologous expression results in OME production in Marinobacter atlanticus and Escherichia coli. Based on the ability of BdpA to alter membrane curvature in vivo, we propose that BdpA and its homologs comprise a newly identified class of prokaryotic BAR (P-BAR) domains

Nonisotropic Self-Organization of Single-Component Hairy Nanoparticle Assemblies

Solvent-free assemblies of hairy nanoparticles (HNPs) are providing avenues to avoid issues of mixing, agglomeration, and limited inorganic content that plague nanocompositses based on polymer–nanoparticle blending. Here we demonstrate that the order within, and the elongational characteristics of, the neat HNP assembly (aHNP) evolve as the architecture of the polymeric corona in solution transitions from the concentrated (CPB) to semidilute (SDPB) polymer brush regimes (silica nanoparticle: radius <i>r</i>₀ = 8 nm with 120 kDa polystyrene grafts at σ = 0.01–0.1 chains/nm²). Specifically, local HNP packing adopts a nonisotropic local arrangement at intermediate graft densities where the transition from CPB-to-SDPB in solution is approximately <i>r</i>₀. In concert, the neat HNP assembly responds to viscoelastic elongational deformation in a manner analogous to semicrystalline elastomers. Domain orientation under load and subsequent buckling upon recovery lead to the appearance of two- and four-point small-angle X-ray patterns. The correlation between the corona architecture of the HNP and the physical characteristics of the solvent-free aHNP provides a framework akin to block-copolymers to tune mechanical, optical, and electrical properties of fibers and films via ordered mesoscale morphology

Bioassembled Layered Silicate-Metal Nanoparticle Hybrids

Here we report on the bioenabled assembly of layered nanohybrids using peptides identified with regard to their affinity to the nanoparticle surface. A dodecamer peptide termed M1, determined from a phage peptide display library, was found to bind to the surface of a layered aluminosilicate (montmorillonite, MMT). Fusion of a metal binding domain to the M1 peptide or the M1 peptide by itself was able to direct the growth of metal nanoparticles, such as gold and cobalt-platinum, respectively, on the MMT. This method of producing hybrid nanoclay materials will have utility in catalytic, optical, biomedical, and composite materials applications

Large Scale Solution Assembly of Quantum Dot–Gold Nanorod Architectures with Plasmon Enhanced Fluorescence

Tailoring the efficiency of fluorescent emission <i>via</i> plasmon–exciton coupling requires structure control on a nanometer length scale using a high-yield fabrication route not achievable with current lithographic techniques. These systems can be fabricated using a bottom-up approach if problems of colloidal stability and low yield can be addressed. We report progress on this pathway with the assembly of quantum dots (emitter) on gold nanorods (plasmonic units) with precisely controlled spacing, quantum dot/nanorod ratio, and long-term colloidal stability, which enables the purification and encapsulation of the assembled architecture in a protective silica shell. Overall, such controllability with nanometer precision allows one to synthesize stable, complex architectures at large volume in a rational and controllable manner. The assembled architectures demonstrate photoluminescent enhancement (5×) useful for applications ranging from biological sensing to advanced optical communication