Polarization fluctuation dominated electrical transport processes of polymer based ferroelectric-field-effect transistors

Ferroelectric field-effect transistors (FE-FETs) consisting of tunable dielectric layers are utilized to investigate interfacial transport processes. Large changes in the dielectric constant as a function of temperature are observed in FE-FETs in conjunction with the ferroelectric to paraelectric transition. The devices offer a test bed to evaluate specific effects of polarization on the electrical processes. FE-FETs have dominant contributions from polarization-fluctuation rather than static dipolar disorder prevalent in high k paraelectric dielectric-based FETs. Additionally, photo-excitation measurements in the depletion mode reveal clear features in the FET response at different temperatures, indicative of different transport regimes.Comment: 6 figure

Mechanism of Biocontrol of Aspergillus flavus in Groundnut by Species of Trichoderma

Aflatoxin contamination of groundnut by Aspergillus flavus is a serious problem affecting the quality and commercial value of groundnut kernels. Biological management of A. flavus infection at pre- and post-harvest levels by using species of Trichoderma is a promising approach. Trichoderma isolates from the fields of Andhra Pradesh and Karnataka states of India were evaluated for their ability to control A. flavus (strain Af 11-4) in the laboratory. Out of 212 isolates of Trichoderma, 36 were potent antagonists and these were analyzed for the production of volatile and diffusible antibiotics. Twenty-one of the 36 isolates produced volatile antibiotics and 15 produced diffusible antibiotics. Biocontrol mechanism of their action was analyzed by estimating extracellular enzyme production viz, chitinase, protease and glucanase. Maximum chitinase activity was associated with the isolate T. viride (Tv 24), T. pseudokoningii (Tp 29) and T. harzianum (Th 42). T. harzianum showed a maximum protease activity while T. koningii (Tk 83) and T. longibrachiatum (Tl 102) produced glucanases in the presence of glucose

Self-Assembled Photochromic Molecular Dipoles for High-Performance Polymer Thin-Film Transistors.

The development of high-performance multifunctional polymer-based electronic circuits is a major step toward future flexible electronics. Here, we demonstrate a tunable approach to fabricate such devices based on rationally designed dielectric super-lattice structures with photochromic azobenzene molecules. These nanodielectrics possessing ionic, molecular, and atomic polarization are utilized in polymer thin-film transistors (TFTs) to realize high-performance electronics with a p-type field-effect mobility (μFET) exceeding 2 cm2 V-1 s-1. A crossover in the transport mechanism from electrostatic dipolar disorder to ionic-induced disorder is observed in the transistor characteristics over a range of temperatures. The facile supramolecular design allows the possibility to optically control the extent of molecular and ionic polarization in the ultrathin nanodielectric. Thus, we demonstrate a 3-fold increase in the capacitance from 0.1 to 0.34 μF/cm2, which results in a 200% increase in TFT channel current

Electrically Induced Mixed Valence Increases the Conductivity of Copper Helical Metallopolymers

Abstract: Controlling the flow of electrical current at the nanoscale typically requires complex top‐down approaches. Here, a bottom‐up approach is employed to demonstrate resistive switching within molecular wires that consist of double‐helical metallopolymers and are constructed by self‐assembly. When the material is exposed to an electric field, it is determined that ≈25% of the copper atoms oxidize from CuI to CuII, without rupture of the polymer chain. The ability to sustain such a high level of oxidation is unprecedented in a copper‐based molecule: it is made possible here by the double helix compressing in order to satisfy the new coordination geometry required by CuII. This mixed‐valence structure exhibits a 104‐fold increase in conductivity, which is projected to last on the order of years. The increase in conductivity is explained as being promoted by the creation, upon oxidation, of partly filled d z 2 orbitals aligned along the mixed‐valence copper array; the long‐lasting nature of the change in conductivity is due to the structural rearrangement of the double‐helix, which poses an energetic barrier to re‐reduction. This work establishes helical metallopolymers as a new platform for controlling currents at the nanoscale

Competitive saprophytic ability of the sorghum stalk rot pathogens in fungicide amended soils

The competitive saprophytic ability (CSA) of the four sorghum stalk rot pathogens was estimated. Presence of fungicides in the soil as residues showed a profound effect iu reducing their CSA. Aureofungin has drastically reduced the CSA of all the stalk rot pathogens while carbendazim, quintazene and chloronab had severe effect. Methoxv ethvl mercuric chloride had the least effect

Comparisons of isolates of Fusarium avenaceum from white lupin and other crops by pathogenicity tests, DNA analyses and vegetative compatibility tests

Isolates of Fusarium avenaceum, mostly from crops of white lupin or wheat, were tested for pathogenicity on white lupin and wheat plants and compared by DNA tests and, in a limited study, vegetative compatibility. Most of the 80 isolates were pathogenic on both plant species after inoculation on shoot bases. Disease severity was greater at higher incubation temperatures that ranged from 15/10 degrees C to 25/20 degrees C (day/night temperatures). Isolates from lupin crops tended to be more pathogenic, on average, on lupins than on cereals. Polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of the rDNA distinguished two groups of isolates that occurred in different proportions among isolates from lupins and cereal crops. Random amplified polymorphic DNA (RAPD)-PCR analyses indicated considerable genetic variation among isolates, but there was some similarity among groups of isolates from populations in the same field. Genetic diversity was confirmed by a high degree of vegetative incompatibility among 20 isolates using nitrate nonutilizing mutants. There were no relationships among pathogenicity, RFLP group, RAPD group and vegetative compatibility group.Peer reviewe