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Shiv Nadar University

(SoNS) School of Natural Sciences

Ambipolar organic thin film transistors (OTFTs) based on a partially fluorinated copper phthalocyanine (F4CuPc) were fabricated and characterized. We have demonstrated that the ambipolar charge transport is primarily dependent on the gate dielectric/ organic semiconductor interface © 2007 IEEE.

Physics

World University root node

Proceedings of the 14th International Workshop on the Physics of Semiconductor Devices, IWPSD

F4CuPc based ambipolar organic thin-film transistors

The crystal structure of the N,N,N′,N′- tetramethylethylenediammonium dithiocyanate salt has been examined by experimental charge density studies from high-resolution X-ray diffraction data. The corresponding results are compared with multipole refinements, using theoretical structure factors obtained from a periodic density functional theory calculation at the B3LYP level with a 6-31G** basis set. The salt crystallizes in space group P1̄ and contains only a single ion pair with an inversion center in the cation. The salt has thus one unique classical N +-H⋯(NCS)- hydrogen bond but also has six other weaker interactions: four C-H⋯S, one C-H⋯N, and one C-H⋯Cπ. The nature of all these interactions has been examined topologically using Bader's quantum theory of "atoms in molecules" and all eight of the Koch-Popelier criteria. The experimental and theoretical approaches agree well and both show that the inter-ion interactions, even in this simplest of systems, play an integrated and complex role in the packing of the ions in the crystal. Electrostatic potential maps are derived from experimental charge densities. This is the first time such a system has been examined in detail by these methods. © 2007 American Chemical Society.

Chemistry

Journal of Physical Chemistry A

Investigation of inter-ion interactions in N,N,N′N′- tetramethylethylenediammonium dithiocyanate via experimental and theoretical charge density studies

Aurivillius type bismuth layer structured ferroelectrics (BLSF) have been found to possess strong relationship between tetragonal strain (c/a) and extrinsic/ intrinsic conductivity. The extrinsic part of the conductivity is known to depend upon space charge in the sample. The present paper discusses effects of 30 atomic % doping of Ca, La and Pb on tetragonal strain, conductivity and dielectric constant/loss with temperature and frequency. Tetragonal strain increases on doping calcium and lead while it shows a decrease on doping lanthanum. The calcium and lanthanum doped samples show pronounced space charge part of dielectric constant while lead doped sample shows nearly constant permittivity values. No phase transition is observed in the calcium doped sample up to 600°C while for the lanthanum doped sample a decrease of 141°C is observed in the value of Curie temperature compared to that for the undoped sample.

Ferroelectrics

Electrical investigations of aurivillius type Sr0.7A 0.3Bi2Nb2O9 (A = Ca, La and Pb) ferroelectric ceramics

We report the observation of an intermediate mesh phase with rhombohedral symmetry, corresponding to the space group R3m, in a mixed surfactant system formed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the organic salt 3-sodium-2-hydroxy naphthoate (SHN). It occurs between a random mesh phase (LαD) and a lamellar phase (L α) at low temperatures; at higher temperatures, the L αD phase transforms continuously into the L α phase with an increasing surfactant concentration (φs). To separate the effects of salt and φs on the phase behavior, the ternary system consisting of cetyltrimethylammonium 3-hydroxy-naphthalene-2-carboxylate (CTAHN), sodium bromide (NaBr), and water was studied. The intermediate mesh phase is found in this system at high NaBr concentrations. The micellar aggregates, both in the intermediate and random mesh phases, are found to be made up of a two-dimensional network of rod-like segments, with three rods meeting at each node. The average mesh size increases with φs, and the transition from the random mesh phase to the intermediate phase is found to occur when it is approximately 1.5 times the lamellar periodicity. The intermediate mesh phase is absent in the equimolar dodecyltrimethylammonium bromide (DTAB)-SHN system, indicating the role of the surfactant chain length in the formation of this phase. This system exhibits a random mesh phase over a very wide range of water content, with the average mesh size decreasing upon an increasing φs, contrary to the trend seen in the CTAB-SHN system. © 2007 American Chemical Society.

Langmuir

Structure of mesh phases in a cationic surfactant system with strongly bound counterions

We report a study on the feasibility of using an intramolecular dipole to enhance charge separation for organic photovoltaic applications. We have developed a poly(1,4-phenylenevinylene) derivative, poly{2-[(9,9-di-n-propyl-9H-7-nitrofluoren-2-yl)]-5-(2-ethylhexyloxy)-1,4-phenylenevinylene} 12, which has electronically asymmetric chromophores as a result of the para attachment of alkoxy and nitrofluorenyl groups on the phenyl units of the polymer backbone. The luminescence of the polymer with the electronically asymmetric chromophores was found to be smaller by a factor of eight when compared to the equivalent polymer but without the nitro group attached to the fluorenyl unit. Light-induced electron spin resonance experiments showed that the polymer with the electronically asymmetric chromophores had more photo-induced spins, showing that the quenching of the luminescence was due to intramolecular charge separation. Single layer photovoltaic devices containing neat films of 12 showed efficiencies similar to other single layer devices and this was ascribed to poor transport of the separated charges. This was confirmed by a strong improvement in device power efficiency to 0.52% at AM1.5 by blending the polymer with an electron transporting material. © 2007 Elsevier B.V. All rights reserved.

Organic Electronics

Electronically asymmetric poly(1,4-phenylenevinylene)s for photovoltaic cells

The interrelationship of latency period in viral infection and overall infection process in host community are of critical importance in context of pest control programme. Both of them regulate the overall system stability as they are dynamically linked to predation by natural enemies in the system. The present paper deals with the role of latency period in viral infection through mathematical modeling and analysis. We propose a four dimensional mathematical model with delayed infection in pest community. It is shown that there exists a certain value of delay, say T* such that for T &gt; T* the system exhibits global stability towards disease-free equilibrium. But for T &lt; T* system exhibits stability switches of the endemic equilibrium. Finally, some conclusive remarks have been drawn through numerical simulations of the model. © 2007 Elsevier Inc. All rights reserved.

Mathematics

Mathematical Biosciences

Role of latency period in viral infection: A pest control model

The object of the present paper is to study an integrated pest management (IPM) problem in an agroecosystem (paddy-fish culture) through mathematical modeling and analysis, where release of sterile males and spraying of pesticide have been used as control measures for pest population. Using optimal analysis of the model, we have shown that restricted and proper use of control measures might enhance the crop production of the system in an economically viable way. The paper also considers the vulnerability of the underlined ecosystem due to the effect of temperature on the pest growth. Using Liapunov-like function, we have found out a suitable range of temperature, where this IPM strategy remains effective. Some important remarks have finally been made on the basis of numerical simulation. © 2006 Elsevier Inc. All rights reserved.

An improved integrated pest management model under 2-control parameters (sterile male and pesticide)

In the present study, 3217 UniGene sequences of Neurospora crassa downloaded from the National Center for Biotechnology Information (NCBI) were mined for the identification of microsatellites or simple sequence repeats (SSRs). A total of 287 SSRs detected gives density of 1SSR/14.6 kb of 4187.86 kb sequences mined suggests that only 250 (7.8%) of sequences contained SSRs. Depending on the repeat units, the length of SSRs ranged from 14 to 17 bp for mono-, 14 to 48 bp for di-, 18 to 90 bp for tri-, 24 to 48 bp for tetra-, 30 for penta- and 42 to 48 bp for hexa-nucleotide repeats. Tri-nucleotide repeats were the most frequent repeat type (88.8%) followed by di-nucleotide repeats (5.9%). An attempt was also made with the help of bioinformatics approach to find out primer pairs for identified SSRs and primers were found only for 239 sequences. But, this part needs experimental validation. Annotation of SSRs containing sequences was also carried out. © 2006 Elsevier GmbH. All rights reserved.

Life Sciences

Fulltext

Microbiological Research

In silico mining in expressed sequences of Neurospora crassa for identification and abundance of microsatellites

Ion implantation used for doping quartz with photoactive impurity atoms amorphizes the matrix already at moderate fluences. Following our recent studies on dynamic, laser-induced or chemical epitaxy of ion-irradiated α-quartz, this paper focuses on the cathodoluminescence (CL) spectra obtained after Ge, Ba, Rb and double Rb/Ge ion implantation, under the conditions of dynamic or chemical epitaxy. In addition to "intrinsic" subbands in the CL-spectra, several blue and violet bands correlated with the particular implanted ion species were observed. In the case of Ba, nearly complete dynamic epitaxial growth was achieved, but not for Ge. In the case of Rb, full chemical epitaxy was obtained upon annealing in oxygen or air, but the CL output decreased above 1000 K due to Rb outdiffusion. Double Rb/Ge implantation and annealing in air appears as a very promising novel route to achieve high CL light output and full recrystallization. © 2005 Elsevier B.V. All rights reserved.