Physics

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Shiv Nadar University

Charge transport in copper phthalocyanine (CuPc), partially fluorinated CuPc(F4CuPc), and fluorinated CuPc(F16CuPc) based organic thin film transistors is studied using dual SiO2/ polymethylmethacrylate gate dielectrics. We demonstrate the strong influence of air/moisture induced electron traps on electron transport when the lowest unoccupied molecular orbital is close to the vacuum irrespective of hydroxyl-free dielectrics used in the devices. © 2010 American Institute of Physics.

(SoNS) School of Natural Sciences

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Journal of Applied Physics

Electron transport in copper phthalocyanines

Knowledge of the elastic properties of Li-Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05-0.20 and 0.20-0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30-40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes. © 2010 Elsevier B.V. All rights reserved.

Journal of Power Sources

Elastic softening of amorphous and crystalline Li-Si Phases with increasing Li concentration: A first-principles study

A new, solution-processable, low-bandgap, diketopyrrolopyrrole- benzothiadiazole-based, donor-acceptor polymer semiconductor (PDPP-TBT) is reported. This polymer exhibits ambipolar charge transport when used as a single component active semiconductor in OTFTs with balanced hole and electron mobilities of 0.35 cm2 V-1s-1 and 0.40 cm 2 V-1s-1, respectively. This polymer has the potential for ambipolar transistor-based complementary circuits in printed electronics. Copyright © 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Advanced Materials

A low-bandgap diketopyrrolopyrrole-benzothiadiazole-based copolymer for high-mobility ambipolar organic thin-film transistors

We argue that supersymmetric transformation could be applied across the heterojunction formed by joining of two mixed semiconductors. A general framework is described by specifying the structure of ladder operators at the junction for making quantitative estimation of physical quantities. For a particular heterojunction device, we show that an exponential grading inside a nanoscale doped layer is amenable to exact analytical treatment for a class of potentials distorted by the junctions through the solutions of transformed Morse-type potentials. © 2010 Elsevier B.V. All rights reserved.

Physics Letters, Section A: General, Atomic and Solid State Physics

Supersymmetry across nanoscale heterojunction

A novel series of soluble thieno[3,2-b]thiophene (TT) oligomers with alternating TT and bithiophene or fluorene triad architectures have been synthesized for field-effect transistor (FET) applications. Their optical, thermal and electronic properties were investigated using UV-Vis and photoluminescence spectroscopy, thermal gravimetric analysis, and cyclic voltammetry. Compared with α,α′-dihexylsexithiophene (D6HT), these oligomers exhibit blue-shifted absorption spectra, 0.1 eV to 0.3 eV lower than the highest occupied molecular orbital (HOMO) energy levels and accordingly higher ambient stability. Their crystallinity and morphology features of these oligomers were further investigated with X-ray diffraction and atomic force microscopy using vacuum-deposited thin film on Si/SiO2 substrate. Symmetrically structured TT-oligomers including HT2TT, HTTT2, HTTTT and DDFTT exhibit ordered film morphology and promising FET performance with devices fabricated by either vacuum deposition or solution processing techniques. Interestingly, HTTT2 shows interconnected terrace island morphology, which is often observed for pentacene. All p-type transistors show promising performance, with HT2TT demonstrating a hole mobility up to 0.025 cm2V -1s-1 and an on/off current ration ∼1.2 × 103 with vacuum sublimated film deposited on 70 °C substrate. © The Royal Society of Chemistry 2010.

Journal of Materials Chemistry

Synthesis of thieno[3,2-b]thiophene derived conjugated oligomers for field-effect transistors applications

We demonstrate doping of nanocrystalline CdS thin films with Co ions by ion implantation at an elevated temperature of 573 K. The modifications caused in structural and optical properties of these films are investigated. Co-doping does not lead to amorphization or formation of any secondary phase precipitate for dopant concentrations in the range of 0.34-10.8 at.% used in the present study. However, we observe a systematic reduction in the d-spacing with increasing cobalt concentration. Optical band gap of CdS does not show any obvious change upon Co-doping. In addition, implantation gives rise to grain growth and increase in the surface roughness. The results are discussed in the light of ion-matter interaction in the keV regime. © The Royal Society of Chemistry 2010.

Nanoscale

Effect of substrate temperature on implantation doping of Co in CdS nanocrystalline thin films

In this work, an extended elliptic function method is proposed and applied to the generalized shallow water wave equation. We systematically investigate on how to classify new exact travelling wave solutions expressible in terms of quasi-periodic elliptic integral functions and doubly periodic Jacobian elliptic functions. The derived new solutions include rational, periodic, singular and solitary wave solutions. An interesting comparison with the canonical procedure is provided. In some cases the obtained elliptic solution has singularity at a certain region in the whole space. For such solutions we have computed the effective region where the obtained solution is free from such a singularity. © 2010 The Royal Swedish Academy of Sciences.

Physica Scripta

New exact solutions of a generalized shallow water wave equation

We continue the previous study on the existence of different intermediate Hamiltonians in type A N-fold supersymmetric systems and carry out an exhaustive investigation on the N=3 case. In contrast with the N=2 case, we find various patterns in the existence of intermediate Hamiltonians due to the presence of two different intermediate positions in a factorized type A 3-fold supercharge. In addition, all the N=3 models are strictly restricted to at most elliptic type, which enables us to make the complete classification of the systems which admit intermediate Hamiltonians. Finally, we show realizations of third-order parasupersymmetry and variant generalized 3-fold superalgebras by such systems. © 2010 Elsevier Inc.