Physics

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Shiv Nadar University

A novel solution processable donor-acceptor (D-A) based low band gap polymer semiconductor poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4- c]pyrrole-1,4-dione-alt-thienylenevinylene} (PDPPF-TVT), was designed and synthesized by a Pd-catalyzed Stille coupling route. An electron deficient furan based diketopyrrolopyrrole (DPP) block and electron rich thienylenevinylene (TVT) donor moiety were attached alternately in the polymer backbone. The polymer exhibited good solubility, film forming ability and thermal stability. The polymer exhibits wide absorption bands from 400 nm to 950 nm (UV-vis-NIR region) with absorption maximum centered at 782 nm in thin film. The optical band gap (Eoptg) calculated from the polymer film absorption onset is around 1.37 eV. The π-energy band level (ionization potential) calculated by photoelectron spectroscopy in air (PESA) for PDPPF-TVT is around 5.22 eV. AFM and TEM analyses of the polymer reveal nodular terrace morphology with optimized crystallinity after 200 °C thermal annealing. This polymer exhibits p-channel charge transport characteristics when used as the active semiconductor in organic thin-film transistor (OTFT) devices. The highest hole mobility of 0.13 cm 2 V -1 s -1 is achieved in bottom gate and top-contact OTFT devices with on/off ratios in the range of 10 6-10 7. This work reveals that the replacement of thiophene by furan in DPP copolymers exhibits such a high mobility, which makes DPP furan a promising block for making a wide range of promising polymer semiconductors for broad applications in organic electronics. © The Royal Society of Chemistry 2012.

World University root node

(SoNS) School of Natural Sciences

Fulltext

Journal of Materials Chemistry

Furan substituted diketopyrrolopyrrole and thienylenevinylene based low band gap copolymer for high mobility organic thin film transistors

The recent up to ~2 fb -1 of data from the ATLAS and CMS experiments at the CERN Large Hadron Collider at 7 TeV put an upper bound on the production cross section of a Higgs-like particle. We translate the results of the H→WW→lνlν and H→γγ as well as the combined analysis by the ATLAS and CMS into an allowed region for the Kaluza-Klein (KK) mass M KK and the Higgs mass M H for all the known Universal Extra Dimension (UED) models in five and six dimensions. Our bound is insensitive to the detailed KK mass splitting and mixing and hence complementary to all other known signatures. © 2011 Elsevier B.V.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

A bound on universal extra dimension models from up to 2 fb -1 of LHC data at 7 TeV

We report hole and electron doping in Y0.38La 0.62(Ba2-xLax)Cu3Oy thin films synthesized by the pulsed laser deposition technique and subsequently annealed in oxygen ambient or in a vacuum. X-ray diffraction studies suggested a single phase in p-type thin films and transport measurements showed a superconductor-to-insulator transition at x = 0.46. Hall measurements indicated electrons were successfully doped when the thin films were annealed in vacuum. The n-type samples demonstrated metallic behaviour within moderate temperature ranges, and a low in-plane resistivity (ρab) and a high carrier density for 0.32 ≤ x ≤ 0.46. The increase in ρab for higher La doping levels, probably caused by charge compensation, is also discussed. The present result could be a significant step in searching for electron-doped superconductivity in the YBa2Cu3Oy system. © 2012 IOP Publishing Ltd.

Superconductor Science and Technology

The influence of la substitution and oxygen reduction in ambipolar La-doped YBa2Cu3Oy thin films

Electrostatic self-assembly of colloidal and nanoparticles has attracted a lot of attention in recent years, since it offers the possibility of producing novel crystalline structures that have the potential to be used as advanced materials for photonic and other applications. The stoichiometry of these crystals is not constrained by charge neutrality of the two types of particles due to the presence of counterions, and hence a variety of three-dimensional structures have been observed depending on the relative sizes of the particles and their charge. Here we report structural polymorphism of two-dimensional crystals of oppositely charged linear macroions, namely DNA and self-assembled cylindrical micelles of cationic amphiphiles. Our system differs from those studied earlier in terms of the presence of a strongly binding counterion that competes with DNA to bind to the micelle. The presence of these counterions leads to novel structures of these crystals, such as a square lattice and a √3 x √3 superlattice of an underlying hexagonal lattice, determined from a detailed analysis of the small-angle diffraction data. These lower-dimensional equilibrium systems can play an important role in developing a deeper theoretical understanding of the stability of crystals of oppositely charged particles. Further, it should be possible to use the same design principles to fabricate structures on a longer length-scale by an appropriate choice of the two macroions.

Proceedings of the National Academy of Sciences of the United States of America

Tuning DNA-amphiphile condensate architecture with strongly binding counterions

American Journal of Physics

Erratum: “An elementary exposition of the Efimov effect” [Am. J. Phys. 79, 274–281 (2011)]

As printed and flexible plastic electronic gadgets become increasingly viable today, there is a need to develop materials that suit the fabrication processes involved. Two desirable requirements are solution-processable active materials or precursors and low-temperature processability. In this article, we describe a straightforward method of depositing ZnO films by simple spin coating of an organometallic diethylzinc precursor solution and annealing the resulting film at low temperatures (≤200 °C) without involving any synthetic steps. By controlling the humidity in which annealing is conducted, we are able to adjust the intrinsic doping level and carrier concentration in diethylzinc-derived ZnO. Doped or conducting transport layers are greatly preferable to undoped layers as they enable low-resistance contacts and minimize the potential drops. This ability to controllably realize doped ZnO is a key feature of the fabrication process that we describe in this article. We employ field-effect measurements as a diagnostic tool to measure doping levels and mobilities in ZnO and demonstrate that doped ZnO with high charge carrier concentration is ideal for solar cell applications. Respectable power conversion efficiencies (up to 4.5\%) are achieved in inverted solar cells that incorporate diethylzinc-derived ZnO films as the electron transport layer and organic blends as the active material. Extensions of this approach to grow ternary and quaternary films with organometallic precursor chemicals will enable solution based growth of a number of semiconductor films as well as a method to dope them. © 2012 The Royal Society of Chemistry.

ZnO layers for opto-electronic applications from solution-based and low-temperature processing of an organometallic precursor

A real time contamination of the Ru surface and corresponding effect on its work function were studied using extreme ultraviolet photoelectron spectroscopy with a 13.5-nm wavelength of light. The change in work function indicates formation of molecular dipoles, oriented outward from the Ru surface. X-ray photoelectron spectroscopy investigations suggest variation in electromagnetic interaction with the components of the adsorbed foreign species when the emission angle from the target surface was changed from 0° to 50°; H 2O and C-O n show a strong coupling at lower angles and OH dominates at higher angles, whereas carbon is found in the mid-range peaking at 30°. © 2012 American Institute of Physics.

Journal of Applied Physics

Adsorption dynamics and angular dependency of contaminants on Ru mirror surfaces

In this paper, we report the device characteristics of ambipolar thin-film transistors (TFTs) based on a diketopyrrolopyrrole-benzothiadiazole copolymer. This polymer semiconductor exhibits the largest comparable electron and hole mobility values in a single organic semiconductor. The key to realizing such high mobility values, which are $0.5&cm}{2}/hbox{V}̇hbox{s, is molecular design, i.e., the use of suitable surface treatments of the source/drain contact electrodes and device architectures, particularly top-gate configurations. The subthreshold characteristics of the TFT devices are greatly improved by the use of dual-gate device geometry. We also report the first measurement of the velocity distribution of electron and hole velocities in an ambipolar organic semiconductor. © 2012 IEEE.

IEEE Transactions on Electron Devices

Characteristics of high-performance ambipolar organic field-effect transistors based on a diketopyrrolopyrrole-benzothiadiazole copolymer

We report hole and electron doping in La-doped YBa 2Cu 3O y (YBCO) thin films synthesized by the pulsed laser deposition technique and subsequent in situ postannealing in ambient oxygen and vaccum. The n-type samples show a metallic behavior below the Mott limit and a high carrier density of ∼2.8×1021 cm -3 at room temperature (T) at the optimally reduced condition. The in-plane resistivity(ρ ab) of the n-type samples exhibits a quadratic T dependence in the moderate-T range and shows an anomaly at a relatively higher T probably related to pseudogap formation analogous to underdoped Nd 2-xCe xCuO 4 (NCCO). Furthermore, ρ ab(T), T c, and T with minimum resistivity (T min) were investigated in both p and n sides. The present results reveal the n-p asymmetry (symmetry) within the metallic-state region in an underdoped cuprate and suggest the potential toward ambipolar superconductivity in a single YBCO system. © 2012 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Metallic state in La-doped YBa 2Cu 3O y thin films with n-type charge carriers

Thin films of Ta incorporated TiO2 grown by pulsed laser deposition under specific growth conditions show room temperature ferromagnetism. Ta introduces carriers and concomitantly cationic defects, the combination of which leads to ferromagnetism. In this paper, we report on the dependence of the carrier and cationic defect density (compensation) on various parameters such as oxygen growth pressure, temperature and Ta concentration. Most likely, the Ti vacancies act as magnetic centers and the free electrons help with the exchange leading to ferromagnetism via Ruderman-Kittel-Kasuya- Yosida mechanism. Copyright 2012 Author(s).