Physics

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TiO2 thin films are of importance in oxide electronics, e.g., Pt/TiO2/Pt for memristors and Co-TiO2/TiO 2/Co-TiO2 for spin tunneling devices. When such structures are deposited at a variety of oxygen pressures, how does TiO2 behave as an insulator? We report the discovery of an anomalous resistivity minimum in a TiO2 film at low pressure (not strongly dependent on deposition temperature). Hall measurements rule out band transport and in most of the pressure range the transport is variable range hopping (VRH) though below 20 K it was difficult to differentiate between Mott and Efros-Shklovskii's (ES) mechanism. Magnetoresistance (MR) of the sample with lowest resistivity was positive at low temperature (for VRH) but negative above 10 K indicating quantum interference effects. © 2012 Author(s).

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AIP Advances

Variable range hopping in TiO2 insulating layers for oxide electronic devices

Extreme ultraviolet (EUV) radiation induced growth of carbon and oxygen desorption were investigated on a Ru surface by Auger electron spectroscopy (AES) in the presence and absence of additional photoelectrons (PEs) from a focusing Ru mirror. A decrease in EUV reflectivity with carbon growth in the presence of additional PEs has been observed. Conversely, a carbonaceous Ru surface was cleaned in sequential AES, and discussed in terms of secondary electron assisted dissociation of residual hydrocarbons and water molecules, followed by a chemical reaction between adsorbed carbon and oxygen atoms. © 2012 American Vacuum Society.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

Tracking electron-induced carbon contamination and cleaning of Ru surfaces by Auger electron spectroscopy

Time dependent changes in 13.5 nm extreme ultraviolet (EUV) reflectivity of Ru mirrors due to variations in surface composition were investigated. The surface properties of Ru films were analyzed in situ by means of X-ray photoelectron spectroscopy (XPS), and further verified by Auger electron spectroscopy (AES). Moreover, the impact on EUV reflectivity (EUVR) with time was examined in situ via continuous and/or discrete EUV exposures. The rapid decrease in EUVR was observed in the presence of photoelectrons (PEs) from Ru mirror of the EUV setup, whereas no significant variation was recorded by screening out additional PEs. Detailed XPS and AES analyses suggest that carbon deposition via dissociation of residual hydrocarbons plays a dominant role in the presence of additional PEs, and thus reduces the reflectivity rapidly. Using EUV photoelectron spectroscopy, systematic reduction of the secondary electron yield from the Ru mirror surface was observed in consecutive scans, and therefore supports the formation of carbonaceous Ru surface in the presence of additional PEs. © 2012 American Institute of Physics.

Journal of Applied Physics

Time dependent changes in extreme ultraviolet reflectivity of Ru mirrors from electron-induced surface chemistry

We investigate the effects of competition between two complex,PT -symmetric potentials on the PT -symmetric phase of a particle in a box. These potentials, given by V Z (x) = iZsign(x) and V epsi;(x) = iepsi; [δ (x - a) - δ(x + a)], represent long-range and localized gain/loss regions, respectively. We obtain the PT - symmetric phase in the (Z, ε) plane, and find that for locations a near the edge of the box, surprisingly, the PT -symmetric phase is strengthened by additional losses to the loss region. Consequently, we predict that a broken PT -symmetry will be restored by increasing the strength ε of the localized potential. By comparing the results for this problem and its lattice counterpart, we show that a robust PT -symmetric phase in the continuum is consistent with the fragile phase on the lattice. Our results demonstrate that systems with multiple, PT -symmetric potentials show unique, unexpected properties. © 2012 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Competing PT potentials and the re-entrant PT-symmetric phase: A particle in a box

In this work, we report design, synthesis and characterization of solution processable low band gap polymer semiconductors, poly{3,6-difuran-2-yl-2,5-di(2- octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-phenylene} (PDPP-FPF), poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1, 4-dione-alt-naphthalene} (PDPP-FNF) and poly{3,6-difuran-2-yl-2,5-di(2- octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-anthracene} (PDPP-FAF) using the furan-containing 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DBF) building block. As DBF acts as an acceptor moiety, a series of donor-acceptor (D-A) copolymers can be generated when it is attached alternatively with phenylene, naphthalene or anthracene donor comonomer blocks. Optical and electrochemical characterization of thin films of these polymers reveals band gaps in the range of 1.55-1.64 eV. These polymers exhibit excellent hole mobility when used as the active layer in organic thin-film transistor (OTFT) devices. Among the series, the highest hole mobility of 0.11 cm 2 V -1 s -1 is achieved in bottom gate and top-contact OTFT devices using PDPP-FNF. When these polymers are used as a donor and [70]PCBM as the acceptor in organic photovoltaic (OPV) devices, power conversion efficiencies (PCE) of 2.5 and 2.6\% are obtained for PDPP-FAF and PDPP-FNF polymers, respectively. Such mobility values in OTFTs and performance in OPV make furan-containing DBF a very promising block for designing new polymer semiconductors for a wide range of organic electronic applications. © 2012 The Royal Society of Chemistry.

Journal of Materials Chemistry

Furan containing diketopyrrolopyrrole copolymers: Synthesis, characterization, organic field effect transistor performance and photovoltaic properties

A light-emitting field-effect transistor was fabricated, with its architecture based on a distinct heterojunction located midway between the source and drain contacts. Tetracene enabled hole transport on one side of the heterojunction (hole mobility ∼0.071 cm 2/Vs), while amorphous solution-processed zinc tin oxide supported electron transport on the other side (electron mobility ∼0.81 cm 2/Vs). The drain current vs. gate voltage curves of this device have a bell-shaped profile that is characteristic of lateral heterojunction bipolar field-effect transistors. The green light emission-from tetracene-closely follows the trend in drain current and is naked-eye visible in a darkened room. © 2012 American Institute of Physics.

Applied Physics Letters

A light emitting transistor based on a hybrid metal oxide-organic semiconductor lateral heterostructure

Universal extra dimension (UED) models tend to favor a distinctively heavier Higgs mass than in the standard model and its supersymmetric extensions when the Kaluza-Klein (KK) scale is not much higher than the electroweak one, which we call the weak scale UED, in order to cancel the KK-top contributions to the T parameter. Such a heavy Higgs, whose production through the gluon fusion process is enhanced by the KK-top loops, is a fairly model independent prediction of the weak scale UED models regardless of the brane-localized mass structure at the ultraviolet cutoff scale. We study its cleanest possible signature, the Higgs decay into a Z boson pair and subsequently into four electrons and/or muons, in which all the four-momenta of the final states can be measured and both the Z boson masses can be checked. We have studied the Higgs mass, 500 GeV (and also 700 GeV with √s=14TeV), and have found that we can observe significant resonance with the integrated luminosity 10fb -1 for six-dimensional UED models. © 2012 American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Heavy Higgs boson at the Tevatron and the LHC in universal extra dimension models

We calculate loop-induced Higgs production and decay processes which are relevant for the LHC in various six-dimensional Universal Extra Dimension models. More concretely, we focus on the Higgs production through gluon fusion and the Higgs decay into two photons induced by loop diagrams. They are one-loop leading processes and the contribution of Kaluza-Klein particles is considered to be significant. These processes are divergent in six dimensions. Therefore, we employ a momentum cutoff, whose size is fixed from the validity of perturbative calculation through naive dimensional analysis. In these six-dimensional Universal Extra Dimension models, the Higgs production cross section through gluon fusion is highly enhanced and the Higgs decay width into two photons is suppressed. In particular in the case of the compactification on Projective Sphere, these effects are remarkable. The deviation of the h (0) → 2γ signal from the prediction of the Standard model is much greater than that in the case of the five-dimensional minimal UED model. We also consider threshold corrections in the two processes and these effect are noteworthy even when we take a higher cutoff and/or a heavy KK scale. Comparing our calculation to the recent LHC results which were published at the Lepton-Photon 2011 and at the December of 2011 is performed briefly. © 2012 SISSA.

Journal of High Energy Physics

Higgs production and decay processes via loop diagrams in various 6D Universal Extra Dimension models at LHC

We work out the strongly interacting sector of a non-minimal Universal Extra Dimension (nmUED) scenario with one flat extra spatial dimension orbifolded on S 1 /Z 2 in the presence of brane-localized kinetic and Yukawa terms. On compactification, these terms are known to have significant, nontrivial impact on the masses and the couplings of the Kaluza-Klein (KK) excitations. We study the masses of the level '1' KK gluon and the quarks and find the modified strong interaction vertices involving these particles. The scenario conserves KK parity. Possibility of significant level-mixing among the quarks from different KK-levels is pointed out with particular reference to the top quark sector. Crosssections for various generic final states involving level '1' KK-gluon and KK-quarks from first two generations are estimated at the Large Hadron Collider (LHC) via an implementation of the scenario in MadGraph-5 with the help of FeynRules. The decay branching fractions of both strong and weakly interacting KK excitations are studied to estimate yields in various different final states involving jets, leptons and missing energy. These are used to put some conservative constraints on the nmUED parameter space using the latest LHC data. Nuances of the scenario are elucidated with reference to the minimal Universal Extra Dimension (mUED) and Supersymmetry (SUSY) and their implications for the LHC are discussed. © 2012 SISSA, Trieste, Italy.

Non-minimal universal extra dimensions: The strongly interacting sector at the Large Hadron Collider

We discuss the choice of input parameters for the renormalization of the chargino and neutralino sector in the minimal supersymmetric standard model in the on-shell scheme. We show that one should choose the masses of a bino-like, a wino-like and a Higgsino-like state as inputs in order to avoid large corrections to the masses of the other eigenstates in this sector. We also show that schemes where the Higgsino-like input state is a neutralino are more stable than those where the mass of the Higgsino-like chargino is used as input. The most stable scheme uses the masses of the wino-like chargino as well as the masses of the bino- and Higgsino-like neutralinos as inputs. {\textcopyright} 2012 American Physical Society.