Physics

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Shiv Nadar University

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.

(SoNS) School of Natural Sciences

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

F4CuPc based ambipolar organic thin-film transistors

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

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.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Epitaxy and cathodoluminescence in α-quartz after Ge, Ba and Rb ion implantation

Theoretical Investigations of Core-level Spectroscopies in Strongly Correlated Systems My Parents My Teachers

We report the modification of molecular beam epitaxy grown strain-relaxed single crystalline Si1-xGex layers for x=0.5 and 0.7 as a result of irradiation with 100 MeV Au ions at 80 K. The samples were structurally characterized by Rutherford backscattering spectrometry/channeling, transmission electron microscopy (TEM) and high-resolution X-ray diffraction before and after irradiation with fluences of 5×1010, 1×1011 and 1×1012 ions/cm2, respectively. No track formation was detected in both the samples from TEM studies and finally, the crystalline to amorphous phase transformation at 1×1012 ions/cm2 was examined to be higher for Si0.3Ge0.7 layers compared to Si0.5Ge 0.5 layers. © 2005 Elsevier Ltd. All rights reserved.

Solid State Communications

Composition dependent structural modification in relaxed Si 1-xGex films by 100 MeV Au beam

Single-phase Pb1-xMnxS (0.03 ≤ x ≤ 0.37) nanoparticle films were prepared using an electroless solution growth technique. Face centered cubic structure with a decrease of lattice parameter for an increase of x in the alloy films was observed. Composition dependence of optical and electrical properties is discussed. The optical bandgap (Eg) could be varied from 1.50 to 2.50 eV by changing the x in the range 0.03 ≤ x ≤ 0.37 for the films. Effect of the grain size and the effect of alloying on optical properties are distinguished for the ternary nanoparticle films. Variable range hopping has been identified as mechanism for conduction in the p-type semiconductor Pb1-xMnxS nanoparticle films. Mobility μ of the majority carriers shows a decrease with increase in Mn concentration x and follows a T0.4 temperature dependence, indicating the surface scattering of carriers in the nanoparticle films. © 2006 The Electrochemical Society. All rights reserved.

Journal of the Electrochemical Society

Study of solution grown variable bandGap Pb1-xMnxS semiconductor nanoparticle films

Verhandlungen der Deutschen Physikalischen Gesellschaft

The highly distorted hcp lattices of zinc and cadmium: Comparison of different ab-initio approaches

We provide some explicit examples wherein the Schrödinger equation for the Morse potential remains exactly solvable in a position-dependent mass background. Furthermore, we show how in such a context, the map from the full line (-∞, ∞) to the half-line (0, ∞) may convert an exactly solvable Morse potential into an exactly solvable Coulomb one. This generalizes a well-known property of constant-mass problems. © World Scientific Publishing Company.

Fulltext

Modern Physics Letters A

Morse potential and its relationship with the Coulomb in a position-dependent mass background

To lowest order of perturbation theory we show that an equivalence can be established between a PT -symmetric generalized quartic anharmonic oscillator model and a Hermitian position-dependent mass Hamiltonian h. An important feature of h is that it reveals a domain of couplings where the quartic potential could be attractive, vanishing or repulsive. We also determine the associated physical quantities. © Institute of Physics, Academy of Sciences of Czech Republic 2006.