Optical properties of a light-emitting polymer directly patterned by soft lithography

Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 81 (2002) and may be found at http://link.aip.org/link/?APPLAB/81/1955/1We present the optical properties of a directly patterned light-emitting polymer. The patterned poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-paraphenylenevinylene film is fabricated using hot embossing lithography. The effect of the embossed microstructure on the light emitted from the polymer is examined by measuring the angle-dependent photoluminescence and its photonic band structure. The imposed grating modifies the emitted light by Bragg scattering into free space light that would otherwise be trapped as waveguide modes. This simple patterning technique may find application in improving the performance of light-emitting polymer devices

Cholangitis and Budd Chiari Syndrome as Complications of Simple Cystic Liver Disease

We report the case of a 63 year old woman who developed the complications of cholangitis and Budd Chiari syndrome secondary to polycystic disease of the liver. The two complications were not present simultaneously, and both resolved after decompression of the liver cysts

Photonic band structure and emission characteristics of a metal-backed polymeric distributed feedback laser

Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 81 (2002) and may be found at http://link.aip.org/link/?APPLAB/81/954/1Optical losses associated with the metallic contacts necessary for charge injection are an obstacle to the development of an electrically pumped polymer laser. We show that it may be possible to overcome these losses by demonstrating the operation of a distributed-feedback polymer laser fabricated upon a silver substrate. The device lasing threshold was ~150 times greater than that of an otherwise similar metal-free device, though similar to early polymer lasers. The device emission characteristics correlated well with the measured photonic band structure, allowing an explanation of the effect of the microstructure on device operation

Operating characteristics of a semiconducting polymer laser pumped by a microchip laser

Copyright © 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 82 (2003) and may be found at http://link.aip.org/link/?APPLAB/82/313/1We report the demonstration of a compact, all-solid-state polymer laser system featuring a microchip laser as the pump source. The laser was configured as a surface-emitting, two-dimensional distributed feedback laser, based on the conjugated polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene). Pulsed, band-edge lasing was observed at 636 nm above a threshold pump energy of 4 nJ. The laser exhibited an energy slope efficiency of 6.8%, with a maximum output energy of 1.12 nJ at a pump energy of 20.4 nJ. The output beam had an azimuthally polarized annular profile with a beam quality factor (M2) of 2.2, close to the theoretical value of the lowest-order Laguerre–Gaussian and Bessel–Gaussian annular modes. We explain the origin of the azimuthal polarization as due to a coherent combination of the resonant fields supported by the two gratings

Quantum critical dynamics of a S = 1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy

We present a 13C-NMR study of the magnetic field driven transition to complete polarization of the S=1/2 antiferromagnetic Heisenberg chain system copper pyrazine dinitrate Cu(C_4H_4N_2)(NO_3)_2 (CuPzN). The static local magnetization as well as the low-frequency spin dynamics, probed via the nuclear spin-lattice relaxation rate 1/T_1, were explored from the low to the high field limit and at temperatures from the quantum regime (k_B T << J) up to the classical regime (k_B T >> J). The experimental data show very good agreement with quantum Monte Carlo calculations over the complete range of parameters investigated. Close to the critical field, as derived from static experiments, a pronounced maximum in 1/T_1 is found which we interpret as the finite-temperature manifestation of a diverging density of zero-energy magnetic excitations at the field-driven quantum critical point.Comment: 5 pages, 4 figure

Direct calculation of the hard-sphere crystal/melt interfacial free energy

We present a direct calculation by molecular-dynamics computer simulation of the crystal/melt interfacial free energy, $\gamma$, for a system of hard spheres of diameter $\sigma$. The calculation is performed by thermodynamic integration along a reversible path defined by cleaving, using specially constructed movable hard-sphere walls, separate bulk crystal and fluid systems, which are then merged to form an interface. We find the interfacial free energy to be slightly anisotropic with $\gamma$ = 0.62$\pm 0.01$, 0.64$\pm 0.01$ and 0.58$\pm 0.01 k_BT/\sigma^2$ for the (100), (110) and (111) fcc crystal/fluid interfaces, respectively. These values are consistent with earlier density functional calculations and recent experiments measuring the crystal nucleation rates from colloidal fluids of polystyrene spheres that have been interpreted [Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of $\gamma$ for the hard-sphere system of $0.55 \pm 0.02 k_BT/\sigma^2$, slightly lower than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Low threshold edge emitting polymer distributed feedback laser based on a square lattice

Copyright © 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 86 (2005) and may be found at http://link.aip.org/link/?APPLAB/86/161102/1We report the demonstration of a low-threshold, edge-emitting polymer distributed feedback laser based on a square lattice. The lattice constant was 268 nm, which corresponds to a lattice line spacing in the ΓM symmetry direction of the Brillouin zone of 189 nm. The latter was employed to provide feedback at 630 nm via a first order diffraction process. The device operated on two longitudinal modes, which were situated on the band-edge near the M symmetry point. The two modes had thresholds of 0.66 nJ and 1.2 nJ—significantly lower than comparable surface-emitting DFB lasers. Angle dependent photoluminescence experiments were performed to investigate the effect of the square lattice on the laser operation and the origin of the low threshold

Perceptions Of School By Two Teenage Boys With Asperger Syndrome And Their Mothers: A Qualitative Study

This qualitative study aimed to develop an understanding of the challenges faced by teenage boys with Asperger syndrome and their mothers. A case study approach was used to collect data from two 13-year-old boys who have Asperger syndrome and their mothers in Queensland, Australia. Data were collected through the use of semi¬structured interviews. The words of the boys and their mothers provide a valuable insight into the personal experiences and feelings of the par¬ticipants. An inductive approach to data analysis identified four themes: (1) developmental differences; (2) problems associated with the general characteristics of Asperger syndrome (i.e. communication and social difficulties, restricted range of interests, a need for routine); (3) stress; and (4) 'masquerading'. The first three themes relate strongly to the current literature, but the emergence of masquerading is of particular interest in developing a fuller understanding of the experiences of individuals with Asperger syndrome at school