Anomalous temperature-dependent behaviors of electroluminescence phenomena in disordered ITO/PEDOT/PF/Ca/Al polymer light-emitting diodes

In this study we systematically investigated the anomalous Berthelot-type optical property dependence of the electroluminescence (EL) that occurs in polymer light-emitting diode (PLED) structures. Devices were operated at 0.1 and 0.5 mA over a temperature range from 300 to 20 K. Initially, the emission intensity increased as the temperature decreased, until a maximum was reached at the turning-point temperature T_t. After this, the intensity decreased with further decrease of temperature down to 20 K. A smaller reduction in intensity was exhibited by the device with 0.5 mA, a larger one exhibited by the device with 0.1 mA. The strong electron-electron scattering arising from high excitation, high microcrystalline randomization and high hopping frequency led to the corresponding dominance of the Berthelot-type process by a large T_t. It can be seen in the Arrhenius plot of the integrated EL intensity that a smaller activation energy can be expected to facilitate the redistribution of the thermal carriers, overcoming the energy barrier and the large degradation of luminescence. This results in not only better than carrier confinement, but also enhances the quantum efficiency of PLED structures requiring lower excitation.     

Structure of planar integral self‐affine tilings

For a self‐affine tile in $\mathbf {R}^2$ generated by an expanding matrix $A\in M_2(\mathbf {Z})$ and an integral consecutive collinear digit set ${\mathcal D}$, Leung and Lau [Trans. Amer. Math. Soc. 359 , 3337–3355 (2007).] provided a necessary and sufficient algebraic condition for it to be disklike. They also characterized the neighborhood structure of all disklike tiles in terms of the algebraic data A and ${\mathcal D}$. In this paper, we completely characterize the neighborhood structure of those non‐disklike tiles. While disklike tiles can only have either six or eight edge or vertex neighbors, non‐disklike tiles have much richer neighborhood structure. In particular, other than a finite set, a Cantor set, or a set containing a nontrivial continuum, neighbors can intersect in a union of a Cantor set and a countable set.     

Ion-implanted treatment of (Ba,Sr)TiO3 films for DRAM applications

The effects of ion implantation on the properties of spin-on sol–gel Ba_0.7Sr_0.3TiO₃ (BST) thin films were studied by implanted Ar⁺, N⁺, and F⁺ doses. The F⁺-implanted BST samples present leakage current density <10⁻⁶ A/cm² at 2.5 V and dielectric constant 450. The leakage current of F⁺-implanted BST samples was reduced about one order of magnitude as compared with that of samples with implanted Ar⁺, N⁺ or without implantation. The thickness shrinkage from 135 to 115 nm was observed in F⁺-implanted BST films (before annealing treatment) and a respective increase in the refractive index from 1.84 to 2.05 was measured. After annealing the implanted samples, the changes of thickness and refractive index depend on the concentration of implanted dose. Based on an infrared transmission study of the samples we suggest that the ion-implanted samples with smaller dose (5×10¹⁴ cm⁻²) have fewer −OH contaminants than the non-implanted or implanted samples with the larger doses (1×10¹⁵ cm⁻²). Based on the results presented, we conclude that suitable ion implantation densifies the spin-on sol–gel BST films and reduces the −OH contaminants in the films.     

Acid-Catalyzed Cyclodehydration of Quinazolone Prepolymers

The effect of p-toluenesulfonic acid and phosphoric acid on the cyclodehydration of quinazolone prepolymers has been investigated. Isothermal weight loss during the curing process was monitored closely to follow the extent of cyclization. The optimum weight loss corresponding to 2 mol water is used as an indication of the formation of a fully cyclized quinazolone structure without concurrent decarboxylation. This can be achieved by incorporating the catalyst at 2 wt% concentration, which permits a lower curing temperature than those previously reported. The polymers formed in the presence of catalyst have thermal stability superior to those prepared without catalyst. The glass transition temperature is also raised. This we conclude to be a direct result of the decrease in the amount of incomplete quinazolone rings along the polymer backbone as a result of more efficient cyclization catalyzed by the acids.     

Photorefractive properties of ion-implanted waveguides in strontium barium niobate crystals

0.61 Ba_0.39Nb₂O₆, SBN61), either by proton or helium ion implantation. Proton-implanted samples show a large increase of dark conductivity that reduces or even prevents the recording of refractive index gratings. For waveguides formed by helium implantation this effect is absent, and they can be used for efficient holographic recording. Photorefractive properties of the waveguides are investigated by two-beam coupling. After implantation with 2.0 MeV He⁺ and doses of (0.5-5)×10¹⁵ cm^-2, the samples have to be polarized again, because heating or charge effects at the crystals surface during the implantation process decreases or even reverses the effective electrooptic coefficients in the waveguiding layer. For repoled samples, we find logarithmic gain coefficients of up to 45 cm^-1 with time constants for the build-up of the purely π/2-shifted refractive index grating of the order of 1 ms for the blue lines of an Ar⁺ laser. Photoconductivity depends nonlinearly on light intensity with an exponent x≈0.55. With increasing implanted helium dose, both electronic and nuclear damage of the waveguiding layer grows, and the photorefractive properties of the waveguides are considerably degraded. Received: 20 February 1997/Revised version: 1 May 1997     

Marangoni effects in aqueous polypropylene glycol foams

The foam behavior of three polypropylene glycols covering the molecular weight range between 192 and 725 g/mol has been examined. Static and dynamic surface tension data, as well as bubble size distribution and retention time in the foam, were incorporated into a simple model of foam stability. The latter clearly indicates that surface tension differences between the plateau border and lamellar region adjacent to the bubble surface are the dominant factor in controlling foamability, causing liquid flow in the direction opposite to liquid drainage, a process termed the Marangoni effect.     

Enhanced analysis of purine and pyrimidine bases by the use of double-strand polyaniline coatings in micellar electrokinetic capillary chromatography

A double-strand polymeric complex, which suppresses electroosmotic flow relative to fused-silica, is described. The polymeric complex contains a strand polyaniline (PAN) with the second strand containing polyacrylic acid (PAA) and methacrylate (MA) groups. The complex is referred to as PAN:P(AAMA). This polymeric complex has pH-controlled electroactive and hydrophobic characteristics and can be easily coated onto fused-silica. Enhanced separations of theophylline, theobromine, caffeine and adenine, thymine, uracil and cytosine were obtained by the use of the coated capillary in the micellar electrokinetic capillary electrophoresis (MEKC) system. The purine and pyrimdine bases were separated on the coated capillary with a 20 mM, pH 7 phosphate buffer which contains 0.05 M sodium dodecyl sulfate (SDS) as an additive.