Volume 105, Issue 7, 01 April 2009
Index of content:
A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer105(2009); http://dx.doi.org/10.1063/1.3106051View Description Hide Description
By utilizing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline: as an effective charge generation layer (CGL), we extend our recently demonstrated single-emitting-layer white organic light-emitting diode (WOLED) to realize an extremely high-efficiency tandem WOLED. This stacked device achieves maximum forward viewing current efficiency of 110.9 cd/A and external quantum efficiency of 43.3% at and emits stable white light with Commission Internationale de L’Eclairage coordinates of (0.34, 0.41) at 16 V. It is noted that the combination of effective single units and CGL is key prerequisite for realizing high-performance tandem WOLEDs.
Enhanced photoluminescence of silicon oxide nanowires brought by prolonged thermal treatment during growth105(2009); http://dx.doi.org/10.1063/1.3091261View Description Hide Description
Silicon oxidenanowires synthesized during carbonization of polyimide thin film on a silicon substrate exhibited marked enhancement in photoluminescence(PL) at 420 nm by prolonging the growth period. Maximum intensity was recorded when the nanowire diameter coarsened from 70 to 165 nm by extending the growth period from 1 to 3 h. The enhancement was attributed to the increase in concentration of neutral oxygen vacancies on the surface of the nanowires. It was also demonstrated that the PL peak can be shifted to 600 nm while maintaining the enhanced intensity by postannealing the nanowires in a reducing atmosphere.
High-temperature conductance loss dominated defect level in h-BN: Experiments and first principles calculations105(2009); http://dx.doi.org/10.1063/1.3086388View Description Hide Description
The dielectric properties of hexagonal boron nitride are investigated in detail. The permittivities hold extremely low values ranging from room temperature to , however, the dielectric loss tangents increase rapidly above . At , the dielectric loss tangent is 20 times more than that at room temperature. The first principles calculations show that the boron vacancy that gives an acceptor energy level near the valence band presents the lowest ionization energy in the investigated defects, and the calculated ionization energy agrees with the experimental value. It indicates that the rapid increase in dielectric loss tangents at high temperature is contributed by electrical conductivity produced by ionization under thermal excitation.
105(2009); http://dx.doi.org/10.1063/1.3106054View Description Hide Description
Pure and Bi-doped (BCCTO, , 0.15, 0.25, and 0.3) ceramics were fabricated by the solid-state sintering method. The results indicate that the additional bismuth has a great influence on both the microstructures and the electric properties. A new phase can be observed in the doped samples from the x-ray diffraction patterns. Additionally, the CCTO gain size can be controlled by bismuth content. All of the BCCTO samples show high dielectricpermittivity ( at ) and varistor effect, and the relaxation peak shifts to higher frequency. The resistance rises with the increase in bismuth, and the activation energy at the grain boundary is reduced from 0.65 to 0.47 eV.