Modelling gratings on either side of the substrate for light extraction in light-emitting diodes

We present a three-dimensional model based on rigorous coupled wave analysis (RCWA) which allows us to study the influence of periodic structures on light extraction in light-emitting diodes. The gratings can be placed both at the interface between the emitting layers and the substrate, where they coherently interact with the dipole field, or at the interface between the substrate and air, where multiple incoherent reflections in the thick substrate contribute to the overall extraction. Even in the case of a grating at the interface between the substrate and air, these multiple incoherent reflections in the substrate still contribute to the overall extraction for large devices, an effect which has been mostly ignored in literature FDTD simulations.     

TRAPDOR double-resonance and high-resolution MAS NMR for structural and template studies in zeolite ZSM-5

A combination of ²⁷Al magic-angle spinning (MAS)/multiple-quantum (MQ) MAS, and ²⁷Al–{¹⁴N} TRAnsfer of Population in DOuble-Resonance (TRAPDOR) nuclear magnetic resonance (NMR) was used to study aluminium environments in zeolite ZSM-5. ²⁷Al–{¹⁴N} TRAPDOR experiments, in combination with ¹⁴N NMR were employed to show that the two tetrahedral peaks observed in the ²⁷Al MAS/3Q-MAS spectra of as-synthesized ZSM-5 are due to aluminium atoms occupying crystallographically inequivalent T-sites. A ¹³C–{²⁷Al} TRAPDOR experiment was used to study the template, tetrapropyl ammonium bromide (TPABr), in the three-dimensional pore system of ZSM-5. The inequivalency of the methyl groups of TPA was observed in the ¹³C–{²⁷Al} TRAPDOR spectra of as-synthesized ZSM-5 and the motion of the methyl end of the propyl chain appeared to be more restricted in the sinusoidal channel than in the straight channel.     

Zipping up 'the crushed fullerene' C60H30:C60 by fifteen-fold,consecutive intramolecular H2 losses

MALDI TOF-MS of tribenzo[l:1':1"]benzo[1,2-e:3,4-e':5,6-e"]triacephenanthrylene (1a, C60H30) gives C60.+ by multiple intramolecular cyclodehydrogenation reactions.     

Charge transport parameters of the pentathienoacene crystal

Pentathienoacene, the thiophene equivalent of pentacene, is one of the latest additions to the family of organic crystal semiconductors with a great potential for use in thin film transistors. By using density functional theory and gas-phase ultraviolet photoelectron spectroscopy, we investigate the microscopic charge transport parameters of the pentathienoacene crystal. We find that the valence band exhibits a stronger dispersion than those in the pentacene and rubrene single crystals with marked uniaxial characteristics within the molecular layer due to the presence of one-dimensional pi-stacks; a small hole effective mass is also found along the direction perpendicular to the molecular layers. In the conduction band, strong intermolecular sulfur-sulfur interactions give rise to a significant interstack electronic coupling whereas the intrastack dispersion is greatly reduced. The intramolecular vibronic coupling (reorganization energy) is stronger than that in pentacene but comparable to that in sexithiophene; it is larger for holes than for electrons, as a result of low-frequency modes induced by the sulfur atoms. The polarization energy is large, but its effect on the vibronic coupling remains small. Charge transport is discussed in the framework of both band and hopping models.