Dependence of the emission from tris(8-hydroxyquinoline) aluminum based microcavity on device thickness and the emission layer position

In this work, we present a systematic study of the emission from bilayer organic microcavity light emitting diodes with two metal mirrors. The devices consisting of two organic layers, N,NV-di(naphthalene-1-yl)-N,NV-diphenylbenzidine as the hole transport layer and tris (8-hydroxyquinoline) aluminum as the emitting layer, and two metal mirrors were fabricated and characterized by transmittance, reflectance, photoluminescence, and electroluminescence measurements. The effects of layer thickness, interface position, and the choice of anode(bottom mirror) were investigated. The transmittance and reflectance spectra were modeled using a transfer matrix model, and the optical functions for all the materials used were determined by spectroscopic ellipsometry. The dependence of the photoluminescence and electroluminescence spectra on the device thickness and interface position is discussed

Charge transport and trapping in Cs-doped poly(dialkoxy-p-phenylene vinylene) light-emitting diodes

Al/Cs/MDMO-PPV/ITO (where MDMO-PPV stands for poly[2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4phenylene vinylene] and ITO is indium tin oxide) light-emitting diode (LED) structures, made by physical vapor deposition of Cs on the emissive polymer layer, have been characterized by electroluminescence, current-voltage, and admittance spectroscopy. Deposition of Cs is found to improve the balance between electron and hole currents, enhancing the external electroluminescence efficiency from 0.01 cd A-1 for the bare Al cathode to a maximum of 1.3 cd A-1 for a Cs coverage of only 1.5×1014 atoms/cm2. By combining I-V and admittance spectra with model calculations, in which Cs diffusion profiles are explicitly taken into account, this effect could be attributed to a potential drop at the cathode interface due to a Cs-induced electron donor level 0.61 eV below the lowest unoccupied molecular orbital. In addition, the admittance spectra in the hole-dominated regime are shown to result from space-charge-limited conduction combined with charge relaxation in trap levels. This description allows us to directly determine the carrier mobility, even in the presence of traps. In contrast to recent literature, we demonstrate that there is no need to include dispersive transport in the description of the carrier mobility to explain the excess capacitance that is typically observed in admittance spectra of p-conjugated materials

'�Eor China's benefit' : the evolution and devolution of German influence on Chinese military affairs, 1919 - 1938

In the years between 1919 and 1938, Germany and China, two nations each plagued in its own way by the foreign political fall-out of World War I, by internal unrest and by the disastrous global economic situation of the inter-war era, established extraordinarily close military and military economic ties. German military advisers helped in the organisation and training of the troops of several Chinese warlords and, after the re-establishment of the Chinese Republic under Chiang Kaishek, of the Nationalist government's armed forces. At the same time, German arms manufacturers and German trading companies delivered weapons and other war materials to arm and equip China's soldiers, who fought first against each other and later against Mao Zedong's Communist guerillas and Japanese invaders. Still, despite outward appearances, any kind of German military support for China was never official. Successive Weimar German governments tried everything in their power to stop the widely-condemned Sino-German military cooperation, while Adolf Hitler's National Socialists only tolerated it for as long as it did not interfere with their long-term political agenda. In the end, however, the German influence on Chinese military affairs was only minimal. German military advisers and German arms shipments, contrary to repeated world-wide accusations throughout the years, were too few in number and too small in amount to have any real impact on war-ravaged China. The breakdown of Sino-German relations due to National Socialist Germany's alliance with Japan and the Sino-Japanese War eradicated every trace China's informal military supporters had left behind after their withdrawal in 1938