Abstract: Fluorescent and phosphorescent organic light emitting diodes (OLEDs) were measured in high magnetic field up to 9 T. The current efficiency steeply increased below 100 mT as reported but gradually decreased when the field was larger. In the range of 0.1 - 6.5 T, the decrease was proportional to the square of the magnetic field, whereas in the range between 6.5 T and 9 T, it was proportional to the square root of the magnetic field. In contrast, phosphorescent OLED did not show magnetic field dependence. Unipolar devices of n-type Alq3 (Tris-(8-hydroxyquinolino) aluminum) and p-type α-NPD (N’,N’-Di(naphthalene-1-yl)-N,N’ dipheyl-benzidine) showed positive linear magnetoresistance only for minority carriers. The mechanism of the quadratic dependence of the electroluminescent intensity is discussed based on the experimental results.
Abstract: We have carried out very high temperature heat treatment at 1400-2700 °C of about 10 nm-thick amorphous carbon thin films deposited on refractory substrates MgO, Al<sub>2</sub>O<sub>3</sub>, and yttria-stabilized zirconia (YSZ) using pulsed laser deposition techniques. After the annealing, a few nanometer scale <i>sp</i><sup>2</sup> crystallization of the films and a large corrugation with a height of more than 1 μm were observed by Raman spectroscopy analysis and optical/atomic force microscopes, respectively. The corrugation is probably caused by the formation of gases at the film/substrate interface during the heat treatment.
Notes: appears in Top 25 Hottest Articles of "Diamond and Related Materials" through January to March 2010 as shown in < http://top25.sciencedirect.com/subject/materials-science/15/journal/diamond-and-related-materials/09259635/archive/26 >.
Abstract: We carried out the preparation and characterization of new carbon films deposited using an organic molecular beam deposition apparatus with very high substrate temperature (from room temperature to 2670Â K), which we newly developed. When we irradiated molecular beam of organic semiconductor perylene tetracarboxylic acid dianhydride (PTCDA) on Y<sub>0.07</sub>Zr<sub>0.93</sub>O<sub>2</sub> (111) at 2170Â K, a new carbon material was formed via decomposition and fusing of the molecules. The films were characterized with an atomic force microscope (AFM), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Zirconium carbide (ZrC) films were identified beneath the topmost carbon layer by XRD and XPS analyses, which results from chemical reactions of the substrate and the molecules. Partially graphitized aromatic rings of PTCDA were observed from Raman spectroscopy. The present technique - very high temperature chemical vapor deposition using organic semiconductor sources - will be useful to study a vast unexplored field of covalent carbon solids.
Abstract: We fabricated heterojunctions using organic semiconductor pentacene sandwiched between two different magnetic electrodes: Co-doped TiO<sub>2</sub> (Co:TiO<sub>2</sub>) and Fe. The conductance of the junctions was measured as a function of magnetic field. We found that the characteristics of the junctions are strongly dependent on the method used to deposit the Fe top electrode on pentacene. The magnetotransport properties can be explained by the effect of the interface morphology and spin polarization of interface traps.
Notes: Copyright (C) 2008 The Japan Society of Applied Physics
Notes: in Japanese.
(the title of the chapter means "New chemical vapor deposition growth of new carbon films on very high temperature substrates and analysis by Raman spectroscopy" and that of the book means "Graphene: Functions and Applications" in English)
