ACCURATE THICKNESS DENSITY MEASUREMENTS OF ORGANIC LIGHT-EMITTING-DIODES/

We report on the use of Rutherford backscattering spectroscopy for thi ckness analysis of organic light-emitting diode structures (OLEDs) wit h subnanometer resolution and a spatial resolution <1 mm. A careful st udy of ion beam induced effects revealed some organic film degradation , but not so severe as to inhibit meaningful measurements. The method is independent of the substrate and is still applicable if the organic film is capped with a metal cathode. Common OLED materials have been the subject of this study: -methoxy,5-(2'-ethylhexoxy)-1,4-phenylene-v inylene (MEH-PPV), N',N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1' biphen yl-4,4'-diamine (TPD), and tris-(8-hydroxyquinoline) aluminum (Alq(3)) . The densities of thin films of evaporated TPD (rho = 1.22 +/- 0.05 g /cm(3)) and Alq(3) (rho = 1.51 +/- 0.03 g/cm(3)) have been established . (C) 1998 American Institute of Physics. [S0021-8979(98)06919-9].