Rutherford backscattering and secondary ion mass spectrometry investigation of Mg:Ag–tris(8-hydroxy quinoline) aluminum interfaces

The presence or absence of silver diffusion from Mg:Ag cathodes in tris(8-hydroxy quinoline) aluminum (Alq3) type organic light emitting diodes (OLEDs) has been investigated by Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). Comparison of experimental and simulated RBS data indicated a very abrupt Ag–Alq3 interface, consistent with there being no uniform diffusion of silver into the organic layer of the OLED during deposition, i.e. <0.5 at.% Ag in the first 20% of the organic layer. Silver diffusion through the organic layers of an OLED cannot, therefore, be the root cause of common electrical shorting problems. SIMS profiles of the same sample were obtained using O2+, O− and Ar+ primary ion beams, and in each case different depth profiles were obtained. The variation in the SIMS results is due to ion beam mixing effects, matrix effects and migration of metal ions in an electrostatic field created by a charged surface. It was concluded, therefore, that SIMS is not a suitable technique for studying metal-on-organic interfaces.