Ag-organic layered samples for optoelectronic applications: interface width and roughening using a 500 eV Cs+ probe in dynamic secondary ion mass spectrometry.

The performance of organic optoelectronic devices depends a lot on interface structure and width. Dynamic secondary ion mass spectrometry (SIMS) has been widely used to investigate interfaces in classical semiconductor devices and limitations are quite well understood. For low-energy dynamic SIMS on organic optoelectronic devices, sputter-induced diffusion processes and roughness formation have only been investigated sparsely. In this work we use low-energy dynamic SIMS depth profiling on metal-organic multilayered model samples with compositions similar to organic optoelectronic devices to investigate limitations in the calculation of interface widths due to sputter-induced roughness formation. The samples consist of silver and organic compounds (e.g., tris(8-hydroxyquinolinato) aluminum (Alq(3)) and metal phthalocyanines) sequentially deposited by thermal evaporation in vacuum onto a Si substrate. They are analyzed by a 500 eV Cs(+) primary ion beam. Surface roughness at the SIMS crater bottoms is characterized by AFM as a function of crater depth. We find that the roughness in SIMS craters is limited to approximately 1.5 nm, which is much smaller than the interface width of the as-deposited interfaces. Thus, for the studied organic-inorganic interfaces, low-energy dynamic SIMS can yield accurate information about interface morphology, allowing the study of its dependence on sample preparation conditions and its implication on device properties.