The thermal annealing treatment of an organic non-crystalline film of spirofluorene causes the randomization of the molecular orientation through molecular migration. However, the magnitude of the randomization depends on the depth in the film. The comparison of variable-angle spectroscopic ellipsometry, thermally stimulated current, and field-effect transistor characteristics measurements revealed that the molecular orientation in the bulk was randomized by annealing but was still partially maintained at the organic/substrate interface. This difference in condensed states between the interface and the bulk originates from a difference in glass transition temperature.
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