Nanoscale photophysics of Alq(3) films

We use near-field scanning optical microscopy (NSOM) and spectroscopy to pr obe the photophysics of thin films of molecular semiconductor tris-8-hydrox yquinoline aluminum (Alq(3)) on a 10-100 nm scale. Photoluminescence NSOM i s used to simultaneously map variations in emission and morphology of both solution-cast and vacuum-deposited films. Vacuum-deposited films annealed a t 200 degreesC (T > T-g) exhibit greater fluorescence and topographical con trast than films annealed at 100 degreesC (T < T-g), with the most dramatic changes occurring in films less than 50 nm thick. These results indicate t he formation of microcrystalline domains in annealed Alq3 films, which vary with annealing temperature and film thickness. We have also used NSOM to l ocally photo-pattern films on a 100 nm scale and to directly measure excito n diffusion. Our results indicate very long diffusion lengths in comparison to indirect methods.