2 - Experimental methods in Alq3 thin films research

Abstract

Twelve thin films of Alq3 molecules have been evaporated on glass substrates in three batches, four samples in each one, and soon after stored in a dry box or in a vacuum. At different times, but within a maximum of 4days, they were each taken out of its safe storage, measured for optical absorption and emission, annealed at different temperatures in wet and dry atmospheres of O2, N2, and air, and then measured again. One of them, the reference sample, was taken out of the dry box and measured without annealing. Since these initial experimental procedures, all samples were kept in the laboratory atmosphere, and, with the exception of two destroyed during annealing, the other 10 samples were measured every so often for 6years. In particular, the thickness of the films was measured at the beginning and at the end, when very little molecular material or nothing at all was still on the substrates. Laser beam and confocal microscope were used to observe the films at the end of their life span. Optical transmission (absorption) of films was measured again only after 6years to avoid disturbing the natural process of molecular degradation with light. Optical emission (photoluminescence, PL) was measured often during the whole span of 6years. A comprehensive history of samples is briefly summarized, confocal microscopy images are displayed and discussed, and typical optical absorption and emission bands with their lineshape parameters are illustrated.