Effect of deposition temperature on the quality of Alq3 films and Alq3-Co interfaces

Abstract

The quality of organic semiconductor [tris(8-hydroxyquinoline)aluminum] Alq₃ films and interface of Alq₃-Co heterostructure plays a crucial role in the performance of organic spintronic devices. Four Alq₃ thin films were deposited at four different substrate temperatures ranging from 30 °C to 90 °C to study the effects of deposition temperature on its structure using x-ray reflectivity (XRR) and Grazing-incidence small-angle x-ray scattering (GI-SAXS) studies. While XRR yields the internal structure of the films, GISAXS yields morphology. XRR studies reveal good-quality Alq₃ films with smooth surfaces roughness less than 10 Å. Electron density gradually increases from 0.40 e/ų to 0.43 e/ų with increasing deposition temperature, which indicates continual reduction of porosity in the films. GI-SAXS studies demonstrate that with increasing deposition temperature pore separation increases from 210 Å to 810 Å and pore depth decreases progressively from 300 Å to 150 Å in the Alq₃ films. To study Co diffusion into the Alq₃ layer, four Si/W/Alq₃/Co/Alq₃ multilayers were investigated using XRR and grazing-incidence x-ray standing wave (GI-XSW) measurements simultaneously. The Alq₃ layers in the multilayers were deposited at the four different substrate temperatures as mentioned above. The combined XRR & GI-XSW analysis shows that with increasing growth temperature of Alq₃ layer, penetration of Co into Alq₃ through Co on Alq₃ interface gradually reduces from 300 Å to 130 Å with reduced concentration. This study demonstrates that by modulating the deposition temperature of Alq₃ film, quality of Alq₃ films and interface of Co-Alq₃ heterostructures can be improved significantly, which is required for better performance of organic spintronic devices.