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

The quality of organic semiconductor [tris(8-hydroxyquinoline)aluminum] Alq 3 films and interface of Alq 3 -Co heterostructure plays a crucial role in the performance of organic spintronic devices. Four Alq 3 thin films were deposited at four different substrate temperatures ranging from 30 o C to 90 o C to study the effects of deposition temperature on its structure using x-ray reflectivity (XRR) and Grazing-incidence small-angle scattering (GI-SAXS) studies. While XRR yield internal structure of the films, GISAXS yield morphology. XRR studies reveal good-quality Alq 3 films with smooth surfaces roughness less than 10 Å. Electron density gradually increases from 0.40 e/Å 3 to 0.43 e/Å 3 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 Alq 3 films. To study Co diffusion into the Alq 3 layer, four Si/W/Alq 3 /Co/Alq 3 multilayers were investigated using XRR and grazing-incidence x-ray standing wave (GI-XSW) measurements simultaneously. The Alq 3 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 Alq 3 layer, penetration of Co into Alq 3 through Co on Alq 3 interface gradually reduces from 300 Å to 130 Å with reduced concentration. This study demonstrates that by modulating the deposition temperature of Alq 3 film, quality of Alq 3 films and interface of Co-Alq 3 heterostructures can be improved significantly, which is required for better performance of organic spintronic devices.