Effects of Annealing on the Mechanical Properties of Pentacene and Tris(8-hydroxyquinoline) Aluminum Films

Abstract

Annealing is reported as an effective process to improve electrical properties of organic semiconducting films. The mechanical properties of pentacene and tris(8-hydroxyquinoline) aluminum (Alq₃) films annealed at 140°C were investigated in this study by nanoindentation testing. AFM observations of as-coated and annealed pentacene films indicate grain growth from 160 to 258 nm. The annealing process decreases pentacene and Alq₃ film hardness by 23 and 36% from those of the as-coated films, 0.643 and 0.523 GPa. Grain growth and decreasing hardness are attributed to thermal diffusion and recrystallization of molecules.

Keywords:

• organic semiconducting film
• annealing
• nanoindentation
• mechanical property
• morphology
• grain growth

Acknowledgments

This work was supported in part by a Grant-in-Aid for Scientific Research (C) (Grant No. 22560094) from the Japan Society for the Promotion of Science. This work was also supported in part by a Research Aid fund from Nagaoka University of Technology.