Solid-to-Solid Crystallization of Organic Thin Films: Classical and Nonclassical Pathways.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Organic Electronics

Background:

• Solid-to-solid crystallization of organic molecules is complex and poorly understood.
• Organic crystals often exhibit instability, hindering detailed study.
• Bis-(8-hydroxyquinoline) copper (CuQ2) is a π-conjugated small molecular semiconductor relevant to organic electronics.

Purpose of the Study:

• To investigate the solid-to-solid crystallization processes of CuQ2 thin films.
• To elucidate the temperature-dependent mechanisms of CuQ2 crystallization.
• To understand the role of nucleation, growth, and particle migration in CuQ2 crystal formation.

Main Methods:

• Annealing of bis-(8-hydroxyquinoline) copper (CuQ2) thin films at various temperatures (80 °C, 120 °C, 150 °C).
• Observation and analysis of crystallization phenomena using microscopy and structural characterization techniques (implied).
• Monitoring of particle nucleation, growth, migration, attachment, and reconstruction processes.

Main Results:

• Classical film-to-nanorods crystallization observed at 80 °C.
• A mix of classical and nonclassical nucleation and growth occurred at 120 °C.
• Nonclassical crystal growth, including particle migration and outside-to-inside growth, was evident at 150 °C.
• Submicron CuQ2 particles demonstrated migration over dozens of micrometers at 150 °C.

Conclusions:

• Crystallization mechanisms of CuQ2 are temperature-dependent, transitioning from classical to nonclassical pathways.
• Crystal growth involves particle nucleation, growth, migration, attachment, and reconstruction.
• The observed particle migration at higher temperatures offers new insights into solid-state assembly of organic semiconductors.