Dewetting of an Organic Semiconductor Thin Film Observed in Real-time

An experiment was conducted to show that a molecular monolayer (ML) of diindenoperylene (DIP) molecules dewets on a timescale of tens of minutes through formation of bilayer islands. DIP was purified by gradient sublimation before use. Si(100) wafers covered by their native oxide were cleaned ultrasonically with acetone, isopropanol, and ultrapure water, followed by heating to 700K in the UHV growth chamber. Thin DIP films were prepared by organic molecular beam deposition (OMBD) at a growth rate of δ1Å min-1 under UHV conditions. The dewetted DIP sample was cooled down to room temperature to freeze dewetting after the X-ray measurement and studied by AFM after intermediate exposure to air. It was observed that during growth, the appearance of a first and second order Bragg reflection corresponding to the ML height of δ17 Å can be seen.