Scanning tunneling microscopy of a disordered Alq3–metal interface

Scanning tunneling microscopy is used to observe the structure of the first monolayer of Alq3 on Cu(1 1 0). Individual molecules can be resolved at very low coverage where there is also evidence of significant surface mobility. As Alq3 surface coverage increases, molecules aggregate by forming pairs and chain-like structures without ever establishing long range order. Interfacial disorder is maintained even after annealing to 590 K. The tendency to form chain-like aggregates is attributed to anisotropic intermolecular interactions. Anisotropies in these interactions are implicated in chain formation by illustrative density functional theory calculations and the role of direct dipolar interactions, anisotropic van der Waals interactions, and substrate-mediated interactions is discussed.

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► Alq3 molecules on Cu(1 1 0) visualized with STM.
► First layer is strongly disordered.
► Chain-like aggregates form due to anisotropic intermolecular interactions.