Dynamic interfaces in an organic thin film

作者：Tao Chenggang; Liu Qiang; Riddick Blake S; Cullen William G; Reutt Robey Janice; Weeks John D; Williams Ellen D^*

来源：Proceedings of the National Academy of Sciences of the United States of America, 2008, 105(43): 16418-16425.

DOI：10.1073/pnas.0805811105

• fluctuations and noise
• molecular interactions
• phase coexistence
• scanning tunneling microscopy
• diffusion kinetics

Low-dimensional boundaries between phases and domains in organic thin films are important in charge transport and recombination. Here, fluctuations of interfacial boundaries in an organic thin film, acridine-9-carboxylic acid on Ag(111), have been visualized in real time and measured quantitatively using scanning tunneling microscopy. The boundaries fluctuate via molecular exchange with exchange time constants of 10-30 ms at room temperature, with length-mode fluctuations that should yield characteristic f(-1/2) signatures for frequencies less than approximate to 100 Hz. Although acridine-9-carboxylic acid has highly anisotropic intermolecular interactions, it forms islands that are compact in shape with crystallographically distinct boundaries that have essentially identical thermodynamic and kinetic properties. The physical basis of the modified symmetry is shown to arise from significantly different substrate interactions induced by alternating orientations of successive molecules in the condensed phase. Incorporating this additional set of interactions in a lattice-gas model leads to effective multicomponent behavior, as in the Blume-Emery-Griffiths model, and can straightforwardly reproduce the experimentally observed isotropic behavior. The general multicomponent description allows the domain shapes and boundary fluctuations to be tuned from isotropic to highly anisotropic in terms of the balance between intermolecular interactions and molecule-substrate interactions.

• 出版日期2008-10-28