Probing the Thermodynamics of Moire Patterns in Molecular Self-Assembly at the Liquid-Solid Interface

Three types of moire patterns, denoted as alpha-, beta-, and gamma-patterns, were observed in the molecular self-assembly of 1,3,5-tris(4-cyanophenyl)benzene (TCPB) on HOPG. Their relative stability was studied through thermally induced phase transitions monitored in situ by scanning tunneling microscopy. The incommensurate gamma-pattern is thermodynamically more stable than the commensurate alpha- and beta-patterns. The preference in the gamma-pattern was explained by a static distortion wave, which was exclusively observed in this pattern. Through the lateral relaxation of TCPB lattice, the free energy of the gamma-pattern can be reduced with respect to that of the alpha- and beta-moire patterns. This investigation provides insights into the thermodynamics of surface-confined supramolecular systems where the molecular lattice is incongruent with the substrate.