We report a structural modulation that occurred in the rubrene monolayer grown on Bi(001) surface. A small sinusoidal variation of surface height plus the periodic distortion of molecular orientations have been observed by low-temperature scanning tunneling microscopy. Further analyses demonstrate that this modulation results from the lattice rotation of the rubrene monolayer with respect to Bi(001) substrate. Depending on the rotational direction of rubrene lattices, the modulation may exhibit either stripe ripples or zigzag patterns. The experimental data are discussed in terms of the mass density wave.

• Received 3 March 2011

DOI:https://doi.org/10.1103/PhysRevB.83.235433