Real-time STM observation of molecular dynamics on a metal surface

Dynamic processes of molecular assembly on a metal surface were examined using scanning tunneling microscopy (STM). Molecules of a porphyrin derivative were deposited on a Cu(1 1 1) surface and were found to be highly mobile at room temperature. The real-time STM observation enabled visualization of molecular activity such as surface diffusion, domain formation and phase transition. The high mobility of the molecules caused build-up and break-down of molecular domains. Metastability of the molecular assembly caused various domain formations with different molecular alignments, including square and hexagonal motifs. A phase transition from a hexagonal to a square domain structure was successfully observed by sequential STM imaging.