SCANNING TUNNELING MICROSCOPY STUDY OF A POLYIMIDE LANGMUIR-BLODGETT-FILM

The microscopic molecular structure of a polyimide Langmuir-Blodgett (LB) film monolayer was studied by scanning tunneling microscopy (STM) and molecular simulation. An STM image of a polyimide monolayer on graphite showing the polymer chains was observed for the first time. The STM image directly indicated that the alignment direction of the polymer chains of polyimide is parallel to the deposition direction of the LB film. In order to investigate the microscopic interpretation of the molecular structure theoretically, molecular dynamics calculations of the optimum polyimide structure on graphite were carried out. The polyimide chain on graphite has a zigzag structure with bends at the ether-bonded oxygen atoms. The distance between oxygen atoms at successive bends is 17.8 angstrom and the bend angle is about 119 deg. These values are in fair agreement with the STM image. Therefore, it was confirmed that the STM image can be interpreted as showing the individual molecular chains of the polyimide monolayer.