SCANNING TUNNELING MICROSCOPY OF POLYIMIDE MONOLAYERS PREPARED BY THE LANGMUIR-BLODGETT TECHNIQUE

Monolayers of poly[N,N'-bis(phenoxyphenyl)pyromellitimide] (PI) have been deposited onto a graphite substrate with the help of the Langmuir-Blodgett (LB) technique and subsequently investigated with a scanning tunneling microscope (STM) operating in air in the constant-current mode. The PI monolayer produces a regular array of bright spots with periodicities of 1.15 and 0.85 nm along the two axes over areas as large as 100 nm ˟ 100 nm. The images of both the graphite substrate and the PI monolayer may be obtained on the same area of the same sample just by changing the STM operating conditions. Apparently the molecular order in the LB film of the starting material on the water surface is preserved in the PI monolayer on the graphite, in spite of the transfer procedure and the removal of the long alkyl chains. We suggest that each bright oval spot in the array corresponds to a rigid segment (aromatic and imide rings) and that the direction of the polymer backbone is coincident with the axis with 1.15-nm periodicity. Our results demonstrate for the first time that it is possible with scanning tunneling microscopy to resolve an individual polymer chain segment. © 1990, American Chemical Society. All rights reserved.