Molecular structures of lipid monolayers on ITO glass and on graphite imaged by an STM

Abstract

The ordering of solid supported monomolecular layers of a fatty acid, a binary lipid mixture and a polymerized diacetylenic lipid is studied by scanning tunneling microscopy (STM) in air and in water. We introduce the optically transparent semiconducting indium tin oxide (ITO) coating as a substrate for tunneling experiments on Langmuir-Blodgett (LB) films. Under ambient conditions ITO exhibits no resolvable atomic structure, ruling out observable periodicities due to the substrate. The arrangement of the lipid molecules in the condensed phase exhibits crystallographic data in good agreement with X-ray and electron diffraction experiments. Variations of the two-dimensional ordering can be investigated on a nanometer scale for different participating molecules. For the experiments in water, an STM specially designed for the use in a Langmuir-Blodgett trough is described. © 1992.