Imaging of liquid crystals with tunneling microscopy

Abstract

We have used the scanning tunneling microscope (STM) to image a wide variety of organic liquid crystal molecules adsorbed onto a graphite substrate. From the images it is apparent that the STM is resolving individual liquid crystal molecules, as well as the different functional groups within the molecules. The high resolution allows direct observation of features that were not previously known, or had to be inferred from X-ray diffraction, neutron scattering, dilatometry, and other means. In this work, we image four diverse examples of liquid crystal molecules, and measure their packing arrangement and internal bond angles. We find that liquid crystal phases occur at the substrate boundary which have a higher degree of order and stability than the corresponding bulk phase. This surface phase remains intact even when heated 10-15 °C above the bulk isotropic transition temperature.