Near—Atomic Resolution Imaging of Ferroelectric Liquid Crystal Molecules on Graphite by STM
David M. Walba 1,
Forrest Stevens 1,
Daniel C. Parks 2,
Noel A. Clark 2, and
Michael D. Wand 3
1 Department of Chemistry and Biochemistry and Optoelectronic Computing Systems Center, Campus Box 215, University of Colorado, Boulder, CO 80309-0215, USA.
2 Department of Physics and Optoelectronic Computing Systems Center, Campus Box 390, University of Colorado, Boulder, CO 80309-0390, USA.
3 Displaytech, 2200 Central Avenue, Boulder, CO 80301, USA.
Near-atomic resolution images of a two-dimensional heteroepitaxial crystal composed of the relatively "functionally rich" chiral liquid crystal mesogen MDW 74 on graphite have been obtained by scanning tunneling microscopy (STM). This work is aimed at developing an improved understanding of the commercially crucial phenomenon of liquid crystal alignment by studying well-characterized surfaces. Herein is reported molecular-level characterization of the surface underlying a ferroelectric liquid crystal in situ, a requisite starting point for understanding the liquid crystal-solid interface at the molecular level. The results are also important in the context of developing a model for the molecular. origins of the contrast observed in STM images of organic monolayers on conductor surfaces. The data and analysis provide strong evidence that neither frontier orbital alone (highest occupied or lowest unoccupied molecular orbital) is sufficient to describe the observed tunneling efficiency.
Submitted on August 30, 1994
Accepted on December 6, 1994
