| The study of chirality in 3-dimensions began with Pasteur's examination of chiral crystals. Studying chiral 2-dimensional crystal structures is the first step to explore chiral phenomena in the 2-dimensional realm. Self-assembled monolayers (SAMs) on graphite surface formed by chiral alkane derivatives are ideal structural targets. The primary method to study these SAMs is the high-resolution scanning tunneling microscope (STM). The development of an ultrahigh vacuum (UHV) compatible STM is described first. The designs of vibration isolation system, scanning head, control interface and the tip/sample in situ changing system are described in detail. A preliminary STM study of the CO/Fe(100) system in UHV was as a performance test of this instrument.; Using this home-built STM, structures of a series of alkane and alkane derivative SAMs on the graphite surface are studied. Three types of novel surface chiral structures are discovered. In the first, surface chirality is generated by surface-induced asymmetric distortion. This was observed for the octadecanol SAM, where two molecules in the chevron pair bend oppositely, creating a chiral domain by breaking the symmetry. The second involves the chiral assembly of racemic mixture of enantiomers, as in the cases of SAMs of oleyl alcohol, oleic acid and elaidic acid iodination products. The third novel structure is formed by the out of plane flipping of the adsorbate as in the case of the brassidic acid 4,4′-bipyridine salt SAM.; In addition to the chiral structures examined here, a number of new adsorbate structures were studied. A racemic mixture may show quasi-phase separation, with one enantiomer self-assembled into a row and the other enantiomer self-assembled into the neighboring row. The two types of rows pack alternately. This is unique only on the surface and was observed in the SAMs of oleyl alcohol and oleic acid iodination products. The conformation of the carboxylic acid head group is determined by STM in the brassidic acid SAM. The formation of a multilayer film is observed for the alkane derivative SAMs, in contrast to previous research. The structure of an ester SAM on the graphite surface is studied, exhibiting a characteristic zigzag structure. |
