Molecular alignment in organic thin films

Molecules can be oriented when they are adsorbed onto a solid surface with an appropriate surface structure. Examples are shown which illustrate a unidirectional alignment. 4-Dimethylamino-4′-nitrostilbene (DMANS) exhibits an oriented adsorption when evaporated onto a cleaved face of a glycine single crystal. The same compound exhibits also a high degree of orientational order when an evaporated film of the compound is mechanically brushed in a direction. The mechanism of the molecular alignment is discussed based on the results of polarized optical absorption, optical second-harmonic generation, X-ray diffraction and scanning force microscopy.