Atomic-force microscope observation and molecular-scale flattening of the single-crystal surface of 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST).

The surface of an organic electro-optic crystal tends to be covered with a degenerate rough layer, which may cause light scattering or unfavorable transmission of light. We demonstrate a novel method of removing this layer and flattening the (001) surface of a 4-dimethylamino- N -methyl-4-stilbazolium tosylate (DAST) crystal on a molecular scale by applying suitable force on the tip of an atomic-force microscope (AFM). When the loading force on the AFM tip is kept near 10 nN, the DAST molecules can be removed layer by layer. This method produced a large, flat terrace of 250,000 nm(2) , and the molecular-scale flatness of this area was confirmed by AFM observation.