Crystalline organic molecular thin film with electrical switching property: Scanning probe microscopy and optical spectroscopy study

We report on the growth and characterization of crystalline 1, 1 -dicyano-2,2-(4-dimethylaminophenyl)ethylene (DDME) thin film with electrical switching property. X-ray diffraction analysis indicates that bulk singlecrystal DDME belongs to monoclinic, space group P2(1), and Z = 2 structure. Optical spectroscopy shows that the film chemical structure is consistent with that of the powder material, suggesting that DDME material is very stable during the vacuum thermal deposition process. Scanning probe microscopy and transmission electron microscopy observations reveal that the as-deposited film has extended crystal structure and smooth surface morphology in micrometer scale. Parallel molecular stacking structure is repeatedly observed in the film surfaces with the axis of the molecular stack parallel to the substrate. The ac crystal plane is found to be one of the most stable surfaces of the DDME film in ambient conditions. Nanometer scale data storage is realized on the film by applying pulse voltage between the STM tip and the substrate. The switching mechanism is briefly discussed.