Silver iodide nanowires grown within tubular J-aggregates

Silver iodide nanowires have been grown within tubular J-aggregates of the cyanine dye 3,3'-bis(2-sulfopropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimida-carbo-cyanine (C8S3) from aqueous AgNO₃ solutions. Crystal structure analysis by selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDXS) of single nanowires revealed that they are of silver iodide (AgI), while previously they were presumed to be of metallic silver. Iodine has not been added intentionally, but it is a remnant from the chemical synthesis of the dye and present in a dye:iodine ratio of almost 2:1, as revealed by inductively coupled plasma mass spectrometry (ICP-MS). The AgI wires grow as single crystals with lengths of several 10-100 nm and width of 6.5 ± 0.5 nm. The width and the orientation of the crystal relative to the aggregate axis are defined by the tubular structure of the templating dye aggregate. Caused by the nucleation at the tube wall the main growth is not along the usually preferred [0 0 0 1] direction but along the extension of the basal plane, which is furthermore tilted by an angle of 6° ± 2° against the main axis of the aggregate. This self-assembled system represents an organic-inorganic hybrid system with a well-defined semiconductor nanowire, AgI, that is strictly oriented with respect to the aggregated phase of conjugated molecules.