Hexagonal polyimide oligomers: Synthesis, properties, and their use as templates

Our recent studies on methods of fabricating nanoscale features involved the synthesis of toroidal molecular templates with aromatic sulfonate groups that could be used as masks for electrodeposition. Ionically conductive organic templates, rigid cyclic polyimide oligomers containing sulfonated groups, were synthesized from linear building block precursors using kinetically-determined cyclization, and characterized. Dynamic light scattering (DLS) demonstrated that the macrocyclic hexamers self-associate strongly to form large aggregate structures in solution at room temperature; the association behavior depends on concentration. Concentration-dependent morphologies were observed using transmission electron microscopy (TEM). The molecules self-associated, producing supramolecular arrays of hexagonal liquid crystals that were physisorbed on a planar surface. Molecular resolution images of these superstructures were recorded at room temperature using scanning tunneling microscopy (STM). Two types of deposition were observed. The first is a two-dimensional (2D) close-packed honeycomb. The second form, 6 nm diameter nanofibrils, could be single tubes, or associated into oriented aggregates. The hexagonal arrays were visualized as a large open framework honeycomb, with 4--5 nm diameter nanochannels. The templates, with internal diameters as small as 4 nm, are ideally suited for electrodeposition to generate highdensity nanowires or nanodots. The idea and challenge is to deposit a regular self-organized array of cyclic molecules on a substrate, and then electrodeposit metal or semiconductor nanofibrils within the macrocycles, forming a hexagonal architecture. Water and ionic salts are readily absorbed by the sulfonate groups; also the internal cavities are large enough to allow relatively free ion diffusion. This was used as a prefabricated template for electrodeposition of InSb. We have been able to electrodeposit InSb into the nanochannels and then remove the organic oligomers, leaving a hexagonal array of templated InSb nanofibrils.