Fabrication and UHV-STM Observation of Melamine-Aldehyde Nanostructures from Solutions on Au

In the present study, surface organic nanostructures consisting of melamine and terephthalaldehyde were prepared by solution method, i. e. solvent evaporations of the aqueous solutions. The prepared samples were observed using scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV). In UHV observation, no oligomers as reaction products were imaged. Instead, unknown beltlike molecular rows and disordered phase appeared. In the case of coexisted area of the unknown and disordered phases, tip-induced phase transition was observed. The beltlike rows were attributed to the arrangement of terephthalaldehyde molecules. Based on the high-resolution observation, the tentative model of the TPA arrangement was proposed. The elongated keeping of the sample in UHV to progress the oligomer formation did not lead to formation of oligomers. From the present experimental results, we consider that the stability of the reaction products in UHV is low and such reactant molecules were probably included in the mobile disordered phases. GNR )