Two-dimensional self-assembled networks of aldehyde functionalized molecules

Molecular self-assembly is one of the most important bottom-up fabrication strategies to produce two-dimensional (2D) networks at solid surfaces. The formation of complex 2D surface structures at the molecular scale relies on the self-assembly of functional organic molecules on solid substrates. Molecules with aldehyde groups have shown to be promising for the formation of self-assembled molecular networks and 2D covalent organic frameworks.

We have studied the self-assembly of a tetra-aldehyde substituted aromatic molecule (PTTA), on HOPG and the (111) surfaces of Au and Ag using scanning tunneling microscopy in both ultrahigh vacuum and at the solid-liquid interface.

Room temperature deposition of PTTA in UHV on Au(111) leads to a close-packed self-assembled network. The 2D layer is characterized by a one-molecule oblique unit cell defined by lattice vectors of 8 Å and 12 Å. A very similar structure is observed at the solid-liquid interface for a drop casted solution of PTTA in phenyloctane, a non-polar solvent, on HOPG. The similar unit cell on the two surfaces suggests that the PTTA network structure is determined primarily by molecule–molecule interactions. Changes in the structure as a function of annealing temperature, and results on the Ag(111) surface will also be discussed.