Pre-nucleation dynamics of organic molecule self-assembly investigated by PEEM

Abstract

Pre-nucleation dynamics, nucleation and templated self-assembly of a conjugated planar aromatic molecule are investigated by photoemission electron microscopy (PEEM). The high resolution of individual molecular layers in PEEM, in combination with a numerical simulation, reveals the dynamic behaviour of molecules during the pre-nucleation deposition period and their temperature dependence. The in situ deposition of p-sexiphenyl (6P) molecules on Cu(110) and Cu(110) 2 × 1-O surfaces in ultrahigh vacuum, when monitored by PEEM in real-time allows (a) layer densities, (b) meta-stable layer filling by 6P molecules, (c) dynamic surface redistributions during layer filling and (d) critical density spontaneous dewetting to be accurately measured. The comparison of 6P deposited on Cu(110) to Cu(110) 2 × 1-O enables temperature dependent 6P nucleation processes on Cu(110) to be elucidated from PEEM. The interplay between energetically stable molecular arrangements and kinetically stabilised arrangements is shown to dominate the pre- and post-nucleation processes. In combination with additional data obtained during post-nucleation deposition times, such as surface diffusion anisotropies and nucleation energies, it is concluded that the pre-requisite for 6P nucleation, in a lying down orientation, is the formation of a double tilted layer with at least one layer being meta-stable.