A low energy electron microscopy study of the initial growth, structure, and thermal stability of 4,4′-biphenyldicarboxylic acid domains on Cu(001)

Abstract

The growth of 4,4(')-biphenyldicarboxylic acid (BDA) on Cu(001) has been studied using low energy electron microscopy and selective area low energy electron diffraction. The emergence of large islands and hydrogen bonding to perpendicularly oriented, adjacent molecules is confirmed. The two benzene rings of adsorbed BDA are twisted along the molecular axis. Unconventional growth of the domains, followed by a second nucleation stage, is observed at room temperature. This unanticipated feature is attributed to the accumulation of stress in the islands. Ostwald ripening in the films and the decay of BDA domains at 448 K exhibits features that are consistent with diffusion limited behavior.

Visualization of nucleation and growth of supramolecular networks on Cu(001) and Au(111)

“…While for BDA adsorbed on, e.g. Au (111), both rings are expected to be in-plane [43], we found in a previous µLEED study, that they are also twisted on Cu(001) [38].…”

“…Analytical solutions for l c exist only for a few special geometries [59]. In a previous study we showed indications for a diffusion limited BDA island decay [38]. Diffusion limited decay was also found in a similar system, namely PTCDA on Ag(100) [54].…”

“…After insertion into the LEEM, the sample was further cleaned by cycles of sputtering and annealing. In a previous study [38], carbon proved to be a particularly persistent contamination. That is because of the notorious low carbon sputter yield with Ar-sputtering and the deposition of fresh carbon during each experiment.…”

“…Hydrogen bonds, which can be highly selective, play an important role in the self-assembly process. One of the more frequently studied building blocks are benzoic acid groups [41,42,11,12,38,43,16,44]. It has been reported that benzoic acids adsorb on Cu(001) as deprotonated carboxylate species [41,42,11].…”

“…Re-evaporation (or desorption) into vacuum does not occur, the molecules decompose on the surface above 450 K. Below these temperatures, BDA exists in two phases on Cu(001): a dilute phase and a two-dimensional (2D) crystalline phase which nucleates from the dilute phase [38]. In the crystalline phase the molecules form a well-ordered, square network with a c(8×8) superstructure, as was found by scanning tunneling microscopy (STM) and µLEED [12,38]. An example of the µ-diffraction pattern obtained from the structure is shown in Fig.…”