Substrate-mediated ordering and defect analysis of a surface covalent organic framework

Abstract

We investigate the growth of a two-dimensional polymer obtained by dehydration of 1,4-benzenediboronic acid (BDBA). The molecules are vapor deposited under ultrahigh vacuum conditions on well-oriented noble metal---Ag(111), Ag(100), Au(111), and Cu(111)---surfaces. Molecular flux and substrate temperature are varied to obtain a polymer of optimum quality, whose structure best approaches that of an ideal honeycomb network. We find that a high molecular flux (\ensuremath{\sim}0.1 monolayer/minute) is necessary to initiate BDBA polymerization on all surfaces at room temperature. Once polymerization has extensively taken place, the robust surface network can resist a temperature of 450 \ifmmode^\circ\else\textdegree\fi{}C. However, various kinds of defects are present within this two-dimensional surface polymer. Statistical analyses, primarily based on the minimal spanning tree approach, are performed to quantify polymer order. They indicate that Ag(111) and Ag(100) surfaces are better templates than Au(111) surfaces for polymer formation, far more than Cu(111) ones. The influence of the metal nature on the polymer growth is discussed with respect to the surface diffusion of adsorbed molecules.