Surfaces*

Assembly of 2D patterns on crystal surfaces has been widely investigated to reveal the structural and energetic relationships between substrate and overlying architecture. Progress has been achieved in understanding and controlling their assembly, yet little is known about the mechanism by which they nucleate. Understanding the dominant pathways and formation kinetics would enable precise control over phase and morphology during synthesis of 2D materials. In our study, short peptides were selected for their ability to bind on MoS₂ (0001). We studied nucleation and growth of 2D films of these peptides with in situ AFM and compared our results to MD simulations. We find the peptide arrays exhibit an epitaxial relationship to the underlying lattice, but assemble row-by-row from dimeric growth. The nuclei are ordered from the earliest stages. Although the final crystals are 2D, due to the 1D nature of the constituent rows, there is no critical size and the nucleation rate varies linearly with concentration and is finite for all concentrations above the solubility limit. Our results verify long-standing but unproven predictions of CNT while revealing the key interactions responsible for ordered assembly.