Control of Intermolecular Bonds by Deposition Rates at Room Temperature: Hydrogen Bonds versus Metal Coordination in Trinitrile Monolayers

TL;DR

This study investigates how deposition rates influence the formation of hydrogen bonds and metal coordination in monolayers of a trinitrile molecule on copper and silver surfaces, revealing substrate-dependent bonding behaviors.

Contribution

It demonstrates that ultralow deposition rates can control intermolecular bond formation and structure selection, highlighting the role of adatom kinetics on different metal surfaces.

Findings

Hydrogen-bonded polymorph observed on both Cu(111) and Ag(111).

Metal-coordinated porous polymorph forms on Cu(111) but not on Ag(111).

Deposition rate influences structure formation through adatom kinetics.

Abstract

Self-assembled monolayers of 1,3,5-tris(4'-biphenyl-4"-carbonitrile)benzene, a large functional trinitrile molecule, on the (111) surfaces of copper and silver under ultrahigh vacuum conditions were studied by scanning tunneling microscopy and low-energy electron diffraction. A densely packed hydrogen-bonded polymorph was equally observed on both surfaces. Additionally, deposition onto Cu(111) yielded a well-ordered metal-coordinated porous polymorph that coexisted with the hydrogen-bonded structure. The required coordination centers were supplied by the adatom gas of the Cu(111) surface. On Ag(111), however, the well-ordered metal-coordinated network was not observed. Differences between the adatom reactivities on copper and silver and the resulting bond strengths of the respective coordination bonds are held responsible for this substrate dependence. By utilizing ultralow deposition rates, we demonstrate that on Cu(111) the adatom kinetics plays a decisive role in the expression of intermolecular bonds and hence structure selection.