One dimensional chains of nickelocene fragments on Au(111)

TL;DR

This study explores how nickelocene molecules decompose and self-assemble on Au(111) surfaces at different temperatures, revealing formation of one-dimensional chains and potential for nanoscale magnetic systems.

Contribution

It demonstrates temperature-dependent adsorption, dissociation, and self-assembly of nickelocene on Au(111), including the formation of non-magnetic 1D chains and dimers, with insights from STM and DFT.

Findings

NiCp$_2$ molecules adsorb and form ordered patterns at 4.2 K.

At 77 K, molecules dissociate into NiCp and Cp fragments.

NiCp fragments self-assemble into chiral 1D chains.

Abstract

We investigate the temperature-dependent deposition of nickelocene (NiCp$_2$) molecules on a single crystal Au(111) substrate, revealing distinct adsorption behaviors and structural formations. At low temperatures (4.2 K), individual NiCp$_2$ molecules adsorb on the herringbone elbows and step edges, forming ordered patterns as molecular coverage increases. However, at 77 K, the molecules dissociate, yielding two main fragments: NiCp fragments that are Ni atoms capped by cyclopentadienyl (Cp) rings, which preferentially adsorb at FCC hollow sites, and Cp radical fragments exhibiting strong substrate interactions. NiCp fragments self-assemble into one-dimensional (1-D) chains along the $\langle 1 1 \bar{2} \rangle$ directions, displaying higher protrusion in STM images. The strain and steric hindrance from the Cp protons induce chiral patterns within the chains, which are well-reproduced by our DFT simulations. In contrast, the Cp fragments maintain distances due to short-range repulsive forces and exhibit low diffusion barriers. Interestingly, the fragments are non-magnetic, as confirmed by both STM measurements and DFT calculations, in contrast to the magnetic signals from intact Nc molecules. In addition to linear chains, dimers of the Ni-Cp fragments form along the $\langle 1 \bar{1} 0\rangle$ directions, requiring gold adatoms for their creation. These results demonstrate the feasibility of constructing complex nanostructures based on metallocenes via on-surface synthesis, opening the possibility for realizing low-dimensional magnetic systems by selecting substrates that preserve the magnetic moment of the fragments.