There are different approaches to the fabrication of nanostructures, microscopic architectures which are envisioned to have applications in electronics, sensing, catalysis, and other areas. In one of these approaches, the bottom-up approach, the nanostructures are synthesized from molecular building blocks which can form bonds with each other, leading, for example, to a linear polymer. Frequently, such bottom-up reactions occur at the surface of a metal which catalyzes the reaction of the molecules.

Initially, The bonds between the building blocks are passivated by bromine atoms (shown in orange). In this state, the molecules cannot react with each other. The molecules must be activated by increasing the temperature above a certain threshold. This leads to cleavage of the bromine atoms and the formation of bonds between the molecular cores.

The bromine atoms which are split off the molecules during this reaction remain in the vicinity of the newly formed nanostructures and may hinder the growth of larger structures. In order to avoid a detrimental effect of the otherwise useless bromine atoms, we developed a method to remove them from the surface so that they cannot interfere with the on-going reaction.

We removed the unwanted bromine atoms by exposing them to hydrogen gas. Hydrogen adsorbs at the surface and the hydrogen molecule splits into two hydrogen atoms. Both of them diffuse on the surface until they react with one of the bromine atoms. The resulting hydrogen bromide is unstable on the surface and desorbs, leaving behind a bromine-free surface.

 

This work was published in the Journal of Physical Chemistry C in 2015.